Jaime Wisniak

Simultaneous prediction of the critical and sub-critical phase behavior in mixtures using equations of state II. Carbon dioxide-heavy n-alkanes

In the present study we present the final development of the Global Phase Diagram-based semi-predictive approach (GPDA), which requires only 2–3 key data points of one homologue to predict the complete phase behavior of the whole homologues series. The ability of GPDA to predict phase equilibria in CO2–heavy n-alkanes is compared with the equations of state LCVM and PSRK. It is demonstrated that both LCVM and PSRK are more correlative rather than predictive because their parameters are evaluated by the local fit of a considerable amount of VLE experimental data. In addition, these models fail to predict accurately the VLE of systems, which have not been considered in the evaluation of their parameters. They are also particularly inaccurate in predicting LLE and critical lines. In contrast, GPDA is reliable in the entire temperature range and for all types of phase equilibria. It yields an accurate prediction of the global phase behavior in the homologues series and their critical lines. Moreover, increasing asymmetry does not affect the reliability of GPDA; it predicts very accurately even the data of the heaviest homologues of the series.

Analysis of residuals — a useful tool for phase equilibrium data analysis

It is shown that analysis of the goodness of a fit using only the coefficient of determination R 2 or the mean average deviation is not enough and should be accompanied by a statistical study of the behavior of the residuals. This study should not be visual but using proper statistics. Different techniques such as normal probability plots, half-normal probability plots, detrended probability plots, rankits and Durbin-Watson are presented and illustrated with examples from the area of fluid behavior and fluid phase equilibrium. q 1999 Elsevier Science B.V. All rights reserved.

An assessment of thermodynamic consistency tests for vapor-liquid equilibrium data

Consistency tests are techniques that allow, in principle, the assessment of experimental vapor-liquid equilibrium data on the basis of the Gibbs-Duhem equation. Much empiricism and arbitrariness is frequently observed in the analysis and application of consistency tests, a situation that may question their usefulness. Perfect data satisfy exactly the Gibbs-Duhem relation, but acceptable data obey it within a tolerable limits (consistency criteria) which does not give a unique answer, regarding the quality of the data, when different consistency procedures are used. As with any approximation, application of consistency tests requires rigour, reasonable assumptions and models, and an examination of the data and results of the test. In this work, a set of guidelines that allow a critical interpretation of consistency analysis is proposed and special attention is given to the point-to-point test which is extensively used today in data evaluation.

Correlation of the boiling points of mixtures

Abstract A modified Swietoslawski equation has been developed to correlate the boiling points of mixtures. Vapor—liquid equilibrium data have been determined at 760 mm for the binary systems normal butanol-tertiary butanol and normal butanol-secondary butanol. Both systems present slight negative deviations from ideal solution behavior. The boiling points of the two binaries and of several other non-ideal systems were satisfactorily correlated by means of the above equation. Prediction of ternary boiling points from binary data and simplifications in the correlation which are useful for practical applications are also discussed.

Prediction of the critical locus in binary mixtures using equation of state: II. Investigation of van der Waals-type and Carnahan–Starling-type equations of state

Abstract The ability to predict critical lines of members of the methane–, perfluoromethane– and water–alkanes homologous series is compared for van der Waals (vdW)-type and Carnahan–Starling (CS)-type equations of state. A temperature dependent combining rule for the binary attraction parameter is discussed and employed. It is found that the appropriate choice of the adjustable parameters yields quite accurate results for both equations. A new application of global phase diagrams is proposed for the quantitative description of real mixtures. In this diagram, the boundaries of the different types of phase behavior are presented in the k12–l12 plane. Analysis of this diagram has allowed us to reach conclusions that cannot be obtained by a simple fit of data points. In particular, it is demonstrated that the global phase diagrams shape defines the correlative ability of the equations. It is found that CS-type equations tend to predict a larger region of liquid–liquid immiscibility, the accuracy of the result depends on the particular experimental system. Changes in the density dependence of the attraction term of the two-parameter equations influence mostly the predicted critical volumes and not their qualitative performance. In addition, the development of a CS-type equation suitable for engineering calculations is discussed.

Potential uses of jojoba oil and meal — a review

Abstract The chemical composition of jojoba oil is unique in that it contains little or no glycerin and that most of its components fall in the chain-length range of C 40 C 42 . Linearity and close-range composition are probably the two outstanding properties that give jojoba oil its unique characteristics. Jojoba oil molecules contain two double bonds separated by an ester bond. These three active centers have been proven to be the source of a very large number of intermediates or final products. This paper describes the applications of natural jojoba oil and reviews in particular the reactions that lead to derivatives with potential industrial application: (1) production of semisoft waxes by geometrical isomerization; (2) production of hard waxes by hydrogenation; (3) additives for high-pressure high-temperature applications; (4) extractants for mercury cations; and (5) selective extractants for the nuclear industry. In addition, a general view of the potential uses of jojoba meal as animal feed is presented.

Prediction of the critical locus in binary mixtures using equation of state. I. Cubic equations of state, classical mixing rules, mixtures of methane-alkanes

Abstract This work compares the critical lines predicted by six cubic equations of state (EOS) and classical mixing rules with the experimental data available for the mixtures of methane–alkanes up to and including octane. A simple method for calculating the critical line is proposed. The influence of the values of the unlike pair parameter k 12 is followed and analyzed from the point of view of the global phase diagram. It is shown that different cubic EOS can yield similar semi-quantitative and even quantitative predictions with the optimized values of this parameter. The results are compared with the information available in the literature.

Vapour-liquid equilibria in associating solutions

Abstract Isobaric vapour—liquid equilibria data were measured for the binary mixtures of acetic acid—propionic acid and formic acid—propionic acid at 760 mm Hg. The data were tested against a new thermodynamic model which extends the one proposed by Marek in that it is suitable for the case of binary mixtures containing two associating species and takes into account hetero-dimerization in the vapour phase. The proposed model converts into that of Christian for the particular case of an ideal liquid solution. The model fits well the system acetic acid—propionic acid with regard to the thermodynamic consistency of the overall activity coefficients, but does not fit the second mixture so well, probably because higher degrees of polymerization have to be included in it.

Volumetric Properties of Toluene with Ethyl Acrylate, Butyl Acrylate, Methyl Methacrylate, and Styrene at 25°C

Densities of the binary systems of toluene with ethyl acrylate, butyl acrylate, methyl methacrylate, and styrene have been measured as a function of the composition, at 25°C and atmospheric pressure, using an Anton Paar DMA 5000 oscillating U-tube densitometer. The calculated excess volumes were correlated with the Redlich–Kister equation and with a series of Legendre polynomials. The excess volumes are negative for systems toluene + (ethyl acrylate, butyl acrylate, and styrene) and positive for the system toluene + methyl methacrylate.

Application of cubic equations of state to the fit of vapor pressures of pure components

Abstract A simplified technique is proposed for the application of cubic equations of state (EOS) to the calculation of vapor pressures of pure compounds and the method can be adapted to any EOS capable of predicting coexisting vapor and liquid phases. The procedure approximates vapor pressures using the zero-pressure liquid fugacity in the low temperature range, allowing a direct estimation of the parameters of a temperature cohesion function α ( T r ). Estimation of the whole vapor pressure curve, from low temperatures to the critical point, is possible using minimal information about saturation states. The technique proposed here is illustrated for a generalized form of the cubic EOS.