Patent ID: 8084640

Claim:
A continuous process for preparing an unsaturated carboxylic anhydride of formula (I): R—C(O)—O—C(O)—R (I) wherein R is an unsaturated organic radical having 2 to 12 carbon atoms, comprising: feeding a carboxylic acid of formula (II) R—COOH (II) wherein R is as defined above, and an aliphatic carboxylic anhydride to a reaction region containing a heterogeneous catalyst in a molar ratio of carboxylic acid to aliphatic carboxylic anhydride of 1.9/1 to 2.1/1; transanhydridizing the aliphatic carboxylic anhydride with the carboxylic acid of formula (II) in the reaction region containing a heterogeneous solid-state catalyst; and separating the unsaturated carboxylic anhydride of Formula (I), a carboxylic acid obtained by hydrolysis of the aliphatic carboxylic anhydride and unconverted reactants in a rectification column having an upper, middle and lower region, wherein an inert boiling oil is initially charged in the bottom of the column, the carboxylic acid formed as a by-product is withdrawn at the top of the column, the unconverted reactants are recycled into the reaction region and the product of the formula I is obtained via a side draw, between the middle and lower column region.