Accurate statistical associating fluid theory for chain molecules formed from Mie segments

Area of Science:

• Physical Chemistry
• Thermodynamics
• Statistical Mechanics

Background:

• Accurate equations of state (EOS) are crucial for predicting fluid properties.
• Previous statistical associating fluid theory for variable range interactions (SAFT-VR) models had limitations for Mie potentials.
• Understanding chain molecule behavior requires precise descriptions of intermolecular interactions.

Purpose of the Study:

• To develop a highly accurate equation of state (EOS) for chain molecules interacting via Mie potentials.
• To rigorously assess the EOS's ability to describe vapor-liquid equilibria and second-derivative thermophysical properties.
• To improve upon existing SAFT-VR Mie models, particularly in the near-critical region.

Main Methods:

• Utilized Barker and Henderson high-temperature perturbation expansion up to third order for monomer systems.
• Calculated the radial distribution function from a second-order expansion for reference monomer fluids.
• Applied Wertheim's first-order thermodynamic perturbation theory (TPT1) for chain molecule properties.

Main Results:

• The new SAFT-VR Mie EOS shows significant improvement over previous versions.
• Accurate prediction of vapor-liquid equilibria (coexistence densities, vapor pressures) and thermophysical properties (heat capacities, expansivities, speed of sound).
• Excellent agreement with molecular simulation data for monomer and chain fluids, including Lennard-Jones potentials.

Conclusions:

• The reformulated SAFT-VR Mie EOS provides a robust description for a wide range of Mie potentials.
• Achieved enhanced accuracy in the near-critical region for chain molecules.
• Enables improved global representation of thermodynamic properties and phase equilibria for pure fluids and mixtures.