Multicomponent adsorption Henry equation

The DA equation does not conform to Henry s law in the low pressure region. The Henry s law limit for pore filling models in multicomponent adsorption equilibrium was discussed by Rudisill and Le Van [58]. 

Many simple systems that could be expected to form ideal Hquid mixtures are reasonably predicted by extending pure-species adsorption equiUbrium data to a multicomponent equation. The potential theory has been extended to binary mixtures of several hydrocarbons on activated carbon by assuming an ideal mixture (99) and to hydrocarbons on activated carbon and carbon molecular sieves, and to O2 and N2 on 5A and lOX zeoHtes (100). Mixture isotherms predicted by lAST agree with experimental data for methane + ethane and for ethylene + CO2 on activated carbon, and for CO + O2 and for propane + propylene on siUca gel (36). A statistical thermodynamic model has been successfully appHed to equiUbrium isotherms of several nonpolar species on 5A zeoHte, to predict multicomponent sorption equiUbria from the Henry constants for the pure components (26). A set of equations that incorporate surface heterogeneity into the lAST model provides a means for predicting multicomponent equiUbria, but the agreement is only good up to 50% surface saturation (9). 

Adsorption Chromatography. The principle of gas-solid or liquid-solid chromatography may be easily understood from equation 35. In a linear multicomponent system (several sorbates at low concentration in an inert carrier) the wave velocity for each component depends on its adsoiption equilibrium constant. Thus, if a pulse of the mixed sorbate is injected at the column inlet, the different species separate into bands wliich travel through the column at their characteristic velocities, and at the outlet of the column a sequence of peaks corresponding to the different species is detected. Measurement of the retention time (tl) under known flow conditions thus provides a simple means of determining the equilibrium constant (Henry constant) ... 

Characteristic parameters of nearly all types of adsorption isotherm models are the Henry coefficients as well as the saturation capacities valid for large concentrations. In general, it is advisable to check the validity of the identified single-component isotherm equation before further considering the determination of additional multicomponent interaction parameters. In general, the decision on a certain isotherm equation should be made on the basis of the ability to predict experimentally observed overloaded concentration profiles. In any case, consistency with the Henry coefficients determined from initial pulse experiments with very low sample amounts must be assured. 

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