Title of Invention	PROCESS FOR THE HYDROFORMYLATION OLEFINICALLY UNSATURATED COMPOUNDS
Abstract	A process for the hydroformylation of olefinically unsaturated compounds having from 3 to 12 carbon atoms in a heterogeneous reaction system using a catalyst consisting of an aqueous solution comprising complexes of rhodium with water- soluble organic phosphorus (III) compounds selected from the group consisting of triarylphosphines, trialkylphosphines and arylated or alkylated diphosphates whose organic radicals contain sulfonic acid groups or carboxyl groups as ligands and, if desired, excess water-soluble organic phosphorus (III) compounds, at pressures of from 0.4 to 10 MPa and temperatures of from 50 to 180°C,wherein the reaction of the reactants is carried out in a reaction column having from 5 to 120 separation stages, and selected from the group consisting of a tray column, a column with ordered packing and a column with random packing elements.

Title of Invention

PROCESS FOR THE HYDROFORMYLATION OLEFINICALLY UNSATURATED COMPOUNDS

Abstract

A process for the hydroformylation of olefinically unsaturated compounds having from 3 to 12 carbon atoms in a heterogeneous reaction system using a catalyst consisting of an aqueous solution comprising complexes of rhodium with water- soluble organic phosphorus (III) compounds selected from the group consisting of triarylphosphines, trialkylphosphines and arylated or alkylated diphosphates whose organic radicals contain sulfonic acid groups or carboxyl groups as ligands and, if desired, excess water-soluble organic phosphorus (III) compounds, at pressures of from 0.4 to 10 MPa and temperatures of from 50 to 180°C,wherein the reaction of the reactants is carried out in a reaction column having from 5 to 120 separation stages, and selected from the group consisting of a tray column, a column with ordered packing and a column with random packing elements.

