P. Svejda

Excess properties of binary mixtures of 2,2,4-trimethylpentane with one polar component

Abstract The excess proerties (g E , h E , v E , c p E ) of 2,2,4-trimethylpentane with several polar components of different polarity [acetonitrile, 2-butanone, bisdichloroethylether, t-butylchloride, chlorobenzene] have been determined. If the dipole-dipole interaction could be averaged over the different orientations, the net effect should be a spherical but temperature dependent contribution to the interaction potential. This would give rise to a negative c p E which could be estimated from the difference between g E and h E . The investigation has shown that the experimental values of c p E are the more positive, the stronger the dipole moment of the polar molecule. Obviously, there exist preferred orientations between the dipolar molecules, which cannot be broken up easily for stronger dipole moments.

Application of hard convex body and hard sphere equations of state to the critical properties of binary mixtures

Abstract The critical properties of hydrocarbon mixtures, perfluorocarbon + hydrocarbon, perfluoromethylcyclohexane + siloxane, acetone + hydrocarbon and polydimethyl siloxane mixtures have been calculated from an equation of state for hard convex bodies and from Guggenheims equation of state for hard spheres. In general, the results of both equations agree well with experimental data. It appears, however, that taking shape factors into account (by using the hard convex body equation) does not lead to a significant improvement in the agreement between theory and experiment for the critical properties.

Excess properties of the mixture bis(2-dichloroethyl)ether (chlorex) + 2,2,4-trimethylpentane (isooctane)

The excess properties of the mixture bis(2-dichloroethyl)ether (chlorex) + 2,2,4-trimethylpentane (isooctane), i.e. excess volumevE, excess enthalpyhE, excessGibbs energygE and excess heat capacitycpE are reported. The excess volume is small, negative on the chlorex side and positive on the isooctane side. The excess enthalpy at 293.15 K is 1 913 J mol−1 for equimolar composition, the excessGibbs energy amounts to 1 367 J mol−1 under the same conditions. The system undergoes phase separation below 290.47 K. Due to the nearness of the critical point,cpE exhibits a strong maximum at the critical composition (xisooctane=0.508), though the basic part ofcpE is negative. Discussion focusses on the effects of polarity of chlorex as mixing partner, on near-critical properties, and on mixing rules of avan der Waals-type equation of state.ZusammenfassungDie Exzeßeigenschaften der Mischung Bis(2-dichlorethyl)ether (Chlorex) + 2,2,4-Trimethylpentan (Isooktan), d.s. ExzeßvolumenvE, ExzeßenthalpiehE, Exzeß-Gibbs-EnergiegE und Exzeß-WärmekapazitätcpE werden berichtet. Das Exzeßvolumen ist klein, negativ auf der Chlorex-Seite und positiv auf der Isooktan-Seite. Die Exzeßenthalpie beträgt für 293.15 K und äquimolare Zusammensetzung 1 913 J mol−1, die Exzeß-Gibbs-Energie 1 367 J mol−1 unter den gleichen Bedingungen. Das Mischsystem zeigt eine Phasentrennung unterhalb von 290.47 K. Wegen der Nähe des kritischen Punktes hat die Exzeß-WärmekapazitätcpE ein starkes Maximum bei der kritischen Zusammensetzung (xisooctane=0.508), obwohl der Basis-Anteil voncpE negativ ist. Die Diskussion behandelt die Effekte der Polarität von Chlorex als Mischungspartner, die Eigenschaften infolge der Nähe des kritischen Punktes und Mischungsregeln einer Zustandsgleichung vomVan-der-Waals-Typ.

Volumetric and dielectric properties of the binary liquid systems: 1,2-dichloroethane + n-alkanes or + 2,2,4-trimethylpentane

Abstract Hahn G., Svejda, P. and Dallos, A., 1993. Volumetric and dielectric properties of the binary liquid systems: 1,2-dichloroethane + n-alkanes or + 2,2,4-trimethylpentane. Fluid Phase Equilibria, 86: 293-313 Molar excess volumes of the liquid mixtures of 1,2-dichloroethane + heptane, +nonane, +decane, +dodecane, +tetradecane, +hexadecane and +2,2,4-trimethylpentane (isooctane) have been determined at 293.15 and 313.15K from density measurements at atmospheric pressure. Also, the static dielectric constants and refractive indices of these mixtures have been measured as a function of composition at both temperatures. Trans/gauche equilibria of 1,2-dichloroethane in the liquid alkanes could be calculated. The conformational changes of the components during the mixing process are discussed.

Excess Gibbs energies of mixtures of polar liquids + liquids of similar structure, but varying polarizability

Abstract Vapour pressures of binary liquid mixtures of 1-chlorobutane, 2-butanone and ethanenitrile + 2,2,4-trimethylpentane, + 2,4,4-trimethyl-1-pentene or 2,4,4-trimethyl-2-pentene were measured by the static method at 313.15 K, partially also at 293.15 K and the molar excess Gibbs energies determined. Excess volume data (by vibrating tube) at both temperatures necessary to evaluate the measurements and the isothermal compressibilities of 1-chlorobutane and of 2,4,4-trimethyl-2-pentene at 293.15 K are also presented. The results could be discussed in terms of different polarizabilities of the structurally closely related pentane/pentene-compounds on mixing with liquids of increasing polarity by means of a general van der Waals equation of state for hard convex bodies.

Effect of the association of alkanols on their thermodynamic properties

Abstract After a short discussion on the association models of alcohols from the point of view of activity concepts, the peculiarities of association in the equation of state concept are treated in detail, with restriction to high densities. It is shown that there association appears only as an integral value, where the integral (called the Helmholtz energy integration constant) is over the non-linearity correction to the attractive van der Waals term. Association is not seen in the hard convex bodies mixing rules, which means that isothermal compressibilities of alcoholic mixtures can be predicted from the knowledge of excess volume. The peculiarities of the Helmholtz energy integration constant cause the entropy of pure alcoholic liquids to be quite different from that of the hard convex body assembly, and present some problems in the treatment of mixtures.

Gas-liquid critical temperatures of mixtures of propane, butane, pentane, sulfur hexafluoride, dichlorodifluoromethane and chlorotrifluoromethane with less volatile compounds of a range of varying polarities

Christou, G., Young, C.L. and Svejda, P., 1991. Gas-liquid critical temperatures of mixtures of propane, butane, pentane, sulfur hexafluoride, dichlorodifluoromethane and chlorotri-fluoromethane with less volatile compounds of a range of varying polarities. Fluid Phase Equilibria, 67: 45-53.

A generalized van der Waals equation of state VI. results with non-polar and polar molecules

Abstract A generalized van der Waals equation of state has been devised with a modeling of the anisotropic hard core of the molecule and assuming that the attractive van der Waals term becomes linear in density at sufficiently high densities. Corrections for non-linear density dependence have to be taken into account at medium and low densities. These corrections are near universal for non-polar substances, but change drastically with the polarity of the molecule. The temperature dependence of the attractive constant is small for spherical and for polar molecules, but becomes increasingly significant with increasing anisotropy of the molecular shape. With this equation the thermal behaviour of ethane, propane, butane, pentane, benzene, oxygen, monochlorodifluoromethane, acetonitrile, and ammonia could be correlated at subcritical temperatures within the experimental error of measurements.