FR2778657A1 - Production of acetic acid by carbonylation process devoid of a co-promoter - Google Patents

Abstract

A process for the production of acetic acid by carbonylation with carbon monoxide of methanol and/or a reactive derivative in a carbonylation reactor containing a liquid reaction composition devoid of co-promoter and comprising an iridium carbonylation catalyst, methyl iodide co-catalyst, a finite concentration of water, acetic acid, methyl acetate and an aluminum-containing compound. A process for the production of acetic acid by carbonylation with carbon monoxide of methanol and/or a reactive derivative in a carbonylation reactor containing a liquid reaction composition devoid of co-promoter and comprising an iridium carbonylation catalyst, methyl iodide co-catalyst, a finite concentration of water, acetic acid, methyl acetate and an aluminum-containing compound. It is absent of any promoter consisting of ruthenium, osmium, tungsten, rhenium, zinc, cadmium, iridium, gallium and/or mercury. The water concentration is at or below that at which the maximum in the graph of carbonylation rate versus water concentration occurs and the aluminum-containing compound is present as promoter in the liquid reaction composition at a molar ratio of aluminum : iridium of 0. 1:1 - 1.5:1. An Independent claim is made for a process for the production of acetic acid by carbonylation with carbon monoxide of methanol and/or a reactive derivative in a carbonylation reactor containing a liquid reaction composition substantially devoid of co-promoter consisting of alkali metal iodides, alkaline earth metal iodides, metal complexes capable of generating I<-> and/or salts capable of generating I<-> and in the absence in the reaction composition of any promoter.

Description

CARBONYLATION PROCESS WITH A BASED CATALYST

IRIDIUM FOR THE PREPARATION OF ACETIC ACID

The present invention relates to a process for the preparation of acetic acid and, in particular, to a process for the preparation of acetic acid by carbonylation, in the presence of an iridium-based catalyst and an iodide cocatalyst. methyl. The preparation of carboxylic acids by carbonylation processes with a catalyst based

iridium is known and 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 WO-A-95/31426.

WO-A-95/31426 describes a process for preparing 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. carbon, in the presence of a catalytic system based on an iridium compound and a halogenated cocatalyst. The process is characterized by maintaining, in the reaction medium, a volume of water of between more than 0 and%, typically between 0.5 and 8%, preferably between 2 and 8%; an ester volume corresponding to the carboxylic acid and to the alcohol varying between 2 and 40%; and iodides in a soluble form such that the atomic ratio of iodides to iridium is between more than 0 and 10, typically between more than 0 and 3, of

preferably, between more than 0 and 1.5. The volume of co-

halogenated catalyst in the reaction medium is between more than 0 and 10%; typically between 0.5 and 8%, and preferably between 1 and 6%. Iodides

suitable include alkaline metal iodides

earthy and alkali metal, and in particular, lithium iodide. The process of WO-A-95/31426 is,

otherwise, free of promoter.

In EP-A-0643034, a process is described for the carbonylation of methanol and / or one of its reactive derivatives, in the presence of acetic acid, an iridium-based catalyst, methyl iodide, d 'at least a limited concentration of water, methyl acetate and a promoter chosen from ruthenium and osmium. Of

batch and continuous experiments are described there.

In continuous experiments, the water concentration

is just 6.8% by weight.

Our application EP-A N0 0752406, filed on April 18, 1996, describes a process for preparing acetic acid comprising (1) the continuous introduction of methanol and / or one of its reactive derivatives and carbon monoxide. in a carbonylation reactor which contains a liquid reaction composition comprising a

iridium-based carbonylation catalyst, a co-

methyl iodide catalyst, limited concentration of water, acetic acid, methyl acetate and at least one promoter; (2) contacting methanol and / or its reactive derivative with carbon monoxide in the liquid reaction composition to form acetic acid; and (3) recovering acetic acid from the liquid reaction composition, characterized in that there are continuously maintained in the liquid reaction composition, throughout the duration of the reaction, (a) water, in concentration not exceeding 6.5% by weight, (b) methyl acetate, in concentration between 1 and 35% by weight and (c) methyl iodide, in

concentration between 4 and 20% by weight.

