Deactivation of hydrodechlorination catalysts: II — Experiments with 1,1-dichloroethylene and 1,1-dichloroethane

Abstract In an earlier paper [K.A. Frankel, B.W.-L. Jang, J.J. Spivey, G.W. Roberts, Appl. Catal. A, in press], it was shown that certain alumina and Pt/alumina catalysts deactivated rapidly during the hydrodechlorination (HDC) of 1,1,1-trichloroethane (111-TCA) at temperatures between 423 and 623 K. Large quantities of coke were formed on these catalysts at some conditions. In the present research, the deactivation associated with four intermediates in the HDC of 111-TCA; 1,1-dichloroethylene (11-DCE), 1,1-dichloroethane (11-DCA), chloroethane, and ethylene, was investigated. Experiments were carried out with ηδ-alumina and 3% Pt/η-alumina at 423 and 523 K, atmospheric pressure, and at a H 2 /chlorinated hydrocarbon/He ratio of 10/1/89. The ηδ-alumina, without Pt, catalyzed the removal of one molecule of HCl from each of the saturated chlorocarbons. Deactivation of the ηδ-alumina was rapid with 111-TCA and 11-DCA, and relatively slow with chloroethane. There was no reaction over ηδ-alumina when 11-DCE was fed. The fresh Pt/η-alumina catalyst was able to remove all of the Cl from the chlorocarbons. This catalyst deactivated with 111-TCA and 11-DCA, but no deactivation was observed with 11-DCE and chloroethane. At comparable conditions, much more coke was deposited on the Pt/η-alumina catalyst with 111-TCA than with any of the other compounds. Hydrochloric acid did not appear to cause deactivation. A reaction scheme is proposed to summarize the major reaction pathways and to identify potential causes of catalyst deactivation.