Title of Invention	"ACRYLIC ACID, WATER-ABSORBENT POLYMER STRUCTURES BASED ON RENEWABLE RESOURCES AND METHOD FOR PRODUCING SAID STRUCTURES"
Abstract	The present invention relates to a process for production of acrylic acid, comprising at least the following steps: a. dehydration of glycerine to a dehydration product comprising acrolein; b. gas phase oxidation of the dehydration product to obtain a monomer gas comprising an acrylic acid; c. bringing into contact of the monomer gas with a quench means to obtain a quench phase comprising acrylic acid; d. processing of the quench phase to obtain a monomer phase comprising acrylic acid. The present invention also relates to a process for preparation of polymers by radical polymerisation of acrylic acid, preferably for preparation of water-absorbing polymers, the water-absorbing polymers obtainable by this process, water-absorbing polymers based to at least 25 wt.% upon partially neutralized acrylic acid, a composite, a process for producing a composite, the composite obtainable by this process, the use of acrylic acid in the preparation of water-absorbing polymer structures, a device for preparation of acrylic acid, a process for preparation of acrylic acid and the acrylic acid obtainable by this process.

Title of Invention

"ACRYLIC ACID, WATER-ABSORBENT POLYMER STRUCTURES BASED ON RENEWABLE RESOURCES AND METHOD FOR PRODUCING SAID STRUCTURES"

Abstract

The present invention relates to a process for production of acrylic acid, comprising at least the following steps: a. dehydration of glycerine to a dehydration product comprising acrolein; b. gas phase oxidation of the dehydration product to obtain a monomer gas comprising an acrylic acid; c. bringing into contact of the monomer gas with a quench means to obtain a quench phase comprising acrylic acid; d. processing of the quench phase to obtain a monomer phase comprising acrylic acid. The present invention also relates to a process for preparation of polymers by radical polymerisation of acrylic acid, preferably for preparation of water-absorbing polymers, the water-absorbing polymers obtainable by this process, water-absorbing polymers based to at least 25 wt.% upon partially neutralized acrylic acid, a composite, a process for producing a composite, the composite obtainable by this process, the use of acrylic acid in the preparation of water-absorbing polymer structures, a device for preparation of acrylic acid, a process for preparation of acrylic acid and the acrylic acid obtainable by this process.

