UNIFAC Larsen

Larsen, B.L., Rasmussen, P., Fredenslund, A. A modified UNIFAC group-contribution of phase equilibria and heats of mixing. Ind. Eng. Chem. Res., 1987,26 2274-2286. 

The GC concept has received great attention for the prediction of activity coefficients during the last 30 years. It has been applied to many different types of properties of pure compounds, as shown in Section 16.2, but also for phase equilibrium calculations for mixtures. Especially well known is the UNIEAC equation for the activity coefficient. The UNIFAC model is available in several modified forms, e.g., by Larsen et al. and Gmehling and Weidlich. ° These modified UNIFAC models contain, unlike the original UNIFAC, temperature-dependent interaction parameters. 

Predictions of calculated versus experimental data were in the following order of absolute average duration (aad) of Xy. SAFT of 1.90 x IQr, PR eos of 3.7 x Qr UNIFAC with Magnussen et al. [12] parameters of 3.5 x 10, and UNIFAC with Larsen parameters of 5.4 x 10. SAFT was also best for extrapolation of both lie and solubility. SAFT also predicted the ternary systems that tested best. 

Appendix 1 gives the equations for calculating the combinational part and the residual part of the activity coefficient for the UNIFAC equation modified by Larsen et al. [LAR 87]. The volume (q) and surface groups (qi)... 

The UNIquac Functional group Activity Coefficient (UNIFAC) model modified by Larsen et al. [LAR 87] does not take into account the sulfur groups among the common amino acids, methionine and cysteine cannot be decomposed into functional groups (Table 3.3). 

The UNIFAC model is a continuously evolving concept. For the last versions, referred to as Modified UNIFAC, see Gmehling and Weidlich (1986) and Larsen et al (1987). 

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