Nguyen Van Nhu

Excess properties of mixtures of polar components and hydrocarbons of varying local polarisability

Abstract The inhomogeneous electric field of a neighbouring polar molecule exerts a special induction in an unsaturated hydrocarbon, giving rise to more negative excess properties. This effect has been investigated for the excess Gibbs energy g E and the excess volume v E for mixtures of the polar components 1-chlorobutane, 2-butanone, and ethanenitrile with the four hydrocarbons cyclohexane, cyclohexene, 1,4-cyclohexadiene, and benzene at 293.15 K and 313.15 K. The measurements of g E were done by VLE (static vapour pressures by a continuous dilution apparatus) and checked by LLE for the systems with phase separation. Excess volumes were determined via a vibratim tube densimeter. Equation of state calculations enabled the evaluation of the interaction virial coefficient B 12 . The special induction effect, which shows up strongly in g E and v E of the liquid mixtures, is only weakly reflected in B 12 .

The second virial coefficients of some halogenated ethanes

The second virial coefficients of 1,1-difluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane and 1-chloro-1,1-difluoroethane have been calculated on the basis of two-centre-Lennard-Jones + superimposed dipole model potentials and compared with experimental results. These can be explained taking into account the reduced dipole moments and the angle between dipole moment and molecular axis.

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.

An equation of state for non-polar substances based on the generalized van der Waals model

Abstract Van Nhu, Nguyen, Iglesias-Silva, G.A. and Kohler, F., 1993. An equation of state for non-polar substances based on the generalized van der Waals model. Fluid Phase Equilibria, 91: 215-237. An equation of state is proposed on the basis of the generalized van der Waals model. The equation is a development of an earlier model (Svejda and Kohler, 1983, Ber. Bunsenges. Phys. Chem., 87: 672-680) to cover the whole range of densities and temperatures with a small number of parameters. The performance of the equation is shown for eleven non-polar substances, i.e. argon, nitrogen, oxygen, methane, ethene, ethane, propene, propane, butane, pentane, and benzene, and is very satisfactory for the subcritical region and satisfactory for the supercritical region. Features of the formulation are a positive medium density correction, which becomes increasingly positive for low temperatures, and a temperature dependence of the attractive coefficient such that the coefficient decreases from a plateau value at low temperatures to a plateau value at high temperatures.

Excess properties and phase equilibria calculated from a generalized van der Waals equation of state for the example of the mixture methane + ethane

Abstract A generalized van der Waals equation of state, formulated recently for pure non-polar substances, is now adapted for the treatment of mixture. The main contribution to the van der Waals attractive term, the critical temperature Tc, is now considered as a mixture parameter for the equivalent substance (the one-fluid mixture model). It is determined from the orthobaric liquid density of the mixture, i.e. from the excess volume. All other parameters are supposed to be additive in mole fraction. With these mixing rules, the equation gives good agreement for the excess Gibbs energy of methane + ethane over a larger temperature range. The phase equilibria are calculated according to the algorithm of Deiters (1985) and cover the whole range of temperatures and composition up to the critical curve. Apart from the immediate neighborhood of the critical points of the mixtures, the agreement is very satisfactory. The densities in the homogeneous region and the interaction second virial coefficients are also well reproduced.

The temperature dependence of the isothermal compressibility of liquids along the orthobaric curve

Abstract Correlations are presented for the reduced inverse compressibility along the orthobaric curve. Special emphasis is placed on an one-parameter description, which allows the extrapolation of isothermal compressibility to other temperatures, and where the one parameter gives an indication of the polarity of the liquid. Furthermore, the sensitivity of the one parameter to the value of the critical density can be used in turn as a check on this value.

Excess enthalpy and excess volume of cyclohexanone+tetrachloroethene

Abstract The excess enthalpy hE and the excess volume vE of the system cyclohexanone + tetrachloroethene have been measured. The values at equimolar composition are hE (293.15 K) = 263 J mol−1, VE (293.15 K) = 0.113 and vE (313.15 K) = 0.153 cm3 mol−1. The hE value is found to be more positive than that of cyclohexanone + tetrachloromethane, as is usually found, and the vE values obtained seen more viable than data in the literature, which show a very improbable temperature dependence.