Experimental and numerical study of the thermal destruction of hexachlorobenzene

Abstract

Hexachlorobenzene (HCB) was used as a model chlorocarbon molecule to investigate the thermal decomposition process of a polychlorinated aromatic compound in pyrolytic environments. The thermal decomposition of 1.07% HCB in nitrogen atmosphere was studied to determine important chlorocarbon pyrolysis reaction pathways. Reactions were carried out at 1 atm pressure in a tubular flow reactor 1.0 cm i.d.. The degradation of HCB plus intermediate and final product formation was analyzed from 900 to 1200°C, with a mean residence time of 2.0 s. The product yield distributions are reported. Initial decomposition was observed at 900°C with formation of Cl 2 and C 12Cl 10(cy). Pronounced decomposition and molecular growth were observed at higher temperatures as evidenced by the formation of CCl 4, C 2Cl 4, C 2Cl 6, C 4Cl 6, C 8Cl 8(cy), C 10Cl 8(cy), C 12Cl 8 (cy), C 18Cl 10 (cy) and soot. A detailed kinetic reaction mechanism based upon fundamental thermochemical principles and transition state theory was developed and used to model our experimental results. Sensitivity analysis was used to determine important reactions pathways responsible for the formation and destruction of species. The computed results agree qualitatively with all the experimental trends and quantitative agreement is obtained with several of the composition profiles. Important radical-molecule addition reactions leading to molecular growth are identified using sensitivity analysis and production rate calculations.