Phase Equilibrium Measurements Research Articles

Experimental Solubility Data for Binary Mixtures of Ethane and 2,2,4-Trimethylpentane at Pressures up to 6 MPa Using a New Variable-Volume Sapphire Cell

A variable volume apparatus of low cell volume (approximately 10 cm3) was designed and commissioned for measuring phase equilibrium and thermodynamic property data. The experimental procedure and equipment capability for phase equilibrium measurements were validated by measuring isothermal phase equilibrium (T–P–x) data for binary mixtures involving carbon dioxide + n-hexane and ethane + n-octane. There is good agreement between data measurement using the new equilibrium cell and previous measurements reported in the literature. New T–P–x data were also measured for the binary mixture of ethane + 2,2,4-trimethylpentane. The data were correlated using the Peng–Robinson equation of state and the van der Waals mixing rule. The expanded uncertainties in the measurements were evaluated as 0.07 K, 0.02 MPa, and 0.008 for the temperature, pressure, and liquid mole fraction, respectively.

Water Activity and Phase Equilibria Measurements and Model Simulation for the KCl–SrCl2–H2O System at 323.15 K

Water activities for the ternary system of KCl–SrCl2–H2O and its sub-binary system SrCl2–H2O were elaborately measured using an isopiestic method at 323.15 K. The solubility isotherms for the KCl–SrCl2–H2O system were determined by the isothermal equilibrium method. It is found that the measured isopiestic composition lines for the KCl–SrCl2–H2O system deviated from the Zdanovskii rule, especially at a lower water activity. The Pitzer–Simonson–Clegg model was used to correlate the measured water activity and solubility data, simulate the thermodynamic properties, and predict the solubility of the ternary system. The reliability of the solubility data measured in this work was evaluated by comparing with the solubility isotherms calculated with the Pitzer–Simonson–Clegg model. The measured water activity and solubility results are of great importance for predicting the phase diagram of other multicomponent systems that related to this ternary system.

Liquid-liquid separation of hexane/hex-1-ene and cyclohexane/cyclohexene by dicyanamide-based ionic liquids

The work presented focused on the experimental liquid-liquid phase equilibrium measurements in ternary systems {ionic liquid (1)+hex-1-ene (2)+hexane (3)} and (ionic liquid (1)+cyclohexene (2)+cyclohexane (3)} at temperature T=298.15K and ambient pressure. The dicyanamide-based ionic liquids (ILs) were discussed as solvents for two types of separation problems of hexane/hex-1-ene and cyclohexane/cyclohexene. The objective of this work was to explore the feasibility of six ILs, namely N-ethyl-N-methylmorpholinium dicyanamide, [EMMor][DCA], (3-hydroxypropyl)-1-methylmorpholinium dicyanamide, [N-C3OHMMor][DCA], 1-(3-hydroxypropyl)-3-methylimidazolium dicyanamide, [N-C3OHMIM][DCA], 1-(3-hydroxypropyl)pyridinium dicyanamide, [N-C3OHPy][DCA], (3-cyanopropyl)pyridinium dicyanamide, [N-C3CNPy][DCA] and (3-cyanopropyl)methylpyrrolidinium dicyanamide,[N-C3CNMPyr][DCA]. The separating ability of the investigated ILs was compared with the previously measured by us in ternary LLE ILs for these chosen separation problems. The effect of cation for the same anion was examined with respect to the selectivity and solute distribution ratio in these processes. The separation effectiveness of the [N-C3CNMPyr][DCA] in comparison with other ILs used in this work is the best for hexane/hex-1-ene separations but lower than those presented by us earlier for [EMIM][DCA], however with better solute distribution coefficient. The experimental tie-lines were correlated with the non-random two liquid NRTL model. The proposed [N-C3CNMPyr][DCA] may be used as an alternative solvent for the separation of alkenes from alkanes and [EMMor][DCA] for cyclohexane/cyclohexene separation.

