PROCESS FOR PRODUCING ORGANIC ACIDS

Abstract: A process for the production of organic carboxylic acids by the catalytic reaction of mixtures of formic acid and organic esters in contact with a homogeneous catalyst system containing rhodium metal atom and lithium iodide.

Description: PROCESS FOR PRODUCING ORGANIC ACIDS BACKGROUND OP THE INVENTION The production of organic compounds using carbon monoxide or synthesis gas, which is a mixture of carbon monoxide and hydrogen. as reactant has bcen known for r significant period of tine. It is well known that one can produce methanol directly from synthesis gas and that ethanol can be further reacted by hydroformylation. homologation and carbonylation reactions to produce acetaldehyde. ethanol and acetic acid or its methyl ester. respectively. It is also known that esters. ethers. and other organic compounds can be reacted with carbon monoxide or synthesis gas to produce orygenated organic compounds. The difficulties, however, have resided in the ability to carry out any one of these chosen reactions to produce the desired compound at acceptable efficiency, conversion rate and selectivity. In aluost all instances the reaction is generally catalyzed using a Group VIII transition metal compound as catalyst and a halogen as the promoter. It is known that many other metal compounds and promoters can be used. In addition, the prior art has disclosed the use of secondary activators or ligands in conjunction with the metal catalysts and promoters. These secondary activators can be other metallic salts or compounds0 amines. phosphorus compounds, as well as a multitude of other compounds that have been disclosed in the published literature. Thus. a typical catalyst system contains the metal atom catalyst. promoter and, optionally. ligands. solvents and secondary activators. Though a significant amount of literature does exist describing the production of oxygenated organic compounds, to our knowledge it does not disclose or suggest our invention. Several of the pertinent patents in this area are discussed below. French Patent No. 2,317,269, discloses the production of aliphatic carboxylic acids by the reaction of an alcohol vith carbon monoxide in the presence of a catalyst containing at least three essential components. irides atom. copper atom and halogen. This is not our process. In European Patent hpplication No. 0018927; there is described a process for the production of monocarboxylic acids by the carbonylation of an alcohol using a nickel catalyst, a halide and a solvent; in this reference synthesis gas is used. In the process of this invention of this instant application an organic acid is produced from formic acid and an organic ester using a cobalt atom catalyst and lithium iodide. In European Patent Pçplication No. 0045637, there is disclosed the direct conversion of formic acid esters to their corresponding carboxylic acids without the presence of carbon monoxide using as catalyst a soluble iridium salt and an iodine promoter. This is not our catalytic process. Another known procedure for producing acetic acid is the catalytic isomerization of methyl formate as shown by the reaction: EMI3.1 This procedure is shown in U.S.-A- 1,697,109. The process described is a vapor phase isomerization reaction carried out at 2000C to 450-C at a pressure up to 200 atmospheres using a metal oxide or acetate catalyst. It does not disclose the use of mixtures of formic acid and an organic ester as starting materials. U.S.-A- 2,508,513 claims an iron metal atom based catalyst. e.g. nickel, promoted with methyl iodide for the isomerization of methyl formate to acetic acid. carried out at 3000C to 4000C and a pressure up to 400 atmospheres. Carbon monoxide may be present. It does not disclose the production of organic carboxylic acids from mixtures of formic acid and an organic ester. U.S.-A- 3,060,233, discloses the carbonylation of methanol to acetic acid using a metal of the iron group of the Periodic Table and a halide. It does not disclose use of rhodium or the use of a mixture of formic acid and an organic ester. U.S.-A- 3,769,329 discloses the production of carboxylic acids from alcohols, or the ester. ether and halide derivatives thereof. and carbon monoxide using a rhodium catalyst and a halogen component. It does not mention lithium iodide, nor does it react a mixture of formic acid and an organic ester. U.S.