Modeling the Adsorption of CO₂/N₂ Mixtures on Siliceous Nanoporous Materials

In this work, the CO₂/N₂ separation behavior of Silicalite-1 and pure silica MCM-41 adsorbents, synthesized by hydrothermal process starting from different molar gel compositions, was evaluated at several different working pressure values by means of the ideal adsorbed solution theory (IAST). Prior to IAST calculations, CO₂ and N₂ adsorption isotherms at 293 K were collected for all synthesized materials and successfully fitted using the Freundlich empirical model. It was found that, for a hypothetic application in a PSA/VSA process, the Silicalite-1 type microporous adsorbent with the highest Na content synthesized here allows an easy regeneration (high working capacity) to be achieved, even if the CO₂/N₂ selectivity is not very high. At the same time, the most ordered among the produced M41S mesoporous materials, obtained using a Na₂O/SiO₂ molar ratio in the synthesis gel at least equal to 0.15, appear to be very promising adsorbents for CO₂ separation because of their very high CO₂/N₂ selectivity.