Study on pyrolysis kinetics and reaction mechanism of Beizao oil shale

Abstract

The evaluation of pyrolysis kinetics and the reaction mechanism of organic matter and mineral matrix for oil shale is a rather difficult work due to the concomitant structure and complicated reactions. The pyrolysis process of Beizao oil shale was studied in a thermogravimetric analyzer at various heating rates with obvious existence of two stages. The kinetic parameters were estimated via a model-free method known as Friedman method and a multistep model-fitting method called Coats-Redfern method. A two-stage reaction model is proposed based on thermogravimetric analysis and the obtained kinetic parameters. The results indicated that the reaction model g(α) = −[ln(1 − α)]2 might be in charge of Stage I, and reaction mechanism for Stage II could be interpreted by g(α) = −[ln(1 − α)]3. Furthermore, the curve of conversion rate α was predicted based on the obtained kinetic parameters, and the reaction parameters and models were validated by an extra heating rates beyond those used to generate them. It was speculated that the two-stage reactions could be attributed to the thermal decomposition of organic matter with bitumen as intermediate in Stage I, and the devolatilization of inorganic components, mainly clay aluminosilicates and calcite, in Stage II.