Phase Equilibria In Fluid Mixtures Research Articles

Densimetry for the Quantification of Sorption Phenomena on Nonporous Media Near the Dew Point of Fluid Mixtures

Phase equilibria of fluid mixtures are important in numerous industrial applications and are, thus, a major focus of thermophysical property research. Improved data, particularly along the dew line, are needed to improve model predictions. Here we present experimental results utilizing highly accurate densimetry to quantify the effects of sorption and capillary condensation, which exert a distorting influence on measured properties near the dew line. We investigate the (pressure, density, temperature, composition) behaviour of binary (CH4 + C3H8) and (Ar + CO2) mixtures over the temperature range from (248.15 to 273.15) K starting at low pressures and increasing in pressure towards the dew point along isotherms. Three distinct regions are observed: (1) minor sorption effects in micropores at low pressures; (2) capillary condensation followed by wetting in macro-scale surface scratches beginning approximately 2% below the dew-point pressure; (3) bulk condensation. We hypothesize that the true dew point lies within the second region.

Equation-of-state modeling of confined-fluid phase equilibria in nanopores

Perturbed-chain statistical associating fluid theory (PC-SAFT) is coupled with Young–Laplace equation to investigate and represent fluid-phase equilibria in nanosize pores. The calculated pure-substance properties at capillary condensation (critical temperature, critical pore radius, surface tension, condensed-phase equilibrium pressure, and saturated densities) are found to be consistent with experimental data, theoretical models, and molecular simulation. The information obtained for pure substances can then be applied to predict the phase equilibria of fluid mixtures in porous mediums. The promising results presented in this work establish a strong platform for further development of an effective model toward engineering applications in real settings of confined fluids such as chemical systems encountered in unconventional reservoirs (e.g., shale oil and shale gas).

Exploring fluctuations and phase equilibria in fluid mixtures via Monte Carlo simulation

Monte Carlo simulation provides a powerful tool for understanding and exploring thermodynamic phase equilibria in many-particle interacting systems. Among the most physically intuitive simulation methods is Gibbs ensemble Monte Carlo (GEMC), which allows direct computation of phase coexistence curves of model fluids by assigning each phase to its own simulation cell. When one or both of the phases can be modelled virtually via an analytic free energy function (Mehta and Kofke 1993 Mol. Phys. 79 39), the GEMC method takes on new pedagogical significance as an efficient means of analysing fluctuations and illuminating the statistical foundation of phase behaviour in finite systems. Here we extend this virtual GEMC method to binary fluid mixtures and demonstrate its implementation and instructional value with two applications: (1) a lattice model of simple mixtures and polymer blends and (2) a free-volume model of a complex mixture of colloids and polymers. We present algorithms for performing Monte Carlo trial moves in the virtual Gibbs ensemble, validate the method by computing fluid demixing phase diagrams, and analyse the dependence of fluctuations on system size. Our open-source simulation programs, coded in the platform-independent Java language, are suitable for use in classroom, tutorial, or computational laboratory settings.

Modeling the Vapor-Liquid Equilibrium of Mixtures Involving Noble Gases, Alkanes, and Refrigerants and some Ionic Liquids Using Perturbed Hard-Sphere Equation of State

The present study is a continuation of our previous work (S.M. Hosseini, J. Moghadasi, M.M. Papari, F. Fadaei Nobandegani, J. Mol. Liq. 160 (2011) 67-71) related to the examination of the ability of the perturbed hard- sphere equation of state (EOS) in predicting thermodynamic properties of pure fluid and mixtures.In our previous study, aperturbed hard-sphere equation of state was developed to predict pressure-volume-temperature-composition surfaces of pure and mixturesof ionic liquids (ILs). The present paper aims to extend the model to vapor-liquid equilibria of some binary mixtures consisting of ionic liquids, refrigerants, hydrocarbons, and monatomic fluids. The novelty of the present work is the application ofourperturbed hard-sphere equation of statetomodel the phase equilibria of various mixtures. The outcomes of the computation are compared with the experimental data. Our results demonstrate that this EOS can properly model phase equilibria of fluid mixtures with acceptable accuracies.

