GB2298200A

GB2298200A - Catalyst system comprising iridium and rhodium catalyst, alkyl halide and at least one ruthenium, osmium or rhenium promoter for use in alcohol carbonylation

Info

Publication number: GB2298200A
Application number: GB9603422A
Authority: GB
Inventors: Martin Francis Giles; John Glenn Sunley
Original assignee: BP Chemicals Ltd
Current assignee: BP Chemicals Ltd
Priority date: 1995-02-21
Filing date: 1996-02-19
Publication date: 1996-08-28
Also published as: GB9603422D0; GB9503383D0

Abstract

A process for the production of a carboxylic acid (R n -COOH) by carbonylation of an alkyl alcohol (R n -OH) and/or a reactive derivative thereof (eg R n -O-CO-R n ) which process comprises contacting an alkyl alcohol and/or a reactive derivative thereof with carbon monoxide in a liquid reaction composition in a carbonylation reactor characterised in that the liquid reaction composition comprises: (a) a catalyst comprising iridium and rhodium, (b) an alkyl halide, (c) at least a finite concentration of water and (d) as promoter, at least one of ruthenium, osmium and rhenium. A catalyst system system is also provided comprising: (a) a catalyst comprising iridium and rhodium, (b) an alkyl halide and (d) as promoter, at least one of ruthenium, osmium and rhenium.

Description

PROCESS FOR THE PRODUCTION OF A CARBOXYLIC ACID The present invention relates to a process for the production of a carboxylic acid by carbonylation of an alkyl alcohol and/or a reactive derivative thereof in the presence of a catalyst comprising iridium and rhodium.

European patent application publication number EP-06 181 83-A relates to a process for obtaining carboxylic acids comprising (n+1) carbon atoms or the corresponding esters, by contacting carbon monoxide with at least one reagent chosen from among compounds having the formulae:(l) R(OH)m;(2)RX;(3)ROR';(4)ROCOR';in which formulae R and R' are identical or different and represent a Ci-ClO hydrocarbyl radical; X represents chlorine, bromine or iodine and m is 1 or 2, the reaction being effected in the presence of a catalytic system comprising at least one rhodium compound, at least one iridium compound or at least one compound incorporating these two metals, and at least one halogenated promoter.The halogenated promoter can take the form of a halide alone or in combination with other elements such as, for example, hydrogen, a Cl-Clo alkyl radical, a Cl-Clo acyl radical or a C6-C10 aryl radical.

Carbonylation processes in the presence of ruthenium and osmium catalysts are also known. Thus, UK patent GB 1234641 describes a process for the production of an organic acid or an ester by carbonylation of an alcohol, halide, ester, ether or phenol in the presence of a noble metal catalyst selected from iridium, platinum, palladium, osmium and ruthenium and their compounds and a promoter which is halogen or halogen compound.

According to Jenner et al in J. Mol. Catalysis 40 (1987) 71-82 ruthenium compounds are effective carbonylation catalysts for converting primary alcohols into acids and esters at high CO pressures. In the reported experiments standard conditions were 450 bar CO pressure and low CO pressures were said to lead to high yields of hydrocarbons and a lower yield of ester.

UK patent application GB 2029409 describes a process for the preparation of aliphatic carboxylic acids and esters by reacting carbon monoxide with alcohols at an elevated pressure of 34 atmospheres or greater in the presence of a ruthenium catalyst and halogen-containing promoter.

Japanese laid open application JP 51080813 to Mitsui Petrochemical Industries Ltd describes a method of producing carboxylic acids and/or esters thereof characterised in that alcohols and carbon monoxide are heated and reacted in the presence of a rhenium catalyst and halogen compounds.

The technical problem to be solved is to provide an improved process for the carbonylation of alkyl alcohols and/or reactive derivatives thereof in the presence of a catalyst comprising iridium and rhodium.

