The high-temperature pyrolysis of 1,3-hexachlorobutadiene

Abstract

Comprehensive product yield determinations from the high-temperature, gas-phase pyrolysis of 1,3-hexachlorobutadiene (C 4Cl 6) using two fused-silica tubular flow reactors are reported. The effects of reactor surface-area-to-volume (S/V) ratio were evaluated by conducting detailed product analyses with 0.1 cm i.d. and 1.0 cm i.d. reactors (high and low S/V ratio, respectively). Under low S/V ratio, initial decomposition was observed at 1023 K with formation of tetrachlorovinylacetylene (C 4Cl 4), tetrachloroethene (C 2Cl 4), and carbon tetrachloride (CCl 4), and molecular chlorine (Cl 2). Hexachlorobenzene (C 6Cl 6(cy)), C 8Cl 8(cy), and C 12Cl 8(cy) were also observed as products at higher temperatures. Under high S/V ratio, C 2Cl 4 decomposition was initiated at 873 K. In addition to the products observed under low S/V ratio, C 3Cl 4, C 5Cl 6, C 12Cl 10, and C 16C 10 were also observed. As in the case of C 2 chlorinated hydrocarbons we have studied, organic product yields were higher for the low S/V ratio experiments. Previously published detailed pyrolysis mechanisms for trichloroethene (C 2HCl 3) and C 2Cl 4 were used to provide predictions of the high-temperature reaction behavior of C 4Cl 6. Minor revisions of the C 2Cl 4 model produced reasonable agreement with observed C 4Cl 6 product distributions without compromising previous agreement with C 2Cl 4 product distributions. The model predictions were in better agreement with product distributions obtained using the lower S/V ratio reactor, a result also observed for C 2HCl 2 and C 2Cl 4 pyrolysis. Plausible radical-molecule addition reactions leading to C 2Cl 4, C 4Cl 4, C 6Cl 6 (cy), C 8Cl 8 (cy), and C 12Cl 8 (cy) formation were identified with the assistance of sensitivity analysis and production rate calculations.