Full Text	ACRYLIC ACED, WATER-ABSORBENT POLYMER STRUCTURES BASED ON RENEWABLE RESOURCES AND METHOD FOR PRODUCING SAID STURCTURES The present invention relates to a process for preparation of acrylic acid, a process for preparation of polymers by radical polymerisation of acrylic acid, preferably for preparation of water-absorbing polymers, the water-absorbing polymers obtainable by this process, water-absorbing polymers based to at least 25 wt.% upon partially neutralized acrylic acid, a composite, a process for producing a composite, the composite obtainable by this process, the use of acrylic acid in the preparation of water-absorbing polymer structures, a device for preparation of acrylic acid, a process for preparation of acrylic acid and the acrylic acid obtainable by this process. High requirements are made of the purity of acrylic acid which is used in the preparation of polymeric compounds. This is particularly the case when the polymers are so-called superabsorbers, which are incorporated into wound dressings or hygiene articles. These polymers can absorb and thus bind aqueous liquids to form a hydrogel. Superabsorbers are, therefore, used in particular in hygiene articles such as diapers, incontinence articles, sanitary napkins and the like for the absorption of body fluids. A comprehensive overview of superabsorbers, their application and their preparation is given by F.L. Buchholz and A. T. Graham (Editors) in "Modern Superabsorbent Polymer Technology", Wiley-VCH, New York, 1998. In the preparation of superabsorbent polymers, generally an acrylic acid is used which has been obtained as pure acrylic acid by catalytic gas phase oxidation of propylene to acrolein, which is then converted in a further catalytic gas phase oxidation to acrylic acid, subsequent absorption of the gaseous reaction mixture in water, distillation of the thus-obtained aqueous acrylic acid solution to obtain a crude acrylic acid and further purification of the crude acrylic acid by distillation or crystallisation. It is disadvantageous in this process for production of acrylic acid that the temperatures between 300 and 450°C used in both stages lead to formation of oligomers and further undesired cracking products. This results in the accumulation of an undesirably large amount of compounds which are less volatile than acrylic acid or compounds which are difficult to separate from acrylic acid, such as acetic acid, which must be separated from the acrylic acid. This separation, which as a rule occurs by distillation, leads to a further thermal stress on the acrylic acid, which favours the disadvantageous formation of dimeric or oligomeric acrylic acid. A high acrylic acid dimer or acrylic acid oligomer content is, however, disadvantageous, since these dimers or oligomers are built into the polymer backbone during the preparation of superabsorbers by radical polymerisation of acrylic acid in the presence of crosslinkers. During the post-treatment of the surface of the polymer particles, which occurs following the polymerisation, for example as a surface post-crosslinking, the polymerized-in dimers, however, split to form p-hydroxypropionic acid, which is dehydrated under the post-crosslinking conditions to form acrylic acid. A high dimeric acrylic acid content in the acrylic acid used in the production of superabsorber therefore leads to the acrylic acid monomer content increasing during a thermal treatment of the polymer, as occurs during post-crosslinking. Since the soluble parts, in particular the acrylic acid monomers in the superabsorbent polymers, can cause skin irritation, a use of these polymers in hygiene articles requires a particularly low content in extractable components. Also other, often toxic compounds remain in the acrylic acid obtained by the catalytic gas phase oxidation. Among these impurities are included, in particular, aldehydes, which have a disruptive effect on the course of polymerisation, with the result that the polymers still comprise considerable amounts of soluble components Acrylic acids produced in previous ways from propylene comprises not inconsiderable amounts of ketones having double bonds, in particular protoanemonin (PTA). This compound can, on contact with skin, cause signs of poisoning, such as, for example, reddening, itching or blister formation. Superabsorbers which comprise large amounts of PTA as soluble components are therefore of concern from a dermatological viewpoint. Furthermore, PTA disrupts the polymerisation, as described in US-A-2002/0120085. This leads to the obtaining of superabsorbing polymers with less good absorption, transport and retention properties for body fluids, so that when using Superabsorbent polymers of this type in hygiene articles such as diapers or sanitary napkins, wearer comfort is worsened, for example by "leakage". Several processes have already been described in the state of the art, with which the content in the above-mentioned compounds, in particular of aldehydes, or PTA, in the acrylic acid obtained by gas phase oxidation of propylene can be reduced. EP-A-0 574 260 suggests using, in the production of superabsorber, if possible, an acrylic acid which is characterized by a {3-hydroxypropionic acid content of not more than 1000 ppm. Such an acrylic acid is obtained by distilling conventional acrylic acid us directly as possible before the polymerisation. DE-A-101 38 150 suggests, in order to reduce the amount of aldehyde in the acrylic acid, bringing this into contact with an aldehyde trapper, in order to convert the aldehydes into high-boiling compounds, which can then be separated by means of distillation. Various methods have been proposed in the state of the art for the removal of PTA, such as the addition of a nitrous acid salt, of nitrogen oxide or of nitrobenzene (JP 81-41614) or the addition of one or more para-phenylene diamines (EP-A-567 207) to the acrylic acid. The disadvantage of the above-described processes for reducing the amount of aldehydes and ketones in acrylic acid is, however, among others, that, in so far as the impurity content of the acrylic acid is not known exactly, these reagents must be used in excess for the purpose of as complete a removal as possible of impurities from the acrylic acid. On the one hand, reagents which are reactive to the acrylic acid must be added. The portion of these reagents which is not converted must then be removed again. Reagents which are not removed are comprised in the superabsorbent obtained from such an acrylic acid as soluble components, which can come into contact with the skin of the hygiene article wearer when the superabsorbers are used in hygiene articles. Furthermore, the processes known from the prior art for removal of aldehydes in ketones from acrylic acid only very seldom remove these impurities completely. In addition to the disadvantages which are traced back to impurities in the acrylic acid used in the production of superabsorbers, known superabsorbers also have the disadvantage that, unless they at least partially comprise natural polymers, such as celluloses, they are hardly based upon renewable raw materials. While it is successful to produce many of the components used in hygiene articles, in particular in disposable diapers, from biological starting materials, replacement of the superabsorbers based upon cross-linked polyacrylates by natural superabsorbing polymers, such as cross-linked, derivatised starches or celluloses, is generally associated with significant losses in respect of the absorbent properties. This mostly leads to the necessity of using considerably more of the absorbents based upon natural polymers, simply in order to approach the same absorbent properties in a hygiene article. This is disadvantageous, because the hygiene articles become more voluminous and heavier, which significantly restricts wearing comfort and leads to a larger waste volume, which, in addition to dumping space or combustion expenditure also requires greater transport capacity for the removal of waste. All of this has a disadvantageous effect upon the environmental friendliness of the absorbers based upon natural polymers. The object of the present invention was to overcome the disadvantages arising from the state of the art. In particular, the present invention had the object of making available polymers, in particular superabsorbers, which have a particularly low content in extractable, possibly toxic components. Furthermore, the object of the present invention was to provide polymers, in particular superabsorbers, which are environmentally friendly and still have excellent application properties. In particular it was desired to provide superabsorbers with improved environmental friendliness while retaining the same good absorbent properties. In addition, it was an object of the present invention to improve the environmental friendliness of further processing products comprising the polymers according to the invention, such as composites in general and hygiene articles in particular, without the desired functions, such as absorbent capability, wearing comfort and simple producibility of these further processing products suffering. It was also an object of the present invention to provide a process for preparing polymers of this type and the monomers suitable for their production, whereby this process should take place as far as possible without the use of reactive compounds for removal of impurities from the monomers used in the preparation of the polymers. In addition, an object of the present invention was to suggest a process and a device for the production of monomers and polymers, which can be integrated with as little conversion expenditure as possible into existing industrial manufacturing processes and devices. A contribution to the solution of the above mentioned objects is provided by a process for preparation of acrylic acid, comprising at least the following steps: a. dehydration of glycerine to an acrolein-comprising dehydration product; b. gas phase oxidation of the dehydration product to obtain an acrylic acid-comprising monomer gas; c. bringing into contact of the monomer gas with a quenching means to obtain an acrylic acid-comprising quench phase; d. processing of the quench phase to obtain an acrylic acid- comprising monomer phase. A further contribution to the solution of the above objects is provided by a process for preparation of a polymer by radical polymerisation of acrylic acid comprising at least the following steps: A. dehydration of glycerine to an acrolein-comprising dehydration product; B. Gas phase oxidation of the dehydration product to obtain an acrylic acid-comprising monomer gas; C. bringing into contact of the monomer gas with a quench means to obtain an acrylic acid-comprising quench phase; D. processing of the quench phase to obtain an acrylic acid- comprising monomer phase; E. polymerisation of the monomer phase. In one aspect of the process according to the invention it is preferred that the glycerine is obtained by saponification of fats. These fats can be animal fats as well as vegetable fats. Animal fats are obtained in particular from processing of animals. Vegetable fats are obtained in large amounts from oil extraction from oily fruits such as rape, soya., sesame, olives and sunflower seeds. Large amounts of glycerine are generated, in particular, by the production of so-called "Bio diesel" from rape seed oil, as known from WO-A-2004/029016, among others. It is thus preferred in the process according to the invention, that the glycerine is generated m the production of liquid fuels from natural raw materials. This is given, in particular for saponification devices following oil mills. In one aspect of the process according to the invention, it is preferred that the dehydration occurs at least partially in the liquid phase. As liquid phase, aqueous systems are particularly preferred. If the dehydration should be carried out at least partially or completely in a liquid phase, this had the advantage, in particular if this is an aqueous phase, that for high glycerine concentrations, high acrolein concentrations in the aqueous phase can be achieved. These aqueous phases with high acrolein concentrations can be used directly in the next stage of the gas phase oxidation. In order to protect the oxidation catalyst from carbonisation, it is preferred to provide a separating unit between dehydration and oxidation. In this separating unit the accompanying materials which are different from acrolein and the acrolein are conducted to the gas phase oxidation. In this way, significantly longer catalyst lifetimes can be achieved. A further advantage of the liquid phase dehydration is that a rinsing effect can be achieved with the liquid phase, with which a formation of coating on a solid state catalyst can be significantly reduced, which leads to increased catalyst running times and thus to a reduced need for regeneration of the catalyst. A further advantage of the liquid phase dehydration is that it can be carried out at relatively moderate temperatures, within a range from 160 to 270°C, preferably within a range from 180 to 260°C and more preferably within a range from 215 to 245°C. These temperature ranges lie significantly below the decomposition and boiling temperature of glycerine of about 290°C, which leads to reduction of sump and cracking products as well as other impurities, which have a disadvantageous effect on the operating time of the gas phase oxidation. It is, however, provided in a further embodiment of the process according to the invention that the dehydration is carries out near to the decomposition point of glycerine, in order to increase the yield. In this embodiment, the temperatures are within a range from 170 to 290 °C, preferably within a range from 190 to 289 °C and more preferably within a range from 225 to 288 °C. It is preferred that the liquid phase dehydration occurs in a circular operation mode, in which in the case of a solid state catalyst the glycerine-containing liquid phase is conducted by means of a pump over the catalyst in a pressurized system. With liquid catalysis or homogeneous catalysis at least a partial flow from the reactor is conducted in the cycle. Converted glycerine, consumed catalyst and optionally removed water are added to the partial flow which has been fed back into the reactor during the cycle, preferably at the reactor entry. Should the partial flow be obtained from an acidic homogeneously catalysed dehydration, it is advantageous that the partial flow is at least partially neutralised. By this measure the formation of side products by reactions in the partial flow can be repressed or even completely prevented. It is further advantageous to deplete materials with higher boiling points than acrolein, characterised as high boiling, from the partial flow. This can occur, for example by means of separating units comprising membranes, which membranes are preferably semi-permeable. In this way higher turnovers and significantly fewer side-products can be obtained, in addition to higher selectivity, in a gentle way. In a further embodiment of the process according to the invention, it is preferred that the dehydration occurs at least partially or also fully in a gas phase. The dehydration in the gas phase has proven particularly useful in the conversion of glycerine from saponification of fat and from the production of biodiesel. This glycerine generally has a high salt load, which can be separated very well by the evaporation step of the gas phase dehydration. As for the liquid phase dehydration, it is also preferred that the gas phase dehydration occurs in the presence of water. Accordingly, it is preferred in the process according to the invention that the glycerine is used in an aqueous phase. In the case of the liquid phase dehydration, this liquid glycerine phase generally has a water content within a range from 0 to 97 wt.%, for example 0 to 30 wt.%, preferably within a range from 60 to 95 wt.%, particularly preferably within a range from 70 to 90 wt.%, whereby, however, a smaller water content, for example a water content within a range from 0 to 20 wt.% and from 0 to 10 wt.% of water, respectively based upon the aqueous phase, is also conceivable. In the case of a gas phase dehydration, the aqueous glycerine phase generally has a water amount within a range from 0 to 97 wt.%, preferably within a range from 60 to 95 wt.% and yet more preferably within a range from 70 to 90 wt.%, respectively based upon the aqueous glycerine phase, whereby it can also be particularly advantageous here to use smaller amounts of water, for example a water content within a range from 0 to 20 wt.% or from 0 to 10 wt.%. The further principal component of the glycerine phase is glycerine. Further advantages of the gas phase dehydration are high turnovers up to a quantitative yield with, at the same time, high space-time-yields. According to another embodiment of the process according to the invention, it is preferred to combine gas phase dehydration and liquid phase dehydration with each other According to one form of the process according to the invention, the glycerine can first be conducted to the gas phase dehydration and then to the liquid phase dehydration or the other way around. The first-mentioned order has the advantage that glycerine charges with heavy salt loads originating from fat saponification can first be freed from these salt loads by evaporation in the gas phase dehydration, in order to be then further converted in the liquid phase dehydration by means of the cycle to high yields and selectivities with few side-products. According to a further embodiment of the process according to the invention a dehydration catalyst is used in the process. Dehydration catalysts can be acidic as well as basic catalysts. Acidic catalysts are particularly preferred because of the low tendency to form oligomers. The dehydration catalyst can be used as a homogeneous as well as a heterogeneous catalyst. If the dehydration catalyst is present as a heterogeneous catalyst, it is preferred that the dehydration catalyst is in contact with a carrier x. As carrier x. are considered all solids which appear suitable to the skilled person. In this context it is preferred that the solid has suitable pore volumes, which are suited for a good binding and taking up of the dehydration catalyst. In addition, total pore volumes according to DIN 66133 within a range from 0.01 to 3 ml/g are preferred and within a range from 0.1 to 1.5 ml/g particularly preferred. In addition, it is preferred that the solids suitable as carrier x. have a surface area within the range from 0.001 to 1000 m2/g, preferably within the range from 0.005 to 450 m2/g and yet more preferably within the range from 0.01 to 300 m2/g according to BET test according to DIN 66131. A bulk good, which has an average particle diameter within the range from 0.1 to 40 mm, preferably within the range from 1 to 10 mm and yet more preferably within the range from J .5 to 5 mm, can be used as carrier for the dehydration catalyst. The wall of the dehydration reactor can also serve as carrier. Furthermore, the carrier can itself be acidic or basic or an acidic or basic dehydration catalyst can be applied to an inert carrier. As application techniques are cited in particular immersion or impregnation or the incorporation into a carrier matrix. Particularly suited as carrier x., which can also have dehydration catalyst properties, are natural or synthetic silicate materials, such as, in particular, mordenite, montmorillonite, acidic zeolites, carrier materials supporting mono-, di- or polybasic inorganic acids, in particular phosphoric acids, or acidic salts of inorganic acids, such as oxidic or silicate materials, for example A^Os, TiOs, oxides and mixed oxides, such as, for example, gamma-AlaOs and ZnO-A^Oj as well as Cu-Al mixed oxides of heteropolyacids. According to an embodiment according to the invention, the carrier x. consists at least partially of an oxidic compound. Such oxidic compounds should have at least one of the elements Si, Ti, Zr, Al, P or a combination of at least two thereof. Such carriers can also function as dehydration catalysts through their acidic or basic properties. A preferred class of compounds which function both as carrier x. and as dehydration catalyst comprises silicon-aluminium-phosphorus oxides. Preferred basic materials which function as both dehydration catalyst and as carrier x. compnse alkali, alkaline earth, lanthanum, lanthanide or a combination of at least two thereof in their oxidic form. Such oxidic or basic dehydration catalysts are commercially obtainable from Degussa AG and from Sudchemie AG. Ion exchangers represent a further class. These can also be present in both basic and acidic form. As homogeneous dehydration catalysts are considered in particular inorganic acids, preferably phosphorous-comprising acids and more preferably phosphoric acids. These inorganic acids can be immobilized on the carrier x. by immersion or impregnation- The use of heterogeneous catalysts has proven particularly successful, in particular in gas phase dehydration. In liquid phase dehydration, however, both homogeneous and heterogeneous dehydration catalysts are used. In a further embodiment of the inventive process it is preferred that the dehydration catalyst is an inorganic acid. By the term acid is understood in this text materials which behave according to the Bronsted definition. All acids known to the skilled person and appearing suitable are considered. Preferably mentioned are S- and P-comprising acids, whereby the P-comprising acids are preferred. It is further preferred in connection with the liquid phase dehydration that this dehydration catalyst, which is also characterised as homogeneous, is present in a solution. This solution is preferably the aqueous glycerine-comprising phase used for dehydration. These homogeneous catalysts are used in an amount within a range from 0.0001 to 20 wt.%, preferably within a range from 0.001 to 15 wt.% and more preferably within a range from 0.01 to 10 wt.%, respectively based on the phase to be dehydrated. In addition, it is preferred that in the inventive process, a dehydration catalyst is used with an HO value within a range from +1 to -10, preferably within a range from +2 to —8.2 and yet more preferably in the liquid phase dehydration within a range from +2 to -3 and in the gas phase dehydration within a range from — 3 to -8.2. The HO value corresponds to the acidic function according to Hammett and can be determined by the so-called amine titration and use of indicators or by absorption of a gaseous base - see "Studies in Surface Science and Catalytics", vol. 51, 1989: "New Solid Acids and Bases, their catalytic Properties", K. Tannabe et. al. Further details on the production of acrolein from glycerine can also be found in DE 42 38 493 Cl. In a further embodiment of the process according to the invention, the gas phase oxidation in step b) of the process according to the invention occurs in the presence of one or more oxidation catalysts, which comprise transition metals in elemental or in chemically bound form or both. It is preferred that the oxidation catalysts comprise at least one of the elements molybdenum, tungsten, vanadium or a combination of at least two thereof in at least partially oxidized form. Oxidation catalysts of this sort are preferably used as heterogeneous catalysts in contact with a carrier y. It is then preferred that the oxidation catalysts are incorporated into this carrier y. As suitable carrier y. are considered, in principle, the compounds mentioned in connection with carrier x., whereby carriers based upon silicon oxide or aluminium oxide or aluminium-silicon oxide are particularly preferred. Oxidation catalysts of this type are widely described in the literature. Reference is here made, for example, to DE-A-26 26 887, EP-A-0 534 294 and to US-A-2002/0198406. Oxidation catalysts of this type for the conversion of acrolein to acrylic acid are commercially obtainable, for example from Nippon Kayaku KK and from Degussa AG. It is further preferred in the process according to the invention that the dehydration product, optionally in an aqueous phase, is conducted to the gas phase oxidation. It is here preferred that the dehydration product comprises at least 10 wt.