Kinetics of MSWI Fly Ash Thermal Degradation. 1. Empirical Rate Equation for Native Carbon Gasification

The thermal degradation rate of organic carbon on fly ashes from different municipal solid waste incinerators, MSWIs, is studied in batch experiments in air. A global parameter, total organic carbon (TOC), is used to measure the decrease of reagent concentration in time. The TOC vs time data are well fitted by deconvolution treatment with a sum of two first-order reactions, Ri and Rj. To identify the limits of deconvolution, kinetics of the model systems dibenzofuran (DF)-biphenyl (BPh)-SiO2 and DF-BPhactive carbon-SiO2 are studied. Both Ri and Rj are carbon oxidation reactions to CO2, the oxidized carbon being not from adsorbed organic compounds but from the native carbon matrix of MSWI fly ash. Large negative ΔSq values indicate that Ri and Rj transition states are more compact and stiffer than the reagent ones. Structural changes are more important than chemical transformations since the entropic term is predominant in determining the ΔGq values. The key experimental information for the formulation of a generalized kinetic model and a mechanism for carbon gasification (Part 2) is the temperature dependence of the preexponential parameters in the empirical rate equation.