A PROCESS FOR THE CO-PRODUCTION OF CARBOXYLIC ACIDS

Abstract: The invention relates to a process for the co-production of carboxylic acids of formula R¹COOH and/or R²COOH and carboxylic acids of the formula R¹CH₂COOH and/or R²CH₂COOH by reacting one or more compounds of the formula R¹XR² in which X represents a moiety and in which R¹, R² and R³ represent similar or dissimilar hydrocarbon moieties which may be substituted with one or more inert substituents, with carbon monoxide and hydrogen in the presence of a rhodium catalyst and an iodide and/or bromide source, characterized in that the reaction is carried out under virtually anhydric conditions and in the presence - per mole of the compound R¹XR² - of at least 2 moles of a carboxylic acid of the formula R⁴COOH, in which R⁴ represents a hydrocarbon moiety which may be substituted with one or more inert substituents

Description: A PROCESS FOR THE CO-PRODUCTION OF CARBOXYLIC ACIDS The invention relates to a process for the co-production of carboxylic acids and carboxylic acids having one carbon atan more in the molecule. The invention in particular relates to the co-production of acetic acid and propionic acid fran methyl acetate, dimethyl ether, acetic anhydride or ethylidene diacetate. US patent specification 4,111,982 gives a description of a process for the co-production of acetic acid and propionic acid by the reaction of methanol, ethylene carbon monoxide and water in the presence of a rhodium compound and iodine or an iodine compound. One of the starting materials used in this process, ethylene, is a ccsnpaund which is usually produced fran petroleum, Whereas interest tends towards a method in which all the starting materials are based on coal (synthesis gas). From US patent specification 3,769,329 it is known that carboxylic acids can be obtained by carbonylation of alcohols. The carbonylation is carried out by reacting the alochol with CO in the presence of a rhodium compound and bromine or iodine or a bromine compound or an iodine compound, optionally in the presence of hydrogen. If the reaction is carried out in the presence of water, the starting material used may be not alcohol, but an ester or ether derived therefrom. The carboxylic acid formed contains one carbon atan more than the alochol or the alcohol-derived moiety present in the ester or ether. Thus the carbonylation for instance of methanol or methyl acetate according to US patent specification 3,769,329 leads to the formation of acetic acid. No Invention is made in this specification of the formation of propionic acid. It has now been found that if the abore-mentioned rhodiumcatalysed conversion of methylacetate of dimethyl ether is carried out under almost anhydric conditions in the presence of hydrogen and at least 2 moles of a carboxylic acid per stole of the starting ccnçcund, this will lead to the co-production of acetic acid and propionic acid. In addition, small quantities of normal and isobutyric acid may also be formed. The invention relates to a process for the co-production of carboxylic acids of the formula R1COOH and/or R2COOH and carboxylic acids of the formula R1CH2COOH and/or RêCH2COOH ba reacting one or more compounds of the formula R XR2 in which X represents a -O-, EMI2.1 miety and in which R11 Rê and R3 represent similar or dissimilar hydrocarbon moieties which may be substituted with one or mare inert substituents, with carbon monoxide and hydrogen in the presence of a rhodium catalyst and an iodide and/or bromide source, characterized in that the reaction is carried out under virtually anhydric conditions and in the presence - per mole of the compound R1XR2 - of at least 2 moles of a carboxylic acid of the formula R4COOH, in which R4 represents a hydrocarbon moiety which may be substituted with one or more inert substituents. The carbonylation of methyl acetate or dimethyl ether under almost anhydric conditions has been described in the literature, but owing to the use of different reaction conditions, the products obtained therein are different fran those obtained in the process