Combustion Kinetics of Biochar Prepared by Pyrolysis of Macadamia Shells

Abstract

The use of macadamia shells (MSs) has become an active research direction because of increasing production. This paper considers the combustion characteristics of MSs and their biochars that were investigated with thermogravimetry analysis (TGA). Combustion thermographs were obtained at different heating rates, using isoconversional methods expressed by combustion kinetics. The Kissinger-Akahira-Sunose (KAS) method authenticated the MSs, MSs-300, and MSs-600 average activation energy at 91.6 kJ/mol, 60.5 kJ/mol, and 50.1 kJ/mol, respectively. The Flynn-Wall-Ozawa (FWO) method authenticated these at 97.1 kJ/mol, 68.7 kJ/mol, and 59.5, kJ/mol. The Coats-Redfern method verified the samples combustion via a complex multi-step mechanism; the first stage mechanism had different activation energies at different heating rates. With increased heating rates, the activation energies of biochar decreased, and the activation energies of MSs for the second combustion zone also decreased. At the same heating rate, MSs-600 had higher activation energy values than MSs-300. The TGA curves and kinetic parameters demonstrated the superiority of the biochar derived MSs as a fuel substrate over its precursor.