Silica-alumina zeolite adsorbents for oxygen generation via pressure swing adsorption: Mechanisms and challenge

The adsorptive generation of oxygen from air has become increasingly important in the chemical and medical industries due to the growing demand for O2 with high purity. Among the commonly used three methods of cryogenic distillation, pressure swing adsorption (PSA) and membrane separation for N2/O2 separation, PSA has received much attention due to the advantages of small volume, low management cost, and short start-up time, etc. Zeolites, with their unique pore structure, highly polarized pore environment, and abundant ion exchange sites, are widely employed as an efficient adsorbent in N2/O2 separation. Hence, in this work, a review about the application of zeolites in O2 generation via PSA was performed. In detail, the common PSA techniques applied for O2 generation were summarized and compared from both the characteristics and application scenarios firstly. Then, the main mechanisms of O2 separated from N2 in air over zeolite by adsorption were summarized from three aspects of the steric effect, kinetic effect and equilibrium effect. Based on above, the requirements for silica-alumina zeolite adsorbents to improve the O2 purity clarified from skeleton topology, extra-framework cations as well as physical & chemical properties. Moreover, the operation conditions and impurities having a significant effect on the product O2 quality were discussed. Finally, both the challenges and prospects of air separation and O2 generation are proposed based on existing research results.