according to the invention. For instance, the preparation of a acetic anhydride by the reaction of methyl acetate or dimethyl ether with CO in the presence of methyl iodide and a compound of a Group VIII metal is known fran UK patent specification 1,468,940. The reaction is carried out under anhydric conditions and, as can be seen fran the examples, in the absence of carboxylic acids. In this patent specification no mention is made of the formation of acetic acid or propionic acid. UK patent specification 1,523,346 relates to a similar process for the preparation of acetic anhydride by carbonylation of methyl acetate. It is stated that the presence of hydrogen can have a favourable effect on the course of the reaction, since it suppresses the formation of soot and carbon dioxide, but that it stimulates the formation of the by-product acetic acid. However, example 13 shows that the quantity of acetic acid formed in the presence of hydrogen is considerably smaller than the quantity used in the process according to the present invention; no Invention is made of the formation of propionic acid. From UK patent specification 1,538,782 it is known that ethylidene diacetate can be prepared by reaction of methyl acetate and/or dimethyl ether with carbon monoxide and hydrogen under anhydric conditions in the presence of a Group VIII noble metal catalyst, a bromide or an iodide and a promoter. This process leads to the formation of acetic anhydride, acetaldehyde and acetic acid as by-product, but the quantity of acetic acid formed is smaller than the minimum required in the process according to the present invention to bring about the formation of propionic acid. Further it is seen fran Examples V and VIII of UK patent specification 1,538,782 that for obtaining reaction products the presence of a promoter is essential; in the process according to the invention this is not the case. It is not known what mechanism gaverns the reaction or reactions involved in the process according to the invention. The "overall" reaction which takes place wnen methyl acetate is the starting material may be represented by the following reaction equation: EMI3.1 When dimethyl ether, ethylidene diacetate or acetic anhydride is the starting material, the respective reaction equations will be: EMI4.1 Independent of each other, the hydrocarbon moieties R1, 4 R, R and R preferably dependent alkyl, cycloalkyl, alyl, aralkyl or alkaryl groups which optionally may be substituted with one or more inert substituents, i.e. substituents which are inert under the reaction conditions, e.g. halogen atoms. Preferably the hydrocarbon moieties are unsubstituted and preferably they contain 1-20, in particular 1-6 carbon atoms. Naturally, the composition of the reaction product obtained in the process according to the invention is dependent on the R1XRê compound chosen. In order to keep this composition as simple as possible, the compound R1XRê preferably used is one in which the moieties R1 and R2 are identical. Examples of compounds of this type that are particularly preferred are methyl acetate, dimethyl ether, ethylene acetate and acetic anhydride. If compound R1XRê isd an ester, it should be taken into account that, as a side reaction, sooe ester interchange between the ester and the carboxylic acid R4CoCH may occur. Therefore it is preferred to use a carboxylic acid R4COOff which corresponds with the acid-derived moiety of the ester. Thus, the reaction between, for instance, methyl acetate, CO and H2 is preferably carried out in acetic acid. If in the compound R1XR2 moiety X represents the group EMI4.2 then preference is given to the use of a carboxylic acid in which moiety R is identical to R or R , which moieties are preferably identical as well, as mentioned hereinbefore. The molar ratio of the carboxylic acid R4CCOIH to compound R1XRê generally lies between 2:1 and 20:1, preferably between 3:1 and 15:1 and most preferably between 4:1 and 15:1. However, larger quantities of the carboxylic acid R4COOH can be used. The rhodium catalyst may be of any suitable