GB2146637A - Producing carboxylic acids by carbonylation - Google Patents

Abstract

Carboxylic acids or esters are produced by liquid phase carbonylation reaction of an alcohol or a derivative thereof with carbon monoxide carried out in the presence of a catalyst system containing a rhodium component and an alkyl iodide or bromide, and water, an iodide salt being added to the rhodium/alkyl halide catalyst system so as to maintain the iodine ion concentration in the carbonylation reaction solution at 0.3 mol/ l or higher.

Description

SPECIFICATION Process for producing carboxylic acids The present invention relates to a process for producing carboxylic acids, for example, acetic acid.

Carboxylic acids are useful chemicals having a high industrial value.

Acetic acid has been produced on a commercial basis by, for example, carbonylation of methanol. A process for producing carboxylic acids and esters thereof by reacting an alcohol or its derivative with carbon monoxide in the presence of a rhodium compound and a halogen compound has been disclosed, for example, in the specification of Japanese Patent Publication No.3334/1972. Usually, the alcohol is charged as such into the reaction system as the starting material. A reaction scheme for the reaction is shown as if the alcohol is reacted with carbon monoxide to form a carboxylic acid or its ester. However, from the viewpoint of the reaction mechanism, it has been believed that the carboxylation reaction proceeds via an alkyl halide (see Ind. Eng. Chem. Prod. Res. Dev., 15(1), 46(1976)).It has also been known that the carboxylic acids or esters thereof can be obtained not only from the alcohols but also from alcohol derivatives capable of forming alkyl halides in the reaction system, such as esters or ethers.

According to the present invention there is provided a process for producing carboxylic acids or esters by liquid phase carbonylation reaction of an alcohol or a derivative thereof with carbon monoxide carried out in the presence of a catalyst system containing a rhodium component and an alkyl halide which is an alkyl iodide or bromide, and water, an iodide salt being added to the rhodium/alkyl halide catalyst system so as to maintain the iodide ion concentration in the carbonylation reaction solution at 0.3 molls or higher.

In the process of the present invention for producing carboxylic acids and esters thereof, the starting materials to be charged in the reaction system are not limited to the alcohols but they include also alcohol derivatives such as alkyl esters, alkyl ethers and alkyl halides. Non-limitative examples of suitable reactants are alcohols such as methanol, ethanol, propanol, butanol, 1,3-propanediol and 1,4-butanediol; esters such as methyl acetate, methyl propionate and ethyl propionate; halides such as methyl iodide, methyl bromide, ethyl iodide and ethyl bromide; ethers such as dimethyl ether, diethyl ether and methyl ethyl ether; and other alcohols and derivatives thereof as disclosed in the specification of Japanese Patent Publication No.

3334/1972.

A catalytic amount of a rhodium compound is used in the carbonylation reaction. It is believed that the rhodium compound is present in the reaction system in the form of a halogenorhodium carbonyl complex, i.e. rhodium coordinated with a halogen and carbon monoxide, having a catalytic effect in the carbonylation reaction [see, for example, Adv. Organometall. Chem., 17,255(1979]. It has also been found that rhodium compounds other than the halogenorhodium carbonyl complexes are also converted into the halogenorhodium carbonyl complexes under the reaction conditions [see, for example, Adv. Organometall. Chem., 17, 255(1979)]. The rhodium components herein are not limited to halogenorhodium carbonyls but other rhodium compounds are included therein.As non-limitative examples of the rhodium components to be used in the present invention, there may be mentioned RhX3 (wherein X is C, Br or 1), RhX3.3H2O (wherein X is ce or Br), Rh2(CO)16, Rh(CO)X [(C6H5)3M]2 (wherein Xis C, Br or I and M is P, As or Sb), Rh(CO)2X[(C6H5)3M] (wherein Xis C, Br or I and M is P, As or Sb), HRh(Co) [(C6H5)3P]3, [Rh(C2H4)2C]2 and K4Rh2X2(SnX3)4 (wherein Xis C, Br or I) and those disclosed in the specification of Japanese Patent Publication No.3334/1972.