Measurement and correlation of ternary phase equilibrium of (hexane + ethyl acetate) with four ILs

The ternary liquid-liquid phase equilibria (LLE) for four systems including {hexane+ethyl acetate+1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF4])}, 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim][BF4]), 1-hexyl-3-methylimidazolium trifluoromethanesulfonate ([Hmim][OTf]), and 1-octyl-3-methylimidazolium trifluoromethanesulfonate ([Omim][OTf])} were determined at 298.15K and atmospheric pressure. All the investigated systems exhibited Treybal type I behaviour. The solute distribution ratio (β) and the selectivity (S) were calculated for each system to estimate the efficiency of the separation of a hexane+ethyl acetate mixture using ionic liquids as the solvent. The influence of the anion and substituent group of the cation imidazolium rings of the ionic liquid on the LLE was revealed. Two models, NRTL and UNIQUAC, were used to correlate the experimental LLE results for which the binary interaction parameters were obtained. The UNIFAC model was used to predict the LLE data of the ternary systems, and the results were compared with experimental data.

Phase equilibrium measurements and thermodynamic modeling of binary mixtures containing a diesel compound n-dodecane + biodiesel compounds: Ethyl dodecanoate and ethyl octanoate

The vapor pressures of two binary systems ethyl dodecanoate (1)+n-dodecane (2) and ethyl octanoate (1)+n-dodecane (2), were measured by means of a static apparatus at temperatures between 373.15K and 453.15K. The data were correlated with the Antoine equation. From these data, the molar excess Gibbs energies GE were obtained with Barker’s method and fitted to the Redlich-Kister equation. The binary mixture (ethyl octanoate (1)+n-dodecane (2)) exhibits maximum azeotropic behavior. Positive values of the excess Gibbs energy are obtained for all the investigated constant temperatures and over the whole composition range. The data were also correlated by using Wilson equation and good results were obtained in the prediction of the total pressure and thermodynamic excess properties; however deviations were observed with respect to the experimental and predicted GE, using modified UNIFAC (Dortmund) group contribution model. Additionally, the NRTL model was applied to regress the experimental GE. The investigated systems were successfully represented by the NRTL model.

Designing eutectic mixtures for the extraction of 2-phenylethanol (PEA) from aqueous phase

The field of industrial biotechnology is rapidly growing. This includes the use of biosynthesis of the fragrance-row materials in chemical industry, food industry, cosmetical and pharmaceutical industry. The production of 2-phenylethanol (PEA), which is an important flavor and fragrance compound, with a rose-like odor has been significantly increased last decade. The ionic liquids (ILs) and binary eutectic mixtures (EM) are proposed as an entrainers for the extraction of PEA in a biphasic biosynthesis. ILs and DES reveal many unique properties which make them very interesting for applications in modern ‘green’ technologies. In this work we present new experimental results on (solid, or liquid + liquid) phase equilibrium (SLE/LLE) measurements of twelve binary systems composed of pyrrolidinium-based ILs (namely: 1-butyl-1-methylpyrrolidinium chloride, [BMPYR][Cl] and 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide [BMPYR][NTf2] as well as 1-hexyl-1-methylpyrrolidinium chloride, [HMPYR][Cl] and 1-hexyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide [HMPYR][NTf2] with alcohols (1-decanol, 2-methyl-1-butanol, 2-methyl-2-butanol) and oleic acid. Additionally, three ternary LLE mixtures are presented {IL, or EM + PEA + water} at T = 308.15 K and ambient pressure. The data reveals that [HMPYR][NTf2] ionic liquid is more attractive than [BMPYR][NTf2] and that EMs ([BMPYR][NTf2] + 2-methyl-2-butanol) and ([HMPYR][NTf2] + 2-methyl-2-butanol) present worst selectivities and solute distribution ratios than those observed for pure ILs. However, they may be assumed as an alternative, less cost solvents for the separation of PEA from the water phase using liquid-liquid extraction at ambient conditions.

