Kim MH

Vol. 24,  No. 1, pp. 41-49, Mar.  2018
10.7464/ksct.2018.24.1.041

CO2 adsorption Calcium-exchanged Y zeolites High working capacity Selectivity factor Local basicity

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Y zeolites with different extra-framework cations, such as Na+, Li+, Ca2+, and Cu2+, with different charge and ionic radius have been investigated to greatly enhance a working capacity (W) of CO2 adsorption at 25 ℃ and a CO2/CO selectivity factor (S). A sample of NaY with a very small amount of 0.012% Ca2+ was fully reversible for seven times repeated CO2 adsorption/ desorption cycles, thereby forming no surface carbonates unlikely earlier reports. Although at pressures above 4 bar, 2.00% CaY, 1.60% CuY and 1.87% LiY all showed a CO2 adsorption very similar to that measured for NaY, they gave a significant decrease in the adsorption at lower pressures, depending on the metal ion. At 0.5 ~ 2.5 bar, the extent of CO2 adsorption was in the order NaY > 1.60% CuY > 2.00% CaY > 1.87% LiY. All the Na+-based metals-exchanged zeolites have a FAU (faujasite) framework and a Si/Al value near 2.6; thus, there is no discernible difference in the framework topology, framework chemical compositions, effective aperture size, and channel structure between the zeolite samples. Therefore, the distinctive behavior in the adsorption of CO2 with a character as a weak Lewis acid is associated with the site basicity of the zeolites, and the interaction potentials of the cations. Different trend was shown for a CO adsorption due to weaker quadrupole interactions. Adsorption of CO2 and CO on samples of CaY with 0.012 to 5.23% Ca disclosed a significant dependence on the Ca loading. The CO2 adsorption increased when the cation exists up to ca. 0.05%, while it decreased at higher Ca amounts. However, values for both W and S could greatly increase as the bare zeolite is enriched by Ca2+ ions. The 5.23% CaY had W = 2.37 mmol g-1 and S = 4.37, and the former value was comparable to a benchmark reported in the literature.