Modeling vapor–liquid equilibrium of various binary mixtures with a statistically based equation of state

The present study is a continuation of previous work (F. Yousefi, J. Moghadasi, M. M. Papari, A. Campo, Ind. Eng. Chem. Res. 48 (2009) 5079–5084) related to the assessment of the ability of the Tao-Mason (TM) equation of state (EOS) in predicting thermodynamic properties of fluid mixtures. In our previous study, we extended the TM EOS to predict pressure–volume–temperature–composition of fluid mixtures. The present paper aims to model vapor–liquid equilibria of some binary mixtures of ionic liquids, refrigerants, hydrocarbons, and monatomic fluids. In this study, the Sheikh-Papari-Boushehri (SPB) correlations have been employed to predict temperature-dependent parameters appeared in the EOS. The novelty of the present work is the application of Tao-Mason (TM) EOS to fluid phase equilibria of mixtures. The outcomes of the computations are compared with the experimental data. Our results demonstrate that the TM EOS can properly model phase equilibria of fluid mixtures with acceptable accuracies.

Properties and phase equilibria of fluid mixtures as the basis for developing green chemical processes

The properties and phase equilibria of fluid mixtures can have great influence on chemical product formation and process development. In this work, examples are presented that illustrate the reaction and separation characteristics of high temperature water, supercritical carbon dioxide, and ionic liquids based on real-time images made with diamond anvil cells or visual cells. In the formation of ferrosilite from quartz (SiO 2) and fayalite (Fe 2SiO 4), the diffusion of SiO 2 to the solid fayalite substrate requires less than seconds to occur in water at high temperatures due to the enhanced solubility of SiO 2, which has great technological significance for developing processes for industrially important luminescent materials. It is proposed that luminescent materials based on the zinc silicate (Zn 2SiO 4) family can be made with low environmental burden. The enhanced solubility of natural products in water at high temperatures allows for the fractionation of biomass to produce fermentable feedstocks and chemical products as well as for the efficient separation of natural products. The volumetric properties of n-alkylphenolics with CO 2 can allow for efficient separation from their solid matrix due to viscosity reduction and foaming induced by changes in pressure. The lack of solubility of ionic liquids in supercritical CO 2 allows for biphasic systems that can be used to efficiently separate phenolic compounds. Equations of state can provide suitable correlation. The viscosity reduction provided by solvents such as water, supercritical carbon dioxide, or organic liquids on ionic liquids allows ionic liquids to be put into a metastable state so that chemical conversions can occur in ionic liquids below their melting point at room temperature. The physical properties and phase behavior of water and carbon dioxide and mixtures with target compounds are very important for developing new green chemical processes.

Summary

Summary

PREDICTION OF PHASE EQUILIBRIA IN BINARY MIXTURES USING AN IMPROVED EQUATION OF STATE AND A THEORETICALLY CONSISTENT MIXING RULE

Prediction of thermodynamic properties and phase equilibria in fluid mixtures using a simple cubic equation of state is still a challenging problem. In this paper, we have predicted vapor/ liquid phase equilibria of several binary fluid mixtures using our previously developed improved Peng-Robinson equation of state and a theoretically consistent mixing rule. Our mixing rule combines the mixing rule of Wong-Sandier with a physically based combination rule. Mixtures are composed of nonpolar, nonassociating polar and associating polar fluids. Comparisons of theoretical predictions with experimental data show a very good performance of our approach in describing vapor/liquid phase equilibria of several mixtures, namely, carbon dioxide/ propane, ethane/hexane, butane/methanol, benzene/methanol, acetone/methanol, methanol/ ethanol, methanol/1-butanol, methanol/water and ethanol/water.

A comparative study of numerical methods for calculating phase equilibrai in fluid mixtures from an equation of state

