HU208298B - Process for producing saturated carboxylic acids - Google Patents

Abstract

Prepn. of (n + 1)C carboxylic acid by reacting carbon monoxide with a n C alcohol in the presence of a Rh catalyst comprising: maintaining a liq. reaction medium of: (a) at least a finite amt. of water, (b) catalyst stabiliser, (c) the iodide deriv. of the alcohol, (d) the ester of the carboxylic acid and alcohol, (e) Rh-catalyst, (f) the carboxylic acid. The novelty is that the catalyst stabiliser is from quaternary ammonium iodides having the formula (I) - (III), where R1-2 and R3-5= H or 1-20C alkyl where at least one R3-5 gp. = 1-20C alkyl. - Pref. 0.5-8 wt.% water is maintained in the reaction medium. Pref. the catalyst stabiliser is generated in situ by quaternising a corresp. amine with the iodide deriv. of the alcohol.

Description

The present invention relates to an improved process for the preparation of saturated carboxylic acids containing η + 1 carbon atoms by carbonylation of alcohols containing n carbon atoms - from 1 to 20 - in the presence of radium catalysts. More particularly, the present invention relates to the preparation of acetic acid by carbonylation of methanol with rhodium catalyst.

The production of acetic acid by rhodium-catalyzed carbonylation of methanol is a well-known process that is run on an industrial scale. Such a process is an example of similar processes in which an alcohol containing n carbon atoms is converted by carbonylation (i.e. reaction with carbon monoxide) to a carboxylic acid containing η + 1 carbon atom. The reaction of the alcohol with carbon monoxide is usually carried out in the liquid phase in the presence of a dissolved radium catalyst and a promoter which is an iodine derivative of the alcohol. The process is described in more detail in GB 1233 121, and Applied Industrial Catalysis Vol. 1 (1983) 275-96. pages 2 to 4 of the manual provide details on the conversion of methanol to acetic acid.

Several basic studies have led to the conclusion that the catalysis process in such processes is actually carried out by the [Rh (CO) ₂ I ₂ ] ^e rhodium (I) anion. Reaction kinetic studies suggest that catalysis is accomplished by a cycle of reaction steps including the formation of rhodium (III) by oxidative addition of the iodide derivative of alcohol to [Rh (CO) 2 I 2] ^e and CO) 2 I _2] ^e by subsequent regeneration of acyl iodide reductive elimination of rhodium (III) of from. The oxidation and reduction reactions rádium® and rhodium (III) oxidation stages between this cycle raises a problem since in certain circumstances, rhodium (III) salts, e.g. RHL ₃ or [Rh (CO) ₂ I _5] ^2_ are formed which or insoluble or insoluble in the medium in which the process is carried out. Therefore, the catalyst tends to precipitate, and thus, in practical implementation, may deplete the radium from the catalytic cycle. Loss of catalyst from the reaction medium and the catalytic cycle is inadmissible, firstly because it causes a reduction in the production of the process and secondly because it is difficult to recover radium, which is extremely valuable.

It has been observed that the highest propensity to precipitate insoluble rhodium (III) compounds occurs when the level of carbon monoxide is low and / or when the process is carried out in the presence of less than 14-15% by weight of water. On an industrial scale, the former may cause problems in portions of methanol carbonylation plants where carbon monoxide overpressure is low, while the latter means that most methanol carbonylation plants must operate in a constant concentration of 14-15% by weight of water in the carbonylation reactor.

