Effects of the Adsorbent Preparation Method for CO2 Capture from Flue Gas Using K2CO3/Al2O3 Adsorbents

The effect of the preparation method on the CO2 adsorption capacity of K2CO3/Al2O3 adsorbents is examined. The multi-step impregnation (MI) method enables uniform dispersion of active species (K2CO3) in the broad macropores without blocking narrower mesopores. This facilitates higher loading of accessible K2CO3 for CO2 adsorption and, hence, higher adsorption capacity. The single-step impregnation (SI) method suffers from blockage of narrower mesopores by excessive growth of K2CO3. This limits the CO2 accessibility toward active species in the porous structure because of the formation of larger active species aggregates. For 50 wt % K2CO3/Al2O3 prepared by MI and SI methods, the maximum CO2 adsorption capacity at CO2 partial pressure of 8 kPa is found to be 3.12 and 2.1 mmol/g, respectively. The regeneration efficiency of 50MI and 50SI are observed to be nearly 65 and 56%, respectively, at 130 degrees C in multi-cycle testing. The experimental data for CO2 adsorption were described by the Langmuir isotherm, and the isosteric heat as a function of fractional coverage of the adsorbent was evaluated by means of the vant Hoff equation. The isosteric heat showed a decreasing trend with an increase in the surface coverage of the adsorbent. From the results, it is concluded that the adsorbent prepared by the MI method shows better performance because of its tunable textural and morphological properties to achieve higher CO2 adsorption capacity.