Phase equilibrium measurements and thermodynamic modelling for the systems involving valeric acid, ethanol, ethyl valerate and water plus CO2

This work reports phase equilibrium measurements for binary, ternary, quaternary and five components mixtures of CO2, ethanol, valeric acid, water and ethyl valerate at high pressures. Experiments were carried out using a high-pressure variable-volume view cell with operating temperatures ranging from 303.15K to 353.15K and pressures up to 15MPa. The CO2 mole fraction ranged from 0.4780 to 0.9412 for the binary system {CO2(1)+valeric acid(2)}, from 0.3801 to 0.9811 for {CO2(1)+ethyl valerate(2)}, from 0.5649 to 0.9193 for the ternary system {CO2(1)+ethanol(2)+valeric acid(3)} at an ethanol to valeric acid mole ratio of (3:1) and from 0.5907 to 0.9373 for {CO2(1)+ethanol(2)+ethyl valerate(3)} at an ethanol to ethyl valerate mole ratio of (1:1). For the quaternary {CO2(1)+ethanol(2)+water(3)+ethyl valerate(4)} and the five components system {CO2(1)+ethanol(2)+valeric acid(3)+water(4)+ethyl valerate(5)} fixed compositions were investigated at CO2 mole fraction of 0.7336 and 0.7211, respectively, while the mole ratio of other compounds were fixed at typical esterification conditions. For the systems investigated, vapour-liquid (VL), liquid-liquid (LL) and vapour-liquid-liquid (VLL) phase transitions were observed. The experimental data sets were successfully modeled using the Peng-Robinson cubic equation of state with the Boston-Mathias alpha function and using the van der Walls quadratic mixing rule. The PR-BM showed good performance in the prediction of the phase transitions for the ternary, quaternary and five components systems based on the binary interaction parameters obtained from the binary CO2+valeric acid, CO2+ethyl valerate and CO2+ethanol experimental data.

Measurement and correlation for phase equilibrium of HFO1234yf with three pentaerythritol esters from 293.15 K to 348.15 K

2,3,3,3-Tetrafluoroprop-1-ene (HFO1234yf) is recently recognized as a new generation refrigerant to replace R134a in automotive air-conditioning system and other refrigeration applications. The knowledge of phase equilibrium property for refrigerant with lubricant oil is therefore interested in these systems. A systematic research program on the phase equilibrium of HFO1234yf with lubricant oils has been carried out in our laboratory, and the purpose is to investigate the influence of the molecular structure of oils, pressure and temperature on the phase behavior of HFO1234yf and lubricant oil system. In this work, the measurements of phase equilibrium for HFO1234yf+pentaerythritol tetrahexanoate (PEC6), HFO1234yf+pentaerythritol tetraheptanoate (PEC7), and HFO1234yf+pentaerythritol tetraoctanoate (PEC8) between 293.15K and 348.15K were performed by means of isochoric saturation method. The experimental data were correlated using the PR EOS and HVOS mixing rule combined with Wilson excess free-energy model. The average relative deviations between experimental results and the calculated pressure by the model for HFO1234yf+PEC6, HFO1234yf+PEC7, and HFO1234yf+PEC8 system were 1.23%, 1.19%, and 1.39%, respectively. The maximum relative deviations were 4.04%, 4.34%, and 4.84%, respectively.

Measurement and correlation of phase equilibrium of the aqueous two-phase system formed by Fe2(SO4)3 + PEG 4000 + H2O at different temperatures

Liquid-liquid equilibrium (LLE) data for the Fe2(SO4)3+polyethylene glycol 4000 (PEG 4000)+H2O system were determined experimentally at T=(323.15, 333.15 and 343.15) K. The effect of temperature on the binodal curves and tie-lines were studied and it was found that an increasing in temperature caused the expansion of two-phase region.Additionally, experimental density, sound velocity, refractive index and viscosity data were also reported at T=(323.15, 333.15 and 343.15) K.The Chen-NRTL, modified Wilson and extended UNIQUAC models and the Othmer-Tobias and Bancroft equations were used to correlate the experimental tie-line data obtaining a good representation of the equilibrium. Furthermore, the Merchuk equation was used to correlate the binodal curves.