-A- 3,798,267, relates to the conversion of methyl formate to acetic acid in the presence of a catalyst system consisting essentially of activated carbon and a halogen promoter. The reference uses catalyst and starting materials different than those employed in the invention of this application. U.S.-A- 4,194,056, discloses the production of carboxylic acid from methyl formate using a soluble rhodium catalyst, halogen promoter and carbon monoxide. This is not the process of the instant invention, nor does this reference suggest or disclose the use of lithium iodide and the unexpected results achieved by its use. U.A.-A-Patent No. 4,212,989, describes a process for producing carboxylic acids or their esters by reacting an alcohol or an ether with carbon monoxide using a Group VIII metal catalyst and an iodine promoter. The reference contains no suggestion or disclosure of the production of organic carboxylic acids from mixtures of formic acid and an organic ester. British Patent Specification 1,286,224, relates to the reaction of methyl formate vith carbon monoxide in contact with a rhodium catalyst and a halogen promoter to produce acetic acid. It contains no recognition of the distinct advantages achieved with the use of lithium iodide. in fact it does not mention this specific compound. nor does it involve use of mixtures of formic acid and an organic ester as initial reactants. British Patent Specification 1,293,193, relates to the direct conversion of formic acid esters to the corresponding carboxylic acids, in the presence of carbon monoxide. a catalyst that is a Group lib or VIII metal and an organic polar solvent. it does not disclose use of rhodium atom plus lithium iodide to convert mixtures of formic acid vith other organic esters to organic carboxylic acids. Japanese Patent Publication 50-16773, discloses the production of an organic acid from the corresponding formic acid ester in the presence of carbon monoxide using a catalyst system containing cobalt. iron or mercury and a halogen plus an alkali metal salt of a lower aliphatic carboxylic acid, triamine or cyclic anne. Japanese Patent Publication 51-65703, discloses the reaction of methyl formate in the presence of carbon monoxide using a system containing a rhenium catalyst and halogen compound to produce acetic acid. Japanese Patent Publication 56-22745, discloses the isowerisation of r formic acid ester to the corresponding acid in the presence of carbon monoxide, palladium atom, halogen and base. Japanese Patent Application No. 56-73040, relates to a process for producing acetic acid by isomerizing methyl formate in the presence of carbon monoxide using i nickel catalyst, an iodine compound and an organic nitrogen compound. Japanese Patent Application 56-83439, discloses a method for producing acetic acid by heating methyl formate and carbon monoxide in contact with a catalyst containing palladium. ruthenium and/or irridium metal atom and a halide promoter. None of the five Japanese Patent Applications disclose a process for producing acetic acid from a mixture of formic acid and an organic ester using a catalyst mixture consisting essentially of rhodium metal atom and lithium iodide. It can be seen that the prior art contains many disclosures dealing with the catalytic production of acetic acid. One of the disadvantages in many of these reference is the presence of water with the eventual need to remove it from the desired organic acid product. This removal is both complicated and costly. Other disadvantages often include the simultaneous occurrence of other reactions leading to the formation of by-products. such as, dimethyl acetal. methyl acetate, ethanol. etc. These reactions compete with the organic acid production resulting in lov conversion rate and selectivity to organic acid. Many processes employed for the production of organic acids use a catalyst system containing a source of metal atom and r source of halide atom. The alkali metal halides are often mentioned as suitable halide sources, but no distinction is made between any specific one of the alkali metal halides or between any other halogen compound. SUGARY OF THE INVENTION A catalyst system and process for the production of organic acids at high efficiency, selectivity and conversion rate by the reaction of mixture± of an organic ester, such as methyl