Isothermal Vapor Liquid Equilibrium Research Articles

Measurement and correlation of the isothermal vapor-liquid equilibrium data for carbon dioxide and dimethyl ether system

Vapor-liquid equilibrium (VLE) data for the binary system of carbon dioxide (CO2)+dimethyl ether (DME) were measured at six equally spaced (10 K) temperatures between 283.15 and 333.15 K. The data in the two-phase region were measured by using a circulation-type equilibrium apparatus in which both vapor and liquid phases are continuously recirculated. The equilibrium compositions of vapor and liquid phases and pressure were reported at each temperature. The experimental VLE data were correlated with PR-EoS using the Wong-Sandler (W-S) mixing rule and the universal mixing rule (UMR). The overall average values of AAD-P (%) and AAD-y through the temperature range from 283.15 to 333.15 K were 1.0% and 0.012 for the W-S mixing rule and 0.88% and 0.014 for the UMR, respectively. All values are small and acceptable. Calculated results with these equations have given satisfactory results compared with the experimental data.

Phase Equilibria of H2S-Hydrocarbons (Propane, n-Butane, and n-Pentane) Binary Systems at Low Temperatures

Isothermal vapor–liquid equilibrium measurements of three binary systems, H2S + propane, H2S + n-butane, and H2S + n-pentane, have been performed with a static synthetic apparatus at low temperatures. The method of Barker has been implemented to determine the corresponding nonrandom two-liquid (NRTL) parameters and to calculate the liquid mole fractions. The results have been further used along with literature data to adjust binary interaction parameters of the Peng–Robinson equation of state. Good agreement with Dechema values has been found.

Isothermal Vapor–Liquid Equilibrium Data for the Propan-1-ol + Dodecane System at (323.0, 343.4, 353.2, 363.1, and 369.2) K

Isothermal vapor–liquid equilibrium (VLE) data (P–T–x–y) were measured and modeled for the propan-1-ol + dodecane system at (323.0, 343.4, 353.2, 363.1, and 369.2) K. The VLE data were measured using a dynamic–analytic method. The equilibrium cell used is a modified ebulliometer which allows for recirculation of both the liquid and the vapor phases and is capable of measuring systems of high relative volatility. The sampled equilibrium phases were analyzed and quantified using a gas chromatograph with a thermal conductivity detector. The measured experimental data were modeled using the γ–φ approach with the nonrandom two-liquid (NRTL) activity coefficient model to account for the liquid phase nonideality and the vapor phase assumed to be ideal. Fitting of the activity coefficient model was undertaken by nonlinear least-squares regression of the experimental data. Thermodynamic consistency testing of the experimental data was undertaken with the Van Ness test, with the data successfully passing the test.

The potential of head-space gas chromatography for VLE measurements

Head-space gas chromatography (HS-GC) is thought to allow the performance of (vapour+liquid) equilibrium (VLE) measurements in a fast and automated way. However, two decades after the first applications of HS-GC for this purpose, the potential of this technique is not fully developed yet. Measurements of isothermal VLE and activity coefficients of mixtures can be obtained in a high throughput scenario. However, several considerations have to be taken into account before starting the analysis, such as the equilibration time or the minimum sample volume and the GC response factors. These aspects can strongly influence on the validity of the results and should therefore be determined for each mixture.In this paper, four azeotropic mixtures of interest in the pharmaceutical and chemical industry, i.e., (ethylacetate+water), which forms a heterogeneous azeotrope, (ethylacetate+isooctane), (acetonitrile+toluene) and the ternary mixture (acetonitrile+toluene+tetrahydrofuran), are considered to show the potential of HS-GC for VLE measurements. The thermodynamic analysis of VLE data leads to activity coefficients for the mixtures at (35, 50, and 70)°C. In addition, the experimental data are compared with thermodynamic models and data from the literature, when available.