type. Suitable catalysts are, for instance, rhodium oxide and rhodium hydroxide, rhodium salts of mineral acids, such as hydrogen chloride, nitric acid and sulphuric acid and rhodium salts of organic acids, preferably of alkane carboxylic acids having 1-20 carbon atoms. The rhodium may also be complexes in a zero-valent form with ligands such as carbon monoxide, acetylacetone or organic compounds of nitrogen, phosphorus, arsenic or antimony. The quantity of rhodium catalyst preferably lies between 0.01 and 10, in particular between 0.05 and 5%m per mole of compound R1XRê. Larger or smaller quantities can, however, be used. The iodide or bromide source may be elementary iodine or branine, a compod R5I or R Br, in which the moiety R5is preferably an alkyl group with 1-12 carbon atoms or a cycloalkyl, aryl, aralkyl or alkaryl group having not more than 12 carbon atms, or an acyl iodide or acyl bromide R5COI or R5COBr in which R5 has the above-mentioned meaning, hydrogen iodide or hydrogen bromide, an alkali mental iodide or an alkaline earth metal iodide, for instance lithium iodide or sodium iodide or an alkali metal bromide or an alkaline earth metal bromide. If desired, two or more iodide and/or bromide sources may be used. The quantity of the iodide or bromide source added to the reaction mixture is not critical. The number of gram atoms of iodine or bromine added in the elementary form or as iodide or bromide lies, for instance, between 0.1 and 200, preferably between 5 and 50 gram atoms per gram atan of rhodium. The process according to the invention is preferably carried out in the presence of one or more promoters. Suitable promoters are the oxides of amines, phosphines, arsines and stibines. A group of promoters used by preference are those having the formula YzR'R' 'R"1, in which Y represents oxygen, sulphur or selenium, Z represents phosphorus, antimony or arsenic and the moieties R', R", R"' independent of one another each represents a hydrogen atom or an alkyl, cycloalkyl, aryl or aralkyl group. These groups may be substituted, if required, with one or more substituents which under the reaction conditions are inert for instance, halogen atoms. The moisties R" and R" ' together may represent an alkylene group which preferably has not more than 20 carbon atoms. Each alkyl group preferably contains not more than 20 carbon atoms, each cycloalkyl group preferably contains not more than 7 carbon atoms and each alkyl group is preferably a phenyl group. Pratoters in which R', R " and R"' independent of one another represent an aryl group or a phenyl group are specially preferred. The moieties R" and R"' preferably are identical, Z preferably represents a phosphorus atom. Oxides, sulphides and selenides of phosphine, arsines or stibines containing two or more phosphorus, arsenic or antimony atoms are also suitable as praroters. Another group of suitable promoters is made up of compounds of the formula YZ(OR') (OR") (OR"'), in which Y, Z, R', R" and R "' have the meanings stated hereinbefore. This group includes for instance esters of phosphoric acid and thiophosphoric acid. Also suitable are compounds of the formula YZ [(O)aR'][(O)bR"][(O)cR"'], in which Y, Z, R', R" and R"' have the meanings stated hereinbefore, each of a, b and c is O or 1, and a + b + c equals 1 or 2. Examples of suitable promoters are trimethylphosphine oxide, tri-n-butylphosphine oxide, triphenylphosphine oxide, tri-p-tolylphosphine oxide, tetraphenyl dimethylene diphosphine dioxide (diphosdioxide), tetraphenyl trimethylene diphosphine dioxide, tri-n-butyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, diphenyl methylphosphonate, methyl dimethylphosphonate, methyl diethylphosphonate and methyl diphenyl phosphonate, trimethylarsine oxide, tri-isopropylstibine oxide, tricyclohexylarsine oxide, triphenylstibine oxide, diphenylethylarsine oxide, ethylenebis- (diphenylarsine) oxide, tri phenylphosphine sulphide and tributylphosphine sulphide. Examples of suitable N-amine oxides are pyridine N-oxide, the picoline N-oxides and trimethylamine N-oxide. Complexes