A solution to the problem of precipitation of rhodium (III) compounds is disclosed in EP 55618 and EP161874. The

EP 55618 discloses that the propensity of radium catalysts to precipitate in parts of an alcohol carbonylation plant that are deficient in carbon monoxide (e.g., injection tanks, transfer pipes, and feed loops) can be eliminated if a catalyst stabilizer is present. unit. Preferred stabilizers are: (a) NNN'.N'-tetramethyl orthophenylene diamine and 2,3'-dipyridyls, (b) (R ₁ ) (R ₂ ) PR ₃ -P (R ₄ ) (R ₅ ) Substituted diphosphines of the general formula (c) HOOC-Y _r COOH and (HOOC-Y ₂ 2) (HOOC-Y ₃ ) NY ₁ N (Y ₄ -COOH) (Y 5-COOH) carboxylic acids of dibasic or polybasic form and (d) ) compounds of germanium, antimony, tin or any alkali metal.

EP 1538 341, a related subject, discloses that imidazole or thiol-type stabilizers may be used. The present invention illustrates the use of N-methylimidazole.

EP 161874 discloses that the use of a catalyst stabilizer selected from metal iodides and quaternary ammonium iodides reduces the tendency of the catalyst to precipitate even with less water. Preferred stabilizers are alkali metal and alkaline earth metal iodides, such as lithium iodide. N-methyl picolinium iodide, as quaternary ammonium iodide, is also particularly prominent.

The foregoing description of the prior art thus demonstrates that using one of the many catalyst stabilizers has the potential to reduce the precipitation of radium catalysts as insoluble rhodium (III) compounds. However, in our studies, we have found that there is a problem using quaternary ammonium iodides, such as N-methylimidazolium iodide and N-methyl picolinium iodide, where such iodides tend to form poorly soluble rhodium-containing complexes, leading to loss of rhodium-containing complexes.

The present invention provides a process for the preparation of saturated carboxylic acids containing (n + 1) carbon atoms by reacting carbon monoxide with an alcohol containing n carbon atoms - from 1 to 20 - in the presence of a rhodium catalyst. feeding the ester of the ester with carbon monoxide to a carbonylation reactor and removing the carboxylic acid from the carbonylation reactor by maintaining a liquid reaction medium in the carbonylation reactor which (a) contains 0.1 to 12% by weight of water, and ( (b) a group of quaternary ammonium iodides of the formulas (1), (2), (3a) or (3b):

R is hydrogen or C1-20 alkyl,

R ¹ is hydrogen or C 1-6 alkyl, with the proviso that at least one of R ¹ contains from 2 to 20% by weight of a catalyst stabilizer other than hydrogen.

The invention illustrates the problem outlined above

EN 208 298 Β of selected quatemeric ammonium iodides, which are not prone to formation of poorly soluble rhodium-containing complexes, even under very extreme conditions considered to be rhodium precipitators. The selected quaternary ammonium iodides also have the additional advantage of being particularly effective in preventing precipitation when the water content of the carbonylation reactor is relatively low compared to conventional processes. The stabilizers of the present invention are far superior to the stabilizers disclosed in EP 161874.

In a preferred embodiment of the process outlined above, the rhodium catalyst and the catalyst stabilizer together with the carboxylic acid are removed from the carbonylation reactor. The carboxylic acid, the rhodium catalyst and the catalyst stabilizer are then introduced into a zone where there is a carbon monoxide deficiency relative to the carbonylation reactor and where, for example, the carboxylic acid is separated from the other components. The rhodium catalyst and the catalyst stabilizer are then returned to the carbonylation reactor. In this preferred embodiment, the separation and refining process is characterized in that the rhodium catalyst and the catalyst stabilizer are always present when there is a carbon monoxide deficiency.

The technology is particularly suitable when the water content of the carbonylation reactor is lower than conventionally used, i.e. in the range of 0.1 to 12% by weight, preferably 0.5 to 8% by weight.

Given that the alcohol has n carbon atoms, although it can be essentially any alcohol containing 1 to 20 carbon atoms and at least one hydroxy group, the preferred raw materials are C 1 -C 8 monofunctional aliphatic alcohols. The most preferred raw materials are methanol, ethanol and propanes, of which methanol is of primary importance as the process for converting methanol to acetic acid is an industrially proven technology.

