MXPA01004019A - Carbonylation of methanol in the presence of a rhodium/iridium/iodide ion catalytic system - Google Patents

Abstract

The present invention provides a process for the carbonylation of an alcohol, ether or ester to products comprising a carboxylic acid, the anhydride thereof or coproduction of the carboxylic acid and anhydride. More particularly, the present invention provides a process for the carbonylation of methanol to produce acetic acid by reacting methanol with carbon monoxide in a liquid reaction medium containing a catalyst comprising rhodium, iridium, iodide ion, and said reaction medium further comprising water, acetic acid, methyl iodide, and methyl acetate and subsequently recovering acetic acid from the resulting reaction product.

Description

CARBONILATION OF METHANOL IN THE PRESENCE OF A CATALYTIC SYSTEM OF RHODIUM / IRIDIUM / ION OF YODURO FIELD OF THE INVENTION The present invention relates to homogeneous carbonylation catalyst systems, and more particularly to a homogenized multimetal carbonylation system stabilized and promoted together with a soluble inorganic iodide salt, in particular, an alkali metal or alkaline earth metal salt. or quaternary iodide salt of nitrogen or phosphorus.

DESCRIPTION OF THE RELATED TECHNIQUE Producing acetic acid by means of carbonylation of methanol with a rhodium salt catalyst is a well known commercial process as described in US Patent No. 3,769,329 issued by Paulik et al, and described by Eby and Singleton (Appl. Ind. Catal. 1, 275, (1983), USA, 329, describes the use of organic halides such as methyl iodide to promote the reaction, In US 329 it is mentioned that a substantial amount of water, typically about 14-15% in weight is necessary to achieve a high reaction rate Hjortjaer and Jensen (Ind. Eng. Chem; Proc. Res. Dev. 16, 281-285 (1977)) have shown that increasing the water of reaction of about a finite amount to about 14% by weight increases the reaction rate of methanol carbonylation, however, having a large amount of water present in the process incurs a high operating cost to separate the water from the acetic acid product. It has been found that under the conditions of Paulik et al. at less than 14-15% by weight of water content in a carbonylation reaction system, the carbonylation rate is significantly reduced and the rhodium catalyst tends to be destabilized and consequently, precipitated out of the reaction system. The patents of E: U.A. No. 5,001, 259; 5,026,908; and 5,144,068, Smith et al., describe a method for solving the difficulties of the high content of reaction water and catalyst destabilization described above. These patents disclose the use of a rhodium salt catalyst in a carbonylation system with low water content, ie water concentration of at least a finite amount to less than 14% by weight, preferably less than 7% by weight. weight. The carbonylation reaction is further promoted and the catalyst is stabilized to prevent precipitation using an alkali metal iodide salt or soluble alkaline earth metal, i.e., such as lithium iodide, or using an ammonium iodide or soluble quaternary phosphonium salt . A disadvantage of the process described in E.U.A. '259 et al. is described in E.U.A. 5,155,265; E.U.A. 5,155,266; E.U.A. 5,202,481; E.U.A. ^ g ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ l ^^^^^^^^^^^ ^^^^^^^^^^^^^ fe ^^^ g ^ ^^^^^^^^^^^^ g ^^^ i 5,206,434; E.U.A. 5,371, 286, and 5,783,734. The process increases the concentration of impurities of iodide, unsaturated compounds, and carbonyl. These patents emphasize the need to eliminate these impurities from the process. Another disadvantage of the process of E.U.A.'259 et al, is that as the water content is reduced, the reaction rate is also reduced. Accordingly, efforts have been directed to maintain and increase the reaction rate under water conditions of less than 14-15% by weight. A method to increase the reaction rate, as shown in E.U: A. '608, is to increase the partial pressure of hydrogen in the reaction system. Increasing the partial pressure of hydrogen can be achieved by having hydrogen in the carbon monoxide supply material fed to the carbonylation reaction. Commercial carbon monoxide supply materials often contain hydrogen as an impurity and under normal circumstances, there is no need to remove these impurities. E.U.A. 4,994,608 emphasizes the need to control hydrogen in the carbon monoxide feed to reduce the formation of carbon dioxide. In addition to having hydrogen present in the carbon monoxide feed, hydrogen can be generated in situ by the competent water-gas displacement reaction that occurs during the reaction. Therefore, due to the formation of this hydrogen in situ, it is suggested in E.U: A.'608 that the amount of hydrogen