Thus, according to the present invention there is provided a process for the production of a carboxylic acid by carbonylation of an alkyl alcohol and/or a reactive derivative thereof which process comprises contacting an alkyl alcohol and/or a reactive derivative thereof with carbon monoxide in a liquid reaction composition in a carbonylation reactor characterised in that the liquid reaction composition comprises:(a) a catalyst comprising iridium and rhodium, (b)an alkyl halide, (c) at least a finite concentration of water and (d) as promoter, at least one of ruthenium, osmium and rhenium.

Also according to the present invention there is provided a catalyst system for the production of a carboxylic acid by carbonylation of an alkyl alcohol and/or a reactive derivative thereof in the presence of at least a finite concentration of water which catalyst system comprises (a) a catalyst comprising iridium and rhodium, (b) an alkyl halide and (c) at least one of ruthenium, osmium and rhenium.

The present invention solves the technical problem defined above by the use of ruthenium, osmium and/or rhenium promoter.

The use of ruthenium, osmium and/or rhenium promoter, to increase the carbonylation rate, may allow operation at reduced iridium and rhodium concentrations which can have benefits for reduced by-product formation. The use of ruthenium, osmium and/or rhenium promoter may also allow operation under conditions where the concentration of iridium and/or rhodium and, in particular rhodium, in the reaction composition may be limited, for example by solubility and/or stability constraints either in the reactor or in the product recovery stages where the product is separated from the catalyst under conditions of reduced carbon monoxide partial pressure.

The iridium component of the catalyst in the liquid reaction composition may comprise any iridium containing compound which is soluble in the liquid reaction composition. The iridium component of the catalyst may be added to the liquid reaction composition for the carbonylation reaction in any suitable form which dissolves in the liquid reaction composition or is convertible to a soluble form.Examples of suitable iridium-containing compounds which may be added to the liquid reaction composition include IrCI3, IrI3, IrBr3, [Ir(CO)2I]2, [Ir(CO)2C1]2, [Ir(CO)2Br]2, [Ir(CO)2I2]- H+, [Ir(CO)2Br2]- H+, [Ir(CO)2I2] H+, [Ir(CH3 )13 (CO)2]- H+, Ir4(CO)12, IrCl3.4H2O, IrBr3 .4H2O, Ir3 (CO) 12, iridium metal, Ir203, IrO2, Ir(acac)(CO)2, Ir(acac)3, iridium acetate, [Ir3O(OAc)6(H2O)3][OAc] and hexachloroiridic acid H2[IrCl6], preferably, chloride-free complexes of iridium such as acetates, oxalates and acetoacetates, more preferably acetates which are soluble in one or more of the components of the liquid reaction composition such as water, alcohol and/or acid and may be added to the reaction as a solution therein, for example as a solution in acetic acid and/or water.

Preferably, the concentration of the iridium component of the catalyst in the liquid reaction composition is in the range 100 to 6000 ppm by weight of iridium.

The rhodium component of the catalyst in the liquid reaction composition may comprise any rhodium containing compound which is soluble in the liquid reaction composition. The rhodium component of the catalyst may be added to the liquid reaction composition in any suitable form which dissolves in the liquid reaction composition or is convertible to a soluble form. Examples of suitable rhodium-containing compounds which may be added to the liquid reaction composition include [Rh(CO)2Cl]2, [Rh(CO)2I]2, [Rh(Cod)Cl]2, rhodium (III) chloride, rhodium (III) chloride trihydrate, rhodium (III) bromide, rhodium (III) iodide, rhodium (III) acetate and rhodium dicarbonylacetylacetonate.

The concentration of the rhodium component of the catalyst in the liquid reaction composition is any effective amount in the range in the range from 1 ppm by weight of rhodium up to its limit of solubility in the reaction composition or product recovery system, preferably in the range from 10 to 5000 ppm, and typically in the range from 10 ppm to 1500 ppm by weight of rhodium.

The molar ratio of the iridium component to the rhodium component of the catalyst in the liquid reaction composition is suitably in the range 1:0.01 to 1:100, preferably 1:0.1 to 1:10.