The overall stoichiometry of the procedure is

RZOH + CO-> R ² can be described by the COOH process, wherein R ² is an organic group corresponding to the known names listed in the previous paragraph. From this scheme, the carboxylic acid product obtained from a particular alcohol can be readily determined, for example, in the case of methanol (R ² -methyl) and ethanol (R ² -ethyl), the carboxylic acid products are acetic acid or propionic acid.

Although the methods of the present invention can be operated by batching, continuous operation is preferred in most cases. During continuous operation, the alcohol and / or an alcohol ester and the product carboxylic acid are fed into a carbonylation reactor with carbon monoxide, water sufficient to maintain the concentration in the reactor, a rhodium catalyst, an iodide derivative, and a catalyst stabilizer. Note that the last four components are not fed to the process, but are continuously fed back into the reactor from the product stream, and only the possible loss of material is required. As the components are continuously fed into the carbonylation reactor, the product stream of carboxylic acid, water, rhodium catalyst, iodide derivative and catalyst stabilizer is continuously lost. The net effect of this is that the carbonylation reactor reaches a steady state and maintains a stable liquid reaction medium consisting of a constant amount of water, catalyst stabilizer, iodide derivative, carboxylic and alcohol esters, rhodium catalyst and carboxylic acid. In practice, due to the rapid esterification reaction between the carboxylic acid and the alcohol, the carbonylation reactor contains little free alcohol.

It is advantageous for the process of the invention that the liquid reaction medium contains, in a steady state, the following amounts of each of the components:

Water Wider Range Weight% 0.1-12 advantageous crowd% 0.5-8 Ester of carboxylic acid and alcohol 0.1-10 2-8 Jodidszármazék 5-20 10-16 Catalyst stabilizers 2-20 10-20 Rhodium catalyst (PPm) 100-1800 300-1200

Specifically, the preferred composition range for carbonylation of methanol to acetic acid is 0.5-8% by weight of water,

2-8 wt% methyl acetate, 10-16 wt% methyl iodide, 10-20 wt% catalyst stabilizer, and 300-1200 ppm rhodium catalyst with additional acetic acid and trace amounts of impurities.

The temperature in the carbonylation reactor is preferably maintained at 100-200 ° C and the carbon monoxide pressure maintained at 10-200 bar. The preferred temperature is in the range of 140 'C to 200' C and the preferred pressure is in the range of 10 to 100 bar. Under these conditions, the carbonylation reaction proceeds rapidly.

With respect to the above three groups of catalyst stabilizers, it is preferred that at least one of the R groups is identical to the organic group R ^{2 in} alcohol, iodide derivative and carboxylic acid. On the other hand, R ¹ is preferably hydrogen or C 1-6 alkyl, with the proviso above. Preferred catalyst for each of the groups of formula (1) and (2) stabilizer may be mentioned as examples thereof, are those wherein the groups R ¹ is hydrogen, methyl, ethyl, propyl, isopropyl, butyl, sec-butyl and tert butyl.

A particularly preferred group of catalyst stabilizers are the iodide salts of the cation (4), wherein:

(i) R ¹ and R ² are methyl, (ii) R ⁵ is hydrogen, (iii) R ³ is C 1 -C 6 alkyl or hydrogen, and (iv) R ⁴ is C 1 -C 6 alkyl.

HU 208 298 Β

The most preferred representatives of this group are those in which:

(1) R ³ is ethyl,

R ^1, R ² and R ⁴ is methyl, and

R ⁵ is hydrogen; or (2) R ³ and R ⁵ are hydrogen, and

R ^1, R ² and R ⁴ is methyl.

Another particularly preferred group of catalyst stabilizers are the iodide salts of the cation (5):

R ⁶ is either hydrogen or methyl,

R ⁷ is C 1 -C 4 alkyl and R ¹ is methyl.

