Simultaneous estimation of phase behavior and second-derivative properties using the statistical associating fluid...

Area of Science:

• Thermodynamics
• Chemical Physics
• Materials Science

Background:

• Statistical Associating Fluid Theory (SAFT) is a powerful tool for modeling fluid phase behavior.
• Existing SAFT equations struggle to accurately predict derivative properties of condensed liquids.
• Modeling repulsion-dispersion interactions is crucial for accurate thermodynamic predictions.

Purpose of the Study:

• To present a modified SAFT equation of state with a variable range version.
• To improve the description of vapor-liquid equilibria and compressed liquid properties for long-chain n-alkanes.
• To enhance the prediction of derivative properties, such as isothermal compressibility and speed of sound.

Main Methods:

• Utilized the m-n Mie potentials to model repulsion-dispersion interactions.
• Developed a new method for optimizing molecular parameters in the equation of state.
• Incorporated data from the saturation line, densities, and speed of sound in the condensed liquid phase for parameter fitting.

Main Results:

• The modified SAFT equation provides highly accurate predictions for vapor-liquid equilibria and compressed liquid properties of n-alkanes.
• The model successfully describes derivative properties, outperforming other SAFT-like equations.
• A clear dependence of molecular parameters on n-alkane chain length was observed, indicating physical significance.

Conclusions:

• The proposed SAFT modification, using variable range m-n Mie potentials, significantly enhances model performance and applicability.
• The accurate prediction of derivative properties is attributed to the variable repulsive term in the intermolecular potential.
• The systematic parameter optimization procedure ensures consistency and accuracy across various properties for n-alkanes.