关键词: modified van Laar’s theory;internal pressure;activity coefficient equation; polymersolution;activity coefficient at infinite dilutionminipage

Abstract: The original van Laar’s theory has been modified. The internal pressures of components
andmixture are expressed by Frank’s relation and the excess entropy for mixing of
components is alsoconsidered. A new activity coefficient equation, which can be
satisfactorily applied to polymersolutions, is obtained. The calculated results for the VLE
of 179 polymer solutions show that theaccuracy of fit is evidently superior to UNIQUAC
equation.

Key words: modified van Laar’s theory, internal pressure, activity coefficient equation, polymersolution, activity coefficient at infinite dilutionminipage