oxychlorination

In oxychlorination, ethylene reacts with dry HCl and either air or pure oxygen in a heterogeneous catalytic reaction to form EDC and water.

While there are many different commercial oxychlorination processes, in each case the reaction is carried out in the vapor phase in either a fixed bed or fluid bed reactor containing a modified Deacon catalyst. Unlike the Deacon process, however, oxychlorination of ethylene occurs readily at temperatures well below those required for HCl oxidation. The catalyst typically contains cupric chloride (CuCl₂) as the primary active ingredient, impregnated on a porous support such as alumina, and may also contain numerous additives.

OxyVinyls patented Oxychlor®-8 catalyst is ideally suited for fluid bed reactor operation.  This sixth generation catalyst is the result of continuous research and development, which has led to increased efficiencies and ease of operability.  Oxychlor catalysts are extremely robust and highly tolerant to process upsets and diverse operating conditions.  In addition to easy operability, the latest generation of catalyst operates at higher temperatures, facilitating heat removal and higher reactor productivity, along with improved feedstock efficiencies and reduced catalyst losses.

The oxychlorination reaction is exothermic (”H_rxn = -239 kJ/mol EDC made) and requires heat removal for temperature control, which is essential for efficient production of EDC. Higher reactor temperatures lead to more by-products, mainly through increased ethylene oxidation to carbon oxides and increased EDC cracking. (Cracking of EDC yields VCM, and subsequent oxychlorination and cracking steps lead progressively to by-products with higher levels of chlorine substitution.) High temperatures (>300°C) can also deactivate the catalyst through increased sublimation of CuCl₂.

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane, chloroform, carbon tetrachloride, ethyl chloride, chloral, 2-chloroethanol, all of the chloroethylene congeners, and higher boiling compounds. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed (by caustic washing) to prevent the formation of solids which can foul and clog processing equipment downstream.

Oxychlorination process feed purity can also contribute to by-product formation, although the problem usually is only with the low levels of acetylene which are normally present in HCl from the EDC cracking process. Since any acetylene fed to the oxychlorination reactor will be converted to highly chlorinated C2 products, selective Hydrogenation of this acetylene to ethylene and ethane is widely used as a preventive measure.

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