Thermal conversion behaviors and products of spent mushroom substrate in CO2 and N-2 atmospheres: Kinetic, thermodynamic, TG and Py-GC/MS analyses

Abstract

This study aims at characterizing pyrolysis/gasification behaviors and products of spent mushroom substrate (SMS) in the CO2 and N-2 atmospheres. The major decomposition stages occurred between 200 and 600 degrees C with the mass losses of 60.4 and 61.5% at 20 degrees C/min in the CO2 and N-2 atmospheres, respectively. The maximum mass loss rate grew with the increased heating rate, while DTG curves shifted toward a higher temperature. Volatiles were released easier in the N-2 than CO2 atmosphere with a higher comprehensive devolatilization index and decomposition rate. At above 750 degrees C, the char gasification in the CO2 atmosphere resulted in a significant mass loss as well as a less char yield. Average activation energies by the Flynn-Wall-Ozawa method were estimated at 212 and 214 kJ/mol in the CO2 and N-2 atmospheres, respectively. The higher thermodynamic parameters in the N-2 than CO2 atmosphere indicated the higher reactivity of the pyrolysis in the N-2 atmosphere. The reaction mechanisms of the volatiles decomposition were best described by g(alpha) = (1-alpha)(-1)-1 (R2 model) in the range of 200-370 degrees C in both atmospheres. The major pyrolysis products at 800 degrees C were identified using Py-GC/MS and composed mostly of aromatic compounds such as toluene and x-methyl-naphthalenes.