A modified SAFT equation of state is developed by applying the perturbation theory of Barker and Henderson to a hard-chain reference fluid. With conventional one-fluid mixing rules, the equation of state is applicable to mixtures of small spherical molecules such as gases, nonspherical solvents, and chainlike polymers. The three pure-component parameters required for nonassociating molecules were identified for 78 substances by correlating vapor pressures and liquid volumes. The equation of state gives good fits to these properties and agrees well with caloric properties. When applied to vapor−liquid equilibria of mixtures, the equation of state shows substantial predictive capabilities and good precision for correlating mixtures. Comparisons to the SAFT version of Huang and Radosz reveal a clear improvement of the proposed model. A brief comparison with the Peng−Robinson model is also given for vapor−liquid equilibria of binary systems, confirming the good performance of the suggested equation of state. ...

Perturbed-Chain SAFT: An Equation of State Based on a Perturbation Theory for Chain Molecules

The perturbed-chain SAFT (PC−SAFT) equation of state is applied to pure associating components as well as to vapor−liquid and liquid−liquid equilibria of binary mixtures of associating substances. For these substances, the PC−SAFT equation of state requires five pure-component parameters, two of which characterize the association. The pure-component parameters were identified for 18 associating substances by correlating vapor pressure and liquid density data. A comparison to an earlier version of SAFT confirms the good results for pure substances. When only one associating compound is present in a mixture, the PC−SAFT equation of state does not require mixing rules for the association term. Using one binary interaction parameter kij for the dispersion term only, the model was applied to azeotropic and nonazeotropic vapor−liquid equilibria at low and at high pressures, as well as to liquid−liquid equilibria. Simple mixing and combining rules were adopted for mixtures with more than one associating compound...

Application of the Perturbed-Chain SAFT Equation of State to Associating Systems

We present a review of recent advances in the statistical associating fluid theory (SAFT). In contrast to the “chemical theory”, in which nonideality is explained in terms of chemical reactions between the species, SAFT and similar approaches relate nonideality to the intermolecular forces involved. Such physical theories can be tested against molecular simulations, and improvements to the theory can be made where needed. We describe the original SAFT approach and more recent modifications to it. Emphasis is placed on pointing out that SAFT is a general method and not a unique equation of state. Applications to a wide variety of fluids and mixtures are reviewed, including aqueous mixtures and electrolytes, liquid−liquid immiscible systems, amphiphilic systems, liquid crystals, polymers, petroleum fluids, and high-pressure phase equilibria.

Molecular-Based Equations of State for Associating Fluids: A Review of SAFT and Related Approaches

The development of van der Waals cubic equations of state and their application to the correlation and prediction of phase equilibrium properties is presented and analyzed. The discussion starts with a brief account of the contributions to equation of state development during the years before van der Waals. Then, the original equation proposed in the celebrated thesis of van der Waals in 1873 and its tremendous importance in describing fluid behavior are analyzed. A chronological critical walk through the most important contributions during the first part of the 1900s is made, to arrive at the proposal that I consider to be the most outstanding since van der Waals:  the equation proposed by Redlich and Kwong in 1949. The contributions after Redlich and Kwong to the modern development of equations of state and the most recent equations proposed in the literature are analyzed. The application of cubic equations of state to mixtures and the development of mixing rules is put in a proper perspective, and the ...

The state of the cubic equations of state

Water is not restricted to moderate temperatures and low pressures, but can exist up to very high temperatures, far above its critical point at 647 K. In this supercritical regime, water can be gradually compressed from gas-like to liquid-like densities. The resulting dense supercritical states have extraordinary properties which can be tuned by temperature and pressure, and form the basis for innovative technologies. This Review covers the current knowledge of the major properties of supercritical water and its solutions with nonpolar, polar, and ionic compounds, and of the underlying molecular processes.

Supercritical water as a solvent.

Progress in developing equations of state for the calculation of fluid-phase equilibria is reviewed. There are many alternative equations of state capable of calculating the phase equilibria of a diverse range of fluids. A wide range of equations of state from cubic equations for simple molecules to theoretically-based equations for molecular chains is considered. An overview is also given of work on mixing rules that are used to apply equations of state to mixtures. Historically, the development of equations of state has been largely empirical. However, equations of state are being formulated increasingly with the benefit of greater theoretical insights. It is now quite common to use molecular simulation data to test the theoretical basis of equations of state. Many of these theoretically-based equations are capable of providing reliable calculations, particularly for large molecules.

http://depa.fquim.unam.mx/amyd/archivero/TEORIADEECUACIONESDEESTADO_3411.pdf

Equations of state for the calculation of fluid-phase equilibria

Vapour-liquid and liquid-liquid phase equilibria of binary mixtures containing helium: comparison of experiment with predictions using equations of state

Binary mixtures of water + five noble gases : comparison of binodal and critical curves at high pressures

Conformal solution theory in conjunction with the one-fluid model and the Guggenheim equation of state are used to calculate the critical properties of binary and ternary mixtures characterised by molecules of identical size (identical h conformal parameters) but different energy parameters (different f conformal parameters). When the geometric mean combining rule is used to obtain contributions from unlike interactions, binary mixtures of equal size components generate Type I, II and III phase behaviour. The critical properties of ternary mixtures composed of binary subsystems of different phase behaviour types are examined. Results are presented at different temperatures and pressures covering both vapour–liquid and liquid–liquid equilibria. The results illustrate the diversity of phenomena exhibited by ternary mixtures and the relationship of the behaviour exhibited to the relative strength of dissimilar interactions between different pairs of molecules. A progressive transition between vapour–liquid and liquid–liquid equilibria and higher order critical phenomena are likely to be common features of the phase behaviour of ternary mixtures.

Phase behaviour of ternary mixtures: a theoretical investigation of the critical properties of mixtures with equal size components

Experimental measurements of pressure and temperature are reported over a wide composition range for the
 phase coexistence of carbon dioxide–benzene–water ternary mixtures. Phase coexistence was observed
 at temperatures and pressures up to 600 K and 300 MPa, respectively. The experimental measurements
 were determined largely by a “synthetic” method which involved determining “knick-points
” in the temperature–pressure
 curves supported by additional visual observations. The ternary mixtures exhibit
 both two-phase/one-phase and three-phase/two-phase transitions. The experimental measurements are supplemented
 by equation of state calculations using the Guggenheim
 equation of state
 in conjunction with
 conformal solution theory and the one-fluid model.

https://researchbank.swinburne.edu.au/file/be323690-e0a2-48d3-912c-e2b07efd1ef2/1/PDF (Published version).pdf

Ya Song Wei

Papers

Equations of state for the calculation of fluid-phase equilibria

Vapour-liquid and liquid-liquid phase equilibria of binary mixtures containing helium: comparison of experiment with predictions using equations of state

Binary mixtures of water + five noble gases : comparison of binodal and critical curves at high pressures

Phase behaviour of ternary mixtures: a theoretical investigation of the critical properties of mixtures with equal size components

Phase behaviour of carbon dioxide–benzene–water ternary mixtures at high pressures and temperatures up to 300 MPa and 600 K