GB821958A - Purifying acrylonitrile by distillation - Google Patents

Abstract

Acrylonitrile is obtained from a dilute aqueous solution thereof, which contains lactonitrile as an impurity, by subjecting the solution to steam-stripping while maintaining the pH of the solution at about 6 to 9 by addition of an hydroxide, phosphate, borate, or carbonate of an alkali or alkaline-earth metal, or a corresponding ammonium compound. Under these conditions the lactonitrile is dissociated into acetaldehyde and hydrogen cyanide; and these compounds distil over with the acrylonitrile, so that the residue may safely be discharged to waste. On condensation, the distillate stratifies into a water layer and an acrylonitrile layer. The water layer may be returned as reflux to the stripping column. The acrylonitrile layer, which contains acetaldehyde and hydrogen cyanide, is further treated to obtain a pure product. In an example, an aqueous acrylonitrile solution, obtained by water-scrubbing a gas from the reaction of HCN with acetylene, and having a total HCN concentration of 2140 p.p.m. of which 1140 p.p.m. is as free HCN and the remainder is in the form of lactonitrile, is adjusted to a pH of 6.3 by the addition of 0.5N caustic soda. The solution is then stripped with steam over a period of 20 minutes at 100 DEG C. After stripping, the concentration of HCN in the column-bottoms, either in the form of lactonitrile or as free HCN, is found to be only 78 p.p.m.ALSO:Acrylonitrile is obtained from a dilute aqueous solution thereof, which contains lactonitrile as an impurity, by subjecting the solution to steam-stripping while maintaining the pH of the solution at about 6 to 9 by addition of an hydroxide, phosphate, borate or carbonate of an alkali or alkaline-earth metal, or a corresponding ammonium compound. Under these conditions the lactonitrile is dissociated into acetaldehyde and hydrogen cyanide; and these compounds distil over with the acrylonitrile, so that the residue may be safely discharged to waste. On condensation, the distillate stratifies into a water layer and an acrylonitrile layer. The water layer may be returned as reflux to the stripping column. The acrylonitrile layer, which contains acetaldehyde and hydrogen cyanide, is further treated to obtain a pure product. In an example, an aqueous acrylonitrile solution, obtained by water-scrubbing a gas from the reaction of HCN with acetylene, and having a total HCN concentration of 2140 p.p.m. of which 1140 p.p.m. is as free HCN and the remainder is in the form of lactonitrile, is adjusted to a pH of 6.3 by addition of 0.5 N caustic soda. The solution is then stripped with steam for 20 minutes. After stripping, the total concentration of HCN in the column-bottoms is only 78 p.p.m.