A review on microwave pyrolysis of lignocellulosic biomass

This article briefly reviews the technique of lignocellulosic biomass pyrolysis by using microwave heating. Lignocellulosic biomass, such as crops, wood, agricultural and forestry residues, is a major biomass resource and has been recognized as a sustainable feedstock for the production of bioenergy and green materials. Microwave heating can be better than conventional heating because of various advantages. Hot spots, which form under microwave irradiation, would have significant influence on the yield and characteristics of microwave processing products. The solid products of microwave pyrolysis at proper microwave power levels can have high heating values and specific surface areas with higher gas and solid yields but lower liquid yield than conventional pyrolysis. By using microwave pyrolysis, almost half of lignocellulosic biomass can be converted into gas product, which is mainly composed of H2, CH4, CO, and CO2, with more bioenergy because of its high H2 and CO yields. The addition of proper catalysts provides substantial influence on the product selectivity of microwave pyrolysis. The gas and liquid yields as well as the heating performance of microwave pyrolysis can be dramatically promoted by adding catalysts. The activation energy and pre-exponential factor of microwave pyrolysis are much lower than those of conventional pyrolysis, revealing that the reaction kinetics for the two methods could be different. According to various advantages, microwave pyrolysis of lignocellulosic biomass can be a promising bioenergy technique.