Kinetic evaluation of dehydration in MxNa96-xLSX (M= Li+, Ca2+ and Ag+) zeolites and resulting effects on selective adsorption of N2 and O2

Abstract

Abstract The purpose of this study is to evaluate the dehydration kinetics of MxNa96-x-LSX (M = Li+, Ca2+ and Ag+) zeolites and assess their potential for N2/O2 adsorption and selectivity using ideal adsorbed solution theory. In order to achieve our objective, MxNa96-x-LSX (M = Li+, Ca2+, and Ag+) zeolites were prepared via conventional ion exchange methods from Na-LSX zeolite. Meanwhile, their structural and textural properties were characterized by N2 adsorption-desorption, TG-DTG, ICP-OES, XRD, FT-IR, EDS, elemental mapping and SEM techniques. The kinetics (activation energy, pre-exponential factor, and most probable mechanism/model) of dehydration process were investigated via Kissinger, Flynn-Wall-Ozawa and Coats-Redfern methods. The results show a strong dependence on the choice of mechanism function, which can help in proposing the best relevant kinetic model. Moreover, the results further reveal that Li+ and Ca2+ ions (which are inexpensive) in Li-LSX and Ca-LSX fill the low-energy sites SI, SI′, SII, and SII′ first and then SIII and SIII′ sites. Li-LSX and Ca-LSX hold comparative advantages, which suggest that they would be the most promising adsorbents for air separation and pure oxygen production by pressure swing adsorption. However, Ag-LSX presents superior performance at relatively low pressures. Therefore, the quantitative evaluation of kinetic parameters of dehydration is necessary to provide the theoretical principles in understanding N2 and O2 adsorption phenomena.