It has been known that, in the conventional carbonylation reactions, a water gas shift reaction (hereinafter referred to simply as shift reaction) occurs as a side reaction in addition to the main carbonylation reaction [see, for example, Adv. organometall. chem., 17,255, (1979)]. In the shift reaction, carbon monoxide is reacted with water to form carbon dioxide and hydrogen as shown in equation (1):

It has also been known that the reactant alcohol is hydrogenated by the hydrogen formed in the shift reaction as shown in equation (2): [see for example, J. Organometall. chem., 236, C-23 (1982)]:

Wherein R represents an alkyl group.

Thus, the conventional processes for the carbonylation reaction have a serious defect in that the carbon monoxide is lost due to the shift reaction and that hydrogen thus formed leads to a loss of another starting material, i.e. the alcohol.

Further, by-production of carbon dioxide and hydrogen gas, resulting from the shift reaction, increases the gas pressure in the carbonylation and thereafter it is required to purge a part of the gas and thereby depress the increase of the gas pressure.

After intensive investigations made for the purpose of overcoming those defects of the conventional processes for the carbonylation reaction, it has now been found that when an extremely large amount of an iodide salt is incorporated in the reaction solution in addition to the alkyl halide, the side reactions can be controlled remarkably, and, surprisingly, the carbonylation reaction rate is improved.

By means of the present invention, the above-mentioned defects of the conventional carbonylation processes can be largely overcome and the carbonylation rate can be increased to improve the productivity.

It has been known that the carbonylation reaction rate is proportional primarily to the rhodium concentration in the reaction solution [see, for example, Ind. Eng. Chem., Prod. Res. Dev., 15(1),46(1976)]. By means of the present invention, the amount of the expensive rhodium component can be reduced.

The carbonylation reaction in the conventional processes, too, is effected in the presence of a halide such as an iodide. However, the major part of the halide is present in the form of an alkyl halide which is an actual reactant to be carbonylated. Namely, the major part of the halide comprises a nonionic compound such as methyl iodide. Ionic halogen compounds comprise mainly hydrogen halide formed in a very small amount by the hydrolysis of the alkyl halide in the reaction system in general.

In some known disclosures related to the above reaction, halogen compounds have been indicated as being used in the form of various precursors such as metal halides. However, as will be shown in Examples 27 and 28 given below, when sodium iodide or potassium iodide is used alone as the halogen source, the carbonylation reaction does not proceed in a heating time equal to a standard one employed when methyl iodide is used (i.e. in 70 min after initiation of the heating). It is also described in J. Mol. Catal. 16,299(1982) that an iodide source (such as an alkali metal iodide) incapable of forming a quite large amount of methyl iodide in the reaction system does not function as an accelerator for the reaction.

A process has been known wherein a stabilizer is used in an amount necessary for maintaining the rhodium component in its soluble form (see Japanese Patent Laid-Open No. 134,436/1982). Among various stabilizers listed in that specification are alkali metal compounds and, in fact, 0.2 molls of potassium iodide is added to a model liquid in the separation step in Example 19 given in said specification. The process described in said Japanese Patent Laid-Open No. 134,436/1982 is effective in preventing a reduction in amounts of dissolved rhodium under an insufficient CO condition by the addition of an alkali metal salt.

However, that Japanese specification is silent on the influence of potassium iodide on the carbonylation reaction effected under an elevated CO pressure.

The known processes wherein potassium iodide was used did not show that the carbonylation reaction could be accelerated by adding an iodide salt to a rhodium/alkyl iodide catalyst system.

According to the present invention, an iodide salt is added to a combination of rhodium and an alkyl halide which are indispensable components of the fundamental carbonylation reaction catalyst system to realize a particularly high iodine ion concentration in the reaction solution to thereby accelerate the main reaction of forming a carboxylic acid from an alcohol while side reactions such as shift reactions are inhibited. Alcohols or derivatives thereof, rhodium compounds and alkyl halides which have been used in the known processes may also be used in the process of the present invention.

The carboxylic acid which is the product of the present invention is obtained frequently in the form of its ester formed by a reaction thereof with the starting alcohol. Even though water is not charged in the reaction system, water formed by the esterification reaction is contained in the system. The term "the presence of water" in the production of carboxylic acid involves also such a case. However, the carbonylation of an ester or ether in the absence of water to form an acid anhydride is ciearly distinguished from the above-mentioned reaction.