Measurement of VLE data of carbon dioxide + dimethyl carbonate system for the direct synthesis of dimethyl carbonate using supercritical CO2 and methanol

Isothermal vapor–liquid equilibrium data for the binary system of carbon dioxide+dimethyl carbonate (DMC) were measured at 278.15, 283.15, 293.15, 303.15, 313.15, 323.15 and 333.15K using a circulation-type equilibrium apparatus in which both vapor and liquid phases were recirculated. The equilibrium compositions of vapor and liquid phases and pressures were reported at each temperature. The measured data were correlated with the Peng–Robinson equation of state (PR-EoS) using the Wong–Sandler mixing rules combined with the NRTL excess Gibbs free energy model and the Peng–Robinson equation of state (PR-EoS) using the Universal mixing rule. Calculated results with these equations can be used to estimate the thermodynamic properties of this binary system of CO2 (1)+DMC (2).

Isothermal Vapor–Liquid Equilibrium for Binary Mixtures of Polyoxyethylene Dodecanoate with Methanol, Ethanol, or Propan-2-ol

Isothermal vapor–liquid equilibrium (VLE) data have been measured for oligomeric polyoxyethylene dodecanoate (POEDDA) with methanol, ethanol, or propan-2-ol. A synthetic method was used to determine experimentally p–T–x data in the temperature range of (343.2 to 423.2) K. For each binary system, four feed compositions were studied over the concentration range from 0.100 to 0.400 of POEDDA in mole fractions. These new VLE data were fitted to the Antoine equation and also correlated with the nonrandom two-liquid (NRTL) and the universal quasichemical activity coefficient (UNIQUAC) models. The results reveal that the performance of the UNIQUAC and the NRTL models are almost the same. The solvent activities were directly calculated from VLE data and compared to those calculated from the NRTL and the UNIQUAC models.

Phase equilibria (LLE and VLE) of refining operations for enzymatic biodiesel production via quantum mechanical COSMO‐RS method

AbstractPhase equilibria, both liquid–liquid equilibria (LLE) and vapor‐liquid equilibria (VLE), are equally important in the refining operations of biodiesel production. Equilibrium distributions of components at the down‐processing of enzymatic ethanolysis reaction were investigated through quantum mechanical COnductor‐like Screening MOdel‐Real Solvent method with implemented vapor pressure equations. Due to the composite nature of fatty acid ethyl ester (FAEE) components as the biodiesel fuel, multicomponent predictive phase equilibria approach was applied for a model reaction system of refined soybean oil with 30% molar excess amount of ethanol. Simulation results for the LLE at 303 K were in significant agreement with reported experimental data. Minimum boiling azeotropes were found for FAEE‐glycerol binaries at isothermal (at 423 and 473K) and isobaric (at reduced pressures) VLE simulations. Similar results were also found at the VLE of glycerol purification operations for multicomponent real case simulations. The feasibilities of simple and rigorous unit operations were also pointed up in this study. © 2012 American Institute of Chemical Engineers AIChE J, 2012

Vapor-liquid Equilibrium Data Concerning Refrigerant Systems (R116 + R143a)

Development of modern refrigeration systems is critical for the success of new global environmental protection efforts. The binary system of refrigerants: Hexafluoroethane (R116) + 1,1,1- trifluoroethane (R143a), has been studied with the aim of providing PTxy data. Isothermal vapor-liquid equilibrium data have been generated using the “static-analytic” method from 258 to 328K at pressures from 0.39 to 3.89MPa. The modelcomposed of the Peng-Robinson equation of state, the Mathias-Copeman alpha function, the Wong-Sandler mixing rules and the NRTL cell theory is applied herein to correlate the data and calculate the critical line.