Full Text	Process for the hydroformylation of olefinically unsaturated compounds The invention relates to an improved process for the hydroformyiation of oiefinically unsaturated compounds in the presence of an aqueous catalyst solution comprising water-soluble rhodium complexes by use of a reaction column as reactor. The reaction of compounds containing olefinic double bonds with carbon monoxide and hydrogen is the customary industrial method of preparing aldehydes (oxo process). The process is not restricted to the use of olefinic hydrocarbons, but can be extended to starting materials which not only have a double bond but also bear functional groups, predominantly groups which remain unchanged under the reaction conditions. The classical oxo process employs cobalt as catalyst. Its effectiveness is based on the formation of cobalt carbonyl compounds by action of hydrogen and carbon monoxide at pressures above 20 MPa and temperatures of about 120°C and more on metallic cobalt or cobalt compounds. In the last 30 years, cobalt has increasingly been replaced by rhodium as catalyst. The platinum metal is used as a complex which comprises, preferably, phosphenes as ligands in addition to carbon monoxide. The use of rhodium as catalyst allows the process to be carried out at lower pressures and, in addition, higher yields are achieved and the unbranched products which are more valuable for further processing are preferentially formed if straight-chain terminal olefins are used as starting materials. A further refinement of the oxo process comprises the transition from catalysts which are homogeneously dissolved in the reaction medium, i.e. in the starting material and in the reaction product, to aqueous catalyst solutions which are present as a separate phase in addition to that formed by the starting material and reaction product. This variant of the reaction is described, for example, in DE B-26 27 354. Its particular advantage is that the reaction product and the catalyst can readily be separated under mild conditions without use of thermal process steps, so that losses which occur as a result of further reactions of the aldehydes formed are avoided. Furthermore, very high yields are achieved and, when using unbranched terminal olefins, the aldehydes obtained are very predominantly n- aldehydes. In practice, the oxo process using an aqueous catalyst phase is usually carried out in stirred reactors which have initially been charged with a solution of the catalyst system in water. Olefinically unsaturated compounds and synthesis gas are introduced into the reaction vessel and reacted with one another with intimate mixing. The reaction product leaves the reactor together with aqueous catalyst solution, unreacted starting materials (synthesis gas, olefin) and hydrogenation products of the olefinically unsaturated compounds via an immersed tube. The gas phase, essentially synthesis gas, olefin and saturated hydrocarbon formed from the olefin, is separated from the liquid products in a separation vessel and recirculated to the reactor. Part of the circulating gas is freed of the condensable reaction products in a condenser and is discharged into the waste gas system. The liquid separated off in the separation vessel is passed to a phase separator. Here, the crude organic reaction product separates from the aqueous catalyst phase. While the organic reaction product is conveyed via a pump to a stripping column, a further pump conveys the aqueous catalyst phase back to the reactor with the heat of the exothermic reaction being removed in a heat exchanger and used to generate process steam. Water can be fed to the reactor together with the cooled catalyst solution to compensate water losses which occur via the waste gas and via the oxo product. The crude oxo product introduced into the stripping column is conveyed in countercurrent to part of the synthesis gas which in this way becomes laden with the olefin dissolved in the crude product. The preheated synthesis gas/olefin mixture is fed to the reactor. A further substream of synthesis gas is preheated in a heat exchanger using process heat. The fresh olefin is also preheated and vaporized in a heat exchanger by means of waste heat from the aldehyde distillation before it enters the reactor, while the crude oxo product from the stripping column is passed directly without cooling to the distillation. Finally, a buffer vessel for temporary storage of product is provided in case of a malfunction in the plant. In an industrially particularly advantageous embodiment of a production plant for carrying out the oxo process, synthesis gas and olefin are introduced via double roses which serve as predistributors into the reactor in which the aqueous catalyst solution is present. The fine dispersion of the reactants in the reaction mixture is achieved by means of a sparging stirrer. To remove the heat of reaction, the reactor is provided with a cooling matrix. The liquid and gaseous components ascend through a guide tube in the reactor and separate at its upper end. The gas is either recirculated into the reactor or discharged from the reaction system as offgas. The aqueous catalyst solution separates from the crude, organic product. The crude product is introduced into a stripping column, freed of dissolved olefins by means of the synthesis gas passed through the stripping column in countercurrent and finely fractionated into its components in a column. The heat required for the distillation is obtained directly via the cooling matrix. For this purpose, the liquid aldehyde from the bottom of the column is introduced via a phase separator into the cooling matrix in which it vaporizes and it is then conveyed in vapor form via the phase separator back into the column. The above-described apparatus for carrying out the oxo process using an aqueous catalyst phase has given excellent service in industrial practice. However, there is interest in further optimizing the process. This is an object of the present invention. Specifically, the invention has the object of improving the economics by changing the way in which the process is carried out and/or by simplifying the apparatus employed in the process. Further objects are to increase the conversion and the yield of desired product and to improve safety. The invention provides a process for the hydroformylation of ofefinically unsaturated compounds in a heterogeneous reaction system using a catalyst consisting of an aqueous solution comprising complexes of rhodium with water-soluble organic phosphorus(lll) compounds as ligands and, if desired, excess water-soluble organic phosphorus(lll) compounds, at pressures of from 0.4 to 10 MPa and temperatures of from 50 to 180°C. According to the present invention, the reaction of the reactants is carried out in a reaction column. Apart from carrying out the reaction between olefinic compound and synthesis gas in a heterogeneous reaction system using an aqueous catalyst phase, it is an essential feature of the invention that the reaction is carried out in a reaction column as reactor. The differences between the novel process and the processes customary hitherto which have a stirred tank as central apparatus of the reaction plant are conspicuous. Apart from further changes, the mixing of the reactants and the catalyst solution without use of a stirrer and the absence of a separate stripping apparatus for recovering the olefin dissolved in the product are of particular significance. For the purposes of the present invention, the term reaction columns refers to the apparatuses used, in particular, for distillation, rectification and extraction in chemical engineering. As hydroformylation reactors, they are provided with feed openings for the reactants and the catalyst solution and with devices for taking off product, catalyst solution and offgas. As reaction columns, it is possible to use the various types of column which are widely used in industrial practice, in particular tray columns and columns with ordered packing or random packing elements. In these, the catalyst solution is fed in at the top of the column, advantageously onto the uppermost tray of the column. Below the top of the column, preferably in the upper region (i.e. in the upper half) of