Preferred examples are compounds in which:

(1) R ⁶ is hydrogen, and

R ⁷ is ethyl; or (2) R ⁶ is hydrogen, and

R ⁷ is tert-butyl;

(3) R ⁶ and R ⁷ is methyl.

Catalyst stabilizers can be prepared by quaternizing the corresponding amines of formula I or II, R and R ¹ as defined above, or 2- or 4-hydroxypyridine with an organic iodide of formula R 1. The R group in the organic iodide may be the same or different from the R group in the corresponding amine. Of course, it is preferable to quaternize the amines corresponding to the preferred catalyst stabilizers as defined above. In the case where the R groups are the same as the R ² groups, it is possible to prepare the catalyst stabilizer in situ by feeding the appropriate amine when the process is started or after the feed or feed streams are fed back. In our experience, the quaternization of such amines is rapid under the operating conditions of the process. After a single quaternization, the catalyst stabilizer can be recycled in the usual manner.

The invention is illustrated by the following examples:

Experimental procedure:

A) Preparation of the catalyst stabilizer.

25 mmol of said amine are dissolved in acetic acid together with 25 mmol of methyl iodide. The mixture was heated at 180 ° C in a pressure vessel for 12 hours under nitrogen.

B. Test procedure.

Solubility of quaternary ammonium iodide salts of rhodium catalysts.

To the cooled reaction mixture was added additional methyl iodide and a rhodium stock solution in aqueous acetic acid to give a solution of rhodium 550 ppm water 2% by weight methyl iodide 2% by weight acetic acid.

The above test solution was stirred at 25 ° C for 1 hour and the resulting solution was analyzed for water content, iodide ion and soluble rhodium. The results are summarized in the following table:

additive Water (weight) iodide (lake- in%) Final Rh (ppm) Generated Rh (%) N-Methyl-imide azole 2.19 13.93 190.6 57.3 3-picoline 2.06 12.47 18.5 96.4 imidazole 2.36 18.92 149.4 66.5 2-Ethyl-imidazole 2.49 19.39 79.1 82.3 2-Ethyl-4-methyl- imidazole 2.19 13.37 515.4 5.0 benzimidazole 2.81 13.57 59.8 89.7 1,2-Dimethyl- imidazole 2.44 11.13 79.0 85.6 4-methyl-imidazole 2.07 12.84 519.8 5.1 pyridine 1.98 13.23 38.4 92.9 2,6-lutidine 2.19 14.14 41.8 92.3 3,5-lutidine 2.23 10.39 260.7 52.1 3,4-lutidine 2.27 11.98 569.8 <0.1 4-tert-Butyl-piri- dyne 1.96 10.56 527.4 <0.1 2-Hydroxy-pyridine 1.92 7.87 494.9 9.4 3-Hydroxy-pyridine 2.00 13.05 395.7 27.3 4-Hydroxy-pyridine 2.49 10.50 500.3 8.1

The results show that quaternized (R-methyl) 4-methylimidazole, 2-ethyl-4-methyl has less rhodium (III) precipitation than the previously described materials (e.g. N-methylimidazole, 3-picoline or imidazole). -imidazole [(1); R ^{1 is} methyl and ethyl], 3,4-lutidine [(2); R ¹ - methyl] 4-tert-butylpyridine for 2-hydroxypyridine and 4-hydroxypyridine.

C) Comparison of quaternary ammonium iodide stabilizers with lithium iodide.

The following experiments demonstrate that the quaternary ammonium iodide stabilizers of the present invention are not only more soluble than those previously described (e.g., imidazole), but also are more capable of inhibiting the precipitation of higher rhodium than alkali metal iodides.

(i) Preparation of a catalyst stock solution.

A Fischer Porter vessel was charged with 1.57 g of rhodium triiodide, 7.4 g of water, 0.92 g of hydrogen iodide and 34.0 g of acetic acid. It is aspirated and filled with carbon monoxide to a pressure of 8 bar, then sealed and heated at 130 ° C for 4 hours. Meanwhile, Rhl ₃ dissolves to give a clear orange solution.