Vapor–liquid equilibrium data for the dimethyl ether (RE170) + decafluorobutane (R3-1-10) system at temperatures from 313.28 to 392.83 K and pressures up to 4.9 MPa

Isothermal vapour–liquid equilibrium data have been measured for the RE170+R3-1-10 binary system at nine temperatures between 313.28 and 392.83K, and pressures between 0.57 and 4.9MPa. The experimental method used in this work is of the static-analytic type, taking advantage of two pneumatic capillary samplers (ROLSI™, Armines’ patent) developed in the CEP/TEP laboratory. The data were obtained with accuracies within ±0.02K, ±0.0006MPa and ±0.009 for molar compositions. The particularity of this system is to present an azeotrope. The isothermal P, x, y data are well represented with the Peng and Robinson equation of state using the Mathias Copeman alpha function and the Wong–Sandler mixing rules involving the NRTL gE model.

Phase equilibrium for the binary azeotropic mixture of trifluoroiodomethane (R13I1) + 1,1,2,2-tetrafluoroethane (R134) at temperatures from 258.150 to 283.150 K

Isothermal vapor–liquid equilibrium data of binary trifluoroiodomethane (R13I1) + 1,1,2,2-tetrafluoroethane (R134) systems at 258.150, 263.150, 273.150 and 283.150 K were measured by a recirculation apparatus with visual windows. The measured uncertainties of the temperature, pressure, and compositions are less than ±5 mK, ±0.0005 MPa, and ±0.005, respectively. All the experimental data were correlated by the Peng–Robinson (PR) EoS with the Huron–Vidal (HV) mixing rule utilizing the non-random two-liquid (NRTL) activity coefficient model. Azeotropic behavior can be found at the measured temperature range.

Experimental and Molecular Modeling Study of the Three-Phase Behavior of (n-Decane + Carbon Dioxide + Water) at Reservoir Conditions

Knowledge of the phase behavior of mixtures of oil with carbon dioxide and water is essential for reservoir engineering, especially in the processes of enhanced oil recovery and geological storage of carbon dioxide. However, for a comprehensive understanding, the study of simpler systems needs to be completed. In this work the system (n-decane + carbon dioxide + water) was studied as a model (oil + carbon dioxide + water) mixture. To accomplish our aim, a new analytical apparatus to measure phase equilibria at high pressure was designed with maximum operating temperature and pressure of 423 K and 45 MPa, respectively. The equipment relies on recirculation of two coexisting phases using a two-channel magnetically operated micropump designed during this work, with sampling and online compositional analysis by gas chromatography. The apparatus has been validated by comparison with published isothermal vapor-liquid equilibrium data for the binary system (n-decane + carbon dioxide). New experimental data have been measured for the system (n-decane + carbon dioxide + water) under conditions of three-phase equilibria. Data for the three coexisting phases have been obtained on five isotherms at temperatures from 323 to 413 K and at pressures up to the point at which two of the phases become critical. The experimental work is complemented here with a theoretical effort in which we developed models for these molecules within the framework of the statistical associating fluid theory for potentials of variable range (SAFT-VR). The phase behavior of the three binary subsystems was calculated using this theory, and where applicable, a modification of the Hudson and McCoubrey combining rules was used to treat the systems predictively. The experimental data obtained for the ternary mixture are compared to the predictions of the theory. Furthermore, a detailed analysis of the ternary mixture is carried out based on comparison with available data for the constituent binary subsystems. In this way, we analyzed the observed effects on the solubility when the third component was added.

Isothermal vapor-liquid equilibria for the binary system of dimethyl ether (CH3OCH3)+ methanol (CH3OH)

Isothermal vapor-liquid equilibrium data for the binary mixture of dimethyl ether (CH3OCH3)+methanol (CH3OH) were measured within the temperature range of 308.15–328.15 K. The data in the two-phase region were measured by using a circulation-type equilibrium apparatus in which both vapor and liquid phases are continuously recirculated. The experimental data were correlated with the Peng-Robinson equation of state (PR-EoS) using the Wong-Sandler mixing rules combined with the NRTL excess Gibbs free energy model. The values calculated by the PR-EOS with the W-S mixing rules show good agreement with our experimental data.