the column, the olefinic compound is fed into the reactor. Catalyst solution, olefin and reaction product, which travel downward in the interior of the column, flow in countercurrent to the ascending synthesis gas introduced at the bottom of the column. Reaction product and catalyst solution are taken off in the lower part (the lower half) of the reactor, while the gaseous components leave the column in its upper region. The reactants and catalyst solution do not have to be introduced into the reactor at one feed point each. It is thus not necessary for the total amount of olefin to be introduced entirely at one point and in the upper region and the total amount of synthesis gas to flow into the reaction space only at the bottom of the reaction column. Rather, the reactants can be introduced at different points along the column. The number of feed points can be up to the number of separation stages of the column. Equipping the reactor with a plurality of feed lines for the individual participants in the reaction allows it to be matched individually to the requirements of the respective reaction, e.g. with regard to the reactivity of the olefin used, the desired reaction rate, the completeness of the conversion and the desired composition of the reaction product. Merely by way of example, the reactivity of the olefin will be examined in more detail. In the case of olefins which react quickly, a larger amount of olefin will be able to be fed to the reactor than in the case of relatively unreactive olefins, so that the reactive unsaturated hydrocarbons are introduced into the reactor via not only one feed line but via a plurality of feed lines. This opportunity of varying the streams also allows the same reactor to be used for reacting various starting materials. The introduction of catalyst solution at various points along the reactor will be restricted to special cases, e.g. to maintain the required catalyst concentration in the case of increased catalyst consumption caused by impurities in the starting materials or else to control the temperature by removing heat of reaction from the reactor. Below the top of the reactor, it is possible to feed the catalyst solution into the column either separately from the olefin or together with the olefin. Use of a reaction column instead of a stirred tank as reactor is also advantageous because a plurality of separation stages (e.g. column trays) are connected in series in the column. The series arrangement of a plurality of separation stages in the column has the effect of converting the characteristics of a stirred tank into the characteristics of a cascade of stirred tanks. Olefin and synthesis gas react with one another in the presence of the catalyst solution until the respective chemical and physical equilibrium is established. For this reason, the conversion in the reaction column is higher than in a stirred tank. Reaction columns having from 5 to 120 separation stages, in particular from 15 to 40 separation stages, have been found to be useful in the process of the invention. A critical factor in the choice of the reaction column which is suitable in a particular case is its load range. This term refers to the uniform hydrodynamic loading of the column cross section due to ascending gas/mass stream and the downflowing liquid/mass stream. Each reaction column has a particular load range which depends on the type of column internals and the properties of the feed mixture and within which uniform flow loading and thus heat and mass transport are ensured. The hydroformylation reaction is strongly exothermic. The heat evolved in the reaction can be used either internally in the reaction for preheating the reactants and for distillation of the reaction product and/or externally for generating steam. The thermal energy is advantageously removed via the reaction product and the circulated catalyst solution, although heat recovery is not restricted to these embodiments. The synthesis gas rising through the reaction column flows, as stated above, in countercurrent to the reaction product. The gaseous phase permeates the liquid stream and in the process extracts unreacted olefin dissolved in the reaction product and transports it into the reaction zone. The olefin conversion is significantly improved in this way, without a specific extraction unit having to be installed in the hydroformylation plant. As catalysts, use is made of water-soluble rhodium complexes containing water-soluble phosphorus(lll) compounds as ligands. Examples of water- soluble phosphorus(lll) compounds which form complexes with rhodium are triarylphosphines, trialkylphosphines and arylated or alkylated diphosphines whose organic radicals contain sulfonic acid groups or carboxyl groups. Their preparation and use is known, for example, from DE-B-26 27 354, EP 0 103 810 B1, EP 0 163 234 B1 and EP 0 571 819 A1. Further groups of suitable compounds are sulfonated or carboxylated organic phosphites and heterocyclic compounds of trivalent phosphorus. The conditions under which the reaction occurs can be varied within wide limits and adapted to individual circumstances. They depend, inter alia, on the starting material, on the catalyst system chosen and on the desired degree of conversion. The hydroformylation of the starting materials is usually carried out at temperatures of from 50 to 180°C. Preference is given to temperatures of from 80 to 140°C, in particular from 100 to 130°C. The total pressure is in a range from 0.4 to 10 MPa, preferably from 1 to 6 MPa and in particular from 1.5 to 5 MPa. The molar ratio of hydrogen to carbon monoxide is usually in the range from 1:10 to 10:1; mixtures comprising hydrogen and carbon monoxide in a molar ratio of from 3:1 to 1:3, in particular 1:1, are preferred. The rhodium concentration is from 20 to 1000 ppm by weight, preferably from 50 to 500 ppm by weight and in particular from 100 to 300 ppm by weight, in each case based on the aqueous catalyst solution. Although it is possible to use the stochiometric rhodium-phosphorus complex as catalyst, the reaction is preferably carried out in the presence of excess phosphorus ligand, i.e. ligand which has not undergone complex formation with rhodium. Preference is given to using from 3 to 200 mol of phosphorus in the form of a water-soluble organic phosphorus compound per mol of rhodium. Molar ratios of rhodium to phosphorus in the range from 1:50 to 1:100 have been found to be particularly useful. The rhodium-phosphorus complex used as catalyst does not have to have a uniform composition, but can be, for example, a mixture of rhodium complexes which differ in the type of phosphorus ligands present. Likewise, the phosphorus ligand present in the aqueous catalyst solution can be composed of a mixture of different water-soluble organic phosphorus compounds. The catalyst is usually formed from the components rhodium or rhodium compound, organic phosphorus compound and synthesis gas under the conditions of the hydroformylation reaction. However, it can also be introduced into the reaction stage as a preformed catalyst, i.e. a separately prepared catalyst. It has been found to be advantageous to circulate the catalyst and to make up for any catalyst losses which occur by introduction of fresh catalyst. To increase the conversion per unit time of olefinically unsaturated compounds which are only sparingly soluble in the aqueous catalyst solution, it may be advisable to add a phase transfer reagent (solubilizer) to this solution. This alters the physical properties of the interfaces between the two liquid phases and thus aids transition of the organic reactants into the aqueous catalyst phase. Solubilizing action is displayed by compounds whose hydrophilic groups are ionic (anionic or cationic) or nonionic. Examples of anionically active compounds are, inter alia, the sodium, potassium and ammonium salts of carboxylic acids, preferably those having from 8 to 20 carbon atoms. Cationic solubilizers include tetraalkylammonium and N-alkylpyrridinium salts. Nonionic phase transfer reagents are, for example, alkyl and alkylphenyl polyethylene glycols and trialkylamine oxides. The reactants olefin and synthesis gas can be preheated before introduction into the reactor. The liquid