GB1227887A - - Google Patents

Abstract

1,227,887. Anhydrides of polycarboxylic acids. LUWA A.G. 9 Dec., 1968 [13 Dec., 1967], No. 58436/68. Heading C2C. , A method for the continuous production of an anhydride from a polycarboxylic acid comprises, as a first stage, subjecting a dilute solution of the acid to concentration by thin film evaporation of water therefrom, as a second stage,subjecting the concentrated acid, substantially without cooling, to thin film heat treatment to effect dehydration thereof and, as a third stage, effected prior to any partial condensation, rectifying the vaporous anhydride to separate the anhydrate from any impurities present therein. The example prepares maleic anhydride in an apparatus in which: pressure control means are placed between the first and second stages to allow of different pressures being used in each; the impurities from the third stage are recycled to the second; and the rectified anhydride is condensed in a triple condenser system, pure anhydride being drawn off from the first condenser and water/anhydride mixture from the second which is recycled to the process, while in the third condenser any remaining anhydride is washed out of the gases and the resulting highly dilute maleic acid recycled if desired. Reference is also made to dehydrating citraconic and phthalic acids. The process may be operated under reduced, normal or elvated pressures.