Vapor–liquid–liquid Equilibrium Research Articles

Modeling Vapor–Liquid–Liquid Phase Equilibria in Fischer–Tropsch Syncrude

Vapor–liquid–liquid equilibrium (VLLE) during product recovery and separation after Fischer–Tropsch synthesis affects the efficiency of downstream processing. Proper prediction of the VLLE is necessary to improve this processing step in the Fischer–Tropsch process; however, there is little guidance on what thermodynamic models to use. A similar problem presents itself in processes related to biomass conversion. The selection of an appropriate thermodynamic model to describe the nonideal VLLE of water–oxygenate–hydrocarbon mixtures was investigated. Cubic equations of state, virial equations of state, activity coefficient models, and equations of state with advanced mixing rules were considered. The evaluation was conducted using both default and optimized parameters. Predictive performance was improved when binary interaction parameters were optimized using experimental data, but parameter optimization is onerous and it is not always practical. It was found that cubic equations of state should not be used...

Isothermal Vapor–Liquid Equilibrium (VLE) and Vapor–Liquid–Liquid Equilibrium (VLLE) Data for Two Binary Systems Containing Perfluorohexane with Carbon Monoxide or Hydrogen Sulfide at (293, 313, and 333) K

Isothermal vapor–liquid equilibrium (VLE) and vapor–liquid–liquid equilibrium (VLLE) data are presented for binary systems containing perfluorohexane (C6F14) with carbon monoxide (CO) or hydrogen sulfide (H2S). Measurements were undertaken at three temperatures, viz. (293, 313, and 333) K, with pressures ranging from (0.322 to 24.497) MPa. An apparatus based on the “static-analytic” technique was used for the measurements. The equilibrium cell is equipped with a pneumatic capillary sampler, and equilibrium phase analysis is undertaken using a gas chromatograph. The uncertainties in the experimental measurements are 0.02 K, 0.0012 MPa, and 0.006 for temperature, pressure, and equilibrium phase mole fraction, respectively. The experimental data was modeled using the direct method using three different sets of thermodynamic models. The VLE data measured for the CO + C6F14 system were correlated using the Peng–Robinson equation of state with the Mathias–Copeman alpha function and the Wong–Sandler mixing rule ...

(Vapour + liquid + liquid) equilibrium measurements and correlation for the {1,1,1,2-tetrafluoroethane (R134a) + n-butane (R600)} system

In this paper, a study of the (vapour+liquid+liquid) equilibrium (VLLE) for the (R134a+R600) system was carried out using an apparatus based on the vapour-phase recirculation method at temperatures ranging from (227.127 to 232.817)K. Two numerical methods were used to obtain the second liquid phase compositions coexisting in equilibrium, and good agreement was found between them. The Antoine equation was used to correlate the experimental pressures and temperatures, and no crude random errors were found. Then, all of the experimental results were correlated by the Peng–Robison (PR) equation of state (EoS) using the Huron-Vidal (HV) mixing rule combined with the non-random two-liquid (NRTL) activity coefficient model. The vapour phase compositions were calculated using the regressed parameters, which agree well with the experimental values, and the maximum deviation is less than 0.008. Moreover, the study of the relationship between VLLE and VLE for the (R134a+R600) system and the comparison between (R134a+R600) and (R134+R600a) systems show the internal consistency of the measurements.

Experimental and modeling study of the phase behavior of (methane + CO2 + water) mixtures.

