MXPA97010438A - Catalyzed carbonilation process with iridiopara acet acid production - Google Patents

Abstract

The present invention relates to a process for the production of acetic acid by carbonylation, with carbon monoxide, of methanol and / or a reactive derivative thereof, in a carbonylation reactor containing a liquid reaction composition comprising a carbonylation catalyst. of iridium, co-catalyst of methyl iodide, a finite concentration of water, acetic acid, methyl acetate and at least one promoter, where the water concentration is at or below that at which the maximum in the graph of carbonylation rate versus water concentration, and because, in the liquid reaction composition, a co-promoter selected from alkali metal iodides, alkaline earth metal iodides, metal complexes capable of generating I, salts capable of generate I and mixtures of two or more of the above

Description

IRON-CATALYZED CARBONILATION PROCESS FOR THE PRODUCTION OF ACETIC ACID Field of the Invention The present invention relates to a process for the production of acetic acid and, in particular, to a process for the production of acetic acid by carbonylation in the presence of a iridium catalyst, a methyl iodide cocatalyst and a promoter. Description of the State of the Art The preparation of carboxylic acids is already known by iridium-catalyzed carbonylation processes and is described, for example, in GB-A-1234121, US-A-3772380, DE-A-1767150, EP-A -0616997, EP-A-0618184, EP-A-0618183, EP-A-0657386 and OA-95/31426. In WO-A-95/31426 a process is described for the production of carboxylic acids or their esters having (n + 1) carbon atoms by reaction in liquid phase of carbon monoxide with at least one alcohol having (n) carbon atoms, in the presence of a catalyst system based on an iridium compound and a halogenated co-catalyst . The process is characterized by maintaining, in the reaction medium, water in a volume ranging from more than 0 to 10%, usually between 0.5 and 8%, preferably between 2 and 8%; the ester corresponding to the carboxylic acid and alcohol in a volume ranging between 2 and 40%; and iodides in soluble form of a nature such that the atomic ratio of the iodides to the iridium ranges from more than 0 to 10, usually from more than 0 to 3 and preferably from more than 0 to 1.5. The volume of halogenated co-catalyst in the reaction medium ranges from more than 0 to 10%, usually between 0.5 and 8% and preferably between 1 and 6%. Suitable iodides include alkaline earth metal and alkaline metal iodides, and specifically lithium iodide. On the other hand, the process described in WO-A-95/31426 is carried out without promoters. EP-A-0643034 describes a process for the carbonylation of methanol and / or a reactive derivative thereof in the presence of acetic acid, an iridium catalyst, methyl iodide, at least a finite concentration of water, methyl acetate and a promoter selected between ruthenium and osmium. In this reference, discontinuous and continuous experiments are described. In continuous experiments, the concentration of water is as low as 6.8% by weight. The published European Patent Application No. 0752406 filed on 06/18/96 describes a process for the production of acetic acid comprising (1) continuously feeding methanol and / or a reactive derivative thereof and carbon monoxide to a carbonylation reactor containing a liquid reaction composition comprising an iridium carbonylation catalyst, methyl iodide cocatalyst, a finite concentration of water, acetic acid, methyl acetate and at least one promoter; (2) contacting the methanol and / or reactive derivative thereof with the carbon monoxide in the liquid reaction composition, to produce acetic acid; and (3) recovering acetic acid from the liquid reaction composition; characterized in that during the entire course of the reaction, (a) water is maintained continuously in the liquid reaction composition at a concentration not exceeding 6.5% by weight, (b) methyl acetate in a concentration of 1 to 35. % by weight and (c) methyl iodide in a concentration of 4 to 20% by weight. In processes performed with promoters, described in EP-A-0643034 and in European Application No. 96302734.7, ionic contaminants are said to be, for example, (a) corrosion metals, in particular nickel, iron and chromium, and (b) phosphines or nitrogen-containing compounds or ligands that can quaternize in situ, should be kept to a minimum in the liquid reaction composition since said contaminants have an adverse effect on the reaction by generating I "in the liquid reaction composition, which has an adverse effect on the reaction rate Similarly, it is said that contaminants such as alkali metal iodides, for example lithium iodide, should also be kept to a minimum.In WO-A-96/237757, which is directed to the preparation of iridium carboxylates and their use, inter alia. in carbonylation reactions, and