Title of Invention

A PROCESS FOR THE PREPARATION OF POLYMERIC ABSORBENTS USEFUL FOR GELLING ORGANIC LIQUIDS

Abstract

The present invention provides a process for the preparation of slightly cross linked polymers capable of absorbing organic liquids in the presence of a ppm level additive. The absorbents of the present invention comprises polymers having a proper balance of hydrophilic and hydrophobic character in its chemical structure. The process being simple and generic in nature can be extended to synthesis of gels as absorbents for various other substrates of importance.

Full Text

This invention relates to a process for the preparation of polymeric absorbents useful for gelling organic liquids. More particularly it relates to the process for the preparation of polymeric absorbents which are crosslinked (5 to 50%) and are capable of absorbing organic liquids in the presence of a ppm level metal additive. The polymers prepared by the process of the present invention have a proper balance of hydrophilic and hydrophobic character in its chemical structure. The polymers prepared by this technique are known as polymer gels or more commonly and herein after referred as gels. Polymer gels consist of crosslinked macromolecules which form a three dimensional network in which solvent molecules are absorbed by osmotic forces. Polymer gels have an equilibrium absorption capacity, which is governed by a balance of osmotic pressure of the solvent and the elastic stress of the network. Polymer gels, which absorb water, are referred to as hydrogels. Those hydrogels, which can absorb large quantities of water, such as in excess of 100 gram of water per gram of the dry gel are called supera,bsorbents. Polymeric superabsorbents have been widely used in personal care products such as sanitary napkins and diapers. They have also been used in agricultural applications such as for irrigating dry and arid land. Recent developments and new applications of superabsorbents have been outlined in literature (Buchholz, F.L, Chemtech, Sept. 38, (1994)). Superabsorbing gels are prepared by polymerizing highly hydrophilic monomers such as acrylamide and acrylic acid along with a small quantity of multifunctional monomers and using a suitable initiator, typically a radical initiator, in water as a solvent. Superabsorbent hydrogels do not absorb organic solvents, and many of them in fact collapse in organic solvents such as acetone and alcohol. Gels, which can absorb organic solvents, have been developed to a limited extent. Examples of such gels are chlorosulfonated polyethylene gels {Varma, A. J, Lele, A, K and Mashelkar, R. A., Chem. Engg. Sci., 50, 3835 (1995)} and polyethylene oxide gels {Graham, N.B, Nwachuku, N. E, and Walsh, D. J., Polymer, 23, 1345 (1982)}. r There are several advantages of absorbing organic liquids into gels. For example, the liquid can be transformed into a soft solid by entrapping into the three dimensional matrix of a gel. Soft solids have typical properties that are intermediate between solids and liquids. For example, gelled organic liquids can have a high viscosity as well as a finite modulus, hi general, gelled liquids find applications in pastes, lotions, creams, shampoos, oil drilling fluids and in fuels. Gelled fuels are particularly useful for cooking and chafing dishes. They are easier and safer to transport and are more effective owing to the slower diffusive release of the fuel from the gelled matrix. Such gelled fuels typically contain an alcohol, usually methanol or ethanol as the fuel, which may be mixed with other d to C& alcohols. It is desirable to gel the fuel in such a manner that it does not separate from the matrix on standing or on application of pressure. Alcohol based gels have been formed by different gelling agents. US Patent No. 3,754,877 discloses the use of olefm modified hydroxyalkyl cellulose as the gelling agent. US Patent No. 4,436,525 discloses gelling of a 3:1 mixture of methyl alcohol and isopropyl alcohol with a fatty acid soap and sodium hydroxide. US Patent No. 3,759,674 discloses dispersions of ethylene-acrylic acid copolymers and amine emulsifiers in water, which form gels when mixed with alcohols. These gels contain about 10 to 30% by weight of solids. US Patent No. 3,148,958, US Patent No. 4,261,700 and US Patent No. 4,365,971 disclose the use of carboxy vinyl polymers such as Carbopol ethylene acrylic acid copolymer partially neutralized by weak amines as the gelling agent for alcohols. US Patent No. 5,641,890 discloses the use of an amine neutralized anionic polymer such as Carbopol 676 along with an amphoteric rheological additive such as dispersed alumina for gelling alcohol. The gel so formed contains about 