Potential Theory In Analysis Of Equilibrium Data
POTENTIAL THEORY IN ANALYSIS OF EQUILIBRIUM DATA
FOR SUPERCRITICAL ADSORPTION
L. Czepirski, B. Laciak
University of Mining and Metallurgy, Faculty of Fuels and Energy,
al. Mickiewicza 30, 30-059 Cracow, Poland
High pressure adsorption is of particular use for the characterization of microporous materials. Low temperature adsorption on such materials is frequently complicated by excessive equilibration times due to activated diffusion. The use of adsorbates with small kinetic molecule diameter at temperatures above the critical temperature help to alleviate this problem. p>
Examples of adsorption isotherms for active carbon – gases systems at supercritical temperatures are presented.
The evaluation of some correlations that describe adsorption equilibria was carried out and the hypothesis that equilibrium data could be represented by the potential theory was tested.
Application of potential theory to the systems under study results in temperature – invariant characteristic curves. Using the molar volumes of gases in adsorbed state as an affinity coefficient to each adsorbate, it was demonstrated that characteristic curves for various adsorbates on a given adsorbent at different temperatures are superimposable on single reduced characteristic curve.
Experimental isotherms were also interpreted by the use of the Dubinin – Radushkevich equation. All of the D-R plots show linearity which demonstrates the possibility of application of D-R equation for analysis the microporous structure of carbonaceous adsorbents.
Modification of the Dubinin – Astakhov equation is given and discussed. The proposed form of D-A equation is preserved and physical background of its parameters is modified in accordance with the behavior of the adsorbate at supercritical temperature.
The equilibrium data can be directly related to gases separation to provide essential for contribution process modeling, such as pressure swing adsorption accomplished by selective adsorption.
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