To date, CO2 capture and geological storage provide a practical way to mitigate the excessive CO2 emission into the atmosphere. Since the CO2 adsorption separation is the first and most energetic and intensive step, it is of importance to select the proper adsorbent for the design of an efficient process. As unique solid adsorbents, zeolites are highly effective for removing CO2 that are present in a large gas flow.
NaY zeolite particles with a high surface area of 723 m2/g were synthesized by a hydrothermal method. Adsorption isotherms of pure gases CO2 and N2 on the synthesized NaY particles were measured at temperatures 303, 323, 348, 373, 398, 423, 448 and 473 K and pressures up to 100 kPa. It was found that the adsorption isotherm of CO2 on the synthesized zeolite is higher than that on other porous media reported in the literature. All measured adsorption isotherms of CO2 and N2 were fitted to adsorption models of Sips, Toth, and UNILAN in the measured temperature/pressure range, and Henry's law adsorption equilibrium constants were obtained for all three adsorption models. The adsorption isotherms measured in this work suggest that the NaY zeolite may be capable of capturing CO2 from flue gas at high temperatures. In addition, isosteric heats of adsorption were calculated from these adsorption isotherms. It was found that temperature has little effect on N2 adsorption, while it presents a marked decrease for CO2 with an increase of adsorbate loading, which suggests heterogeneous interactions between CO2 and the zeolite cavity. Ideal adsorbed solution theory (IAST) was applied to predict the adsorption isotherms of CO2-N2 gas mixture. It turned out that the total adsorbed amounts at pressure 100 kPa were mainly CO2 (>88%). The mole fraction of adsorbed CO2 decreases as temperature is increased.
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