Vapor–liquid–liquid Equilibrium Research Articles

Separation of CO2 and H2S Using Room-Temperature Ionic Liquid [bmim][MeSO4

We have developed a ternary equation of state (EOS) model for the CO 2 /H 2 S/1-butyl-3-methylimidazolium methylsulfate ([bmim][MeSO 4 ]) system to understand separation of these gases using room-temperature ionic liquids (RTILs). The present model is based on a modified RK (Redlich-Kwong) EOS, with empirical interaction parameters for each binary system. The interaction parameters have been determined using our measured VLE (vapor-liquid equilibrium) data for H 2 S/[bmim][MeSO 4 ] and literature data for CO 2 / [bmim][MeSO 4 ] and CO 2 /H 2 S. Due to limited VLE data for H 2 S/[bmim][MCSO 4 ], we have also used VLLE (vapor—liquid—liquid equilibrium) measurements to construct the EOS model. The VLLE for H 2 S/ [bmim][MeSO 4 ] is highly asymmetric with a narrow (mole fraction H 2 S between 0.97 and 0.99) LLE gap which is the first such case reported in the literature and exhibits Type V phase behavior, according to the classification of van Konynenburg and Scott. The validity of the ternary EOS model has been checked by conducting VLE experiments for the CO 2 /H 2 S/[bmim][MeSO 4 ] system. With this EOS model, solubility (VLE) behavior has been calculated for various (T, P, and feed compositions) conditions. For large (9/1) and intermediate (1/1) CO 2 /H 2 S feed ratios, the CO 2 /H 2 S gas selectivity is high (10 to 13, compared with <4.5 in the absence of ionic liquid) and nearly independent of the amount of ionic liquid added. For small CO 2 /H 2 S mole ratios (1/9) at 298.15 K, increasing the ionic liquid concentration increases the CO 2 /H 2 S gas selectivity from about 7.4 to 12.4. For high temperature (313.15 K) and large CO 2 /H 2 S feed ratios, the addition of the ionic liquid provides the only means of separation because no VLE exists for the CO 2 /H 2 S binary system without the ionic liquid.

Phase Behavior for the Carbon Dioxide + N-Pentadecane Binary System

Vapor−liquid (VLE), liquid−liquid (LLE), and vapor−liquid−liquid equilibria (VLLE) data for the carbon dioxide + n-pentadecane system at (293.15, 303.15, 313.15, 333.15, and 353.15) K up to 17.50 MPa and phase compositions of the two liquid phases and vapor phase as a function of temperature along the liquid−liquid−vapor (LLV) line are reported. The experimental method used in this work was a static-analytical method with liquid and vapor phase sampling. The new experimental results are discussed and compared with available literature data. Measured data and literature data for the carbon dioxide + n-pentadecane system were modeled with the Soave−Redlich−Kwong (SRK) EoS using classical van der Waals (two-parameter conventional mixing rule, 2PCMR) mixing rules. A single set of interaction parameters was used to predict the complex phase behavior in the binary mixture carbon dioxide + n-pentadecane.

First-Principles Prediction of Vapor−Liquid−Liquid Equilibrium from the PR+COSMOSAC Equation of State

We present the prediction of vapor−liquid−liquid equilibrium (VLLE) from a newly developed PR+COSMOSAC equation of state (EOS). Unlike semiempirical thermodynamic models whose parameters vary with the data used in regression and reparameterization are usually necessary for describing VLLE, this theoretically sound model with its parameters determined from first-principles calculations is not biased against descriptions of either VLE or LLE and can thus be used to predict the occurrence conditions of VLLE. In this model, the molecular interaction and size parameters in the Peng−Robinson EOS are determined directly from a solvation model based on first principle solvation calculations. This new EOS contains neither species dependent parameter nor binary interaction parameters and can be used to predict vapor pressure, liquid density, critical properties of pure substances, and VLE and LLE of mixtures. Without adjustment to the model parameters, this method can predict VLLE with accuracy similar to that of the method modified UNIFAC model. This model is particular useful for the design of new processes involving chemicals whose interaction parameters are not available due to the lack of experimental data.

