Investigation of kinetic and thermodynamic parameters of coal pyrolysis with model-free fitting methods

Abstract Kinetic analyses are important means for understanding the complicated coal pyrolysis process. This work conducted non-isothermal pyrolysis of four low-medium rank coals with thermogravimetric analyzer at different heating rates (5, 10 and 20 K/min). Four model-free fitting approaches including KAS, OFW, Starink and Friedman methods were used to analyze pyrolysis kinetics of the coals. Thermodynamic parameters including enthalpy ( Δ H ) Gibbs free energy ( Δ G ) and entropy ( Δ S ) were calculated with the activation values ( E ) obtained with KAS method. For the kinetic analysis, the KAS, OFW and Starink methods gives close E values over the whole conversion range, but the Friedman method shows more deviant results. The thermodynamic favorability of coal pyrolysis is discussed, both Δ H and Δ G increase with conversion consistently with the variation of E, revealing that pyrolysis is endothermic and thermodynamic favorability is reduced with conversion rises. The minus Δ S implies that coal structures evolve from disordered to organized ones as universally accepted. These results are expected to deepen our understanding and to optimize the conditions of coal pyrolysis.