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Commercial type X zeolites (Linde 13X) are nitrogen selective. Oxygen is the less abundant component in air; hence oxygen selective sorbents are desired for air separation. Mixed Na-Ce type X zeolites containing different ratios of Ce3+/Na+ ions are prepared by partial ion exchange of commercial X zeolite. The adsorption isotherms of nitrogen, oxygen and argon are measured and the pure-component selectivity ratios are compared and analyzed against commercial zeolites (13X) for air separation. Oxygen selectivity over nitrogen (∼1.5) and argon (∼4.0) are seen for mixed Na-Ce type X zeolite (Si/Al = 1.25; Ce3+/Na+ < 4.0) from Henry's constant determined from low pressure adsorption measurements. The oxygen and nitrogen isotherms cross over for mixed Na-Ce type X zeolite (Si/Al = 1.25; Ce3+/Na+ < 4.0), and the pressure at which cross they over increases as Ce3+/Na+ approaches 1. The oxygen selectivity as claimed in the patent by N.V. Choudary, R.V. Jasra, and S.G.T. Bhat (US Patent no. 6,087,289, 2000) is seen only at very low pressures in the volumetric adsorption measurement and the hydrogen treatment of the Ce-exchanged samples have no effect on the adsorption characteristics. |
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