where the use of promoters is not mentioned, it is established, in contrast to WO-A-95/314326, that alkali or alkaline-earth ions are preferably eliminated since their presence may have a detrimental influence on the kinetics and selectivity of subsequent reactions where the iridium carboxylate will be used as the catalyst. There continues to be a need to have an iridium-catalyzed carbonylation process promoted and improved. The technical problem is solved by the use, in an iridium catalyzed carbonylation process and promoted, of a liquid reaction composition defined in terms of the water composition and containing a co-promoter selected from alkali metal iodides, iodides of alkaline earth metals, metal complexes capable of generating I ", salts capable of generating I" and mixtures of two or more of the above. SUMMARY OF THE INVENTION Therefore, the present invention provides a process for the production of acetic acid by carbonylation, with carbon monoxide, of methanol and / or a reactive derivative thereof, in a carbonylation reactor containing a liquid reaction composition. comprising an iridium carbonylation catalyst, methyl iodide co-catalyst, a finite concentration of water, acetic acid, methyl acetate and at least one promoter, characterized in that the water concentration is at or below that at which the maximum is presented in the graph of carbonylation rate versus water concentration, and because, in the reaction composition liquid, a co-promoter selected from alkali metal iodides, alkaline earth metal iodides, metal complexes capable of generating 1, salts capable of generating I "and mixtures of two or more of the foregoing is employed Detailed Description of the Invention The process of the present invention provides several technical advantages Thus, the need to use an ion exchange resin bed in order to treat the liquid reaction composition for removing corrosion metals, alkali metal and / or alkaline earth metal contaminants can be reduced. The higher carbonylation rate at the low water concentration of the present invention may allow to operation at a reduced concentration of iridium catalyst, while maintaining the carbonylation rate. This has the advantage of a lower production rate of by-products, such as propionic acid. The rate of production of byproducts such as propionic acid, methane, hydrogen and carbon dioxide can be reduced.

Greater stability of the catalyst and the promoter, particularly at low water concentrations, can also be advantageously achieved. Water can be formed in situ in the liquid reaction composition, for example, by the esterification reaction between the reactant methanol and the acetic acid product. Small amounts of water can also be produced by hydrogenation of methanol to produce methane and water. The water can be introduced into the carbonylation reactor together or separately from other components of the liquid reaction composition. The water can be separated from the other components of the reaction composition extracted from the reactor and can be recycled in controlled amounts to maintain the required concentration of water in the liquid reaction composition. With reference to the aforementioned published European Application No. 0752406, it is said herein that the carbonylation reaction increases as the concentration of water in the liquid reaction composition is reduced from a concentration greater than 6.5% by weight, it passes through a maximum at a water concentration not exceeding 6.5% by weight and then decreases as very low water concentrations are reached. In Figure 8 of said application, a graph of the reaction rate versus water concentration is shown, whose graph clearly shows a maximum. The concentration of water at which the carbonylation rate is at a maximum increases, as it is said, as the concentration of methyl acetate increases in the liquid reaction composition. It is believed that the concentration of water at which the carbonylation rate is at a maximum decreases as the concentration of methyl iodide in the liquid reaction composition increases. For the purposes of the present invention, the concentration of water in the liquid reaction composition is preferably kept below 6%, more particularly below 4.5% by weight. By operating at said low water concentration according to the present invention, the advantage of being able to facilitate the recovery of acetic acid from the reaction composition extracted from the carbonylation reactor is obtained because the amount of water to be separated from the acetic acid is less.; the separation of water from acetic acid constitutes a high energy part of the recovery process and the fact of having a lower concentration of water translates into less difficulties and / or processing costs. In the process of the present invention, suitable reactive methanol derivatives include methyl acetate, dimethyl ether and