20 to 30 percent by weight of water. The gel is formed by non-covalent physical cross-links originating from interactions between the polymer and the amine. A typical gel contains about 70 weight percent alcohol and about 1 weight percent each of the polymer and the amine. The disclosures of these references are interesting but they do not give any structural features for the polymer absorbent, nor do they give directions for synthesizing a solvent absorbing covalently crosslinked polymer gel. Whereas the disclosures of the above references have used a commercial polymer, in the present invention the' polymer gel is prepared in-situ by polymerizing selected monomers which contain a proper balance of hydrophilic and hydrophobic character in the presence or absence of a suitable transition metal compound. The proper choice of monomers containing hydrophilic and hydrophobic functional groups is particularly necessary for absorption of C1 to C6 alcohol and their mixtures, without the need for presence of water. The gel so prepared does not require any other gelling agent besides the polymer itself. The gelled fuels may or may not contain any water. Absence of water can significantly improve burning characteristics thus giving an improved gel. Polymerization of the monomer in the presence of a suitable transition metal compound helps in controlling the crosslinking reaction as well as forming structural complexes with the organic liquid. This improves the absorption capacity of the polymer for the organic liquid. The gel so prepared does not require any other gelling agent and/or thickening agent to increase the viscosity besides the polymer unlike the disclosures of the above references. The present invention is aimed at synthesizing polymer gels that can osmotically absorb large quantities of organic solvents to form gelled liquids. The organic solvents include aromatics, acids, ketones, alcohols, glycols and amines. One particular application of gelled solvents is fuels and in one preferred embodiment as gelled fuel for cooking and heating food. The gelled solvent contain 0.1 to 10 weight percent of a polymer gel, the rest being the organic solvent and/or their mixtures which are osmotically absorbed in the gel. The polymer gel contains hydrophilic and hydrophobic functional groups and is preferably formed by polymerizing a vinyl monomer having a chemical structure of the type CH2=CH-Ri-R2-R3, where RI and R3 are hydrophilic groups and R2 is a hydrophobic group. The polymerization is preferably carried out in the presence of ppm levels of a transition metal compound that can complex with the polymer. The object of this invention is to provide a process for the preparation of polymeric absorbents useful for gelling organic liquids. Accordingly, the present invention provides a process for the preparation of polymeric absorbents useful for gelling organic liquids which comprises mixing one or more monomers wherein the monomers used have a general formula CHb^CH-Ri-Rj-Rs wherein Rj and Rj are hydrophilic groups which may be either singular or a combination of amide, ester, ether sulphonic acid, carboxylic acid and hydroxyl functional groups, Rs may be either singular or a combination of primary, secondary or tertiary aliphatic saturated or unsaturated hydrocarbons, aromatic hydrocarbons or cycloaliphatic hydrocarbons selected from acrylamide or their derivatives exemplified by various monomers such as herein described in the range of 0.1 to 40 mol % with the cross linker, and a free radical initiator and a transition metal source in the range of 5 to 500 ppm optionally in the presence of a solvent selected from group comprising water, mixture of water and alcohol, 1, 4-dioxane, dimethyl sulfoxide and dimethyl formamide, benzene and xylene, subjecting the mixture to conventional polymerization methods, removing the polymer, crushing the polymer to obtain polymer powder, washing with solvent to remove unreacted monomers, drying the polymer by conventional methods to obtained the desired product. In one of the embodiments of the present invention the monomers used have a general formula CH2=CH-Ri-R2-R3 wherein, RI and RS are hydrophilic groups which may be either singular or a combination of amide, ester, ether sulphonic acid, carboxylic acid and hydroxyl functional groups, R3 may be either singular or a combination of primary, secondary or tertiary aliphatic saturated or unsaturated hydrocarbons, aromatic hydrocarbons or cycloaliphatic hydrocarbons selected from acrylamide or their derivatives exemplified by various monomers given in table-1 herein below: Table-1 (Table Removed) In yet another embodiment the amount of the comonomer in the polymerization mixture