Selected Topics on the De Novo Synthesis of PCDD/PCDF on Fly Ash

Abstract

Based on laboratory experiments with fly ash from municipal waste incinerators and model mixtures, the main reactions for the denovosynthesis of PCDD/PCDF were identified. According to the results, particles of carbonaceous material from incomplete combustion were converted to a series of chlorinated aromatic compounds including PCDD/PCDF. In the process, two basic reactions were involved: a) the transfer of inorganic chloride to the macromolecular carbonaceous structure with formation of carbon-chlorine bonds, and b) the oxidative degradation of the structure. In both processes, transition metal ions, especially Cu(II), were involved as reaction partners or catalysts. Important parameters for the reaction are: the composition of the fly ash, the temperature range from 300 to 350°C, and the presence of oxygen in the gas phase. Key words: polychlorinated dibenzodioxins; polychlorinated dibenzofurans; PCDD; PCDF; fly ash; de novosynthesis; formation mechanism