Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid anhydrides
Reexamination Certificate
2000-12-26
2003-04-01
Killos, Paul J. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid anhydrides
Reexamination Certificate
active
06541666
ABSTRACT:
The present invention relates to a process for the co-production of acetic anhydride and acetic acid and in particular to a process for the co-production of acetic anhydride and acetic acid by carbonylation of a carbonylatable feedstock comprising methyl acetate and/or dimethyl ether and optionally also comprising methanol and/or water, in the presence of a rhodium carbonylation catalyst, alkyl iodide co-catalyst and an iodide salt promoter.
Processes for the production of acetic anhydride by carbonylation in the presence of a rhodium carbonylation catalyst, alkyl iodide co-catalyst and lithium iodide promoter are known, for example from U.S. Pat. No. 4,374,070 which relates to the production of acetic anhydride in the presence of rhodium, an iodine compound and lithium.
The carbonylation of a feedstock comprising methanol, methyl acetate and water to produce a mixture of acetic acid and acetic anhydride is described in EP-A-087870.
Preparation of acetic acid by isomerisation of methyl formate under substantially anhydrous conditions in the presence of carbon monoxide and a rhodium catalyst, halide promoter and quaternary Group V atom is described in EP-B-0109212.
EP-A-0144949 describes a process for the production of organic carboxylic acids from formic acid and organic esters in contact with a catalyst system consisting essentially of rhodium metal atom and lithium iodide. In the examples relatively large amounts of formic acid are used and acetic anhydride is not produced.
Seuillet et al in Applied Catalysis A 93 (1993) 219-229 describe acetic anhydride synthesis from methyl formate catalysed by rhodium-iodide complexes. According to Seuillet et al, the synthesis proceeds via the homologation of methyl formate into methyl acetate followed by carbonylation of the latter. According to Seuillet et al the influence of various parameters on the two steps is different such that the “one pot” synthesis of acetic anhydride from methyl formate requires a two steps procedure. Such a two step procedure is described in U.S. Pat. No. 5,214,205. According to Seuillet et al when methyl formate is added to conditions optimised for production of acetic anhydride from methyl acetate (methyl formate/methyl acetate=0.1), the initial reaction consists of the production of acetic acid and methyl acetate (via a transesterification process), with the anhydride appearing only when methyl formate has almost disappeared. According to Seuillet et al during these runs, methyl formate and acetic anhydride were never observed simultaneously. Seuillet et al performed their experiments in a batch autoclave.
Japanese laid-open patent application S62[1987]-145041 describes the simultaneous manufacture of acetic acid and acetic anhydride by heating methyl formate and methyl acetate under pressure of carbon monoxide in the presence of a rhodium catalyst, iodine compounds and accelerating agents comprising aluminium and boron compounds.
There remains a need for an improved process for the co-production of acetic anhydride and acetic acid.
It has now been found that if methyl formate and/or formic acid is/are introduced into a process for the co-production of acetic anhydride and acetic acid by carbonylation of a carbonylatable feedstock comprising methyl acetate and/or dimethyl ether and optionally also comprising methanol and/or water, in the presence of a rhodium carbonylation catalyst, alkyl iodide co-catalyst and an iodide salt promoter consisting essentially of an alkali metal iodide and/or alkaline earth metal iodide, not only is acetic anhydride produced at acceptable rates, but the amounts of by-products such as ethylidene diacetate are reduced.
This finding is unexpected particularly in view of the teaching of Seuillet et al that the conditions favourable to the production of acetic anhydride from methyl acetate are unfavourable to the formation of methyl acetate from methyl formate.
Thus according to the present invention there is provided a process for the co-production of acetic anhydride and acetic acid which process comprises introducing a carbonylatable feedstock comprising methyl acetate and/or dimethyl ether and optionally also comprising methanol and/or water, to a carbonylation reactor in which there is maintained a liquid reaction composition comprising acetic anhydride, acetic acid, rhodium carbonylation catalyst, alkyl iodide co-catalyst and an iodide salt promoter consisting essentially of an alkali metal iodide and/or alkaline earth metal iodide, contacting said carbonylatable feedstock with carbon monoxide in said liquid reaction composition to produce acetic anhydride and acetic acid, and introducing to the carbonylation reactor methyl formate and/or formic acid.
In the process of the present invention, the methyl formate and/or formic acid is a valuable source of the components of carbon monoxide and can be used to advantage in a location where a source of these compounds is available adjacent to an existing carbonylation process for the production of acetic anhydride. Furthermore, not only has it been found that the introduction of methyl formate and/or formic acid does not have an adverse effect on the carbonylation rate, but also the presence of these compounds reduces the formation of by-products when the carbonylation process uses an iodide salt promoter consisting essentially of an alkali metal iodide and/or alkaline earth metal iodide.
In the process of the present invention the carbonylatable feedstock comprises methyl acetate and/or dimethyl ether and optionally, also comprises methanol and/or water. Acetic anhydride is produced by the carbonylation of methyl acetate and/or dimethyl ether. Acetic acid is produced from methanol, water, methyl formate and/or formic acid. Thus the proportions of acetic anhydride and acetic acid produced are dependent upon the relative amounts of these components of the feedstock. It is important that the amount of methanol, water, methyl formate and/or formic acid should not be so large that the amount of acetic anhydride produced is insufficient to maintain a concentration of acetic anhydride in the liquid reaction composition. Suitable carbonylatable feedstocks include methyl acetate/methanol mixtures, dimethyl ether/methanol mixtures and methyl acetate/methanol/water mixtures.
The amount of methyl formate and/or formic acid introduced into the carbonylation reactor is suitably in the range from 0.1 to 20% by weight of the total feed of liquid components to the reactor, preferably in the range from 0.1 to 10% by weight of the total feed of liquid components to the reactor, provided that the amount of methanol, water, methyl formate and/or formic acid is not so great that there is no acetic anhydride maintained in the liquid reaction composition in the reactor.
It has been found that methyl formate will be present in the liquid reaction composition, suitably at a concentration in the range from greater than zero to 1000 ppm. However, when formic acid is introduced into the reactor rather than methyl formate, this decomposes more quickly than methyl formate and it has been found that there is a lower standing concentration of formic acid in the liquid reaction composition, suitably in the range from greater than zero to 100 ppm.
The process of the present invention is suitable performed at a temperature in the range from 150 to 220° C., preferably in the range from 175 to 200° C.
The process of the present invention is suitably performed at a pressure in the range from 1000 kPa to 10000 kPa, preferably at a pressure in the range from 2000 to 5000 kPa.
Carbon monoxide used in the present invention is preferably at least 95% pure. Suitable impurities are hydrogen, carbon dioxide, methane, nitrogen, noble gases and C
1
to C
4
hydrocarbons. Preferably, the amount of hydrogen in the carbon monoxide used is in the range from 0 to 10.0% by volume.
The rhodium carbonylation catalyst may be pre-formed and added to the liquid reaction composition or may be formed in situ in the liquid reaction composition. Suitable rhodium compounds wh
Allan Robert Edward
Watson Derrick John
BP Chemicals Limited
Killos Paul J.
Nixon & Vanderhye
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