Study of KOH-activated hydrochar for CO2 adsorption

Abstract

The use of solid porous materials for CO2 capture is a more environmentally benign approach than conventional wet scrubbing using amine-based solutions. Therefore, in this study, porous carbon materials were prepared using sawdust through hydrothermal carbonization (HTC) to produce hydrochar, followed by KOH activation. The results showed that KOH-activated hydrochar had a specific surface area of 646–1195 m2/g, and a micropore area of 547–1059 m2/g, indicating a microporous structure was developed. The highest CO2 adsorption capacity at tested adsorption temperatures was achieved from activated hydrochar obtained at 750 °C (40 °C: 0.95 mmolCO2/gsample; 75 °C: 0.80 mmolCO2/gsample), which is higher than pristine hydrochar (40 °C: 0.05 mmolCO2/gsample; 75 °C: 0.04 mmolCO2/gsample). Physisorption through pore diffusion and surface coverage and chemisorption involving formation of covalent bonds between adsorbent’s surface functionality and CO2 both contributed to CO2 adsorption. Importantly, the presence of N-containing chemicals, particularly the presence of N-containing functional groups on the surface, played an important role in CO2 adsorption capacity. Based on the current results and relevant literature, the development of ultra-micropore and the introduction of more N-containing functional groups to the surface would be the research focuses to further increase the CO2 adsorption capacity.