GB719911A - Purifying acrylonitrile by extractive distillation - Google Patents

Abstract

Acrylonitrile is purified from acetonitrile by submitting the crude acrylonitrile to extractive distillation employing water as extractant and maintaining a very high concentration of water in the liquid phase in the distillation column, whereby purified acrylonitrile vapours leave the head of the column together with water vapours. The overhead vapours are condensed, and the condensate is allowed to separate into two liquid layers; the aqueous layer is returned to the column as reflux, and the acrylonitrile layer is submitted to further distillation to remove water. In an example, 404 parts per minute of a vapour mixture containing acrylonitrile (94 per cent.), acetonitrile (3 per cent.) and water (3 per cent.), are fed to the second tray from the base of a 30-tray perforated plate column, while 1,600 parts per minute of water at 70 DEG -80 DEG C. are fed to the second tray from the top of the column. The temperature of the column-reboiler is maintained at about 85 DEG C.; and the liquid-temperature in the column below the water feed point is maintained at about 71 DEG C. The upper layer of the distillate contains acrylonitrile (95.5 per cent.), water (3.5 per cent.), and less than 1 per cent. of acetonitrile. The base product, withdrawn from the reboiler at the rate of 1,659 parts per minute contains water (96.6 per cent.), acetonitrile (0.4 per cent.), and acrylonitrile (2.3 per cent.) This product is distilled in a conventional column to recover a distillate containing the acrylonitrile, which is recycled to the extractive distillation.