Performance of Li exchange hierarchical X zeolite for CO2 adsorption and H2 separation

Li exchange hierarchical X zeolite (Li-H-X) was prepared by decationization of X zeolite by NH4Cl solution followed by Li exchange and subsequent calcination. NH4-X and Li-X were prepared to compare the results of LiH-X. XRD, FE-SEM, EDS, N2 adsorption-desorption, and micro-/mesoporous volume were performed. The higher mesoporosity was confirmed in Li-H-X due to the framework dealumination during decationization. Static and dynamic sorption capacity of sorbents was evaluated to identify the performance of sorbent. The CO2 and H2 equilibrium adsorption capacity of Li-H-X was found to be 9.6 mmol g-1 and 0.78 mmol g-1, respectively, at 298 K and 20 bar, which was 25 % (CO2) and 30 % (H2) higher than Li-X. Static experimental data were validated using the Langmuir, Freundlich, and Sips models. The CO2 & H2 dynamic sorption capacity of Li-H-X sorbent for binary gas (CO2/H2, 25/75 %) was 4.145 mmol g-1 and 0.258 mmol g-1 at 303 K and 10 bar. The higher sorption capacity of Li-H-X was obtained due to large micro-/mesoporous volume of sorbent, which may allow to access unoccupied sites at higher pressure. This result reveals that micro-/mesoporous structure of zeolite adsorbs significantly higher CO2 from binary gas stream, which can use to separate pure H2 from gas stream.