methyl iodide. In the process of the present invention, a mixture of methanol and reactive derivatives thereof can be used as reactants. Preferably, methanol and / or methyl acetate are used as reactants. If methyl acetate or dimethyl ether is used, the use of water as a co-reactant to produce acetic acid is necessary. At least part of the methanol and / or reactive derivative thereof will be converted to, and therefore be present as, methyl acetate in the liquid reaction composition by reaction with acetic acid product or solvent. In the process of the present invention, the concentration of methyl acetate in the liquid reaction composition is suitably from 1 to 70% by weight, preferably from 2 to 50% by weight, more preferably from 5 to 40% by weight. In the process of the present invention, the concentration of methyl iodide cocatalyst in the liquid reaction composition is preferably 1 to 30% by weight, more preferably 1 to 20% by weight. An advantage derived from achieving high carbonylation rates at low concentrations of methyl iodide and water, by the addition of co-promoters according to the present invention, may be that of producing less corrosion. An alternative method to increase the speed is to increase the concentration of methyl iodide, but this can cause greater corrosion. In the process of the present invention, the iridium carbonylation catalyst is preferably present in the liquid reaction composition at a concentration of 400 at 5,000 ppm, measured as iridium, more preferably from 500 to 3,000 ppm, measured as iridium, and even more preferably from 700 to 3,000 ppm, measured as iridium. In the process of the present invention, the rate of the carbonylation reaction increases as the iridium concentration does. The iridium catalyst in the liquid reaction composition can comprise any compound containing iridium and which is soluble in the liquid reaction composition. The iridium catalyst can be added to the liquid reaction composition for the carbonylation reaction in any suitable form that is dissolved in the liquid reaction composition or can be converted to a soluble form. Examples of suitable iridium containing compounds that can be added to the liquid reaction composition include: IrCl3, Irl3, IrBr3, [Ir (CO) 2I] 2, [Ir (C0) 2C1] 2, [Ir (CO) 2Br] 2, [Ir (CO) 2I2] "H +, [Ir (CO) 2Br2] ~ H +, [Ir (CO) 2I4]" H \ [Ir (CH3) I3 (CO) 2] "H +, Ir4 (CO) 12, IrCl3.3H20, IrBr3.3H20, Ir4 (CO) 12, iridium metal, lr203, Ir02, Ir (acac) (CO) 2, Ir (acac) 3, acetate of preferably iridium complexes, free of chloride, such as acetates , oxalates and acetoacetates, which are soluble in one or more of the components of the carbonylation reaction, such as water, alcohol and / or carboxylic acid. co. Particularly preferred is the crude iridium acetate which can be used in an acetic acid solution or an aqueous solution of acetic acid. In the process of the present invention, at least one promoter is present in the reaction composition. Suitable promoters are preferably selected from the group consisting of ruthenium, osmium, tungsten, rhenium, zinc, cadmium, indium, gallium and mercury, and more particularly are chosen from ruthenium and osmium, with ruthenium being preferred to a large extent. Preferably, the promoter is present in an effective amount up to the limit of its solubility in the liquid reaction composition and / or in any of the liquid streams from the process recycled to the carbonylation reactor from the acetic acid recovery stage. The promoter is suitably present in the liquid reaction composition at a promoter: iridium molar ratio of [0.5 to 15]: 1, preferably [2 to 10]: 1, more preferably [2 to 7.5] ] :1. A suitable promoter concentration is from 400 to 5,000 ppm. The promoter can comprise any compound that contains a suitable promoter metal and that is soluble in the liquid reaction composition. The promoter can be added to the liquid reaction composition for the carbonylation reaction in any suitable form which is dissolved in the liquid reaction composition or can be converted to a soluble form. Examples of suitable ruthenium-containing compounds, which can be used as promoter sources, include ruthenium chloride (III), ruthenium chloride (III) trihydrate, ruthenium chloride (IV), ruthenium bromide (III), ruthenium metal, oxides of ruthenium, ruthenium (III) format, [Ru (C0) 3I3] "H +, [Ru (C0) 2I2] n, [Ru (CO) 4I2], [Ru (CO) 3I2] 2, tetra (aceto) chloro-ruthenium (II, III), ruthenium acetate (III), ruthenium propionate (III), ruthenium butyrate (III), ruthenium pentacarbonyl, triruthenium dodecacarbonyl and ruthenium mixed halocarbonyl, such as dichlorotricarbonyl ruthenium (II) dimer, dibromotri-carbonyl ruthenium ( II) dimer and other organo-rhrutenium complexes such as tetrachlorobis (4-cymene) di-ruthenium (II), tetrachlorobis (benzene) diruthenium (II), dichloro (cycloocta-1, 5-diene) ruthenium (II) polymer and tris ( acetylacetonate) ruthenium (III) Examples of suitable osmium-containing compounds that can be used as promoter sources include osmium chloride (III ) hydrated and anhydrous, metal osmium, osmium tetraoxide, triosmium dodecacarbonyl, [Os (CO) 4I2], [Os (CO) 3I2] 2, [Os (CO) 3I3] "H +, pentachloro-m-nitrodiosmium and osmium halocarbonyl mixed such as tricarbonyldichloroosmium (II) dimer and other organosomal complexes. Examples of suitable tungsten-containing compounds that can be used as promoter sources include W (CO) 6, WC14, WC16, WBr5, WI2 or C9H12 W (CO) 3 and any chloro-, bromo- or iodo-carbonyl tungsten compound. Examples of suitable rhenium-containing compounds that can be used as promoter sources include the following: Re2 (CO) 10, Re (CO) 5Cl, Re (CO) 5 Br, Re (CO) 5I, ReCl3.xH20, [Re (CO (CO)] ) 4I] 2, [Re (CO) 4I2] "H + and ReCl5.yH20 Examples of suitable cadmium containing compounds that can be used as promoter sources, include Cd (0Ac) 2, Cdl2, CdBr2, CdCl2 / Cd (0H 2 and cadmium acetylacetonate Examples of suitable mercury-containing compounds that can be used as promoter sources include Hg (OAc) 2, Hgl2, HgBr2, HgCl2, Hg2I2, and Hg2Cl2 Examples of suitable zinc-containing compounds that can be used as promoter sources, they include Zn (OAc) 2, Zn (OH) 2, Znl 2, ZnBr 2, ZnCl 2 and zinc acetylacetonate Examples of suitable gallium containing compounds that can be used as promoter sources include gallium acetylacetonate, acetate gallium, GaCl3, GaBr3, Gal3, Ga2Cl4 and Ga (0H) 3. Examples of suitable indium-containing compounds that can be used as Promoter sources include indium acetylacetonate, indium acetate, InCl3, InBr3, Inl3, Inl and In (OH) 3.

A co-promoter chosen from alkali metal iodides, alkaline earth metal iodides, metal complexes capable of generating I ", salts capable of generating I" and mixtures of two or more of the above is used in the liquid reaction composition. Suitable alkali metal iodides include lithium iodide. Suitable alkaline earth metal iodides include calcium iodide. Suitable metal complexes capable of generating I "include complexes of the lanthanide metals, for example, lanthanum and cerium, and nickel, iron, aluminum and chromium, generally Al (0Ac) 2 (0H) and Ce (0Ac) 3, hydrated. capable of generating I "include, for example, acetates which are capable of being converted in situ to I" and organic salts, such as quaternary ammonium iodides and phosphonium iodides, which can be added as such.A preferred co-promoter is Lithium iodide The co-promoter selected from alkali metal iodides, alkaline earth metal iodides, metal complexes capable of generating I ", salts capable of generating I" and mixtures of two or more of the above, is suitably present in such quantities which is effective in increasing the carbonylation rate The amount of said co-promoter introduced into the liquid reaction composition should be chosen so as to take into account the presence of I "from other as sources because, it is believed, an excessive amount of I "in the liquid reaction composition can be detrimental.Using lithium as a co-promoter in a molar ratio of ruthenium to iridium of about 2: 1, the molar ratio of lithium to iridium it can be suitably in the order of [0.1 to 2]: 1, preferably in the order of [0.5 to 1.5]: 1. Similar ranges can also be used for the co-promoters of quaternary ammonium iodide and phosphonium iodide At high molar ratios of ruthenium to iridium, for example 5: 1 or higher, even higher proportions of lithium can be used to achieve a promotional effect, typically, for example when lithium is used as a co-promoter and when the molar ratio of ruthenium to iridium is [2: 1] approximately, the molar ratio of lithium to iridium is suitably in the order of [0.5 to 1.5]: 1. Among other factors, the oxidation state of the metallic center in the reaction solution makes it difficult to specify ranges of concentration suitable for other sources of iodide ions. Normally, however, for divalent and trivalent metal salts, a range of suitable co-promoter can be from [0.1 to]: l moles equivalent to iridium with a promoter ratio of [2 to 10]: 1 molar equivalents to iridium. The reactant carbon monoxide may be essentially pure or may contain inert impurities such as carbon dioxide, methane, nitrogen, noble gases, water and paraffinic hydrocarbons Cx to C4. The presence of hydrogen in the carbon monoxide fed and generated in situ by the water gas displacement reaction is preferably kept at low values since its presence can result in the formation of hydrogenation products. Thus, the amount of hydrogen in the reactant carbon monoxide is preferably less than 1 mole%, more preferably less than 0.5 mole% and even more especially less than 0.3 mole%; and / or the partial pressure of hydrogen in the carbonylation reactor is preferably lower than a partial pressure of 1 bar, more