Impacts of nano-scale pore structure and organic amine assembly in porous silica on the kinetics of CO2 adsorptive separation

Nano structure including pore structure and amine assembly is critical for improving sorption and desorption kinetics for adsorptive CO 2 separation. The present work delineates (1) the influence of the nano-scale pore structure of amine-functionalized solid sorbents, and (2) effect of changing the assembly of amine molecules on surface of nano-porous SiO 2 on the rates of adsorption and desorption of CO 2 . 50PEI-MSN sorbent with inverted cone-shaped pores was prepared by using mesoporous silica nanospheres (MSN) with inverted cone-shaped pores for the loading of polyethyleneimine (PEI). Co-structure-directing (CSD) method was used to synthesize the sorbent with arranged amine assembly at nano-scale (2N-CSD). By comparison with 50PEI-SBA15 as a benchmark sorbent, both sorbents have improved sorption and desorption kinetics. There are significant effects of nano pore structure and amine assembly on the sorption and desorption kinetics. The inverted cone-shaped pores in MSN allow loading polymeric amines in their narrower ends and leaving larger pore mouths open for the transport of CO 2 ; 50PEI-MSN shows a maximum sorption rate of 81.4 mg·g −1 ·min −1 with average sorption rate of 25.4 mg·g −1 ·min −1 at 80 °C which are 34% and 59% higher than the corresponding values for 50PEI-SBA15; a maximum desorption rate of 38.4 mg·g −1 ·min −1 with average desorption rate of 11.8 mg·g −1 ·min −1 ramping from 30 to 95 °C which are 37% and 156% higher than the corresponding values for 50PEI-SBA15. The arranged monolayer-like amine assembly on surface of nanoporous SiO 2 likely provides high amine sorption sites through improved accessibility of amine, and 2N-CSD shows a maximum sorption rate of 60.5 mg·g −1 ·min −1 , with average sorption rate of 12.8 mg·g −1 ·min −1 at 30 °C which are 108% and 205% higher than the corresponding values for 50PEI-SBA15; a lower maximum desorption rate of 9.7 mg·g −1 ·min −1 and average desorption rate of 9.8 mg·g −1 ·min −1 ramping from 30 to 95 °C which is 250% higher than the corresponding value for 50PEI-SBA15. The present work demonstrates the importance of tailoring nano-scale pore structure and amine assembly for significantly improving sorption and desorption kinetics of adsorptive CO 2 separation.