Zeolite is one of the most common adsorbents which are major part of PSA system. The chemical compositions of zeolite adsorbents can be changed by the ion exchanges of positive ions. The ion exchange can affect the adsorptive selectivity of oxygen and nitrogen by varying the size of slit and adsorpt...
Zeolite is one of the most common adsorbents which are major part of PSA system. The chemical compositions of zeolite adsorbents can be changed by the ion exchanges of positive ions. The ion exchange can affect the adsorptive selectivity of oxygen and nitrogen by varying the size of slit and adsorption potentials. Therefore, it is very important to optimize the air separation by means of the understanding of the proper ion exchanges and characteristics of zeolite adsorbent. In this study, commercial zeolites, types A and X, was ion-exchanged with various metal ions, and the ion-exchange kinetics and equilibrium ion-exchange capacity were investigated. The properties of ion-exchanged zeolites were also examined by XRD, FTIR, SEM, EDS, and TGA. To produce high purity oxygen from air by Pressure Swing Adsorption(PSA), Not only was a zeolite absorbent which has highly adsorption selictivity of nigrogen deveolped but also a PSA process was designed. The crystal structure and acid features of the zeolite could be regulated by exchanging cation or replacing Si and A1 ofthe crystal structure with other elements. And it could be applied to a wide range of petrochemical process and precision chemical process based on the characteristics of replaced elements. The matal ions Li, Ag, Ca, Br, Sr, etc. were investigated for ion exchange with zeolite. Sr ion was showed the highest ion exchange rate among these metal ions and all metal ions were exchanged with Na ion at equivalent rate. The selectivity of ions was in the order Sr2+ > Ag+ > Ba2+ > Ca2+ > Li+. It is verified that the original structure of the zeolites is maintained after the ion exchange by XRD, FTIR, SEM and EDS, and that almost all of the Na+ ions within the zeolite are ion-exchanged. Compared with the NaX adsorbent, the ion exchanged zeolite X adsorbent remarkably improved its adsorption performance of nitrogen at the conditions of 283~313K temperature and 0.1~10 atm pressure. The adsorbed amounts of both nitrogen and oxygen are high at low temperature. In addition, thy increase as pressure rises. The experimental data obtained were correlated by the Langmuir, Freundlich, Langmuir-Freundlich, Redlich-Peterson and Toth equations. The Langmuir and Freundlich isotherms model showed a good agreement with the experimental data. The case of zeolite NaA and zeolite NaX, which is not ion-exchanged, the nitrogen absorption amounts are nearly same, but the nitrogen absorption amounts for zeolite MX are remarkably larger than zeolite MA in case of the ion-exchanged. At an equilibrium pressure under 0.5 atm, adsorption performance of nitrogen on the ion exchanged zeolite adsorbent increased in the order of Ag+ > Li+ > Ca2+ > Sr2+ > Ba2+ > K+, whereas at an equilibrium pressure over 1 atm showed in the order of Li+ > Ag+ >Ca2+ > Sr2+ > Ba2+ > K+. Absorption of the Li increases gradually as the pressure gets higher, and it shows the higher value at 1atm compared to the Ag’s value. Nitrogen/Oxygen separation factor of Li ion exchanged zeolite X adsorbent was 13.021 at the partial pressure of nitrogen/oxygen gas mixture similar to air and 293K adsorption temperature. The Li-X absorbent is considered as a better solution for the environmental and economical aspects.
Zeolite is one of the most common adsorbents which are major part of PSA system. The chemical compositions of zeolite adsorbents can be changed by the ion exchanges of positive ions. The ion exchange can affect the adsorptive selectivity of oxygen and nitrogen by varying the size of slit and adsorption potentials. Therefore, it is very important to optimize the air separation by means of the understanding of the proper ion exchanges and characteristics of zeolite adsorbent. In this study, commercial zeolites, types A and X, was ion-exchanged with various metal ions, and the ion-exchange kinetics and equilibrium ion-exchange capacity were investigated. The properties of ion-exchanged zeolites were also examined by XRD, FTIR, SEM, EDS, and TGA. To produce high purity oxygen from air by Pressure Swing Adsorption(PSA), Not only was a zeolite absorbent which has highly adsorption selictivity of nigrogen deveolped but also a PSA process was designed. The crystal structure and acid features of the zeolite could be regulated by exchanging cation or replacing Si and A1 ofthe crystal structure with other elements. And it could be applied to a wide range of petrochemical process and precision chemical process based on the characteristics of replaced elements. The matal ions Li, Ag, Ca, Br, Sr, etc. were investigated for ion exchange with zeolite. Sr ion was showed the highest ion exchange rate among these metal ions and all metal ions were exchanged with Na ion at equivalent rate. The selectivity of ions was in the order Sr2+ > Ag+ > Ba2+ > Ca2+ > Li+. It is verified that the original structure of the zeolites is maintained after the ion exchange by XRD, FTIR, SEM and EDS, and that almost all of the Na+ ions within the zeolite are ion-exchanged. Compared with the NaX adsorbent, the ion exchanged zeolite X adsorbent remarkably improved its adsorption performance of nitrogen at the conditions of 283~313K temperature and 0.1~10 atm pressure. The adsorbed amounts of both nitrogen and oxygen are high at low temperature. In addition, thy increase as pressure rises. The experimental data obtained were correlated by the Langmuir, Freundlich, Langmuir-Freundlich, Redlich-Peterson and Toth equations. The Langmuir and Freundlich isotherms model showed a good agreement with the experimental data. The case of zeolite NaA and zeolite NaX, which is not ion-exchanged, the nitrogen absorption amounts are nearly same, but the nitrogen absorption amounts for zeolite MX are remarkably larger than zeolite MA in case of the ion-exchanged. At an equilibrium pressure under 0.5 atm, adsorption performance of nitrogen on the ion exchanged zeolite adsorbent increased in the order of Ag+ > Li+ > Ca2+ > Sr2+ > Ba2+ > K+, whereas at an equilibrium pressure over 1 atm showed in the order of Li+ > Ag+ >Ca2+ > Sr2+ > Ba2+ > K+. Absorption of the Li increases gradually as the pressure gets higher, and it shows the higher value at 1atm compared to the Ag’s value. Nitrogen/Oxygen separation factor of Li ion exchanged zeolite X adsorbent was 13.021 at the partial pressure of nitrogen/oxygen gas mixture similar to air and 293K adsorption temperature. The Li-X absorbent is considered as a better solution for the environmental and economical aspects.
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