In this work we report phase equilibrium measurements on the system (methane + carbon dioxide + water) carried out with a high-pressure quasi-static-analytical apparatus. The measurements have been made under conditions of two-phase vapor-liquid equilibrium, three-phase vapor-liquid-liquid equilibrium (VLLE), and four-phase vapor-liquid-liquid-hydrate equilibrium. The compositions of three coexisting fluid phases have been obtained along eight isotherms at temperatures from (285.15 to 303.5) K and at pressures up to either the upper critical end point (UCEP) or up to the hydrate formation locus. Compositions of coexisting vapor and liquid phases have been obtained along three isotherms at temperatures from (323.15 to 423.15) K and pressures up to 20 MPa. The quadruple curve, along which hydrates coexist with the three fluid phases, was also measured along its entire length. The VLLE data obtained for this mixture have been compared with the predictions of the statistical associating fluid theory for potentials of variable range (SAFT-VR), implemented with the square-well potential and using parameters fitted to pure-component and binary-mixture data. Specifically, we used the SAFT-VR parameters reported by Mı́guez and co-workers [Mı́guez, J. M.; dos Ramos, M. C.; Piñeiro, M. M.; Blas, F. J. J. Phys. Chem. B 2011, 115, 9604]. The pressure along the quadruple curve was compared with the predictions of two different thermodynamic models. Furthermore, a detailed study of the ternary mixtures was carried out based on comparison with available ternary data of the type (CO2 + n-alkane + water) and available data for the constituent binary subsystems. In this way, we analyzed the observed effects on the solubility when the n-alkane component was changed or a third component was added.

Kinetics and polarity effects in the synthesis of the ionic liquid, 1-hexyl-3-methyl-imidazolium bromide, using compressed CO2

Compressed carbon dioxide, as a solvent medium, offers unique benefits for the synthesis of ionic liquids (ILs) especially for the ability to combine reaction and separation. The second-order reaction rate constants were determined for the synthesis of 1-hexyl-3-methylimidazolium bromide ([HMIm][Br]) at 313.15K and 333.15K and 30–150bar from the reactants, 1-methylimidazole and 1-bromohexane. Two different scenarios were encountered based upon the pressure: a one-phase supercritical mixture of the reactants becoming a vapor-liquid IL/CO2 system at complete conversion; or a two-phase CO2-expanded liquid (CXL) that yielded a three-phase vapor-liquid-liquid equilibrium (VLLE) at intermediate conversions. Despite multiphase phenomena, the vast majority of the reaction occurs in the reactant-rich liquid phase. The kinetic rate constants were comparable with traditional organic solvents. The reaction rates were higher in the CXL mode than in the initially supercritical mixtures. The changes in the kinetic rate constant with pressure (CO2 composition) could be explained and quantified using Kamlet–Taft (KT) polarity parameters that were measured in the mixtures using solvatochromic probes.

Isobaric Vapor-Liquid-Liquid Equilibria for 1-Butanol + Water + 2,3-Butanediol at 101.3 kPa

Vapor-liquid-liquid equilibria (VLLE) data were determined for the ternary system 1-butanol + water + 2,3-butanediol at 101.3 kPa. A binary heterogeneous minimum boiling azeotrope was found at 365.95 K with mass fractions of 0.526 and 0.474 for 1-butanol and water, respectively. A modified UNIQUAC model was used to predict VLLE by using experimental data, including VLE of 1-butanol + 2,3-butanediol, VLE of water + 2,3-butanediol, LLE of 1-butanol + water, and one LLE tie-line of 1-butanol + water + 2,3-butanediol. The experimental data were compared with the calculated values. The absolute average relative deviations (AARD) are 1.65%, 1.72%, and 2.22% for organic liquid phase, aqueous liquid phase, and vapor phase, respectively. It demonstrates an appropriate fit of the modified UNIQUAC model.

Modeling Water Containing Systems with the Simplified PC-SAFT and CPA Equations of State

Numerous studies have been presented for modeling of water containing systems with the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EOS), and more than 20 water parameter sets have been published with emphasis on different applications. In this work, eight of these sets and new estimated parameters with different association schemes are systematically compared on describing properties of pure water, the liquid–liquid equilibria (LLE) of water with hydrocarbons, and the vapor–liquid (VLE) and/or vapor–liquid–liquid equilibria (VLLE) of water with 1-alcohols. An interactive procedure is further proposed for including the LLE of water with hydrocarbons into the pure fluid parameter estimation. The results show that it is possible for PC-SAFT to give an accurate description of the LLE of water and hydrocarbons while retaining satisfactory accuracy for both vapor pressure and saturated liquid density of water. For the aforementioned aqueous systems, the PC-SAFT correlations...

