Study of Adsorption Properties of Zeolites NaX, CaA, and CaNaA in Separation of Air Components
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udy of Adsorption Properties of Zeolites NaX, CaA, and CaNaA in Separation of Air Components A. A. Tishin* National Research Nuclear University MEPhI, Moscow, 115409 Russia *e-mail: [email protected] Received February 24, 2020; revised April 9, 2020; accepted April 10, 2020
Abstract―The volumetric method has been used to study the adsorption properties of zeolites CaA, NaX, and CaNaA; adsorption isotherms and adsorption capacities for nitrogen, oxygen, and air have been obtained. The nitrogen/oxygen selectivity values of zeolites have been determined. The experimental adsorption isotherm of air has been compared with the adsorption isotherm obtained for the pure components. The experiments have revealed that the most promising zeolite for use in a membrane–adsorption oxygen concentrator is zeolite CaNaA. Keywords: hybrid technologies, temperature swing adsorption, air separation, adsorption, pressure swing adsorption, adsorption isotherms DOI: 10.1134/S0965544120080149
Currently, the separation of air into its components is implemented using three main technologies [1]: adsorption, membrane, and cryogenic ones. The applicability of each of these technologies often depends on the required volumes of production of separation products [2, 3]. Thus, when producing oxygen in low volumes and concentrations up to 50%, the membrane separation method is used [4]. This method is based on the difference in the rates of penetration of molecules of a feed mixture through the membrane under the action of a driving force [5]. In the case of moderate demand for oxygen with concentrations up to 93–95%, the adsorption separation method [6] is used, which is based on the adsorption process [7]. When it is necessary to produce significant volumes of high purity oxygen, the cryogenic method is used [2]. The essence of the cryogenic method is to use the differences in the boiling points of the air components [8]. Initially, air is liquefied by lowering the temperature, after which the liquid air is heated, and nitrogen begins to evaporate. The cryogenic method has become widespread in industry, since it allows almost unlimited quantities of high-purity air components to be produced [9]. The adsorption method is applied in medicine; based on it, a large number of medical oxygen equipment has been developed [10]. The membrane method is used where small dimensions of equipment and low oxygen concentrations are required [11], for example, in rehabilitation medicine. The adsorption separation method is based on the difference in the sorption capacities for components of
a feed gas mixture and on the difference in the rate of adsorption of the components [12]. In other words, one or several components of the feed mixture are selectively sorbed by the surface of a solid adsorbent [2, 13]; most commonly, zeolites are used for air separation [6, 14]. In this case, the adsorption capacity depends on the temperature and pressure at which the process proceeds. Based on these factors, all adsorption processes are divided into two types: pressure
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