CATALYST DEACTIVATION DURING DEEP OXIDATION OF CHLOROHYDROCARBONS

A commercial chromia-alumina catalyst was investigated for an extended period of time for the oxidation of two gas streams containing volati le organic compounds (VOCs) with compositions similar to those expecte d from groundwater air strippers. The first gas stream (chlorinated st ream) contained 500 PPM of C1 to C2 chlorohydrocarbons, while the seco nd stream (mixed stream) contained 450 PPM of C5 to C-9 hydrocarbons p lus 50 ppm of trichloroethylene. Catalyst deactivation was studied at constant conversion of the main reaction, achieved by increasing the t emperature, when needed, to compensate for the loss of intrinsic catal yst activity. The catalytic activity and selectivity were found to be a function of the type of feed stream and the reactor configuration. A lthough the catalyst used for the oxidation of the chlorinated stream did not require any temperature increase when used fore 153 days-on-st ream in a fixed bed reactor, the results suggest progressive loss in c atalyst activity down the catalyst bed. A fluid bed reactor was found to be more effective than a fixed bed reactor in maintaining the catal yst activity for the oxidation of the chlorinated stream. The physical attrition of catalyst particles in the fluid bed reactor accompanied with the loss of chromium, via oxychloride formation, appears to be be neficial in maintaining the catalyst activity by constantly exposing t he fresh catalyst surface. The catalyst used for mixed stream oxidatio n required a temperature increase of 33-degrees-C over 210 days-on-str eam to maintain constant conversion. This decrease in catalytic activi ty was related to a decrease in BET surface area.