Ideal constant spreading pressure

Among the theories of predicting mixed-gas adsorption equilibria from pure component adsorption isotherms, the ideal adsorbed solution theory (IAST) [14] has become the standard and often serves as a benchmark for the purpose of comparison by other models. IA ST is a thermodynamically rigorous theory based on the mixing of individual components at constant spreading pressure to form an ideal solution. It has the advantages that (1) no mixture data are required and (2) the theory is independent of the actual model of physical adsorption. 

Ideal adsorbed solution theory (lAST) was used in this study because it is the most common approach used to predict the multicomponent adsorption isotherms onto activated carbon by using only single solute equilibrium data. The lAST is based on the assumption that the adsorbed mixture forms an ideal solution at a constant spreading pressure. The model can be represented by the following Equation 6.4 ... 

The function n (P) is the pure component equilibrium capacity, and is the pure component hypothetical pressure that yields the same spreading pressure as that of the mixture. By assuming ideal mixing at constant n and Y, the total amount adsorbed, / , is found to be... 

Radke and Prausnitz (1972) su ested that when the solute species adsorb simultaneously horn a dilute solution onto the adsorbent surface at constant temperature and spreading pressure tc, the adsorbed phase forms an ideal solution activity coefficients far all species are unity in the adsorbed phase. The following relations were proposed for a system containing n solutes ... 

Tihe interaction of a soluble constituent A with a spread monolayer of an insoluble constituent B was first studied by Schulman and Rideal (1). A was injected into the liquid substrate, and its penetration into B was studied by measuring the change in surface potential, AV, and surface pressure, An, of the spread monolayer at constant area. Assuming that the resulting mixed (A + B) monolayer was ideal, the surface density of A was inferred to be proportional to An. A positive An was taken as evidence for interaction between A and B. 

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