Pyrolysis of rice husk in molten lithium chloride: Biochar structure evolution and CO2 adsorption

Abstract

Biochars are attained by direct pyrolysis of the mixture of rice husk (RH) powders and lithium chloride within 600–800 °C. The physical and chemical properties of RH biochars are studied using diverse characterization techniques. Effects of pyrolysis temperature and salt/biomass ratio on the structure properties and CO2 adsorption performances of RH biochars are tested at 25 °C and 100 kPa. The results show that the CO2 uptakes of RH biochars first ascend and then descend with incremental pyrolysis temperature and basically increase with the elevation of the salt/biomass ratio. The biochar prepared at 700 °C with the salt/biomass ratio of 7.5 in an air atmosphere presents the highest CO2 uptake of 2.70 mmol/g, which is much higher than the one (1.98 mmol/g) obtained at 700 °C without addition of LiCl salts in a nitrogen stream mainly due to its bigger specific surface area, higher contents of chemisorbed oxygen and carbon defect structures. Pyrolysis of rice husk in molten LiCl can effectively improve the porosity and the surface functionality of the biochar, thereby enhancing its CO2 capture performance.