phase leaves the reaction column in the lower part, preferably at the bottom of the column, and goes via a heat exchanger into a phase separator. Here, it separates into the organic reaction product and the aqueous catalyst solution. The offgas taken from the reactor in the upper part, in particular at the top of the column, consists essentially of carbon monoxide and hydrogen. It may further comprise reaction product, saturated compounds formed by hydrogenation of the olefinic compounds and water. Olefinic starting material is present in the offgas particularly when, for example for reasons of process economics, the reaction has not been carried out to complete conversion of the unsaturated compound. The olefin can be recovered from the offgas by known methods, e.g. by condensation, or reacted in a second reaction stage to convert it into hydroformylation product. The reaction product present in the offgas is also separated off and returned to the reaction column or passed directly to the distillation stage. The process of the invention can be applied to olefinically unsaturated compounds of any structure. Accordingly, both olefins having an internal double bond and olefins having terminal double bonds and likewise straight-chain or branched olefins are suitable as starting material. Furthermore, the olefins can also be substituted by functional groups, in particular groups which are not changed during the course of the reaction. Multiply olefinically unsaturated compounds are also possible as starting materials. The process has been found to be particularly useful in the hydroformylation of olefinically unsaturated hydrocarbons having from 3 to 12 carbon atoms in the molecule, preferably propylene and the isomeric butenes. Possible embodiments of the process of the invention are shown schematically by way of example in the accompanying drawings. In the process outlined in Figure 1, synthesis gas is fed into a reaction column 1 at the bottom of the column via a line 2 and olefin is fed in at feed points 4, 5 and 6 along the length of the reactor via a line 3. The catalyst solution is pumped via a line 7 into the top of the column and onto the uppermost separation stage of the column. Downward-flowing olefin reacts in the reactor with ascending synthesis gas in the presence of the catalyst to form aldehyde until equilibrium is established. Olefin dissolved in the product is stripped from the liquid phase by the upward-flowing synthesis gas stream and is likewise converted into aldehyde. The crude aldehyde which has been freed of olefin is taken off together with the catalyst solution in the lower part of the reaction column and is passed directly via a line 8 to a heat exchanger 9. The recovered heat can be used, for example, for the generation of stream and/or for the distillation of reaction product. The heat exchanger is followed by a separator 10 in which organic product and aqueous catalyst solution are separated. The catalyst phase is pumped via a heat exchanger 11, where the remaining heat in it is removed, to the top of the reaction column 1, if appropriate after addition of supplementary amounts of water or catalyst solution from containers 12 and 13. Off gas is taken from the reaction system via line 14. It comprises predominantly carbon monoxide and hydrogen and small amounts of, inter alia, unreacted olefin and reaction product. Olefin and product are not discarded but instead can, like carbon monoxide and hydrogen, be utilized, for example in the process itself. It is also possible for the gas mixture to be reacted in an after-reactor with the olefin recovered from the offgas so as to convert both of them into further, desired product. The process variant shown in Figure 2 differs from the process of Figure 1 in that the offgas leaving the reactor 1 via line 14 is cooled in a heat exchanger 15. A two-phase system consisting of gaseous and liquid phase is formed. Both phases are separated in a separator 16 and the gaseous phase is removed from the system while the liquid phase is returned to the reaction column 1 via line 17. The plant components denoted by the reference numerals 2 to 13 correspond, (as do the reaction column 1 and the offgas line 14) to those of Figure 1. WE CLAIM; 1. A process for the hydro form ylation of olefmically unsaturated compounds having from 3 to 12 carbon atoms in a heterogeneous reaction system using a catalyst consisting of an aqueous solution comprising complexes of rhodium with water-sohible organic phosphorus (III) compounds selected from the group consisting of triarylphosphines, trialkylphosphines and arylated or alkylated diphosphates whose organic radicals contain sulfonic acid groups or carboxyl groups as ligands and, if desired, excess water-soluble organic phosphorus (III) compounds, at pressures of from 0.4 to 10 MPa and temperatures of from 50 to 180°C,wherein the reaction of the reactants is carried out in a reaction column having from 5 to 120 separation stages, and selected from the group consisting of a tray column, a column with ordered packing and a column with random packing elements. 2. The process as claimed in claim 1, wherein the reaction column is provided with feed openings for the reactants and the catalyst solution and with devices for taking off product, catalyst solution and offgas. 3. The process as claimed in claim 1 or 2 wherein the reaction column has from 15 to 40, separation stages. 4. The process as claimed in one or more of claims 1 to 3 wherein the reactants namely olefmicaliy unsaturated compounds and synthesis gas, and the catalyst solution are fed into the reaction column at separate feed points. 5. The process as claimed in one or more more of claims 1 to 4, wherein the olefmicaliy unsaturated compound is introduced in the upper region of the reaction column at one feed point or at a plurality of feed points. 6. The process as claimed in one or more of claims 1 to 5, wherein the synthesis gas is introduced in the lower region of the reaction column, preferably at the bottom of the reaction column, at one feed point or at a plurality of feed points. 7. The process as claimed in one or more of claims 1 to 6, wherein the catalyst solution is introduced in the upper region of the reaction column, in particular onto the uppermost separation stage of the reaction column. 8. The process as claimed in one or more of claims 1 to 4, wherein the reactants namely olefinically unsaturated compound and synthesis gas, and the catalyst solution are each introduced at a plurality of feed points arranged along the reaction column. 9. The process as claimed in one or more of claims 1 to 3, and 5 to 7 wherein olefinically unsaturated compound and catalyst are introduced together below the top of the column at one or more feed points along the reaction column. 10. The process as claimed in one or more of claims 1 to 9, wherein the reactants are preheated before being introduced into the reaction column. 11. The process as claimed in claim 10, wherein preheating is carried out using heat evolved in the process. 12. The process as claimed in one or more of claims 1 to 11, wherein the heat reaction is removed by means of an auxiliary medium such as water or steam. 13. The process as claimed in one or more of claims 1 to 12, wherein the offgas is separated into a gaseous phase and a liquid phase and the liquid phase is returned to the reaction column. A process for the hydroformylation of olefinically unsaturated compounds having from 3 to 12 carbon atoms in a heterogeneous reaction system using a catalyst consisting of an aqueous solution comprising complexes of rhodium with water- soluble organic phosphorus (III) compounds selected from the group consisting of triarylphosphines, trialkylphosphines and arylated or alkylated diphosphates whose organic radicals contain sulfonic acid groups or carboxyl groups as ligands and, if desired, excess water-soluble organic phosphorus (III) compounds, at pressures of from 0.4 to 10 MPa and temperatures of from 50 to 180°C,wherein the reaction of the reactants is carried out in a reaction column having from 5 to 120 separation stages, and selected from the group consisting of a tray column, a column with ordered packing and a column with random packing elements.

