CONTINUOUS PROCESS FOR THE PREPARATION OF MALEIC ANHYDRIDE FROM AN AQUEOUS SOLUTION OF MALEIC ACID BY DISTILLATION

摘要

Maleic anhydride of at least 99% by weight purity and containing 0-0À1% by weight of fumaric acid is prepared in a continuous process from an aqueous solution of maleic acid by: (a) Heating the maleic acid solution in a concentration zone at a temperature of between 100 and 150 C. and at a pressure of between 400 and 760 mm. Hg until the water content of the maleic acid is reduced to 0-10% by weight (b) Treating the maleic acid obtained in stage (a) in a conversion zone at a temperature of between 150 and 200 C. and at a pressure of between 40 and 300 mm. Hg until from 10 to 97% by weight of the maleic acid is converted into maleic anhydride, to give a liquid phase of impure maleic acid and a purified gaseous phase containing maleic anhydride and water vapour (c) Treating the impure liquid phase produced in stage (b) with an aqueous solution of maleic acid in a dissolution and filtration zone to provide a solid residue containing the impurities and any fumaric acid which may have been formed, which is removed from the system, and a filtrate consisting of an aqueous solution of purified maleic acid, which is either recycled partly to stage (a) and partly to the impure liquid phase produced in stage (b) or is removed from the system (d) Condensing in a condensation zone the gaseous phase consisting of maleic anhydride and water vapour produced in stage (b) at a temperature higher than the dewpoint of the water vapour present in the gaseous phase, thus obtaining maleic anhydride of the desired purity washing the residual vapour with water and returning, if desired, to stage (a) the solution thus obtained containing maleic acid. The temperature employed in step (a) is preferably 135 C. and pressure 500 mm. Hg. The maleic acid solution used as starting material may be obtained by washing the effluent of a catalytic oxidation reactor for hydrocarbons, such as benzene, with or without the previous condensation of part of the maleic anhydride.