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

Abstract

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 qH2O>qCO2≫qN2. The isosteric heat of adsorption (Qst) 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.