Pure Non-polar Fluids Research Articles

A new correlation for VLE data: Application to binary mixtures containing nitrogen

Recently we proposed simple analytical expressions for the calculation of the equilibrium pressure, as well as the mole fractions of both liquid and vapor phases at the vapor-liquid equilibrium of binary mixtures. They are based on a recently proposed molecular model for the vapor pressure of pure non-polar fluids, which, for a given temperature, only requires as input the values of the two Lennard-Jones molecular parameters and the acentric factor, which are parameters related to the molecular shape of each substance, and whose values are readily available. The mixing rules contain adjustable parameters that must be obtained for each mixture. In this work, we test the applicability of the models for some mixtures containing nitrogen. In particular, we find that the calculation of mole fractions must be performed with particular care in some cases. We show that the model for the pressure clearly improves the results obtained with classical equations of state for most of the mixtures studied.

A molecular model for correlating vapor-liquid equilibrium of propane+hydrocarbon mixtures

Simple analytical expressions are proposed for the calculation of the equilibrium pressure and the mole fractions of both liquid and vapor phases of propane+hydrocarbon binary mixtures. The new proposed expressions are based on a simple analytical expression for the vapor pressure of pure non-polar fluids, which, for a given temperature, only requires as input the values of the Lennard-Jones molecular parameters and the acentric factor. A properly modified Lorentz-Berthelot mixing rule is used, the interaction parameters being given as simple functions of the temperature and concentration with eight constants for each binary mixture. A different model is proposed to calculate the vapor mole fraction in which four appropriate constants are needed for each mixture. Here, it is shown how the models can reproduce accurately and straightforwardly the vapor liquid equilibrium properties (pressure, liquid mole fraction, and vapor mole fraction) of binary mixtures containing propane.

An analytical pressure–temperature–composition correlation for the VLE of CO 2 binary mixtures

An analytical expression relating the vapour–liquid equilibrium pressure, temperature and composition of binary mixtures formed by CO 2 and a non-polar fluid is proposed. The model is based on a simple analytical expression for the vapour pressure of pure non-polar fluids which, for a given temperature, only requires as input the Lennard-Jones molecular parameters and the acentric factor values. A properly modified Lorentz–Berthelot mixing rule is used, the interaction parameters being given as simple functions of temperature and composition with eight constants for each binary mixture. The model is shown to reproduce accurately and in a simple way the pressure (for a given liquid mole fraction) or the liquid composition (for a given pressure) of nine CO 2+hydrocarbon systems at different temperatures.

Prediction of surface tension for pure non-polar fluids based on density functional theory

A method for the prediction of surface tension of non-polar fluids has been developed based on the density functional theory. The Barker–Henderson perturbation theory and statistical associating fluid theory are used to establish an equation of state (EOS). The parameters m, σ and ε/ k of the EOS are correlated by simultaneously fitting the saturated vapor pressure and the liquid density data. The surface region of a pure liquid is divided into many extreme thin layers. The chemical potentials of different layers in the surface region are equal and lead to a constant by optimizing the surface thickness. The density profile is obtained from the optimized surface thickness and a hyperbolic tangent function. By use of the regressed parameters in the EOS, the surface tensions for 18 pure non-polar fluids are predicted and the results are satisfactory.

Molecular models for the vapor-liquid equilibrium of simple binary mixtures

Simple analytical expressions are proposed for the calculation of the equilibrium pressure, as well as (for a given temperature and pressure) the mole fractions of both liquid and vapor phases at the vapor-liquid equilibrium of binary mixtures. They are based on a recently proposed molecular model for the vapor pressure of pure nonpolar fluids, which, for a given temperature, only requires as input the values of the two Lennard-Jones (LJ) molecular parameters and the acentric factor, which are parameters related to the molecular shape of each substance and whose values are readily available. The model for the equilibrium pressure of a binary mixture (which also permits one to obtain the liquid phase mole fraction) is similar to that derived from Raoult’s law, where a properly modified Lorentz-Berthelot mixing rule is used, the interaction parameters being given as simple functions of the temperature and composition with eight appropriate constants for each binary mixture. A different model is needed to calculate the vapor mole fraction in which five appropriate constants are needed for each mixture. Here, we show how the models reproduce accurately and straightforwardly the vapor liquid equilibrium properties (pressure, liquid mole fraction, and vapor mole fraction) of eight binary systems over a broad temperature range, including some data at or near the critical locus.

A SIMPLE CALCULATION OF THE PRESSURE AND LIQUID MOLE FRACTION AT THE VLE OF ETHANE/LIGHT HYDROCARBON BINARY MIXTURES

An analytical expression for the calculation of the pressure and liquid mole fraction at the VLE of ethane/light hydrocarbon binary mixtures is proposed. The model is based on a simple analytical expression for the vapor pressure of pure non-polar fluids, which, for a given temperature, only requires as input the values of the Lennard-Jones molecular parameters and the acentric factor. A properly modified Lorentz-Berthelot mixing rule is used, the interaction parameters being given as simple functions of the temperature and composition with eight constants for each binary mixture. The model is shown to reproduce accurately and simply the pressure (for a given liquid mole fraction) or the liquid composition (for a given pressure) of six ethane + hydrocarbon systems at different temperatures.

