Preparation of biochar adsorbent materials by pyrolysis of rapeseed pollen in supercritical CO₂

In order to improve the biomass properties and to increase the activated carbon yield, a supercritical carbon dioxide (SC-CO₂) pre-treatment technique was developed in this paper to prepare porous activated carbon (AC) precursors. Supercritical carbon dioxide has special physicochemical properties and may form unique pore structure evolution patterns during pretreatment. AC on the market is usually made from expensive and exhaustible raw materials. Activated carbon prepared from agricultural by-products has been widely used in recent years. Biochar precursors were prepared by pretreating rapeseed pollen (RP) in SC-CO₂, and then biochar adsorbent materials were prepared by KOH activation method. The effect of pretreatment temperature and time on final activated carbon yield and properties was investigated. The results showed that the SC-CO₂ pretreatment could effectively improve the performance and yield of the biochar adsorbent materials. Compared with direct activation of rapeseed pollen, the yields were increased by 36–91 %. The specific surface area of directly activated rapeseed pollen was only 194.19 m² g⁻¹, whereas the optimal specific surface area after pretreatment was 2338.22 m² g⁻¹. The surface area of activated carbon is comparable to that of commercial activated carbon, and KOH activation contributes to the formation of micropores in activated carbon.