Effect of micropore and mesopore structure on CO2 adsorption by activated carbons from biomass

Activated carbons (ACs) were produced by a one step process with CO2 as the physical activation agent at 800 °C. The ACs were further activated chemically using KOH, HNO3 or CH3COOH and heat-treated at 300 or 600 °C for 1 or 2 h to modify their properties. The effect of CO2 concentration, activation time, types of chemical agents and the post heat-treatment conditions on CO2 capture were investigated. Results showed that the optimum conditions for AC production from corn stalks was at 800 °C for 30 min with a CO2 concentration of 20% during the physical activation. Chemical agents and further heat-treatment modified the pore structure of the ACs, resulting in a performance improvement for CO2 adsorption. The BET surface area of one sample (HNO3 activation +100 °C water bath 1 h + post heat-treatment at 600 °C for 2 h) was 639. 8 m2/g. The maximum CO2 adsorption capacity of the sample was 7.33 wt%, which is higher than that of a commercial AC (6.55 wt%). The CO2 adsorption is dominantly dependent on the mesopore volume when the BET surface area is smaller than 500 m2/g while the adsorption is closely associated with micropore area when the BET surface area is larger than 500 m2/g. The adsorption kinetics agreed well with the Bangham kinetic model.