High-pressure phase equilibria in the (carbon dioxide + 1-hexanol) system

(Vapour + liquid) equilibria (VLE) and (vapour + liquid + liquid) equilibria (VLLE) data for the (carbon dioxide + 1-hexanol) system were measured at (293.15, 303.15, 313.15, 333.15, and 353.15) K. Phase behaviour measurements were made in a high-pressure visual cell with variable volume, based on the static-analytic method. The pressure range under investigation was between (0.6 and 14.49) MPa. The Soave–Redlich–Kwong (SRK) equation of state (EOS) with classical van der Waals mixing rules (two-parameters conventional mixing rule, 2PCMR), was used in a semi-predictive approach, in order to represent the complex phase behaviour (critical curve, LLV line, isothermal VLE, LLE, and VLLE) of the system. The topology of phase behaviour is reasonably well predicted.

A review of the isobaric (vapor+liquid+liquid) equilibria of multicomponent systems and the experimental methods used in their investigation

Abstract An overview of the multicomponent systems for which isobaric (vapor + liquid + liquid) equilibrium (VLLE) data has been published, is presented. This overview comprises 36 ternary and three quaternary systems. For each one of these systems is specified a reference, pressure range, experimental method and the amount of equilibrium data determined. This is followed by a brief description for each experimental method of the specific procedure carried out to determine the (vapor + liquid) equilibrium in the case where the liquid is heterogeneous. Lastly, a final assessment is presented of the experimental procedures used to determine the (vapor + liquid + liquid) equilibria (VLLE).

Separation of CO 2 and H 2S using room-temperature ionic liquid [bmim][PF 6

We have developed a ternary equation of state (EOS) model for the CO 2/H 2S/1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6]) system in order to understand the separation of these gases using room-temperature ionic liquids (RTILs). The present model is based on a generic RK (Redlich-Kwong) EOS, with empirical interaction parameters for each binary system. These interaction parameters have been determined using our previously measured VLE (vapor–liquid equilibrium) data for CO 2/[bmim][PF 6] and literature data for H 2S/[bmim][PF 6] and CO 2/H 2S. VLLE (vapor–liquid–liquid equilibrium) measurements have been made and validate EOS model predictions which suggest that the CO 2/[bmim][PF 6] and H 2S/[bmim][PF 6] systems are Type V phase behavior, according to the classification of van Konynenburg and Scott. The validity of the ternary EOS model calculations has also been checked by conducting VLE experiments for the CO 2/H 2S/[bmim][PF 6] system. With this EOS model, isothermal ternary phase diagrams and solubility (VLE) behavior have been calculated for various ( T, P, and feed compositions) conditions. The CO 2/H 2S gas selectivity is nearly independent of the amount of ionic liquid addition and ranged from about 3.2 to 4.0. For large CO 2/H 2S mole ratios (9/1) at 298.15 K, the addition of the ionic liquid increases the CO 2/H 2S gas selectivity from about 1.2 to 3.7. For high temperature (333.15 K) and high CO 2/H 2S feed ratios, the addition of the ionic liquid provides the only means of separation because no VLE exists for the CO 2/H 2S binary system without the ionic liquid.

Determination of vapour–liquid and vapour–liquid–liquid equilibrium of the chloroform–water and trichloroethylene–water binary mixtures

The vapour–liquid equilibrium (VLE) and vapour–liquid–liquid equilibrium (VLLE) data are the basis for the design of distillation columns for the recovery or removal of residual extractant such as chloroform from wastewater. In this study, a new dynamic condensate-circulation still was designed and used for determination of VLE and VLLE of chloroform–water and trichloroethylene–water binary systems at 101.3 kPa. The phase diagrams of equilibrated vapour-phase composition versus overall liquid-phase composition y 1– x 1 (where subscript 1 references organic component in the binary system) and equilibrated temperature versus vapour-phase or overall liquid-phase composition T– x 1( y 1) were plotted by using the VLE and VLLE data and the data on mutual solubility. The experimental results showed that the two binary systems used have highly non-ideality and form heteroazeotropes, and their heteroazeotrope points are ( t = 55.8 °C, x 1 = y 1 = 0.856) for chloroform–water and ( t = 73.9 °C, x 1 = y 1 = 0.716) for trichloroethylene–water system. The activity coefficients of the component acted as solvent are in general, while the activity coefficients of the component acted as solute are very high in the equilibrated liquid phase. Correlation of the VLE and VLLE data respectively for the two binary systems with the NRTL (non-random two liquids) activity coefficient model gave satisfactory results.