The iodide salts to be used in the present invention include the following compounds (a) and (b): (a) metal iodides of formulae (3) and (4): M1In (3) M11n+2 wherein M1 represents a metal having a valency of n,and (b) onium-type iodides containing Group Va elements of the Periodic Table represented by formulae (5) and (6): TAKE IN HERE TAKE IN HERE

Wherein M2 represents a Group Va element of the Periodic Table and R1 to R4 independently each represent a hydrogen atom or an alkyl or aryl group.

Non-limitative examples thereof include Lil.

Non-limitative examples thereof include Lil, Nal, KI, Rbl, Csl, Bel2, Mg 12, Cal2, Kl3, Csl3, NH413, Gal3, Curl3, Mini2, Lil.3H2O, Mg12.8H2O, NH41, N(CH3)41, N(C6H5)41, NH3CH31, PH41, P(CH3)4I, P(C6H5)41, P(CeH5)3CH3l, AsH41, As(CH3)41, As(C6H5)41 and As(C6H5)3CH3I.

Hydrogen iodide itself contains ionic iodine and is present in the reaction liquid in the conventional techniques. However, it reacts with an alkanol derivative to form an alkyl iodide to form an equilibrium mixture and, therefore, even if hydrogen iodide alone is added in a very large amount, the iodine ion concentration in the reaction liquid cannot be increased correspondingly.

Aluminium iodide is unsuitable for use in this process, since it reacts with the carboxylic acid in the reaction solution to form aluminum carboxylic and hydrogen iodide and a high concentration of the iodide ion in the reaction mixture cannot be maintained.

Further, salts of transition metal ions of iron group (Fe, Co and Ni) are not preferred as well, since they accelerate the shift reaction.

The iodide salts may be charged into the reaction system in the form of precursors from which the iodide salts can be formed under the reaction conditions. Precursors containing the iodine component of the iodine salt include hydrogen iodide and organic iodides such as alkyl odides which can be converted into hydrogen iodide in the reaction system.Precursors containing cationic component of the iodide salt include the following compounds (c) to (g): (c) metal hydroxides of formula (7): M3(OH)n (7) wherein M3 represents a metal having a valency of n, (d) carboxylic acid salts of formula (8):

wherein M4 represents a metal having a valency of n and R represents a hydrogen atom or an alkyl or aryl group, (e) metals in their elemental form and metal oxides, (f) trivalent compounds containing Group Va elements of the Periodic Table of formula (9)::

wherein M5 represents a Group Va element of the Periodic Table and R1 to R3 independently each represent a hydrogen atom or an alkyl or aryl group, and (g) other metal compounds As described above with reference to the selection of the metal iodides, a metal to be used as the cationic component should be selected from those excluding aluminum and desirably excluding iron group transition metals.

Precursors containing cationic component of the iodide salt include, as non-limitative examples, the following compounds: LiOH, KOH, NaOH, Rb(OH), Cs(OH), Be(OH)2, Mg(OH)2, LiOAc, KOAc, Be(OAc)2, Li, K, Na, Li2O, K2O, BeO, MgO, NH3, NMe3, N(C6H5)3, PH3, PMe3, P(C6H)3, AsMe3 and Sb(CsH)3.

According to the present invention, at least 0.3 molls of the iodine ion is present in the form of a stable iodide salt in the reaction system due to the presence of the above-mentioned cationic component.

According to the present invention, the carbonylation reaction of the reactant with carbon monoxide is effected in the presence of the catalyst system comprising the rhodium component, alkyl halide and iodide salt at a suitable temperature under a suitable pressure which will be referred to below to obtain the carboxylic acid or its ester.

The concentration of the rhodium component in the reaction liquid is 104to 10-1 mol/t, preferably 10-3 to 5 x 10-2 mol/.

The concentration of the alkyl halide in the reaction liquid is in the range of 10-2 to 10 molls, preferably 10-1 to 2 mol/e.

The amount of the iodide salt to be added is selected at will so as to attain an iodine ion concentration in the reaction liquid of at least 0.3 molls and the maximum amount is that for forming a saturated solution.

Preferably, the iodide salt is used within an amount range to attain an iodine ion concentration of from 0.5 mol/t to the solubility limit.