which may be formed by the reaction of oxides, sulphides or selenides of phosphines, arsines or stibines with alkyl halides or hydrogen halides, such as [(C2H5)3AsO-H-OAs(C2H5)3]+I- or [(C6H5)3PO-H-OP(C6H5)3]+I3 are also suitable promoters. The abowe-mentioned promoters are usually used in catalytic quantities. These quantities are not critical. Suitable quantities lie between, for example, 0.1 and 100, preferably between 0.5 and 10 mole per gram atom of rhodium. Further, the process may suitably be carried out in the presence of small quantities - for instance of up to 100 equivalents per gram atom of rhodium - of a strong acid as the promoter. Suitable strong acids are those which, in an aqueous solution, at 200C have a pKa lower than 3.5, for instance p-toluenesulphonic acid or trifluormethanesulphonic acid or mineral acids, such as hydrochloric acid, sulphuric acid or perchloric acid. The process is carried out under virtually anhydric conditions. HowEver, such small quantities of water as may be present in commercially available starting materials, e.g. rhodium (III) chloride trihydrate, are permissible. The reaction mixture preferably contains not more than 2, in particular not more than 0.2 %w water. The process according to the invention may be carried out either in the liquid phase or in the gaseous phase. The hydrogen and the carbon monoxide may be added simultaneously if desired. Although usually carbon monoxide and hydrogen are added in more or less equimolar quantities, the molar ratios between the two compounds may vary within wide limits, for instance in the range of from 10:1 to 1:10. The carbon monoxide:hydrogen molar ratio preferably lies between 1:0.5 and 1:3. Inert gases, such as nitrogen, noble gases, carbon dioxide or methane may optionally be present in the reaction mixture. The process may be carried out batchwise, continuously or semi-cDntinuously. The process according to the invention is preferably carried out at a temperature between 50 and 3000C, in particular between 50 and 2000C and most preferably between 125 and 175 C. Either low pressure of, for instance, 5 bar or high pressures of, for instance, 1000 bar may be used. Usually high pressures are not econanical on account of the investment and energy costs involved. The pressure preferably lies between 20 and 100 bar. The process according to the invention may be carried out in the presence of an additional solvent, if desired. However, compound RlXR2, such as methyl acetate, ethyl acetate, methyl propiponate, ethyl propionate, dimethyl ether, diethyl ether or methyl t-butyl ether and/or the carboxylic acid R4COOH, for instance acetic acid or propionic acid, may in itself serve as a solvent as well. In that case it should naturally be ensured that the carboxylic acid R4COOH is present in such a proportion to compound R1XRê as is required according to the invention. Suitable additional solvents include cyclic ethers, such as tetrahydrofuran, 1,3-dioxane, 1,4-dioxane and the dioxolanes, sulphones and sulphoxides, such as dimethyl sulphone, sulphonate, 2-methyl sulphonate, 3-methyl sulphonate, dimethyl sulphoxide and diethyl sulphoxide. Butyrolacetone is a very suitable solvent. The additional solvent is generally used in quantities sufficient to keep the reaction mixture homogeneous for instance 5-20 %v, calculated on the total reaction mixture. The reaction mixture obtained in the process according to the invention may be processed by knawn techniques, such as fractional distillation. If desired, the products may be subjected to further purification treatments. With respect both to the starting materials and to conversion of the acids formed, the process may be integrated into existing processes. For instance, the process is excel lently suitable for the co-production of acetic acid and propionic acid from methyl acetate which in its turn can be prepared by carbonylation of methanol. Whilst the propionic acid obtained may be of interest in itself, the acetic acid formed as a by-product can be esterified with methanol to form methyl acetate, which