preferably less than 0.5 bar and even more especially lower than 0.3 bar. The partial pressure of carbon monoxide in the reactor is in the range from more than 0 to 40 bar, in general from 4 to 30 bar. The total pressure of the carbonylation reaction is suitably from 10 to 200 bar gauge, more preferably from 15 to 100 bar gauge, especially from 15 bar to 50 bar gauge. The temperature of the carbonation reaction is suitably 100 to 300 ° C, preferably 150 to 220 ° C. The process of the present invention is preferably carried out as a continuous process. The acetic acid product can be recovered from the liquid reaction composition by extracting steam and / or liquid of the carbonylation reactor and recovering acetic acid from the extracted material. Preferably, the acetic acid is recovered from the liquid reaction composition by continuously extracting liquid reaction composition from the carbonylation reactor and recovering acetic acid from the extracted liquid reaction composition by one or more instantaneous and / or fractional distillation stages wherein the Acetic acid is separated from the other components of the liquid reaction composition, such as iridium catalyst, metal iodide cocatalyst, promoter, methyl acetate, unreacted methanol or reactive derivative thereof, water and acetic acid solvent, which are they can recycle to the reactor to maintain their concentrations in the liquid reaction composition. To maintain the stability of the iridium catalyst during the recovery step of the acetic acid product, the water of the process streams containing iridium carbonylation catalyst for recycling to the carbonylation reactor, should be maintained at a concentration of at least 0. , 5% by weight. Description of the Drawings The invention will now be illustrated by way of example only and with reference to the following examples and accompanying Figures 1 to 5, which graphically represent the rate of carbonylation at different water concentrations for promoted reactions. with ruthenium already different concentrations of methyl iodide and methyl acetate. General Description of the Carbonization Experiments All experiments were performed using a 300 ml zirconium autoclave equipped with a magnetic drive stirrer fitted with gas dispersing impellers, a liquid catalyst injection device and cooling coils. A supply of gas to the autoclave was provided from a ballast vessel, feed gas being provided to maintain the autoclave at a constant pressure. The rate of gas absorption at a certain point in the reaction was used to calculate the carbonylation rate, such as the number of moles of reactant consumed per liter of cold degassed composition of the reactor per hour (moles / l / h), at a particular composition of the reactor (total reactor composition based on a cold degassed volume). The concentration of methyl acetate was calculated over the course of the reaction from the initial composition, assuming that one mole of methyl acetate was consumed for each mole of carbon monoxide consumed. The organic components of the head space of the autoclave were not taken into account. For each discontinuous carbonylation experiment, the catalyst, H2IrCl6, dissolved in a portion of the charge Liquid from the acetic acid / water autoclave was loaded into the liquid injection device. The autoclave was then tested under pressure with nitrogen, ventilated by means of a gas sampling system and flooded with carbon monoxide several times (three times at 3-10 bar gauge). If a promoter or additive was used, it was placed in the autoclave and covered with a portion of the acetic acid charge (approximately 10 g) before the pressure test. The remaining liquid components of the reaction composition were charged into the autoclave by means of a liquid addition port. The autoclave was then pressurized optionally with 5 bar gauge carbon monoxide and slowly vented. The autoclave was then pressurized with carbon monoxide (usually 6 bar gauge) and heated with stirring (1500 rpm) at the reaction temperature, 190 ° C. The total pressure was then raised to 3 bar gauge approximately below the desired operating pressure by feeding carbon monoxide from the ballast vessel. Once the temperature stabilized (approximately 15 minutes), the catalyst was injected using an overpressure of carbon monoxide. The catalyst injector device has an efficiency greater than 90%. The reactor pressure was maintained at a constant value (± 0.5 bar gauge) by feeding gas from the ballast vessel throughout the experiment. The Gas absorption of the ballast vessel was measured using data recording means throughout the course of the experiment. The reaction temperature was maintained within ± 1 ° C of the desired reaction temperature by means of a heating mantle connected to a Eurotherm control system (Registered Trade Mark). In addition, the excess heat of reaction was dissipated by means of