It is believed that reducing CO2 emissions into the atmosphere is essential for the purpose of preventing global warming. Solid amine adsorbents have been intensively investigated for their excellent CO2 selectivity, fast adsorption kinetics, and high adsorption capacity in industrial CO2 capture, but the expensive and complex fabricating of supports restricts their application prospect. Herein, an azeotropic-distillation nano-SiO2 (AD-SiO2) support with a pore volume of 2.52 cm3/g was synthesized from coal fly ash, using the CO2-assisted precipitation and n-butanol azeotropic distillation methods. A serial of amine@AD-SiO2 adsorbents were synthesized via impregnating the triethyltetramine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), or polyethyleneimine (PEI) onto the AD-SiO2 support, respectively. The synthesized amine@AD-SiO2 adsorbents exhibited outstanding adsorption capacities of 3.50–6.13 mmol/g under 90 °C and 100% CO2 atmosphere. Furthermore, liquid-phase NMR revealed that the CO2 adsorption capacity decreased along with the increase of amine's molecular weight, due to the ratio drop of primary amine and secondary amine. According to kinetic modeling, the CO2 adsorption rate decreased with an increase in amine's molecular weight and a reduction in CO2 partial pressure. The cyclic adsorption-regeneration tests indicated that the slight decay of amine@AD-SiO2 adsorbents was ascribed to the volatilization of tiny-molecular amines of TETA and TEPA. The PEHA@ AD-SiO2 adsorbent still possessed a final CO2 uptake of 4.24 mmol/g after 50 cycles, with merely 0.18% decay per cycle. Therefore, with a further understanding of the adsorption properties of various adsorbents, AD-SiO2 with simple synthesis and affordable cost has promising applications for future industrial CO2 capture.

Facile and efficient amine@AD-SiO2 adsorbents from coal fly ash: Comparison of CO2 adsorption capacity and stability for various amines

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