Abstract:

The biochars I, R, S and M were prepared at 300, 500 and 700℃ with the grasses of king grass, rice straw, bagasse and corn straw as raw materials, respectively. The effects of different pyrolysis temperatures on the structure and composition of biochar were studied. Results showed that with pyrolysis temperature increasing, the yield of the four kinds of biochars decreased, carbon content and ash content increased. The yields of I, R, S and M at 300℃ were 45.81%, 48.67%, 46.81% and 46.00%, and the yields at 700℃ were 33.95%, 35.47%, 25.42% and 31.23%. The ash contents and I, R, S and M at 700℃ increased by 54.39%, 65.44%, 95.54% and 71.85% compared those at 300℃. The C/N ratio of R, S, and M were increased with pyrolysis temperature increasing, but that of R was opposite. The pH values of the four biochars increased with pyrolysis temperature increasing. The pH values of I, R, S and M at 700℃ were 7.68, 9.87, 7.59 and 9.33. I and S was porosity and the number of pore increased with the increase of pyrolysis temperature. Both R and M formed a certain amount of flocs at 700℃. EDX analysis revealed that the elemental composition of Si was contained higher in R. Infrared spectroscopy showed that with the increase of pyrolysis temperature, the alkane groups, methyl groups (—CH₃) and methylene groups (—CH₃) of the four kinds of biochars gradually disappear. The biochar structure was dominated by aromatic compounds and oxygen functional groups, and the structure was more stable.

Key words: pyrolysis temperature, ash contents, gramineae plant, biochar