Water is an indispensable component of the reaction system to form a carboxylic acid from an acryl halide formed by the carbonylation of the alkyl halide in the reaction system. A hydrogen halide formed in this stem is reacted with the alcohol to form the alkyl halide again and regenerate the water.

It has been known that the presence of water accelerates the formation of carboxylic acid also in the conventional processes wherein no iodide salt is used (see line 13, column 10 and line 6, column 15 in the specification of Japanese Patent Publication No.3334/1972). However, as the water concentration in the reaction liquid is increased, not only the carbonylation reaction but also side reactions such as the formation of CO2 and CH4 are accelerated remarkably (see Table 2).

The above-mentioned facts relating to the necessity of water and influences thereof apply also to the present invention. The presence of water is effective also for keeping a desired concentration of a water-soluble iodide such as an alkali metal iodide in the reaction system. The amount of water necessitated for this purpose is generally at least 1 molff in methyl acetate, though it varies depending on the composition. The effect of increasing the carbonylation rate can be obtained even when the water concentration is less than 1 molls (see Example 21). However, in this case, a solid is contained in the reaction mixture after cooling.

In the accompanying drawings, the single Figure shows the relationships between the water concentration ([H2O]f) and the carbonylation reaction rate (cO molls .h) in the reaction of the present invention and comparative Examples.

The effect of the added iodide salt in increasing the carbonylation reaction rate is recognized over a wide range of water concentration as shown in the Figure. As shown by an arrow A, the addition of 0.6 molls of the iodide salt can reduce the water concentration to about 5 molls while the reaction rate almost equal to that realized by using no iodide or realized with a water concentration of 10 molls (see Tables 2 and 8 given below) is maintained. The same inclination can be observed when the methanol concentration is altered (see an arrow B and Table 10 given below).

In the conventional processes for producing carboxylic acids by the carbonylation, the water concentration in the reaction liquid is generally up to about 20 mol, for example, 8 to 11 mol/t (15 to 20 wt.%; line 14, column 11 in the specification of Japanese Patent Publication No. 33428/1980). However, when the reaction is carried out in the presence of a smaller amount of water according to the present invention as described above, advantages such as an increase in the reaction selectivity (control of the formation of by-products such as CO2, or CH4 by the shift reaction) and reduction of energy consumption required for the separation of water in the purification process can be obtained.

When a water concentration equal to that employed in the conventional processes is employed in the present invention, the carbonylation reaction rate is higher than that realized in the conventional processes and the shift reaction can be controlled.

The water concentration employed in the present invention is generally at least 1 moll{. The minimum water concentration with which no precipitate is formed varies depending on the composition of the reaction liquid and variety and amount of the iodide. When the methanol (in fact, present in the form of methyl acetate) concentration is high as in Example 21, the water concentration is relatively high. When the methanol concentration is low, a sufficiently homogeneous solution can be obtained with a water concentration of 1 molt. The upper limit of the water concentration is generally about 20 molls which is almost equal to that of the conventional processes.In view of both acceleration of the carbonylation reaction and control of the shift reaction, a particularly preferred water concentration is in the range of 3 to 10 mobile.

The reaction temperature is usually in the range of 50 to 300 C, preferably 100 to 2400C.

The reaction pressure is such that the partial pressure of carbon monoxide is usually 0.05 to 1000 atm, preferably 0.3 to 300 atm and particularly 0.5 to 100 atm.

The alcohols or derivatives thereof, may be the same as those used in known processes, for example, as disclosed in the specification of Japanese Patent Publication No. 3334/1972. The alcohols include, for example, primary, secondary and tertiary aliphatic alochols having up to 20 carbon atoms, such as methanol, ethanol, propanol, isopropyl alcohol, isobutanol and t-butyl- alcohol; aromatic and alicyclic hydroxyl compounds having 6 to 20 carbon atoms; and polyhydric alcohols having 2 to 20 carbon atoms, such as 1,3-propylene glycol and 1,4-butanediol. Esters, ethers and halides of these alcohols may also be used as the starting alcohol derivatives in the present invention.