in the carbon monoxide feed is from about 0.3 to about 10 mol%. The carbonylation process iridium catalysed methanol as described in EP 752.406 emphasizes the need to maintain a low concentration of hydrogen in the carbon monoxide feed to the reactor to avoid the formation of hydrogenated byproducts. Iridium is a strong hydrogenation catalyst under the conditions of the iridium catalyzed process. Therefore, it is suggested in EP '406 that the amount of hydrogen in the carbon monoxide feed be less than 0.3 mol% and the partial pressure of hydrogen in the carbonylation reactor be less than 0.3 bar. Methods described in the art for increasing the carbonylation rate with rhodium-containing catalysts include the use of promoters. EP 643,034 describes the use of ruthenium or osmium as co-promoters. EP 618, 183 broadly describes the use of rhodium as a promoter to increase the rate of carbonylation reactions catalyzed by iridium. Similarly, GB 2,298,200 broadly describes the use of ruthenium, osmium, or rhenium with rhodium also as a co-promoter to increase the iridium-catalyzed carbonylation reaction. FR-A-2750985 discloses a methanol carbonylation process employing a system of two reaction zones and rhodium and iridium catalysts. However, it is not clear from these references if iridium could be added to a rhodium catalyzed system when iodide salts inorganic are present. It had previously been thought that ionic iodides, such as alkali metal or alkaline earth metal iodides, inhibit and consequently deactivate the iridium catalyst. Dokleva and Forster in Adv. Catalysts 34, 81 (1986) and references cited therein, in particular, Forster, J. Chem. Soc, Dalton. Trans., 1979, p. 1639, have indicated that ionic iodides reduce the carbonylation rate of methanol when an iridium catalyst is employed. The use of rhodium salt and iridium salt catalysts for methanol carbonylation is described in Canadian Patent 2,120,407 and GB 2,298,200. Can '407 and GB' 200 also teach that ionic iodides poison the iridium catalyst. It is suggested therein to limit the amount of ionic iodides from 0 to about 2% by weight. Sources of ionic iodides include: 1) alkali metal or alkaline earth metals as a promoter; 2) of corrosion metals common in the reaction system; and 3) of phosphonium or ternary ammonium ions as promoters. More recent patent publications also teach that the use of alkali metal iodides and alkaline earth metal iodides should be avoided in iridium-catalyzed carbonylation. These references include WO 98/22420, EP 846,674 A1, EP 849 248 A1, EP 849 251 A1. Although, EP 849 248 A1 indicates that under certain conditions wherein the water concentration in the reactor is at or below that at which the maximum occurs in the graph of carbonylation rate against water concentration can be added metal iodides alkaline and alkaline earth metals. HE to ^^^^^^^ ^^^^^^^^ and * ^^^^^^ teaches that under these conditions J &jp presence of iodide ion in high concentration can be harmful, when the carbonylation catalyst is only iridium. There is no mention therein of the use of alkali metal or alkaline earth metal iodides in a mixed rhodium-iridium catalyzed carbonylation reaction generating iodide ions in the liquid reactor composition. EP 752.406 cautions to minimize the ionic contaminants derived from corrosion metals, particularly nickel, iron and chromium, or phosphines and nitrogen containing compounds or ligands which may quaternize in situ due to the belief that these ions also poison the system of iridium salt catalyst. Poisoning occurs by generating iodide ion in the liquid reaction composition that has an adverse effect on the reaction rate. The present invention addresses the technical difficulties described above. A method for improving the carbonylation rate while maintaining the stability of the rhodium catalyst and limiting the formation of impurities is disclosed.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a process for producing a carboxylic acid by carbonylation of an alkyl alcohol and / or a reactive derivative thereof, that is, an alkyl ester or ether, in the presence of a homogeneous catalyst. ionic iodide catalyst stabilizer / co-promoter, iridium salt, and an alkyl iodide promoter. The ionic iodide / co-promoter stabilizer may be in the form of a soluble salt of an alkali metal or alkaline earth metal salt or an ammonium or quaternary phosphonium salt which generates an effective amount of iodide ion in the reaction solution. The stabilizer / co-promoter is preferably a soluble iodide salt of alkali metals or alkaline earth metals, in particular lithium iodide. Alternatively, the stabilizer may be an ammonium iodide or soluble quaternary phosphonium salt. The alkyl halide is preferably methyl iodide.

