Low temperature CO2 capture on biomass-derived KOH-activated hydrochar established through hydrothermal carbonization with water-soaking pre-treatment

This work scrutinizes the development of activated hydrochar (HC) as a low-cost bio-sorbent for low temperature CO2 capture. Accordingly, rambutan peel (RP) was used as a lignocellulosic precursor to produce HC via water-soaking pre-treatment of the biomass followed by hydrothermal carbonization. Then to enhance the microporosity, the developed HC was activated using potassium hydroxide (KOH) at various operating conditions including different activation temperatures (600–900 °C), activation times (60–180 min) and KOH:HC ratios (1:1–4:1). The KOH-activated HC possessed the highest CO2 adsorption capacity (122.37 mg g−1 at 30 °C and 1 atm) when activated using KOH:HC ratio of 2:1 at 850 °C for 120 min with the involvement of water-soaking pre-treatment. Results indicated that water-soaking of biomass prior to the HTC, the HTC process itself and chemical activation of HC could individually enhance the CO2 capture capacity of the resulting adsorbent. Gas selectivity study verified the high affinity of the developed adsorbent towards CO2 compared to other gases such as air, methane and nitrogen. Apart of that, very stable performance of the adsorbent in ten cycles of CO2 adsorption/desorption was demonstrated. Conclusively, the kinetic study proposed that CO2 adsorption mechanism on the adsorbent was governed by physisorption.