may be varied between 1 mole percent to 99 mole percent, more preferably between 9 to 91 mole percent. In another embodiment the solvent used (optionally) for polymerization may be selected from polar or non polar solvent such as water or an aqueous mixture of alcohols, 1,4-dioxane, dimethyl sulfoxide and dimethyl formamide, benzene and xylene In yet another embodiment the crosslinker may be of acrylic/ methacrylic or styrenic in nature or comprise of mixtures of these and have two or more unsaturations such as N, N-methylene bisacrylamide, ethylene glycol dimcthacrylate, ethylene glycol diacrylate, trimethylol propane triacrylate, trimethylol propane trimethacrylate, divinyl benzene and more preferably N, N-methylene bis acrylamide, and ethylene glycol dimethacrylate. In another embodiment the mole percent of the multi functional monomer may be typically between 0.1 mol% and 40 mol%, preferably between 1 mol% and 30mol% and most preferably between 5 mol% and 20 mol%. In yet another embodiment the source of transition metal may be metal, metal salts or metal complexes of cobalt, chromium, copper, manganese and iron exemplified by chromium trioxide, cobalt chloride, manganese hydroxide, and ferric oxide. In another embodiment the amount of transition metal may be varied between 5 ppm to 5OOppm, more preferably between 10 ppm to 250 ppm In yet another embodiment the initiator used for thermal polymerization may be selected from a class of compounds such as azo, perodixes, hydroperoxides, persulphates, preferably from persulphates and azo initiators. In another embodiment of the present invention, tetramethyl ethylenediamine may be selected as polymerization accelerator along with persulfate initiator in water as the solvent, and its amount may be varied between 1% to 4% by weight of the total feed. In yet another embodiment the polymerization of the polymer gel may be preferentially carried out thermally between 50 - 90°C and more preferably between 50- 70°C. In yet another embodiment the polymer gel may be prepared in water-alcohol mixture in the composition range of 0 to 100 volume percent of alcohol, preferably between 0 to 75 volume percent alcohol. The concentration of the monomer in solution may be varied between 5 to 50 wt percent, preferably between 5 to 20 %. In another embodiment the solvent used for washing may be selected from water, acetone, aqueous mixture of alcohols. In yet another embodiment, the polymer gel may be crushed to a soft mass after polymerization. In another embodiment the absorbed organic liquid may be selected from aliphatic alcohols, C1 to C6, preferably C1 to C3 and most preferably C1 to C2. In a feature of the present invention the preferred range of modulus of the swollen polymer gel may be 0.1 to 2 MPa and a preferable range of 0.2 to 0.6 MPa. In a feature of the present invention the conventional methods used for the polymerization may be as follows: 1) Thermal polymerization in which initiator is activated by supplying thermal energy. 2) Photochemical polymerization by using a radiation source. 3) In solution polymerization, the monomer and the initiator are dissolved in a suitable solvent in which the resultant polymer is soluble or swellable. 4) Bulk polymerization is carried out with liquid monomer by dissolving initiator in it. 5) In suspension polymerization the insoluble monomer is suspended in water in the form of droplets with the help of a suspending agent and then polymerized. 6) Emulsion polymerization is the one in which the monomer is dispersed in aqueous phase as a uniform emulsion and polymerized. 7) In precipitation polymerization the resulting polymer is precipitated from the reaction mixture. In another feature it is preferred that the organic liquid does not separate out from the gel by the action of temperature and pressure. In the case of the present invention the organic liquid is osmotically absorbed in the gel by the action of strong intermolecular forces. The gel does not contain macroporosity and hence the solvent can not separate from the gel by application of the pressure. The choice of monomers described above also ensures that the organic solvent will not separate from the gel by changing the temperature. The process of the present invention is described herein below with reference to the examples, which are illustrative only and should not be construed to limit the scope of the present invention in any manner. Example 1 To a well stirred solution of one mole of Acrylamido-2-methyl-propane sulfonic acid, (AMPS), containing 20 ml distilled water, 0.154 gm N, N1-methylene bis acrylamide (Bis-Am), 0.04 gm ammonium persulfate (APS) and 0.06 ml tetra ethylene methylene diamine, (TEMED) were added