Destruction of carbon tetrachloride in the presence of hydrogen-supplying compounds with ionisation and catalytic oxidation

Catalytic combustion with and without pre-catalytic actions (i.d., ionisation/ozonisation (I/O)) of tetracloromethane (CCl4) over alumina-supported copper-chromite (Cu-Cr) and manganese (Mn) dioxide catalysts with and without the presence of hydrogen-rich compounds, i.e. n-hexane and toluene, was evaluated. Experiments were performed at conditions of lean carbon tetrachloride (CCl4) concentration (from 500 to 3000 ppm V) in excess air, between 100 and 500 degreesC in a continuous reaction line at laboratory scale. n-Hexane and toluene were added to the feedstream in variable concentration, between 100 and 500 ppm V. Ionisation/ozonisation of pure CCl4 streams and of streams of hexane or toluene admixtures showed the efficiency of the hydrogen donor role of the hydrocarbons on CCl4 conversion. The tests of ionisation/ozonisation were performed at different residence times in the ionisation reactor and a rate equation with second-order in CCl4 concentration was found to represent the ionisation process. Over Cu-Cr and Mn catalysts, both n-hexane and toluene improved the CCl4 combustion when added at low concentration (ca. 300 degreesC) but inhibited it when they were present at high concentration (ca. 350 degreesC). Catalytic combustion assisted with ionisation process enhanced CCl4 conversion at low temperatures in comparison with conventional catalytic combustion (e.g. 90% of 1000 ppm V Of CCl4-hexane mixture was converted on Cu-Cr at 250 degreesC and 5000 h(-1) by the combined actions of catalytic and ionisation processes). Selectivity to CO2 was controlled on the two catalysts. Mn was more active but less selective than Cu-Cr catalyst. Various oxygenated and chlorinated by-products, in particular COCl2, were formed during ionisation Of CCl4 streams. By-products were greatly reduced and COCl2 disappeared at 250 degreesC on catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.