Full Text

Process for the hydroformylation of olefinically unsaturated compounds
The invention relates to an improved process for the hydroformyiation of
oiefinically unsaturated compounds in the presence of an aqueous catalyst
solution comprising water-soluble rhodium complexes by use of a reaction
column as reactor.
The reaction of compounds containing olefinic double bonds with carbon
monoxide and hydrogen is the customary industrial method of preparing
aldehydes (oxo process).
The process is not restricted to the use of olefinic hydrocarbons, but can
be extended to starting materials which not only have a double bond but
also bear functional groups, predominantly groups which remain
unchanged under the reaction conditions.
The classical oxo process employs cobalt as catalyst. Its effectiveness is
based on the formation of cobalt carbonyl compounds by action of
hydrogen and carbon monoxide at pressures above 20 MPa and
temperatures of about 120°C and more on metallic cobalt or cobalt
compounds.
In the last 30 years, cobalt has increasingly been replaced by rhodium as
catalyst. The platinum metal is used as a complex which comprises,
preferably, phosphenes as ligands in addition to carbon monoxide. The
use of rhodium as catalyst allows the process to be carried out at lower
pressures and, in addition, higher yields are achieved and the unbranched
products which are more valuable for further processing are preferentially
formed if straight-chain terminal olefins are used as starting materials.
A further refinement of the oxo process comprises the transition from
catalysts which are homogeneously dissolved in the reaction medium, i.e.
in the starting material and in the reaction product, to aqueous catalyst
solutions which are present as a separate phase in addition to that formed
by the starting material and reaction product. This variant of the reaction is
described, for example, in DE B-26 27 354. Its particular advantage is that
the reaction product and the catalyst can readily be separated under mild
conditions without use of thermal process steps, so that losses which occur
as a result of further reactions of the aldehydes formed are avoided.
Furthermore, very high yields are achieved and, when using unbranched
terminal olefins, the aldehydes obtained are very predominantly n-
aldehydes.
In practice, the oxo process using an aqueous catalyst phase is usually
carried out in stirred reactors which have initially been charged with a
solution of the catalyst system in water. Olefinically unsaturated
compounds and synthesis gas are introduced into the reaction vessel and
reacted with one another with intimate mixing. The reaction product leaves
the reactor together with aqueous catalyst solution, unreacted starting
materials (synthesis gas, olefin) and hydrogenation products of the
olefinically unsaturated compounds via an immersed tube. The gas phase,
essentially synthesis gas, olefin and saturated hydrocarbon formed from
the olefin, is separated from the liquid products in a separation vessel and
recirculated to the reactor. Part of the circulating gas is freed of the
condensable reaction products in a condenser and is discharged into the
waste gas system.
The liquid separated off in the separation vessel is passed to a phase
separator. Here, the crude organic reaction product separates from the
aqueous catalyst phase. While the organic reaction product is conveyed
via a pump to a stripping column, a further pump conveys the aqueous
catalyst phase back to the reactor with the heat of the exothermic reaction
being removed in a heat exchanger and used to generate process steam.
Water can be fed to the reactor together with the cooled catalyst solution to
compensate water losses which occur via the waste gas and via the oxo
product. The crude oxo product introduced into the stripping column is
conveyed in countercurrent to part of the synthesis gas which in this way
becomes laden with the olefin dissolved in the crude product. The
preheated synthesis gas/olefin mixture is fed to the reactor. A further
substream of synthesis gas is preheated in a heat exchanger using
process heat. The fresh olefin is also preheated and vaporized in a heat
exchanger by means of waste heat from the aldehyde distillation before it
enters the reactor, while the crude oxo product from the stripping column is
passed directly without cooling to the distillation. Finally, a buffer vessel for
temporary storage of product is provided in case of a malfunction in the
plant.
In an industrially particularly advantageous embodiment of a production
plant for carrying out the oxo process, synthesis gas and olefin are
introduced via double roses which serve as predistributors into the reactor
in which the aqueous catalyst solution is present. The fine dispersion of the
reactants in the reaction mixture is achieved by means of a sparging stirrer.
To remove the heat of reaction, the reactor is provided with a cooling
matrix. The liquid and gaseous components ascend through a guide tube
in the reactor and separate at its upper end. The gas is either recirculated
into the reactor or discharged from the reaction system as offgas. The
aqueous catalyst solution separates from the crude, organic product. The
crude product is introduced into a stripping column, freed of dissolved
olefins by means of the synthesis gas passed through the stripping column
in countercurrent and finely fractionated into its components in a column.
The heat required for the distillation is obtained directly via the cooling
matrix. For this purpose, the liquid aldehyde from the bottom of the column
is introduced via a phase separator into the cooling matrix in which it
vaporizes and it is then conveyed in vapor form via the phase separator
back into the column.
The above-described apparatus for carrying out the oxo process using an
aqueous catalyst phase has given excellent service in industrial practice.
However, there is interest in further optimizing the process. This is an
object of the present invention. Specifically, the invention has the object of
improving the economics by changing the way in which the process is
carried out and/or by simplifying the apparatus employed in the process.
Further objects are to increase the conversion and the yield of desired
product and to improve safety.
The invention provides a process for the hydroformylation of ofefinically