acetate and formic acid has been found. The catalyst system charged to the reactor in our process contains rhodium atoms, lithium iodide and optionally an organic ligand. The use of lithium iodide in this system within the ranges defined results in unexpectedly high efficiency, high conversion rate or activity and high selectivity not heretofore achieved. particularly in the production of essentially anhydrous acetic acid from formic acid and methyl acetate. DESCRIPTION OF THE INVENTION In the catalytic reactions to produce oxygenated organic compounds there are several criteria required of the catalyst. The catalyst must be as stable as possible, it should have a high activity or conversion rate, and it should have as high a selectivity for the desired product as possible. Stability of the catalyst relates to how long the catalyst remains functional before either breaking down or losing its catalytic effect. Activity or conversion rate relates to the amounts of reactants the catalyst converts to product per unit of time, generally expressed in g. mole per liter per hour (g tole/lth ). electivity relates to the quantity of desired product produced, generally expressed in aole percent, based on the total amount of both desired products and undesired products produced. The goal to be achieved is high values for all three criteria and continued efforts are being made to find new catalyst compositions to reach this goal without having a significant detrimental effect on the overall process. Toward this goal the prior art has developed catalyst systems containing a wide variety of metal atoms, promoters and activators, in many cases with diverse other components added. Though these catalyst systems are effective, improvement is always desirable. The present invention is based on the unexpected and unpredictable discovery that the rhodium-lithium iodide system is an unexpectedly superior catalytic system for the production of organic acids from mixtures of formic acid and organic ester at unexpected high efficiency selectivity and conversion rate. It was also found that a ligand, ER''3, can also be present as an optional component of the system. This unexpected improvement in efficiency, selectivity and conversion rate is achieved when the systems components are maintained within a defined range and when lithium iodide is present as the source of the halogen component in the system. Optionally methyl lodid and/or a solvent and/or diluent can also be present. The improved catalyst system of this invention can be portrayed as containing the components Rh-LiI-ER3,, wherein Rh is the rhodium containing compound and tR'3 is optionally present. In the process of our invention mixtures of esters and formic acid are reacted using a particular catalyst system containing rhodium atoms and lithium iodide. This system produces commercially desirable organic acids at unexpectedly high efficiency. conversion rate and selectivity, with a minimum of by-products and without formation of water. The overall reaction that occurs with a simple ester is theoretically: EMI9.1 In the above formula R can be an alkyl group having from 1 to 30 carbon atoms, preferably from 1 to 15 carbon atoms and most preferably from 1 to 5 carbon atoms; an alkenyl group having from 2 to 30 carbon atoms, preferably from 2 to 15 carbon atoms and most preferably from 2 to 5 carbon atoms; or an aryl, aralkyl or alkaryl group having 6 or 10 ring carbon atoms, e.g., phenyl and naphthyl, with from 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, in the alk-soiety thereof and R' can be an alkyl group having from 1 to 3 carbon atoms, preferably 1 carbon atom . The R groups can be linear or branched and they can be unsubstituted or substituted with groups which will not have an adverse effect on the reaction; further; the alkyl groups can contain more than one unsaturated bond. Illustrative of suitable esters one can mention methyl formate, ethyl formate, methyl acetate, ethyl acetate, the propyl acetates, methyl propionate, ethyl propionate, iso-propyl propionate, methyl butyrate, ethyl butyrate, iso-propyl butyrate, methyl bentoate, propyl benzoate, methyl salicylate, iso-propyl salicylate, dimethyl malonate, diethyl malonate, dimethyl succinate, dilsopropyl succinate, dimethyl acetate, dimethyl phthalate, methyl cinnamate. When R and R' ' are the same, only one