DETAILED DESCRIPTION OF THE INVENTION More particularly, the present invention provides a process for the carbonylation of an alcohol, ether or ester to products comprising a carboxylic acid, the anhydride thereof or co-production of the carboxylic acid and anhydride. Still more particularly, the present invention provides a process for the carbonylation of methanol to produce acetic acid by reacting methanol with carbon monoxide in a liquid reaction medium containing a catalyst comprising rhodium salt, a stabilizer / co-promoter of ionic iodide, and iridium salt; water, acetic acid, methyl iodide promoter, and methyl acetate; and subsequently recovering acetic acid from the resulting reaction product. The procedure is carried out ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^ to hold in the reaction medium during the course of the reaction approximately a finite amount to less than 14% by weight of water together with (a) a salt that provides an effective amount on the scale of about 2% by weight to 20% by weight of an ionic iodide in the reaction solution as a catalyst stabilizer / co-promoter selected from the group consisting of alkali metal and alkaline earth metal salts and / or nitrogen or phosphorus quaternary salt, (b) about 5% by weight to 30% by weight of methyl iodide, and (c) about 0.5% by weight to 30% by weight of methyl acetate. The iodide ionic stabilizer / co-promoter may be in the form of a soluble alkali metal salt or alkaline earth metal salt or an ammonium or quaternary phosphonium salt which generates an effective amount as defined above of iodide ion in the solution of reaction. The catalyst stabilizer / co-promoter is preferably lithium iodide, lithium acetate or mixtures thereof. The catalyst system may further comprise a transition metal salt as a co-promoter selected from the group consisting of salts of ruthenium, tungsten, osmium, nickel, cobalt, platinum, palladium, manganese, titanium, vanadium, copper, aluminum, tin, and antimony.

The present invention may include hydrogen, generally added together with the carbon monoxide supply material to the carbonylation reactor. It has been found that the presence of hydrogen increases the reaction rate and minimizes the formation of organic impurities. An advantage of the present invention is that a higher carbonylation rate is achieved when iridium salt is added to the catalyst system comprising rhodium salt and an alkali metal or alkaline earth metal salt, and / or ammonium or phosphonium salts soluble quaternary, 10 providing an effective amount on the scale from about 2% by weight to 20% by weight of an ionic iodide in the reaction solution over the use of rhodium salt alone. It has been found that the stabilizer / co-promoter stabilizes the rhodium / iridium catalyst without precipitation occurring during the carbonylation reaction and providing additional catalyst activity. Another advantage of the present invention is that the production of impurities such as acetaldehyde and especially unsaturated aldehydes such as crotonaldehyde and 2-ethyl crotonaldehyde is significantly reduced when the rhodium / iridium / iodide ion catalyst system is employed. using conditions equivalent to those used with the rhodium / iodide salt catalyst system alone. Such an advantage improves the quality of the product and reduces the need for additional purification to remove impurities. • toMa ^ - * ~ - --- - - - ~ ^ * "^ J ^^^^ ~ >. *** -! ^ ¿^^ =: ¿^« i i.

