Pyrolysis of banana peel with microwave and furnace as the heating sources: The distinct impacts on evolution of the pyrolytic products

Abstract

Microwave pyrolysis features with different heating mechanisms and heat transfer directions from traditional pyrolysis with furnace heating, which might impact evolution of volatiles and nature of biochar in varied ways. This was investigated in this study by pyrolysis of wet and dried banana peel with microwave heating and furnace heating at 400 and 600 °C in a fixed-bed reactor. The results showed that microwave pyrolysis could drastically promote gasification of volatiles to form significantly more gases like H2 via dehydrogenation and CO via cracking and decarbonylation. This was especially evident in the pyrolysis of wet banana peel with abundant water as the heat transfer medium. The dominance of cracking/gasification of volatiles in microwave pyrolysis was due to the rapid heating and the minimized heat transfer limitation, which suppressed the secondary condensation and thus diminished the formation of bio-oil and biochar. Microwave pyrolysis also favored the cracking of the cellulose/hemicellulose-derived aliphatic organics via cracking but promoted the formation of phenolics via cracking of lignin in banana peel. Moreover, the excessive cracking reactions in the microwave pyrolysis led to the biochar of more excellent thermal stability, lower abundance of oxygen-containing functionalities like CO and more rugged morphology than that with furnace heating source.