469303 Effect of Branching on Phase Behavior of Chain Molecules from a New SAFT Based Model

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Yuchong Zhang and Walter G. Chapman, Department of Chemical and Biomolecular Engineering, Rice University, Houston, TX

A new model is proposed to accurately predict the effect of branching on the thermodynamics of chain molecules based on Statistical Associating Fluid Theory (SAFT). Despite numerous experimental and simulation results demonstrating the different phase behavior for isomers, few theoretic models have been developed to predict and explain the effect. Current branch chain models are mostly based on lattice theory, yielding results only qualitatively in agreement with experimental data. Since SAFT has proved extremely successful in characterizing chain molecules, the model proposed in the study makes use of one version of SAFT that assumes Lennard Jones dimer as the reference fluid, and accounts for the branching effect through approximation of Wertheim’s Second Order Perturbation Theory (TPT2). Both the number of branches and position where branches grow are taken into consideration explicitly.

The model is firstly applied to isomeric alkanes and then extended to polyolefins with various branching distribution. Given minimal parameters, the model is applicable to various systems from pure component to mixtures, from melt blends to polymer solutions. Vapor liquid equilibrium (VLE) and liquid liquid equilibrium (LLE) results generated from the model reflect the changes in thermodynamic properties due to addition of branches in good agreement with experimental data. In the future, association will be introduced to facilitate the applicability of the model to a wider category of molecules, specifically those with functional groups.

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