Separation of the mixture pyridine + methylbenzene via several acidic ionic liquids: Phase equilibrium measurement and correlation

For the purpose of selecting the effective solvents to separate basic N-compound pyridine from coal tar, three acidic imidazolium-based ILs, 1-butyl-3-methylimidazolium hydrogen sulfate, [Bmim][HSO4], 1-butyl-3-methylimidazolium dihydrogen phosphate, [Bmim][H2PO4], and 1-butyl-3-methylimidazolium perchlorate, [Bmim][ClO4], were chosen for the extraction process. The liquid-liquid equilibrium tie-line data for the ternary systems of [Bmim][HSO4], [Bmim][H2PO4] and [Bmim][ClO4] + pyridine + methylbenzene were measured at T = 298.15 K under 101.3 kPa. Meanwhile, the interaction energies between the ILs, and pyridine and methylbenzene respectively were calculated. The results indicated that the selected ILs had strong interactions with pyridine than with methylbenzene, which were also verified by the distribution ratio and selectivity calculated from the experimental data. In addition, the experimental LLE data were correlated by the NRTL and UNIQUAC models, and the NRTL model showed good agreement in correlation than the UNIQUAC. The average RMSDs for the NRTL and UNIQUAC models of the investigated systems are 0.0153 and 0.0161, respectively.

Gas-containing semiclathrate hydrate formation by tetra-n-butylammonium carboxylates: Acrylate and butyrate

Semiclathrate hydrates are water-based host-guest materials that consist of water and ionic guest substances such as quaternary ammonium salts. Widely-used tetra-n-butylammonium (TBA) salts are designed for gas selectivity and capacity with respect to the industrial application of these materials. This study reported on the formation of semiclathrate hydrates of TBA carboxylates with guest gas characterized by phase equilibrium measurements and single crystal X-ray diffraction. Specifically, TBA acrylate and TBA butyrate are used for ionic guest substances, and this may induce a tetragonal P42/mmm semiclathrate hydrate structure. In the four systems of (TBA acrylate or TBA butyrate) + (CH4 or CO2) + H2O, the measured three (gas–hydrate–aqueous) phase equilibrium data exhibited better promotion effects due to the TBA acrylate and TBA butyrate when compared with that of the widely-used TBA bromide. The slopes on pressure–temperature plane suggest differences in the incorporation of CH4 and CO2 in these hydrates. Characterization of the hydrate phases by X-ray diffraction analyses supports this mechanism. However, it is necessary to further understand the complicated gas incorporation in semiclathrate hydrate structures that are handled by ionic guest substances and the guest gas itself.

Phase Equilibrium Measurement and Thermodynamic Modeling of the 4-Methylpentan-2-one/3-Methylphenol, and 4-Methylphenol/Water Ternary Systems at 298.2, 313.2, and 323.2 K and 0.1 MPa

The tie-line data for the {4-methylpentan-2-one + 3-methylphenol, 4-methylphenol + water} ternary systems at 298.2, 313.2, and 323.2 K were measured under 101.3 kPa. The partition coefficient and separation factor were computed in order to estimate the extraction capacity of 4-methylpentan-2-one, which indicated that 4-methylpentan-2-one has an excellent performance in terms of extracting methylphenols from water. The activity coefficient models, nonrandom two-liquid (NRTL) and universal quasichemical (UNIQUAC), were used to correlate experimental results, yielding root-mean-square deviations (RMSDs) below 0.5%. This indicated that both models represent the experimental data very well.

Apparatus for Low-Temperature Investigations: Phase Equilibrium Measurements for Systems Containing Ammonia

In this paper, a low-temperature apparatus was designed to measure vapor–liquid and vapor–liquid–liquid equilibria for binary systems containing ammonia. The standard combined uncertainties of the temperature, pressure, and the mole fraction are less than ±5 mK, ±0.0008 MPa, and ±0.005, respectively. The saturated vapor pressures of the ammonia, n-butane, and 1-butene were measured, and there were quantitative similarities between the experimental data and the data from Refprop 9.1, with differences less than 0.0007 MPa. The reliability of the experimental setup was verified. The experimental data of the (ammonia + n-butane) system and the (ammonia + 1-butene) system were presented. The homogeneous azeotropic behavior was shown at T = (293.150 and 283.150) K and a heterogeneous azeotropic was found at 273.150 K for the (ammonia + 1-butene) system. Besides, a heterogeneous azeotropic was found at T = (273.150 and 263.150) K for the (ammonia + n-butane) system. All the experimental data were correlated with...