The alcohol concentration in the reaction solution may vary over a wide range according to the present invention. The alcohol in the reaction liquid may also be in the form of a carboxylic acid ester or alkyl halide formed by the reaction with the carboxylic acid or hydrogen halide and water in the reaction system.

Therefore, the alcohol concentration in the reaction solution may refer to the total of the three compounds, i.e. the alcohol itself and two derivatives thereof. In the above-mentioned specification of Japanese Patent Laid-Open No. 134436/1982, the methanol concentration refers to the total concentration of methanol, methyl iodide and methyl acetate corresponding to "unstable methyl group". The total methanol concentration disclosed therein is 1.44 molls (suggesting that a major part thereof is methyl iodide, since the total iodide concentration is 1.40 moll).

Such an alcohol (including derivatives) concentration of around 1 molls is most commonly employed in the continuous production of the carboxylic acids. However, in the following Examples, a higher alcohol concentration is employed so as to facilitate the determination of changes in the carbonylation and side reaction rates by effecting experimental batch reactions and analyzing the reaction liquid and gas. It is to be noted, however, that no essential difference lies between the results of the following Examples and those of the continuous reaction effected with a lower alcohol concentration of around 1 mol/4 (it has been known that the carbonylation reaction is a zero-order reaction with respect to the alcohol concentration).

The present invention will now be described with reference to but is in no manner limited to the following Samples; Example 1 {Comparative Example) Acetic acid was produced by carbonylating methanol in the presence of a fundamental catalyst comprising only a rhodium component and methyl added iodide salt but free of any iodide salt. The experiment was effected as follows: Compounds shown in the following Table 1(107 me in total) were charged in a 400-mB Hastelloy B autoclave provided with an agitator. Carbon monoxide was introduced therein to elevate the pressure to 40 kg/cm2G.

TABLE 1 Compound Amount RhCe3.3H2O 0.24 mmol H2O 1.02mol CH3OH 1.24 CH3l 0.080 CH3CO2H 0.59 The mixture was heated under stirring. About 15 min after the initiation of the heating, the temperature of the reaction solution reached 185"C. Then, the temperature was maintained at 185"C. A gas absorption rate in a period of 45 to 75 min after the initiation of the heating was measured on the basis of the liquid temperature. The carbonylation reaction rate was determined from the gas absorption rate. 70 min after the initiation of the heating, the autoclave was cooled and the quantities of carbon dioxide and methane in the autoclave were determined according to gas chromatography.After completion of the reaction, the water concentration in the solution was 14.6 molls and the iodide ion concentration (hereinafter referred to as [IE'lf was 0.033 moll. The rates of the reaction carried out in the absence of the iodine salt were as follows: carbonylation reaction rate (hereinafter referred to as γCO): 1.96 mol/t.h co2-formation reaction rate (hereinafter referred to as wyco): 18.9 mmol/f.h CH4-formation reaction rate (hereinafter referred to as zCH4): 9.39 mmol/f.h Example 2 (Referential example showing influences of water concentration) The same procedure as in Example 1 was repeated except that a part of methanol was replaced with methyl acetate or the amount of water charged was altered to alter the water concentration in the reaction system. The same amounts of the rhodium compound and methyl iodide as in Example 1 were used but the amount of acetic acid charged was controlled to maintain the total amount of the solution at 107 me.The manner of the reaction was also the same as in Example 1 except that the gas absorption rate was measured on the basis of gas temperature, and the autoclave was air-cooled to 100"C 70 min after the initiation of the heating and then cooled with ice/water.

The results are shown in Table 2. It is understood that γCO was increased in proportion to the water concentration in the reaction system and that in a region of a high water concentration, the amounts of CO2 and CH4 formed by the shift reaction were increased remarkably. When no iodide salt was used, the iodine ion concentration which was increased as the water concentration was increased was generally up to 0.1 mol/t and even when the water concentration was extremely high, the concentration was up to 0.2 molt. A relationship between the water concentration and the carbonylation reaction rate obtained from the data in Table 2 is shown by curve | in Figure 1.

TABLE 2 Water con.