carboxylic acid is produced. Thus, methyl acetate produces acetic acid. When R and B' are not the same, a mixture of organic acids is obtained. Thus, ethyl acetate or methyl propionate, or mixtures thereof, produce acetic acid and propionic acid mixtures. The theoretical stoichiometry of the reaction is the reaction of 1 mole of formic acid per mole of ester. However, this can be varied over a molar ratio of formic acid to organic ester of from 0.1:1 or lower to 10:1 or higher. The rhodium component of the catalyst system can be supplied from any number of sources. many of these are known to those of ordinary skill in the art. Thus, it is not necessary for an understanding thereof to specifically enumerate every suitable type and every specific compound since any of the known rhodium compounds can be used. The essential rhodium component of the catalyst system of the present invention may be provided by introducing into the reaction zone a compound of rhodium or may be provided by introducing into the reaction zone rhodium. Among the materials which may be charged to the reaction zone to provide the rhodium component of the catalyst system of the present invention are rhodium metal, rhodium salts and oxides, organo rhodium compounds and coordination compounds of rhodium. Specific examples of materials capable of providing the rhodium constituent of the catalyst system of the present invention may be taken from the following non-limiting partial list of suitable materials. RhCl2 RhBr3 RhI2 RhCl3 3H2O RhBr3 3H2O Rh2(CO)4C12 Rh2(CO)4Br2 Rh2(CO)4I2 Rh2 (CO)8 Rh[(C6H5)3P]2(CO)I Rh[(C6H5)3P]2(CO)Cl Rh metal Rh(NO3)3 RhCl[(C6H5)3P]2(CH3I)2 Rh(SnCl3)[(C6H5)3P]2 RhCl(CO)[C6H5)3As]2 RhI(CO)[(C6H5)3Sb]2 [(n-C4H9)4N][Rh(CO)2X2] where X=Cl-, Br-, I [(n-C4H9)4AS]2[Rh(CO)2Y4] where X=Br-, I [(n-C4H9)4P][Rh(CO)I4] Rh[(C6H5)3P]2(CO)Br Rh[(n-C4H9)3P]2(CO)Br Rh[(n-C4H9)3P]2(CO)I RhBr((C6H5)3P)3 RhI[(C6H5)3P]3 RhCl[C6H5)3P]2 RhCl[(C6H5)3P]3H2 [(C6H5)3P]3Rh(CO)H Rh2O3 [Rh(C H ) 4)2 K4Rh2Cl2(SnCl2)4 K4Rh2Br2(SnBr3)4 K4Rh2I2(SnI2)4 In addition. one can use the other Group VIII transition metals comprising the iron triad. i.e., iron. ruthenium. osmium; the cobalt triad. i.e.. cobalt, rhodium. iridium; or the nickel triad. i.e., nickel, palladium, platinum. Though these vill catalyze the reaction. the preferred metals are nickel and rhodium, with the most preferred being rhodium. The rhodium or Group VIII transition metal atom concentration can vary over a wide range. Enough metal atom must be present to achieve reasonable reaction rates; however, excess may on occasion result in undesired by-products formation. For simplicity. the rhodium atom will be used in the specification with the understanding that it also applies to the other transition metals of Group VIII. The mole ratio of rhodium to ester can vary from 1:25 to 1:40,000, the preferred range is from 1:50 to 1:5,000, vith the most preferred range being from 1:100 to 1:2,000. The amount used is not a critical feature in this invention. The second component of the catalyst system is lithium iodide. It can be charged directly. or it can be formed in situ by any combination of lithium compound and iodine component that will result in the formation of lithium iodide during the reaction. Lithium bromide can also be used but the iodide is preferred. The presence of lithium iodide or lithium bromide is a critical feature of this invention. Direct charge of lithium iodide is the preferred form. However, any convenient combination of compounds for in situ formation of lithiun iodide can be used. This includes the use of lithium carborylates, carbonates and the like with a halogen compound. A suitable combination for in situ formation is lithium carboxylate and an alkyl halide. Though any combination of carboxylate and halide can be used. if the feedstock is RCOOR' then the preferred combination is RCOOLi and a I. For example, if the ester is methyl acetate, then the preferred combination is lithium acetate and methyl iodide. Sufficient lithium iodide must be present to exert a promoting effect on the reaction and to result in high efficiency. conversion rate and selectivity to the corresponding acid. The mole ratio of Rh:LiI can vary over a wide range. A Rh:LiI mole ratio of from 1:1 to 1:1000 can be employed, the preferred range is from 1:2 to l:40 and most preferably it is from 1:8 to 1:1O. As