Adsorption Isotherms for Multicomponent Systems

When two or more adsorbable components exist with the possibility of occupying the same adsorption sites, isotherm relationships become more complex. The simplest is extension of the Langmuir type isotherm by assuming no interaction between adsorbing molecules. In the case two components, the extended Langmuir isotherm (Markham and Benton, 1931) is given as 

This equation enables quick estimation of equilibrium relations of 

From Eq. (3-42), it follows that the separation factor for a mixture of two components can be given directly by the ratio of the equilibrium constants. 

This relation holds independent of concentration and can naturally be extended to an arbitrary combination of components. 

Lewis et al. (1950) showed that for adsorption of two components with a constant total pressure of P = pt+ pi, the following relation holds between the amount adsorbed of each component, 91 and 93. 

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