Accurate numerical methods are needed to determine phase equilibria in fluid mixtures for industrial applications, especially when mixtures exhibit critical points. In this paper we test the reliability and consistency of predictions of three major approaches for computing vapor-liquid-phase equilibria in binary fluid mixtures based on the Soave-Redlich-Kwong equation of state and van der Waals one-fluid mixing rules. These approaches are fugacity method, Gibbs minimization method and area method. To examine the accuracy of the three methods, calculated results for the vapor-liquid-phase equilibria in two selected binary mixtures, namely, carbon dioxide/butane and carbon dioxide/propane, are compared with experimental data over a range of high temperatures (278–398 K) and elevated pressures (0.3–7 MPa). It has been found that the area method, which provides both necessary and sufficient conditions for Gibbs energy minimization of the entire system, is more reliable than either the fugacity method or Gibbs minimization method in determining the vapor-liquid-phase equilibria, especially close to the critical loci of the mixtures. The Gibbs minimization performs better than the fugacity method in locating phase equilibria in the vicinity of the critical locus of the mixtures. Far away from the critical loci of the mixtures all the three methods are found to be equally reliable. The area-method-based calculations illustrate that the SRK EOS/VDW MR model can predict reasonably well the vapor-liquid-phase equilibria in these binary mixtures. However, the SRK EOS/VDW MR model, which contains only a single binary interaction parameter, is unable to describe accurately the pressure dependence of the vapor- and the liquid-phase compositions.

The Role of Computer Simulation in Studying Fluid Phase Equilibria

Abstract Computer simulations provide a method for studying mixtures in which the intermolecular forces are precisely defined. They can be used to study specific systems, where laboratory experiments may be too costly, time consuming, or difficult, or to develop better theoretical equations of state. In this paper we first review some of the most promising methods for studying phase equilibria in fluid mixtures. These can be divided into direct methods, which simulate the two-phase system itself, and indirect methods in which the chemical potential of a homogeneous phase is determined. Examples of the use of each of these approaches given, including the determination of vapour-liquid equilibria for binary mixtures and of the properties of dilute solutions. This is followed by an application in which the objective is to develop a better equation of state for polar and associated fluids. Here, computer simulation is used to develop a more suitable reference term in the equation of state for such fluids.

Models for phase equilibria in fluid mixtures

Models for phase equilibria in fluid mixtures

Phase equilibria in fluid mixtures at high pressures

Abstract

Phase equilibria in fluid mixtures

Phase equilibria in fluid mixtures

Phase equilibria in fluid mixtures

Phase equilibria in fluid mixtures

Fluid mixtures at high pressures

In the present survey some important trends in the high pressure thermodynamics of fluid mixtures of non-electrolytes are reviewed. First the pressure dependence of excess functions such as the excess Gibbs energy G, the excess enthalpy 5E, the excess en— tropy 5E, and the excess heat capacity CE is discussed. They can be obtained from a knowledge of the xcess volume VE as a function of pressure, temperature, and composition. Experimental results demonstrate that the variations of E as a function of pressure can be important and that even a change of the sign of VE with increasing pressure has been found in some cases. The pressure dependence of HE values thus obtained agree well with literature values determined from direct f lowcalorimetric measurements. Until now most thermodynamic information has had to be deduced from high-pressure phase equilibria and critical phenomena where our knowledge is much better. The pressure dependence and critical phenomena of liquid-gas, liquid-liquid, and gasgas equilibria will be shortly reviewed. Mainly binary systems will be treated, but phase-separation phenomena in some ternary systems will also be considered. New developments during recent years have shown that the limits between liquid-gas, liquid-liquid, and gas-gas equilibria are not well defined and that continuous transitions occur. This continuity will be demonstrated on recent results for binary mixtures of hydrocarbons with tetrafluoromethane and nitrogen. Methods for the calculation and correlation of high-pressure phase equilibria in fluid mixtures under pressure are reviewed. They start from equations of state or from theories of mixtures using sometimes rather complicated mixing rules for the mixture parameters. Some results are presented and compared with experimental data. The significance of high-pressure phase equilibria in fluid mixtures for practical applications is briefly discussed e.g. f or fluid extraction, supercritical fluid chromatography (SFC), and for some high—pressure techniques and processes.