In the methods, with promoters, described in EP-

A-0643034 and European application N 96302734.7, it is said that ionic contaminants such as, for example, (a) metals subject to corrosion, in particular, nickel, iron and chromium and (b) phosphines or nitrogen compounds or ligands which are likely to quaternize in situ should be kept at a minimum concentration in the liquid reaction composition as these will have a negative effect on the reaction by generating I- ions in the liquid reaction composition , as these have a negative effect on the speed of the reaction. Similarly, it is said that contaminants such as alkali iodides, for example lithium iodide,

should be kept at a minimum concentration.

In WO-A-96/237757, which relates to the preparation of iridium carboxylates and their use in, inter alia, carbonylation reactions, the use of promoters not being mentioned, it is indicated, unlike WO- A-65/314326, that the alkali or alkaline earth ions are preferably eliminated, since their presence can have an unfavorable influence on the kinetics and the selectivity of the subsequent reactions in which the carboxylates

of iridium will be used as a catalyst.

European patent application N 97310012.6, filed in December 1997, related to a process for the carbonylation of a liquid composition containing a promoter and a co-promoter, in which the co-promoter is chosen from alkali iodides, alkaline earth metals , metal complexes and salts capable of generating

I- ions. The use of a promoter and a co-

promoter gives a process having high yields and

relatively high selectivity.

We have now discovered that the carbonylation process can be carried out without resorting to a co-promoter by using a compound containing

aluminum, as a promoter.

Accordingly, the present invention relates to a process for preparing acetic acid by carbonylation, with carbon monoxide, methanol and / or a reactive derivative thereof in a carbonylation reactor containing a substantially free liquid reaction composition. co-promoter and comprising an iridium-based carbonylation catalyst, a methyl iodide cocatalyst, a limited concentration of water, acetic acid, methyl acetate and a compound containing aluminum, in which the water concentration is equal to or less than that for which the maximum occurs on the curve of the carbonylation rate as a function of the water concentration and the aluminum-containing compound is present, at as a promoter, in the liquid reaction composition in

an aluminum: iridium molar ratio of 0.1: 1 to 1.5: 1.

The present invention uses a liquid reaction composition comprising an aluminum-containing compound. The composition does not require the presence of conventional promoters and / or co-promoters in the carbonylation process. The term “co-promoter” is understood to mean alkali metal iodides, alkaline earth iodides,

metal complex capable of generating I- ions

and / or salts capable of generating I- ions. By “conventional promoters” is meant ruthenium, osmium, tungsten, rhenium, zinc, cadmium,

indium, gallium and mercury.

The increase in the rate of carbonylation for the low low water concentrations of the present invention can allow operation with a reduced concentration of iridium catalyst, while maintaining the rate of carbonylation. This has the advantages of a reduced training speed.

by-products such as propionic acid.

The rate of formation of by-products such as propionic acid, methane, hydrogen and

carbon dioxide can be reduced.

Water can form in situ in the liquid reaction composition, for example, due to the esterification reaction between methanol (reactant) and the acetic acid produced. Small amounts of water can also be produced by hydrogenating methanol to give methane and water. The water can be introduced into the carbonylation reactor at the same time as the other compounds of the liquid reaction composition, or separately. The water can be separated from the other compounds of the reaction composition withdrawn from the reactor and it can be recycled in controlled amounts to maintain the required water concentration in the composition.

liquid reaction.

In EP-A N 0752406 mentioned above, it is said that the rate of the carbonylation reaction increases as the water concentration in the liquid reaction composition is reduced from a concentration greater than 6.5% by weight. by a maximum for a water concentration not exceeding 6.5% by weight, then decreases as we approach very low water concentrations. In Figure 8 of the above-mentioned application, a curve of the reaction rate as a function of the water concentration is given which clearly shows a maximum. It is said that the water concentration at which the rate of carbonylation reaches a maximum increases as the concentration of methyl acetate in the liquid reaction composition increases. It is believed that the water concentration at which the rate of carbonylation 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 maintained below 6%, more preferably below 4.5% by weight. The use at a water concentration as low as that recommended by the present invention has the advantage that the recovery of acetic acid from the reaction composition withdrawn from the carbonylation reactor is facilitated, insofar as the quantity of the water which has to be separated from the acetic acid is reduced; the separation of water and acetic acid is an energy-intensive operation in the recovery process and a reduced water concentration results in a reduction

the difficulty of implementation and / or costs.

