Limitations of the Wilson method

The Wilson equation cannot describe local maxima or minima in the activity coefficient. However, its single significant shortcoming is that it cannot mathematically predict the splitting of a liquid into two partially miscible phases. It is therefore completely unsuitable for problems involving liquid-liquid equilibria.

For liquid-liquid equilibria, you should use the non-random two-liquid (NRTL) equation instead. See NRTL — Non-random two-liquid method for more information.