THERMAL-REACTION KINETICS AND MECHANISM OF PCDF, PCDD, AND PCB PARENTCOMPOUNDS 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 activ ated carbon (C) supported on silica gel (SiO2) are studied in batch ex periments using the total organic carbon (TOC) global parameter. The r ate constants along with the activation and thermodynamic parameters a re determined. A nonlinear trend is observed for the Arrhenius and Eyr ing 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 control led by a surface reaction at lower temperatures while the reaction is diffusion limited at higher temperatures. The TOC decrease of activate d carbon -SiO2 mixtures is due to oxidation to CO2, the rate-limiting steps being the chemical and physical processes at the lower and highe r temperatures considered. The nature of the transition states is inve stigated, considering frequency factor (A), activation entropy (Delta S-not equal), and activation enthalpy (Delta H-not equal).