Preparation of carboxylic acid anhydrides

Claim 1

A process for the preparation of acetic anhydride which comprises reacting methyl bromide or methyl iodide with carbon monoxide in a first reaction zone in the presence of a rhodium catalyst and a promoter for said catalyst at a temperature of 20°-500° C. under a carbon monoxide partial pressure of 0.1-15,000 psi to produce acetyl bromide or acetyl iodide, distilling the resulting reaction mixture to recover said thus-produced acyl bromide or iodide from said first reaction zone and reacting said thus-recovered acetyl bromide or iodide under substantially anhydrous conditions at a temperature of 0°-300° C. in a second reaction zone with a reactant consisting essentially of methyl acetate or dimethyl ether to produce said acetic anhydride and to regenerate said methyl bromide or iodide and distilling the reaction mixture produced in said second reaction zone to separate said acetic anhydride from the remaining components of the reaction mixture of said second reaction zone, said promoter comprising a lithium component.