(ii) Test Procedure. Stabilization of rhodium catalyst with iodides.

In Example 1, 2.0 g of catalyst stock solution and 0.50 g of methyl iodide were added with 25 mmol of lithium iodide.

19.15 g of acetic acid and stir for 5 minutes. After sampling, the mixture was poured into a Fischer Porter vessel under nitrogen at 1 bar and heated at 180 ° C for 22 hours. Even after cooling4

HU samples were taken, both samples were centrifuged and subsequently analyzed for radium, water and iodide ion.

2-4. In Examples 1 to 4, the amines are quaternized as described in the solubility experiments, and then catalyst stock and methyl iodide are added as described in Example 1.

The results are shown in the following table:

Example additive Water ¹ * (% by weight) Iodides ²⁾ (to mass) Initial Rh (ppm) Final rh (Ppm) Generated rh (%) 1 Lithium Jo did 2.20 10.25 517.2 183.8 64.5 2 3,4-lutidine 2.09 11.92 500.6 281.3 43.8 3 4-tert-Butyl pyrido 1.96 10.08 521.3 243.9 53.2 4 4-Methyl- imidazole 1.76 11.43 522.3 243.5 53.4

The mean initial and final water concentrations are ² > Final iodide concentrations.

The reduced catalyst removal achieved with the selected quaternary ammonium iodides shows that they are more potent stabilizers for rhodium catalysts under the test conditions.

Claims (8)

PATENT CLAIMS A process for the preparation of (n + 1) saturated carboxylic acids having carbon monoxide and an alcohol containing n carbon atoms, wherein n 1-20 is a rhodium catalyst, an alcohol corresponding iodide derivative and quaternary ammonium iodide as a catalyst stabilizer for alcohol and / or feeding the alcohol and the ester of the carboxylic acid together with carbon monoxide into the carbonylation reactor and recovering the carboxylic acid from the carbonylation reactor, characterized in that the reaction in the carbonylation reactor is carried out in a liquid reaction medium containing (a) 0.1-12% water; (b) a group of quaternary ammonium iodides of the formulas (1), (2), (3a) or (3b) - in the formulas 298 B 2 R is independently hydrogen or C 1-20 alkyl, R ¹ is independently hydrogen or C 1-6 alkyl, with the proviso that at least one of R ¹ contains from 2 to 20% by weight of a catalyst stabilizer other than hydrogen. 2. A process according to claim 1, wherein the catalyst stabilizer is one wherein at least one of the R groups is identical to the organic group in the n-carbon alcohol. 3. A process according to claim 1, wherein the catalyst stabilizer is selected from the group consisting of a cation of formula (4) wherein R ¹ and R ² are methyl; R ³ is C 1-6 alkyl or hydrogen; R ⁴ is C 1-6 alkyl; and ^R5 is hydrogen iodide anion salt formed. 4. A process according to claim 3 wherein R ^{3 is} ethyl and R ^{4 is} methyl or R ^{3 is} hydrogen and R ^{4 is} methyl. 5. A process according to claim 1, wherein the catalyst stabilizer is selected from the group consisting of a cation of formula (5) wherein R ⁶ is either hydrogen or methyl; R ⁷ is C 1-4 alkyl; and R ¹ is an anion salt of methyl iodide. 6. The method of claim 5, characterized in that it is used as a catalyst stabilizer, wherein R ⁶ is hydrogen and ^R7 is ethyl, or R ⁶ is hydrogen and ^R7 is tert-butyl, R ⁶ and R represent ⁷ is methyl. The process according to claim 1, wherein the concentration of water in the carbonylation reactor is in the range of 0.5 to 8% by weight. 8. A process according to claim 1, wherein the catalyst stabilizer is prepared in situ by quaternizing the corresponding amine with the corresponding alcohol iodide in the carbonylation reactor.