Direct catalytic hydrodechlorination of toxic organics in wastewater

Abstract

AbstractThe in‐situ catalytic hydrodechlorination of chlorinated hydrocarbons in waste‐water‐generating HCl and a hydrocarbon‐free chlorine is demonstrated as a viable wastewater remediation technique. Catalyst screening studies with a shaker‐type hydrogenation reactor have shown that the commercial Pd/C catalyst is highly effective in hydrochlorinating various chlorinated hydrocarbons in synthetic wastewater at room temperature and near atmospheric pressure. 1, 1, 2‐trichloroethane hydrodechlorination experiments in an autoclave reactor shows that initial rates are well correlated with first‐order dependence of the reactant hydrocarbon adsorbed on carbon. Initial rates are also independent of hydrogen pressure, and adsorption on the carbon support is Langmuir type. Activation energies calculated at different catalyst loadings varied from 29 to 38 MJ/mol.1,1,2‐trichloroethane hydrodechlorination activity is much lower for Pd/Al2O3 than Pd/C because the reactant hydrocarbon does not adsorb on alumina. When the carbon support does not readily adsorb the reactant hydrocarbon, the hydrodechlorination rates dropped significantly. These results confirm the role of the carbon support in providing the major path to reaction and thereby significantly increasing reaction rates compared to direct adsorption from solution onto the palladium.