Thermal and Crystallographic Properties of Tetra-n-butylammonium Bromide + Tetra-n-butylammonium Chloride Mixed Semiclathrate Hydrates

The thermal and crystallographic properties of tetra-n-butylammonium bromide + tetra-n-butylammonium chloride (TBAB + TBAC) mixed semiclathrate hydrates prepared from mixed aqueous solutions were investigated using phase equilibrium measurements, differential scanning calorimetry (DSC), and powder X-ray diffraction. The equilibrium temperatures gradually vary with both xguest {i.e., the mole fraction of guests to (guests + water)} and xTBAB {i.e., TBAB to (TBAB + TBAC)}. The maximum equilibrium temperatures for each concentration changed from (xTBAB = 0.4 to 0) and were observed at xTBAB = 0 below xguest = 0.012. The dissociation enthalpies of tetragonal mixed hydrates are between those of the pure hydrates. In the tetragonal pure and mixed hydrates, these results indicate that the thermal stabilities are dependent upon the increase of hydration number by the relaxation of crystal distortion with decreasing xguest and xTBAB. In orthorhombic systems, a single endothermic DSC peak is split to a higher tempe...

Phase equilibrium investigation with ionic liquids and selectivity in separation of 2-phenylethanol from water

This work presents some important issues and topics related to possible extraction of 2-phenylethanol (PEA) from aqueous phase “in situ” during the biosynthesis with ionic liquids (ILs). It consists of a series of experimental phase equilibrium measurements in binary and ternary systems. Three ILs as extraction media are proposed for the extraction process based on phase equilibria in ternary systems {IL (1)+PEA (2)+water (3)} at temperature T=308.15K and ambient pressure. The systems are composed of the following ILs: 1-hexyl-1-methylmorpholinium bis{(trifluoromethyl)sulfonyl}imide, [HMMOR][NTf2], 1-allyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [AMIM][NTf2], and diethylmethylsulfonium bis{(trifluoromethyl)sulfonyl}imide, [S221][NTf2]. A differential scanning calorimetry (DSC) was used to determine the thermal properties of the ILs. The synthesis of new [HMMOR][NTf2] IL and its thermal and physicochemical properties as density, viscosity, surface tension were presented. The volume expansivity, as well as the surface thermodynamic functions, such as surface entropy and enthalpy have been derived from the temperature dependence of the surface tension values, as well as the critical temperature, parachor and speed of sound for all ILs were presented. The correlation of the liquidus curves in binary systems and tie-lines in ternary systems was undertaken with the NRTL equation. These results of solubility can be used to design future alternative technological processes of the extraction of PEA from fermentation broth.

Review of vapor-liquid equilibria of gas hydrate formers and phase equilibria of hydrates

There is significant interest in clathrate hydrates of natural gases for flow assurance in the oil and gas industries, and for their development as an energy resource. Numerous applications of gas hydrates, e.g., seawater desalination, gas separation, hydrogen storage, and natural gas transportation, require detailed investigations of their thermodynamic properties. Therefore, phase equilibrium measurements and predictions constitute a major portion of the scientific literature in the field of gas hydrates. There exists a wealth of experimental data over a wide range of temperature, pressure, and composition, in the absence and presence of thermodynamic inhibitors at low to moderate concentrations. These hydrate and vapor-liquid phase equilibria measurements and data are reviewed in this paper. These data are not only important in tuning hydrate phase equilibrium predictions, but also in process design of technological systems involving gas hydrates.

Characterisation of a microwave re-entrant cavity resonator for phase-equilibrium measurements and new dew-point data for a (0.25 argon + 0.75 carbon dioxide) mixture