In the process of the present invention, suitable reactive derivatives of methanol include methyl acetate, dimethyl ether and methyl iodide. A mixture of methanol and its reactive derivatives can be used, as a reactant, in the process of the present invention. Preferably, methanol and / or methyl acetate are used, as reagents. If methyl acetate or dimethyl ether is used, water as a coreactant is needed to form acetic acid. At least part of the methanol and / or its reactive derivative will be converted, and therefore, present, in the form of methyl acetate in the liquid reaction composition, following its reaction.

reaction with the product acetic acid or the solvent.

In the process of the present invention, the concentration of methyl acetate in the liquid reaction composition is suitably between 1 and 70% by weight, preferably 2 and

% by weight, and more preferably 5 and 40% by weight.

In the process of the present invention, the concentration of methyl iodide cocatalyst in the liquid reaction composition is suitably between 1 and 30% by weight,

preferably between 1 and 20% by weight.

One of the advantages of obtaining high carbonylation rates at low concentrations of

methyl iodide and water through the addition of co-

promoter according to the present invention can be reduced corrosion, an alternative method for increasing the rate being to increase the concentration of methyl iodide, which can lead to increased corrosion. In the process of the present invention, the iridium-based carbonylation catalyst is suitably present in the liquid reaction composition at a concentration between 400 and 5000 ppm, expressed as iridium, preferably between 500 and 3000. ppm, expressed as iridium, and better still, between 700 and 3000 ppm, expressed as iridium. In the process of the present invention, the rate of the carbonylation reaction increases as

the iridium concentration increases.

The iridium-based catalyst in the liquid reaction composition can include any iridium-containing compound 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 which dissolves in the liquid reaction composition or can be converted to a soluble form. Examples of suitable iridium-containing compounds which can be added to the liquid reaction composition include IrCl3, IrI3, IrBr3, [Ir (CO) 2I] 2, [Ir (CO) 2Cl] 2, [Ir (CO) 2Br] 2, [Ir (CO) 2I2] -HA, [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 as metal, Ir203, IrO2, Ir (acac) (CO) 2z, Ir (acac) 3, iridium acetate, [Ir30 (OAc) 6 (Hz20) 3] [OAc], and hexachloro-iridic acid, [H2IrCl6], preferably chlorine-free iridium complexes such as acetates, oxalates and acetoacetates which are soluble in one (or more) compound (s) of the carbonylation reaction such as water, alcohol and / or carboxylic acid. Iridium green acetate which can be used in acetic acid or aqueous acetic acid solution is

particularly preferred.

In the process of the present invention, an aluminum-containing compound is present, as a promoter, in the reaction composition. Preferably, the promoter containing aluminum is present in an effective amount up to the limit of its solubility in the liquid reaction composition and / or in any liquid effluent from the process recycled to the carbonylation reactor originating from step recovery of acetic acid. The aluminum-containing compound is present, as a promoter, in the liquid reaction composition with

an aluminum: iridium molar ratio of 0.1: 1 to 1.5: 1.

The aluminum-containing promoter can be added to the liquid reaction composition for the carbonylation reaction in any suitable form which dissolves in the liquid reaction composition or can be converted to a soluble form. As examples of suitable aluminum-containing compounds which can be added to the liquid reaction composition, either alone or as mixtures, there may be mentioned aluminum oxides, for example, Al2O3; aluminum hydroxides, for example Al (OH) 3; aluminum halides, for example, AlBr3, AlCl3, AlI3 and AlF3, nH20; aluminum alkoxides; aluminum acetates, for example, [Al (OAc) 20H]; mixed iodide-acetate-aluminum compounds; and aluminum hydrides, for example, AlH3 and borated aluminum hydride. Preferred aluminum-containing compounds which can be added to the reaction composition

liquid are [Al (OAc) 20H], AlI3 and iodide compounds

acetate-aluminum mixture.