P– x data for binary systems using a novel static total pressure apparatus

A new static isothermal vapor–liquid equilibrium (VLE) apparatus, designed for operation at pressures up to 2000 kPa incorporates novel dual-mode piston pumps which, in the micro-mode, can dispense microlitre volumes repeatably. Pure component vapor pressure and VLE measurements for two test systems (water + 1-propanol at 313.17 K and n-hexane + 2-butanol at 329.22 K) showed excellent agreement with literature data. New VLE data are presented for n-dodecane + 1-propanol at 342.8 and 352.7 K, and n-dodecane + 2-butanol at 342.7 and 352.7 K. An accurate new method for finding the cell net interior volume from cumulative injected liquid volumes and corresponding pressures is presented. For systems of high relative volatility the liquid equilibrium composition ( x i ) may differ significantly from the charge composition ( z i ) in the region dilute in the more volatile component. Exact equations for the fractional difference ( z i − x i )/ x i conveniently show the influence of relative volatility, system pressure, vapor space, and vapor non-ideality, and are illustrated for the n-dodecane + 1-propanol system. Equations showing the dependence of the limiting activity coefficient on the virial coefficient values ( B 11, B 12, and B 22) used in their computation indicate that the influence may be considerable for derivatives numerically larger than about 4 × 10 −5 mol cm −3.

Thermophysical study of the n-hexane or n-heptane with 1-chloropropane systems

Densities, speeds of sound and refractive indices at atmospheric pressure and at a temperature range of 283.15–313.15K, and isothermal vapour liquid equilibrium at 298.15K for the binary mixtures of n-hexane or n-heptane with 1-chloropropane have been determined. Excess volumes, excess isentropic compressibilities, refractive index deviations and excess Gibbs functions were calculated from the experimental data. All these properties provide an insight into the nature of interactions operating on the present systems.

Isothermal vapor–liquid equilibria for methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K, 373.15 K

Isothermal vapor–liquid equilibrium (VLE) data were measured for the binary system methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K, 373.15 K, respectively. The measurements were carried out in a novel recirculation equilibrium equipment. Three activity coefficient models including Wilson, NRTL and UNIQUAC, as well as the Soave–Redlich–Kwong equation of state were used to correlate the experimental data. The correlation results showed that a good consistency between the experimental data and the Wilson model can be achieved.

Finding a suitable thermodynamic model and phase equilibria for hydrodeoxygenation reactions of methyl heptanoate

Replacement of fossil fuels with biomass-based components is of increasing public and scientific interest. Unfortunately, most biomass-based compounds contain oxygen and oxygen content must be diminished before use of the compounds as fuel. Removal is usually done catalytically, with hydrogen supplied to convert the oxygen to water. Hydrodeoxygenation (HDO) of biomass-based compounds is often studied with model compounds, and the system investigated here was methyl heptanoate+m-xylene. Modeling of the reaction kinetics requires that behavior of the reaction mixture as a function of reaction time must be described. A suitable thermodynamic model for non-ideal system at high pressure and temperature is needed, and this demands correct modeling of the solubility of hydrogen and the water of reaction. For validation of the thermodynamic models isothermal vapor–liquid equilibrium (VLE) for the methyl heptanoate+m-xylene system was measured at 398.15K and 408.15K with a circulation still. The experimental VLE exhibited slight negative deviation from Raoult’s law. No azeotropic behavior was found. The experimental VLE results were correlated with the Wilson model with temperature-dependent parameters and used in testing of the SRK, original UNIFAC, UNIFAC-Dortmund, and PSRK predictive models. PSRK was preferred for further estimations. All VLE measurements passed the point consistency tests. Simulated reaction conditions for HDO of methyl heptanoate at the initial and final points were calculated to determine the effect of vapor–liquid equilibrium on the composition of reaction mixtures.