unsaturated compounds in a heterogeneous reaction system using a
catalyst consisting of an aqueous solution comprising complexes of
rhodium with water-soluble organic phosphorus(lll) compounds as ligands
and, if desired, excess water-soluble organic phosphorus(lll) compounds,
at pressures of from 0.4 to 10 MPa and temperatures of from 50 to 180°C.
According to the present invention, the reaction of the reactants is carried
out in a reaction column.
Apart from carrying out the reaction between olefinic compound and
synthesis gas in a heterogeneous reaction system using an aqueous
catalyst phase, it is an essential feature of the invention that the reaction is
carried out in a reaction column as reactor.
The differences between the novel process and the processes customary
hitherto which have a stirred tank as central apparatus of the reaction plant
are conspicuous. Apart from further changes, the mixing of the reactants
and the catalyst solution without use of a stirrer and the absence of a
separate stripping apparatus for recovering the olefin dissolved in the
product are of particular significance.
For the purposes of the present invention, the term reaction columns refers
to the apparatuses used, in particular, for distillation, rectification and
extraction in chemical engineering. As hydroformylation reactors, they are
provided with feed openings for the reactants and the catalyst solution and
with devices for taking off product, catalyst solution and offgas. As reaction
columns, it is possible to use the various types of column which are widely
used in industrial practice, in particular tray columns and columns with
ordered packing or random packing elements. In these, the catalyst
solution is fed in at the top of the column, advantageously onto the
uppermost tray of the column. Below the top of the column, preferably in
the upper region (i.e. in the upper half) of the column, the olefinic
compound is fed into the reactor. Catalyst solution, olefin and reaction
product, which travel downward in the interior of the column, flow in
countercurrent to the ascending synthesis gas introduced at the bottom of
the column. Reaction product and catalyst solution are taken off in the
lower part (the lower half) of the reactor, while the gaseous components
leave the column in its upper region.
The reactants and catalyst solution do not have to be introduced into the
reactor at one feed point each. It is thus not necessary for the total amount
of olefin to be introduced entirely at one point and in the upper region and
the total amount of synthesis gas to flow into the reaction space only at the
bottom of the reaction column. Rather, the reactants can be introduced at
different points along the column. The number of feed points can be up to
the number of separation stages of the column. Equipping the reactor with
a plurality of feed lines for the individual participants in the reaction allows it
to be matched individually to the requirements of the respective reaction,
e.g. with regard to the reactivity of the olefin used, the desired reaction
rate, the completeness of the conversion and the desired composition of
the reaction product. Merely by way of example, the reactivity of the olefin
will be examined in more detail. In the case of olefins which react quickly, a
larger amount of olefin will be able to be fed to the reactor than in the case
of relatively unreactive olefins, so that the reactive unsaturated
hydrocarbons are introduced into the reactor via not only one feed line but
via a plurality of feed lines. This opportunity of varying the streams also
allows the same reactor to be used for reacting various starting materials.
The introduction of catalyst solution at various points along the reactor will
be restricted to special cases, e.g. to maintain the required catalyst
concentration in the case of increased catalyst consumption caused by
impurities in the starting materials or else to control the temperature by
removing heat of reaction from the reactor. Below the top of the reactor, it
is possible to feed the catalyst solution into the column either separately
from the olefin or together with the olefin.
Use of a reaction column instead of a stirred tank as reactor is also
advantageous because a plurality of separation stages (e.g. column trays)
are connected in series in the column. The series arrangement of a
plurality of separation stages in the column has the effect of converting the
characteristics of a stirred tank into the characteristics of a cascade of
stirred tanks. Olefin and synthesis gas react with one another in the
presence of the catalyst solution until the respective chemical and physical
equilibrium is established. For this reason, the conversion in the reaction
column is higher than in a stirred tank. Reaction columns having from 5 to
120 separation stages, in particular from 15 to 40 separation stages, have
been found to be useful in the process of the invention.
A critical factor in the choice of the reaction column which is suitable in a
particular case is its load range. This term refers to the uniform
hydrodynamic loading of the column cross section due to ascending
gas/mass stream and the downflowing liquid/mass stream. Each reaction
column has a particular load range which depends on the type of column
internals and the properties of the feed mixture and within which uniform
flow loading and thus heat and mass transport are ensured.
The hydroformylation reaction is strongly exothermic. The heat evolved in
the reaction can be used either internally in the reaction for preheating the
reactants and for distillation of the reaction product and/or externally for
generating steam. The thermal energy is advantageously removed via the
reaction product and the circulated catalyst solution, although heat
recovery is not restricted to these embodiments.
The synthesis gas rising through the reaction column flows, as stated
above, in countercurrent to the reaction product. The gaseous phase
permeates the liquid stream and in the process extracts unreacted olefin
dissolved in the reaction product and transports it into the reaction zone.
The olefin conversion is significantly improved in this way, without a
specific extraction unit having to be installed in the hydroformylation plant.
As catalysts, use is made of water-soluble rhodium complexes containing