slowly. The contents were thoroughly mixed and the solution was degassed by N2 gas bubbling through it for 10-15 mints. The tubes were then sealed and polymerization was carried out in at 60°C for 24 hrs. After the polymerization, the polymer rod was taken out of the tube washed with water for 24 hrs, dried and then crushed in a mortar. Example 2 To a well stirred solution of one mole of AMPS containing 20 ml distilled water with 125 ppm transition metal, 0.308 gm Bis-Am, 0.04 gm APS and 60jjJ TEMED were added slowly. The contents were thoroughly mixed and the solution was degassed by N2 gas through it for 10-15 mints. The tubes were then sealed and the polymerization was carried out in at 60°C for 24 hrs. After the polymerization, the polymer rod was taken out of the tube, washed with water for 24 hrs, dried and then crushed in a mortar. Example 3 To a well stirred solution of one mole of N-tertiary butylacrylamide, (N-t-BAm) containing 23 ml dimethy sulfoxide (DMSO), 0.1 mole of AMPS, 0.154 gm Bis-Am, 0.08 gm azo bis isobutyro nitrile (AIBN) were added slowly. The contents were thoroughly mixed and the solution was degassed by N2 gas through it for 10-15 mints. The tubes were then sealed and the polymerization was carried out in at 60°C for 24 hrs. After polymerization, the polymer rod was taken out of the tube, washed with water for 24 hrs, dried and then crushed in a mortar. Example 4 In an another case, 0.1 mole of N-t-BAm is dissolved in 20 ml water by heating it at 50°C. To this well dissolved solution, 1 mole of AMPS, 0.154 gm Bis-Am, 0.04 gm APS, 60jj.l TEMED were added slowly. The contents were thoroughly mixed and the solution was degassed by N2 gas bubbling through it for 10-15 mints. The tube was then sealed and polymerization was carried out at 70°C for a period for 24 hrs. After the polymerization, the polymer rod was taken out of the tube and washed with water for 24 hrs, dried and then crushed in a mortar. Example 5 To a well stirred solution of 1 mole of N-isopropylacrylamide containing 23 ml 1,4-dioxane, 0.154 gm Bis-Am, O.OSgm A1BN were added r slowly. The contents were thoroughly mixed and the solution was degassed by N2 gas through it for 10-15 mints. The tubes were then sealed and the polymerization was carried out in at 60°C for 24 hrs. After the polymerization the rod was taken out of the tube, washed with water for 24 hrs, dried and then crushed in a mortar. Example 6 To a well stirred solution of one mole of AMPS monomer containing, 10ml, 75:25 ethanol-water mixture, 0.154 gm Bis-Am, 0.08 gm A1BN were added. The contents were thoroughly mixed and the solution was degassed by N2 gas bubbling through it for 10-15 mints. The tube was then sealed and the polymerization was done at 60°C for a period of 24 hrs. After the polymerization the rod was taken out of the tube, washed with water for 24 hrs, dried and then crushed in a mortar. Example? To a clear solution of 2-hydroxy ethyl methacrylate, 0.08 gm AIBN was added slowly. The contents were thoroughly mixed and the solution was degassed by N2 gas bubbling through it for 10-15 mints. The tube was then sealed and the polymerization was done at 60°C for a period of 24 hrs. After the polymerization the rod was taken out of the tube, washed with water for 24 hrs, dried and then crushed in a mortar. Example 8 To a clear solution 1.85 gms of acryloyl 6-amino caproic acid containing 23 ml 1,4-Dioxane, 0.136 ml ethylene glycol dimethacrylate, 0.08 gm AIBN were added slowly. The contents were thoroughly mixed and the solution was degassed by N2 gas bubbling through it for 10-15 mints. The tube was then sealed and the polymerization was done at 70°C for a period of 24 hrs. After the polymerization the rod was taken out of the tube, washed with water for 24 hrs, dried and then crushed in a mortar. Example 9. In the present invention the modulus of the swollen PAMPS gels with different degree of crosslinking is measured by a compression test in which the gel is compressed to controlled strains (a) and the stress required for compression (CT) is recorded. The relation between the stress and strain for a swollen polymer gel is given by (Formula Removed) The plot of a versus (a-I/a2) gives the modulus as the slope of the line. A soft polymer gel has a finite modulus, which is directly proportional to the crosslink density of the gel. In the present invention the modulus of the PAMPS increases as crosslink density increases. Its non-flowing nature and finite modulus define the solid nature of the organic liquid absorbed gels. Example 10 i (Table Removed) Example 11 This example shows the heating efficiency of the polymer gel prepared by the process of the present invention. Wherein one container may be