Critical constants of conformed mixtures

Kreglewski, Aleksander; Kay, Webster B.

doi:10.1021/j100844a035

Cited by 87 publications

(33 citation statements)

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“…Using this approach, the critical isotherm can only be found by chance, so that the estimation of critical points (especially the critical pressure) from such data seems to be not very reliable and, as shown in the comparison. However, the results obtained with the PSRK model are in very good agreement with the experimental data obtained in this work and by other authors, e.g., Kreglewski and Kay [13] for the system propane (1) + n-butane (2). The measurement of further reliable data is necessary as proved by the divergent quality of experimental literature data even for these simple systems.…”

Section: Resultssupporting

confidence: 90%

Experimental Determination of Critical Points of Pure Components and Binary Mixtures Using a Flow Apparatus

Horstmann

Fischer

Gmehling³

1999

Chem. Eng. Technol.

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Equations of state can be successfully employed for the description of the phase equilibrium behavior of multicomponent mixtures using binary data alone. Especially in the vicinity of the critical point often only a limited number of phase equilibrium data or data of low quality are available. Critical points of mixtures provide additional information about the location and border of the two-phase region. The PSRK model (Predictive Soave-Redlich-Kwong) [1] combines the SRK equation of state with the group contribution model UNIFAC by the PSRK mixing rule. For the extension of the range of applicability and the improvement of the results of PSRK or other group contribution equations of state the systematic measurement of data required for the fitting of the group interaction parameters is desired. In addition to phase equilibrium data also critical data are of great importance. For this reason a new flow apparatus for the measurement of critical data of pure components and mixtures was developed, which can be operated at temperatures between 280 and 470 K and pressures up to 35 MPa.A common approach for the determination of critical points of mixtures in closed systems is the isothermal or isobaric method connected with an analysis of the gas and liquid phases for the determination of the two-phase region ending at the critical point. Another usual method is the visual detection of critical points where the temperature is varied until the phase border disappears while the temperature increases, or the meniscus reappears while the temperature decreases. The corresponding pressure automatically results from the phase equilibrium pressure. A prerequisite for the measurement of critical points is the exact adjustment of the critical density which requires a variable volume cell.A flow apparatus for the measurement of critical properties of pure components was introduced by Rosenthal and Teja [2]. The variation of density in this apparatus is enabled with the help of a regulation valve at the outlet of the optical cell. Because of the flow mode short retention times are achieved. That is why this technique also allows the determination of critical points of components which show a thermal decomposition. The critical data are determined at different flow rates. Extrapolation of these data to the retention time t = 0 allows the determination of the critical data of such unstable components.The apparatus developed in this study also works in a flow mode and is applicable for pure components as well as binary and multicomponent mixtures. An advantage of this approach is that phase equilibrium is reached before the substances enter the cell. Moreover, the content of the cell is pushed aside so that cleaning and controlled filling of the cell is not necessary. Unfortunately, the critical volume cannot be determined and quite large amounts of substances are needed. Principle of MeasurementA schematic diagram of the apparatus is shown in Fig. 1. Two thermostatted chromatography syringe pumps (Model 260D, ISO) in which the pure...

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Section: Resultssupporting

confidence: 90%

Experimental Determination of Critical Points of Pure Components and Binary Mixtures Using a Flow Apparatus

Horstmann

Fischer

Gmehling³

1999

Chem. Eng. Technol.

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“…I n the original evaluation, the Chueh-Prausnitz correlation was more accurate for methane-free mixtures. However, since the errors were high for some binary systems, methods proposed by Ekiner and Thodos (1966) and Kreglewski and Kay (1969) as well as the Smith and Watson (1937) chart were evaluated. Ekiner and Thodos (1966) obtained an expression for the critical pressure of methane-free binary hydrocarbon mixtures which was dependent on the pseudocritical pressure, the composition of the mixture, and three binary interaction parameters which have been generalized as functions of a critical pressure parameter.…”

Section: Critical Pressurementioning

confidence: 99%

“…They report an average deviation of 3.25% for 23 hydrocarbon mixtures. Kreglewski and Kay (1969), using the conformal solution approach, have correlated the critical pressure as follows:…”

Section: Critical Pressurementioning

confidence: 99%

A critical review of correlations for the critical properties of defined mixtures

1973

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An extensive critical evaluation of available correlations for predicting critical properties of binary defined hydrocarbon as well as some multicomponent hydrocarbon and hydrocarbon-nonhydrocarbon mixtures is presented using all available literature data. The Li method is recommended for critical temperature prediction based upon its accuracy and simplicity, although the Chueh-Prausnitz method is equivalent in accuracy. The Kreglewski method is most accurate for critical pressure prediction. All methods evaluated yielded high errors for the critical properties of methane-containing mixtures. Current correlations on critical volume are discussed, and correlational work on prediction using an excess volume approach is described. CALVIN CONCLUSIONS AND SIGNIFICANCEAn extensive evaluation of available correlations for the critical properties of defined mixtures has been made. The Li (1971) and the Chueh-Prausnitz (1967b) equations are equivalent in accuracy for calculation of the critical temperature of defined binary and multicomponent systems as well as hydrocarbon-nonhydrocarbon systems. Critical pressure of binary hydrocarbon systems not containing methane is best predicted by the Kreglewski (1969) method using the Li equation to estimate critical temperature. No accurate method currently exists for estimating critical pressure of binary, methane-containing systems.Additional experimental data and correlational work on critical volumes are required before any prediction method can be recommended. An indirect approach to critical pressure determination using an equation of state can be used after an accurate method of predicting critical volume is developed. An approach using excew volume criteria appears to be promising.Many correlations have been developed for predicting true critical properties of mixtures. One of three approaches is generally followed in developing these correlations.The empirical approach involves calculations of the form n G, = 2 X, G C i + G a r r where G, is the critical property desired and G,,,, is a correction term which is often called the excess property of the mixture. Exceys properties are normally estimated from empirical relations. i = lCorrespondence concerning this paper should be addressed to T. E. Daubert.The second approach is based on the rigorous thermodynamic conditions for the critical state, that is, the second and third partial derivatives of the molar Gibbs free energy G with respect to composition at constant temperature and pressure must be equal to zero. Determination of T,, V,, and P , for the mixtures involves a simultaneous solution of an extended form of the deriv'itives and an equation of state such as reported by Spear et al. (1971).The third approach is the theory of conformal solutions which states that all thermodynamic properties of a mixture can be evaluated from those of the pure compounds if the components conform to certain simple postulates of statistical mechanics. A conformal solution is one whose pair potential as a function of intermolecular dis...

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“…Many studies are concerned with empirical correlations for critical properties [10][11][12][13][14][15][16][17][18][19] and several popular equations of states (EOS) like RK [20], SRK [21], PR [22] and SAFT [23][24][25] have been used to determine critical points. It has been long recognized, however, that although these EOSs can describe fluid properties fairly well far away from the critical point, because they are mean-field based, they cannot yield the correct limiting properties at the critical point.…”

Section: Introductionmentioning

confidence: 99%

Critical temperatures and pressures for hydrocarbon mixtures from an equation of state with renormalization-group theory corrections

Jiang

Prausnitz

2000

Fluid Phase Equilibria

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Critical constants of conformed mixtures

Cited by 87 publications

References 0 publications

Experimental Determination of Critical Points of Pure Components and Binary Mixtures Using a Flow Apparatus

Experimental Determination of Critical Points of Pure Components and Binary Mixtures Using a Flow Apparatus

A critical review of correlations for the critical properties of defined mixtures

Critical temperatures and pressures for hydrocarbon mixtures from an equation of state with renormalization-group theory corrections

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