Novel Pei@Csh Adsorbents Derived from Coal Fly Ash Enabling Efficient and In-Situ Co2 Capture: The Anti-Urea Mechanism of Pore-Expanded Csh Support

The solid amine adsorption is considered to be the most promising technology for post-combustion CO2 capture, but it still has drawbacks for high cost of support materials and easy occurrence of CO2-induced chemical deactivation. Herein, we proposed a novel environmentally friendly method for efficient and stable solid amine adsorbents: The calcium silicate hydrate (CSH) support with pore volume of 3.0 cm3·g-1 was synthesized from coal fly ash (CFA) with the pore-expanded assistance of azeotropic distillation, and then the PEI@CSH adsorbents were prepared by impregnating polyethylenimine (PEI) into the pores of CSH support. The adsorption capacity of the prepared 60%PEI@CSH-0.1 adsorbent reached 198 mg·g-1 and exhibited excellent cyclic stability of only 1.9% attenuation after 10 cycles under ideal regeneration conditions. Even under realistic regeneration conditions (at 150 ℃ with 100% CO2), the CO2 uptake still remained 103 mg·g-1 after 10 cycles, which showed obvious advantages than the commercial SiO2 supports. A serials of characterization techniques of FT-IR, solid-state NMR and DFT calculation were performed to explained the anti-urea mechanism of CSH support; consequently, the CSH support promoted the conversion of primary amines to secondary amines in PEI molecules, and thus effectively inhibited the inactivation caused by the formation of urea compounds. Therefore, the PEI@CSH adsorbents provides a low-cost and high-efficiency approach for both in-situ CFA utilization and CO2 mitigation inside the coal-fired power plants.