Prediction of thermodynamic properties of alkylphenol + hydrocarbon binary systems on the basis of pure liquid properties

Voutsas

Yakoumis

et al. 1996

Ind. Eng. Chem. Res.

895

707

An equation of state (EoS) suitable for describing associating fluids is presented. The equation combines the simplicity of a cubic equation of state (the Soave−Redlich−Kwong), which is used for the physical part and the theoretical background of the perturbation theory employed for the chemical (or association) part. The resulting EoS (Cubic Plus Association) is not cubic with respect to volume and contains five pure compound parameters which are determined using vapor pressures and saturated liquid densities. Excellent correlations of both vapor pressures and saturated liquid volumes are obtained for primary-alcohols (from methanol up to 1-tridecanol), phenol, tert-butyl alcohol, triethylene glycol, and water. Moreover, excellent prediction of saturated liquid volumes may be obtained from parameters which have been estimated by regressing only vapor pressures. Finally, we suggest a method for reducing the number of adjustable parameters for alcohols to three while maintaining the good correlation of vapor pressures and saturated liquid volumes. We investigate the possibility of using the homomorph approach for estimating the EoS parameters and explain the problems observed. The estimated pure compound parameters have been tested in the prediction of second virial coefficients with satisfactory results.

“…data) according to Pimental and McClellan (1960). e Ksiazczak and Moorthi (1985). relationships will hold for other homologous series, e.g., acids, amines, pyridines, etc.…”

Section: Parameter Estimationmentioning

confidence: 99%

An Equation of State for Associating Fluids

Voutsas

Yakoumis

et al. 1996

Ind. Eng. Chem. Res.

895

707

Extension of CPA and SAFT to New Systems: Worked Examples and Guidelines

Thermodynamic Models for Industrial Applications

Folas

2009

Application of CPA and other association equations of state (EoS) to new associating systems (for which parameters are not available in the literature) includes the following three (often interconnected) stages:1. Choice of pure component parameters. 2. Establishment of the number of possible association sites and choice of an appropriate association scheme. 3. Cross-association and solvation schemes.Stage 2 is at first based on Tables 8.11 and 8.12 (Chapter 8). However, various association schemes are possible for a specific compound and, moreover, various sets of parameters of CPA/SAFT models can be obtained which equally well correlate the available vapor pressure and liquid density data. Experience has shown that, when possible, it is best to select the most appropriate parameter set for an associating compound using, in addition to pure compound properties, LLE data of the compound under investigation with an inert compound, e.g. n-alkane. For example, water-hexane LLE data can be used to determine the optimum parameters for water, among the various sets which represent the vapor pressure and liquid density data of water equally well.In this way, reliable parameters were estimated in the cases of water and glycols as many LLE data are available for these highly immiscible systems with alkanes. LLE data for partially miscible systems like methanol or ethanol with alkanes (for which VLE data are also available) are useful for the same purpose. There are families of compounds such as amines where LLE data are not available for mixtures with alkanes. Then, optimum sets of parameters can be estimated using, in addition to pure compound properties, other 'sensitive' data, e.g. VLE at low temperatures. Second, virial coefficients can also be used but their accuracy, especially at low temperatures, should be evaluated carefully.In this chapter, we will illustrate how association models like CPA and SAFT can be extended to 'new' compounds and systems, not previously studied, where the association sites/schemes and types of crossassociation/solvation are not known a priori. A working approach will be illustrated first for the case study of sulfolane, while other systems (aniline and phenols) will be briefly considered next. The underlying purpose of the chapter is to provide 'mechanisms and working tools' for extending association EoS to new compounds and mixtures without significant changes to the framework, e.g. without introducing new terms in the models for explicit accounting of the polarity and other effects beyond those already considered in the models (physical, chain and association terms).

Applications of SAFT to Polar and Associating Mixtures

Thermodynamic Models for Industrial Applications

Folas

2009

It could be argued that the majority of the applications of SAFT variants are found in the field of nonassociating mixtures, especially polymer solutions and blends (Chapter 14). A few applications for associating mixtures were developed in the decade 1990-2000, but since then the number of applications for associating mixtures has increased substantially and some characteristic publications are summarized in Table 13.1. Mostly, applications to aqueous mixtures as well as systems with alcohols and organic acids have been considered. Few publications deal with multifunctional chemicals such as glycols and alkanolamines, while non-associating polar chemicals (ketones, esters, nitriles, etc.) have also been considered (in most cases with polar and sometimes quadrupolar/induction terms being added). Comparisons against other models, especially the CPA, ESD and NRHB EoS, have been presented in the literature. From a scientific and development point of view, the nature of association schemes and the combining rules for solvating/cross-associating mixtures are worthy of investigation. We will illustrate the major conclusions and present some typical results for some of these applications, roughly divided according to the associating compound considered. Water-hydrocarbonsAqueous systems with hydrocarbons have been studied with various SAFT models with varying degrees of success. There is some disagreement in the overall assessment of the model in the various publications. The different performance of SAFT variants for water-hydrocarbons may be due to details of the specific SAFT model investigated (sites of water, mixing rules, which dispersion term is used, etc.) but they seem more to be due to the parameterization for water, i.e. determination of pure water parameters. The major findings in water-hydrocarbon studies are summarized below in chronological order:1. The first investigations with the original SAFT 9,46 for water-alkanes indicate that SAFT has severe difficulties in representing both water and alkane solubility with the same interaction parameter (k ij ).