Chapter 8 Pyrolysis of Halogenated Hydrocarbons

Abstract

This chapter discusses the pyrolysis of halogenated hydrocarbons. The replacement in a hydrocarbon of one or more hydrogen atoms with chlorine atoms leads to the class of chlorinated hydrocarbons. Chlorinated hydrocarbons are also known as chlorocarbons and can be viewed as formed from an organic radical (alkyl, cycloalkyl, aryl, etc.) and one or more chlorine functional groups. In chlorinated aliphatic hydro-carbons, the chlorine atoms are attached to an aliphatic structure. The compounds such as benzyl chloride, where, besides chlorine, the aliphatic structure is substituted with an aryl group, are still considered aliphatic. A variety of aliphatic hydrocarbons substituted with fluorine, bromine, iodine, and with combination of halogens (including chlorine) have practical applications. These compounds include intermediates in organic synthesis, monomers for various plastics, flame retardants, fire extinguishing agents, aerosol spray propellants, foam blowing agents, cleaning solvents, and refrigerant agents. Pyrolysis of aliphatic halocarbons takes place inadvertently during waste incineration or intentionally with the purpose of synthesis of other halogenated compounds. The mechanisms of pyrolysis of aliphatic hydrocarbons substituted with halogens other than chlorine show many similarities with that of chlorinated ones. The replacement in an aromatic hydrocarbon of one or more hydrogen atoms with chlorine atoms leads to the class of aromatic chlorinated hydrocarbons. Pyrolysis of chlorinated aromatic hydrocarbons is strongly related to the formation of chlorinated dibenzo- p -dioxins, chlorinated dibenzofurans, and PCBs (DLCs). Oxidative pyrolysis and the presence of a solid support during pyrolysis may increase the generation of DLCs.