Statistical associating fluid theory (SAFT) is a powerful model for thermodynamic property and phase equilibrium calculations for fluid mixtures. In this paper, the model development, modifications, and generalizations proposed over the past decade are reviewed. Emphasis is given to developments resulting in equations of state applicable to real fluids. In addition, theoretical models are reviewed. Applications are discussed, and representative calculations are presented with emphasis on aqueous systems and polymers. Despite its wide acceptance, SAFT has several limitations that are discussed here.

Nonrandom hydrogen bonding (NRHB) lattice theory is extended here to multicomponent fluid mixtures rigorously. The model accounts for nonideal thermodynamic behavior of mixtures due to molecular connectivity of nonspherical molecules, weak van der Waals forces between first-neighbor molecular segments, and hydrogen-bonding interactions. The random distribution of molecules in the lattice is calculated using the generalized Staverman theory, while for the nonrandom correction, the Guggenheim quasi-chemical theory is adopted. Finally, the hydrogen-bonding contribution is based on Veytsman statistics as implemented in lattice fluid theory by Panayiotou and Sanchez. The equation of state is coupled with the mass action law due to hydrogen bonding, and both are solved simultaneously. The model is applied for the calculation of vaporliquid, liquid-liquid, and vapor-liquid-liquid equilibria at low and high pressures of binary mixtures of fluids with large molecular size differences and/or different types of interactions between unlike molecules. In addition, the model is applied to correlate low-pressure polymer-solvent data. Good agreement between experimental data and model predictions/correlations is obtained in all cases. Comparisons against mixture predictions from the model ignoring nonrandom contributions and from lattice-fluid-hydrogen-bonding model show a clear improvement of the NRHB model.

This work reports the results of an investigation on industrial requirements for thermodynamic and transport properties carried out by the Working Party on Thermodynamic and Transport properties () of the European Federation of Chemical Engineering, EFCE (). A carefully designed questionnaire was sent to a number of key technical people in companies in the oil and gas, chemicals, and pharmaceutical/biotechnology sectors. Twenty-eight companies have provided answers which formed the basis for the analysis presented here. A number of previous reviews, specifically addressed to or written by industrial colleagues, are discussed initially. This provides the context of the survey and material with which the results of the survey can be compared. The results of the survey have been divided into the themes: data, models, systems, properties, education, and collaboration. The main results are as follows. There is (still) an acute need for accurate, reliable, and thermodynamically consistent experimental data. Quality is more important than quantity. Similarly, there is a great need for reliable predictive, rather than correlative, models covering a wide range of compositions, temperatures, and pressures and capable of predicting primary (phase equilibrium) and secondary (enthalpy, heat capacity, etc.) properties. It is clear that the ideal of a single model covering all requirements is not achievable, but there is a consensus that this ideal should still provide the direction for future development. The use of new methods, such as SAFT, is increasing, but they are not yet in position to replace traditional methods such as cubic equations of state (especially in oil and gas industry) and the UNIFAC group contribution approach. A common problem with novel methods is lack of standardization, reference data, and correct and transparent implementations, especially in commercially available simulation programs. The survey indicates a great variety of systems where further work is required. For instance, for electrolyte systems better models are needed, capable of describing all types of phase behavior and mixtures with other types of components. There is also a lack of data and methods for larger complex molecules. Compared with the previous reviews, complex mixtures containing carbon dioxide associated with a wide range of applications, such as capture, transport, and storage are becoming interesting to a number of survey participants. Despite the academic success of molecular simulation techniques, the survey does not indicate great interest in it or its future development. Algorithms appear to be a neglected area, but improvements are still needed especially for multiphase reactive systems (simultaneous chemical and physical equilibrium). Education in thermodynamics is perceived as key, for the future application of thermodynamics in the industry. A number of suggestions for improvement were made at all three levels (undergraduate, postgraduate, and professional development) indicating that the education is correctly percei...

A unified treatment of the phase equilibria and interfacial properties of fluids is presented. This is done through the development of a framework model, which is applicable to nonpolar systems as well as to highly nonideal systems with strong specific interactions, to systems of small molecules as well as to polymers, glasses, and gels, to liquids as well as to vapors and supercritical systems, and to homogeneous as well as to inhomogeneous systems. One key characteristic of this equation-of-state model is its capacity to estimate the nonrandom distribution of the free volume in the system. A quasi-thermodynamic approach of inhomogeneous systems is used for modeling the fluid-fluid interface. The present model is referred to as the nonrandom hydrogen-bonding model. The key differences between this model and the previous quasi-chemical hydrogen-bonding model are the following: (1) The combinatorial term is replaced by the generalized Staverman term. ( 2) The nonrandomness factor is also generalized. Two alternative expressions are presented in this work. (3) The shape factor, s, is no longer an adjustable parameter. It is set equal to the UNIFAC q/r ratio and obtained from the corresponding UNIFAC compilations in the literature. (4) A most recent quasi-thermodynamic approach is used for the fluid-fluid interface. In the first part of this series of papers, the model is applied for the estimation of basic thermodynamic properties of pure fluids, such as vapor pressures, orthobaric densities, heats of vaporization, surface tensions, and glass transition temperatures.