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.
Read more about this topic: Trichloroethylene
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