(Vapor+liquid+liquid) equilibrium measurements and correlation for {1,1,2,2-tetrafluoroethane (R134)+isobutane (R600a)} system

Abstract In this paper, a study of the (vapour + liquid + liquid) equilibrium (VLLE) for the (R134a + R600) system was carried out using an apparatus based on the vapour-phase recirculation method at temperatures ranging from (227.127 to 232.817) K. Two numerical methods were used to obtain the second liquid phase compositions coexisting in equilibrium, and good agreement was found between them. The Antoine equation was used to correlate the experimental pressures and temperatures, and no crude random errors were found. Then, all of the experimental results were correlated by the Peng–Robison (PR) equation of state (EoS) using the Huron-Vidal (HV) mixing rule combined with the non-random two-liquid (NRTL) activity coefficient model. The vapour phase compositions were calculated using the regressed parameters, which agree well with the experimental values, and the maximum deviation is less than 0.008. Moreover, the study of the relationship between VLLE and VLE for the (R134a + R600) system and the comparison between (R134a + R600) and (R134 + R600a) systems show the internal consistency of the measurements.

Phase Equilibrium (VLE, LLE, and VLLE) Data of the Ternary System: Ionic Liquid [OMIM][PF6] + Butan-1-ol + Butyl Acetate

Vapor–liquid equilibrium (VLE), liquid–liquid equilibrium (LLE), and vapor–liquid–liquid equilibrium (VLLE) data were measured for the ternary mixture of 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]), butan-1-ol, and butyl acetate. Results showed that the selectivity of butan-1-ol and butyl acetate can be enhanced by ionic liquid [OMIM][PF6]. The experimental VLE and LLE data were correlated using NRTL model, and the calculated values agreed well with the experimental values.

Isobaric Vapor–Liquid–Liquid Equilibria for the Ternary Systems Ethanol + Water + Propyl Acetate and 1-Propanol + Water + Propyl acetate

In order to break azeotropes appearing in mixtures of water and either ethanol or 1-propanol, an azeotropic distillation process is proposed using propyl acetate as entrainer. Therefore, isobaric vapor–liquid–liquid equilibrium (VLLE) data at atmospheric pressure have been obtained for the ternary systems ethanol + water + propyl acetate and 1-propanol + water + propyl acetate. Data correlation has been carried out in four different ways and a comparison between the results obtained in each correlation has been done. The set of parameters obtained from the best correlation has been used in the VLLE estimation. Effects of using propyl acetate as entrainer in the azeotropic distillation have been discussed, and a three-column distillation sequence to separate 1-propanol and water has been proposed.

Calculation of Vapor–Liquid–Liquid Equilibria at Atmospheric and High Pressures

Numerical values of the NRTL equation parameters for calculation of the vapor–liquid–liquid equilibria (VLLE) at atmospheric pressures for 27 ternary mixtures are presented. These values were fitted to the experimental VLLE and vapor–liquid equilibrium (VLE) data to describe simultaneously, as accurately as possible, VLE and liquid–liquid equilibria (LLE). Coefficients obtained in this manner allow calculation of the VLLE and VLE of ternary mixtures and binary subsystems with sufficient accuracy. In the case of VLLE, the model, called NRTL-VLL, usually gives mean deviations between the calculated and measured component concentrations of less than 1.3 mol %. Average deviations of the calculated and measured temperatures (or pressures) for most of the mixtures did not exceed 0.45 K (or 3%). Simultaneously, the model calculates the VLE of the homogeneous part of the considered ternary systems and their binary subsystems with good or fairly good accuracy. VLLE calculations were also carried out for four model...

