Correlation of Solvent Activities

As an example we will give here the expression for the activity coefficient of the solvent for a model which combines the p free-volume combinatorial term with a segment-based Wu-NRTL residual term [44]. The p free-volume combinatorial term combines combinatorial contributions and free-volume contributions [45]. The activity coefficient of the solvent is given by Eq. (44). 

The free volume of a component is defined by Eq. (47), where v, is the molar volume of liquid component i, Vi dw is the hard-core volume or van der Waals volume of this component and can be calculated using the Bondi tables [46], and p is a correction factor, which is calculated from Eq. (48) in the p free-volume model [45]. 

The residual term is given by Eq. (49) together with Eqs. (50), where Osp and Ops are adjustable interaction parameters, a is the NRTL-nonrandomness parameter, which was fixed by Pedrosa et al. at 0.4. 

X is the effective mole fraction of segments of species i and qi is the effective segment number of species i, which are given by Eqs. (51) and (52) = 1 and = r. 

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