compound can be recirculated to the reactor. EXAMPLE I The process was carried out in a 300 ml magnetically stirred Hastelloy C autoclave (Hastelloy is a trade mark) containing 35 ml (0.6 mole) acetic acid and 1 mmole rhodium (III) chloride trihydrate and methylacetate, methyl iodide or lithium iodide and optionally triphenylphosphine, triphenylphosphine oxide, dimethyl methylphosphonate or p-toluenesulphonic acid in the quantities given in Table A. The autoclave was flushed with carbon monoxide and then filled with a mixture of carbon monoxide and hydrogen (molar ratio 1:1) under pressure. The temperatures and pressures used are given in Table A. The autoclave was kept at the tewperature mentioned for 15 hours. Subsequently the reaction mixture was cooled and analysed by means of gas-liquid chromatography. The methyl acetate conversion was unvariably 100%. The yields of propionic acid and of normal and isobutyric acid are given in Table A in hm, calculated on methyl acetate converted. All the experiments in addition yielded acetic acid as a co-product in at least equlmolar quantities calculated on propionic acid produced. TABLE A Exp. Lodide- Promoter Methyl- Temp. Pressure Yield of Yield of source acetate propionic i + n butyric acid acid No. mmole mmole mole C bar % m % m 1 MeI(30) - 0.2 145 40 33 2 MeI(30) - 0.1 145 40 40 3 MeI(30) p-TS(3) 0.2 150 40 47 5 4 MeI(30) - 0.05 145 40 44 5 MeI(30) p-TS(3) 0.1 150 60 60 5-10 6 MeI(30) TPPO(4) 0.1 160 60 72 5-10 7 MeI(15) TPPO(4) 0.1 160 60 78 10-15 8 LIl p-TS(3) 0.1 150 60 10 9 MeI(7.5) TPPO(4) 0.1 160 60 72 10-15 10 MeI(15) DMMP(4) 0.1 160 60 60 5-10 Mel = methyl iodide p-TS = p-totuenesulphonic acid TPPO = triphenylphosphosphine oxide DMMP = dimethyl methylphosphonate TABLE A (cont'd) Comparative experiments Exp. Lodide- Promoter Methyl- Temp. Pressure Yield of Yield of source acetate propionic i + n butyric acid acid No. mmole mmole mole C bar % m % m 11 MeI(30) - 0.4 160 40 trace 12* MeI(30) p-TS(3) 0.1 140 60 trace 13** MeI(30) p-TS(3) 0.1 155 40 trace 14*** Mel(15) TPPO(4) 0.1 160 60 trace Mel = methyl iodide p-TS = p-totuenesulphonic acid TPPO = triphenylphosphosphine oxide * In this experiment not 35 ml acetic acid but 35 ml sulphonate was used. ** In this experiment not 1 mol rhodium (III) chloride trihydrate but 1 mmole ruthenium (III) choride trihydrate was used. *** In this experiment not 1 mmole rhodium chloride trihydrate but 0.7 mmole palladium diacetate was used. Comparison of Experiments 1 and 2 shows that raising the acetic acid:methyl acetate molar ratio from 3:1 to 6:1 increses the yield of propionic acid. Experiment 11 shows that when said molar ratio is lower than 2:1, no propionic acid is formed. Experiment 12 shows that not even the presence of the active pratter p-toluenesulphonic acid allows propionic acid to be formed in the absence of acetic acid. Experiments 13 and 14 show that under the reaction conditions used compounds of Ru and Pd do not catalyse the desired conversion. E$AMPIE II The process was carried out in a 300 ml magnetically stirred Hastelloy C autoclave (Hastelloy is a trade mark) containing 35 ml of an alkane carboxylic acid, 1 mmole rhodium (III) chloride trihydrate, 15 mmole methyl iodide and 4 rrrrole triphenylphosphine oxide, and 7.5 ml methyl acetate, methyl propionate ethyl propionate, acetic anhydride or ethylidene diacetate. The autoclave was flushed with carbon monoxide and subsequently filled with a mixture of carbon monoxide and hydrogen (molar ratio 1:1) at a pressure of 60 bar. The autoclave was kept at a temperature of 1600C for 15 hours. Then the reaction mixture was cooled and analysed by gas-liquid chromatogrphy. Conversion was 100% in the experiments using methyl acetate, methyl propionate, acetic anhydride and ethylidene diacetate and 80% in the experiment using ethyl propionate. The alkane carboxylic acids and the concentrations in which the various carboxylic acids were present in the reaction mixture are given in Table B. TABLE B alkane carboxylic acid carboxylic concentrations acid in reaction mixture, %w methyl acetate propionic acid acetic acid 19 propionic acid 67 n-btxtyric acid 6.3 isobutyric acid 4.9 methyl propionate acetic acid acetic acid 74 propionic acid 22 n-butyric acid 1.3 isobutyric acid 1.2 methyl propionate propionic acid acetic acid 9 propionic acid 78 n-butyric acid 6 isobutyric acid 4.5 ethyl propionate propionic acid propionic acid 87 n-butyric acid 3.5 isobutyric acid 2.6 acetic anhydride acetic acid acetic acid 87 propionic acid 9.5 n-butyric acid 0.5 isobutyric acid 0.5 ethylidene acetic acid acetic acid 85 diacetate propionic acid 13.1 n-butyric acid 1.0 isobutyric acid 1.0