%, preferably at least 20 wt.% and yet more preferably at least 40 wt.% acrolein. The amount of water should lie within the range from 0.001 to 50 wt.%, preferably within the range from 0.1 to 50 wt.%, particularly preferably within the range from 10 to 40 wt.% and yet more preferably within the range from 12 to 20 wt.%, whereby these and the above wt.% values are based respectively upon the phases fed into the gas phase oxidation. A further embodiment of the process according to the invention provides that glycerine is introduced into a dehydration space as aqueous glycerine phase with a glycerine concentration within a range from 0.1 to 90, preferably within a range from I to 80 and particularly preferably within a range from 2 to 50 wt.%, respectively based upon the aqueous glycerine phase. This dehydration space comprises both a fluid phase and a gas phase, whereby the concentration of glycerine in the fluid phase is greater than in the gas phase and whereby the concentration of acrolein in the gas phase is greater than in the fluid phase. Preferably the concentration of glycerine in the fluid phase is greater than in the gas phase at least by a factor of 1.1, preferably at least by a factor of 2 and particularly preferably at least by a factor of 5. It is further preferred that the concentration of acrolein in the gas phase is greater than in the fluid phase at least by a factor of 1.1, preferably at least by a factor of 2 and particularly preferably at least by a factor of 5. In this embodiment it is further preferred that the acrolein comprised in the gas phase is removed from the dehydration space, which is preferably designed as a pressure reactor. In connection with this embodiment it is further preferred that more dehydration of glycerine to acrolein occurs in the fluid phase than in the gas phase. Preferably more dehydration of glycerine to acrolein occurs in the fluid phase than in the gas phase by a factor of 1.1, preferably at least by a factor of 2 and more preferably at least by a factor of 5. It is further preferred in this embodiment that the acrolein formed in the fluid phase is transferred into the gas phase. It is further preferred in this embodiment that the volume of the dehydration space taken up by the fluid phase is larger than the volume taken up by the gas phase. The volume of the dehydration space taken up by the fluid phase is larger than the volume taken up by the gas phase, preferably by a factor of 1.1, preferably at least by a factor of 2 and particularly preferably at least by a factor of 5. The factors used here can be determined, for example, on the basis of investigations of the phase equilibria. This embodiment of the process according to the invention for production of acrylic acid preferably comprises the following process steps: a. dehydration of glycerine in the form of an aqueous glycerine solution to a dehydration product comprising acrolein in the form of an aqueous acrolein solution by means of liquid phase dehydration with at least partial transfer of the aqueous acrolein solution into the gas phase, whereby the weight ratio of acrolein to glycerine in the gas phase is greater than the weight ratio of acrolein to glycerine in the aqueous acrolein solution by a factor of at least 2, preferably at least 4, particularly preferably at least 10 and most preferably at least 100; b. gas phase oxidation of the acrolein in the vapour phase to obtain a monomer gas comprising acrylic acid; c. bringing into contact of the monomer gas with a quench means to obtain a quench phase comprising acrylic acid; d. processing of the quench phase to obtain a monomer phase comprising acrylic acid. Accordingly the process for producing a polymer in this particular embodiment of the process according to the invention comprises the following process steps: A. Dehydration of glycerine in the form of an aqueous glycerine solution to a dehydration product comprising acrolein in the form of an aqueous acrolein solution by means of liquid phase dehydration with at least partial transfer of the aqueous acrolein solution into the gas phase, whereby the weight ratio of acrolein to glycerine in the vapour phase is larger than the weight ratio of acrolein to glycerine in the aqueous acrolein solution by a factor of at least 2, preferably at least 4, particularly preferably at least 10 and most preferably at least 100; B. gas phase oxidation of the acrolein in the gas phase to obtain a monomer gas comprising acrylic acid; C. bringing into contact of the monomer gas with a quench means to obtain a quench phase comprising acrylic acid; D. processing of the quench phase to obtain a monomer phase comprising acrylic acid; E. polymerisation of the monomer phase. The gas phase oxidation is preferably carried out within a temperature range from 200 to 400°C, preferably within the range from 250 to 350°C and more preferably within a range from 280 to 340°C. It is further preferred in the process according to the invention that the monomer gas comprises the acrylic acid in an amount within the range from 5 to 50 wt.%, preferably within a range from 10 to 40 wt.% and yet more preferably within a range from 15 to 30 wt.%, respectively based on the monomer gas. In a further embodiment of the process according to the invention it is preferred to use water or an organic compound with a boiling point within the range from 50 to 250°C, preferably within a range from 70 to 180°C and yet more preferably within a range from 105 to 150°C or water and this organic compound as quench means in process step c). As organic compounds of this type are considered in particular aromatics and more preferably alkylated aromatics. The quench means is generally brought into contact with the monomer gas in a suitable column, preferably in counter-current flow. For the case that the quench means comprises at least 50 wt.%, preferably at least 70 wt.% water, it is preferred that the aqueous quench means charged with acrylic acid is processed in a further step with a separation means, which is preferably not very soluble with water. The phase which is richest in acrylic acid is subjected either to a distillation or to a crystallisation or both, preferably first to a crystallisation. The crystallisation can be carried out both as layer and as suspension crystallisation. Suitable layer crystallisation devices are commercially obtainable from Sulzer AG. Suitable suspension crystallisation processes generally use a crystal generator followed by a washing column. Such devices and processes are commercially obtainable from Niro Prozesstechnologie B.V. As extraction/separating means is considered particularly an aromatic compound, more preferably an alkyl aromatic and further preferably toluene. If an organic compound should be used as separating means, this organic compound charged with acrylic acid can likewise be subjected to a distillation and crystallisation or a combination of both. A crystallisation suitable for this is disclosed in EP-A- 1 015 410. It is additionally preferred in the process according to the invention that the quench phase comprises the acrylic acid in an amount within the range from 30 to 90 wt.%, preferably within the range from 35 to 85 wt.% and yet more preferably within a range from 45 to 75 wt.%, respectively based upon the monomer phase. In a further embodiment of the process according to the invention, it is preferred that the processing of the quench phase occurs at temperatures below the boiling point of acrylic acid. A suitable measure therefor is that the quench phase already has a temperature of less than 40°C by use of a correspondingly cold quench means. The thus-temperature controlled quench phase can then be conducted to an extraction or to a crystallisation or both for processing, whereby the temperatures preferably lie within a range from -40 to 40°C, preferably within a range from -20 to 39°C and particularly preferably within a range from -10 to 35°C. According to a further aspect of the process according to the invention, it is preferred that the monomer phase comprises the acrylic acid in an amount within the range from 99 to 99.98 wt.%, respectively based upon the monomer phase. Such acrylic acid contents in a monomer phase appear in particular if the processing occurs by distillation. For the case that the processing occurs by means of extraction and crystallisation, it can be preferred that the acrylic acid is present in an amount from 30 to 70 wt.%, preferably in an amount within the range from 40 to 60 wt.% and yet more preferably in an amount within a range from 45 to 65 wt.% in the monomer phase together with water, and the impurities which are different to water and acrylic acid amount to less than 0.02 wt.%, based upon the monomer phase. This aqueous monomer phase has the advantage that it can be used in the aqueous polymerisation of the monomer phase without further dilution steps, which is necessary for the highly concentrated monomer phase. In addition, the invention relates to a device for production of acrylic acid which comprises the following components connected with each other in fluid-conveying fashion: la. a dehydration reactor; 2a. a gas phase oxidation reactor; 3 a. a quench unit; 4a. a processing unit. In addition, the invention relates to a device for production of polymers, which first comprises the above listed components 1 a. to 4a. connected with each other in fluid-conveying fashion and also a polymerisation unit 5b. By fluid-conveying is understood a connection of the individual components or of their components by means of pipe systems or other transport possibilities for gases and liquids, such as tank vehicles. It is preferred in the inventive device that the dehydration reactor comprises a compound reservoir suitable for accepting glycerine, followed by a reaction area designed to accept catalyst, in turn followed by a quencher with a line to the gas phase oxidation reactor. These components are formed from common materials used in the chemical industry which are inert under the reaction conditions, such as stainless steel or glass. For the case that the reaction area accepts the catalyst as bulk material, it comprises appropriate containers. In another design, the reaction area can also comprise walls which function as catalyst. The quencher is designed as a column, into which water or high-boiling organic solvent can be introduced. A further aspect of the device according to the invention comprises an evaporator after the compound reservoir and before the reaction area. These embodiments are particularly suitable for gas phase dehydration. For the case that the glycerine with a high salt load from fatty acid saponification is used, it is preferred that the evaporator comprises a salt separator. If the dehydration occurs in the liquid phase and the acrolein should be evaporated according to the above-described particular embodiment of the process according to the invention in process step a', the device according to the invention comprises additionally an evaporation device la' arranged between the dehydration reactor la. and the gas phase oxidation reactor 2a., which is connected to the gas phase oxidation reactor 2a. in such a way that the vapour phase obtained in the evaporation device 2a' is fed into the gas phase oxidation reactor 2a. According to another embodiment of the device according to the invention, it is preferred that the reaction area comprises a lower product outlet which leads into the quencher. This construction has proven itself in particular in liquid phase dehydration. In a further design of the device according to the invention, it is preferred that the reaction area is integrated in a cycle, with which reagents and reaction product can be conducted within the cycle. As gas phase oxidation reactors are considered all reactors known to the skilled person and suitable for the process according to the invention, which are capable of converting acrolein by gas phase oxidation to acrylic acid. Preferred in this context are pipe bundle reactors or plate reactors, which are cooled with a cooling agent, preferably with a salt melt. These pipe bundle or plate reactors accommodate a suitable catalyst on the side to which cooling agent is applied. On the one hand, this can be present as a bulk powder and on the other hand the surfaces of the pipes or of the plates can be coated with the catalyst. Preferably used quench units are likewise those types which are known in previous large scale gas phase oxidation of acrolein to acrylic acid. Quench units of this type are formed as columns or towers and, as for the reactors, can be commercially purchased, for example from Deggendorfer Werft GmbH. As processing unit are likewise considered all known distillation and crystallisation as well as extraction devices known to the skilled person from large scale acrylic acid synthesis by means of gas phase oxidation of acrolein. Suitable polymerisation units, which are used in process step E. for polymerisation of the monomer phase, are, on the one hand, discontinuously operating stirrer vessels and on the other hand continuously operating systems, such as bulk polymerisation devices, extruders and the like. A comminution and drying follows these polymerisation reactors. The thus-obtained superabsorbent precursor can, iurthermore, be subjected to a surface- or post-crosslinking. More details concerning this are found in the previously mentioned work from Graham and Buchholz. If the polymers are cross-linked, partially neutralized polyacrylates, reference is made in connection with the exact procedure to the third chapter (page 69 et seq.) in "Modern Superabsorbent Polymer Technology", F.L. Buchholz and AT. Graham (Editors) in Wiley-VCH, New York, 1998, which forms part of this disclosure. In addition, it is preferred that the process according to the invention for production of acrylic acid or the process according to the invention for production of a polymer occurs using the devices described above and more closely illustrated in the figures. In this way, water absorbing polymer structures can be obtained as particularly suitable superabsorbers. A contribution to the solution of the above-mentioned objects is also made by water-absorbing polymer structures obtainable by radical polymerisation of the acrylic acid obtainable by means of the above-described synthetic process in the presence of cross-linkers. A contribution to the solution of the previously mentioned objects is also made by water-absorbing polymer structures, which are based to at least 25 wt.%, preferably to at least 50 wt.%, yet more preferably to at least 75 wt.% and most preferably to at least 95 wt.% on acrylic acid, whereby at least 80 wt.%, preferably at least 90 wt.% and most preferably at least 95 wt.% of the acrylic acid monomers used in the production of the water-absorbing polymer structures have been obtained by a synthetic process starting from non-fossil, renewable organic material. These non-fossil, renewable organic materials are in particular materials not generated from petroleum, or coal or brown coal as well as natural gas. These non-fossil, renewable organic materials are, rather, products of agriculture and forestry, in particular fats and oils from glycerine and fatty acids. Preferably, these water-absorbing polymer structures are obtainable by a process comprising the following process steps: i) polymerisation of the acrylic acid in the presence of a cross-linker to form a polymer gel; li) optionally, comminution of the polymer gel; iii) drying of the optionally comminuted polymer gel to obtain water-absorbing polymer structures, and iv) optionally, surface post-treatment of the water-absorbing polymer structure. According to a particular embodiment of the water-absorbing polymer structures according to the invention, these are based to at least 25 wt.%, preferably to at least 35 wt.% and most preferably to at least 45 wt.% upon natural, biodegradable polymers, preferably upon carbohydrates such as celluloses or starches. Preferred polymer structures according to the invention are fibres, foams or particles, whereby fibres and particles are preferred and particles particularly preferred. Preferred polymer fibres according to the invention are dimensioned such that they can be incorporated into or as yarns for textiles and also directly into textiles. It is preferred according to the invention that the polymer fibres have a length within the range from 1 to 500, preferably 2 to 500 and particularly preferably 5 to 100 mm and a diameter within the range from 1 to 200, preferably 3 to 100 and particularly preferably 5 to 60 denier. Preferred polymer particles according to the invention are dimensioned so that they have an average particle size according to ERT 420.2-02 within the range from 10 to 3000 µm, preferably 20 to 2000 µm and particularly preferably 150 to 850 µm. It is further preferred that the proportion of particles with a particle size within a range from 300 to 60 µm is at least 50 wt.%, particularly preferably at least 75 wt.%, It is further preferred according to the invention that the water-absorbing polymer structures have at least one, preferably both of the following properties: a CRC value (CRC = Centrifugation Retention Capacity) determined according to ERT 441.2-02 (ERT = Edana Recommended Test Method) of at least 20 g/g, preferably at least 25 g/g and most preferably at least 30 g/g; an absorption under a pressure of 20 g/cm2 determined according to ERT 442.2-02 of at least 15 g/g, preferably at least 17.5 g/g and most preferably at least 20 g/g. The CRC values and the vales for the absorption under pressure generally do not lie above 1 50 g/g. A further contribution to the solution of the above mentioned objects is made by water-absorbing polymer structures, which are characterized by the following properties: the polymer structure is based to at least 25 wt.%, preferably to at least 50 wt.%, yet more preferably to at least 75 wt.% and most preferably to at least 95 wt.% on acrylic acid, whereby at least 80 wt.%, preferably at least 90 wt.% and most preferably at least 95 wt.% of the acrylic acid monomers used in the preparation of the water-absorbing polymer structures has been obtained by a synthesis process which starts from non-fossil, renewable organic material, (P2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least 25%, preferably at least 35% and most preferably at least 45%, whereby a value of at most 75 to 95 % as upper limit is generally not exceeded; (P3) the polymer structure has a CRC value determined according to ERT 441 .24)2 of at least 20 g/g, preferably at least 25 g/g and most preferably at least 29 g/g, whereby a CRC value of 60 g/g as upper limit is generally not exceeded. In a further aspect of the polymer structure described in the previous paragraph, said polymer structure has at least properties ß1 and ß2. All further developments given in this text for the polymer structure are also valid for the polymer structure of this paragraph. Another contribution to the solution of the above-mentioned objects is made by water-absorbing polymer structures which are based to at least 10, preferably at least 25, particularly preferably at least 50 and more preferably at least 75 and more preferably at least 80 wt.%, based upon the polymer structure, upon acrylic acid and which are characterised by the following properties: (el) the polymer structure has a sustainability factor of at least 10, preferably at least 20, particularly preferably at least 50, yet more preferably at least 75, further preferably at least 85 and even more preferably at least 95; (s2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least 25%, preferably at least 35% and most preferably at least 45%, whereby a value of at most 75 to 95 % as upper limit is generally not exceeded; (e3) the polymer structure has a CRC value determined according to ERT 441.2-02 of at least 20 g/g, preferably at least 25 g/g and most preferably at least 29 g/g, whereby a CRC value of 60 g/g as upper limit is generally not exceeded. In another embodiment of the polymer structure described in the previous section, this polymer structure has at least properties el and e2. All further developments given in this text for the polymer structure are also valid for the polymer structure of this paragraph. In some cases the above-mentioned upper limits can also be up to 10% or up to 20% lower. It is preferred for the polymer structures described in the two previous sections that these are based, in addition to the acrylic acid, upon a di- or polysugar. These di- or polysugars are preferably present as a further component of the polymer structure in an amount of at least 1 wt.%, preferably at least 5 wt.% and yet more preferably at least 15 wt.%, based upon the polymer structure, so that the sum of the wt.% of the components of the water-absorbing polymer structure is 100 wt.%. Preferred for sugars of these types are poly-chain sugars, which preferably have a number average molecular weight determined by means of gel permeation chromatography and light scattering within the range from 10,000 to 1,000,000 and preferably within the range from 50,000 to 500,000 g/mol. These preferably consist of linear and thus unbranched chains. All sugar compounds known to the skilled person and appearing suitable are considered as sugars of this type. Thus, for example, celluloses and starches can be mentioned, whereby one or at least two different starches are preferred. Among starches, in turn amylase-eontaining starches are preferred. The amylase content preferably lies within a range from 10 to 80 and particularly preferably within a range from 20 to 70 wt.%, based upon the starches. It is furthermore preferred that the di- or polysugars have a particle size such that at least 50 wt.%, preferably at least 70 wt.% and yet more preferably at least 85 wt.% of the particles are smaller than 50 urn. The particle size is determined by means of sieve analysis. Such products are, for example, commercially available under the trade name Eurylon® 7 or Foralys® 380 from the company Roquette, France. Such water-absorbing polymer structures can be prepared and are thus obtainable preferably by providing a surface crosslinked water-absorbing polymer; mixing the surface crosslinked water-absorbing polymer with a di- or poly sugar. It is here preferred that the water-absorbing polymer is based to at least 50 wt.%, preferably at least 80 wt.% and yet more preferably at least 95 wt.% upon acrylic acid which comes from the inventive dehydration process used for polymerisation partially neutralised and with a crosslinker. The sustainability factor gives the proportion of the polymer structure which is based upon materials based upon non-fossil, renewable organic materials. A sustainability factor of 100 means that the polymer structure is fully based upon non-fossil, renewable organic materials. A further contribution to the solution of the above-described objects is provided by a composite comprising the water-absorbing polymer structures according to the invention or water-absorbing polymer structures which are obtainable by radical polymerisation of the acrylic acid obtainable by the above-described synthetic process in the presence of cross-linkers. It is preferred that the polymer structures according to the invention and the substrate are firmly bound together. As substrates, sheets made from polymers, such as, for example, made from polyethylene, polypropylene or polyamide, metals, non-wovens, fluff, tissues, wovens, natural or synthetic fibres, or other foams are preferred. It is, furthermore, preferred according to the invention that the polymer structures are comprised in the composite in an amount of at least 50 wt.%, preferably at least 70 wt.% and yet more preferably at least 90 wt.