Distribution kinetics for temperature-programmed pyrolysis

Pyrolysis is usually modeled with nth-order or sigmoidal (nucleation or aut ocatalytic) kinetics and with parallel reactions having distributed activat ion energies: The underlying chemistry, however, consists of thermolytic bo nd cleavage, recombination reactions, and volatilization of low molecular w eight (MW) products. A new approach is based on a dynamic population-balanc e equation for the molecular weight distribution of a pyrolyzing macromolec ular material in a temperature-programmed thermogravimetric process. Random chain scission, repolymerization, chain-end scission yielding gas products , and loss of low-MW matter by vaporization are included in the model. Zero th and first moments of the balance equation provide coupled differential e quations for the time dependence of moles, n(t), and mass, m(t), of the sam ple. Separate changes in n and m account for the changes in the average mol ecular weight during pyrolysis. The activation energy for random chain scis sion is relatively larger than that for chain-end scission or repolymerizat ion. The model simulates observations for temperature-programmed pyrolysis, including nth-order and acceleratory (nucleation) behavior.