GB2140004A - Catalytic production of carboxylic acids or anhydrides from olefins - Google Patents

Abstract

A carboxylic acid or an anhydride is prepared by reacting, at elevated temperature and superatmospheric pressure, an olefin with carbon monoxide and a carboxylic acid in the liquid phase and in the presence of a supported Group VIII metal catalyst. The Group VIII metal is preferably rhodium.

Description

SPECIFICATION Preparation of carboxylic acids or anhydrides This invention relates to a process for the reaction of an olefin with a carboxylic acid and carbon monoxide to form a carboxylic acid or anhydride.

The reaction of an olefin with carbon monoxide and a carboxylic acid to form anhydrides and acids has been previously described in UK Patent Nos 1,398,530; 1,367,607 and 1,448,010 in which the use of a soluble Group VIII noble metal catalyst is disclosed. The catalysts described are either used in solution as a liquid phase catalyst or on an inert support and the reaction effected in the vapour phase.

It is an object of the present invention to provide a process using a supported metallic catalyst with the carboxylic acid reactant in the liquid phase.

According to the present invention a process for the preparation of a carboxylic acid or anhydride comprises reacting at elevated temperature and superatmospheric pressure an olefin with carbon monoxide and a carboxylic acid the latter being in the liquid phase, in the presence, as catalyst, of an effective amount of a supported noble metal in metallic form of Group VIII of the Periodic Table.

Preferably the process is effected in the presence of hydrogen to assist in maintaining the Group Villi noble metal in the metallic state. Conveniently the partial pressure of hydrogen is at least equal to 5% of the total pressure e.g. to 20% of the total pressure, but higher levels of hydrogen can be used if required.

Conveniently the Group VIII noble metal is rhodium.

A suitable inert support for the rhodium is carbon, silica or alumina or the wall of a reaction vessel.

Alternatively the rhodium can be in the form of a rhodium sponge.

The support can also be a graphitised carbon as described in UK Patent No 1565074.

The graphitised carbon may be prepared by heat treating a carbon starting material such as an oleophilic graphite described in GB 1,168,785 or a carbon black. Preferably the starting material has a BET surface area of at least 100 more preferably at least 500 m2/g. The preferred heat treatment for preparing the graphitised carbon comprises successive (i) heating in an inert atmosphere at 900 to 3300"C, (ii) oxidizing at 300 to 1 2000C, preferably 300 to 600"C, (iii) heating in an inert atmosphere at 900 to 3000"C.

The amount of rhodium on the support can be from 0.5% by wit upwards, conveniently 1 -10% by wit based on the support.

Conveniently the olefin is a C2 to C10 olefin e.g.

ethylene, propylene, a butene, pentene, hexene or the like.

Conveniently the carboxylic acid is an aliphatic monocarboxylic acid such as acetic acid, propionic acid, butyric acid or the like.

Conveniently the molar ratio of carbon monoxide to olefin is in the range 1.10 to 10:1.

Preferably the process is effected at temperatures in the range 140"C to 250"C and pressures of 40 bar to 140 bar although conditions outside these limits can be used if desired provided the carboxylic acid reactant is maintained in the liquid phase.

Preferably a halide-containing promoter is present with the catalyst, selected for example from iodides and bromides, particularly lower alkyl iodides such as methyl or ethyl iodide.

Preferably the atomic ratio of halide: Group VIII metal is greater than 10:1 preferably greater than 100:1 and more preferably greater than 250:1 for example from 250:1 to 750:1.

Water can be added to the reaction but when this is done anhydride is converted to acid. Preferably, therefore, when the object is to maximise production of anhydrides, water is excluded. In this case anhydrous or substantially anhydrous reactants are preferably employed.

The invention is illustrated by the following examples: Example 1 Acetic acid (55 g), ethyl iodide (10 g) and 5% metallic rhodium on carbon (0.2 g) were charged to a stainless steel autoclave which was pressured to 800 psig with a 1:1 mixture of CO and ethylene and to a further 60 psig with H2 at room temperature. The vessel was then heated and stirred for 20 minutes at 220"C. At this temperature the initial pressure was 1400 psig.

Gas Chromatography (G.C.) analysis of the reaction mixture showed it to contain 6.9 g of acetic anhydride, 1.6 g of acetopropionic anhydride and 5.5 g of propionic acid. These products were formed in a two step reaction in which firstly the acetic acid, ethylene + carbon monoxide formed aceto propionic anhydride which then reacted with acetic acid to form acetic anhydride and propionic acid.

Example 2 The rhodium on carbon catalyst was filtered off from the reaction solution of Example 1, washed with acetone and dried in an oven at 800C. The reaction was then repeated exactly as before, using the recovered rhodium on carbon as catalyst. G.C.

analysis of the second reaction mixture showed it to contain 6.6 g of acetic anhydride, 1.4 g of acetopropionic anhydride and 5.1 g of propionic acid. Hence, no significant loss in activity occurred on recycling the catalyst.

After removal of the rhodium on carbon, the reaction mixture was analysed to determine the concentration of dissolved rhodium and found to contain only 6 ppm. The following comparative experiment showed that this small amount of dissolved rhodium could not accountforthe high activity of the catalyst mixture: the reaction was repeated under identical conditions except that 6 ppm of dissolved rhodium (as RhC13) were used in place of the rhodium on carbon. The rate of form tion of products was much slower; after 3 hours only 2.4 g of acetic anhydride, 0.3 g of acetropionic anhydride and 2.8 g of propionic acid were formed.

Example 3 A stainless steel autoclave was charged with a mixture of propionic acid (60 g), ethyl iodide (10 g) and 5% metallic rhodium on carbon (0.2 g).

Carbon monoxide (300 psig), ethylene (300 psig) and hydrogen (60 psig) were then pressed into the autoclave at room temperature. The vessel was stirred for 20 minutes at 220"C. At this temperature the initial pressure in the reaction was 1100 psig.

G.C. analysis of the reaction mixture showed it to contain 3.2 g of propionic anhydride.

The process described in the above examples has two main advantages over the prior art systems: (i ) The reaction using the hetrogeneous catalyst can be performed in the liquid phase.

(ii) it is relatively easy to recover and recycle the catalyst.

Claims (6)

1. A process for the preparation of a carboxylic acid or an an hydride which process comprises reacting at elevated temperature and superatmospheric pressure an olefin with carbon monoxide and a carboxylic acid the latter being in the liquid phase in the presence, as catalyst, of a effective amount of supported noble metal in metallic form of Group VIII of the Periodic Table.

2. A process as claimed in claim 1 wherein a halide-containing promoter is present.

3. A process as claimed in claim 1 or claim 2 wherein hydrogen is present in sufficient amount to assist in maintaining the Group VIII metal in the metallic state.

4. A process as claimed in any one of the preceding claims wherein the support is carbon, silica or alumina.

5. A process as claimed in any of claims 1 to 3 wherein the support is the wall of a reaction vessel.

6. A processforthe production of a mixture containing one or more of acetic anhydride, propionic acid and aceto propionic anhydride which process comprises reacting at a temperature of 140 to 2500C and a pressure of 40 to 140 bar ethylene with carbon monoxide and acetic acid the latter being in the liquid phase in the presence of hydrogen and, as catalyst, an effective amount of supported rhodium in the metallic form.