%, based upon the total weight of polymer structure and substrate. In a particularly preferred embodiment of the composite according to the invention, the composite is a sheet-like composite, as described in WO-A-02/056812 as "absorbent material". The disclosure of WO-A-02/056812, in particular with respect to the exact construction of the composite, the mass per unit area of its components as well as its thickness is hereby introduced as reference and represents a part of the disclosure of the present invention. A further contribution to the solution of the above-mentioned objects is provided by a process for producing a composite, whereby the water-absorbing polymer structures according to the invention, or the water-absorbing polymers, which can be obtained by radical polymerisation of the acrylic acid obtainable by the above- described synthetic process in the presence of cross-linkers, and a substrate and optionally an additive are brought into contact with each other. As substrate are preferably used those substrates which have already been mentioned in connection with the composite according to the invention. A contribution to the solution of the above-mentioned objects is also provided by a composite obtainable by the above-described process. A further contribution to the solution of the above-mentioned objects is delivered by chemical products comprising the water-absorbing polymer structures according to the invention or a composite according to the invention. Preferred chemical products are in particular foams, moulded bodies, fibres, sheets, films, cables, sealing materials, liquid-absorbing hygiene articles, in particular diapers and sanitary napkins, carriers for plant or fungus growth-regulating agents or plant protection agents, additives for construction materials, packaging materials or soil additives. Preferred chemical products are hygiene articles comprising an upper layer, a lower layer and an intermediate layer arranged between the upper layer and the lower layer, which comprises water-absorbing polymer structures according to the invention. In addition, the invention relates to a process for the production of acrolein which is characterized by the herein described process for dehydration of glycerine to a dehydration product comprising acrolein and the herein described preferred embodiments of this dehydration. The invention further relates to fibres, sheets, adhesives, cosmetics, moulding materials, textile and leather additives, flocculants, coatings or varnishes based upon acrylic acid which is obtainable according to a process according to the invention, or their derivatives or salts. As derivatives of acrylic acid are considered in particular its esters, preferably its alkyl esters and yet more preferably its C( to C'io, yet more preferably €2 to €5 and more preferably C^ to €4 alkyl esters. As salts can be mentioned the alkali or alkaline earth as well as the ammonia salts of acrylic acid. The invention further relates to the use of an acrylic acid which has been obtained by a process according to the invention, or derivatives or salts thereof in fibres, sheets, adhesives, cosmetics, moulding materials, textile and leather additives, flocculants, coatings or varnishes. The invention is now more closely illustrated by means of non-limiting figures and examples. Fig. 1 shows a schematic of the individual stages and steps of the process according to the invention and of the device according to the invention. Fig. 2 shows a gas phase dehydration unit. Fig. 3 shows a liquid phase dehydration unit. Fig. 4 shows a processing unit. Fig. 5 shows a further embodiment of the liquid phase dehydration unit. In Fig. 1, firstly the oils or fats are introduced into a saponifier 1, where an alkaline saponification with bases or alkali alcoholates occurs. The glycerine produced in the saponifier by generally known purification steps such as salting out and distillation is then conduced to a dehydration unit with a dehydration reactor 2 (in order to produce acrolein from the glycerine). The thus-produced acrolein is then conducted in a next step to a gas phase reaction reactor 3, in which it is converted by a gas phase oxidation reaction into acrylic acid. After gas phase reaction reactor 3 follows a quench unit 4, in which the acrylic acid-comprising gas from gas phase reaction reactor 3 is brought into the liquid phase by bringing into contact with a quench means. The liquid mixture of quench means and acrylic acid is conducted to a processing unit 5 following the quench unit 4. There, the acrylic acid is purified to pure acrylic acid (at least 99.98 % acrylic acid) either by crystallisation or distillation or by a combination of these two steps or by extraction or a combination of extraction and crystallisation or a combination of extraction and distillation or a combination of extraction-distillation and distillation, the acrylic acid being present as pure acrylic acid itself or in an aqueous phase. The thus-obtained acrylic acid is then conducted to a polymerisation unit 6. The polymer obtained in the polymerisation unit 6 can be processed according to the subsequent use. A further processing unit, for example a diaper machine or a machine for production of binding and wound material can follow after the polymerisation unit 6. Fig. 2 shows a gas phase dehydration unit, in which a compound reservoir 7 is connected to an evaporator 12. The evaporator 12 is connected upstream to a reaction area 9. The pressurisable reaction area 9 comprises catalyst 8. Both the evaporator 12 and the reaction area 9 comprise heating elements 21, with which the temperatures necessary for evaporation and dehydration of glycerine can be achieved. The reaction area 9 is connected to a quencher 10 via a lower outlet 13. The quencher 10 receives, in its upper area, in addition to the lower product outlet 13, a quench liquid feed 16. In the lower area of the quencher 10, a trapping reservoir for side-products 17 is arranged, which can be emptied by means of exit valve 19. The upper area of the quencher 10 further receives an exit line 11, which conducts the acrolein-comprising dehydration product to gas phase reaction reactor 3. Quench unit 4 follows these. Fig. 3 shows a liquid phase dehydration device, in which glycerine is placed in a compound reservoir 7, which is connected with the upper area of a pressurisable reaction area 9, which in turn comprises catalysts 8. The reaction area 9 is temperature-controlled by means of a heating element 21. In the lower area of reaction area 9, a buffer reservoir 18 is arranged, which forms a cycle with the reaction area by means of a pump, and via which glycerine and acrolein already situated in the reaction area 9 and in the buffer reservoir can be conducted in the cycle. In the upper area of the reaction area 9 is situated a transfer line to a quencher 10, which leads into the upper area of the quencher 10 together with a quench liquid feed 16. Also in the upper area of the quencher 10 is situated an exit line 11 to the gas phase reaction reactor 3, followed in rum by the quench unit 4. In the lower area of the reaction area 9 a trapping reservoir for side-products 17 equipped with an exit valve 9 has an opening. In Fig. 4 the gas coming from the gas phase reaction reactor 3 is introduced into the quench unit 4, in which it is brought into contact with water and absorbed, whereby as absorption liquid an aqueous acrylic acid solution is obtained, in which likewise a part of the side-products arising from the previous synthesis steps is comprised. This aqueous acrylic acid solution is conducted via a feed line 22 to an extraction unit 23. At the latest in the extraction unit 23, the acrylic acid solution is brought into contact with toluene as separating agent (TM). After a careful combination in the extraction unit 23, a phase separation occurs to form an upper phase based substantially on water, and a lower phase based substantially on toluene as separating agent. The phase based substantially on the separating agent is conducted via feed line 24 to the crystallizer 25, which is preferably a scratch cooler. The crystal suspension comprised in crystallizer 25 is then conducted by means of a suspension conduit 26 to a wash column 27, in which a separation of the acrylic acid crystals occurs, in the course of which a mother liquor comprising the separating agent is retained. The mother liquor obtained in the wash column 27 after the separation of the acrylic acid crystals is preferably at least partially conducted back via the mother liquor conduit 28 into the extraction unit 23. It is further preferred that the upper phase based substantially on water comprised in the extraction unit 23 is conducted back to the quench unit 4 via quench conduit 29. In a preferred design of the process according to the invention and of the device according to the invention, acrylic acid still comprised in the composition can be separated by crystallisation from the composition conducted in the quench conduit 29 by means of a further purification device 30, which is, for example, a suspension crystallisation device or a layer crystalliser. It is, furthermore, preferred in another embodiment of the process according to the invention and of the device according to the invention that the composition conducted in the mother liquor conduit 28 (mother liquor separated during the crystallisation) is separated from further impurities before its being conducted back by means of a separating unit 31. This separating unit is preferably likewise a suspension crystallisation device or a layer crystallizer or also a filter. In Fig. 5 is shown schematically that optionally in a pre-mixer 32, via lines A to C, water, glycerine and, in so far as necessary, catalyst, for example an inorganic acid such as phosphoric acid, are combined and conducted to the dehydration reactor 2 formed as a stainless steel pressure reactor. The dehydration of glycerine to acrolein in the liquid phase occurs here. When using a soluble and thus homogeneously distributable catalyst, such as an inorganic acid, it is advantageous to at least partially neutralise this by addition of a base such as NaOH, mostly as a solution, via line D. This measure contributes to the prevention of further reactions which can lead to undesired side products. Following this is a distillation device 33 which comprises in the upper section a volatiles area 34 and in the lower section a high-boilers area 35, whereby the acrolein-comprising phase from the dehydration is introduced between the two areas 34 and 35. In the volatiles area 34 the components with lower boiling points than acrolein would come out guided by exit line E and the still remaining acrolein and the high-boiling components guided in the reflux. In the high-boiler area 35 representing the distiller bottom the high-boilers are concentrated. It is here advantageous to conduct the bottom product in a cycle. From the high-boiler area, the components with higher boiling points than acrolein are discharged and conducted via a high-boiler pump to a high boiler separator 37.The high-boiler separator is advantageously equipped with a membrane. After passing through the high-boiler separator 37 the mixture, comprising predominantly water and glycerine, treed from the high-boilers, is conducted back to the pre-mixer 32 and is thus available again for dehydration. In this way an efficient dehydration of glycerine to acrolein can be achieved by the cyclical route, in which the thus-obtained acrolein from the distiller 33 in sufficient purity for a long-lasting operation of the gas phase oxidation is conducted to the gas phase reaction reactor 3 for oxidation with air conducted in through feed line F to acrolein conducted away via exit line G. EXAMPLES Example1 Dehydration in the gas phase In a gas phase dehydration device described in figure 2 (enclosed within the dashed line), a catalyst is provided in reactor area 9, the catalyst being obtained from 100 parts by weight of Rosenthal balls (alpha-A12O3) with a diameter of 3 mm by mixing with 25 parts by weight of a 20 wt.% phosphoric acid for 1 hour and then separated from excess water by rotary evaporation at 80°C (Ho value between -5.6 and -3). The glycerine evaporated in an evaporator at 295°C is conveyed over 100 ml of this catalyst in a steel pipe in the reaction area as a 20 wt.% aqueous solution with a pump with 40 ml/h at a temperature of 270°C. The acrolein-comprising reaction mixture was brought into contact with water as quench means in the quencher and the thus-obtained aqueous mixture conducted to the gas phase oxidation in a conventional reactor for gas phase oxidation of acrolein to acrylic acid. Example 2: liquid phase dehydration In a device according to Fig. 3, a catalyst as described in example 1 was used for liquid phase dehydration (enclosed within the dashed line), whereby in the place of the Rosenthal balls a silicon dioxide carrier was used (Ho value between 2 and -3). The reaction temperature was 240°C. Water was used as quench means. Following the acrolein synthesis, a gas phase oxidation in a conventional gas phase oxidation reactor followed, as in example 1, followed by an absorption in water in a quench unit. The acrylic acid-water mixtures obtained in example 1 and 2 were combined in a glass separating funnel temperature-controlled to 0°C with 0.5 parts of their volume of toluene. The mixture was shaken vigorously and left to stand for 60 minutes in order to enable a phase separation. The two thus-arising phases were separated. The toluene-comprising phase was subjected to an azeotropic distillation and the thus-obtained acrylic acid distilled before its use in polymerisation. PTA could not be identified by gas chrornatography as an impurity in the acrylic acid obtained from acrolein obtained either by gas phase dehydration or by liquid phase dehydration followed by gas phase oxidation. Exjmpje 3: Polymerisation Dissolved oxygen was removed from a monomer solution consisting of 280 g of the above-obtained acrylic acid, which was neutralized to 70 mol. % with sodium hydroxide, 466.8 g water, 1.4 g polyethylene glycol-300-diacrylate and 1.68 g allyloxypolyethyleneglycol acrylic acid ester by flushing with nitrogen and the monomer solution cooled to the start temperature of 4°C. After reaching the start temperature, the initiator solution (0.1 g 2,2-azobis-2-amidinpropane dihydrochloride in 10 g H2O, 0.3 g sodium peroxydisulfate in 10 g H2O, 0.07 g 30 % hydrogen peroxide solution in 1 g H2O and 0.015 g ascorbic acid in 2 g added. After the end temperature of approximately 100°C was reached, the gel formed was comminuted and dried for 90 minutes at 150°C. The dried polymer was coarsely chopped, ground and sieved to a powder with a particle size of 150 to 850 urn. For post-crosslinking, 100 g of the above-obtained powder was combined with a solution of 1 g l,3-dioxalan-2-one, 3 g water and 0.5 g aluminium sulphate-18-hydrate and then heated for 40 minutes in an oven set to 180°C. Example 4: Preparation of a biodegradable polymer The post-crosslinked polymer obtained in example 3 was mixed under dry conditions with a water-soluble wheat starch (the product Foralys® 380 from the company Roquette, Lestrem, France) in the weight ratio polymer : starch of 4 : 1 and then homogenised for 45 minutes in a roll mixer type BTR 10 of the company Frobel GmbH, Germany. The product had a biodegradability according to the modified Sturm test after 28 days of 39 % and a CRC value of 29.9 g/g. The sustainability factor was about 0.99. Reference characters 1 saponifier 2 dehydration reactor 3 gas phase reaction reactor 4 quench unit 5 processing unit 6 polymerisation unit 7 compound reservoir 8 catalyst 9 reaction area 10 quencher 11 exit line 12 evaporator 13 lower product outlet 14 upper product outlet 15 pump 16 quench liquid feed 17 trapping reservoir for side products 18 buffer reservoir 19 outlet valve 20 cycle 21 heating element 22 feed line 23 extraction unit 24 feed line 25 crystallizer 26 suspension conduit 27 wash column 28 mother liquor conduit 29 quench conduit 30 purification device 31 separating unit 32 pre-mixer 33 distiller 34 volatiles area 35 high-boilers area 36 high-boilers pump 37 high-boilers separator Claims 1. Process for production of acrylic acid, comprising at least the following steps: a. dehydration of glycerine to a dehydration product comprising acrolein; b. gas phase oxidation of the dehydration product to obtain a monomer gas comprising an acrylic acid; c. bringing into contact of the monomer gas with a quench means to obtain a quench phase comprising acrylic acid; d. processing of the quench phase to obtain a monomer phase comprising acrylic acid. 2. Process for production of a polymer by radical polymerisation of acrylic acid, comprising at least the following steps: A. dehydration of glycerine to a dehydration product comprising acrolein; B gas phase oxidation of the dehydration product to obtain a monomer gas comprising acrylic acid; C bringing into contact of the monomer gas with a quench means to obtain a quench phase comprising acrylic acid; D. processing of the quench phase to obtain a monomer phase comprising acrylic acid; E. radical polymerisation of the monomer phase. 3. Process according to claim 2, wherein the polymer is a water-absorbing polymer structure. 4. Process according to claim 3, wherein the water-absorbing polymer structure is obtainable by a process comprising the following process steps: i) polymerisation of the acrylic acid in the presence of a crosslinker to form a polymer gel; ii) optionally comminution of the polymer gel; iii) drying of the optionally comminuted polymer gel to obtain water-absorbing polymer structure; iv) optionally surface post-crosslinking of the water-absorbing polymer structure. 5. Process according to any one of claims 2 to 4, wherein the acrylic acid is present to at least 20 mol%, based on the monomer, as a salt. 6. Process according to any one of the preceding claims, wherein the glycerine is obtained from saponification of fats. 7. Process according to any one of the preceding claims, wherein glycerine is generated in the generation of liquid fuels from natural raw materials. 8. Process according to any one of the preceding claims, wherein the dehydration occurs at least partially in liquid phase. 9. Process according to any one of claims 1 to 11, wherein the dehydration occurs at least partially in a gas phase. 10. Process according to any one of the preceding claims, wherein the glycerine is used in aqueous phase. 11. Process according to any one of the preceding claims, wherein a dehydration catalyst is used. 12. Process according to claim 11, wherein the dehydration catalyst is in contact with a carrier x. 13. Process according to claim 12, wherein the carrier x is a solid with a total pore volume according to DIN 66133 within a range from 0.1 to 1.5 ml/g. 14. Process according to any one of claims 11 to 13, wherein the dehydration catalyst is an inorganic acid. 15. Process according to claim 14, wherein the dehydration catalyst is present in a solution. 16. Process according to any one of the preceding claims, wherein the gas phase oxidation occurs in the presence of an oxidation catalyst comprising a transition metal in elemental or in chemically bound form or both. 17. Process according to any one of the preceding claims, wherein the dehydration product is conducted in an aqueous phase to the gas phase oxidation. 18. Process according to any one of the preceding claims, wherein the gas phase oxidation occurs within a temperature range from 200 to 400 °C. 19. Process according to any one of the preceding claims, wherein the monomer gas comprises the acrylic acid in an amount within the range from 5 to 50 wt.%, respectively based on the monomer gas. 20. Process according to any one of the preceding claims, wherein the quench means comprises water or an organic compound with a boiling point within the range from 50 to 250 °C or water and this organic compound. 21. Process according to any one of the preceding claims, wherein wherein the quench phase comprises the acrylic acid in an amount within the range from 30 to 90 wt.%, based on the monomer phase. 22. Process according to any one of the preceding claims, wherein the processing occurs at temperatures below the boiling point of the acrylic acid. 23. Process according to any one of the preceding claims, wherein the processing occurs by extraction or crystallisation or both. 24. Device for production of acrylic acid comprising connected with each other in fluid-conveying fashion: 1 a. a dehydration reactor (2), 2 a. a gas phase oxidation reactor (3), 3a. a quench unit (4), 4a. a processing unit (5). 25. Device for production of polymers comprising connected with each other in fluid-conveying fashion: 1 b. a dehydration reactor (2), 2b. a gas phase oxidation reactor (3), 3b. a quench unit (4), 4b. a processing unit (5) 5b. a polymerisation unit (6). 26. Device according to claim 24 or claim 25, wherein the dehydration reactor (2) comprises a compound reservoir (7), followed by a reaction area (9) accepting a catalyst (8), followed by a quencher (10) with a line (11) to the gas phase oxidation reactor (3). 27. Device according to claim 26, wherein an evaporator (12) is provided after the compound reservoir (7) and before the reaction area (9). 28. Device according to claim 27, wherein the reaction area (9) comprises a lower product outlet (13) which leads into the quencher (10). 29. Device according to claim 28, wherein the reaction area (9) comprises an upper product outlet (14) which leads into the quencher. 30. Process according to any one of claims 1 and 5 to 23, wherein the process is carried out in a device according to any one of claims 24 and 26 to 29. 31. Process according to any one of claims 2 to 23, wherein the process is carried out in a device according to any one of claims 24 to 29. 32. Water-absorbing polymer structure obtainable by a process according to any one of claims 3 to 23 and 31. 33. Water-absorbing polymer structures which are based to at least 25 wt.% upon optionally partially neutralised acrylic acid, wherein the water-absorbing polymer structures are characterised by a sustainability factor of at least 80%. 34. Water-absorbing polymer structures according to claim 33, wherein the polymer structures are based to at least 25 wt.%, based upon the total weight of the water-absorbing polymer structure, upon natural, biodegradable polymers. 35. Water-absorbing polymer structures, which are characterized by the following properties: (PI) the polymer structure is based to at least 25 wt.% on acrylic acid, whereby at least 80 wt.% of the acrylic acid monomers used in the preparation of the water-absorbing polymer structures has been obtained by a synthesis process which starts from non-fossil, renewable organic material, (p2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least 25%; (p3) the polymer structure has a CRC value determined according to ERT 441.2-02 of at least 20 g/g. 36. Water-absorbing polymer structures, which are based to at least 10 wt.%, based upon the polymer structure, upon acrylic acid and which are characterised by the following properties: (l) the polymer structure has a sustainability factor of at least 10; (2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least 25%; (3) the polymer structure has a CRC value determined according to ERT 441.2-02 of at least 20 g/g. 37. Composite comprising a water-absorbing polymer structure according to any one of claims 32 to 36 and a substrate. 38. Process for the production of a composite according to claim 37, wherein the water-absorbing polymer structure and the substrate are brought into contact with each other. 39. Composite obtainable by a process according to claim 38. 40. Hygiene article comprising an upper sheet, a lower sheet and an intermediate sheet arranged between the upper sheet and the lower sheet, which comprises water-absorbing polymer structures according to any one of claims 32 to 36. 41. Fibres, sheets, moulded masses, textile and leather additives, flocculants, coatings or varnishes based on acrylic acid obtainable by a process according to any one of claims 1 and 5 to 23 or 30 or derivatives or salts thereof. 42. Use of an acrylic acid obtainable according to a process according to any one of claims 1 and 5 to 23 or 30 or their derivatives or salts in fibres, sheets, moulded masses, textile and leather additives, flocculants, coatings or varnishes.