indicated, an organic ligand of the general formula ER3' can optionally be present in the reaction system. The use of such ligands is know, as are their identities, to those skilled in this art. In this formula E represents a Group VA element, e.g.. N, r. As. Sb and Bi. and R'' represents an organic piety. The ligand can serve as a catalyst stabilizer and/or to further enhance efficiency, conversion rate and selectivity, especially when the reaction is carried out at higher temperatures, for example at about 200'C or above. The ligand also serves to inhibit equipment corrosion in some instance. However, the use of a ligand is not mandatory and the reaction can be carried out without it. A large number of organic ligands is known and any of these can be used provided they do not have an adverse effect on the reaction. Among those of particular utility are the tertiary amines and the tri- and pentavalent phosphorus compounds. Though those skilled in the art know these compounds. illustrative of suitable compounds one can mention triethylphosphine. tributylphosphine, tri-2-ethylhexylphosphine, triphenylphosphine, tri(4-methoxyphenyl)phosphine, tri-p-tolylphosphine, tri(3-chlorophenyl)phosphine, diphenyl hexylphosphine, dimethyl (3-methoxyphenyl)phosphine, dibutyl stearylphosphine, tribenzylphosphine, dipropyl phenylphosphine, ethyl dipropylphosphine, tricyclohexylphosphine, cyclohexyl dibutylphosphine. propyl diphenylphosphine. dipropyl phenyiphosphine. phenyl diethylphosphine, tridecylphosphine, trioctadecylphosphine, tribenzylphosphine, methyl diethylphosphine, ethyl diphcnylphosphine, tolyl diethylphosphine, cyclohexyl diethylphosphine, diethyl cyclohexylphosphine, bis-(diphenylphosphino)ethane, bis-(diethylphosphino)-propane, bis-(diphenylphosphino)-butane, bis-(diethylphosphino)octane, trimethylamine, triethylamine, tri-n-butylamine. tri-t-butylamine. tri-2-ethylhexylamine, methyl dibutylamine, tridodecylamine, tristearylamine, ethyl dibutylamine, tricyclohexylamine, triphenylamine, tri(4-methoxyphenyl) amine. tri(p-chlorophenyl)-amine, dibutyl phenylamine, dipentyl cyclopentylamine, ethyl diphenylauine, trinaphthylamine, tri-p-tolylamine, tri-benzylamine, tri(3-methylcyclohexyl)amine, and the arsines, stibines and bismuthines corresponding to the above-identified phosphines and amines. They can be used singly or, if one desires. mixtures containing 2 or more ligands can be used. One can also employ a phosphine oxide or phosphite corresponding to the above phosphines as the ligand; these are also well known. The concentration of ligand charged can vary from a molar ratio of ligand to rhodium of from 50:1 to 1:50. preferably from 10:1 to 1:10. most preferably 3:1 to 1:1. In addition to the ligand one can optionally have a solvent present. Many essentially inert solvents are known as useful, essentially inert diluents and illustrative thereof one can mention 1.4-dioxane. the polyethylene glycol di-ethert or esters. diphenyl ether. sultolane, toluene. carboxylic acids as well as any other diluent or solvent which does not interfere with the reaction to any significant extent. The reaction is preferably carried out in the absence of any solvent or diluent other than those required to introduce reactants or catalyst components. The reaction is carried out at a temperature of from 500C to 3500C. preferably from 1200C to 220 C and most preferably from 140OC to 2000C. When the reaction is carried out at temperatures above 200'C in the presence of an ER"3 ligand. the preferred ligands are the phosphines. especially triphenyl phosphine. The pressure of the reaction can be from 3,45 to 690 bar (50 psig to 10,000 psig), preferably from 6,9 to 414 bar (100 psig to 6,000 psig), most preferably fran 13,8 to 34,5 bar (200 psig to 500 psig). The reaction time varies depending upon the reaction parameters, reactor size and charge. and the individual components employed at the specific process conditions. The reaction can be a batch or continuous reaction. The experiments and examples detailed belov were carried out in a Ha6teloy3 steel autoclave reactor having a volume of 300 ml. vhich was equipped with temperature and pressure sensing means. heating and cooling means, agitator and inlet and outlet means for introducing and removing components from the reactor, The autoclaves used in synthesis gas reactions are well known in the art