Assessing Anhydrous Tertiary Alkanolamines for High-Pressure Gas Purifications

Anhydrous tertiary alkanolamines chemically react with CO2 and H2S, with greater selectivity for the latter. This is in direct contrast to aqueous amine-based solvent systems, which exhibit higher selectivity for CO2 over H2S. Anhydrous tertiary alkanolamines exhibit pressure-induced chemical fixation of CO2 to form zwitterionic ammonium alkylcarbonate ionic liquids, while the same tertiary alkanolamines react with H2S at atmospheric pressures to form hydrosulfide ionic liquids. This difference in capture pressure implies that certain anhydrous alkanolamines could be chemically selective for H2S over CO2. We present here the first published vapor–liquid–liquid equilibrium (VLLE) data of anhydrous ethyldiethanolamine (EDEA) with CH4, C3H8, H2S, and CO2 at 10–50 °C measured by the TPx and TPxy methods. The data are modeled in Aspen Plus using an NRTL-with-solvation model. Data trends and the underlying phenomena are discussed for each gas. We also present process simulations that compare anhydrous EDEA’s performance for CO2 and H2S high-pressure separations to other solvents such as Fluor Solvent (propylene carbonate), Selexol, and aqueous methyldiethanolamine (MDEA) for a representative gas-purification absorber. This work indicates that a niche for anhydrous EDEA in high-pressure gas purifications may be its stronger absorption for CO2 and H2S (relative to physical solvents) and its selectivity for H2S over CO2 (relative to chemical solvents).

Liquid–Liquid, Vapor–Liquid, and Vapor–Liquid–Liquid Equilibrium Data for the Water–n-Butanol–Cyclohexane System at Atmospheric Pressure: Experimental Determination and Correlation

The temperature and the composition of the vapor–liquid–liquid equilibrium (VLLE) and the vapor–liquid equilibrium (VLE) of a ternary mixture of water–n-butanol–cyclohexane were measured at atmospheric pressure (101.32 kPa) in a modified dynamic recirculating still. As found in the literature, the experimental data obtained reveal a ternary azeotrope at 341.86 K with a mole fraction composition of 0.281, 0.034, and 0.685 water, n-butanol, and cyclohexane, respectively. The liquid–liquid equilibrium (LLE) compositions were measured at a constant temperature of 313.15 K and compared with data in the literature collected at other temperatures. Thermodynamic consistency of all the experimental data was demonstrated. The universal quasichemical (UNIQUAC) and the nonrandom two-liquid (NRTL) thermodynamic models were used to correlate the VLE and LLE data, while the original universal functional (UNIFAC) model was used to compare the predicted data.

Phase Equilibria of the Carbon Dioxide + 1-Decanol System at High Pressures

In this work experimental vapor-liquid equilibrium (VLE) data and three-phase vapor-liquid-liquid equilibrium (VLLE) data are presented for the carbon dioxide + 1-decanol system. The VLE data were measured at five temperatures, (303.2, 308.2, 323.2, 333.2, and 343.2) K, and pressures up to 16 MPa. The VLLE data cover pressure-temperature (P-T) values from 289 K and 5 MPa to the upper critical end point (UCEP). We have used two models to represent the complex fluid phase behavior (P-T critical curve, VLLE line, and VLE isotherms) of the carbon dioxide + 1-decanol system: the cubic general equation of state (GEOS) and Peng-Robinson (PR) equation in conjunction with van der Waals two parameters conventional mixing rules (2PCMR). A correlation method involving temperature-dependent interaction parameters and a semipredictive approach with independent temperature interaction parameters have been used. Comparisons with experimental data reported in this work and available in the literature indicate that the topology of fluid phase behavior is satisfactorily given by the semipredictive procedure both for the critical line and in subcritical region, considering the relative simple used cubic equations of state.

