Sorption equilibria, kinetics, and temperature-swing adsorption performance of polyethyleneimine-impregnated silica for post-combustion carbon dioxide capture

The sorption equilibria and kinetics of CO₂, N₂, and H₂O on polyethyleneimine (PEI)-impregnated silica (PEI–silica) were studied to determine CO₂ capture by temperature-swing adsorption (TSA). The experimental isotherms of CO₂ were correlated well by the dual-site Langmuir (DSL) model while those of H₂O were well-predicted by the Brunauer–Emmett–Teller (BET) model. The amounts of the components adsorbed at equilibrium were in the order of q_H2O>q_CO2≫q_N2. The isosteric heat of adsorption (Q_st) of CO₂ on PEI–silica changed from 70 to 55 kJ/mol along the sorption amount. The highly enhanced adsorption affinity of PEI–silica for CO₂ resulted in chemisorption, while the adsorptions of H₂O and N₂ exhibited typical physisorption. PEI–silica exhibited higher selectivity than KOH-treated activated carbon (KOH–AC) for the simulated flue gases, i.e., the mixture of CO₂ and N₂. Although PEI–silica became hydrophobic, the H₂O molecules were expected to affect the CO₂ capture process because of their high adsorption amount and rate. The variation in the non-isothermal kinetic behavior of CO₂ caused by pressure differed from that of H₂O because of the difference between chemisorption and physisorption. PEI–silica exhibited a high CO₂-sorption capacity of 2.3 mmol/g (pure CO₂ at 70 °C) with a high sorption rate (>90% of saturation within 1 min). Compared with the cyclic test that employs desorption in hot N₂, the working capacity decreased more when the desorption was conducted in hot CO₂ flow.