Elucidating the thermal decomposition mechanism and pyrolysis characteristics of biorefinery-derived humins from sugarcane bagasse and rice husk

Abstract

Biomass-derived humins produced in the biorefining of biomass represent an attractive feedstock for thermochemical processes. This work examines the purification and characterization of humins derived from sugarcane bagasse and rice husks (H-SCB and H-RH, respectively), followed by the kinetic and thermodynamic analysis of its pyrolysis. Pyrolysis was assessed via thermogravimetric analysis, and a global reaction model was adopted to address pyrolysis kinetics. To boost the quality of fit between the kinetic model and thermoanalytical data, the analyses are based on Vyazovkin's method. The activation energy of H-SCB increased from 166.09 to 329.76 kJ mol−1. In contrast, the activation energy of H-RH decreased from 163.31 to 84.99 kJ mol−1. According to the results of the generalized master-plot approach, the governing reaction mechanism shifted among order-based models, nucleation, and diffusion-controlled particle mechanisms. Thermodynamic properties showed that the process is endothermic, with the thermal decomposition of H-SCB being more reactive (ΔSaverage = -0.004 kJ mol−1 K−1) compared to H-RH (ΔSaverage = -0.05 kJ mol−1 K−1). Also, the heat absorbed helps the humins to achieve a more ordered state close to a conversion of 0.50. Furthermore, a difference of about 7 kJ mol−1 between the enthalpy of the reaction and the average activation energy indicates the formation of favorable product with humins’ considerable bioenergy potential. These findings are the first reported data on the forecast kinetic curves and pyrolysis mechanism of biorefinery-derived humins, and these results will enable process design for the thermochemical conversion of these emerging materials to produce energy and other products.