GB1049427A - Process for purifying acrylonitrile - Google Patents

Abstract

Acrylonitrile is freed from aldehydes and ketones by a process wherein crude acrylonitrile, which has been obtained by aqueous extraction from acrylonitrile-containing gases of reaction, subsequent separation of the crude acrylonitrile from the main portion of water by distilling in a stripper column, and separation from the distillate of the acrylonitrile-containing organic phase, which process comprises, if necessary, enrichment of the crude acrylonitrile with gaseous hydrocyanic acid, addition of an alkaline reaction medium as a catalyst for the formation of cyanohydrins, subsequent acidification with a mineral acid or an organic acid in a quantity at least sufficient for the neutralization of the previously utilized alkali, removal by distillation of substantially all of the water and, simultaneously at least the major portion of the free hydrocyanic acid, preferably returning the head fraction of the last distillation to the purifying process, especially to the cyanhydrin forming steps. Thin film evaporators are preferred in the rapid distillation stages. The invention is described with reference to a flow sheet (not shown) which provides for a continuous process and comprises four fractional distillation columns.