Vapor–Liquid–Liquid Equilibrium Measurements and Modeling of Ethanethiol + Methane + Water, 1-Propanethiol + Methane + Water and 1-Butanethiol + Methane + Water Ternary Systems at 303, 335, and 365 K and Pressure Up to 9 MPa

New vapor–liquid–liquid equilibrium (VLLE) data for ethanethiol + methane + water, 1-propanethiol + methane + water, and 1-butanethiol + methane + water ternary systems have been measured at three temperatures (303, 335, and 365 K) and pressures up to 9 MPa. A “static-analytic” method was used for performing the measurements; the total system pressure was maintained by CH4. The objective of this work is to provide experimental VLLE data for mixtures of mercaptans (thiols) with other natural gas contents at its crude form, for which no data are available in the open literature. Such data will help the industrial modeling of processes relevant to reduction of sulfur emissions. The Cubic-Plus-Association (CPA) equation of state was applied to describe the phase behavior of the investigated systems. It is shown that the CPA EoS satisfactorily describes the solubilities of mercaptans (thiols) in all phases. However, the model underestimates the water content of the vapor phase, especially at low pressures and at the highest investigated temperature, i.e., at 365 K. Only the ethanthiol + methane + water system showed significant cross-association effects

New Vapor–Liquid–Liquid Equilibrium Data for Ethane and Propane in Alkanolamine Aqueous Solutions

New solubility data of ethane and propane in aqueous methyl diethanolamine (MDEA) and diethanolamine (DEA) solutions were measured at different temperatures and pressures. The data concern vapor–liquid–liquid equilibrium (VLLE) conditions. In this work, two weight-based concentrations of aqueous MDEA (w = 0.25 and w = 0.50) and one aqueous solution of DEA (w = 0.35) were considered. These concentration types are commonly used in the gas processing industry. The Henry’s constant is calculated for each system. In addition, useful correlations are proposed for the solubility, salting-in, three-phase vapor pressure, and activity coefficient at infinite dilution.

Isobaric vapor–liquid–liquid equilibrium for water + cyclohexane + acetic acid at 101.3 kPa

Isobaric vapor–liquid–liquid equilibrium (VLLE) data for the ternary system cyclohexane+water+acetic acid were measured at 101.3kPa. A modified dynamic recirculating still equipped with a mixing section was used to determine the VLLE. The experimental data indicate that a binary heterogeneous azeotrope is present at 342.16K with a composition of 0.3 and 0.7mole fractions of water and cyclohexane, respectively. The VLLE data have been used to test the reliability of the UNIQUAC and NRTL models in the prediction of VLLE. The two model parameters were obtained using VLE and LLE data correlation, respectively. The results indicate that the NRTL model has an acceptable prediction of the VLLE data, and the UNIQUAC model has a prediction of the heterogeneous region.

Vapor–Liquid–Liquid Equilibria Measurements for the Dehydration of Ethanol, Isopropanol, and n-Propanol via Azeotropic Distillation Using DIPE and Isooctane as Entrainers