An apparatus based on a microwave re-entrant cavity resonator, originally built for accurate measurements of the dielectric permittivity of natural gas mixtures, was refurbished and extensively characterised. This was done to enable the future investigation of phase equilibria and (p, ρ, T, x) behaviour of fluid mixtures utilizing the present experimental technique. Vacuum resonance frequencies and Q-factors of the resonator’s modes were modelled using both analytic and finite element methods, and found to compare well with experimental values. The finite element models helped to identify two whispering gallery-type modes not previously reported for such cavity geometries. The models also predict distributions of the electric and magnetic fields in the re-entrant cavity resonator useful for identifying regions in the cavity more sensitive to the presence of a liquid. Following the resonator’s characterisation, its ability to measure dew points was tested using a gravimetrically prepared (0.2501 argon+0.7499 carbon dioxide) mixture over the temperature range from (252 to 280)K at pressures from (2.8 to 6.9)MPa. The combined expanded uncertainty with a level of confidence of approximately 95% (k=2) in dew-point temperature and pressure ranged between (0.025 and 0.044)K and from (0.009 to 0.015)MPa, respectively. We compared the experimental dew-point pressures with the recently developed multi-parameter equation of state optimised for combustion gases (EOS-CG), showing relative deviations in the range of (0.044 to 0.479)%. In contrast, relative deviations of up to −4% from the GERG-2008 equation of state and two different implementations of the Peng-Robinson equation were observed, although these models are not optimised for dew point calculations of carbon dioxide rich mixtures.

Measurement and Prediction of Hydrate Phase Equilibrium of Orange Juice + CO2, C2H4 or C2H6 for Orange Juice Concentration

Phase equilibrium data for hydrates formed in CO 2 + orange juice system, C 2 H 4 + orange juice system and C 2 H 6 + orange juice system were measured in pressures range of (0.68 to 4.40 MPa) and temperatures range of (274.8 to 283.3 K). The experimental data were generated using an isochoric pressure-search method. The effects of orange juice on the hydrate equilibrium conditions were studied. The hydrate equilibrium conditions were calculated by using the Redlich-Kwong-Soave equation of state with a modified version of the Huron-Vidal mixing rule. It is found that the orange juice exhibited an inhibition effect on hydrate formation. The results of the predicted three-phase equilibrium conditions for the CO 2 , C 2 H 4 and C 2 H 6 hydrate formation in water and orange juice were in good agreement with the experimentally data.

Effect of Carbon Chain Length of Organic Salts on the Thermodynamic Stability of Methane Hydrate

This study presents the phase equilibrium conditions for methane hydrate with one of the following organic ammonium salts differing in carbon chain length: tetramethylammonium bromide (TMAB), tetraethylammonium bromide (TEAB), tetrapropylammonium bromide (TPrAB), tetrabutylammonium bromide (TBAB), and tetrapentylammonium bromide (TPeAB). The hydrate phase equilibrium measurements were conducted for a temperature range of 278.94–291.85 K and pressure range of 4.79–14.32 MPa using the step-heating pressure search method. The addition of TBAB or TPeAB shifts the phase equilibria of the semiclathrate hydrates (SCHs) of CH4 to a lower pressure and higher temperature zone. At a given temperature, increasing the mole fraction of TBAB and TPeAB from 0.294 mol % to 0.620 mol % made the shift in phase equilibrium conditions greater. At a given dosage, TBAB consistently outperformed TPeAB in thermodynamically promoting methane hydrate formation. TMAB, TEAB, or TPrAB slightly shifts the phase equilibrium conditions t...

Application of a two-sinker densimeter for phase-equilibrium measurements: A new technique for the detection of dew points and measurements on the (methane + propane) system

We explore a novel method for determining the dew-point density and dew-point pressure of fluid mixtures and compare it to traditional methods. The (p, ρ, T, x) behavior of three (methane+propane) mixtures was investigated with a two-sinker magnetic suspension densimeter over the temperature range of (248.15–293.15)K; the measurements extended from low pressures into the two-phase region. The compositions of the gravimetrically prepared mixtures were (0.74977, 0.50688, and 0.26579) mole fraction methane. We analyzed isothermal data by: (1) a “traditional” analysis of the intersection of a virial fit of the (p vs. ρ) data in the single-phase region with a linear fit of the data in the two-phase region; and (2) an analysis of the adsorbed mass on the sinker surfaces. We compared these to a traditional isochoric experiment. We conclude that the “adsorbed mass” analysis of an isothermal experiment provides an accurate determination of the dew-point temperature, pressure, and density. However, a two-sinker densimeter is required.