Vapor–liquid equilibria at 333.15 K and excess molar volumes and deviations in molar refractivity at 298.15 K for mixtures of diisopropyl ether, ethanol and ionic liquids

In this work, we have studied influence of ionic liquids (ILs) on the azeotrope composition for the system {diisopropyl ether (DIPE) + ethanol} using trihexyltetradecylphosphonium chloride ([P 666,14][Cl]) and trihexyltetradecylphosphonium bis(2,2,4-trimethylpentyl) phosphinate ([P 666,14][TMPP]). Isothermal vapor–liquid equilibrium data at 333.15 K are reported for the ternary systems {DIPE + ethanol + [P 666,14][Cl]} and {DIPE + ethanol + [P 666,14][TMPP]} with varying the mole fraction of ILs from 0.05 to 0.10. The experimental ternary VLE data were correlated using the Wilson equation. In addition, excess molar volumes ( V E) and deviations in molar refractivity (Δ R) data at 298.15 K are reported for the binary systems {DIPE + [P 666,14][Cl]} and {ethanol + [P 666,14][Cl]} by a digital vibrating tube densimeter and a precision digital refractometer. The V E and Δ R were correlated by the Redlich–Kister equation.

Isothermal Vapor–Liquid Equilibrium Data of Propan-1-ol + 2,2,4-Trimethylpentane and Butan-1-ol + 2,2,4-Trimethylpentane at 318.15 K

In this research, vapor–liquid equilibrium (VLE) data were determined at 318.15 K for the mixtures propan-1-ol + 2,2,4-trimethylpentane and butan-1-ol + 2,2,4-trimethylpentane in an isothermic Othmer still with recirculation, where the temperature was kept constant by means of a proportional-integral (PI) cascade control for the vapor phase. The equilibrium concentration for each phase was determined by gas chromatography, and the vapor phase was considered as nonideal. The consistency of the data was verified by means of the Van Ness direct test of thermodynamic consistency, supported by several thermodynamic methods based on the Gibbs–Duhem equation. The correlation of the VLE data was carried out using the Wilson local composition model. The alkanol + 2,2,4-trimethylpentane mixtures studied exhibit positive contributions from ideality and azeotropic behavior.

Isothermal vapour–liquid equilibria and excess enthalpies for the binary mixtures containing an isomeric chlorobutane and diisopropyl ether

Isothermal vapour–liquid equilibria for the four binary mixtures formed by an isomer of chlorobutane (1-chlorobutane, 2-chlorobutane, 2-methyl-1-chloropropane, or 2-methyl-2-chloropropane) and diisopropyl ether has been studied at T = 288.15 K, 298.15 K, and 308.15 K. The experimental data have been satisfactorily checked for thermodynamic consistency using the method of van Ness. The isothermal vapour–liquid equilibrium data have been correlated using the Wilson equation and excess Gibbs energies have been calculated. Moreover, we have measured excess enthalpies at T = 298.15 K using an isothermal flow calorimeter; combining these excess enthalpies with excess Gibbs energies the corresponding entropic contributions to excess Gibbs energy have been obtained. The group contribution method UNIFAC has been used to predict the phase equilibrium behaviour of the mixtures at isothermal conditions.

Isothermal vapour–liquid equilibria in the binary and ternary systems composed of 2,2,4-trimethylpentane, 2-methyl-1-propanol, and 4-methyl-2-pentanone

Vapour–liquid equilibrium data in the three binary 2,2,4-trimethylpentane + 2-methyl-1-propanol, 2-methyl-1-propanol + 4-methyl-2-pentanone, 2,2,4-trimethylpentane + 4-methyl-2-pentanone systems, and in the ternary 2,2,4-trimethylpentane + 2-methyl-1-propanol + 4-methyl-2-pentanone system are reported. The data were measured isothermally at 333.15, 348.15 and 364.15 K covering the pressure range 12–100 kPa. The binary vapour–liquid equilibrium data were correlated using the Wilson and NRTL equations by means of a robust algorithm for processing all isotherms together; resulting parameters were then used for calculation of phase behaviour in the ternary system and for subsequent comparison with experimental data.