Thermal reaction kinetics and mechanism of PCDF, PCDD, and PCB parent compounds and activated carbon on silica

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 (SiO2) 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-SiO2 DD-SiO2, and BPh-SiO2 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 -SiO2 mixtures is due to oxidation to CO2, 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 frequency factor (A), activation entropy (Delta S-not equal), and activation enthalpy (Delta H-not equal).