Understanding pyrolysis mechanisms of pinewood sawdust and sugarcane bagasse from kinetics and thermodynamics

Abstract

The kinetics and thermodynamics of biomass pyrolysis are crucial to exploring the reaction mechanisms of biomass pyrolysis and the way forward to design, optimize, and commercialize the processes. The FWO and KAS isoconversional methods and the Kissinger method were usually used to determine the activation energy and frequency factor, respectively. However, those methods would lead to some important errors involved in the activation energy and frequency factor. A new method for estimating the conversion-dependency frequency factor was proposed based on the kinetic compensation effect, empirical kinetic mechanism function, results from the Friedman method and pattern search method since existing methods having some limitations. The thermodynamic parameters were determined using the Eyring theory and obtained activation energy and frequency factor values. This research revealed that (1) The activation energies determined by the Friedman isoconversional method ranged from 180 to 282 kJ mol−1 in the conversion range between 0.05 and 0.95 for the pyrolysis of both biomass samples; (2) The frequency factor values varied from 2.0 × 1011 to 3.0 × 1018 s−1 in the conversion range of 0.05 – 0.95 for the pyrolysis of both samples; (3) The average change in Gibbs free energy was 207.5 and 205.8 kJ mol−1 for the pyrolysis of pinewood sawdust and sugarcane bagasse, respectively; (4) The difference between activation energy and enthalpy for the pyrolysis of both biomass samples was approximately 5.5 kJ mol−1, indicating favorable product formation with considerable bioenergy potential.