Silica/polyethyleneimine composite adsorbent S-PEI for CO₂ capture by vacuum swing adsorption (VSA)

SBA15 type mesoporous silica was combined with a pore volume equivalent of branched polyethyleneimine PEI (MW 1200) to prepare a high capacity adsorbent S-PEI for the selective capture of CO₂ from post combustion flue gas via pressure / vacuum swing adsorption (VSA). The adsorbent was characterized by helium pycnometry, N₂ adsorption / desorption at 77 K, powder X-ray diffraction XRD and thermogravimetric analysis. The potential of S-PEI for CO₂ capture via VSA was assessed by both CO₂ partial pressure swing adsorption (PPSA) studies via combined thermogravimetric analysis (TGA) / differential thermal analysis (DTA), and by CO₂ pressure / vacuum swing adsorption (VSA) studies via a custom bench gas sorption analyzer. The CO₂ sorption capacities determined by partial pressure swings were consistent with those determined by pressure / vacuum swings as expected by the Henry gas law and therefore demonstrate the validity of PPSA to estimate VSA process working capacities. S-PEI was found to exhibit greater working CO₂ capacity than zeolite 13X at 105 °C under key process conditions (0.05 - 0.15 atm CO₂) from either anhydrous or humidified (̃1 % H₂O) process gas. The amine adsorbent was also found to exhibit a higher H_ads(CO₂) (70-90 kJ.mol^-1 than zeolite 13X (30-40 kJ.mol^-1) as was expected for a chemisorption process. Zeolite 13X however was found to exhibit faster sorption kinetics under anhydrous process conditions consistent with its lower H_ads(CO ₂). Pelletized S-PEI exhibited the same good sorption kinetics as the powder, however with slightly reduced CO₂ working capacity, 2.5 wt% at 105 °C, and minimal void volume, equivalent to 29.3 g of CO₂ per L of sorbent bed. S-PEI was thus found to be attractive for CO₂ capture from post combustion flue gas via VSA.