cooling coils. Each experiment was performed until gas absorption ceased (ie, less than 0.1 bar per minute of gas consumed from the ballast vessel). The ballast container was then isolated and the reactor was abruptly cooled by the use of the cooling coils. The H2IrCl6 (aqueous solution) was supplied by Johnson Matthey. The acetic acid was obtained from the carbonylation of a mixed feed of methanol / methyl acetate and contained very low amounts of propionic acid and its precursors. Methyl acetate, water and methyl iodide were supplied by Aldrich. [Ru (CO) 4I2] was prepared from [Ru3 (C0) 12] (STREM Chemicals) and iodine (Aldrich). Chromium (III), gallium (III), indium (III) and iron (II) iodides were supplied by STREM Chemicals. The compositions of the charges are given in Table 1. EXAMPLES 1 TO 13 V EXPERIMENTS A to J The general procedure described above was used. The compositions of the fillers are indicated in Table 1. Experiments A to J are separate from the present invention for the reason that no promoter was used or co-promoter was not used or the concentration of water was above the one to which the maximum is presented in the graph of carbonylation rate versus water concentration. Experiment D and Examples 1 and 2 of Table 2 demonstrate the effect of the addition of chromium, added as chromium (III) iodide, on the carbonylation activity using an iridium catalyst promoted with ruthenium (approximately 2 molar equivalents of ruthenium to iridium) at 190 ° C and a total pressure of 28 bar gauge. Table 2 shows the velocity data at various concentrations of methyl acetate (MeOAc) and water. For comparative purposes, further experiments were carried out at 190 ° C and a total pressure of 28 bar gauge, using an iridium catalyst promoted with ruthenium (approximately 2 molar equivalents of ruthenium to iridium) to determine the relationship between the speed of carbonylation and water concentration, at 30% w / w MeOAc and 2.1% methyl iodide (Mel) and at 15% w / w MeOAc and 2.0% w / w Mel. The data from these additional experiments are shown graphically in Figures 1 and 2 together with the data derived from Experiments A to D and Examples 1 and 2. The velocity data in Table 2 and Figures 1 and 2 illustrate the beneficial effect of adding chromium, added as chromium (III) iodide, 0.75 molar equivalent to iridium, to a ruthenium promoted reaction when the carbonylation rate decreases as the water concentration does. For example, at 30% w / w MeOAc, 2.1% w / w Mel and 2.0% w / w water, the addition of chromium increases the carbonylation rate from 5.4 to 15.2 mol / l / hr. The comparison of Example 3 with Experiment B demonstrates the beneficial effect, on the carbonylation rate, of the addition of iron, added as iron (II) iodide, 0.75 molar equivalent to iridium, to a ruthenium promoted reaction to 30% p / p MeOAc, 2.1% w / w Mel and 2.0% w / w water. The addition of iron, under these conditions, increases the carbonylation rate from 5.4 to 10.2 mol / l / hr. The comparison of Experiment E with Example 4, Table 3, demonstrates the beneficial effect, on the carbonylation rate, of the addition of chromium, added as chromium (III) iodide, 0.75 molar equivalent to iridium, to a reaction promoted with ruthenium at a relatively high Mel concentration, of 16.9% w / w, at a water concentration of 2% w / w at 30% w / w MeOAc.

For comparative purposes, further experiments were carried out at 190 ° C and a total pressure of 28 bar gauge, using an iridium catalyst promoted with ruthenium, to determine the ratio between the carbonylation rate and the water concentration at 30 ° C. % p / p MeOAc and 16.9% Mel. The velocity data derived from these additional experiments are shown graphically in Figure 3 together with the data from Experiment E and Example 4. Figure 3 illustrates the beneficial effect of the addition of chromium, 0.75 molar equivalent to iridium, to a ruthenium promoted reaction when the carbonylation rate decreases as the water concentration does to 16.9% w / w Mel and 30% w / w MeOAc, increasing the carbonylation rate from 31.1 to 42, 9 mol / l / hr. The comparison of Example 5 with Experiment H, Table 4, demonstrates the beneficial effect, on the carbonylation rate, of the addition of lithium, added as lithium iodide, a molar equivalent to iridium, to a ruthenium promoted reaction at 30 ° C. % w / w methyl acetate, 8.4% w / w methyl iodide and 2% w / w water. The addition of lithium iodide, under these conditions, increases the carbonylation rate from 15.1 to 30.8 mol / l / hr. In addition, the comparison of Experiment F with Experiment G demonstrates that the addition of lithium iodide to an iridium catalyzed reaction without promoting has a detrimental effect on the carbonylation rate under the same conditions. The velocity data derived from Experiments F to H and of Example 5 are summarized in the following Table.