The ruthenium, osmium and/or rhenium promoter may comprise any ruthenium, osmium and/or rhenium containing compound which is soluble in the liquid reaction composition. The promoter may be added to the liquid reaction composition for the carbonylation reaction in any suitable form which dissolves in the liquid reaction composition or is convertible to soluble form.

Examples of suitable ruthenium-containing compounds which may be used include ruthenium (Ill) chloride, ruthenium (III) chloride trihydrate, ruthenium (IV) chloride, ruthenium (III) bromide, ruthenium metal, ruthenium oxides, ruthenium (III) formate, [Ru(CO)3 13 ]-H+, tetra(aceto)chlororuthenium(II, III), ruthenium (III) acetate, ruthenium (III) propionate, ruthenium (III) butyrate, ruthenium pentacarbonyl, trirutheniumdodecacarbonyl and mixed ruthenium halocarbonyls such as dichlorotricarbonylruthenium (II) dimer, dibromotricarbonylruthenium (II) dimer, and other organoruthenium complexes such as tetrachlorobis(4-cymene)diruthenium(II), tetrachlorobis(benzene)diruthenium(II), dichloro(cycloocta- 1,5- diene)ruthenium (II) polymer and tris(acetylacetonate)ruthenium (III).

Examples of suitable osmium containing compounds which may be used include osmium (III) chloride hydrate and anhydrous, osmium metal, osmium tetraoxide, triosmiumdodecacarbonyl and mixed osmium halocarbonyls such as tricarbonyldichloroosmium (H) dimer and other organoosmium complexes.

Examples of suitable rhenium-containing compounds which may be used include Re2(CO) l o, Re(CO)5Cl, Re(CO)sBr, Re(CO)5I, ReCl3.xH2O and ReCI5 .yH2O.

Preferably, the iridium-, rhodium-, ruthenium-, osmium- and rheniumcontaining compounds are free of impurities which generate in situ ionic iodides which may inhibit the reaction, for example, alkali or alkaline earth metal or other metal salts.

The molar ratio of each promoter to combined iridium and rhodium components of the catalyst is suitably in the range 0.1:1 to 15:1, preferably 0.5:1 to 10:1.

The alkyl alcohol reactant may have 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably, 1 to 4 carbon atoms and is most preferably methanol. Preferably the alkyl alcohol is a primary or secondary alcohol. The carboxylic acid product of the carbonylation of an alkyl alcohol having n carbon atoms will be a carboxylic acid having n+l carbon atoms.

Suitable reactive derivatives of the alkyl alcohol include the ester of the alcohol and the carboxylic acid product, for example methyl acetate; the corresponding dialkyl ether, for example dimethyl ether; and the corresponding alkyl halide, for example methyl iodide. A mixture of alkyl alcohol and reactive derivatives thereof may be used as reactants in the process of the present invention for example a mixture of methanol and methyl acetate. Preferably, methanol and/or methyl acetate are used as reactants.

At least some of the alkyl alcohol and/or reactive derivative thereof will be converted to, and hence present as, the corresponding ester with the carboxylic acid product in the liquid reaction composition by reaction with the carboxylic acid product or solvent. Preferably, the concentration in the liquid reaction composition, of alkyl ester, is in the range 0.1 to 70% by weight, preferably 0.5 to 50% by weight, most preferably 0.5 to 35% by weight.

Water may be formed in situ in the liquid reaction composition, for example, by the esterification reaction between alkyl alcohol reactant and carboxylic acid product. Water may be introduced to the carbonylation reactor together with or separately from other components of the liquid reaction composition. Water may be separated from other components of reaction composition withdrawn from the reactor and may be recycled in controlled amounts to maintain the required concentration of water in the liquid reaction composition. Preferably, the concentration of water in the liquid reaction composition is in the range 0.1 to 15% by weight, more preferably 1 to 15% by weight and most preferably 1 to 10 % by weight.

Preferably, the alkyl halide has an alkyl moeity corresponding to the alkyl moiety of the alkyl alcohol reactant. Most preferably, the alkyl halide is methyl halide. Preferably, the alkyl halide is an iodide or bromide, most preferably an iodide. Preferably, the concentration of alkyl halide in the liquid reaction composition is in the range 1 to 20% by weight, preferably 4 to 16% by weight.

