Shock-tube pyrolysis of chlorinated hydrocarbons: Formation of soot

Abstract

Soot formation in pyrolysis of chlorinated methanes, their mixtures with methane, and chlorinated ethylenes were studied behind reflected shock waves by monitoring the attenuation of an HeNe laser beam. An additional single-pulse shock-tube study was conducted for the pyrolysis of methane, methyl chloride, and dichloromethane. The experiments were performed at temperatures 1300–3000K, pressures 0.4–3.6 bar, and total carbon atom concentrations (1–5) × 10 17 atoms/cm 3. The amounts of soot produced in the pyrolysis of chlorinated hydrocarbons are larger than that of their nonchlorinated counterparts. The sooting behavior and product distribution can be generally explained in terms of chlorine-catalyzed chemical reaction mechanisms. The pathway to soot from chlorinated methanes and ethylenes with high H : Cl ratio proceeds via the formation of C 2H, C 2H 2, and C 2H 3 species. For chlorinated hydrocarbons with low H : Cl ratio, the formation of C 2 and its contribution to soot formation at high temperatures becomes significant. There is evidence for the importance of CHCl radical and its reactions in the pyrolysis of dichloromethane.