Description of polymer solutions phase equilibria by cubic equation of state with different mixing rules

Abstract

In this paper, experimental data available in the literature are used to test the Peng-Robinson (PR) equation of state for representing VLE of concentrated polymer solutions in conventional solvents. The most important issues of extending cubic EoS to polymers are the description of the pure component EoS parameters, a and b, for polymers and selection of mixing rules. To capture nonidealities, several existing mixing rules are adopted, namely, vdW1, vdW2, Wong-Sandler, and Zhong and Masuoka. The AE term in the Wong-Sandler mixing rule is evaluated by the Flory-Huggins model. Therefore, the experimental data are calculated by the PR equation of state incorporating different mixing rules, including the consideration of binary interaction parameters and liquid phase parameters. After determining the binary interaction parameter kij, the Flory interaction parameter χ, and the number of solvent-size segments parameter r, using experimental vapor-liquid equilibria data, it was possible to obtain excellent correlations of the VLE data for these systems. The Wong-Sandler rule seems to give better results in representing the properties of polymeric solutions. This can be explained by the size difference between the polymer and the solvent, which means that one parameter is not sufficient to describe this disparity.