water-soluble phosphorus(lll) compounds as ligands. Examples of water-
soluble phosphorus(lll) compounds which form complexes with rhodium
are triarylphosphines, trialkylphosphines and arylated or alkylated
diphosphines whose organic radicals contain sulfonic acid groups or
carboxyl groups. Their preparation and use is known, for example, from
DE-B-26 27 354, EP 0 103 810 B1, EP 0 163 234 B1 and EP 0 571 819
A1. Further groups of suitable compounds are sulfonated or carboxylated
organic phosphites and heterocyclic compounds of trivalent phosphorus.
The conditions under which the reaction occurs can be varied within wide
limits and adapted to individual circumstances. They depend, inter alia, on
the starting material, on the catalyst system chosen and on the desired
degree of conversion. The hydroformylation of the starting materials is
usually carried out at temperatures of from 50 to 180°C. Preference is
given to temperatures of from 80 to 140°C, in particular from 100 to 130°C.
The total pressure is in a range from 0.4 to 10 MPa, preferably from 1 to
6 MPa and in particular from 1.5 to 5 MPa. The molar ratio of hydrogen to
carbon monoxide is usually in the range from 1:10 to 10:1; mixtures
comprising hydrogen and carbon monoxide in a molar ratio of from 3:1 to
1:3, in particular 1:1, are preferred.
The rhodium concentration is from 20 to 1000 ppm by weight, preferably
from 50 to 500 ppm by weight and in particular from 100 to 300 ppm by
weight, in each case based on the aqueous catalyst solution. Although it is
possible to use the stochiometric rhodium-phosphorus complex as catalyst,
the reaction is preferably carried out in the presence of excess phosphorus
ligand, i.e. ligand which has not undergone complex formation with
rhodium. Preference is given to using from 3 to 200 mol of phosphorus in
the form of a water-soluble organic phosphorus compound per mol of
rhodium. Molar ratios of rhodium to phosphorus in the range from 1:50 to
1:100 have been found to be particularly useful. The rhodium-phosphorus
complex used as catalyst does not have to have a uniform composition,
but can be, for example, a mixture of rhodium complexes which differ in the
type of phosphorus ligands present. Likewise, the phosphorus ligand
present in the aqueous catalyst solution can be composed of a mixture of
different water-soluble organic phosphorus compounds. The catalyst is
usually formed from the components rhodium or rhodium compound,
organic phosphorus compound and synthesis gas under the conditions of
the hydroformylation reaction. However, it can also be introduced into the
reaction stage as a preformed catalyst, i.e. a separately prepared catalyst.
It has been found to be advantageous to circulate the catalyst and to make
up for any catalyst losses which occur by introduction of fresh catalyst.
To increase the conversion per unit time of olefinically unsaturated
compounds which are only sparingly soluble in the aqueous catalyst
solution, it may be advisable to add a phase transfer reagent (solubilizer) to
this solution. This alters the physical properties of the interfaces between
the two liquid phases and thus aids transition of the organic reactants into
the aqueous catalyst phase. Solubilizing action is displayed by compounds
whose hydrophilic groups are ionic (anionic or cationic) or nonionic.
Examples of anionically active compounds are, inter alia, the sodium,
potassium and ammonium salts of carboxylic acids, preferably those
having from 8 to 20 carbon atoms. Cationic solubilizers include
tetraalkylammonium and N-alkylpyrridinium salts. Nonionic phase transfer
reagents are, for example, alkyl and alkylphenyl polyethylene glycols and
trialkylamine oxides.
The reactants olefin and synthesis gas can be preheated before
introduction into the reactor. The liquid phase leaves the reaction column in
the lower part, preferably at the bottom of the column, and goes via a heat
exchanger into a phase separator. Here, it separates into the organic
reaction product and the aqueous catalyst solution. The offgas taken from
the reactor in the upper part, in particular at the top of the column, consists
essentially of carbon monoxide and hydrogen. It may further comprise
reaction product, saturated compounds formed by hydrogenation of the
olefinic compounds and water. Olefinic starting material is present in the
offgas particularly when, for example for reasons of process economics,
the reaction has not been carried out to complete conversion of the
unsaturated compound. The olefin can be recovered from the offgas by
known methods, e.g. by condensation, or reacted in a second reaction
stage to convert it into hydroformylation product. The reaction product
present in the offgas is also separated off and returned to the reaction
column or passed directly to the distillation stage.
The process of the invention can be applied to olefinically unsaturated
compounds of any structure. Accordingly, both olefins having an internal
double bond and olefins having terminal double bonds and likewise
straight-chain or branched olefins are suitable as starting material.
Furthermore, the olefins can also be substituted by functional groups, in
particular groups which are not changed during the course of the reaction.
Multiply olefinically unsaturated compounds are also possible as starting
materials. The process has been found to be particularly useful in the
hydroformylation of olefinically unsaturated hydrocarbons having from 3 to
12 carbon atoms in the molecule, preferably propylene and the isomeric
butenes.
Possible embodiments of the process of the invention are shown
schematically by way of example in the accompanying drawings.
In the process outlined in Figure 1, synthesis gas is fed into a reaction
column 1 at the bottom of the column via a line 2 and olefin is fed in at feed
points 4, 5 and 6 along the length of the reactor via a line 3. The catalyst
solution is pumped via a line 7 into the top of the column and onto the
uppermost separation stage of the column. Downward-flowing olefin reacts
in the reactor with ascending synthesis gas in the presence of the catalyst
to form aldehyde until equilibrium is established. Olefin dissolved in the
product is stripped from the liquid phase by the upward-flowing synthesis
gas stream and is likewise converted into aldehyde. The crude aldehyde
which has been freed of olefin is taken off together with the catalyst
