GB1020088A - Improvements in or relating to the recovery and purification of acrylonitrile - Google Patents

Abstract

Acrylonitrile is recovered and purified from a substantially ammonia-free gaseous reaction product containing hydrogen cyanide and saturated and unsaturated carbonyl compounds in addition to acrylonitrile by cooling and partially condensing the reaction product, washing the cooled, partially condensed product with water to absorb acrylonitrile, hydrogen cyanide and the carbonyls, the cooling and absorption steps carried out while maintaining the pH at less than 3, distilling the aqueous solution to recover a distillate containing acrylonitrile, hydrogen cyanide and the carbonyls, allowing the carbonyls and hydrogen cyanide to react to form cyanhydrins, adjusting the pH of the resulting mixture to less than 4 and separating the cyanhydrins from the acrylonitrile and excess hydrogen cyanide by distillation. The pH is maintained at less than 3 by injection of a spray of sulphuric acid into the gases before condensation. The water used in the absorption step is preferably at a pH of less than 3 before use. The final acrylonitrile containing distillate may be further purified, e.g. by fractional distillation.