The carbon monoxide reactant may be essentially pure or may contain inert impurities such as carbon dioxide, methane, nitrogen, noble gases, water and C1 to C4 paraffinic hydrocarbons. The presence of hydrogen in the carbon monoxide and generated in situ by the water gas shift reaction is preferably kept low, for example, less than 1 bar partial pressure, as its presence may result in the formation of hydrogenation products. The partial pressure of carbon monoxide in the reaction is suitably in the range 1 to 70 bar preferably 1 to 35 bar and most preferably 1 to 15 bar.

The pressure ofthe carbonylation reaction is suitably in the range 10 to 200 barg, preferably 10 to 100 barg, most preferably 15 to 50 barg. The temperature ofthe carbonylation reaction is suitably in the range 100 to 300 "C, preferably in the range 150 to 220"C.

Carboxylic acid, such as the carboxylic acid product, may be used as a solvent for the reaction.

Corrosion metals, particularly nickel, iron and chromium should be kept to a minimum in the liquid reaction composition as these may have an adverse effect on the reaction.

The process of the present invention may be performed as a batch or a continuous process, preferably as a continuous process.

The carboxylic acid product may be removed from the reactor by withdrawing liquid reaction composition and separating the acid product by one or more flash and/or fractional distillation stages from the other components of the liquid reaction composition such as iridium and rhodium components of the catalyst, ruthenium, osmium and/or rhenium promoter, alkyl halide, water and unconsumed reactants which may be recycled to the reactor to maintain their concentrations in the liquid reaction composition. The carboxylic acid product may also be removed as a vapour from the reactor.

The invention will now be illustrated by way of example only by reference to the following examples.

In the examples reaction rates are quoted as number of moles of carbon monoxide consumed per litre of cold degassed reactor composition per hour (mol/Vhr).

In the examples the concentrations of components such as methyl acetate and water in the reaction composition during the carbonylation reaction may be calculated from the starting composition, assuming that one mole of ester reactant is consumed for every mole of carbon monoxide that is consumed.

A 150 ml Hastelloy B2 (Trade Mark) autoclave equipped with a Magnedrive (Trade Mark) stirrer and liquid injection facility was used for a series of batch carbonylation experiments. A gas supply to the autoclave was provided from a gas ballast vessel, feed gas being provided to maintain the autoclave at a constant pressure and the rate of gas uptake being calculated (with an accuracy believed to be +1-1%) from the rate at which the pressure falls in the gas ballast vessel.

At the end of each experiment liquid and gas samples from the autoclave were analysed by gas chromatography.

For each batch carbonylation experiment the autoclave was charged with the promoter such as ruthenium (if any) and the liquid components of the liquid reaction composition excluding part (6.5g) ofthe water charge, in which the iridium and/or rhodium components of the catalyst were dissolved.

The autoclave was flushed twice with nitrogen and once with carbon monoxide and was then heated with rapid steady stirring (1000 rpm) to 1900C (+/ 1 0C) under 1 bara of carbon monoxide. The aqueous solution of the iridium and/or rhodium components of the catalyst was then injected into the autoclave under pressure of carbon monoxide. The pressure in the autoclave was subsequently maintained at the desired reaction pressure with carbon monoxide fed on demand from the gas ballast vessel through the liquid injection facility.

Gas uptake from the ballast vessel was measured every 30 seconds and from this was calculated the rate of carbonylation, expressed as moles of carbon monoxide per litre of liquid reaction composition per hour (mol/l/hr). After uptake of carbon monoxide from the ballast vessel had ceased the autoclave was isolated from the gas supply. The contents of the autoclave were cooled to room temperature and the gases were cautiously vented from the autoclave, sampled and analysed by gas chromatography to determine the levels of carbon dioxide and methane by-products. The liquid reaction composition was discharged from the autoclave, sampled and was analysed by gas chromatography which confirmed the formation of acetic acid during the reaction.