Modeling of the Multiphase Behavior of Nitrogen-Containing Systems at Low Temperatures with Equations of State

In this work, we present the modeling of the vapor−liquid−liquid equilibria (VLLE) for three ternary systems that are of interest in the natural gas and oil industry: nitrogen + methane + n-pentane, nitrogen + methane + n-hexane, and nitrogen + methane + n-heptane. The capabilities of the PC-SAFT and SRK equations of state to predict the complex phase behavior exhibited at low temperatures by the systems studied were compared and analyzed. The computer algorithm performing the isothermal multiphase flash calculations in the first case is based on the minimization of the Gibbs energy, while the second is based on the minimization of a modified tangent−plane distance function. The results obtained demonstrate that both equations of state predict with reasonable accuracy the experimentally observed phase behavior of the ternary systems considered.

Three-Phase Vapor−Liquid−Liquid Equilibria for Methane + n-Octane + Monoethylene Glycol + Water at Pressures from (3.1 to 15.0) MPa and Temperatures from (281 to 363) K

Experimental vapor−liquid−liquid equilibrium (VLLE) compositions have been measured, in an equilibrium cell, for the four-component system methane + n-octane + monoethylene glycol (MEG) + water at pressures from (3.1 to 15.0) MPa and temperatures from (281 to 363) K. A total of 27 sets of equilibrium data have been obtained using three different types of feed mixture. The relative volumes of the three phases have also been obtained for each equilibrium data set. The measurements illustrate the pressure and temperature dependence of the dehydrating effect of MEG in the vapor phase and also show that the solubility of the hydrocarbons in the aqueous phase is considerably enhanced by the presence of MEG. Some implications for the design of gas dehydration plants have been briefly discussed.

Vapor−Liquid−Liquid Equilibria for Aqueous Systems with Methyl Acetate, Methyl Propionate, and Methanol

Vapor−liquid−liquid equilibrium (VLLE) properties were measured with a static apparatus for mixtures of water + methyl acetate, water + methyl propionate, water + methyl acetate + methanol, and water + methyl propionate + methanol at temperatures ranging from 313.24 to 348.15 K. Both ternary systems exhibit type I liquid−liquid equilibrium (LLE) behavior. By checking with the Othmer−Tobias equation, the experimental tie-line data of these two ternary systems appeared to be consistent. The binary VLLE data were correlated satisfactorily with the UNIQUAC model for water + methyl acetate and water + methyl propionate. While the UNIQUAC model with the parameters determined from the phase equilibrium data of the constituent binaries overestimated the two-liquid-phase regions of the ternary systems, the representation of the binodal loci was substantially improved as the six parameters of the UNIQUAC model were determined simultaneously from the ternary VLLE data.

Multiphase equilibria for mixtures containing water, acetic acid, propionic acid, methyl acetate and methyl propionate

Isobaric vapor–liquid equilibrium (VLE) data were measured for the binary mixtures of acetic acid + methyl propionate, propionic acid + methyl acetate, propionic acid + methyl propionate, and methyl propionate + methyl acetate in a temperature range of 330.05–413.15 K at 101.3 kPa. Isothermal vapor–liquid–liquid equilibrium (VLLE) data were also measured for water + methyl acetate + methyl propionate over a pressure range of 43.7–157.0 kPa at 323.24 and 343.15 K. The NRTL-HOC and the UNIQUAC-HOC models with the model parameters determined from the phase equilibrium data of the constituent binaries were applied to predict the VLLE properties for water + methyl acetate + methyl propionate. The validity of the prediction from the UNIFAC-HOC and the UNIFAC-Lyngby-HOC was also tested with the ternary VLLE data. Additionally, the best-fitted values of the six binary parameters of the UNIQUAC-HOC were determined, simultaneously, from the isothermal VLLE ternary data as well.

High-pressure vapor–liquid and vapor–liquid–liquid equilibria in the carbon dioxide + 1-heptanol system

Vapor–liquid equilibria (VLE) and vapor–liquid–liquid equilibria (VLLE) data for the carbon dioxide + 1-heptanol system were measured at 293.15, 303.15, 313.15, 333.15 and 353.15 K. Phase behavior measurements were made in a high-pressure visual cell with variable volume, based on the static-analytic method. The pressure range under investigation was between 0.58 and 14.02 MPa. The Soave–Redlich–Kwong (SRK)-EOS coupled with Huron–Vidal (HV) mixing rules and a reduced UNIQUAC model, was used in a semi-predictive approach, in order to represent the complex phase behavior (critical curve, LLV line, isothermal VLE, LLE, and VLLE) of the system. The topology of phase behavior is qualitatively correct predicted.

