Thermal decomposition of chlorobenzene in an atmosphere of hydrogen

The thermal decomposition of chlozobenzene was investigated in a tubular flow reactor at 1 atmosphere total pressure and average residence times of 0.02 - 2.5 seconds. The temperature range from 800 - 1010°C was studied in both a reductive atmosphere of hydrogen and an inert atmosphere of heIium. Complete destruction of chlorobenzene occurs at about 1000°C for an average residence time of 1 second in hydrogen gas. In the inert gas, the complete destruction of the reagent was not observed in the range of conditions which were studied. The major products observed for pyrolysis in hydrogen were benzene, HCl, and C(s). Pyrolysis in helium yielded significantly more C(s), but less benzene and HCl. Significant amounts of PAH and polyphenyl compounds were formed in the inert gas; but these were virtually absent when the pyrolysis occurred in a hydrogen atmosphere. An increase in the surface to volume ratio of the reactor tube was found to consistently accelerate the decomposition of chlorobeorene in hydrogen; but it had no effect on the distribution of major products. The experimental data was analyzed using the plug flow approximation. Expressions for the first order rate constants for the walI and homogeneous phase reactions were obtained as follows: k = 1.13 x 1010 e-(54/RT) (1/sec\u3e: reaction in H2 gas phase. k = 1.4 x 1011 e-(64/RT) {cm/sec}: reaction on the wall