Improved vapor-liquid equilibria predictions for Lennard-Jones chains from the statistical associating fluid dimer theory: Comparison with Monte Carlo simulations Vapor-liquid equilibria of different quadrupolar linear Kihara fiuids have been studied, by using the Gibbs ensemble Monte Carlo technique. Coexistence curves for fiuids with elongations L * = LI u= 0.3, 0.6, and 0.8 and different quadrupoles are given. We analyze the effect of quadrupole moment on critical properties. Quadrupole moment increases the critical temperature, pressure, and density. The magnitude of the increase depends on both anisotrop~ a~d qu~~~ole moment. A new way of reducing the quadrupole is proposed, so that the vanatlon of cnhcal properties due to the quadrupole follows a universal behavior. Quadrupole provokes deviations from the principle of corresponding states. A broadening of the coexistence curve is observed due to the quadrupole. The quadrupole moment increases the slope of the vapor pressure curve vs temperature inverse. Simulation data are used to describe vapor-liquid eqUilibria of carbon dioxide. Good agreement between simulation and experiment is achieved.4166

The virial coefficients up to the fifth of hard conformers of alkanes have been evaluated numerically. The conformers were selected by using the rotational isomeric state approximation. The effect of branching and length of the chain on the anisotropy of alkanes is discussed and a relation between the nonsphericity parameter a and the acentric factor w for this kind of molecule is proposed. We modified the equation of state for tangent hard spheres 6rst proposed by Wertheim [M. S. Wertheim, J. Chem. Phys. 87,7323, (1987)] to allow for overlapping of the constituting hard spheres. This modified version predicts with high accuracy the virial coefficient of the hard conformers of alkanes. Moreover comparison of this equation of state with simulation results of repulsive models of n-alkanes reveals very good agreement. The effect of condensed phase effect on the conformational equilibria of n-alkanes up to n-octane is analyzed.

The vapor-liquid equilibria of 20 substances, most of them widely used as organic solvents, were obtained by means of a Gibbs ensemble Monte Carlo method. All these substances can be represented by linear or angular models with only two bonds. The intermolecular interaction was described by a Kihara potential and, where appropriate, an additional multipolar potential using meaningful microscopic parameters. The results agree excellently with experiment even for ranges of hundreds of kelvin when potential parameters are obtained only from fitting two critical constants. The largest discrepancies are observed for liquids capable of forming hydrogen bonds, especially alcohols, but even in these cases agreement is very fair for temperaturedensity equilibrium bells. Agreement is also very good for vapor pressure up to close to critical pressure, namely 60-80 bar in all cases. The worst agreement is again observed for hydrogen-bonding liquids. Vaporization enthalpies were also calculated for some substances. In this case agreement was only fair but also over a large range of temperatures. Finally, parameters commonly used in chemical engineering, such as the acentric factor and solubility factor, which enable prediction of the mutual solubilities of some hundreds of mixtures, were calculated. Some of these mixtures are not yet apparently measured in spite of their possible industrial interest.

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