{immediately after completion of reaction) γCO γCO2 γCH4 [I-]f mol/l mol/l.h mmol/l.h mmol/l.h mol/l 0.7 0 0.75 0 0.003 5.9 0.82 3.65 1.72 0.008 7.3 1.15 6.02 3.43 0.011 11.0 1.63 13.83 7.27 0.027 14.6 2.03 21.29 10.28 0.059 22.8 2.61 36.99 17.86 0.175 When the same procedure as in Example 1 was repeated except that the water concentration was varied, substantially similar results as in Example 1 were obtained as shown in Table 3. When the reaction mixture was cooled rapidly, the amount of the shift reaction products was reduced slightly but it was still largerthan that of the first order proportion of water concentration.

The rate of [IO]f in Table 2 are slightly higher than those shown in Table 3. It is probably because an HI-forming reaction occurred in the course of the slow cooling. Therefore, to determine the iodine ion concentration in the reaction liquid exactly, it is recommended to rapidly cool a small amount of the sample.

TABLE 3 Water conc.

(immediately after completion of the reaction) wCO ltC 2 CH4 [I-]f mol/l mol/l.h mmol/l.h mmol/l.h mol/l 10.96 1.67 10.28 6.46 0.014 14.60 1.96 18.38 9.39 0.033 18.06 2.10 23.31 12.12 0.046 20.66 2.63 25.46 13.58 0.066 Examples 3 to 5 The same procedure as in Example 1 was repeated except that lithium iodide, Lil-3H2O, in an amount as shown in Table 4 was used. The results thus obtained was subjected to the linear correction on the basis of the data shown in Table 3 so as to realize the same water concentration as in Example 1, since the water content of the reaction system was increased due to the water contained in Lil-3H2O. The results obtained by this operation are shown in Table 4.

TABLE 4 Amount of Lil added yCO wCO2 CH4 [I-]f Ex.

mol/l mol/l-h mmol/l.h mmol/l.h mol/l 3 0.318 2.15 7.38 1.85 0.324 4 0.620 2.33 6.43 1.33 0.622 5 0.847 2.49 6.15 1.31 0.833 Unlike the case of using no lithium iodide (Example 1), the carbonylation rate was increased in proportion to the iodide salt concentration (increasing rate: 0.45 mol/l.h.mol-iodide salt; the value not corrected according to water concentration: 0.79). This fact indicates that the side reactions are controlled remarkably (to less than 1/2 of of γCO2 and 1/5 of γCH4) by the addition of even a small amount of lithium iodide.

Examples 6 to 9 The same procedure as in Example 1 was repeated except that Nal was added to the liquid starting material. The results are shown in Table 5.

TABLE 5 Amount of Nal added γCO γCO2 γCH4 [I-]f Ex.

mol/l mol/l.h mmol/l.h mmol/l.h mol/l 6 0.310 2.10 7.19 1.83 0.308 7 0.656 2.27 7.45 1.66 0.796 8 1.251 2.50 6.13 1.07 1.492 9 2.444 3.06 5.96 1.96 2.292 The addition of sodium iodide accelerated the carbonylation reaction proportionally (the increasing rate: 0.42 mol/l.h.mol-iodide/l). As in the case of using Lil, the side reactions were controlled by using small amounts of sodium iodide.

When no methyl iodide was added, no carboxylic acid could be obtained even when adding Nal (see Example 27).

Examples 10 to 13 The same procedure as in Example 1 was repeated except that potassium iodide was added to the liquid starting material. The results are shown in Table 6 (a symbol * means that [I-]f could not be determined).

TABLE 6 Amount of Kl added γCO γCO2 γCH4 [I-]f Ex.

Mol/l mol/l.h mmol/l.h mmol/l.h mol/l 10 0.325 2.10 9.35 2.45 0.326 11 0.612 2.26 7.43 1.94 0.601 12 1.245 2.38 6.51 1.46 * 13 2.512 2.68 6.77 3.06 * It is understood from this table that the addition of potassium iodide accelerates the carbonylation reaction proportionally (increasing rate: 0.27) and controls the side reactions by using only small amounts of potassium iodide.

Examples 14 to 17 The same procedure as in Example 1 was repeated except that NH41 was added to the liquid starting material. The results are shown in Table 7.