DESCRIPTION OF ILLUSTRATIVE MODALITIES The present invention provides an improvement in carbonylation processes wherein an alcohol, ester, or ether is converted to a carboxylic acid and / or the anhydride thereof. The following description is directed to the carbonylation of methanol to produce acetic acid. However, the technology is applicable to the carbonylation of higher homologues of methanol to form acids that are the highest homologues of acetic acid. A methanol carbonylation process used above comprises reacting methanol with carbon monoxide in a liquid reaction medium containing a rhodium salt catalyst and comprising water, acetic acid, methyl iodide promoter, methyl acetate, and stabilizer / co-promoter of ionic iodide and subsequently recover acetic acid from the resulting reaction product. As described above, a process of carbonylation of methanol previously used included the use of iridium salt catalyst, plus the other components mentioned in conjunction with the rhodium catalyzed except for acknowledging the benefit of the iodide salt system. In the present invention, the metal catalyst comprises rhodium and iridium, and the reaction medium further includes an alkali metal or alkaline earth metal iodide salt and / or an ammonium iodide or quaternary phosphonium salt as a stabilizer / co-promoter of catalyst. The metal catalyst can also include other transition metals. The carbonylation reaction system may also include hydrogen in the ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ H ^ IT &? ^^^^ Q ^ ^^^^^^^^^^^ ^^^^^^^^^^^ ^ ^^^ carbon monoxide feed. Hydrogen of more than about 5 ppm with iridium has no significant effect on the production of unsaturated compounds. This allows H2 to be used if desired in the CO feed or reaction medium. With respect to the production of propionic acid, hydrogen has a significant effect. Therefore, a low hydrogen content in the reaction medium may be more desirable depending on the production of impurities. The metal catalyst can be added to the liquid reaction composition for the carbonylation reaction in any suitable form 10 that dissolves in the liquid reaction composition or is convertible to a soluble form. The amount of rhodium added to the reaction medium is generally between about 100 and 5000 ppm, and is preferably between about 300 and 1000 ppm. Examples of the rhodium catalyst are well known to those skilled in the art and were best described in the U.S. patent. '329 by Paulik et al. The amount of iridium salt added to the reaction medium is generally between about 100 and 5000 ppm, and preferably between about 200 and 2000 ppm. Examples of suitable iridium-containing salts that can be added to the liquid reaction composition include iridium acetate, iridium oxalate, iridium acetoacetate, iridium metal, lRCl 3, lrl 3, lrBr 3, lrCl 3 D 3 H 2 O, lrBr 3 D 3 H 20, lr 2 O 3 > Ir02, [lr (CO) 2l] 2, [lr (CO) 2Cl] 2, [lr (CO) 2Br] 2, [lr (CO) 2l2]? +, [Lr (CO) 2Br2]? +, [ lr (CO) 2l4] "H +, [lr (CH3) l3 (CO) 2]" H +, and lr4 (CO) 12., preferably iridium complexes such as acetates, oxalates and acetoacetates which are soluble in one or ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ I ^^^^ M W ^^ ft ^^^^^^^^^^^^^^ ^^^^^^^ í i ^^^^ more components carbonylation reaction such as water, alcohol and / or carboxylic acid. Other transition metal salts can also be added to the reaction medium. Such transition metal salts may include salts of ruthenium, tungsten, osmium, nickel, cobalt, platinum, palladium, manganese, titanium, vanadium, copper, aluminum, tin, and / or antimony salts. In general, the amount of these transition metal salts is between about 100 and 4000 ppm. Any salt of alkali metal or alkaline earth metal, such as lithium, potassium, magnesium, and calcium salts can be used as a catalyst stabilizer / co-promoter so long as the salt is sufficiently soluble in the reaction medium to provide or generate an effective amount of an ionic iodide soluble for the desired level of catalyst stabilization / promotion. In particular, lithium salts, such as lithium iodide and lithium acetate, are useful, with lithium iodide being preferred. The concentration of iodide ion in the reaction medium is generally between about 2 and 20% by weight, preferably between about 10 and 20% by weight. The concentration of water in the reaction medium is typically between about a finite amount (>50 ppm) and 14% by weight. The water concentration is preferably between about 0.1 and 8% by weight, and most preferably between about 0.5 and 4% by weight. The concentration of methyl acetate in the reaction medium is generally between about 0.5 and 30% by weight, preferably between about 1 and 20% by weight.The concentration of methyl iodide in the reaction medium is typically between about 5 and 30% by weight. and 30% by weight, preferably between about 5 and 15% by weight Acetic acid typically constitutes the remainder of the reaction medium The partial pressure of carbon monoxide in the reactor in the carbonylation reactor is typically about 2-30. bar, preferably approximately 5-20 bar. Due to the partial pressure of by-products and the vapor pressure of the contained liquids, the total reactor pressure is approximately 15-45 bar, with the reaction temperature being approximately 150 to 250 °. C. Preferably, the reactor temperature is about 175 to 220 ° C. The carbon monoxide feed to the carbonylation reactor may contain hydrogen. s commercial carbon monoxide supply materials often contain low levels of hydrogen as an impurity, and there is no need here to try to eliminate such impurities. The addition of iridium to the rhodium / iodide ion system in the present invention reduces the formation of aldehyde by-products. Iridium acts as an efficient hydrogenation catalyst in the present invention wherein hydrogen is provided from the displacement reaction of water gas or hydrogen in the carbon monoxide feed or both.