Phase Behaviors of Water + Acetic Acid + Methyl Acetate + p-Xylene Mixture at 101.32 kPa

In this study, the experimental results exhibit that the mixture of water + acetic acid + methyl acetate + p- xylene has interesting phase behaviors of vapor-liquid equilibrium (VLE) and vapor-liquid-liquid equilibrium (VLLE) under pressure of 101.32 kPa. The VLE and VLLE data were obtained with a condensed-vapor-phase-recirculating still as described in the text. The experimental data are useful to the design and operation of the purification process of acetic acid. The experimental VLE and VLLE data were then correlated with the NRTL and the UNIQUAC activity coefficient mod- els, respectively, as described in the text. Attributed to the presence of acetic acid, which is a strong polar component, the association effect of molecules of this component in the vapor phase was considered and handled with the approach of Hayden and O'Connell for correlation. production, will form a p-xylene-water azeotrope with water content larger than the azetropes of water-ethyl acetate, wa- ter-propyl acetate, water-isobutyl acetate, and water-butyl acetate. The advantage of the large water content and that of p-xylene is a by-product of reaction causes it to be consid- ered as one of the feasible entrainer. To study the feasibility of using p-xylene as an entrainer, the thermodynamic data of the quaternary mixture of water + acetic acid + methyl ace- tate + p-xylene are necessary. Unfortunately, the phase equilibria of this mixture have not been reported in the litera- ture. In this study, the phase behaviors of vapor-liquid equi- librium (VLE) and vapor-liquid-liquid equilibrium (VLLE) were observed and the experimental data of phase equilib- rium of this quaternary mixture useful for process design were provided. Then the experimental VLE and VLLE data were correlated with the non-random two liquid (NRTL) and the universal quasi-chemical (UNIQUAC) activity coeffi- cient models, respectively, as discussed in the latter part of this report.

Homogeneity of the water + ethanol + toluene azeotrope at 101.3 kPa

An all-glass, dynamic recirculating still equipped with an ultrasonic homogenizer has been used in the determination of the vapour–liquid equilibrium (VLE) and vapour–liquid–liquid equilibrium (VLLE). Consistent data for the ternary water + ethanol + toluene system are reported at 101.3 kPa at temperatures in the range of 347–357 K. These data have been compared with previously published VLLE data. The experimental data indicate that a ternary azeotrope is present at 347.60 K. It has been determined experimentally that the ternary azeotrope is homogeneous and not heterogeneous as is claimed in some of the studied references. The experimental results have been used to check the accuracy of the UNIFAC, UNIQUAC and NRTL models, proving that these models predict a bigger heterogeneous region than the experimental one.

A correlation method for isobaric vapor–liquid and vapor–liquid–liquid equilibria data of binary systems

A correlation method for isobaric vapor–liquid equilibria (VLE) and vapor–liquid–liquid equilibria (VLLE) of binary systems was proposed. Taking the coordination number in UNIQUAC model as a fitting parameter (three-parameter UNIQUAC model) and employing an objective function of relative difference between the experimental and the predicted temperatures of VLE data, the experimental VLLE data were fairly reproduced both for water + 1-butanol and 2-butanol + water systems. Especially for 2-butanol + water system, the calculated homogeneous azeotropic point was also in good agreement, which could not be obtained by the conventional procedure. The proposed method was also validated by several examples.

Binary Vapor–Liquid and Vapor–Liquid–Liquid Equilibria of Hydrofluorocarbons (HFC-125 and HFC-143a) and Hydrofluoroethers (HFE-125 and HFE-143a) with Ionic Liquid [emim][Tf2N

Solubility behaviors of binary HFC-125 (CF3−CF2H), HFE-125 (CF3−O−CF2H), HFC-143a (CF3−CH3), and HFE-143a (CF3−O−CH3) systems with room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) have been studied using a gravimetric microbalance method from (283 to 348) K and/or volumetric and cloud-point methods. Vapor–liquid equilibrium (VLE) data for HFC-125 + [emim][Tf2N] and HFE-125 + [emim][Tf2N] systems have been well correlated with our equation-of-state (EOS) model, which predicted vapor–liquid–liquid equilibria (VLLE) for both of these binary systems, and the VLLE have been experimentally proved. As for the binary systems of HFC-143a + [emim][Tf2N] and HFE-143a + [emim][Tf2N], only VLLE experiments have been made, and partial miscibility (temperature and composition: VLLE−Tx) data are well correlated with the NRTL (nonrandom two-liquids) activity model. While the immiscibility gap of the HFC-125 binary system is smaller than that of the HFE-125 system, ...

