Insights into adsorption separation of N₂/O₂ mixture on FAU zeolites under plateau special conditions: A molecular simulation study

Adsorption thermodynamics of N₂ and O₂ on faujasite (FAU) zeolites with different Si/Al molar ratios under plateau conditions of wide ranges of temperature and humidity for pressure swing adsorption (PSA) oxygen production were studied based on validated molecular simulations. Binary adsorption isotherms and N₂/O₂ selectivity on each adsorbent were obtained. The results suggest that dehydrated feed air with very low dew point of 213 K could still lead to ~10 wt% water adsorption capacity in FAU zeolites. The effect of water content was larger than that of temperature change on N₂/O₂ separation performance, causing reductions in N₂/O₂ selectivity of 50.9% and affinities of 15.6% and 10.6% for N₂ and O₂ at 238 K, and those of 45.7%, 13.7% and 11.1% at 298 K on FAU-1.1, respectively. The strong interaction of water with zeolites via hydrogen bond was shown to decrease the pore volume by 25.61%, occupy the cationic sites, and thermodynamically form competitive adsorption over N₂ and O₂. The increase in Si/Al molar ratio suppressed the negative impact of water and temperature change but sacrificed the N₂/O₂ selectivity. To reach an optimal balance between the air separation performance and the adsorbent robustness, X zeolites with Si/Al molar ratio close to 1.5 would be recommended for PSA O₂ production under the plateau special condition.