Oxygen Selectivity on Partially K Exchanged Na-A Type Zeolite at Low Temperature

Abstract

In previous work by the authors on Na-A zeolite (Izumi et al., Japan Patent Toku-Kou-Shou 63-058614, 1988), it was shown that the combination of high-temperature calcination and operation of the adsorption step at low temperatures improved the selectivity for oxygen over nitrogen from air (Izumi et al., CATS J Meeting Abstracts, 31(2A), 10, 1989; Izumi and Suzuki, Adsorption, 6, 2000). Berlin discloses in his U.S. Patent 3282028 (1966) that the partial exchange of potassium ions for sodium ions in the Na-A type zeolite also improved selectivity for oxygen by reducing the uptake rate of nitrogen. It was therefore expected that the oxygen selectivity of Na-K-A with high-temperature calcination and low-temperature adsorption might be enhanced. For the confirmation of optimum conditions for the appearance of oxygen selectivity on Na-K-A, samples were prepared with a K exchange ratio varied from 0–20 mol% (0–2.4 K ions/unit cell), and a calcination temperature varied from 923 to 1073 K, and an experiment concerning oxygen and nitrogen adsorption on Na-K-A was undertaken with a small adsorbent column under pressure swing adsorption (PSA) conditions at adsorption temperatures from room temperature to 213 K. It was found that (a) the K exchange ratio of 7 mol% (0.84 K ions/unit cell), and (b) the calcination temperature of 993 K, resulted in a remarkable increase in oxygen selectivity. Under optimum conditions for Na-K-A, the oxygen separation factor was about 8. Na-K-A has the potential to effectively separate oxygen and nitrogen from air by means of PSA.