Thermal Reaction Kinetics and Mechanism of PCDF, PCDD, and PCB Parent Compounds and Activated Carbon on Silica

Abstract

The kinetics of PCDF, PCDD, and PCB parent compounds, dibenzofuran (DF), dibenzo-p-dioxin (DD), and biphenyl (BPh) as well as those of activated carbon (C) supported on silica gel (SiO 2 ) are studied in batch experiments using the total organic carbon (TOC) global parameter. The rate constants along with the activation and thermodynamic parameters are determined. A nonlinear trend is observed for the Arrhenius and Eyring plots. The TOC decrease of DF-SiO 2 , DD-SiO 2 , and BPh-SiO 2 mixtures is due to the organic reagent desorption, the rate of which is controlled by a surface reaction at lower temperatures while the reaction is diffusion limited at higher temperatures. The TOC decrease of activated carbon-SiO 2 mixtures is due to oxidation to CO 2 , the rate-limiting steps being the chemical and physical processes at the lower and higher temperatures considered. The nature of the transition states is investigated, considering frequencyfactor (A), activation entropy (ΔS ? ), and activation enthalpy (ΔH ? ).