The carbon monoxide reagent can be essentially pure or can contain inert impurities such as carbon dioxide, methane, nitrogen, noble gases, water and C1 to C4 paraffinic hydrocarbons. The hydrogen present in the carbon monoxide feed and generated in situ by the superactivated water-gas reaction is preferably kept at a low level since its presence can lead to the formation of hydrogenation products. Therefore, the amount of hydrogen in the carbon monoxide reagent is preferably less than 1 mol%, more preferably less than 0.5 mol%, and more preferably less than 0.3 mol%. moles and / or the partial pressure of hydrogen in the carbonylation reactor is preferably less than a partial pressure of 1 bar, preferably less than 0.5 bar and more preferably less than 0.3 bar. The partial pressure of carbon monoxide in the reactor is between more than 0 and 40 bars, typically between 4

and 30 bars.

The total pressure of the carbonylation reaction is suitably between 10 and 200 barg, preferably between 15 and 100 barg, and more preferably between 15 and 50 barg. The temperature of the carbonylation reaction is suitably included

between 100 and 300 C, preferably between 150 and 220 C.

The process of the present invention can be implemented in the form of a batch or continuous process, from

preferably as a continuous process.

The acetic acid produced can be recovered from the liquid reaction composition by removing the vapor and / or the liquid fraction from the carbonylation reactor and recovering the acetic acid from the withdrawn material. Preferably, the acetic acid is recovered from the liquid reaction composition by continuously withdrawing the liquid reaction composition from the carbonylation reactor and by recovering the acetic acid from the withdrawn liquid reaction composition by means of one (or more) ) flash distillation and / or fractional distillation step (s), in which (which) acetic acid is separated from other compounds present in the liquid reaction composition such as iridium catalyst, iodide cocatalyst methyl, promoter, methyl acetate, methanol and / or its unreacted reactive derivative, water and solvent for acetic acid which can be recycled to the reactor to maintain their concentrations in the reactor. liquid reaction composition. To maintain the stability of the iridium-based catalyst during the step of recovering the acetic acid produced, the water present in the process effluents containing the iridium-based carbonylation catalyst intended to be recycled to the reactor carbonylation must be

maintained at a concentration of at least 0.5% by weight.

The invention will now be illustrated by means of examples given by way of illustration only and by

reference to the following examples.

General description of carbonylation tests

All the tests were carried out using a 300 ml zirconium autoclave, equipped with a magnetic stirrer provided with fins to disperse the gas, a means for injecting the liquid catalyst and cooling coils. A gas supply to the autoclave was provided from a ballast vessel, the gas supply serving to maintain the autoclave at constant pressure. The rate of gas absorption at a certain point in the reaction was used to calculate the rate of carbonylation, as "number of moles of reagent consumed per liter of cold degassed reactor composition per hour (mol / l / hr), for a particular reactor composition (reactor composition based on a

cold degassed volume).

The concentration of methyl acetate was calculated during the course of the reaction from the starting composition, assuming that one mole of methyl acetate is consumed for each mole of carbon monoxide that is consumed. Organic compounds present in the headspace of the autoclave

have not been taken into account.

For each batch carbonylation run, the catalyst, H2IrCl6, dissolved in part of the acetic acid / water liquid reactor feed, was introduced through the liquid injection means. The reactor pressure was then tested with nitrogen, the reactor was degassed using a gas sampling system, and flushed with carbon monoxide, several times (3 x 3 - 10 barg). When a promoter or additive was used, this was placed in the autoclave and covered with part of the acetic acid charge (about 10 g), before the pressure test. The remaining liquid compounds of the reaction composition were charged to

the autoclave via a liquid addition line.

The autoclave was then optionally placed under a pressure of 5 barg of carbon monoxide and slowly degassed. The autoclave was then pressurized with carbon monoxide (typically 6 barg) and heated with stirring (1,500 rpm) to reaction temperature, 190 C. The total pressure was then raised to at approximately 3 barg below the desired operating pressure by continuing to introduce carbon monoxide from the ballast vessel. Once the temperature stabilized (about 15 minutes), the catalyst was injected using carbon monoxide overpressure. The catalyst injection means has an efficiency of more than 90%. The reactor pressure was maintained at a constant value (0.5 barg) by injecting gas from the ballast vessel throughout the duration of the test. The absorption of gas from the ballast vessel was measured using data recording means throughout the course of the test. The reaction temperature was maintained at 1 ° C of the desired reaction temperature by means of a heating jacket connected to a Eurotherm control system (brand). In addition, the excess heat of reaction was removed by means of cooling coils. Each test was continued until absorption of gas ceased, that is, until less than 0.1 bar of gas per minute was consumed from the ballast vessel. The ballast vessel was then isolated and the reactor intensively cooled by means of the cooling coils. H2IrC16 (in aqueous solution) was supplied by Johnson Matthey. Acetic acid was obtained by carbonylation of a mixed feed of methanol / methyl acetate and contained very small amounts of propionic acid and its precursors. Methyl acetate, water, methyl iodide, and aluminum acetate were supplied by Aldrich. The compositions of the charges are

