Breakthrough behavior is investigated for an activated carbon bed fed with constant concentrations of organic vapors and a stepped concentration of water vapor. The organics are present as single components and binary mixtures, with both hydrophobic and hydrophilic organics considered. Experiments are performed using a fully automated fixed-bed apparatus, which enables breakthrough curve studies for gas mixtures over a wide range of concentrations, from much less than 1 ppm up to saturation. The adsorbed-phase mass transfer coefficient of water is found to be a strong function of water loading. The system response is complex, with behaviors for hydrophilic and hydrophobic compounds being quite different. A model incorporating an accurate description of the highly nonideal adsorption equilibria is developed to simulate all of the fixed-bed experiments and gives good agreement in time, trend, extent, and shape of the breakthrough curves.

A novel method is used to describe adsorption equilibria of nonideal mixtures. The two-dimensional virial equation of state is reorganized so that contributions of single components are separated from those of mixed components. Existing single component adsorption isotherm equations, which describe pure component data better and with fewer parameters than a truncated virial series, are substituted for the pure component terms. The remaining equation of state then contains terms corresponding to the pure component isotherms and terms with virial cross-coefficients for the mixture. The method is applied first to a mixture of Langmuirian adsorbates to demonstrate a sound thermodynamic and mathematical basis. We then consider nonideal binary and ternary mixtures of carbon dioxide, hydrogen sulfide, and propane on H-mordenite and a highly nonideal mixture of n-hexane and water on activated carbon.

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