Effects of pyrolysis temperature on the physicochemical properties of gas and biochar obtained from pyrolysis of crop residues

Pyrolysis of crop residues is an important method to promote the utilization of biomass energy. Pyrolysis experiments of wheat straw, rice straw, corn stover, rape stalk and cotton stalk were carried out under different temperatures. The results showed that the biochar yields decreased and the gas yields increased from 300 °C to 600 °C. Besides, the proportions of CO2 and CO decreased with temperature. Higher temperatures elevated the proportions of CH4, CnHm and H2 and the higher heating values. With increasing temperature, the biochars showed decreased contents of volatile matter, H, O and (O + N)/C ratios, while increased ash, fixed carbon, C, total P and K contents. The carbon and energy conversion efficiencies of biochars decreased with increasing temperature. Significant differences were observed in the pyrolysis products among different crop residues, and some high correlations were identified among the determination parameters in the gases and biochars. At the same temperature, rice straw had the highest biochar yield, and rape stalk showed the highest gas yield and proportions of CH4, CnHm and H2 among the five crop residues. In addition, rape stalk biochar showed higher C, H and S contents and higher heating value, and cotton stalk biochar exhibited a higher fixed carbon.