Chlorination and dehydrochlorination reactions relevant to the manufacture of trichloroethene and tetrachloroethene: Part 1. Reaction pathways

Factors which affect the selectivity of the chlorination of 1,2-dichloroethane and the associated dehydrochlorination reactions have been examined using approximate thermodynamic calculations, equilibrium measurements, and a continuous flow micro-reactor. There is a balance between surface and gas-phase chemistry within the system. Heterogeneous catalysis is not necessary to effect dehydrochlorination of 1,1,2,2-tetrachloroethane to trichloroethene but an attapulgite-supported copper(II) chloride catalyst favours formation of pentachloroethane and its dehydrochlorination product, tetrachloroethene. The latter is the thermodynamic minimum of the system. Below 473 K and with long reaction times (2 h, batch reactor), radical chlorination to form pentachloroethane is dominant. Above 573 K and under flow conditions, free radical dehydrochlorination to form trichloroethene becomes dominant. Heterogeneous chlorination under flow conditions provides a route to pentachloroethane and thence tetrachloroethene. High conversions favour the formation of oligomeric products.

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► The formation of trichloroethene and tetrachloroethene is investigated.
► A role for homogeneous and heterogeneous processes is established.
► Trichloroethene is identified as a kinetic product.
► The chemical foundations for the industrial process are established.