Predicting the Phase Behavior of Polymer Systems with the GC-SAFT-VR Approach

Abstract

The recently developed heteronuclear group contribution SAFT-VR equation (GC-SAFT-VR) [ Peng Peng Fluid Phase Equilib.2009227131144] enables the predictive study of the thermodynamic properties of fluids and their mixtures by using a molecular-based model in which the molecules are described by heterosegmented chains in which each type of segment represents a functional group present in the molecule. Given the success of the GC-SAFT-VR approach in predicting the fluid phase equilibria of mixtures without fitting to any mixture data, and the known difficulties in determining equation-of-state parameters for polymers because of the lack of coexistance data, in this work, we extend the GC-SAFT-VR equation to study the phase equilibria of small molecules in polymer systems. The results demonstrate the ability of the GC-SAFT-VR equation of state to predict the vapor−liquid and liquid−liquid equilibria of polymer solutions and accurately capture the effects of polymer molecular weight and molecular topology on phase behavior.

On the prediction of ternary mixture phase behavior from the GC-SAFT-VR approach: 1-Pentanol+dibutyl ether+n-nonane

“…Within the GC-SAFT-VR approach [28][29][30] molecules are represented by a heteronuclear chain model that describes the different functional groups within each molecule being studied by unique segments. As with the SAFT-VR EOS [31,32], the dispersive interactions between segments that represent the functional groups are treated by a square-well (SW) potential.…”

“…Since the theory has been previously presented [28][29][30], here we provide only a brief overview of the main expressions for each term as they pertain to ternary systems. The ideal Helmholtz free energy of a mixture of three components is given by,…”

“…The next logical step in the development of a groupcontribution approach within the SAFT framework is to implement a heteronuclear model to enable the differentiation of functional groups at the molecular level. This was done by Jackson et al in the SAFT-␥ [24,25] [26][27][28][29][30] approach. Both approaches treat the monomer fluid as a mixture of different (i.e., heteronuclear) monomeric segments; the main difference between the two approaches lies in the treatment of the contribution to the free energy due to chain formation.…”

“…In an extension of previous work [28][29][30], to further probe the nature of the molecular interactions between different functional groups and examine the applicability of the theory to predict the phase behavior of ternary mixtures, we have studied the ternary system of 1-pentanol + dibutyl ether + n-nonane. This binary mixture was chosen primarily because it contains several different types of functional groups, both associating and non-associating.…”

“…In particular, we consider the prediction of the phase behavior of binary mixtures of 1-pentanol + dibutyl ether, 1-pentanol + n-nonane and dibutyl ether + n-nonane, as well as the phase behavior of the ternary mixture 1-pentanol + dibutyl ether + n-nonane at different thermodynamic conditions using the GC-SAFT-VR approach. The functional groups parameters needed to study these fluids i.e., CH 3 , CH 2 , OCH 2 ether, and a terminal OH functional group, were previously determined by fitting to experimental data for selected members of the relevant chemical families [28][29][30]; hence this is a purely predictive study.…”