solution in the lower part of the reaction column and is passed directly via a
line 8 to a heat exchanger 9. The recovered heat can be used, for
example, for the generation of stream and/or for the distillation of reaction
product. The heat exchanger is followed by a separator 10 in which organic
product and aqueous catalyst solution are separated. The catalyst phase is
pumped via a heat exchanger 11, where the remaining heat in it is
removed, to the top of the reaction column 1, if appropriate after addition of
supplementary amounts of water or catalyst solution from containers 12
and 13. Off gas is taken from the reaction system via line 14. It comprises
predominantly carbon monoxide and hydrogen and small amounts of, inter
alia, unreacted olefin and reaction product. Olefin and product are not
discarded but instead can, like carbon monoxide and hydrogen, be utilized,
for example in the process itself. It is also possible for the gas mixture to
be reacted in an after-reactor with the olefin recovered from the offgas so
as to convert both of them into further, desired product.
The process variant shown in Figure 2 differs from the process of Figure 1
in that the offgas leaving the reactor 1 via line 14 is cooled in a heat
exchanger 15. A two-phase system consisting of gaseous and liquid phase
is formed. Both phases are separated in a separator 16 and the gaseous
phase is removed from the system while the liquid phase is returned to the
reaction column 1 via line 17. The plant components denoted by the
reference numerals 2 to 13 correspond, (as do the reaction column 1 and
the offgas line 14) to those of Figure 1.
WE CLAIM;
1. A process for the hydro form ylation of olefmically unsaturated compounds
having from 3 to 12 carbon atoms in a heterogeneous reaction system using a
catalyst consisting of an aqueous solution comprising complexes of rhodium
with water-sohible organic phosphorus (III) compounds selected from the
group consisting of triarylphosphines, trialkylphosphines and arylated or
alkylated diphosphates whose organic radicals contain sulfonic acid groups or
carboxyl groups as ligands and, if desired, excess water-soluble organic
phosphorus (III) compounds, at pressures of from 0.4 to 10 MPa and
temperatures of from 50 to 180°C,wherein the reaction of the reactants is
carried out in a reaction column having from 5 to 120 separation stages, and
selected from the group consisting of a tray column, a column with ordered
packing and a column with random packing elements.
2. The process as claimed in claim 1, wherein the reaction column is provided
with feed openings for the reactants and the catalyst solution and with devices
for taking off product, catalyst solution and offgas.
3. The process as claimed in claim 1 or 2 wherein the reaction column has from
15 to 40, separation stages.
4. The process as claimed in one or more of claims 1 to 3 wherein the reactants
namely olefmicaliy unsaturated compounds and synthesis gas, and the catalyst
solution are fed into the reaction column at separate feed points.
5. The process as claimed in one or more more of claims 1 to 4, wherein the
olefmicaliy unsaturated compound is introduced in the upper region of the
reaction column at one feed point or at a plurality of feed points.
6. The process as claimed in one or more of claims 1 to 5, wherein the synthesis
gas is introduced in the lower region of the reaction column, preferably at the
bottom of the reaction column, at one feed point or at a plurality of feed points.
7. The process as claimed in one or more of claims 1 to 6, wherein the catalyst
solution is introduced in the upper region of the reaction column, in particular
onto the uppermost separation stage of the reaction column.
8. The process as claimed in one or more of claims 1 to 4, wherein the reactants
namely olefinically unsaturated compound and synthesis gas, and the catalyst
solution are each introduced at a plurality of feed points arranged along the
reaction column.
9. The process as claimed in one or more of claims 1 to 3, and 5 to 7 wherein
olefinically unsaturated compound and catalyst are introduced together below
the top of the column at one or more feed points along the reaction column.
10. The process as claimed in one or more of claims 1 to 9, wherein the reactants
are preheated before being introduced into the reaction column.
11. The process as claimed in claim 10, wherein preheating is carried out using
heat evolved in the process.
12. The process as claimed in one or more of claims 1 to 11, wherein the heat
reaction is removed by means of an auxiliary medium such as water or steam.
13. The process as claimed in one or more of claims 1 to 12, wherein the offgas is
separated into a gaseous phase and a liquid phase and the liquid phase is
returned to the reaction column.
A process for the hydroformylation of olefinically unsaturated compounds having
from 3 to 12 carbon atoms in a heterogeneous reaction system using a catalyst
consisting of an aqueous solution comprising complexes of rhodium with water-
soluble organic phosphorus (III) compounds selected from the group consisting of
triarylphosphines, trialkylphosphines and arylated or alkylated diphosphates whose
organic radicals contain sulfonic acid groups or carboxyl groups as ligands and, if
desired, excess water-soluble organic phosphorus (III) compounds, at pressures of
from 0.4 to 10 MPa and temperatures of from 50 to 180°C,wherein the reaction of
the reactants is carried out in a reaction column having from 5 to 120 separation
stages, and selected from the group consisting of a tray column, a column with
ordered packing and a column with random packing elements.

Documents:

« Previous Patent

Next Patent »

Patent Number

225247

Indian Patent Application Number

IN/PCT/2002/00481/KOL

PG Journal Number

45/2008

Publication Date

07-Nov-2008

Grant Date

05-Nov-2008

Date of Filing

17-Apr-2002

Name of Patentee

CELANESE CHEMICALS EUROPE GMBH

Applicant Address

LAUGIALLE 14, 60439 FRANKFURT

Inventors:

#	Inventor's Name	Inventor's Address
1	HOFS, WOLFGANG	AN DER SCHLENKE 7, 46147 OBERHAUSEN

PCT International Classification Number

C07C 45/00

PCT International Application Number

PCT/EP2000/10881

PCT International Filing date

2000-11-04

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	19954665.7	1999-11-13	Germany