One-step conversion of agro-wastes to nanoporous carbons: Role in separation of greenhouse gases

Abstract

Highly microporous carbons have been synthesized from four types of agro-wastes of lignin, walnut shells, orange peels and apricot seeds by one-step carbonization/activation with potassium hydroxide (KOH) in varying ratios. The resultant carbons demonstrated BET specific surface areas of 727-2254 m²/g, and total pore volumes 0.34-1.14 cm³/g. These are higher than the majority of agro-waste derived carbons reported in the literature. For all the carbons, CO₂ adsorption at 298 K was higher than SF₆ followed by N₂ suggesting a possible separation of CO₂ and SF₆ from N₂. The adsorbed amounts of CO₂ at 298 K and 273 K and at pressures up to 760 Torr were 7.24 and 9.4 mmol/g, respectively which, to the best of our knowledge, are the highest CO₂ uptakes in these temperatures by any carbon material reported so far. For all the gases, selectivity, mixed adsorption isotherms and adsorption breakthrough have been simulated from experimental data.

Keywords: Activated carbon; Agro-waste; Carbon dioxide; Greenhouse gas; Sulfur hexafluoride.