Lithium Type X Zeolite as a Superior Sorbent for Air Separation

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Abstract
Li-X, Ba-X, and Li-A zeolites are prepared by ion exchange with the commercial Na-X (13X) and Na-A (4A) zeolites. At the ambient temperature (298 K), only Li-X exhibits a significant enhancement of the N2/O2 adsorption selectivity over the commercial zeolites. At a pressure of 1 atm, the N2/O2 selectivity is increased from approximately 3 for 13X and 4A to approximately 7 for Li-X. Air separations by the two sorbents Li-X and Na-X are compared using a commercial 5-step air-separation pressure swing adsorption (PSA) cycle. The comparison is made by using a mathematical model of proven predictive ability. A parametric comparison shows superior separation results for the Li-X zeolite under all PSA conditions. For example, the Li-X sorbent gives >90% O2 purity and an O2 recovery of over 70% at a feed rate of >5.65 s× 105 L STP/h. In addition, for the same O2 purity and feed rate, the Na-X sorbent gives an O2 recovery of less than 30%. Hence the replacement of the commercially used Na-X sorbent by the Li-X sorbent will result in an energy saving of over 50%.