Nitrogen-doped activated carbons derived from microalgae pyrolysis by-products by microwave/KOH activation for CO2 adsorption

Two types of nitrogen-doped activated carbons derived from microalgae pyrolysis by-products by microwave/ KOH activation (thermal/KOH activation as comparison) were synthesized to separate CO2 from flue gas. The nitrogen-doped activated carbons were characterized, and CO2 adsorption performance, kinetics and thermodynamics and regeneration ability on nitrogen-doped activated carbons were studied. Results display that microwave/KOH activation contributes to developed pore structure and abundant active functional groups, resulting in high CO2 adsorption capacities. CO2 adsorption processes over nitrogen-doped activated carbons (CNMK(2)/chlorella and S-NMK(2)/spirulina) are controlled via external mass transfer and are mainly physisorption. CO2 adsorption capacities of nitrogen-doped activated carbons by microwave/KOH activation are obviously better than thermal/KOH activation. The maximal CO2 adsorption capacities of C-NK(2) and S-NK(2) by thermal/KOH activation are 3.44 mmol/g and 3.09 mmol/g (25 degrees C), respectively, while the maximal CO2 adsorption capacities of C-NMK(2) and S-NMK(2) by microwave/KOH activation reach 4.21 mmol/g and 3.57 mmol/g (25 degrees C), respectively. The improvement of CO2 adsorption capacity (microwave vs. thermal) is attributed to more developed pore structure. CO2 adsorption capacities of C-NMK(2) and S-NMK(2) only reduce slightly (less than 10 %) after ten regeneration tests, showing excellent cyclic stability. The results offer beneficial reference for the application of low-cost microalgae nitrogen-doped activated carbons for CO2 separation, and effectively realize the utilization of microalgae pyrolysis by-products.

Automated summary

Nitrogen-doped activated carbons synthesized by microwave/KOH activation from microalgae pyrolysis by-products exhibit developed pore structure and abundant active functional groups, resulting in high CO2 adsorption capacities. The CO2 adsorption processes are mainly controlled by external mass transfer and are primarily physisorption. Additionally, the CO2 adsorption capacities of nitrogen-doped activated carbons by microwave/KOH activation are significantly better than those by thermal/KOH activation.