Full Text

ACRYLIC ACED, WATER-ABSORBENT POLYMER STRUCTURES BASED ON RENEWABLE RESOURCES AND METHOD FOR PRODUCING SAID STURCTURES
The present invention relates to a process for preparation of acrylic acid, a process for preparation of polymers by radical polymerisation of acrylic acid, preferably for preparation of water-absorbing polymers, the water-absorbing polymers obtainable by this process, water-absorbing polymers based to at least 25 wt.% upon partially neutralized acrylic acid, a composite, a process for producing a composite, the composite obtainable by this process, the use of acrylic acid in the preparation of water-absorbing polymer structures, a device for preparation of acrylic acid, a process for preparation of acrylic acid and the acrylic acid obtainable by this process.
High requirements are made of the purity of acrylic acid which is used in the preparation of polymeric compounds. This is particularly the case when the polymers are so-called superabsorbers, which are incorporated into wound dressings or hygiene articles. These polymers can absorb and thus bind aqueous liquids to form a hydrogel. Superabsorbers are, therefore, used in particular in hygiene articles such as diapers, incontinence articles, sanitary napkins and the like for the absorption of body fluids. A comprehensive overview of superabsorbers, their application and their preparation is given by F.L. Buchholz and A. T. Graham (Editors) in "Modern Superabsorbent Polymer Technology", Wiley-VCH, New York, 1998.
In the preparation of superabsorbent polymers, generally an acrylic acid is used which has been obtained as pure acrylic acid by catalytic gas phase oxidation of propylene to acrolein, which is then converted in a further catalytic gas phase
oxidation to acrylic acid, subsequent absorption of the gaseous reaction mixture in water, distillation of the thus-obtained aqueous acrylic acid solution to obtain a crude acrylic acid and further purification of the crude acrylic acid by distillation or crystallisation.
It is disadvantageous in this process for production of acrylic acid that the temperatures between 300 and 450°C used in both stages lead to formation of oligomers and further undesired cracking products. This results in the accumulation of an undesirably large amount of compounds which are less volatile than acrylic acid or compounds which are difficult to separate from acrylic acid, such as acetic acid, which must be separated from the acrylic acid. This separation, which as a rule occurs by distillation, leads to a further thermal stress on the acrylic acid, which favours the disadvantageous formation of dimeric or oligomeric acrylic acid. A high acrylic acid dimer or acrylic acid oligomer content is, however, disadvantageous, since these dimers or oligomers are built into the polymer backbone during the preparation of superabsorbers by radical polymerisation of acrylic acid in the presence of crosslinkers. During the post-treatment of the surface of the polymer particles, which occurs following the polymerisation, for example as a surface post-crosslinking, the polymerized-in dimers, however, split to form p-hydroxypropionic acid, which is dehydrated under the post-crosslinking conditions to form acrylic acid. A high dimeric acrylic acid content in the acrylic acid used in the production of superabsorber therefore leads to the acrylic acid monomer content increasing during a thermal treatment of the polymer, as occurs during post-crosslinking.
Since the soluble parts, in particular the acrylic acid monomers in the superabsorbent polymers, can cause skin irritation, a use of these polymers in hygiene articles requires a particularly low content in extractable components. Also other, often toxic compounds remain in the acrylic acid obtained by the catalytic gas phase oxidation. Among these impurities are included, in particular,
aldehydes, which have a disruptive effect on the course of polymerisation, with the result that the polymers still comprise considerable amounts of soluble components
Acrylic acids produced in previous ways from propylene comprises not inconsiderable amounts of ketones having double bonds, in particular protoanemonin (PTA). This compound can, on contact with skin, cause signs of poisoning, such as, for example, reddening, itching or blister formation. Superabsorbers which comprise large amounts of PTA as soluble components are therefore of concern from a dermatological viewpoint. Furthermore, PTA disrupts the polymerisation, as described in US-A-2002/0120085. This leads to the obtaining of superabsorbing polymers with less good absorption, transport and retention properties for body fluids, so that when using Superabsorbent polymers of this type in hygiene articles such as diapers or sanitary napkins, wearer comfort is worsened, for example by "leakage".
Several processes have already been described in the state of the art, with which the content in the above-mentioned compounds, in particular of aldehydes, or PTA, in the acrylic acid obtained by gas phase oxidation of propylene can be reduced.
EP-A-0 574 260 suggests using, in the production of superabsorber, if possible, an acrylic acid which is characterized by a {3-hydroxypropionic acid content of not more than 1000 ppm. Such an acrylic acid is obtained by distilling conventional acrylic acid us directly as possible before the polymerisation.
DE-A-101 38 150 suggests, in order to reduce the amount of aldehyde in the acrylic acid, bringing this into contact with an aldehyde trapper, in order to
convert the aldehydes into high-boiling compounds, which can then be separated by means of distillation.
Various methods have been proposed in the state of the art for the removal of PTA, such as the addition of a nitrous acid salt, of nitrogen oxide or of nitrobenzene (JP 81-41614) or the addition of one or more para-phenylene diamines (EP-A-567 207) to the acrylic acid.
The disadvantage of the above-described processes for reducing the amount of aldehydes and ketones in acrylic acid is, however, among others, that, in so far as the impurity content of the acrylic acid is not known exactly, these reagents must be used in excess for the purpose of as complete a removal as possible of impurities from the acrylic acid. On the one hand, reagents which are reactive to the acrylic acid must be added. The portion of these reagents which is not converted must then be removed again. Reagents which are not removed are comprised in the superabsorbent obtained from such an acrylic acid as soluble components, which can come into contact with the skin of the hygiene article wearer when the superabsorbers are used in hygiene articles. Furthermore, the processes known from the prior art for removal of aldehydes in ketones from acrylic acid only very seldom remove these impurities completely.
In addition to the disadvantages which are traced back to impurities in the acrylic acid used in the production of superabsorbers, known superabsorbers also have the disadvantage that, unless they at least partially comprise natural polymers, such as celluloses, they are hardly based upon renewable raw materials. While it is successful to produce many of the components used in hygiene articles, in particular in disposable diapers, from biological starting materials, replacement of the superabsorbers based upon cross-linked polyacrylates by natural superabsorbing polymers, such as cross-linked, derivatised starches or celluloses, is generally associated with significant losses in respect of the absorbent
properties. This mostly leads to the necessity of using considerably more of the absorbents based upon natural polymers, simply in order to approach the same absorbent properties in a hygiene article. This is disadvantageous, because the hygiene articles become more voluminous and heavier, which significantly restricts wearing comfort and leads to a larger waste volume, which, in addition to dumping space or combustion expenditure also requires greater transport capacity for the removal of waste. All of this has a disadvantageous effect upon the environmental friendliness of the absorbers based upon natural polymers.
The object of the present invention was to overcome the disadvantages arising from the state of the art.
In particular, the present invention had the object of making available polymers, in particular superabsorbers, which have a particularly low content in extractable, possibly toxic components.
Furthermore, the object of the present invention was to provide polymers, in particular superabsorbers, which are environmentally friendly and still have excellent application properties. In particular it was desired to provide superabsorbers with improved environmental friendliness while retaining the same good absorbent properties.
In addition, it was an object of the present invention to improve the environmental friendliness of further processing products comprising the polymers according to the invention, such as composites in general and hygiene articles in particular, without the desired functions, such as absorbent capability, wearing comfort and simple producibility of these further processing products suffering.
It was also an object of the present invention to provide a process for preparing polymers of this type and the monomers suitable for their production, whereby
this process should take place as far as possible without the use of reactive compounds for removal of impurities from the monomers used in the preparation of the polymers.
In addition, an object of the present invention was to suggest a process and a device for the production of monomers and polymers, which can be integrated with as little conversion expenditure as possible into existing industrial manufacturing processes and devices.
A contribution to the solution of the above mentioned objects is provided by a process for preparation of acrylic acid, comprising at least the following steps:
a. dehydration of glycerine to an acrolein-comprising dehydration
product;
b. gas phase oxidation of the dehydration product to obtain an acrylic
acid-comprising monomer gas;
c. bringing into contact of the monomer gas with a quenching means
to obtain an acrylic acid-comprising quench phase;
d. processing of the quench phase to obtain an acrylic acid-
comprising monomer phase.
A further contribution to the solution of the above objects is provided by a process for preparation of a polymer by radical polymerisation of acrylic acid comprising at least the following steps:
A. dehydration of glycerine to an acrolein-comprising dehydration
product;
B. Gas phase oxidation of the dehydration product to obtain an acrylic
acid-comprising monomer gas;
C. bringing into contact of the monomer gas with a quench means to
obtain an acrylic acid-comprising quench phase;
D. processing of the quench phase to obtain an acrylic acid-
comprising monomer phase;
E. polymerisation of the monomer phase.
In one aspect of the process according to the invention it is preferred that the glycerine is obtained by saponification of fats. These fats can be animal fats as well as vegetable fats. Animal fats are obtained in particular from processing of animals. Vegetable fats are obtained in large amounts from oil extraction from oily fruits such as rape, soya., sesame, olives and sunflower seeds. Large amounts of glycerine are generated, in particular, by the production of so-called "Bio diesel" from rape seed oil, as known from WO-A-2004/029016, among others. It is thus preferred in the process according to the invention, that the glycerine is generated m the production of liquid fuels from natural raw materials. This is given, in particular for saponification devices following oil mills.
In one aspect of the process according to the invention, it is preferred that the dehydration occurs at least partially in the liquid phase. As liquid phase, aqueous systems are particularly preferred. If the dehydration should be carried out at least partially or completely in a liquid phase, this had the advantage, in particular if this is an aqueous phase, that for high glycerine concentrations, high acrolein concentrations in the aqueous phase can be achieved. These aqueous phases with high acrolein concentrations can be used directly in the next stage of the gas phase oxidation. In order to protect the oxidation catalyst from carbonisation, it is preferred to provide a separating unit between dehydration and oxidation. In this separating unit the accompanying materials which are different from acrolein and the acrolein are conducted to the gas phase oxidation. In this way, significantly longer catalyst lifetimes can be achieved. A further advantage of the liquid phase dehydration is that a rinsing effect can be achieved with the liquid phase, with
which a formation of coating on a solid state catalyst can be significantly reduced, which leads to increased catalyst running times and thus to a reduced need for regeneration of the catalyst. A further advantage of the liquid phase dehydration is that it can be carried out at relatively moderate temperatures, within a range from 160 to 270°C, preferably within a range from 180 to 260°C and more preferably within a range from 215 to 245°C. These temperature ranges lie significantly below the decomposition and boiling temperature of glycerine of about 290°C, which leads to reduction of sump and cracking products as well as other impurities, which have a disadvantageous effect on the operating time of the gas phase oxidation. It is, however, provided in a further embodiment of the process according to the invention that the dehydration is carries out near to the decomposition point of glycerine, in order to increase the yield. In this embodiment, the temperatures are within a range from 170 to 290 °C, preferably within a range from 190 to 289 °C and more preferably within a range from 225 to 288 °C. It is preferred that the liquid phase dehydration occurs in a circular operation mode, in which in the case of a solid state catalyst the glycerine-containing liquid phase is conducted by means of a pump over the catalyst in a pressurized system. With liquid catalysis or homogeneous catalysis at least a partial flow from the reactor is conducted in the cycle. Converted glycerine, consumed catalyst and optionally removed water are added to the partial flow which has been fed back into the reactor during the cycle, preferably at the reactor entry. Should the partial flow be obtained from an acidic homogeneously catalysed dehydration, it is advantageous that the partial flow is at least partially neutralised. By this measure the formation of side products by reactions in the partial flow can be repressed or even completely prevented. It is further advantageous to deplete materials with higher boiling points than acrolein, characterised as high boiling, from the partial flow. This can occur, for example by means of separating units comprising membranes, which membranes are preferably semi-permeable. In this way higher turnovers and significantly fewer side-products can be obtained, in addition to higher selectivity, in a gentle way.
In a further embodiment of the process according to the invention, it is preferred that the dehydration occurs at least partially or also fully in a gas phase. The dehydration in the gas phase has proven particularly useful in the conversion of glycerine from saponification of fat and from the production of biodiesel. This glycerine generally has a high salt load, which can be separated very well by the evaporation step of the gas phase dehydration. As for the liquid phase dehydration, it is also preferred that the gas phase dehydration occurs in the presence of water.
Accordingly, it is preferred in the process according to the invention that the glycerine is used in an aqueous phase. In the case of the liquid phase dehydration, this liquid glycerine phase generally has a water content within a range from 0 to 97 wt.%, for example 0 to 30 wt.%, preferably within a range from 60 to 95 wt.%, particularly preferably within a range from 70 to 90 wt.%, whereby, however, a smaller water content, for example a water content within a range from 0 to 20 wt.% and from 0 to 10 wt.% of water, respectively based upon the aqueous phase, is also conceivable. In the case of a gas phase dehydration, the aqueous glycerine phase generally has a water amount within a range from 0 to 97 wt.%, preferably within a range from 60 to 95 wt.% and yet more preferably within a range from 70 to 90 wt.%, respectively based upon the aqueous glycerine phase, whereby it can also be particularly advantageous here to use smaller amounts of water, for example a water content within a range from 0 to 20 wt.% or from 0 to 10 wt.%. The further principal component of the glycerine phase is glycerine. Further advantages of the gas phase dehydration are high turnovers up to a quantitative yield with, at the same time, high space-time-yields.
According to another embodiment of the process according to the invention, it is preferred to combine gas phase dehydration and liquid phase dehydration with each other According to one form of the process according to the invention, the
glycerine can first be conducted to the gas phase dehydration and then to the liquid phase dehydration or the other way around. The first-mentioned order has the advantage that glycerine charges with heavy salt loads originating from fat saponification can first be freed from these salt loads by evaporation in the gas phase dehydration, in order to be then further converted in the liquid phase dehydration by means of the cycle to high yields and selectivities with few side-products.
According to a further embodiment of the process according to the invention a dehydration catalyst is used in the process. Dehydration catalysts can be acidic as well as basic catalysts. Acidic catalysts are particularly preferred because of the low tendency to form oligomers. The dehydration catalyst can be used as a homogeneous as well as a heterogeneous catalyst. If the dehydration catalyst is present as a heterogeneous catalyst, it is preferred that the dehydration catalyst is in contact with a carrier x. As carrier x. are considered all solids which appear suitable to the skilled person. In this context it is preferred that the solid has suitable pore volumes, which are suited for a good binding and taking up of the dehydration catalyst. In addition, total pore volumes according to DIN 66133 within a range from 0.01 to 3 ml/g are preferred and within a range from 0.1 to 1.5 ml/g particularly preferred. In addition, it is preferred that the solids suitable as carrier x. have a surface area within the range from 0.001 to 1000 m2/g, preferably within the range from 0.005 to 450 m2/g and yet more preferably within the range from 0.01 to 300 m2/g according to BET test according to DIN 66131. A bulk good, which has an average particle diameter within the range from 0.1 to 40 mm, preferably within the range from 1 to 10 mm and yet more preferably within the range from J .5 to 5 mm, can be used as carrier for the dehydration catalyst. The wall of the dehydration reactor can also serve as carrier. Furthermore, the carrier can itself be acidic or basic or an acidic or basic dehydration catalyst can be applied to an inert carrier. As application techniques are cited in particular immersion or impregnation or the incorporation into a carrier matrix.
Particularly suited as carrier x., which can also have dehydration catalyst properties, are natural or synthetic silicate materials, such as, in particular, mordenite, montmorillonite, acidic zeolites, carrier materials supporting mono-, di- or polybasic inorganic acids, in particular phosphoric acids, or acidic salts of inorganic acids, such as oxidic or silicate materials, for example A^Os, TiOs, oxides and mixed oxides, such as, for example, gamma-AlaOs and ZnO-A^Oj as well as Cu-Al mixed oxides of heteropolyacids.
According to an embodiment according to the invention, the carrier x. consists at least partially of an oxidic compound. Such oxidic compounds should have at least one of the elements Si, Ti, Zr, Al, P or a combination of at least two thereof. Such carriers can also function as dehydration catalysts through their acidic or basic properties. A preferred class of compounds which function both as carrier x. and as dehydration catalyst comprises silicon-aluminium-phosphorus oxides. Preferred basic materials which function as both dehydration catalyst and as carrier x. compnse alkali, alkaline earth, lanthanum, lanthanide or a combination of at least two thereof in their oxidic form. Such oxidic or basic dehydration catalysts are commercially obtainable from Degussa AG and from Sudchemie AG. Ion exchangers represent a further class. These can also be present in both basic and acidic form.
As homogeneous dehydration catalysts are considered in particular inorganic acids, preferably phosphorous-comprising acids and more preferably phosphoric acids. These inorganic acids can be immobilized on the carrier x. by immersion or impregnation-
The use of heterogeneous catalysts has proven particularly successful, in particular in gas phase dehydration. In liquid phase dehydration, however, both homogeneous and heterogeneous dehydration catalysts are used.
In a further embodiment of the inventive process it is preferred that the dehydration catalyst is an inorganic acid. By the term acid is understood in this text materials which behave according to the Bronsted definition. All acids known to the skilled person and appearing suitable are considered. Preferably mentioned are S- and P-comprising acids, whereby the P-comprising acids are preferred. It is further preferred in connection with the liquid phase dehydration that this dehydration catalyst, which is also characterised as homogeneous, is present in a solution. This solution is preferably the aqueous glycerine-comprising phase used for dehydration. These homogeneous catalysts are used in an amount within a range from 0.0001 to 20 wt.%, preferably within a range from 0.001 to 15 wt.% and more preferably within a range from 0.01 to 10 wt.%, respectively based on the phase to be dehydrated.
In addition, it is preferred that in the inventive process, a dehydration catalyst is used with an HO value within a range from +1 to -10, preferably within a range from +2 to —8.2 and yet more preferably in the liquid phase dehydration within a range from +2 to -3 and in the gas phase dehydration within a range from — 3 to -8.2. The HO value corresponds to the acidic function according to Hammett and can be determined by the so-called amine titration and use of indicators or by absorption of a gaseous base - see "Studies in Surface Science and Catalytics", vol. 51, 1989: "New Solid Acids and Bases, their catalytic Properties", K. Tannabe et. al. Further details on the production of acrolein from glycerine can also be found in DE 42 38 493 Cl.
In a further embodiment of the process according to the invention, the gas phase oxidation in step b) of the process according to the invention occurs in the presence of one or more oxidation catalysts, which comprise transition metals in elemental or in chemically bound form or both. It is preferred that the oxidation catalysts comprise at least one of the elements molybdenum, tungsten, vanadium
or a combination of at least two thereof in at least partially oxidized form. Oxidation catalysts of this sort are preferably used as heterogeneous catalysts in contact with a carrier y. It is then preferred that the oxidation catalysts are incorporated into this carrier y. As suitable carrier y. are considered, in principle, the compounds mentioned in connection with carrier x., whereby carriers based upon silicon oxide or aluminium oxide or aluminium-silicon oxide are particularly preferred. Oxidation catalysts of this type are widely described in the literature. Reference is here made, for example, to DE-A-26 26 887, EP-A-0 534 294 and to US-A-2002/0198406. Oxidation catalysts of this type for the conversion of acrolein to acrylic acid are commercially obtainable, for example from Nippon Kayaku KK and from Degussa AG.
It is further preferred in the process according to the invention that the dehydration product, optionally in an aqueous phase, is conducted to the gas phase oxidation. It is here preferred that the dehydration product comprises at least 10 wt.%, preferably at least 20 wt.% and yet more preferably at least 40 wt.% acrolein. The amount of water should lie within the range from 0.001 to 50 wt.%, preferably within the range from 0.1 to 50 wt.%, particularly preferably within the range from 10 to 40 wt.% and yet more preferably within the range from 12 to 20 wt.%, whereby these and the above wt.% values are based respectively upon the phases fed into the gas phase oxidation.
A further embodiment of the process according to the invention provides that glycerine is introduced into a dehydration space as aqueous glycerine phase with a glycerine concentration within a range from 0.1 to 90, preferably within a range from I to 80 and particularly preferably within a range from 2 to 50 wt.%, respectively based upon the aqueous glycerine phase. This dehydration space comprises both a fluid phase and a gas phase, whereby the concentration of glycerine in the fluid phase is greater than in the gas phase and whereby the concentration of acrolein in the gas phase is greater than in the fluid phase.
Preferably the concentration of glycerine in the fluid phase is greater than in the gas phase at least by a factor of 1.1, preferably at least by a factor of 2 and particularly preferably at least by a factor of 5. It is further preferred that the concentration of acrolein in the gas phase is greater than in the fluid phase at least by a factor of 1.1, preferably at least by a factor of 2 and particularly preferably at least by a factor of 5. In this embodiment it is further preferred that the acrolein comprised in the gas phase is removed from the dehydration space, which is preferably designed as a pressure reactor. In connection with this embodiment it is further preferred that more dehydration of glycerine to acrolein occurs in the fluid phase than in the gas phase. Preferably more dehydration of glycerine to acrolein occurs in the fluid phase than in the gas phase by a factor of 1.1, preferably at least by a factor of 2 and more preferably at least by a factor of 5. It is further preferred in this embodiment that the acrolein formed in the fluid phase is transferred into the gas phase. It is further preferred in this embodiment that the volume of the dehydration space taken up by the fluid phase is larger than the volume taken up by the gas phase. The volume of the dehydration space taken up by the fluid phase is larger than the volume taken up by the gas phase, preferably by a factor of 1.1, preferably at least by a factor of 2 and particularly preferably at least by a factor of 5. The factors used here can be determined, for example, on the basis of investigations of the phase equilibria.
This embodiment of the process according to the invention for production of acrylic acid preferably comprises the following process steps:
a. dehydration of glycerine in the form of an aqueous glycerine solution to a dehydration product comprising acrolein in the form of an aqueous acrolein solution by means of liquid phase dehydration with at least partial transfer of the aqueous acrolein solution into the gas phase, whereby the weight ratio of acrolein to glycerine in the gas phase is greater than the weight ratio of
acrolein to glycerine in the aqueous acrolein solution by a factor of at least 2, preferably at least 4, particularly preferably at least 10 and most preferably at least 100;
b. gas phase oxidation of the acrolein in the vapour phase to obtain a
monomer gas comprising acrylic acid;
c. bringing into contact of the monomer gas with a quench means to
obtain a quench phase comprising acrylic acid;
d. processing of the quench phase to obtain a monomer phase
comprising acrylic acid.
Accordingly the process for producing a polymer in this particular embodiment of the process according to the invention comprises the following process steps:
A. Dehydration of glycerine in the form of an aqueous glycerine
solution to a dehydration product comprising acrolein in the form
of an aqueous acrolein solution by means of liquid phase
dehydration with at least partial transfer of the aqueous acrolein
solution into the gas phase, whereby the weight ratio of acrolein to
glycerine in the vapour phase is larger than the weight ratio of
acrolein to glycerine in the aqueous acrolein solution by a factor of
at least 2, preferably at least 4, particularly preferably at least 10
and most preferably at least 100;
B. gas phase oxidation of the acrolein in the gas phase to obtain a
monomer gas comprising acrylic acid;
C. bringing into contact of the monomer gas with a quench means to
obtain a quench phase comprising acrylic acid;
D. processing of the quench phase to obtain a monomer phase
comprising acrylic acid;
E. polymerisation of the monomer phase.
The gas phase oxidation is preferably carried out within a temperature range from 200 to 400°C, preferably within the range from 250 to 350°C and more preferably within a range from 280 to 340°C.
It is further preferred in the process according to the invention that the monomer gas comprises the acrylic acid in an amount within the range from 5 to 50 wt.%, preferably within a range from 10 to 40 wt.% and yet more preferably within a range from 15 to 30 wt.%, respectively based on the monomer gas.
In a further embodiment of the process according to the invention it is preferred to use water or an organic compound with a boiling point within the range from 50 to 250°C, preferably within a range from 70 to 180°C and yet more preferably within a range from 105 to 150°C or water and this organic compound as quench means in process step c). As organic compounds of this type are considered in particular aromatics and more preferably alkylated aromatics. The quench means is generally brought into contact with the monomer gas in a suitable column, preferably in counter-current flow. For the case that the quench means comprises at least 50 wt.%, preferably at least 70 wt.% water, it is preferred that the aqueous quench means charged with acrylic acid is processed in a further step with a separation means, which is preferably not very soluble with water. The phase which is richest in acrylic acid is subjected either to a distillation or to a crystallisation or both, preferably first to a crystallisation. The crystallisation can be carried out both as layer and as suspension crystallisation. Suitable layer crystallisation devices are commercially obtainable from Sulzer AG. Suitable suspension crystallisation processes generally use a crystal generator followed by a washing column. Such devices and processes are commercially obtainable from Niro Prozesstechnologie B.V. As extraction/separating means is considered particularly an aromatic compound, more preferably an alkyl aromatic and further preferably toluene. If an organic compound should be used as separating means, this organic compound charged with acrylic acid can likewise be subjected to a
distillation and crystallisation or a combination of both. A crystallisation suitable for this is disclosed in EP-A- 1 015 410.
It is additionally preferred in the process according to the invention that the quench phase comprises the acrylic acid in an amount within the range from 30 to 90 wt.%, preferably within the range from 35 to 85 wt.% and yet more preferably within a range from 45 to 75 wt.%, respectively based upon the monomer phase.
In a further embodiment of the process according to the invention, it is preferred that the processing of the quench phase occurs at temperatures below the boiling point of acrylic acid. A suitable measure therefor is that the quench phase already has a temperature of less than 40°C by use of a correspondingly cold quench means. The thus-temperature controlled quench phase can then be conducted to an extraction or to a crystallisation or both for processing, whereby the temperatures preferably lie within a range from -40 to 40°C, preferably within a range from -20 to 39°C and particularly preferably within a range from -10 to 35°C.
