Patent ID: 8450524

Claim:
A process for producing carboxylic acid anhydrides by the carbonylation reaction of a carboxylic acid ester, derived from an alcohol and a carboxylic acid, with carbon monoxide containing a small amount of hydrogen in a liquid reaction medium in the presence of a Group VIII B catalyst to produce a carboxylic acid anhydride, the reaction medium comprising the Group VIII B catalyst, an organic halide, the carboxylic acid ester, an alkali metal salt, the carboxylic acid anhydride, the carboxylic acid, N-acetylimidazole as a protecting agent, and ethylidene diacetate (EDA) as an organic promoter, wherein the content of the organic promoter in the reaction system is kept by producing the organic promoter from a side reaction or by further adding the organic promoter into the reaction system, wherein the content of the organic promoter of ethylidene diacetate is kept at 0.5 to 20 wt. %.