TABLE 7 Amount of NH4I added γCO γCO2 γCH4 [I-]f Ex.

mol/l mollt-h mmollt-h mmoll4-h moll 14 0.329 2.13 9.53 2.61 0.335 15 0.645 2.35 8.06 2.09 * 16 1.243 2.53 8.23 1.97 1.199 17 2.492 3.21 12.47 3.75 2.300 The addition of ammonium iodide accelerated the carbonylation reaction (increasing rate: 0.50). The side reactions were controlled by using only small amounts of ammonium iodide (when the amount of ammonium iodide was excessive, the γCO2 and γCH4 were increased slightly).

Example 18 The same procedure as in Example 1 was repeated except that 0.321 mol/t of methyltriphenylphosphonium iodide [CH3(C6H5)3PI] was used. γCO was 2.11 mol/f-h and the side reaction rates were: Yco2 of 8.54 mmol/l.h and γCH4 of 1.60 mmol/l.h Example 19 The same procedure as in Example 1 was repeated except that 0.612 mol/l of MgI2 was used. γCO was 2.17 mol/l.h, γCO2 was 7.77 mol/l.h, γCH4 was 1.89 mmol/l.h and [I-]f was 0.613 mol/l.

Example 20 The same procedure as in Example 1 was repeated except that 0.610 mol/l of zinc iodide was added to the liquid starting material. was 2.10 mol/l.h and [I-]f was 0.660 molls.

Examples 21 to 26 The same procedure as in Example 2 was repeated except that sodium iodide was added to the liquid starting material to obtain the results shown in Table 8. A relationship between the water concentration and the carbonylation reaction rate obtained from the data shown in Table 8 is shown by curve Il in Figure 1.

TABLE 8 Amount of Water Conc NaI added (after completion [I-]f γCO γ1 γCO2 γ2 γCH4 γ3 Ex. of the reaction mol/l mol/l mol/l mol/l.h % mmol/l.h % mmol/l.h % 21 0.600 0.7 0.581 0.63 0.81 108 0 22 0.645 5.9 0.641 1.49 182 2.01 56 0 0 23 0.627 7.2 0.613 1.63 142 2.74 46 0.06 1.7 24 0.646 10.9 0.640 1.90 117 5.29 39 0.48 6.6 25 0.653 13.9 0.654 2.25 111 10.57 50 1.86 18.1 26 0.704 22.9 0.780 3.07 118 21.67 59 7.01 39 γ1 is a percentage of γCO in these Examples to γCO (expressed as 100) obtained at the equal water concentration shown in Table 2.Though the reaction hardly occured in the absence of the iodide salt when the water concentration was 0.7 mol/l, a quite high-percentage was obtained in this example. The effect of the addition of Nal was particularly excellent when the water concentration was low. 2 and 3 were values concerning zcO2 and γCH4, respectively, obtained in the same manner as above in comparison with those shown in Table 2. Thus, the shift reaction-controlling effect was observed. This effect was particularly remarkable when the water concentration was low.

Examples 27 and 28 (Comparative Examples) The same procedure as in Example 1 was repeated except that methyl iodide was replaced with the following iodide to obtain the results shown in Table 9.

TABLE 9 Ex. lodide Amount γCO zCO eCH4 salt mmol mol/l.h mmol/l.h mmol/l 27 Nal 69.8 0 6.46 0 28 KI 66.1 0 5.30 0 Unlike the results of Example 1, the carbonylation reaction did not proceed at all when sodium iodide or potassium iodide was used alone as the halogen source.

Examples 29 to 31 The same procedure as in Examples 21 to 26 was repeated except that the total amount of methanol and methyl acetate charged was reduced to 0.31 mol and Nal in an amount shown in Table 10 was used. In this procedure, 0.24 mmol of RhCl3.3H2O and 0.080 mol of methyl iodide were used and the total amount of acetic acid and water was controlled to 107 ml. . The heating time was controlled so that 0.6 to 0.8 molls of unreacted starting material remained (51 to 60 min.) The results are shown in Table 10.

TABLE 10 Amount of Water Conc.

Nal added (after completion [13]f rCO Ex. ofthe reaction) molls molls molls moll4-h 29 1.24 4.0 1.25 2.25 128 30 1.24 8.5 1.28 2.60 115 31 1.38 15.7 1.43 3.07 132 (Note) 1 is a percentage of the above obtained wcO based on the wcO obtained at the same water concentration but in the absence of Nal.

