(320l) Multicompontent Adsorption in Porous Media

The goal of this work is to analyze the adsorption of multicomponent mixtures on the basis of the Potential Theory of Adsorption (PTA). The PTA, first formulated by Polanyi, is a thermodynamic concept used for modeling of gas adsorption on solid. Its applications are multilayer adsorption on homogeneous and heterogeneous surfaces, adsorption from mixtures close to their dew points and adsorption in microporous media. In the latter case a modification of the potential theory formulated by Dubinin is widely used. A specific feature of the PTA is that the mixture is treated in a purely thermodynamic way, without detailed consideration of molecular behavior. This makes it possible to utilize the knowledge accumulated in the bulk phase thermodynamics and to automatically extend the theory onto non-trivially behaving multicomponent mixtures like hydrocarbon mixtures exhibiting retrograde behavior.

Recently, an extension of the PTA onto multicomponent mixtures has been proposed [1]. We do not make a common assumption about adsorbate as a homogeneous phase, but it is considered as a segregated mixture in the external field produced by a solid adsorbent. This has made it possible to develop a purely predictive approach to adsorption of multicomponent mixtures based on the data on single-component adsorption, even for the mixtures which adsorption behavior is far from ideal.

So far, adsorption of hydrocarbon and hydrocarbon mixtures has been described by the Soave-Redlich-Kwong (SRK) equation of state (EoS). It is well known that the SRK EoS gives reasonable estimates of volumetric properties at low pressures, but these estimates may become inaccurate at high pressures. To improve volumetric predictions, in this work, we test the potential theory in conjunction with the different equations of state (like SWBR and SAFT). The EoS used range from empirical approaches, to statistical mechanics based models. Other extensions of the MPTA, like extension onto the microporous media with different capacities with regard to different components, are considered.

[1] - Shapiro, A., Stenby, E.H. Potential Theory of Multicomponent Adsorption. Journal of Colloid and Interface Science, 201, 1998, 146-157.