How are activity coefficients of organic compounds calculated in E-AIM?
There are three methods. The first, and simplest, is to assume Raoult’s law behaviour (mole fraction activity coefficients, reative to a reference state of the pure liquid, equal to unity). The second method, for compounds that are water-soluble, is a Redlich-Kister expansion for which the user must supply the fitted coefficients. Clegg and Seinfeld (J. Phys. Chem. A 110, 5692-5717, 2006) give exmaples of this equation applied to aqueous solutions of dicarboxylic acids. The third option, for compounds that can exist in either or both liquid phases, is UNIFAC. In this case the user must specify the group composition of the molecule. See the model description for details of all three approaches.