Superior CO2 adsorption on pine nut shell-derived activated carbons and the effective micropores at different temperatures

• Pine nut shell-derived activated carbon with superior CO2 uptake is successfully prepared.
• CO2 adsorbed amounts are up to 3.3 mmol/g at 273 K and 0.7 mmol/g at 348 K at 0.15 bar.
• Accurate micropore range for CO2 adsorption at different temperatures are revealed.
• Micropores in the range of 0.33–0.40 nm are effective for CO2 adsorption at 348 K and 0.15 bar.

Pine nut shell-derived activated carbons were prepared at different KOH/C mass ratios and activation temperatures, and they were used to adsorb CO2 at different adsorption temperatures and pressures. The optimal activated carbon had the CO2 adsorption of up to 7.7 mmol/g at 273 K and 5.0 mmol/g at 298 K at 1 bar, the highest capacities at ambient pressure among all the biomass-derived carbons. The micropore distribution of activated carbons was highly dependent on the KOH/C ratio and activation temperature in the preparation. The activated carbons with larger micropores suffered the greater loss of CO2 adsorbed amounts at high adsorption temperatures. The accurate ranges of micropores responsible for CO2 adsorption at different temperatures were fully studied. When the adsorption temperature increased from 273 to 348 K, the ranges of effective micropore for CO2 adsorption at 1 bar narrowed from 0.33–0.82 nm to 0.33–0.52 nm. Under typical flue gas conditions at 348 K and CO2 partial pressure of 0.15 bar, the effective micropore range decreased to 0.33–0.40 nm, and the CO2 adsorbed amount was about 0.7 mmol/g on p-2–973–1.5. The accurate micropore ranges obtained are helpful in the preparation and selection of efficient activated carbons for CO2 adsorption under different conditions.

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