The integrated process of microwave torrefaction and pyrolysis of corn stover for biofuel production

•The first study of integrated microwave torrefaction and pyrolysis of corn stover.•Microwave torrefied pyrolysis favored phenols and hydrocarbons production.•Organic acids were significantly reduced in bio-oils.•Up to 26.7 area% hydrocarbons in the bio-oil were produced.

The integrated process of torrefaction and pyrolysis of corn stover were investigated in this study. The effects of torrefaction conditions on both torrefaction and pyrolysis products were determined. The heating values of torrefied biomass were similar to those of coals and increased comparing to raw biomass. The torrefaction oils contained high value chemicals such as furans and phenolics. The torrefaction process caused a decrease in the pyrolytic oil yields but the total bio-oil yield from torrefaction and pyrolysis were similar to those from raw biomass pyrolysis. The pyrolytic oil from torrefied biomass contained more hydrocarbons and phenols and less organic acids than raw biomass pyrolysis, which indicates that the quality of pyrolytic oil was improved with torrefaction as a thermal pretreatment. The optimum torrefaction condition for both high yield and quality of pyrolytic oil was determined at the reaction temperature around 275 °C and torrefaction time of 30 min. This study implied that torrefaction as a pretreatment can be combined with the pyrolysis for high quality biofuel production.