shown in Table 1.

EXAMPLES 1 to 4 AND TESTS A to F.

The general method described above was used.

The compositions of the charges are indicated in the

Table 1.

Tests A to C do not form part of the invention because either the compound containing aluminum was not used or a co-promoter was present in the

reaction composition.

Tests D and E show the effect of the addition of Al (OAc) 20H at water concentrations where the rate of carbonylation decreases for increasing water concentrations - that is, at water concentrations which are greater than that for which the maximum occurs on the curve of the carbonylation rate as a function of the water concentration. Under these conditions, the addition of the aluminum compound resulted in a reduction in the rate of carbonylation. A reduction in the amount of propionic acid and its precursors (ethyl iodide and ethyl acetate) formed was observed. Example F illustrates the effect on carbonylation rate of addition of Al (OAc) 20H with a mole ratio of 2.0: 1.0 with iridium. The rate was lower than that observed in the absence of any promoter; see Table 2. However, a reduction in the amount of propionic acid and its precursors (ethyl iodide and ethyl acetate) formed was observed. Examples 1 and 2 show the effect on the carbonylation rate of adding an aluminum-containing compound in the absence of a co-promoter, using an iridium-based catalyst, at 190 C and at a total pressure of 28 barg. Velocity data, at various concentrations of methyl acetate (MeOAc) and water

are shown in Table 2.

Example 3 shows that the promoter based

aluminum can be added as AlI3.

Example 4 illustrates the promoter effect on the carbonylation rate of the addition of Al (OAc) 20H with

a mole ratio of 0.5: 1.0 with iridium.

TABLE 1. Compositions of the feeds for reactions with an iridium-based catalyst in a 300 ml batch-type zirconium autoclave Test / Example MeOAc (g) AcOH (g) Mel (g) Water (g) H21rCl6 (g9 ' ) Additive Quantity (g)

A 60.02 68.99 13.96 6.46 0.642

B 60.02 69.00 13.96 6.40 0.636 -

C 60.00 68.80 13.96 6.41 0.637 Lil 0.209

D 60.00 61.89 13.97 13.71 0.643 - -

E 60.00 61.44 13.97 13.71 0.635 Al (OAc) 20 H 0.253 F 59.99 68.48 13.95 6.41 0.634 AI (OAc) 20H 0.500 1 60 100 68.75 13.96 6 , 40 0, 636 Ai (OAc) 20H 0.250 2 60.04 68.76 13.96 6.40 0.634 AI (OAc) 2OH 0.250 3 60.06 68.40 13.97 6.39 0.635 Ai 13 0.640 4 160 , 01 68.90 13.97 6.40 0.635 Al (OAc) 20H 0.120 a) Weight expressed as H2lrC6lepur O0 O) O, M4 Table 2. Carbonylation rate data for reactions with iridium-based catalyst in a 300 ml zirconium autoclave Test / Example Catalyst system Water Speed / mol / hr at Water Speed / mol / hr at Molar ratio% by weight 30% of MeOAc% by weight 25% of MeOAc A Ir alone 2.1 12, 1 0.9 5.9 B Ir only 2.0 13.3 0.9 6.0 C Ir / Li 1: 1 2.0 6.3 0.9 4.4 D Ir only 6.7 19.6 5.5 17.4 E Ir / AI 1: 1 6.7 15, 1 5.5 13.2 F Ir / AI 1: 2 2.0 7.9 09 5.8 1 Ir / AI 1: 1 2 , 0 16.4 0.9 11.1 2 Ir / AI 1: 1 2.0 17.1 0.9 9.9 3 Ir / AI 1: 1 2.0 15.6 0.9 10.6 4 Ir / AI 1: 0.5 2.0 17.3 0.9 11.0 J a) All reactions for a total pressure of 28 barg and 190 C, with a stirring speed tion of 1,500 rpm. About 8.4 wt% MeI to 30 wt% MeOAc.

c The MeI concentration is adjusted slightly downward on the assumption that each mole of iridium can consume a maximum of 4 moles of methyl iodide for

give [Ir (CO) 214] -.

