Temperature-programmed desorption of CO2 from polyethylenimine-loaded SBA-15 as molecular basket sorbents

In this work, we conducted a study on temperature-programmed desorption (TPD) of CO2 over molecular basket sorbent (MBS) consisting of polyethylenimine (PEI) immobilized in mesoporous silica SBA-15. A series of MBS sorbents with different PEI loadings in SBA-15 have been studied for CO2-TPD to gain an insight into the fundamental characteristics of CO2 sorption/desorption mechanism. Effects of sorption temperature, sorption time, and PEI molecular weight on the CO2 sorption capacity and desorption behavior of 50 wt% PEI/SBA-15 sorbent were also examined. The results show that two PEI layers, i.e., the exposed PEI layer and the inner bulky PEI layer may exist in PEI/SBA-15 sorbents, and their proportions vary with PEI loading and sorption temperature. Consequently, a two-layer model for CO2 sorption over PEI/SBA-15 sorbent is proposed, which rationalizes the sorption results with consideration of CO2 sorption kinetics and thermodynamics. It was also found that CO2 sorption capacity decreases with increasing PEI molecular weight, which may be mainly attributed to the decrease of primary amine content and the increase of tertiary amine content as well as increased interactions between polymeric chains in the PEI molecules.