An advantage of W present invention is that a higher carbonylation rate is achieved when iridium salt is added to the catalyst system comprising rhodium salt and an iodide ion such as an ammonium iodide or quaternary phosphonium salt on the Use of rhodium salt in the absence of such stabilizer / co-promoters. Another advantage of the present invention is that it has been found that the addition of iridium salt or iridium and ruthenium salt to a catalyst system comprising rhodium salt and an alkali metal or alkaline earth metal iodide salt or an iodide salt of Ammonium or quaternary phosphonium reduces the production of acetaldehyde and all the impurities derived from acetaldehyde, especially unsaturated aldehydes such as crotonaldehyde and ethyl-crotonaldehyde. A typical reaction system that can be employed for the process of the present invention comprises (a) a liquid phase carbonylation reactor, (b) an instant vaporizer, and (c) a methyl iodide-acetic acid splitter column. . The carbonylation reactor is typically a stirred autoclave within which the liquid contents reacting are automatically maintained at a constant level. Fresh methanol, enough water to maintain at least a finite concentration of water in the reaction medium, recycled catalyst solution from the flash vaporizer base, and recycled methyl iodide and methyl acetate are continuously introduced into this reactor. of the distillation head of the methyl-acid iodide splitter column acetic. A distillation system can be employed to process the condensed head stream of the flash vaporizer. The residue of the flash vaporizer is recycled to the reactor. Carbon monoxide is continuously introduced and completely dispersed with the carbonylation reactor. A gas purge stream is discharged from the reactor head to prevent the accumulation of gaseous by-products and to maintain a pre-set partial pressure of carbon monoxide at a given total reactor pressure. The reactor temperature and pressure are kept constant by methods known in the art. Crude liquid product is extracted from the carbonation reactor at a sufficient speed to maintain a constant level therein and is introduced to the flash vaporizer at an intermediate point between the upper and lower part of it. In the instant vaporizer the catalyst solution is removed as a predominantly base current acetic acid containing the rhodium catalyst and the iodide salt together with minor amounts of methyl acetate, methyl iodide, and water, while the condensed distillation head of the flash vaporizer largely comprises the crude product, acetic acid , together with methyl iodide, methyl acetate, and water. A portion of carbon monoxide together with gaseous byproducts such as methane, hydrogen, and carbon dioxide leaves the top of the flash vaporizer. The acetic acid in the product is extracted from the base of the methyl iodide-acetic acid splitter column (it can also be removed as g ^^^^^^^^^^^^^^^^^^^ g ^^^^^ fe ^^^^^^^^^^^^^ i ^^^^^^^^^ ^ a lateral stream near the ase) for final purification as desired by methods which are obvious to those skilled in the art and which are outside the scope of the present invention. The distillation head of the methyl iodide-acetic acid divider, comprising mainly methyl iodide and methyl acetate, is recycled to the carbonylation reactor. The experiments confirmed the findings in the art that iridium plus iodide ion resulted in a minimum velocity at a non-existent rate of reaction. In particular, it was found that about 10% by weight of iodide ion plus iridium resulted in absence of reactivity. However, the addition of iridium salt to a system of "rhodium catalyst / iodide ion did not produce the unexpected inactivity of iridium caused by the iodide ion, but it did provide a significant improvement of the catalyst activity. Iridium to a radio / iodide ion system as a velocity promoter in a methanol carbonylation system was surprising and unexpected.Also, the significant reduction in the formation of aldehyde impurities, ie, acetaldehyde, crotonaldehyde, was surprising and unexpected. and 2-ethyl crotonaldehyde In addition, the use of hydrogen in combination with the rhodium / iridium / iodide ion catalyst system increased the reaction rate while the impurities remained relatively unchanged compared to the rhodium catalyst system. iodide ion.

