Microwave pyrolysis of coal, biomass and plastic waste: a review

Growing concerns over climate change have prompted the quest for renewable energies to mitigate adverse impacts caused by the excessive use of fossil fuels. In particular, using waste and biomass as fuel precursors is currently under active research. Pyrolysis is a thermal conversion in an inert atmosphere, involving the rapid heating of feedstocks to produce oil, gas and intermediate chemicals. Here, we review pyrolysis of cellulose, lignin, algae, plastic wastes and coal, with focus on microwave-assisted processes. We describe the types of char, bio-oils and gas products. We detail various apparatuses used in microwave-assisted pyrolysis to show that industrial upscaling is possible. Advantages of microwave-assisted pyrolysis include uniform heating of large particulate size of feed, fast switching on and off controls, and no requirement of fluidization. Higher yield of oil should be obtained by microwave-assisted pyrolysis of organic feedstocks.