placed under a chafing dish containing 2-3 litres of water at 31°C in the water pan portion of the chafing dish and an equal quantity of water (29°C) in the food pan. This container is heated by the aid of N-tertiary butylacrylamide copolymer with AMPS, 10 mole percent crosslinker, (Example 3), and from the thermocouples in the water pan and food pan the temperatures of water in these pans are recorded. The average data of the runs are follows: (Table Removed) The process of the above invention has following advantages: 1. The process provides means for the preparation of slightly crosslinked polymers capable of absorbing organic liquids in the presence of a ppm level additive, more particularly it relates to a process for the preparation of alcohol absorbents, which comprise a polymer having a proper balance of hydrophilic and hydrophobic character in its chemical structure. 2. The process being simple and generic in nature can be extended to synthesis of gels as absorbents for various other substrates of importance. We Claim: 1. A process for the preparation of polymeric absorbents useful for gelling organic liquids which comprises mixing one or more monomers wherein the monomers used have a general formula CH2=CH-R1-R2-R3 wherein RI and R3 are hydrophilic groups which may be either singular or a combination of amide, ester, ether sulphonic acid, carboxylic acid and hydroxyl functional groups, Rs may be either singular or a combination of primary, secondary or tertiary aliphatic saturated or unsaturated hydrocarbons, aromatic hydrocarbons or cycloaliphatic hydrocarbons selected from acrylamide or their derivatives exemplified by various monomers such as herein described in the range of 0.1 to 40 mol % with the cross linker, and a free radical initiator and a transition metal source in the range of 5 to 500 ppm optionally in the presence of a solvent selected from group comprising water, mixture of water and alcohol, 1, 4-dioxane, dimethyl sulfoxide and dimethyl formamide, benzene and xylene, subjecting the mixture to conventional polymerization methods, removing the polymer, crushing the polymer to obtain polymer powder, washing with solvent to remove unreacted monomers, drying the polymer by conventional methods to obtained the desired product. 2. A process as claimed in claim 1, wherein the solvent used (optionally) are selected from polar or non polar solvent such as water or an aqueous mixture of alcohols, 1,4-dioxane, dimethyl sulfoxide and dimethyl from amide, benzene and xylene. 3. A process as claimed in claim 1, wherein the cross linker used are selected from acrylic/ methacrylic or styrenic in nature or comprise of mixtures of these and have two or more unstaurations such as N, N-methylene bis acrylamide, ethylene glycol dimethyacrylate, ethylene glycol diacrylate, trimethylol propane triacrylate, trimethylol propane trimethacrylate, divinyl benzene and more preferably N, N-methylene bis acrylamide, and ethylene glycol dimethacrylate. 4. A process as claimed in claim 1, wherein he mole percent of the multi functional monomer used is in the range of 1 mol% and 30 mol% and preferably between 5 mol% and 20 mol%. 5. A process as claimed in claim 1, wherein the source of transition metal are metal, metal salts or metal complexes of cobalt, chromium, copper, manganese and iron exemplified by chromium trioxide, cobalt chloride, manganese hydroxide, ferric oxide. 6. A process as claimed in claim 1, wherein the amount of transition metal used is in the range of preferably 10 ppm to 250 ppm 7. A process as claimed in claim 1, wherein the initiator used for thermal polymerization are selected from a class of compounds such as azo, peroxides, hydroperoxides, persulphates, preferably from persulphates and azo initiators. 8. A process as claimed in claim 1, wherein tetramethyl ethylenediamine is selected as polymerization accelerator along with per sulfate initiator in water as the solvent, and its amount may be varied between 1% to 4% by weight of the total feed. 9. A process as claimed in claim 1, wherein the polymerization of the polymer gel is preferentially carried out thermally between 50-90°C and more preferably between 50- 70°C. 10. A process for the preparation of polymeric absorbents useful for gelling organic liquids as fully described here in before with reference to the examples.

Documents:

2873-del-1998-abstract.pdf

2873-del-1998-claims.pdf

2873-del-1998-complete specification (granted).pdf

2873-del-1998-correspondence-others.pdf

2873-del-1998-correspondence-po.pdf

2873-del-1998-description (complete).pdf

2873-del-1998-form-1.pdf

2873-del-1998-form-19.pdf

2873-del-1998-form-2.pdf

2873-del-1998-form-3.pdf

2873-del-1998-petition-138.pdf