Activated carbons prepared from peanut shell and sunflower seed shell for high CO2 adsorption

Biomass wastes are considered as cost-effective and sustainable precursors to prepare activated carbons for CO2 capture. In this study, two biomass-derived activated carbons were prepared using peanut shell and sunflower seed shell, and the optimal activated carbons were obtained at low KOH/carbon ratio of about 1. The peanut shell derived activated carbon (P-973-1.00) and sunflower seed shell derived activated carbon (S-973-1.25) exhibited CO2 uptake of 1.54 and 1.46 mmol/g, respectively, at 298 K and 0.15 bar, among the activated carbons with the highest CO2 adsorption. Although P-973-1.00 had much lower surface area and micropore volume than S-973-1.25, it possessed higher CO2 uptake at 298 K and 0.15 bar due to the higher volume of micropores in the range of 0.3-0.44 nm. The calculated higher isosteric heat values at lower CO2 uptake indicated the strong affinity of CO2 in these micropores. The ordered micro-sized pores in the activated carbons were favorable for CO2 diffusion into the porous materials and adsorption in the inner micropores. The activated carbons had moderate CO2 selectivity over N-2 at 1 bar, but the selectivity was significantly enhanced at 0.15 bar. The spent activated carbons after vacuum regeneration exhibited stable CO2 adsorption in five cycles, showing the high reusability for CO2 capture.