Comprehensive study of CO2 capture performance under a wide temperature range using polyethyleneimine-modified adsorbents

Amine functional adsorbents for CO2 capture have attracted increasing attention as a possible alternative to aqueous amine. Temperature has been proven to be an important parameter that affects the CO2 capture performance, but previous studies often yielded different optimal temperature ranges during texting and lacked multiple evaluation indicators for adsorption performance. In this study, we prepared silica modified with different loadings (10-55%) and molecular weights (600-25000 Da) of polyethyleneimine (PEI) to compare the adsorption performance under a wide temperature range (30-120 °C), which covered the temperature requirements in most applications of CO2 capture and separation. To evaluate these adsorbents comparatively, CO2 adsorption capacity, CO2 adsorption kinetics, thermal stability and cyclic adsorption-desorption stability were determined. In general, the adsorbents with higher PEI loadings and molecular weights, such as 45-55 wt.% loadings or 1200-25000 Da molecular weights, were more suitable for CO2 capture at relatively high temperatures, such as 90-120 °C. However, the performance of these adsorbents was not as good as several other adsorbents with lower PEI loadings or molecular weights for application at lower temperature, such as in CO2 capture at ambient temperature. In addition, the essential reasons for the influence of temperature were also investigated based on the inherent properties of the adsorbents. The suppression effect and the promotion effect were proposed to explain why the optimum temperature ranges of the adsorbents were so different.