Catalytic hydrodechlorination of chlorinated ethylenes in organic solvents at room temperature and atmospheric pressure

Abstract

The objectives of this study are to hydrodechlorinate chlorinated ethylenes (ETHs) using noble metal catalysts in organic solvents at 20±0.5°C and atmospheric pressure and to evaluate the competitive degradation of chlorinated ethylenes. Tetrachloroethylene (PCE) was catalytically hydrodechlorinated with 10% Pd/C at 20±0.5°C and atmospheric pressure without accumulation of tetrachloroethane (TTCE) and other chlorinated intermediates. Methanol was the best solvent for the degradation of PCE. NaOH addition clearly increased in degradation rate of PCE. The first order degradation rate constants for PCE, trichloroethylene (TCE), and cis-1,2-dichloroethylene (DCE) were 0.18, 0.64, and 2.1min−1, respectively. These values were extremely larger than previous data and organic compounds with less chloride showed larger degradation rate. The degradation rate of PCE significantly decreased by the co-existence of TCE or cis-1,2-DCE. On the other hand, the co-existence of PCE gave little influence on the degradation of TCE and cis-1,2-DCE. These were due to competitive adsorption of chlorinated compounds on active sites on catalyst. The adsorption capacity of Pd/C catalyst for PCE significantly decreased by the co-existence of TCE or cis-1,2-DCE, whereas those of TCE and cis-1,2-DCE were independent from the co-existence of PCE.