Adsorption separation of O2/N2 by Li-RHO zeolite with high oxygen selectivity

Abstract

Zeolites traditionally used for air separation are generally N2 selective adsorbents. However, separation of air by adsorption of lesser amounts of O2 is more desirable. In this study, RHO zeolite was successfully synthesized by the hydrothermal method, and a high oxygen selective adsorbent was developed by introducing Li+ with different exchange degrees into the RHO zeolite framework by ion exchange. The equilibrium isotherms for the adsorption of Li-RHO zeolites with different ion exchange degrees on the pure components O2 and N2 were measured and fitted with the Langmuir model equation. The adsorption results showed that the cation sites and ion exchange degree played a decisive role in adjusting the window pore size of RHO zeolites. A comparison of the adsorption equilibrium selectivity reveals that Li-RHO zeolite achieved thermodynamic O2 selective adsorption. In addition, the ideal adsorption solution theory model (IAST) in this study predicts the highest O2/N2 separation performance parameters of Li-RHO zeolite for N2 (79%)/O2 (21%) binary mixtures. Meanwhile, Li-RHO was simulated simultaneously with industrial nitrogen production adsorbents such as 4A and CMS in an Aspen Adsorption two-tower PSA process. The highest product recovery was achieved for Li-RHO at an approximate purity of 92%. Therefore, Li-RHO may be a viable alternative to 4A and CMS in the PSA process, providing new clues for developing O2-selective adsorbents for air separation.