For comparative purposes, other experiments were carried out at 190 ° C and a total pressure of 28 bar gauge, using an iridium catalyst promoted with ruthenium, both in the absence and presence of lithium iodide, to determine the relationship between carbonylation rate and water concentration, at 30% w / w methyl acetate and 8.4% w / w methyl iodide. The velocity data from these additional experiments are shown graphically in Figure 4, which illustrates the beneficial effect of the addition of lithium iodide to a ruthenium promoted reaction when the rate decreases as the water concentration does. The reaction rate for these experiments was also determined at concentrations of methyl acetate, for example at 15% w / w methyl acetate. The comparison of Experiment I with Example 6 in the following Table demonstrates the beneficial effect of the addition of lithium, added as lithium iodide, at 15% w / w methyl acetate, 0.5% w / w water and 8% p / p methyl iodide.

ExperimenSystem cata- Water (% Velocity / Lithic Example P / P) dad / mol / hr @ 15% MeOAc I Ir / Ru 1: 2 0.5 6.5 6 Ir / Ru / Li 1: 2: 1 0.5 12.2 Figure 5 illustrates the effect, on the carbonylation rate, of the molar ratio of lithium to iridium for a series of reactions promoted with ruthenium at 30% w / w methyl acetate, 2% w / w water and 8.4% p / p methyl iodide. Under these conditions, it can be seen that the optimal molar ratio of lithium to iridium is between 0.5: 1 and 1.5: 1 at both molar ratios of ruthenium to iridium of 2: 1 and 5: 1. Experiment H was repeated using various combinations of promoters and additives, Examples 7 to 14 and Experiments I and J, Table 5. Examples 7 to 11, 13 and 14 demonstrate that various additives, which are all sources of ionic iodide, they are effective as co-promoters under the conditions of the present invention. Examples 8 and 11, with aluminum acetate and cerium acetate respectively, show that co-promoters can be added in their acetate form. The comparison of Experiment J with Example 12 demonstrates that lithium, added as lithium iodide, a molar equivalent to iridium, is a promoter for an iridium catalyst promoted with gallium under the conditions of the present invention. abla 1 Compositions of the charges for reactions promoted with ruthenium in a discontinuous zirconium autoclave of 300 ml or I ^ ) Weight expressed as pure H2IrCl6. -o I abla 2 Cont. Exp./Ej. Water /% p / p Speed Water /% p / p Speed mol / l / hr @ mol / l / hr @ 5% 7.5% MeOAc MeOAc C (741) 5.1 9.2 4.5 6.7 D (804) 5.1 9.2 4.5 5.9 All reactions at a total pressure of 28 bar gauge and 190 ° C with an agitator speed of 1500 rpm. approx. 2.1% Mel at 30% MeOAc approx. 2.0% Mel e 15% MeOAc. Mel's concentration is adjusted slightly downwards based on the approximation that each mole of < \ 3 iridium can consume a maximum of 4 moles of methyl iodide to give [IrfCO ^ I - oo i Table 3 Speed data for reactions iridium / ruthenium catalyzed in 300 ml autoclave a) All reactions at a total pressure of 28 bar gauge and 190 ° C with an agitator speed of 1500 rpm. approx. 16.9% Mel at 30% MeOAc! Mel's concentration is adjusted slightly downwards based on the approximation that each 'mole of iridium can consume a maximum of 4 moles of methyl iodide to give [Ir (CO) 2I4]. " Table 4 Speed data for iridium catalyzed reactions in? N discontinuous zirconium autoclave of 300 ml * O! a) All reactions at a total pressure of 28 bar gauge and 190 ° C with an agitator speed of 1500 rpm. approx. 8.4% Mel at 30% w / w MeOAc The Mel concentration is adjusted slightly downwards based on the approximation that each mole of iridium can consume a maximum of 4 moles of methyl iodide to give [Ir (CO)) 2I4] ~.

