GB821996A - Purification of perchloroethylene - Google Patents

Abstract

A process for the separation of perchloroethylene from a composition containing also trichloroethylene and symmetrical tetrachloro ethane comprises subjecting the composition to a first distillation, rejecting the major portion of the trichloroethylene as the low boiling fraction and collecting the remainder of the composition comprising mainly perchloroethylene and symmetrical tetrachloroethane and subjecting this remainder to a second distillation, rejecting substantially all of the symmetrical tetrachloroethane as distillation bottoms, and collecting the low boiling fraction from the second distillation and subjecting this fraction to a third distillation and collecting purified perchloroethylene as the bottoms product therefrom. Preferably any inorganic compounds which may be present are removed before the distillations commence. Distillation may be effected at increased or reduced pressure, but atmospheric pressure is preferred. In an example, a mixture comprising trichloroethylene 68.0%, perchloroethylene 23.5%, and tetrachloroethane 6.8% was fed at 87.8 DEG C. to the 24th plate of a 36 theoretical plate column and distilled to give a top fraction containing 99.86% and a bottom fraction comprising perchloroethylene 84.6% and tetrachloroethane 15.9% which was redistilled in a column with a feed temperature of 123 DEG C., giving an overhead product containing 99.7% of perchloroethylene. This product was redistilled using a temperature of 121 DEG C. at the feed plate and a top temperature of 116 DEG to 120 DEG C. to produce a bottoms fraction which is pure perchloroethylene. In a modified process in which the trichloroethylene constitutes only a minor quantity of the initial composition, the first and second distillations are consolidated into one. Specifications 468,921, [Group IV], and 793,205, [Group IV (b)], are referred to.