According to a further aspect of the process according to the invention, it is preferred that the monomer phase comprises the acrylic acid in an amount within the range from 99 to 99.98 wt.%, respectively based upon the monomer phase. Such acrylic acid contents in a monomer phase appear in particular if the processing occurs by distillation. For the case that the processing occurs by means of extraction and crystallisation, it can be preferred that the acrylic acid is present in an amount from 30 to 70 wt.%, preferably in an amount within the range from 40 to 60 wt.% and yet more preferably in an amount within a range from 45 to 65 wt.% in the monomer phase together with water, and the impurities which are different to water and acrylic acid amount to less than 0.02 wt.%, based upon the monomer phase. This aqueous monomer phase has the advantage that it can be used in the aqueous polymerisation of the monomer phase without further dilution steps, which is necessary for the highly concentrated monomer phase.
In addition, the invention relates to a device for production of acrylic acid which comprises the following components connected with each other in fluid-conveying fashion:
la. a dehydration reactor;
2a. a gas phase oxidation reactor;
3 a. a quench unit;
4a. a processing unit.
In addition, the invention relates to a device for production of polymers, which first comprises the above listed components 1 a. to 4a. connected with each other in fluid-conveying fashion and also a polymerisation unit 5b.
By fluid-conveying is understood a connection of the individual components or of their components by means of pipe systems or other transport possibilities for gases and liquids, such as tank vehicles.
It is preferred in the inventive device that the dehydration reactor comprises a compound reservoir suitable for accepting glycerine, followed by a reaction area designed to accept catalyst, in turn followed by a quencher with a line to the gas phase oxidation reactor. These components are formed from common materials used in the chemical industry which are inert under the reaction conditions, such as stainless steel or glass. For the case that the reaction area accepts the catalyst as bulk material, it comprises appropriate containers. In another design, the reaction area can also comprise walls which function as catalyst. The quencher is designed as a column, into which water or high-boiling organic solvent can be introduced.
A further aspect of the device according to the invention comprises an evaporator after the compound reservoir and before the reaction area. These embodiments are
particularly suitable for gas phase dehydration. For the case that the glycerine with a high salt load from fatty acid saponification is used, it is preferred that the evaporator comprises a salt separator. If the dehydration occurs in the liquid phase and the acrolein should be evaporated according to the above-described particular embodiment of the process according to the invention in process step a', the device according to the invention comprises additionally an evaporation device la' arranged between the dehydration reactor la. and the gas phase oxidation reactor 2a., which is connected to the gas phase oxidation reactor 2a. in such a way that the vapour phase obtained in the evaporation device 2a' is fed into the gas phase oxidation reactor 2a.
According to another embodiment of the device according to the invention, it is preferred that the reaction area comprises a lower product outlet which leads into the quencher. This construction has proven itself in particular in liquid phase dehydration. In a further design of the device according to the invention, it is preferred that the reaction area is integrated in a cycle, with which reagents and reaction product can be conducted within the cycle.
As gas phase oxidation reactors are considered all reactors known to the skilled person and suitable for the process according to the invention, which are capable of converting acrolein by gas phase oxidation to acrylic acid. Preferred in this context are pipe bundle reactors or plate reactors, which are cooled with a cooling agent, preferably with a salt melt. These pipe bundle or plate reactors accommodate a suitable catalyst on the side to which cooling agent is applied. On the one hand, this can be present as a bulk powder and on the other hand the surfaces of the pipes or of the plates can be coated with the catalyst.
Preferably used quench units are likewise those types which are known in previous large scale gas phase oxidation of acrolein to acrylic acid. Quench units of this type are formed as columns or towers and, as for the reactors, can be
commercially purchased, for example from Deggendorfer Werft GmbH. As processing unit are likewise considered all known distillation and crystallisation as well as extraction devices known to the skilled person from large scale acrylic acid synthesis by means of gas phase oxidation of acrolein.
Suitable polymerisation units, which are used in process step E. for polymerisation of the monomer phase, are, on the one hand, discontinuously operating stirrer vessels and on the other hand continuously operating systems, such as bulk polymerisation devices, extruders and the like. A comminution and drying follows these polymerisation reactors. The thus-obtained superabsorbent precursor can, iurthermore, be subjected to a surface- or post-crosslinking. More details concerning this are found in the previously mentioned work from Graham and Buchholz. If the polymers are cross-linked, partially neutralized polyacrylates, reference is made in connection with the exact procedure to the third chapter (page 69 et seq.) in "Modern Superabsorbent Polymer Technology", F.L. Buchholz and AT. Graham (Editors) in Wiley-VCH, New York, 1998, which forms part of this disclosure.
In addition, it is preferred that the process according to the invention for production of acrylic acid or the process according to the invention for production of a polymer occurs using the devices described above and more closely illustrated in the figures.
In this way, water absorbing polymer structures can be obtained as particularly suitable superabsorbers.
A contribution to the solution of the above-mentioned objects is also made by water-absorbing polymer structures obtainable by radical polymerisation of the acrylic acid obtainable by means of the above-described synthetic process in the presence of cross-linkers.
A contribution to the solution of the previously mentioned objects is also made by water-absorbing polymer structures, which are based to at least 25 wt.%, preferably to at least 50 wt.%, yet more preferably to at least 75 wt.% and most preferably to at least 95 wt.% on acrylic acid, whereby at least 80 wt.%, preferably at least 90 wt.% and most preferably at least 95 wt.% of the acrylic acid monomers used in the production of the water-absorbing polymer structures have been obtained by a synthetic process starting from non-fossil, renewable organic material. These non-fossil, renewable organic materials are in particular materials not generated from petroleum, or coal or brown coal as well as natural gas. These non-fossil, renewable organic materials are, rather, products of agriculture and forestry, in particular fats and oils from glycerine and fatty acids.
Preferably, these water-absorbing polymer structures are obtainable by a process comprising the following process steps:
i) polymerisation of the acrylic acid in the presence of a cross-linker to form a polymer gel;
li) optionally, comminution of the polymer gel;
iii) drying of the optionally comminuted polymer gel to obtain water-absorbing polymer structures, and
iv) optionally, surface post-treatment of the water-absorbing polymer structure.
According to a particular embodiment of the water-absorbing polymer structures according to the invention, these are based to at least 25 wt.%, preferably to at least 35 wt.% and most preferably to at least 45 wt.% upon natural, biodegradable polymers, preferably upon carbohydrates such as celluloses or starches.
Preferred polymer structures according to the invention are fibres, foams or particles, whereby fibres and particles are preferred and particles particularly preferred.
Preferred polymer fibres according to the invention are dimensioned such that they can be incorporated into or as yarns for textiles and also directly into textiles. It is preferred according to the invention that the polymer fibres have a length within the range from 1 to 500, preferably 2 to 500 and particularly preferably 5 to 100 mm and a diameter within the range from 1 to 200, preferably 3 to 100 and particularly preferably 5 to 60 denier.
Preferred polymer particles according to the invention are dimensioned so that they have an average particle size according to ERT 420.2-02 within the range from 10 to 3000 µm, preferably 20 to 2000 µm and particularly preferably 150 to 850 µm. It is further preferred that the proportion of particles with a particle size within a range from 300 to 60 µm is at least 50 wt.%, particularly preferably at least 75 wt.%,
It is further preferred according to the invention that the water-absorbing polymer structures have at least one, preferably both of the following properties:
a CRC value (CRC = Centrifugation Retention Capacity) determined according to ERT 441.2-02 (ERT = Edana Recommended Test Method) of at least 20 g/g, preferably at least 25 g/g and most preferably at least 30 g/g;
an absorption under a pressure of 20 g/cm2 determined according to ERT 442.2-02 of at least 15 g/g, preferably at least 17.5 g/g and most preferably at least 20 g/g.
The CRC values and the vales for the absorption under pressure generally do not lie above 1 50 g/g.
A further contribution to the solution of the above mentioned objects is made by water-absorbing polymer structures, which are characterized by the following properties:
the polymer structure is based to at least 25 wt.%, preferably to at least 50 wt.%, yet more preferably to at least 75 wt.% and most preferably to at least 95 wt.% on acrylic acid, whereby at least 80 wt.%, preferably at least 90 wt.% and most preferably at least 95 wt.% of the acrylic acid monomers used in the preparation of the water-absorbing polymer structures has been obtained by a synthesis process which starts from non-fossil, renewable organic material,
(P2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least 25%, preferably at least 35% and most preferably at least 45%, whereby a value of at most 75 to 95 % as upper limit is generally not exceeded;
(P3) the polymer structure has a CRC value determined according to ERT 441 .24)2 of at least 20 g/g, preferably at least 25 g/g and most preferably at least 29 g/g, whereby a CRC value of 60 g/g as upper limit is generally not exceeded.
In a further aspect of the polymer structure described in the previous paragraph, said polymer structure has at least properties ß1 and ß2. All further developments given in this text for the polymer structure are also valid for the polymer structure of this paragraph.
Another contribution to the solution of the above-mentioned objects is made by water-absorbing polymer structures which are based to at least 10, preferably at least 25, particularly preferably at least 50 and more preferably at least 75 and more preferably at least 80 wt.%, based upon the polymer structure, upon acrylic acid and which are characterised by the following properties:
(el) the polymer structure has a sustainability factor of at least 10, preferably at least 20, particularly preferably at least 50, yet more preferably at least 75, further preferably at least 85 and even more preferably at least 95;
(s2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least 25%, preferably at least 35% and most preferably at least 45%, whereby a value of at most 75 to 95 % as upper limit is generally not exceeded;
(e3) the polymer structure has a CRC value determined according to ERT 441.2-02 of at least 20 g/g, preferably at least 25 g/g and most preferably at least 29 g/g, whereby a CRC value of 60 g/g as upper limit is generally not exceeded.
In another embodiment of the polymer structure described in the previous section, this polymer structure has at least properties el and e2. All further developments given in this text for the polymer structure are also valid for the polymer structure of this paragraph.
In some cases the above-mentioned upper limits can also be up to 10% or up to 20% lower. It is preferred for the polymer structures described in the two previous sections that these are based, in addition to the acrylic acid, upon a di- or polysugar. These di- or polysugars are preferably present as a further component of the polymer structure in an amount of at least 1 wt.%, preferably at least 5 wt.% and yet more preferably at least 15 wt.%, based upon the polymer structure, so
that the sum of the wt.% of the components of the water-absorbing polymer structure is 100 wt.%. Preferred for sugars of these types are poly-chain sugars, which preferably have a number average molecular weight determined by means of gel permeation chromatography and light scattering within the range from 10,000 to 1,000,000 and preferably within the range from 50,000 to 500,000 g/mol. These preferably consist of linear and thus unbranched chains. All sugar compounds known to the skilled person and appearing suitable are considered as sugars of this type. Thus, for example, celluloses and starches can be mentioned, whereby one or at least two different starches are preferred. Among starches, in turn amylase-eontaining starches are preferred. The amylase content preferably lies within a range from 10 to 80 and particularly preferably within a range from 20 to 70 wt.%, based upon the starches. It is furthermore preferred that the di- or polysugars have a particle size such that at least 50 wt.%, preferably at least 70 wt.% and yet more preferably at least 85 wt.% of the particles are smaller than 50 urn. The particle size is determined by means of sieve analysis. Such products are, for example, commercially available under the trade name Eurylon® 7 or Foralys® 380 from the company Roquette, France.
Such water-absorbing polymer structures can be prepared and are thus obtainable preferably by
providing a surface crosslinked water-absorbing polymer;
mixing the surface crosslinked water-absorbing polymer with a di- or poly
sugar.
It is here preferred that the water-absorbing polymer is based to at least 50 wt.%, preferably at least 80 wt.% and yet more preferably at least 95 wt.% upon acrylic acid which comes from the inventive dehydration process used for polymerisation partially neutralised and with a crosslinker.
The sustainability factor gives the proportion of the polymer structure which is based upon materials based upon non-fossil, renewable organic materials. A sustainability factor of 100 means that the polymer structure is fully based upon non-fossil, renewable organic materials.
A further contribution to the solution of the above-described objects is provided by a composite comprising the water-absorbing polymer structures according to the invention or water-absorbing polymer structures which are obtainable by radical polymerisation of the acrylic acid obtainable by the above-described synthetic process in the presence of cross-linkers. It is preferred that the polymer structures according to the invention and the substrate are firmly bound together. As substrates, sheets made from polymers, such as, for example, made from polyethylene, polypropylene or polyamide, metals, non-wovens, fluff, tissues, wovens, natural or synthetic fibres, or other foams are preferred. It is, furthermore, preferred according to the invention that the polymer structures are comprised in the composite in an amount of at least 50 wt.%, preferably at least 70 wt.% and yet more preferably at least 90 wt.%, based upon the total weight of polymer structure and substrate.
In a particularly preferred embodiment of the composite according to the invention, the composite is a sheet-like composite, as described in WO-A-02/056812 as "absorbent material". The disclosure of WO-A-02/056812, in particular with respect to the exact construction of the composite, the mass per unit area of its components as well as its thickness is hereby introduced as reference and represents a part of the disclosure of the present invention.
A further contribution to the solution of the above-mentioned objects is provided by a process for producing a composite, whereby the water-absorbing polymer structures according to the invention, or the water-absorbing polymers, which can be obtained by radical polymerisation of the acrylic acid obtainable by the above-
described synthetic process in the presence of cross-linkers, and a substrate and optionally an additive are brought into contact with each other. As substrate are preferably used those substrates which have already been mentioned in connection with the composite according to the invention.
A contribution to the solution of the above-mentioned objects is also provided by a composite obtainable by the above-described process.
A further contribution to the solution of the above-mentioned objects is delivered by chemical products comprising the water-absorbing polymer structures according to the invention or a composite according to the invention. Preferred chemical products are in particular foams, moulded bodies, fibres, sheets, films, cables, sealing materials, liquid-absorbing hygiene articles, in particular diapers and sanitary napkins, carriers for plant or fungus growth-regulating agents or plant protection agents, additives for construction materials, packaging materials or soil additives. Preferred chemical products are hygiene articles comprising an upper layer, a lower layer and an intermediate layer arranged between the upper layer and the lower layer, which comprises water-absorbing polymer structures according to the invention.
In addition, the invention relates to a process for the production of acrolein which is characterized by the herein described process for dehydration of glycerine to a dehydration product comprising acrolein and the herein described preferred embodiments of this dehydration.
The invention further relates to fibres, sheets, adhesives, cosmetics, moulding materials, textile and leather additives, flocculants, coatings or varnishes based upon acrylic acid which is obtainable according to a process according to the invention, or their derivatives or salts. As derivatives of acrylic acid are considered in particular its esters, preferably its alkyl esters and yet more
preferably its C( to C'io, yet more preferably €2 to €5 and more preferably C^ to €4 alkyl esters. As salts can be mentioned the alkali or alkaline earth as well as the ammonia salts of acrylic acid.
The invention further relates to the use of an acrylic acid which has been obtained by a process according to the invention, or derivatives or salts thereof in fibres, sheets, adhesives, cosmetics, moulding materials, textile and leather additives, flocculants, coatings or varnishes.
The invention is now more closely illustrated by means of non-limiting figures and examples.
Fig. 1 shows a schematic of the individual stages and steps of the process according to the invention and of the device according to the invention.
Fig. 2 shows a gas phase dehydration unit.
Fig. 3 shows a liquid phase dehydration unit.
Fig. 4 shows a processing unit.
Fig. 5 shows a further embodiment of the liquid phase dehydration unit.
In Fig. 1, firstly the oils or fats are introduced into a saponifier 1, where an alkaline saponification with bases or alkali alcoholates occurs. The glycerine produced in the saponifier by generally known purification steps such as salting out and distillation is then conduced to a dehydration unit with a dehydration reactor 2 (in order to produce acrolein from the glycerine). The thus-produced acrolein is then conducted in a next step to a gas phase reaction reactor 3, in which it is converted by a gas phase oxidation reaction into acrylic acid. After gas phase
reaction reactor 3 follows a quench unit 4, in which the acrylic acid-comprising gas from gas phase reaction reactor 3 is brought into the liquid phase by bringing into contact with a quench means. The liquid mixture of quench means and acrylic acid is conducted to a processing unit 5 following the quench unit 4. There, the acrylic acid is purified to pure acrylic acid (at least 99.98 % acrylic acid) either by crystallisation or distillation or by a combination of these two steps or by extraction or a combination of extraction and crystallisation or a combination of extraction and distillation or a combination of extraction-distillation and distillation, the acrylic acid being present as pure acrylic acid itself or in an aqueous phase. The thus-obtained acrylic acid is then conducted to a polymerisation unit 6. The polymer obtained in the polymerisation unit 6 can be processed according to the subsequent use. A further processing unit, for example a diaper machine or a machine for production of binding and wound material can follow after the polymerisation unit 6.
Fig. 2 shows a gas phase dehydration unit, in which a compound reservoir 7 is connected to an evaporator 12. The evaporator 12 is connected upstream to a reaction area 9. The pressurisable reaction area 9 comprises catalyst 8. Both the evaporator 12 and the reaction area 9 comprise heating elements 21, with which the temperatures necessary for evaporation and dehydration of glycerine can be achieved. The reaction area 9 is connected to a quencher 10 via a lower outlet 13. The quencher 10 receives, in its upper area, in addition to the lower product outlet 13, a quench liquid feed 16. In the lower area of the quencher 10, a trapping reservoir for side-products 17 is arranged, which can be emptied by means of exit valve 19. The upper area of the quencher 10 further receives an exit line 11, which conducts the acrolein-comprising dehydration product to gas phase reaction reactor 3. Quench unit 4 follows these.
Fig. 3 shows a liquid phase dehydration device, in which glycerine is placed in a compound reservoir 7, which is connected with the upper area of a pressurisable
reaction area 9, which in turn comprises catalysts 8. The reaction area 9 is temperature-controlled by means of a heating element 21. In the lower area of reaction area 9, a buffer reservoir 18 is arranged, which forms a cycle with the reaction area by means of a pump, and via which glycerine and acrolein already situated in the reaction area 9 and in the buffer reservoir can be conducted in the cycle. In the upper area of the reaction area 9 is situated a transfer line to a quencher 10, which leads into the upper area of the quencher 10 together with a quench liquid feed 16. Also in the upper area of the quencher 10 is situated an exit line 11 to the gas phase reaction reactor 3, followed in rum by the quench unit 4. In the lower area of the reaction area 9 a trapping reservoir for side-products 17 equipped with an exit valve 9 has an opening.
In Fig. 4 the gas coming from the gas phase reaction reactor 3 is introduced into the quench unit 4, in which it is brought into contact with water and absorbed, whereby as absorption liquid an aqueous acrylic acid solution is obtained, in which likewise a part of the side-products arising from the previous synthesis steps is comprised. This aqueous acrylic acid solution is conducted via a feed line 22 to an extraction unit 23. At the latest in the extraction unit 23, the acrylic acid solution is brought into contact with toluene as separating agent (TM). After a careful combination in the extraction unit 23, a phase separation occurs to form an upper phase based substantially on water, and a lower phase based substantially on toluene as separating agent. The phase based substantially on the separating agent is conducted via feed line 24 to the crystallizer 25, which is preferably a scratch cooler. The crystal suspension comprised in crystallizer 25 is then conducted by means of a suspension conduit 26 to a wash column 27, in which a separation of the acrylic acid crystals occurs, in the course of which a mother liquor comprising the separating agent is retained. The mother liquor obtained in the wash column 27 after the separation of the acrylic acid crystals is preferably at least partially conducted back via the mother liquor conduit 28 into the extraction unit 23. It is further preferred that the upper phase based substantially on water
comprised in the extraction unit 23 is conducted back to the quench unit 4 via quench conduit 29. In a preferred design of the process according to the invention and of the device according to the invention, acrylic acid still comprised in the composition can be separated by crystallisation from the composition conducted in the quench conduit 29 by means of a further purification device 30, which is, for example, a suspension crystallisation device or a layer crystalliser. It is, furthermore, preferred in another embodiment of the process according to the invention and of the device according to the invention that the composition conducted in the mother liquor conduit 28 (mother liquor separated during the crystallisation) is separated from further impurities before its being conducted back by means of a separating unit 31. This separating unit is preferably likewise a suspension crystallisation device or a layer crystallizer or also a filter.
In Fig. 5 is shown schematically that optionally in a pre-mixer 32, via lines A to C, water, glycerine and, in so far as necessary, catalyst, for example an inorganic acid such as phosphoric acid, are combined and conducted to the dehydration reactor 2 formed as a stainless steel pressure reactor. The dehydration of glycerine to acrolein in the liquid phase occurs here. When using a soluble and thus homogeneously distributable catalyst, such as an inorganic acid, it is advantageous to at least partially neutralise this by addition of a base such as NaOH, mostly as a solution, via line D. This measure contributes to the prevention of further reactions which can lead to undesired side products. Following this is a distillation device 33 which comprises in the upper section a volatiles area 34 and in the lower section a high-boilers area 35, whereby the acrolein-comprising phase from the dehydration is introduced between the two areas 34 and 35. In the volatiles area 34 the components with lower boiling points than acrolein would come out guided by exit line E and the still remaining acrolein and the high-boiling components guided in the reflux. In the high-boiler area 35 representing the distiller bottom the high-boilers are concentrated. It is here advantageous to conduct the bottom product in a cycle. From the high-boiler
area, the components with higher boiling points than acrolein are discharged and conducted via a high-boiler pump to a high boiler separator 37.The high-boiler separator is advantageously equipped with a membrane. After passing through the high-boiler separator 37 the mixture, comprising predominantly water and glycerine, treed from the high-boilers, is conducted back to the pre-mixer 32 and is thus available again for dehydration. In this way an efficient dehydration of glycerine to acrolein can be achieved by the cyclical route, in which the thus-obtained acrolein from the distiller 33 in sufficient purity for a long-lasting operation of the gas phase oxidation is conducted to the gas phase reaction reactor 3 for oxidation with air conducted in through feed line F to acrolein conducted away via exit line G.
EXAMPLES
Example1 Dehydration in the gas phase
In a gas phase dehydration device described in figure 2 (enclosed within the dashed line), a catalyst is provided in reactor area 9, the catalyst being obtained from 100 parts by weight of Rosenthal balls (alpha-A12O3) with a diameter of 3 mm by mixing with 25 parts by weight of a 20 wt.% phosphoric acid for 1 hour and then separated from excess water by rotary evaporation at 80°C (Ho value between -5.6 and -3). The glycerine evaporated in an evaporator at 295°C is conveyed over 100 ml of this catalyst in a steel pipe in the reaction area as a 20 wt.% aqueous solution with a pump with 40 ml/h at a temperature of 270°C. The acrolein-comprising reaction mixture was brought into contact with water as quench means in the quencher and the thus-obtained aqueous mixture conducted to the gas phase oxidation in a conventional reactor for gas phase oxidation of acrolein to acrylic acid.
Example 2: liquid phase dehydration
In a device according to Fig. 3, a catalyst as described in example 1 was used for liquid phase dehydration (enclosed within the dashed line), whereby in the place of the Rosenthal balls a silicon dioxide carrier was used (Ho value between 2 and -3). The reaction temperature was 240°C. Water was used as quench means. Following the acrolein synthesis, a gas phase oxidation in a conventional gas phase oxidation reactor followed, as in example 1, followed by an absorption in water in a quench unit.
The acrylic acid-water mixtures obtained in example 1 and 2 were combined in a glass separating funnel temperature-controlled to 0°C with 0.5 parts of their volume of toluene. The mixture was shaken vigorously and left to stand for 60 minutes in order to enable a phase separation. The two thus-arising phases were separated. The toluene-comprising phase was subjected to an azeotropic distillation and the thus-obtained acrylic acid distilled before its use in polymerisation.
PTA could not be identified by gas chrornatography as an impurity in the acrylic acid obtained from acrolein obtained either by gas phase dehydration or by liquid phase dehydration followed by gas phase oxidation.
Exjmpje 3: Polymerisation
Dissolved oxygen was removed from a monomer solution consisting of 280 g of the above-obtained acrylic acid, which was neutralized to 70 mol. % with sodium hydroxide, 466.8 g water, 1.4 g polyethylene glycol-300-diacrylate and 1.68 g allyloxypolyethyleneglycol acrylic acid ester by flushing with nitrogen and the monomer solution cooled to the start temperature of 4°C. After reaching the start temperature, the initiator solution (0.1 g 2,2-azobis-2-amidinpropane dihydrochloride in 10 g H2O, 0.3 g sodium peroxydisulfate in 10 g H2O, 0.07 g 30
% hydrogen peroxide solution in 1 g H2O and 0.015 g ascorbic acid in 2 g added. After the end temperature of approximately 100°C was reached, the gel formed was comminuted and dried for 90 minutes at 150°C. The dried polymer was coarsely chopped, ground and sieved to a powder with a particle size of 150 to 850 urn.
For post-crosslinking, 100 g of the above-obtained powder was combined with a solution of 1 g l,3-dioxalan-2-one, 3 g water and 0.5 g aluminium sulphate-18-hydrate and then heated for 40 minutes in an oven set to 180°C.
Example 4: Preparation of a biodegradable polymer
The post-crosslinked polymer obtained in example 3 was mixed under dry conditions with a water-soluble wheat starch (the product Foralys® 380 from the company Roquette, Lestrem, France) in the weight ratio polymer : starch of 4 : 1 and then homogenised for 45 minutes in a roll mixer type BTR 10 of the company Frobel GmbH, Germany.
The product had a biodegradability according to the modified Sturm test after 28 days of 39 % and a CRC value of 29.9 g/g. The sustainability factor was about 0.99.
Reference characters
1 saponifier
2 dehydration reactor
3 gas phase reaction reactor
4 quench unit
5 processing unit
6 polymerisation unit
7 compound reservoir
8 catalyst
9 reaction area
10 quencher
11 exit line
12 evaporator
13 lower product outlet
14 upper product outlet
15 pump
16 quench liquid feed
17 trapping reservoir for side products
18 buffer reservoir
19 outlet valve
20 cycle
21 heating element
22 feed line
23 extraction unit
24 feed line
25 crystallizer
26 suspension conduit
27 wash column
28 mother liquor conduit
29 quench conduit
30 purification device
31 separating unit
32 pre-mixer
33 distiller
34 volatiles area
35 high-boilers area
36 high-boilers pump
37 high-boilers separator