Table 5 Effect of various additives on the rate of carbonylation of methanol, catalyzed with iridium, at 30% w / w methyl acetate and about 2% w / w water using several promoters. * VjJ I 11 (858) Ru (CO) 4I2 2: 1 Ce (OAc) 3 hi- 0.5: 1 32.6 dratado J (851) Gal3 2: 1 - - 14,0 12 (855) Gal3 2: 1 Lil 1: 1 17.6 13 (851) Inl3 2: 1 Lil 1: 1 20.6 14 (917) Ru (CO) 4I2 2: 1 Cal2 0.5: 1 28.3 I 1 a) All the reactions at a total pressure of 28 bar gauge and 190 ° C with a stirrer speed of 1500 rpm. approx. 8.4% p / p Mel at 30% MeOAc p / p Mel's concentration is adjusted slightly downwards based on the approximation that each mole of iridium can consume a maximum of 4 moles of methyl iodide to give [Go (CO) 2I4] ".

Claims (4)

1. NOVELTY OF THE INVENTION Having described the present invention is considered as a novelty and, therefore, claimed as property contained in the following claims: 1. A process for the production of acetic acid by carbonylation, with carbon monoxide, of methanol and / or a reactive derivative thereof, in a carbonylation reactor containing a liquid reaction composition comprising an iridium carbonylation catalyst, methyl iodide co-catalyst, a finite concentration of water, acetic acid, methyl and at least one promoter, characterized in that the water concentration is at or below that at which the maximum is presented in the graph of carbonylation rate versus water concentration, and because, in the liquid reaction composition, a co-promoter selected from alkali metal iodides, alkaline earth metal iodides, metal complexes capable of e generate I ", salts capable of generating I" and mixtures of two or more of the foregoing. 2. - A process according to claim 1, characterized in that the concentration of water in the liquid reaction composition is less than 6% by weight. 3. - A process according to claim 2, characterized in that the concentration of water in the liquid reaction composition is less than 4.5% by weight. 4. - A process according to any of the preceding claims, characterized in that methanol and / or methyl acetate are carbonyl. 5. - A process according to any of the preceding claims, characterized in that the concentration of methyl acetate in the liquid reaction composition is from 5 to 40% by weight. 6. - A process according to any of the preceding claims, characterized in that the concentration of co-catalyst of methyl iodide in the liquid reaction composition is from 1 to 20% by weight. 7. - A process according to any of the preceding claims, characterized in that the iridium carbonylation catalyst is present in the liquid reaction composition in a concentration of 500 to 3000 ppm measured as iridium. 8. - A process according to any of the preceding claims, characterized in that at least one of the promoters is chosen from ruthenium, osmium, tungsten, rhenium, zinc, cadmium, indium, gallium and mercury. 9. A process according to claim 8, characterized in that the promoter is ruthenium. 10,. A process according to any of the preceding claims, characterized in that the promoter is present in the liquid reaction composition at a molar ratio of promoter: iridium of [0.5 to 15]: 1. 11. - A process according to any of the preceding claims, characterized in that the co-promoter is an alkali metal iodide. 12. A process according to claim 11, characterized in that the alkali metal iodide is lithium iodide. 13. - A process according to any of claims 1 to 10, characterized in that the co-promoter is an alkaline earth metal iodide. 14. - A process according to any of claims 1 to 10, characterized in that the co-promoter is a metal complex capable of generating I. "15. A process according to claim 14, characterized in that the metal is lanthanum, cerium, aluminum , nickel, iron or chromium 16. A process according to claim 15, characterized in that the metals are in the form of their iodides 17. A process according to any of claims 1 to 10, characterized in that the A promoter is a salt capable of generating I. 18. A process according to claim 17, characterized in that the salt is a quaternary ammonium iodide or a phosphonium iodide 19. A process according to any of claims 1 to 12, characterized because the co-promoter is lithium, the molar ratio of ruthenium to iridium is approximately [2: 1] and the molar ratio of lithium to iridium is of the order of [0.5 to 1.5]: 1. 20. A process according to any of the preceding claims, characterized in that the temperature of the carbonylation reaction is 150 to 220 ° C and the total pressure is 15 to 100 bar gauge.