Highly efficient CO2 capture on acid-treated sepiolite impregnated with mixed polyethyleneimine and diethanolamine

Abstract

Amine-functionalized solid adsorbents exhibit broad prospects in CO 2 capture from flue gases due to their high adsorption capacity and selectivity. However, reported adsorbents are still facing challenges, including high costs, the easy agglomeration of polyamines, and limited adsorption temperature ranges. In this study, sepiolite-based mixed amine adsorbents are prepared by synergistically impregnating acid-treated sepiolite with a mixture of polyethyleneimine (PEI) and diethanolamine (DEA). Results show that at a PEI/DEA loading ratio of 1:1 and a mixture loading of 60wt%, the CO 2 adsorption capacity of the resulting adsorbent increases from 0.58 mmol/g for acid-treated sepiolite to 2.89 mmol/g at 60 °C, and remains above 2.50 mmol/g after 10 cycles. Meanwhile, the optimized adsorbent maintains a capacity of over 2.44 mmol/g within the temperature range of 30–70 °C. Additionally, the CO 2 selectivity and maximum heat of adsorption for the optimized adsorbent are calculated to be 1184 and 60.08 kJ/mol, respectively. An improved CO 2 adsorption capacity is obtained, an increase from 0.052 mmol/g for acid-treated sepiolite to 1.60 mmol/g. Furthermore, an in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) analysis reveals that the introduction of DEA into PEI helps in polyamine dispersion, thereby enhancing CO 2 adsorption capacity. The CO 2 capture mechanism follows a zwitterionic reaction, where CO 2 is ultimately converted into carbamate and carbamic acid. Overall, the as-prepared sepiolite-based mixed amine adsorbents, which are characterized by high CO 2 adsorption capacity and selectivity, low cost, broad adsorption temperature range, moderate heat of adsorption, and good cycle stability, show promising potential for industrial applications.