The use of additional transition metals such as ruthenium, tungsten, and the like (as described above) was found favorable. It was found that a catalyst system comprising rhodium / iridium / ruthenium / iodide ion catalyst system produces increased reaction rate while the impurities in the reaction remain relatively unchanged. The following examples are included to demonstrate preferred embodiments of the invention. Those skilled in the art should appreciate that the techniques described in the examples that follow represent techniques discovered by the inventor to function well in the practice of the invention, and therefore can be considered to constitute preferred embodiments for their practice. However, in light of the present disclosure, those skilled in the art should appreciate that many changes can be made in the specific embodiments described and still obtain a similar or similar result without departing from the spirit and scope of the invention.

EXAMPLE 1 To a 300 cc Hastalloy B autoclave was added water, glacial acetic acid (ACS Fisher grade), lithium anhydride iodide (Alfa), rhodium triiodide (Engelhard, 21.28% Rhodium), methyl acetate (Aldrich) and methyl iodide. (Fisher). The percentage by weight of the reagents in the autoclave was Sjfefe ~ * ¿gisiz. the following way: water, 3%; Lithium iodide, 0 to 10% as indicated in table 1; methyl acetate, 27%; Methyl iodide, 20%; and acetic acid like the rest. The amount of rhodium used is indicated in table 1. Iridium salt was also added as iridium oxide (Ir02) in an amount indicated in table 1. After the autoclave was loaded with the appropriate components, it was pressurized to 3.515 kg / cm2 gauge with carbon monoxide and drained slowly; this step was repeated two additional times. Then the autoclave was tested for pressure for ten minutes at 28 bar. The pressure was slowly drained at approximately 19 bar and an electric heater applied heat. As the internal reactor temperature reached the target temperature of 195 ° C, the pressure was adjusted to approximately 28 bar by adding carbon monoxide from a high pressure tank as needed. When the reactor solution reached 195 ° C again, the agitator was turned on at approximately 800 rpm and zero time was set for the carbonylation reaction. The measurement of change in the pressure of the carbon monoxide deposit over time was used as a direct indication of the carbonylation rate. A temperature of 195 ° C and pressure of 28 bar were maintained for 30 minutes. The results of the reaction rate, reported as space-time performance (STY) of carbon monoxide measured as moles of carbon monoxide per liter of reaction solution per hour (moles / L-hr.), Are given in the table I. The batch results in table 1 illustrate the advantage of a rod / iridium / iodide ion (BC) catalyst system over a system of rhodium / iridium catalyst without iodide ion (A). The same table shows that 1000 ppm iridium added to the rhodium catalyst / iodide ion system significantly increases the carbonylation rate from 18 to 22 (moles / L-hr). The iridium promoting effect in the rhodium / iodide ion catalyst system is compared in the lines B vs. F. The inefficiency of the iridium / iodide ion catalyst system at as low as 1 and 2% by weight of iodide compared to the iridium catalyst system without iodide ion salt is shown on lines D and E vs. G and H of table 1.

