(115a) Absolute and Net Adsorption in the Ideal Adsorbed Solution Theory

At the last AIChE meeting we saw contributions based on two approaches that applied the Ideal Adsorbed Solution Theory. The first is based on the definition of the Gibbs adsorption isotherm from absolute adsorption and corresponds to the original approach of Myers and Prausnitz (1965). The second is based on the derivation from the net adsorption framework of Talu (2013) and leads to a series of equations which are similar but not the same. Given the fundamental importance of the IAST in the treatment of multicomponent adsorption equilibria we have investigated the two approaches in detail and are able to show that in fact the original formulation based on the absolute adsorption is correct. We will identify the problem in Talu’s derivation and show that a correct derivation even starting from the Net adsorption framework should lead to the same set of equations for the IAST. Furthermore we will show that the Net-IAST approach of Talu leads to numerical complications and physically impossible solutions when implementing it to mixtures were a strongly adsorbed species is combined with a weakly adsorbing one.