Patent ID: 7714165

Claim:
A process for the preparation of unsaturated carboxylic anhydrides of the general formula I, comprising: R—C(O)—O—C(O)—R (I), preparing a ketene; reacting the ketene with an unsaturated carboxylic acid of the general formula II R—COOH (II), in a first reaction region to produce a crude anhydride mixture; further reacting the crude anhydride mixture in a second reaction region; and separating the further reacted crude anhydride mixture in a rectification column to obtain a carboxylic acid fraction at a top of the rectification column, a fraction of purified unsaturated carboxylic anhydride of formula (I) between a middle and lower region of the rectification column and a fraction of unreacted starting materials and intermediate reaction materials formed in the first and second reaction regions in an upper portion of the rectification column; wherein the process for the preparation of unsaturated carboxylic anhydrides of the general formula I is continuous, the rectification column has a top, upper, middle and lower region and a bottom, the bottom of the rectification column is charged with an inert vaporization oil, the carboxylic acid fraction obtained at the top of the rectification column is recirculated to ketene production, the unreacted starting materials and intermediate reaction materials formed in the first and second reaction regions are recirculated to one or both of the first and second reaction regions, the purified unsaturated carboxylic anhydride of formula (I) is isolated, and R is an unsaturated organic radical having from 2 to 12 carbon atoms.