On applying the ideal adsorbed solution theory to multicomponent adsorption equilibria of dissolved organic components on activated carbon

Multicomponent adsorption equilibria of organic components from aqueous solutions on activated carbons were measured and the applicability of the ideal adsorbed solution (IAS) theory was tested. Systematic deviations between experiments and theory were observed. Adsorbed phase activity coefficients which account for these deviations proved to be thermodynamically inconsistent. However, the calculation of spreading pressure in the IAS theory requires extrapolation of single solute isotherms to zero concentration. A correction of extrapolation errors was determined by fitting binary equilibrium data to the IAS theory. For a mixture of N components, N – 1 constants have to be obtained from binary mixtures of N – 1 components with a reference component. For the adsorption of 3 chemically non-interacting organic solutes constants derived from two binary systems allow the prediction of the third binary system as well as of the ternary system. The method is successful only if chemical interactions of the components in the adsorbed phase can be excluded