Claims (10)

1. Process for preparing acetic acid by carbonylation, with carbon monoxide, methanol and / or one of its reactive derivatives in a carbonylation reactor containing a liquid reaction composition essentially free of co-promoter and comprising an iridium-based carbonylation catalyst, a methyl iodide cocatalyst, a limited concentration of water, acetic acid, methyl acetate and an aluminum-containing compound, in which the water concentration is equal to or less than that for which the maximum occurs on the curve of the carbonylation rate as a function of the water concentration and the compound containing aluminum is present, as promoter, in the reaction composition liquid in an aluminum: iridium molar ratio of 0.1: 1 to 1.5: 1. 2. The method of claim 1, wherein any promoter consisting of ruthenium, osmium, tungsten, rhenium, zinc, cadmium, indium, gallium and / or mercury is absent from the liquid reaction composition. 3. Method according to one of the claims above, in which the concentration of iridium-based carbonylation catalyst in the liquid reaction composition is between 400 and 5000 ppm, expressed as iridium, preferably between 500 and 3000 ppm, expressed as iridium, and more preferably between 700 and 3000 ppm, expressed as iridium, the concentration of methyl acetate in the liquid reaction composition is between 1 and 70% by weight, preferably between 2 and 50% by weight and more preferably between 5 and 40% by weight. weight and the concentration of methyl iodide in the liquid reaction composition is between 1 and 30% by weight, preferably between 1 and 20% by weight. 4. Process for preparing acetic acid by carbonylation, with carbon monoxide, methanol and / or a reactive derivative thereof in a carbonylation reactor containing a liquid reaction composition essentially free of co-promoter consisting of alkali iodides, alkaline earth iodides, metal complexes capable of generating I- ions and / or salts capable of generating I- ions and in the absence, in the reaction composition, of any promoter consisting of ruthenium, osmium, tungsten, rhenium, zinc, cadmium, indium, gallium and / or mercury, said reaction composition comprising an iridium-based carbonylation catalyst in a concentration of between 500 and 3000 ppm, expressed as iridium, a methyl iodide co-catalyst in a concentration of between 1 and 30% by weight, a limited water concentration , acetic acid, methyl acetate in a concentration between 1 and 70% and a compound containing aluminum, in which the water concentration is equal to or less than that for which the maximum occurs on the curve of the carbonylation rate as a function of the water concentration and the aluminum-containing compound is present, as a promoter, in the liquid reaction composition with a molar ratio aluminum: iridium from 0.1: 1 to 1.5: 1. 5. Method according to one of the claims above, in which the water concentration in the reaction composition is maintained at a value less than 6% by weight. 6. The method of claim 5, wherein the concentration of water in the reaction composition is maintained at a value less than 4.5% by weight. 7. Method according to one of claims above, wherein the aluminum-containing promoter is added to the reaction composition as an aluminum-containing compound selected from the group consisting of aluminum oxides, aluminum hydroxides, aluminum halides. aluminum, aluminum alkoxides, aluminum acetate, iodide-aluminum acetate compounds, hydrides aluminum and their mixtures. 8. The method of claim 7, wherein the aluminum oxide is A1203; aluminum hydroxide is Al (OH) 3; the aluminum halide is AlBr3, AlCl3, AlI3 and AlF3, nH20; aluminum acetate is [Al (OAc) 20H]; or the aluminum hydride is AlH3 or borated aluminum hydride. 9. Method according to one of claims above, wherein the aluminum-containing promoter is added to the reaction composition as an aluminum-containing compound selected from the group consisting of [Al (OAc) 20H], AlI3 and mixed iodide-acetate-aluminum compounds. 10. Acetic acid prepared according to one of previous claims.