Insect-derived biochar for CO2 adsorption under humid conditions: Elucidating adsorption mechanisms and competitive interactions with water molecules

초록

The CO2 adsorption capacity of biochar depends on the type of biomass used and its physicochemical properties; various sorption parameters including temperature, CO2 concentration, and humidity affect the CO2 adsorption capacity. Biochar derived from defatted black soldier fly larvae (BSFL) biomass was investigated for direct CO2 capture and exhibited a hydrophilic/mesoporous structure that contained high concentrations of alkali and alkaline metals (>10 wt%), which contribute to CO2 chemisorption. The CO2 adsorption efficiency was higher at 25 °C compared with that at 30 °C and 35 °C, probably due to reduced Brownian motion of CO2 molecules at lower temperatures. The adsorption process followed the Langmuir isotherm, suggesting monolayer adsorption. Kinetic modeling indicated that physical and chemical adsorption mechanisms were involved; physisorption predominated. The presence of water molecules resulted in competitive adsorption with CO2, with 2.5 water molecules competing for adsorption sites at 70 % relative humidity and 1200 ppm CO2. In the cyclic adsorption-desorption tests, the CO2 adsorption capacity decreased by approximately 11 % after the first cycle, probably because a portion of the chemically adsorbed CO2 did not fully desorb during regeneration. The findings of this study could aid in the development of more efficient biochar-based materials for CO2 capture.

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