and can be used in this process. Prior to charging the reactants the autoclave vas washed with methanol at 1000C under a nitrogen gas pressure of 34,5 to 69 bar (500 to 1,000 psig) by agitating for 30 minutes. The autoclave was drained. rinsed with dry acetone. and dried with nitrogen or any other inert gas. The liquid components were charged to the cleaned autoclave first and then the solid components were added and stirred. The autoclave was closed and purged with nitrogen. The autoclave contents were heated to the selected temperature, with agitation (usually 750 rpm), in about 45 minutes. The reaction was maintained at the prescribed teiperature for a specified period of time. usually between 0.5 to 5 hours. At the end of the reactor run, the contents were cooled, generally to about 10*C. A vapor phase sample vas taken for gas chromatography analysis: the gas phase was vented through two dry-ice acetone traps and then through a 10 liter saturated solution of calcium hypochlorite to remove metal carbonyls. if formed. The reactor was pressurized three times with nitrogen, 6,2 bar (90 psig) and vented through the same system, The residual reactor contents were dumped into a chilled pressure bottle and sealed. Subsequent analysis was performed using a Rewlett-Packard Model 58B0 gac chromatograph equipped with a 3,2 mm (one-eighth inch) diameter by (ten feet) 3 m long column packed with Chromosorb 101. The following examples serve to further illustrate this invention. In the examples the tern "AcAc" means "acetylacetonate". example 1 The autoclave was charged with 2.06 g of Rh(CO)2AcAc (8 mmoles). 82 g of formic acid (1.8 moles). 17.lg of lithium iodide (128 mmoles) and 70g of methyl acetate (0.95 mole). Following the procedure described above the reaction was carried out at 180 C for 3 hours. under nitrogen. at ambient autoclave pressure. Analysis indicated the following products present in the reaction product: Acetic acid 1.63 moles Formic acid 0.1 mole Methyl acetate Trace The acetic acid yield was 86% of theoretical and its conversion rate to acetic acid was 3.6 gmoles/T.h There was no indication of water formation. In the following examples the same procedure was employed using different organic esters as feedstock to produce the acids indicated at high yield and rate: water was not formed. Example Feedstock Product(s) 2 Propyl propionate Propionic acid Butanoic acid 3 Methyl propionate Propionic acid Acetic acid 4 Ethyl benzoate Benzoic acid Propionic acid Methyl formate formic acid Acetic acid 6 Ethyl butyrate Butanoic acid Propionic acid

Claims: CLAIMS 1. A process for the production of organic carboxylic acids of the formulas RCOOH and R'COOH which comprises the catalytic reaction of a mixture of formic acid and organic ester of the formula RCOOR' in contact with a homogeneous catalyst system consisting essentially of rhodium metal atom and lithium iodide. wherein H is an alkyl group having from 1 to 30 carbon atoms. or acryl, alkyl or alkaryl group having 6 or 10 rings carbon atoms with from 1 to 10 carbon atoms in the alkyl moiety thereof. or an alkenyl having from 2 to 30 carbon atoms and R' is an alkyl group having 1 to 3 carbon atoms. 2. A process as claimed in claim 1 wherein the temperature is from 50 C to 3500C and the pressure is from 3,45 to 690 bar. 3. A process as claimed in claim 1 wherein the mole ratio of Rh:LiI is from 1:1 to 1:1.000. or from 1 : 8 to 1 : 150. 4 A process as claimed in claims 1 to 3 wherein the R groups of the organic ester are alkyl groups having from 1 to 15 carbon atoms, alkenyl groups having from 2 to 15 carbon atoms, or acryl, aralkyl or alkaryl groups having from 6 to 10 ring carbon atoms and from 1 to 4 carbon atoms in the alk-moiety thereof. 5. A process as claimed in claims 1 to 47 wherein the a' group is methyl. 6, A process as claimed in claims 1 to 5 wherein said organic ester is methyl acetate. 7. A process as claimed in claims 1 to 6 wherein an organic ligand of formula ER3'' is present. wherein t is nitrogen, phosphorus, arrenic, antimony and bismuth and R''' is an organic moiety. 8. A process as claimed in claim 7 wherein said ligand is a tertiary phosphine.

Inventors: SCHRECK, DAVID JAMES, WEGMAN, RICHARD WILLIAM
Applicants: UNION CARBIDE CORPORATION
Application year: 1984
Main classification: C07C51
IPC codes: C07C67, C07B61, C07C53, B01J27, C07C51, C07C63