Verfahren zur Herstellung von reinem fumarsaeurefreiem Maleinsaeureanhydrid aus Maleinsaeure oder deren waessrigen Loesungen

摘要

Maleic anhydride, 99.7 to 99.8% pure and free from fumaric acid, is produced by introducing maleic acid, or an aqueous solution or suspension containing at least 50% by weight thereof, into maleic anhydride boiling at atmospheric or reduced pressure thereby vaporizing maleic anhydride and water; cooling the vapours by 3 to 30 DEG C., preferably 5 to 20 DEG C., but not below 100 DEG C., in a first condensation zone; removing the condensed maleic anhydride; cooling the remaining vapours to 30 DEG to 80 DEG C. below that of the first condensation zone, but not below the dew point of water vapour at the prevailing pressure and not below 53 DEG C.; returning the condensate to the vaporizing mixture and condensing the water vapour leaving the second condensation zone. In a specific embodiment maleic acid, or an aqueous solution or suspension thereof, is passed from vessel 1 into vaporizer 2 which contains boiling maleic anhydride at 110 DEG to 200 DEG C. and 50 to 760 mm.Hg., being preferably 115 DEG to 140 DEG C. at 90 to 150 mm. Hg. It is convenient to maintain an amount of anhydride, advantageously 70 to 95% by weight of the contents of the vessel, in 2 such that the mixture remains homogeneously liquid and to introduce the maleic acid into 2.3 to 17 times its own weight of anhydride. The vapours are passed through column 3, maintained at the same temperature as 2, into the first condensation zone 4, where they are cooled by 3 to 30 DEG C. to condense part of the anhydride (approx. 15 to 35%) contained therein, which is collected in pure form in vessel 5. The remaining vapours are cooled in the second condensation zone (6) to such a temperature that the bulk of anyhdride is separated in lquid form but the water vapour remains substantially uncondensed. The condensate from 6 is passed via pipe 7 and column 3 to the vaporizing mixture in 2 and the residual vapours are condensed in column 8, collected in vessel 9 and may be used for washing maleic anhydride gases from the combustion products of benzene. The ratio between maleic anhydride condensed in the first zone to that in the second, controlled by the temperature of the two zones, is 1:6 to 1:1. Examples are given.