| 摘要 |
A method of purifying crude acrylonitrile from an aqueous solution containing 10 to 30 grams of acrylonitrile per litre, methylvinylketone, cyanobutadiene and divinylacetylene in amounts between 15 and 1,000 ppm., and lactonitrile and acetaldehyde in amounts between 0 and 10 g./1., which aqueous solution is obtained by reacting acetylene with hydrocyanic acid and absorbing the gaseous products in water, consists of a continuous azeotropic distillation of said aqueous solution in a column after adding hydrocyanic acid which increases the volatility of the water-acrylonitrile azeotrope in comparison with that of the water-methylvinylketone azeotrope, a vapour which on condensation gives two immiscible layers, the upper of which is mainly purified acrylonitrile, being drawn off from some point acrylonitrile, being drawn off from some point of the column, preferably two-thirds of the way up. The hydrocyanic acid is preferably present in an amount greater than 0.4 g./1. The column may be in two sections of different diameters and containing at least two sets of bubble plates of different sizes, the aqueous solution being fed between the two sections and the vapour phase drawn off above this point. Steam may be blown through the column. The lower of the two immiscible layers may be recycled to the column. The ratio of the amount of mixture condensed at the column head to the amount drawn off part way up is preferably 1:20. Reference has been directed by the Comptroller to Specification 818,722. |
