Characteristics of biochar pellets from corn straw under different pyrolysis temperatures

Biomass resources have the potential to produce clean-energy. However, their physico-chemical properties are inferior to those of coal, and thus, biomass resources are not regarded as ideal feedstock for industrial application. In the present study, the pyrolysis of corn (maize) straw pellets was performed under different temperatures (400, 450, 500, 550 and 600°C) at a 10°C min-1 heating rate and 30 min residence time, and the characteristics of biochar pellets were carefully investigated, particularly their elemental composition, hydrophobicity and mechanical resistance. Fourier transform infrared, proximate analysis and scanning electron microscopy were performed. Results indicated that the mass and energy yields of the biochar pellets decreased from 35.46 to 28.65% and from 50.17 to 45.52%, respectively, at increased temperature. Meanwhile, the higher heating value of the biochar pellets increased from 15.45 MJ kg-1 in the raw materials to 21.86 and 24.55 MJ kg-1 in the biochar produced at 400 and 600°C, respectively. In addition, biochar pellets showed good hydrophobicity, which benefited their storage and transportation, though mechanical resistance decreased. The pellets had compact structures, regular shapes and weakened or no functional groups in contrast with raw pellets, and these properties played important roles in the improvements.