Claims
1. Process for production of acrylic acid, comprising at least the following
steps:
a. dehydration of glycerine to a dehydration product comprising
acrolein;
b. gas phase oxidation of the dehydration product to obtain a
monomer gas comprising an acrylic acid;
c. bringing into contact of the monomer gas with a quench means to
obtain a quench phase comprising acrylic acid;
d. processing of the quench phase to obtain a monomer phase
comprising acrylic acid.
2. Process for production of a polymer by radical polymerisation of acrylic
acid, comprising at least the following steps:
A. dehydration of glycerine to a dehydration product comprising acrolein;
B gas phase oxidation of the dehydration product to obtain a monomer gas comprising acrylic acid;
C bringing into contact of the monomer gas with a quench means to obtain a quench phase comprising acrylic acid;
D. processing of the quench phase to obtain a monomer phase
comprising acrylic acid;
E. radical polymerisation of the monomer phase.
3. Process according to claim 2, wherein the polymer is a water-absorbing
polymer structure.
4. Process according to claim 3, wherein the water-absorbing polymer
structure is obtainable by a process comprising the following process
steps:
i) polymerisation of the acrylic acid in the presence of a crosslinker to form a polymer gel;
ii) optionally comminution of the polymer gel;
iii) drying of the optionally comminuted polymer gel to obtain water-absorbing polymer structure;
iv) optionally surface post-crosslinking of the water-absorbing polymer structure.
5. Process according to any one of claims 2 to 4, wherein the acrylic acid is
present to at least 20 mol%, based on the monomer, as a salt.
6. Process according to any one of the preceding claims, wherein the
glycerine is obtained from saponification of fats.
7. Process according to any one of the preceding claims, wherein glycerine is
generated in the generation of liquid fuels from natural raw materials.
8. Process according to any one of the preceding claims, wherein the
dehydration occurs at least partially in liquid phase.
9. Process according to any one of claims 1 to 11, wherein the dehydration
occurs at least partially in a gas phase.
10. Process according to any one of the preceding claims, wherein the
glycerine is used in aqueous phase.
11. Process according to any one of the preceding claims, wherein a
dehydration catalyst is used.
12. Process according to claim 11, wherein the dehydration catalyst is in contact with a carrier x.
13. Process according to claim 12, wherein the carrier x is a solid with a total
pore volume according to DIN 66133 within a range from 0.1 to 1.5 ml/g.
14. Process according to any one of claims 11 to 13, wherein the dehydration
catalyst is an inorganic acid.
15. Process according to claim 14, wherein the dehydration catalyst is present in a solution.
16. Process according to any one of the preceding claims, wherein the gas phase oxidation occurs in the presence of an oxidation catalyst comprising a transition metal in elemental or in chemically bound form or both.
17. Process according to any one of the preceding claims, wherein the dehydration product is conducted in an aqueous phase to the gas phase oxidation.
18. Process according to any one of the preceding claims, wherein the gas
phase oxidation occurs within a temperature range from 200 to 400 °C.
19. Process according to any one of the preceding claims, wherein the
monomer gas comprises the acrylic acid in an amount within the range
from 5 to 50 wt.%, respectively based on the monomer gas.
20. Process according to any one of the preceding claims, wherein the quench
means comprises water or an organic compound with a boiling point
within the range from 50 to 250 °C or water and this organic compound.
21. Process according to any one of the preceding claims, wherein wherein the
quench phase comprises the acrylic acid in an amount within the range
from 30 to 90 wt.%, based on the monomer phase.
22. Process according to any one of the preceding claims, wherein the processing occurs at temperatures below the boiling point of the acrylic acid.
23. Process according to any one of the preceding claims, wherein the processing occurs by extraction or crystallisation or both.
24. Device for production of acrylic acid comprising connected with each
other in fluid-conveying fashion:
1 a. a dehydration reactor (2),
2 a. a gas phase oxidation reactor (3),
3a. a quench unit (4),
4a. a processing unit (5).
25. Device for production of polymers comprising connected with each other
in fluid-conveying fashion:
1 b. a dehydration reactor (2),
2b. a gas phase oxidation reactor (3),
3b. a quench unit (4),
4b. a processing unit (5)
5b. a polymerisation unit (6).
26. Device according to claim 24 or claim 25, wherein the dehydration reactor
(2) comprises
a compound reservoir (7), followed by
a reaction area (9) accepting a catalyst (8), followed by
a quencher (10) with a line (11) to the gas phase oxidation reactor
(3).
27. Device according to claim 26, wherein an evaporator (12) is provided after the compound reservoir (7) and before the reaction area (9).
28. Device according to claim 27, wherein the reaction area (9) comprises a
lower product outlet (13) which leads into the quencher (10).
29. Device according to claim 28, wherein the reaction area (9) comprises an
upper product outlet (14) which leads into the quencher.
30. Process according to any one of claims 1 and 5 to 23, wherein the process
is carried out in a device according to any one of claims 24 and 26 to 29.
31. Process according to any one of claims 2 to 23, wherein the process is
carried out in a device according to any one of claims 24 to 29.
32. Water-absorbing polymer structure obtainable by a process according to
any one of claims 3 to 23 and 31.
33. Water-absorbing polymer structures which are based to at least 25 wt.% upon optionally partially neutralised acrylic acid, wherein the water-absorbing polymer structures are characterised by a sustainability factor of at least 80%.
34. Water-absorbing polymer structures according to claim 33, wherein the polymer structures are based to at least 25 wt.%, based upon the total
weight of the water-absorbing polymer structure, upon natural, biodegradable polymers.
35. Water-absorbing polymer structures, which are characterized by the
following properties:
(PI) the polymer structure is based to at least 25 wt.% on acrylic acid, whereby at least 80 wt.% of the acrylic acid monomers used in the preparation of the water-absorbing polymer structures has been obtained by a synthesis process which starts from non-fossil, renewable organic material,
(p2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least 25%;
(p3) the polymer structure has a CRC value determined according to ERT 441.2-02 of at least 20 g/g.
36. Water-absorbing polymer structures, which are based to at least 10 wt.%,
based upon the polymer structure, upon acrylic acid and which are
characterised by the following properties:
(l) the polymer structure has a sustainability factor of at least 10; (2) the polymer structure has a biodegradability determined according
to the modified Sturm Test according to Appendix V of Guideline
67/548/EWG after 28 days of at least 25%; (3) the polymer structure has a CRC value determined according to
ERT 441.2-02 of at least 20 g/g.
37. Composite comprising a water-absorbing polymer structure according to
any one of claims 32 to 36 and a substrate.
38. Process for the production of a composite according to claim 37, wherein
the water-absorbing polymer structure and the substrate are brought into
contact with each other.

