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

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/alumin a catalysts deactivated rapidly during the hydrodechlorination (HDC) of 1,1 ,1-trichloroethane (111-TCA) at temperatures between 423 and 623 K. Large q uantities of coke were formed on these catalysts at some conditions. In the present research, the deactivation associated with four intermediates in t he HDC of 111-TCA; 1,1-dichloroethylene (11-DCE), 1,1-dichloroethane (11-DC A), chloroethane, and ethylene, was investigated. Experiments were carried out with eta delta -alumina and 3% Pt/eta -alumina at 423 and 523 K, atmosp heric pressure, and at a H-2/chlorinated hydrocarbon/He ratio of 10/1/89. The eta delta -alumina, without Pt, catalyzed the removal of one molecule o f HCl from each of the saturated chlorocarbons. Deactivation of the eta del ta -alumina was rapid with 111-TCA and 11-DCA, and relatively slow with chl oroethane. There was no reaction over eta delta -alumina when 11-DCE was fe d. The fresh Pt/eta -alumina catalyst was able to remove all of the Cl from th e chlorocarbons. This catalyst deactivated with 111-TCA and 11-DCA, but no deactivation was observed with 11-DCE and chloroethane. At comparable condi tions, much more coke was deposited on the Pt/eta -alumina catalyst with 11 1-TCA than with any of the other compounds. Hydrochloric acid did not appea r to cause deactivation, A reaction scheme is proposed to summarize the maj or reaction pathways and to identify potential causes of catalyst deactivat ion. (C) 2001 Elsevier Science B.V. All rights reserved.