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

Solid amine adsorbent is recognized as an efficient CO2 capture route for globe climate change mitigation. The pore structure of nano supports generally plays a crucial role in the CO2 adsorption performance of solid amine adsorbents; however, the involving of costly and toxic pore-expanding agents limited their scalable application. Herein, an azeotropic-distillation nano-SiO2 (AD-SiO2) support was recycled from coal fly ash (CFA) using the CO2-assisted precipitation and n-butanol AD methods, and possessed a super pore volume of 2.52 cm3·g−1 and an average pore size of 36.6 nm. After impregnating the triethyltetramine, tetraethylenepentamine, pentaethylenehexamine (PEHA), or polyethyleneimine, the synthesized amine@AD-SiO2 adsorbents achieved the excellent adsorption capacity of 3.50–6.13 mmol·g−1 and the fast adsorption kinetics, owing to the superior pore structure of AD-SiO2 support. Based on the viscosity, TGA and liquid-NMR characterization, we explained that the large amine molecule would block the CO2 diffusion channel and thus restrict the active sites, while the small amine molecule would evaporate during the regeneration process. Inspiringly, the PEHA@AD-SiO2 adsorbent possessed the excellent cyclic stability with merely 0.18 % decay per cycle and achieved a final CO2 uptake of 4.24 mmol·g−1 over 50 cycles. This study notably improved the long-term adsorption capacity of solid amine adsorbents via the pore-expanded AD-SiO2 support from CFA, thereby is a low-carbon technology for large-scale industrial CO2 capture.