39. Composite obtainable by a process according to claim 38.
40. Hygiene article comprising an upper sheet, a lower sheet and an
intermediate sheet arranged between the upper sheet and the lower sheet,
which comprises water-absorbing polymer structures according to any one
of claims 32 to 36.
41. Fibres, sheets, moulded masses, textile and leather additives, flocculants, coatings or varnishes based on acrylic acid obtainable by a process according to any one of claims 1 and 5 to 23 or 30 or derivatives or salts thereof.
42. Use of an acrylic acid obtainable according to a process according to any one of claims 1 and 5 to 23 or 30 or their derivatives or salts in fibres, sheets, moulded masses, textile and leather additives, flocculants, coatings or varnishes.

Documents:

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Patent Number

272853

Indian Patent Application Number

6628/DELNP/2007

PG Journal Number

19/2016

Publication Date

06-May-2016

Grant Date

28-Apr-2016

Date of Filing

27-Aug-2007

Name of Patentee

STOCKHAUSEN GMBH.,

Applicant Address

BäKERPFAD 25, 47805 KREFELD GERMANY.

Inventors:

#	Inventor's Name	Inventor's Address
1	BUB GÜNTHER	KAMPSTRASSE 94, 45772 MARL GERMANY.
2	MOSLER JÜRGEN	BRÜSSELER STRASSE 20, 44577 CASTROP-RAUXEL GERMANY.
3	SABBAGH ANDREAS	ALTER OSTDAMM 58, 48249 DÜLMEN GERMANY.
4	KUPPINGER FRANZ-FELIX	RUDOLF-VIRCHOW-STR. 37A, 45768 MARL GERMANY.
5	NORDHOFF STEFAN	BEISINGER WEG 93, 45657 RECKLINGHAUSEN GERMANY
6	STOCHNIOL GUIDO	HOHES UFER 19, 45721 HALTERN GERMANY
7	SAUER JÖRG	VON-DEM-BUSCHE-STR. 34, 48249 DÜLMEN GERMANY
8	KNIPPENBERG UDO	WAGNERSTR. 13, 45772 MARL GERMANY

PCT International Classification Number

C07C 51/25

PCT International Application Number

PCT/EP2006/001831

PCT International Filing date

2006-02-28

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2005 009586.0	2005-02-28	Germany