Trichloroethylene - Production

Production

Prior to the early 1970s, most trichloroethylene was produced in a two-step process from acetylene. First, acetylene was treated with chlorine using a ferric chloride catalyst at 90 °C to produce 1,1,2,2-tetrachloroethane according to the chemical equation

HC≡CH + 2 Cl₂ → Cl₂CHCHCl₂

The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can either be accomplished with an aqueous solution of calcium hydroxide

2 Cl₂CHCHCl₂ + Ca(OH)₂ → 2 ClCH=CCl₂ + CaCl₂ + 2 H₂O

or in the vapor phase by heating it to 300-500°C on a barium chloride or calcium chloride catalyst

Cl₂CHCHCl₂ → ClCH=CCl₂ + HCl

Today, however, most trichloroethylene is produced from ethylene. First, ethylene is chlorinated over a ferric chloride catalyst to produce 1,2-dichloroethane.

CH₂=CH₂ + Cl₂ → ClCH₂CH₂Cl

When heated to around 400 °C with additional chlorine, 1,2-dichloroethane is converted to trichloroethylene

ClCH₂CH₂Cl + 2 Cl₂ → ClCH=CCl₂ + 3 HCl

This reaction can be catalyzed by a variety of substances. The most commonly used catalyst is a mixture of potassium chloride and aluminum chloride. However, various forms of porous carbon can also be used. This reaction produces tetrachloroethylene as a byproduct, and depending on the amount of chlorine fed to the reaction, tetrachloroethylene can even be the major product. Typically, trichloroethylene and tetrachloroethylene are collected together and then separated by distillation.