China Nonferrous Metallurgy

The waste produced in the industrial production contains dioxins (PCDD/Fs), which are persistent organic pollutants and one of the most toxic substances. Both oxidizing and reducing substances can degrade PCDD/Fs. Oxidant and reducing agents represented by·OH and H2 can destroy the molecular structure of PCDD/Fs through addition reaction and substitution reaction, thus achieving the degradation of PCDD/Fs. However, the existing literature does not fully explain the degradation reaction mechanism. This study deals with the 2,3,7,8-tetrachlorodibenzofuran (2,3,7,8-TCDF) in fly ash at low temperature. The quantum computational chemistry method was adopted to investigate the reaction process characteristics of 2,3,7,8-TCDF reaction with H₂ and OH free radicals. The activation energy and the reaction rate in dechlorination substitution reaction and ring-opening addition reaction are compared. The main findings are as follows. Both H₂ and OH free radicals can degrade 2,3,7,8-TCDF through dechlorination and ring-opening addition reactions. In addition, the substitution reaction has lower difficulty than that of addition reaction. In the degradation process, the C—Cl bond breaking is the easiest, followed by C—O bond breaking, and C—C bond breaking is the most difficult. Compared with H2, the energy required to reach the transition state between·OH and 2,3,7,8-TCDF is smaller and the degradation is less difficult.