To obtain a reliable baseline a number of identical baseline runs may have to be performed to condition the autoclave such that consistent rates are achieved.

This conditioning period is often different from autoclave to autoclave and may depend upon its previous history.

Experiment A A baseline experiment was performed with the autoclave charged with methyl acetate (28.80 g), water (3.673 g), methyl iodide (5.314 g), and acetic acid (45.341 g).

The catalyst solution comprised IrCl3.3H20 (0.331 g) dissolved in water (6.500 g).

The reaction was performed at a pressure of about 22 barg (varying by about i 0.3 barg) and at a temperature of 1900C. The rate of reaction, based upon carbon monoxide uptake, was 9.6 mol/l/hr at a calculated methyl acetate concentration of 15 % by weight and a measured pressure of 22.4 barg. High conversion to acetic acid was observed. The non-condensable gases vented at the end of the experiment were analysed and the measurable gases (nitrogen would be measurable by this method but was not present; hydrogen was not measurable by this analysis method; the % by volume reported is expressed as a percentage of the measurable gases) contained by volume 11.3 % carbon dioxide, 12.5 % methane and carbon monoxide (balance).

This is not an example according to the present invention because the catalyst did not comprise both an iridium and a rhodium component and a promoter comprising at least one of ruthenium, osmium and rhenium was not present in the liquid reaction composition.

Experiments B to I Experiment A was repeated using the reagents and conditions given in Table 1. The results are shown in Table 2. These are not examples according to the present invention.

Example 1 Experiment A was repeated using the reagents and conditions given in Table 1.

The results are shown in Table 2. The rate of reaction, based upon carbon monoxide uptake, was 24.8 mol/l/hr at a calculated methyl acetate concentration of 15 % by weight. High conversion to acetic acid was observed. The noncondensable gases vented at the end of the experiment were measured as before and the measurable gases contained by volume 11.9 % carbon dioxide, 7.3 % methane and carbon monoxide (balance).

This Example is according to the present invention and demonstrates that a catalyst comprising a rhodium component and an iridium component in the presence of a ruthenium promoter is effective in catalysing the carbonylation of methyl acetate to acetic acid.

Examples 2 to 4 Example 1 was repeated using the reagents and conditions given in Table 1. The results are shown in Table 2. These are Examples according to the present invention.

The Examples show a high rate of carbonylation reaction and low methane by- product make. A comparison of Example 3 in which the molar ratio of ruthenium: rhodium: iridium is 2 : 0.1 : 1, with Experiment G having the same amounts of reagents, rhodium and iridium, but having no ruthenium, shows that the addition of the ruthenium promoter in this example increases the carbonylation rate from 11.2 mol/1/hr to 16.6 moVl/hr. Comparison of Example 1 in which the molar ratio of ruthenium : rhodium : iridium is 2:1:1, with Experiment I, having the same amounts of reagents, rhodium and iridium, but having no ruthenium, shows that the addition of the ruthenium promoter in this example increases the carbonylation rate from 16.8 mol/l/hr to 24.8 mol/l/hr.

Table 1

Experiment IrCl3.3H2O RhCl3.3H2O Ru3(CO)12 Methyl Water Methyl Acetic Ru : Ir Ru : Rh (g) (g) (g) Acetate (g) Iodide Acid molar molar (g) (g) (g) Expt. A 0.331 (b) - - 28.80 3.673 (a) 5.314 45.341 Expt. B 0.331 (b) - 0.400 28.80 3.673 (a) 5.314 (c) 44.94 2 1 Expt. C 0.331 (b) - 0.400 28.80 3.673 (a) 5.845 44.41 2.1 Expt. D - 0.246 - 28.80 3.473 (a) 5.05 45.89 Expt. E - 0.246 0.400 28.80 3.473 (a) 5.581 44.959 2 1 Expt. F - 0.025 0.400 28.80 3.673 (a) 5.341 45.220 1 0.05 Expt. G 0.331 (b) 0.025 - 28.80 3.673 (a) 5.34 45.29 Expt. H - 0.025 - 28.80 3.673 (a) 4.81 46.15 Expt. I 0.331 (b) 0.246 - 28.80 3.473 (a) 5.58 45.03 Example 1 0.331 (b) 0.246 0.400 28.80 3.473 (a) 6.111 44.10 2 # 1 2 1 Example 2 0.331 (b) 0.246 0.400 28.80 3.473 (a) 6.111 44.10 2 # 1 2.1 Example 3 0.331 (b) 0.025 0.400 28.80 3.690 (a) 5.872 44.358 2 : 1 1 : 0.05 Example 4 0.331 (b) 0.025 0.400 28.80 3.690 (a) 5.872 44.358 2 : 1 1 : 0.05 a. 6.500g additional water injected with the catalyst (Ir or/and Rh) b. equivalent to 2000 ppm at start of reaction and 1900 ppm at calculated 15 wt. % methyl acetate c. Methyl iodide concentration is low. Experiment C is an identical experiment except the correct methyl iodide concentration was used Table 2

