Influence of air oxidative and non-oxidative torrefaction on the chemical properties of corn stalk

•Higher extractives and lower ash contents are not favorable for deoxidation.•The existence of extractives has an influence on characteristic curves of DTG.•Pyrolysis activity: extractives(low-temp.) > hemicellulose > cellulose > extractives(high-temp.) > lignin.•The moderate removal of hemicellulose can be achieved by air oxidative torrefaction. The non-structural components (extractives and ash) in biomass can affect the torrefaction characteristics. The objective of this study was to investigate the applicability of air oxidative and non-oxidative torrefaction for corn stalk, which has higher organic extractives and lower ash contents. The raw materials were torrefied with air and nitrogen in a fluidized bed reactor at 180℃~235℃ and 200℃~280℃ for 1 h, respectively. The proximate and ultimate analysis results demonstrated that the lower ash content (3.89%) was not favorable for deoxygenation. The organic extractives, extracted materials and mixture were torrefied with nitrogen at 260℃. The results indicated that the addition of organic extractives reduced the deoxidation efficiency of structural components during torrefaction. Compared to raw materials, the moderate and severe removal of hemicellulose can be achieved through torrefaction under air and nitrogen, respectively.