THE HIGH-TEMPERATURE PYROLYSIS OF 1,3-HEXACHLOROBUTADIENE

Comprehensive product yield determinations from the high-temperature, gas-phase pyrolysis of 1,3-hexachlorobutadiene (C4Cl6) using two fused -silica tubular flow reactors are reported. The effects of reactor sur face-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 l ow S/V ratio, respectively). Under low S/V ratio, initial decompositio n was observed at 1023 K with formation of tetrachlorovinylacetylene ( C4Cl4), tetrachloroethene (C2Cl4), and carbon tetrachloride (CCl4), an d molecular chlorine (Cl-2). Hexachlorobenzene (C6Cl6(cy)), C8Cl8(cy), and C12Cl8(cy) were also observed as products at higher temperatures. Under high S/V ratio, C2Cl4 decomposition was initiated at 873 K. In addition to the products observed under low S/V ratio, C3Cl4, C5Cl6, C 12Cl10, and C16C10 were also observed. As in the case of C-2 chlorinat ed hydrocarbons we have studied, organic product yields were higher fo r the low S/V ratio experiments. Previously published detailed pyrolys is mechanisms for trichloroethene (C2HCl3) and C2Cl4 were used to prov ide predictions of the high-temperature reaction behavior of C4Cl6. Mi nor revisions of the C2Cl4 model produced reasonable agreement with ob served C4Cl6 product distributions without compromising previous agree ment with C2Cl4 product distributions. The model predictions were in b etter agreement with product distributions obtained using the lower S/ V ratio reactor, a result also observed for C2HCl3 and C2Cl4 pyrolysis . Plausible radical-molecule addition reactions leading to C2Cl4, C4Cl 4, C6Cl6 (cy), C8Cl8 (cy), and C12Cl8 (cy) formation were identified w ith the assistance of sensitivity analysis and production rate calcula tions.