Improving low-pressure CO2 capture performance of N-doped active carbons by adjusting flow rate of protective gas during alkali activation

Alkali-activated N-doped active carbon (AC) is a promising material for capturing CO2, but the possible role of flow rate of protective gas during alkali activation in adjusting CO2 capture performance of AC is unknown. In this study, N-doped ACs for low-pressure CO2 capture were prepared from chitosan char by KOH activation under flowing N2 to study the effects of protective-gas flow rate on ultramicropore volume, chemical composition, and CO2 capture performance of ACs. The results showed that increasing the flow rate changed the low-pressure CO2 uptake and CO2/N2 selectivity by varying the ultramicropore volume and/or surface N/C ratio of ACs. Adopting a moderate flow rate during AC preparation was most favorable for enhancing low-pressure CO2 capture performance. The sample prepared at this flow rate displayed high CO2/N2 selectivity, excellent recyclability, and moreover, a CO2 uptake of 1.86 mmol/g (0.15 bar, 25 °C) which ranked among the highest values ever reported for N-doped ACs. This research revealed that controlling gas flow rate was an effective strategy to improve the CO2 capture performance of ACs and should be taken seriously during preparation of ACs for CO2 capture.

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