Molecular model for the VLE p- T-x relationships of binary mixtures

An analytical expression for the pressure-temperature-composition relations in the vapour - liquid equilibrium of non-polar binary mixtures is proposed. The model is based on a simple analytical expression for the vapour pressure of pure non-polar fluids, which, for a given temperature, requires as input only the Lennard- Jones molecular parameters and the acentric factor of the substance. The equilibrium mixture pressure is then expressed as a function of the vapour pressure of each component and of a mixture contribution. The molecular parameters required for this mixture contribution are related to the molecular parameters of the pure component through a modified Lorentz-Berthelot mixing rule, where the interaction parameters are given as simple functions of the temperature and composition, with eight appropriate constants for each binary mixture. We show that the model permits one to reproduce or predict in a simple way the pressure (for a given liquid mole fraction) or the liquid composition (for a given pressure).

A new cubic simplified perturbed hard-body equation of state

A new cubic equation of state (EOS) was developed in this study for vapor-liquid equilibrium (VLE) calculations of nonpolar fluids. The repulsive term of this EOS reexpressed the results of Walsh and Gubbins (1990) from their modified thermodynamic perturbation theory of polymerization into a simple form in which a non-spherical parameter was employed to account for the different shapes of molecules. The repulsive compressibility factors calculated from this EOS agree well with the molecular simulation data for various kinds of hard bodies ranging from a single hard sphere to tangent or fused long chain molecules. A simple attractive term was then coupled with the repulsive to complete the EOS in a cubic form. Equation parameters were determined for a diversity of nonpolar real fluids. These parameters were expressed in generalized forms for engineering computations. Satisfactory results from this EOS on the saturated properties of pure nonpolar fluids were obtained. This EOS was also extended to calculate the VLE of nonpolar fluid mixtures. The results are again satisfactory over wide ranges of temperature and pressure.

Generalized quartic equation of state for pure nonpolar fluids

AbstractA generalized quartic equation of state has been developed for pure nonpolar fluids. The equation of state contains four parameters which depend on three properties of the fluid—critical temperature, critical volume, and acentric factor. A mathematical approximation based on previously reported hard‐sphere molecular dynamics simulations has been used to model repulsive contributions to the pressure. Attractive forces were modeled using an empirical term. While the quartic equation yields four roots, one root is always negative and hence physically meaningless, and three roots behave like three roots of a cubic equation. Thus, the new equation of state has the advantages of a cubic, simplicity and unequivocal identification of the roots, while correctly modeling the attractive and repulsive contributions to the pressure. The new equation of state is more accurate than either the Peng‐Robinson or a previously proposed quartic equation of state. Accuracy in the supercritical and compressed liquid regions is improved substantially.

Vapor-liquid equilibria from an improved hard convex body expansion method

Chen, Y.-C. and Chen, Y.-P., 1993. Vapor-liquid equilibria from an improved hard convex body exansion method. Part 1. Pure non-polar fluids. Fluid Phase Equilibria, 86: 63-85. This study applies the hard convex body expansion (HCBE) method to calculate vapor-liquid equilibria of non-polar fluids. A generalized corresponding states approach, as used by Kwon and Leland, is also employed in this work. We redefine a geometrical acentric factor, which is related to the geometry of a convex molecule, for each pure component. For fluids other than the reference components, this parameter is fitted as a function of temperature, which gives optimal correlation results for saturated vapor pressures. Pure compound properties are successfully correlated by the improved HCBE method. The method developed in this study is also capable of the generalized prediction of the properties of pure substances. An extension to mixture calculations will be presented in a future publication.

The most general density-cubic equation of state: application to pure nonpolar fluids

Thermodynamic properties of pure nonpolar fluids are predicted accurately, over wide ranges of temperature and pressure conditions, by the most general density-cubic equation of state. Of particular merit is the accurate prediction of liquid densities and low-temperature vapor pressures. The development of the temperature dependence and the generalization of the equation of state using thermodynamic property data for normal paraffin hydrocarbons, methane through n-decane, are presented herein. The generalized equation of state predicts vapor pressure and vapor and liquid densities to within 1% (average) of the experimental values for these fluids. The equation of state prediction of thermodynamic properties of 32 fluids is compared with the predictions by a popular density-cubic equation namely, the Peng-Robinson equation and a popular BWR-type equation of state. According to these comparisons the most general density-cubic equation is superior to the Peng-Robinson equation and is on par with the BWR-type equation of state. 60 refs.