Vapor–liquid equilibrium (VLE) and vapor–liquid–liquid equilibrium (VLLE) data were measured for the ethanol/diisopropyl ether (DIPE)/water, n-propanol/DIPE/water, and n-propanol/2,2,4-trimethylpentane (isooctane)/water systems at 101.3 kPa. The data were carefully measured in a Guillespie type still, equipped with an ultrasonic homogenizer. The VLE data were found to be thermodynamically consistent, and the LLE part of the VLLE data followed a regular profile according to the Othmer–Tobias correlation. VLLE were observed in the temperature ranges of (334.19 to 336.29) K, (335.31 to 345.76) K, and (347.74 to 352.31) K for the ethanol/DIPE/water, n-propanol/DIPE/water, and n-propanol/isooctane/water systems, respectively. These VLLE regions encompassed wide ranges for water and entrainer composition, with alcohol mole fractions of up to approximately 0.4. The ethanol/DIPE/water and n-propanol/isooctane/water systems displayed ternary heterogeneous azeotropes at (334.19 and 347.74) K, respectively. However, no ternary heterogeneous azeotrope was found for the n-propanol/DIPE/water system. The measured data were subsequently modeled in Aspen Plus with the nonrandom two-liquid (NRTL), universal functional UNIFAC(VLE), UNIFAC(LLE), and universal quasichemical UNIQUAC activity coefficient models, applying the default regression parameters built into Aspen Plus. UNIFAC(VLE) predicted the ethanol/DIPE/water system most accurately, while UNIQUAC performed the best for the n-propanol/DIPE/water. However, none of these models could predict the n-propanol/isooctane/water system with acceptable accuracy. The results of this study strongly support proposals that DIPE or di-n-propyl ether (DNPE) could be used as effective entrainers for alcohol dehydration, replacing the more traditional entrainers like benzene and cyclohexane.

A novel static analytical apparatus for phase equilibrium measurements

A new static analytical apparatus that enables reliable phase equilibria measurements for vapour–liquid equilibrium (VLE), liquid–liquid equilibrium (LLE) and vapour–liquid–liquid equilibrium (VLLE) data of small volumes (maximum 18cm3) has been designed. The operating temperature of the apparatus ranges from 253 to 473K and the operating pressure ranges from 100 to 1600kPa. In this work, the sampling of each phase is accomplished with a single standard mobile Rapid-Online-Sampler-Injector (ROLSI™). To enable sampling with the ROLSI™ sampler at pressures below the carrier gas pressure, a special arrangement of the sampling circuit is necessary. Such a setup was not used in this current study and consequently limited the sampling pressure to pressures above that of the carrier gas. A novel technique that compensates for the volume change within the equilibrium cell, which would normally occur due to movement of the ROLSI™ capillary, was used. The degassing of reagents prior to measurements is carried out on a simple degassing unit using the vacuum rectification method. Phase equilibrium data for previously reported systems were first measured to test the operation of the newly developed apparatus. The test systems included VLE measurements for the 2-methoxy-2-methylpropane+ethyl acetate system at 373.17K; LLE measurements for the hexane+acetonitrile and methanol+heptane systems at 350kPa; and VLLE measurements for the hexane+acetonitrile system at 348.20K. New experimental VLE data were also measured for systems of interest to petrochemical companies, viz. the ethanol+2-methoxy-2-methylbutane system at 398.25 and 413.19K (novel higher temperatures) and the 2-methylpent-2-ene+ethanol system at 383.20K. The VLE data are regressed with thermodynamic models using the combined method. Thermodynamic consistency testing (point and direct tests) is also performed for all the newly measured experimental data.

Calculation of vapour - liquid - liquid – equilibria in quaternary systems

Abstract A method of parameters fitting to the experimental vapour - liquid - liquid equilibrium (VLLE) data is presented for the NRTL and the Uniquac equations for six quaternary mixtures. The same equations but with coefficients taken from the simulator Chemcad database were also used for calculation of the VLLE for the same mixtures. The calculated equilibrium temperatures and compositions for all the three phases were compared with the experimental data for these four cases. The investigated models were also applied for calculation of the compositions and temperatures of ternary azeotropes occurring in the considered quaternary mixtures. The computed values were compared with the experimental ones to appreciate the model's accuracy and to confirm whether the model correctly predicts the presence of homo- or heteroazeotrope. The NRTL equation with coefficients fitted to the VLLE data proved to be the most accurate model. For the mixtures containing water, ethanol and two different hydrocarbons this model shows particularly high accuracy. In three cases the mean deviations between the calculated and measured temperatures do not exceed 0.25 K, and for the fourth mixture the difference equals 0.33. Besides, the mean deviations between the calculated and the measured concentrations in the gas and liquid phases, with one exception do not exceed 1 mole %.