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 CO 2 capture route for globe climate change mitigation. The pore structure of nano supports generally plays a crucial role in the CO 2 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-SiO 2 (AD-SiO 2 ) support was recycled from coal fly ash (CFA) using the CO 2 -assisted precipitation and n-butanol AD methods, and possessed a super pore volume of 2.52 cm 3 ·g −1 and an average pore size of 36.6 nm. After impregnating the triethyltetramine, tetraethylenepentamine, pentaethylenehexamine (PEHA), or polyethyleneimine, the synthesized amine@AD-SiO 2 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-SiO 2 support. Based on the viscosity, TGA and liquid-NMR characterization, we explained that the large amine molecule would block the CO 2 diffusion channel and thus restrict the active sites, while the small amine molecule would evaporate during the regeneration process. Inspiringly, the PEHA@AD-SiO 2 adsorbent possessed the excellent cyclic stability with merely 0.18 % decay per cycle and achieved a final CO 2 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-SiO 2 support from CFA, thereby is a low-carbon technology for large-scale industrial CO 2 capture.