On the temperature dependence of the coefficient of adsorption selectivity
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In the general case of adsorption of binary mixtures of gases of vapors, the coefficient of adsorption selectivityα2 at set values of a1 and a2 is an exponential function of ΔQ/T, where ΔQ=Q2-Q1 is the difference of the differential heats of adsorption of the components. At ΔQ > 0,α2 decreases with T, while at ΔQ < 0,α2 increases with T.
For the system H2S-C3H8-NaX zeolite, within the entire region of variation of a1 and a2, both types of dependences ofα2 upon T are possible. Thus, for example, along the line Ng2=0.05, when the total pressure is increased, the dependence ofα2 upon T changes sign. Lowering the temperature from 40 to –60° at p12=50 mm Hg increasesα2 by ∼ 10-fold, while at p12=760 mm Hg, it decreasesα2 approximately by half.
The question of the shape of the curves of Ng2=const in the case of adsorption of binary mixtures of gases on microporous adsorbents was refined. It was shown that maxima can appear on curves of Ng2 = const only in systems in which the individual adsorption isotherms intersect, which usually corresponds to the adsorption of both components primarily under the action of dispersion forces.
KeywordsZeolite Adsorption Isotherm Binary Mixture Exponential Function Total Pressure
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