Modified UNIFAC (Dortmund) method

The UNIQUAC Functional-group Activity Coefficient (UNIFAC) method provides good order-of-magnitude estimates. We can improve the accuracy of the method by incorporating a temperature-dependent form for the binary group energy interaction parameter and a slightly different formulation for the combinatorial contribution to the activity coefficient.

Researchers at Dortmund developed a three-parameter, temperature-dependent form for the binary interaction parameter[7,8,9,10]. For this modified method, the following equations give the temperature-dependent form of Amk:

where

amk, bmk, and cmk are the binary interaction parameters for groups m and k

The following equation gives the logarithmic form of the modified combinatorial contribution to the activity coefficient:

where

nc is the number of components

is the lattice coordination number, which typically equals 10

xi is the mole fraction of component i in the liquid phase

We use the standard UNIFAC equations to calculate the remaining variables in the preceding equations.