GB695636A - Improvements in or relating to process of purifying acrylonitrile - Google Patents

Abstract

An aqueous solution of acrylonitrile containing volatile impurities is purified by contacting the aqueous solution with a stream of acetylene to strip the volatile impurities therefrom and to obtain a water solution of acrylonitrile substantially free from volatile impurities. The process is of particular utility in the case of acrylonitrile solutions resulting from the reaction of acetylene and hydrogen cyanide in the presence <PICT:0695636/IV (b)/1> of cuprous chloride, the volatile impurities comprising chlorobutadiene, monovinyl acetylene and divinyl acetylene. The acrylonitrile solution freed from volatile impurities may be subjected to steam stripping for recovery of the acrylonitrile whilst the gas fraction consisting of acetylene and the volatile impurities may be passed into an oil absorber where the oil soluble impurities are preferentially absorbed in a suitable oil such as wash oil or other nonreactive aliphatic or aromatic solvent, e.g. a refined hydrocarbon or mineral oil, although mono- and polyaric alcohols such as glycerine and glycol, as well as esters such as dibutyl phthalate may also be used. The acetylene which passes on may be re-used in the acrylonitrile synthesis. The purification process may be carried out at atmospheric or superatmospheric pressure. In the drawing, acetylene and hydrogen cyanide are passed into the reactor 10 containing a hydrochloric acid solution of cuprous chloride and the reaction products comprising acrylonitrile, unreacted acetylene and hydrogen cyanide, together with small amounts if acetaldehyde, chlorobutadiene, monovinyl acetylene, divinyl acetylene, cyanobutadiene and lactonitrile are cooled by cooler 14 and then passed into the absorber 16 to which water is supplied by pipe 17. The acetylene being largely insoluble in water passes out by pipe 18 and enters oil scrubber 20 whilst the absorber 16 is fed with acetylene gas by pipe 21 in an amount sufficient to transfer to the gas phase the chlorobutadiene, monovinyl acetylene and divinyl acetylene and the acetylene thus introduced along with the excess acetylene introduced with the reaction product enters the oil scrubber 20 via pipes 18 and 19. The oil in the scrubber dissolves out the impurities present in the acetylene and the scrubbed out impurities are passed to purifying means 23 from which the purified oil leaves by pipe 24. The oil may be re-introduced to the oil scrubber by pipe 25 whilst the scrubbed acetylene is returned to the acetylene supply line by pipe 12A. The recycled acetylene may be continuously or intermittently purged at 26. The purified aqueous solution of acryonitrile passes from the absorber 16 to the stripper 28 where the arylonitrile is boiled out of the solution and then passes to condenser 33 where it is liquefied. The liquefied product which contains water is passed to separator 34 and the upper layer which consists of acrylonitrile containing a little water is then withdrawn and may be dehydrated whilst the lower water layer is returned to the stripper 28.