A relationship between the water concentration and the carbonylation reaction rate obtained from the data shown in Table 10 is shown by curve IV in Figure 1. Curve Ill shows the results obtained by carrying out the reaction with a low methanol concentration in the absence of Nal in the same manner as in Examples 29 to 31.

Claims (21)

1. A process for producing carboxylic acids or esters by liquid phase carbonylation reaction of an alcohol or a derivative thereof with carbon monoxide carried out in the presence of a catalyst system containing a rhodium component and an alkyl halide which is an alkyl iodide or bromide, and water, an iodide salt being added to the rhodium/alkyl halide catalyst system so as to maintain the iodine ion concentration in the carbonylation reaction solution at 0.3 mol/t or higher.

2. A process as claimed in claim 1 in which the alcohol is a primary, secondary or tertiary aliphatic alcohol having up to 20 carbon atoms, an aromatic or alicyclic hydroxyl compound having 6 to 20 carbon atoms or a polyhydric alcohol having 2 to 20 carbon atoms.

3. A process as claimed in claim 1 in which the derivative of the alcohol is an ester, ether or halide.

4. A process as claimed in any of claims 1 to 3 in which the rhodium component is a rhodium compound capable of being converted to a halogenorhodium carbonyl complex under the reaction conditions.

5. A process as claimed in any of claims 1 to 4 in which the iodide salt is; (a) a metal iodide of the formula M,ln or M,ln+2 wherein M, represents a metal having a valency of n, or, (b) an onium - type iodide of the formula or

wherein M2 represents a Group Va element of the Periodic Table and R, to R4 independently each represent a hydrogen atom or an alkyl or aryl group.

6. A process as claimed in any of claims 1 to 5 in which the iodide salt is charged into the reaction system in the form of a precursor.

7. A process as claimed in claim 6 in which the precursor containing the iodine component of the iodide salt is hydrogen iodide or an organic iodide and the precursor containing the cationic component of the iodide salt is (c) a metal hydroxadeoftheformula M3 (oH}a wherein M3 represents a metal having a valency of n; or (d) a carboxylic acid salt of the formula

wherein M4 represents a metal having a valency of n and R represents a hydrogen atom or an alkyl or aryl group; or (e) a metal in its elemental or oxide form; or (f) a trivalent compound of the formula

wherein Rs represents a Group Va element of the Periodic Table and R, to R3 independently each represent a hydrogen atom or an alkyl or aryl group; or (g) another metal compound.

8. A process as claimed in any of claims 1 to 7 in which the concentration of the rhodium component in the reaction liquid to 104to 10-1 molls.

9. A process as claimed in claim 8 in which the concentration of the rhodium component in the reaction liquid is 10-3 to 5 x 10-2 molK.

10. A process as claimed in any of claims 1 to 9 in which the concentration of alkyl halide in the reaction liquid is 10-2to 10 molls.

11. A process as claimed in claim 10 in which the concentration of alkyl halide in the reaction liquid is 10-1 to 2 molK.

12. A process as claimed in any of claims 1 to 11 in which the iodine ion concentration in the carbonylation reaction solution is maintained as from 0.5 mol/e to the solubility limit.

13. A process as claimed in any of claims 1 to 12 in which the water concentration is 1 to 20 molls.

14. A process as claimed in claim 13 in which the water concentration is 3 to 10 molls.

15. A process as claimed in any of claims 1 to 14 in which the reaction temperature is 50 to 300"C.

16. A process as claimed in claim 15 in which the reaction temperature is 100 to 240"C.

17. A process as claimed in any of claims 1 to 16 in which the reaction pressure is such that the partial pressure of carbon monoxide is 0.05 to 1000 atm.

18. A process as claimed in claim 17 in which the reaction pressure is such that the partial pressure of carbon monoxide is 0.3 to 300 atm.

19. A process as claimed in claim 18 in which the reaction pressure is such that the partial pressure of carbon monoxide is 0.5 to 100 atm.

20. A process according to claim 1 substantially as hereinbefore described with particular reference to any of Examples 3 to 26 and 29 to 31.

21. Carboxylic acids or esters whenever produced by a process as herein described and claimed.