(591c) Prediction of Phase Behaviors of Strong Association Systems by PR+Cosmosac Equation of State

Organic acids (e.g., formic acid and acetic acid) are widely used in the industry especially in the esterification process. Most of the thermodynamic models fails describe the phase behaviors of mixtures containing acids because of the strong association between acid molecules that may lead to the formation of acid dimers (or higher multi-mers). Currently, the Hayden-O'Connell equation of state is one of most successful model for mixtures containing association species. However, rooted from virial expansion, the application of this method is limited to the vapor phase. In this work, we extend the previously developed PR+COSMOSAC equation of state to model systems containing strongly associating species. The association of acid molecules is considered as a chemical reaction, and the association constant can be determined from partial molar Gibbs free energy (chemical potential) of acid monomer and dimmer. We show that a comparable accuracy compared with the Hayden-O'Connell equation of state is achieved for the compressibility factor of formic, acetic, and proponic acids in the vapor phase. The cross association of formic acid and acetic-acid mixture is also well-described by this new method. Furthermore, the PR+COSMOSAC equation of state is readily applicable to the liquid phases. We will illustrate is application the VLE and LLE behaviors of some acid containing systems.