New Solubility Data of Hydrocarbons in Water and Modeling Concerning Vapor−Liquid−Liquid Binary Systems

Solubility data in water of ethane, propane, isobutane, n-butane, n-pentane, and n-hexane have been obtained as a function of temperature in vapor−liquid−liquid equilibrium (VLLE) conditions. The minimum temperature of experiments is 288 K, while the maximum temperature, for each system, is lower than the critical temperature of the corresponding hydrocarbon. New solubility vs temperature correlations are given herein for the studied hydrocarbons in water. Henry's law and activity coefficients at infinite dilution are deduced from the experimental solubility data. Good agreement is found with available literature data.

Partitioning of the two pairs of structurally similar biomolecules N-acetyl- d-glucosamine and N-acetyl- d-mannosamine as well d-phenylalanine and l-phenylalanine to high-pressure liquid phases of the (ethene + water + 2-propanol) system

This study reports experimental data and modeling results for the partitioning of a single solute (from two pairs of structurally similar biomolecules ( N-acetyl- d-glucosamine and N-acetyl- d-mannosamine) and ( d- as well as l-phenylalanine)) to coexisting liquid phases of the high-pressure three-phase (vapor–liquid–liquid) equilibrium (VLLE) of the ternary system (ethene + water + 2-propanol) at 293 and 333 K and at pressures up to 17 MPa. The experiments were performed with an analytical view cell at low solute concentrations (below 1.5 and 3.0 g dm −3 for the aminosugars and the phenylalanines, respectively). At such solute concentrations, the VLL-phase equilibrium of the system (ethene + water + 2-propanol) is only slightly disturbed by the low-volatile fourth compound, and the results for the partition coefficient of the solute are at nearly infinite dilution. The new experimental results are correlated using the modification of Melhem et al. for the (cubic) Peng–Robinson equation of state with two different mixing rules and estimated pure-component properties of the solutes.

Vapor−Liquid−Liquid Equilibria of Hydrofluorocarbons + 1-Butyl-3-methylimidazolium Hexafluorophosphate

In recent reports, we measured the vapor−liquid−liquid equilibria (VLLE) of trifluoromethane (R-23) and pentafluoroethane (R-125) with a room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6], using a volume−mass measurement method along various isotherms. In the present work, we complete similar investigation of VLLE for the methane and ethane series of hydrofluorocarbons (HFCs) in [bmim][PF6]. Compounds studied here are fluoromethane (R-41), 1,1,1,2-tetrafluoroethane (R-134a), 1,1,1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a), and fluoroethane (R-161) in [bmim][PF6]. Observed VLLE behaviors are consistent with the earlier predictions by our equation-of-state (EOS) model, which showed partial immiscibilities in the HFC-rich side solutions, indicating type-III or type-V mixtures according to the Konynenburg−Scott classification. Thus, the present study as well as those with R-23 and R-125 reasonably validate our EOS model. In addition, very large negative excess molar volumes have been observed for all the studied systems, similar to that observed for mixtures with R-23 and R-125.

Vapor−Liquid−Liquid Equilibria of Pentafluoroethane and Ionic Liquid [bmim][PF6] Mixtures Studied with the Volumetric Method

In this article, we investigate vapor-liquid-liquid equilibria (VLLE) of binary systems using a simple volumetric method. Being different from the usual cloud-point method for the determination of liquid-liquid separation boundaries, the present volumetric method is able to determine the direct VLLE properties, such as equilibrium compositions, as well as molar volumes of the two liquid phases, by measuring only weights and volumes of liquid samples. The theory behind this method is described, and detailed error analyses for our simple apparatus are discussed by using well-established systems in the literature: water + 2-butanol and 1-butanol + 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]). Then, results for mixtures of [bmim][PF(6)] and pentafluoroethane (R-125) are provided, as well as those of the test systems above. As predicted in our earlier work, this binary system shows liquid-liquid separations in the R-125-rich side solutions with a lower critical solution temperature. In addition, we have found very large negative excess molar volumes in this system.