Equations of state for the calculation of fluid-phase equilibria (original) (raw)
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Analytical equation of state for molecular fluids: Comparison with experimental data
Physical Review A, 1990
An analytical equation of state for real molecular Auids is presented, based on an extension of a previously presented perturbation theory for hard convex bodies [Song and Mason, preceding paper, Phys. Rev. A 42, xxxx (1990)]. It is a fifth-order polynomial in the density and seems to be valid over the range from the dilute gas to the metastable liquid, both below and above the critical temperature. The temperature-dependent parameters of the equation can be calculated if the intermolecular pair potential is known. However, knowledge of just the second virial coefficient plus some liquid densities is sufficient to predict reasonably accurate parameters and hence the whole pv-T surface. Three scaling constants characterize the equation: an interaction energy, an interaction distance, and a dimensionless nonsphericity or inner hard-core parameter. The equation is tested with experimental p-v-T data for eight selected systems: N2, CO~, C2H6, C3H8, CF4, SF6, NH3, and H20. Agreement is quite remarkable.
is modified in this research. The proposed modification estimates the specific volume of polar and hydrogenbonded liquids and vapor pressure of pure substances with greater accuracy while maintaining the ability of PRFR EOS in predicting critical compressibility factor of pure compounds. The proposed model is applied to correlate and predict the experimental data of vapor-liquid equilibria (VLE) and liquid densities of various binary nonideal and polar solutions. For this purpose eight mixing rules (van der Waals, HVO, WS, MHV1, MHV2, MHV, LCVM and HVOS) were used. Among the mixing rules considered in this work, only the WS and the MHV are the best predictive tools. In the G ex part of the proposed model the NRTL and the UNIQUACtype models were used, respectively. NRTL model has weak predictive capabilities due to its temperaturedependent parameters.
New criteria for the equation of state development: Simple model fluids
Fluid Phase Equilibria, 2008
Recently we have proposed (J. Chem. Phys. 128 (2008) 134508) a new rescaling of fluid density ρ by its critical value ρ 2/3 c to apply the corresponding states law for the attractive Yukawa fluids study. Analysis of precise simulation results allows us to generalize this concept to the case of simple fluids with different interparticle interactions, like Mie (n,m) and Sutherland pair potentials. It is shown, that there is a linear relationship between the critical pressure and critical temperature, as well as the critical density and inverse critical temperature for these frequently used pair potentials. As a consequence, the critical compressibility factor of these model fluids is close to its universal value measured experimentally for different real substances.
New applications of equations of state in molecular models of complex fluid mixtures
Fluid Phase Equilibria, 1998
Two different types of problems are approached by connecting simplified molecular models with equations Ž. of state EOS. For aqueous-organic solutions of gases chemically reacting with solvent, special techniques to handle electrostatic and nonelectrostatic interaction contributions in the calculation of liquid composition and fugacity coefficients are applied for modeling VLE. A modified hole model and the Soave-Redlich-Kwong Ž. Ž. SRK EOS are utilized to describe solubility of gases in water-alkanolamine-acid gas CO , H S mixtures. A 2 2 polydisperse version of a thermodynamic micellization model proposed earlier is formulated and applied to describe asphaltene phase drop-out from crude oils.
The Canadian Journal of Chemical Engineering, 2011
In part I of this series the pure component PHCT-DNSK equation of state (EOS) was presented. In this paper the EOS is extended to describe mixtures, particularly asymmetric mixtures containing one or more low molecular weight spherical compound together with one or more high molecular weight chain-like compound. The EOS utilises theoretically correct mixing rules and is generally able to predict the correct trends quantitatively for binary mixtures, and in most cases outperform other EOSs. With the use of a small, temperature independent, interaction parameter the EOS is able to predict the phase behaviour of the investigated systems qualitatively. The EOS is able to predict the phase behaviour of a multi-component system containing one or more light components and a range of heavy hydrocarbons with improved accuracy compared to other EOSs at reduced computational times.
Phase equilibria of fluid mixtures using a modified perturbed hard-sphere-chain equation of state
Fluid Phase Equilibria, 2000
We propose a new model for the calculation of phase equilibria for the fluid mixtures based on the perturbed Ž. hard-sphere-chain PHSC equation of state. We modified the bonding term of the PHSC equation by introducing the form proposed by Chapman et al. The model predicts Monte Carlo simulation data for the compressibility factor better than those predicted by the PHSC equation in the entire density region. We can describe vaporrliquid equilibria of pure volatile saturated fluids with three characteristic parameters. By introducing two additional binary adjustable parameters, the liquidrliquid coexistence curve of a binary fluid mixture can be calculated. In the predictions of the specific volume of polymers, our model shows better agreement with the experimental data than predictions by the PHSC equation.
Equation of state for compressed liquids from surface tension
International Journal of Thermophysics, 1996
A method for predicting an analytical equation of state for liquids from the surface tension and the liquid density at the freezing temperature (γ 1,ϱ 1) as scaling constants is presented. The reference temperature. Tref. is introduced and the product (T refT 11 2) is shown to be an advantageous corresponding temperature for the second virial coeflicienls. B2(T). of spherical and molecular fluids. Thus, B2(T) follows a promising corresponding states principle and then calculations forα(T) andb(T), the two other temperature-dependent constants of the equation of state, are made possible by scaling. As a result, (γ 1,ϱ 1) are sufficient for the determination of thermophysical properties of fluids from the freezing line up to the critical temperature. The present procedure has the advantage that it can also be used in cases whereT c andP c are not known or the vapor pressure is too small to allow accurate measurements. We applied the procedure to predict the density of Lennard-Jones liquids over an extensive range of temperatures and pressures. The results for liquids with a wide range of acentric factor values are within 5%.
A generalized NRTL model was previously proposed for the modeling of non ideal systems and was extended to the prediction of phase equilibria under pressure according to the cubic NRTL-PR EoS. In this work, the model is reformulated with a predictive k ij temperature and composition dependent mixing rule and new interaction parameters are proposed between permanent gases, ethane and nitrogen with hydrocarbons, ethane with water and ethylene glycol. Results obtained for excess enthalpies, liquid-vapor and liquid-liquid equilibria are compared with those provided by the literature models, such as VTPR, PPR78, CPA and SRKm. A wide variety of mixtures formed by very asymmetric compounds, such as hydrocarbons, water and ethylene glycols are considered and special attention is paid to the evolution of k ij with respect to mole fractions and temperature.
Fluid Phase Equilibria, 2006
In this work, a new two-parameter cubic equation of state is presented based on perturbation theory for predicting phase behavior of pure compounds and of hydrocarbons and non-hydrocarbons. The parameters of the new cubic equation of state are obtained as functions of reduced temperature and acentric factor. The average deviations of the predicted vapor pressure, liquid density and vapor volume for 40 pure compounds are 1.116, 5.696 and 3.083%, respectively. Also the enthalpy and entropy of vaporization are calculated by using the new equation of state. The average deviations of the predicted enthalpy and entropy of vaporization are 2.393 and 2.358%, respectively. The capability of the proposed equation of state for predicting some other thermodynamic properties such as compressibility, second virial coefficient, sound velocity in gases and heat capacity of gases are given, too. The comparisons between the experimental data and the results of the new equation of state show the accuracy of the proposed equation with respect to commonly used equations of state, i.e. PR and SRK. The zeno line has been calculated using the new equation of state and the obtained result compared with quantities in the literatures. Bubble pressure and mole fraction of vapor for 16 binary mixtures are calculated. Averages deviations for bubble pressure and mole fraction of vapor are 9.380 and 2.735%, respectively.