TABLE I Autoclave results by ote ? »¿Ma *, ^^^. > . ^ "^^ Aa ^^^ 'ga ^ ...- ^ - ^^ J ^^ a ^ 1 ^^ a ^^ EXAMPLE 2 Continuous methanol carbonylations were performed in a reaction system as described above, wherein a liquid phase carbonylation reactor was used, followed by an instantaneous vaporizer, and then a methyl iodide-acetic acid splitter column. The reagent composition for each system is given in Table II. The results are given in Table II, and show the effects of hydrogen, iridium and ruthenium in the rhodium catalyst / iodide ion system for the methanol carbonylation process. As can be seen in Table II, the presence of hydrogen in the carbon monoxide feed has the effect of increasing the carbonylation rate in the rhodium catalyst / iodide ion system at the expense of increased impurity formation particularly acetaldehyde and aldehydes unsaturated such as crotonaldehyde and 2-ethyl crotonaldehyde (K vs. L). This presence of hydrogen in the carbon monoxide feed is often unavoidable, since commercial sources of carbon monoxide supply material frequently contain hydrogen as an impurity. However, the addition of iridium to the catalyst system of rhodium / iodide ion significantly reduces the formation of acetaldehyde, crotonaldehyde, and 2.ethyl crotonaldehyde when hydrogen is present in the carbon monoxide feed (L vs. M). The results of continuous operation indicate that the addition of iridium to the rhodium / ion catalyst system of iodide, even in the presence of hydrogen in the carbon monoxide feed increases the carbonylation rate from 20 to 23 mol / L-hr (K vs. M). An additional speed improvement at 26 STY can be achieved by adding ruthenium in the rhodium / iridium / iodide ion 5 (N) catalyst system. As the amount of iridium in the system increases, from 830 ppm to 2060 ppm, STY increases from 23 to 26 moles / L-hr, without an increase in the concentration of acetaldehyde and unsaturated aldehydes (M vs. O). Another benefit of the addition of iridium in the rhodium catalyst / iodide ion system is the significant improvement in the formation of impurities, particularly, of the unsaturated compounds. The base case with the rhodium catalyst / iodide ion system generates a total of about 10 ppm of unsaturated compounds in the reactor. With the presence of iridium, the unsaturated compounds are significantly reduced (L vs. M). When ruthenium is added to the rhodium / iridium / iodide catalyst system, STY increases from 23 to 26 moles / hr, the concentration of acetaldehyde in the reactor is slightly reduced from 530 to 517 ppm (M vs. N), and the concentration of propionic acid increases slightly, from 230 to 271 ppm in the product.

