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

摘要

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 Ptlalumina catalysts deactivated rapidly during the hydrodechlorination (HDC) of 1,1,I-trichloroethane (111- TCA) at temperatures between 42~3 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, I-dichloroethylene (11-DCE), l,l-dichloroethane (ll-DCA), chloroethane, and ethylene, was investigated. Experimentj were carried out with 1l8-alumina and 3% Ptl1l-alumina at 423 and 523 K, atmospheric pressure, and at a H2/chlorinated hydrocarbon/He ratio of 10/1/89. The 1l8-alumina, without Pt, catalyzed the removal of one molecule of HCl from each of the saturated chlorocarbons. Deactivation of the 1l8-alumina was rapid with 111- TCA and 11-DCA, and relatively slow with chloroethane. There was no reaction over 1l8-alumina when 11-DCE was fed. The fresh Ptl1l-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 Ptl1l-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.