Porous Biochar Production from Microwave-Assisted Pyrolysis of Biomass

Biomass is a renewable resource that can be converted into gas, liquid and solid fuels and has a bi-directional cleaning effect on our environment. Compared with direct combustion, the conversion of biomass to biochar by pyrolysis is considered to be an environmentally friendly and efficient method for the treatment of agricultural solid waste. Biochar usually has good adsorption capacity due to its complex porous structure. In this study, microwave-assisted pyrolysis performances of peanut shell, rice husk, and corn stalk to produce biochar will be reported. The yields and pore volumes of biochar obtained at different pyrolysis temperatures (700,750, 800, 850, 900 °C), microwave powers (350,400, 450, 500, 550 W) and residence times (60,90, 120, 150, 180 min) will be detailed. Under the pyrolysis conditions studied, the biochar yields of peanut shell, rice husk and corn stalk were 30.756-43.275 wt. %, 25.71-38.93 wt. % and 23.71-36.95 wt. %, respectively. The experimental results showed that with the increases in pyrolysis temperature, microwave power and residence time, the biochar yield decreased initially and then tended to be stable, while the volume of micro-pores increased. When the pyrolysis temperature was 900 °C, the microwave power was 500 W, and the residence time was 120 min, the micropore structure of corn stalk based biochar was the most developed, and its specific surface area can reach 323.332 m
²
/g without any activation treatment. This study quantitatively revealed the relationship between the pore structure of biochar and experimental conditions (pyrolysis temperature, microwave power and residence time), and the results can provide guidance for the resource utilization of agricultural waste biomass and the production of porous biochar with high adsorption properties.