Nonisothermal Adsorption: Separation of Gas Mixtures by Modulation of Feed Temperature

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Abstract
The purpose of this article was to present the principles and experimental examples of an adsorption process for separating gas mixtures characterized by the following features: the mixture to be treated contains a major component and a minor component, it is desired to produce a fraction of the pure major component and a fraction enriched in the minor component, the adsorbent and the operating conditions are chosen in such way that the major component is essentially not adsorbed, no carrier or purge gas is used, and the regeneration of the adsorbent is obtained with the gas mixture feed heated at a suitable temperature. The experimental example given deals with a mixture of n-pentane/isopentane on a Linde 5A molecular sieve. The process is based on the coupling between temperature and adsorption, as are other temperature swing processes such as cycling zone adsorption. A proper choice of parameters of the temperature modulation (low and high temperature, durations of cold and hot step) leads to a “resonance” where the concentration variation is maximal and a fraction of the pure major component can be obtained. It is shown how these parameters are determined from a knowledge of the adsorption isotherms and from simple experiments. The influence of factors such as total pressure and specific heat of the gases is discussed.