Experiment Rate at 15 wt % CH4 CO2 Reaction Pressure at Methyl Acetate (% v/v) (% v/v) calculated 15 wt. % Concentration (a) (a) methyl acetate (mol/l/hr) (barg) Experiment A 9.6 12.5 11.3 22.4 Experiment B 13.7 14.5 12.4 22.2 Experiment C 13.9 11.2 3.3 22.3 Experiment D 8.7 0.3 7.4 22.7 Experiment E 9.0 1.8 2.9 22.8 Experiment F 1.1 3.5 0.6 22.1 Experiment G 11.2 8.0 12.4 22.6 Experiment H 0.8 - - 22.8 Experiment I 16.8 6.3 12.7 22.3 Example 1 24.8 7.3 11.9 22.6 Example 2 23.0 9.6 17.1 22.3 Example 3 16.6 9.5 4.5 21.9 Example 4 16.5 11.0 11.8 22.2 (a) % by volume of measurable gases (hydrogen not measured by this analysis)

Claims

Claims: 1. A process for the production of a carboxylic acid by carbonylation of an alkyl alcohol and/or a reactive derivative thereof which process comprises contacting an alkyl alcohol and/or a reactive derivative thereof with carbon monoxide in a liquid reaction composition in a carbonylation reactor characterised in that the liquid reaction composition comprises:(a) a catalyst comprising iridium and rhodium, (b) an alkyl halide, (c) at least a finite concentration of water and (d) as promoter, at least one of ruthenium, osmium and rhenium.
2. A process as claimed in claim 1 in which the molar ratio of [each promoter]: [combined iridium and rhodium] is in the range [0.1 to 15]:1.
3. A process as claimed in any one of the preceding claim in which the molar ratio of [iridium]: [rhodium] is in the range 1:[0.01 to 100, preferably 0.1 to 10].
4. A process as claimed in any one of the preceding claims in which the concentration of iridium in the liquid reaction composition is in the range 100 to 6000 ppm and the concentration of rhodium in the reaction composition is in the range 1 ppm up to its limit of solubility in the reaction composition or product recovery system.
5. A process as claimed in any one of the preceding claims in which the concentration of water in the liquid reaction composition is in the range 0.1 to 15%, preferably 1 to 15%, more preferably 1 to 10% by weight.
6. A process as claimed in any one of the preceding claims in which the corresponding ester of the alkyl alcohol and carboxylic acid product is present in the liquid reaction composition at a concentration in the range 0.1 to 70%, preferably 0.5 to 50%, more preferably 0.5 to 35% by weight.
7. A process as claimed in any one of the preceding claim in which the concentration of alkyl halide in the liquid reaction composition is in the range 1 to 20%, preferably 4 to 16% by weight.
8. A process as claimed in any one of the preceding claims in which the alkyl halide is an iodide.
9. A process as claimed in any one of the preceding claims in which the alkyl alcohol has 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms and is most preferably methanol.
10. A process for producing a carboxylic acid by carbonylation of an alkyl alcohol and/or a reactive derivative thereof substantially as herein described with reference to any one of the Examples.