Claims: CLAIMS 1. A process for the co-production of carboxylic acids of ftrrmiia R1COOH and/or R2COOH and carboxylic acids of the formula R1CH2COOH and/or R2CH2COOH by reacting one or more compound of the formula R i in which X represents a EMI14.1 moiety and in which R1, R2 and R3 represent similar or dissimilar hydrocarbon moieties which may be substituted with one or more inert substituents, with carbon monoxide and hydrogen in the presence of a rhodium catalyst and an iodide and/or bromide source, characterized in that the reaction is carried out under virtually anhydric conditions and in the presence per mole of the compound RIXR2 - of at least 2 moles of a carboxylic acid of the formula R4COOH, in which R4 represents a hydrocarbon moiety which may be substituted with one or more inert substituents. 2. A process as claimed in claim 1, characterized in that the hydrocarbon moieties R1, R2, R3 and R4 are unsubstituted and contain 1-20 carbon atoms. 3. A process as claimed in claim 1 or 2, characterized in that the moieties R1 and R2 are identical. 4. A process as claimed in claim 3, characterized in that the compound R1XR2 is methyl acetate, dimethyl ether, ethylidene diacetate or acetic anhydride. 5. A process as claimed in claims 1-4, characterized in that when compound R1XR2 is an ester, the carboxylic acid R4COOH corresponds with the acid-derived moiety of the ester and when in coccound R1XR2 the moiety X represents EMI15.1 the moiety R4 of carboxylic acid R4COOH is identical with R1 or R2. 6. A process as claimed in claims 1-5, characterized in that the molar ratio of carboxylic acid R4COOH to compound R1XR2 lies between 2:1 and 20:1. 7. A process as claimed in claim 5, characterized in that the molar ratio of carboxylic acid R4COOH to compound R iR2 lies between 3:1 and 15:1, in particular between 4:1 and 15:1. 8. A process as claimed in claims 1-7, characterized in that the quantity of rhodium catalyst lies between 0.01 and 10 moles per mole of compound R1XR2 9. A process as claimed in claims 1-8, characterized in that per gram atan of rhodium 0.01-200 gram atom of iodine and/or branium in elementary form or as iodide and/or branide is present in the reaction mixture. 10. A process as claimed in claims 1-9, characterized in that the process is carried out in the presence of a conpund having the formulaYZR'R''R"', YZ(OR')(OR'1)(OR''') or YZ[(O)aR'][(O)R''][(O)R'''], in which Y is oxygen, sulphur or selenium, Z represents phosphorus antimony or arsenic and the moieties R', R" and R''' independent of one another, each represent a hydrogen atan or an alkyl, cycloalkyl, aryl or aralkyl group which may be substituted with an inert substituent, a, b and c each are 0 or 1, and a + b + c equals 1 or 2 as promoter. 11. A process as claimed in claim 10, characterized in that the quantity of promOter lies between 0.1 and 100 mole per gram atan of rhodium. 12. A process as claimed in claims 1-9, characterized in that the process is carried out in the presence of up to 100 equivalents per gram atan of rhodium, of an acid which, in an aqueous solution, at 200C has a pKa of less than 3.5. 13. A process as claimed in claims 1-12, characterized in that the process is carried out at a temperature in the range between 50 and 3000C and a pressure in the range between 20 and 100 bar.

Inventors: DRENT, EIT
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1983
Main classification: C07C51
IPC codes: C07B61, C07C67, C07C51, B01J31, B01J27