SECTION II Results of continuous operation 1'2.3 Rh / Li Rh / Lil Rh / L i Rh / lr / Rh / lr / Li I Rh / lr / Lil / H2 I / Ir l / H2 Lil / H2 / Ru / H2 OIKLMN Total time (hrs) 11 9 12 11 9 14 Lil (% by weight) 10 11 12 11 10 11 Rh (ppm) 570 650 634 650 680 703 Ir (ppm) 900 0 0 830 930 2060 Ru (ppm) 0 0 0 0 650 0 H2 in feed 0 0 1850 1786 1800 2060 CO (ppm) Water (% by weight) 3.1 3.0 2.0 3.0 2.3 2.8 Mel (% by weight) 11.2 12.0 11.3 12.8 11.7 11.0 MeOAc (% by weight) 3.0 3.1 3.1 2.8 3.0 2.8 STY acid (moles / L - 22 20 21 23 26 26 hr) Reactor Acetaldehyde (ppm) 410 423 700 530 517 nd Compounds 0 2 10 0 0 n.d. unsaturated (ppm) Condensate vaporizer distillation head Acetaldehyde (ppm) n.d. 1500 2600 3000 2000 2650 Compounds n.d. 8 35 0 0 0 unsaturated Product Compounds 0 0 0 0 C unsaturated (ppm) Propionic acid 160 75 150 230 271 2 (ppm) r C 1n.d. = not determined 2The reaction temperature was 195 ° C at 28 bar 3Composed Nsaturated = crotonaldehyde + 2-ethylcrotonaldehyde

Claims (12)

NOVELTY OF THE INVENTION CLAIMS

1. In a process for producing acetic acid by reacting methanol with a carbon monoxide feed in a liquid reaction medium containing a catalyst comprising a rhodium salt and an iridium salt, and comprising water, acetic acid, methyl iodide , and methyl acetate and subsequently recover acetic acid from the resulting reaction product, the improvement comprising: maintaining in said reaction medium during the course of said reaction approximately a finite amount to less than 14% by weight of water together with (a) ) an effective amount of iodide ion in the range of about 2 to 20% by weight as catalyst stabilizer / co-promoter selected from the group consisting of alkali metal and alkaline earth metal salts and / or ammonium iodide salts or quaternary phosphonium, (b) about 5% by weight to 30% by weight of methyl iodide, and (c) about 0.5% by weight to 30% by weight of methyl acetate.

2. The process according to claim 1, further characterized in that said metal salt is a lithium salt.

3. The process according to claim 2, further characterized in that said lithium salt is lithium iodide.

4. - The method according to claim 2, further characterized in that said lithium salt is lithium acetate.

5. The process according to claim 1, further characterized in that the rhodium salt is maintained in said reaction medium in a concentration of about 100 ppm to about 5000 ppm and the iridium is maintained in said reaction medium in a concentration from about 100 ppm to about 5000 ppm.

6. The process according to claim 1, further characterized in that the catalyst further comprises a transition metal salt selected from the group consisting of salts of ruthenium, tungsten osmium, nickel, cobalt, platinum, palladium, magnesium, titanium, vanadium, copper, aluminum, tin, and antimony.

7. The process according to claim 1, further characterized in that the catalyst further comprises a ruthenium salt.

8. The process according to claim 1, further characterized in that a finite amount is maintained in the reaction medium at less than 14% by weight of water, approximately 2 to 20% by weight of iodide ion as the iodide of lithium, about 5 to 30% by weight of methyl iodide, and about 0.5 to 30% by weight of methyl acetate, the remainder consisting essentially of acetic acid. «ÉtíÉAtaHiitli m ^^ t tmiSi í - ^? mtJjM *

9. The process according to claim 8 comprising maintaining in said reaction medium during the course of said reaction about 0.1% by weight to about 8% by weight of water.

10. The process according to claim 1, further characterized in that said metal salt is lithium iodide and maintain in said reaction medium during the course of said reaction, approximately 5 to 15% by weight of methyl iodide, approximately 1 to 20% by weight of methyl acetate with the remainder consisting essentially of acetic acid.

11. The process according to claim 1, further characterized in that the iodide in the reaction medium is approximately 10 to 20% by weight.

12. The process according to claim 1, further comprising hydrogen in the carbon monoxide feed at a level greater than about 5 ppm. Mg ^^^^^ | ^^ jÉ ^ ggjyg ^ U &