High Pressure Thermodynamics of Mixtures

Abstract In the present survey some important trends in the high pressure thermodynamics of fluid mixtures of non-electrolytes are reviewed. First the pressure dependence of excess functions such as the excess Gibbs energy G E , the excess enthalpy H E , the excess entropy S E and the excess heat capacity C P E is discussed. It can be obtained from the knowledge of the excess volume V E as a function of pressure, temperature and composition. Experimental results demonstrate that the variations of V E as a function of pressure and temperature can be important and comparable to those of the molar volumes themselves. A detailed discussion shows that further progress in this field depends on the development of an accurate equation of state for mixtures. Since furthermore direct calorimetric measurements are practically completely lacking at high pressures most thermodynamic informations have to be deduced up to now from high pressure phase equilibria and critical phenomena where our knowledge is much better. The pressure dependence and critical phenomena of liquid-gas, liquid-liquid and gas-gas equilibria will be shortly reviewed. Mainly binary systems will be treated but phase separation phenomena in some ternary and multicomponent systems will be equally considered. Recent results concerning the rate of phase separation will be additionally presented. New developments during recent years have shown that the limits between liquid-gas, liquid-liquid and gas-gas equilibria are not well defined and that continuous transitions occur. This continuity will be demonstrated for binary mixtures of hydrocarbons with carbon dioxide and methane and for some inert gas systems. The significance of high pressure phase equilibria in fluid mixtures for practical applications is shortly discussed, e.g. for high pressure extractions, supercritical fluid chromatography and for some other high pressure techniques and processes. Methods for the calculation of fluid phase equilibria in mixtures under high pressure are reviewed. They start from equations of state or from theories of mixtures using sometimes sophisticated mixing rules for the parameters. Some results are presented and compared with experimental data. Finally a characteristic example for the pressure dependence of chemical equilibria in liquid solutions is considered and the standard value of the reaction volume Δ V θ is determined from measurements of the equilibrium constant K as a function of pressure at constant temperature. It is shown how standard values of the reaction enthalpy Δ H θ can be obtained from temperature jump experiments in such solutions at high pressure.

Phase equilibria in fluid mixtures at high pressures: The HeCH 4 system

An experimental study of phase equilibria in the HeCH 4 system has been carried out over the temperature range 95 to 290 K and at pressures to 10 000 atm. The experimental results consist of equilibrium phase composition for twenty-eight isotherms in the region of coexistence of two fluid phases, together with the pressure-temperature trace of the three-phase boundary at which a CH 4-rich solid phase is in equilibrium with the two fluid phases. The system exhibits a fluid-fluid phase separation which persists to temperatures and pressures beyond the range of this experiment. These results, together with those recently obtained for other binary systems, provide information about the form of phase diagrams for binary gas mixtures in the region of pressure-induced phase transitions at high pressures. These findings are relevant to problems of deep atmosphere and interior structures in the outer planets.

Phase Equilibria in Fluid Mixtures at High Pressures: The Neon–Argon System

Results of phase equilibria studies are reported for the neon–argon system at temperatures from 87.34 to 123.83°K and pressures to 3880 atm. These results, combined with those of earlier studies, provide a complete description, partly quantitative and partly qualitative, of the lines and surfaces comprising an important segment of the three-dimensional, pressure–temperature–composition, phase diagram for neon–argon. A three-dimensional sketch of the diagram is used to show the important phase boundary lines and the qualitative features in the region of transition from fluid to solid at high pressures. The relevance of these studies to problems of deep atmosphere structures in the outer planets is briefly discussed.

Phase equilibria in fluid mixtures at high pressures: the helium + argon system

An experimental study of phase equilibria in the system helium + argon has been carried out at temperatures from 98 to 160 K and pressures to 4000 atm. The mixture critical line and the three-phase region solid + liquid + gas have been located over most of this pressure range, and a region of fluid-fluid equilibria has been observed at temperatures above the critical temperature of argon. At pressures above about 1000 atm, in the two-phase region, the mutual solubilities of helium and argon decrease with increasing pressure at all temperatures. The relevance of these findings to problems of deep atmosphere structures in the outer planets is briefly discussed.

Phase Equilibria in Fluid Mixtures at High Pressures: The Helium–Nitrogen System

Experimental phase equilibrium data are reported for the He–N2 system at pressures up to 4000 atm, over the temperature range 78–137°K. The mixture critical line and the three-phase region solid–liquid–gas have been determined over the entire pressure range, and the system is shown to exhibit fluid–fluid phase separations which extend to temperatures above the critical temperature of N2. Some characteristics of phase diagrams for binary fluid mixtures at high pressures are described, and the relevance of these diagrams to problems of deep atmosphere structures of the major planets is briefly considered.