Vapor-liquid Equilibrium Measurements Research Articles

The determination of the Henry’s Coefficient of reactive gases – An example of CO2 in aqueous solutions of monoethanolamine (MEA)

The Henry’s Coefficient of CO2 is a fundamental property, it quantifies the equilibrium between the partial pressure of CO2 in the gas phase and the concentration of dissolved free CO2 in the liquid phase. This value is critical for simulation and may lead to improvements in the process of post combustion capture of CO2. However, because of its reactive nature, CO2 reacts in amine solutions and forms multiple carbon-containing species, so that the free CO2 concentration is very small and difficult to determine. The “N2O analogy” has been used to estimate the physical solubility of CO2 based on the assumption that the two gases behave similarly in water and amine solutions. In the current study, a direct way is proposed for the determination of the Henry’s Coefficient of CO2 in MEA solutions. The method only requires vapor-liquid equilibrium (VLE) measurements of the MEA-CO2-H2O system; and all equilibrium/protonation constants for all solution reactions are sourced from the open literature while activity coefficients for all ionic species were estimated using the Davis equation. The free CO2 concentration in solution can be computed using the total MEA concentration, total CO2 concentration and temperature, which allows the determination of the Henry’s Coefficient from the CO2 partial pressure. A 10-parameter polynomial is used to approximate the Henry’s Coefficient as a function of the total MEA concentration, total CO2 concentration and temperature. VLE calculations were performed using the liquid-phase equilibrium calculations and the polynomial function calculating the Henry’s Coefficient, and the results show the VLE calculations are adequate to describe the VLE data.

Measurement and correlation of isobaric vapour-liquid equilibria for binary systems of 1-(methoxymethoxy)-2-methyl-propane with 1-butanol and isobutanol at 101.33 kPa

Isobaric vapour-liquid equilibria (VLE) experimental results for binary systems of 1-(methoxymethoxy)-2-methyl-propane with 1-butanol and isobutanol at 101.33kPa were determined. Each binary mixture shows a minimum boiling azeotrope at 101.33kPa, in which the azeotropic temperature and composition are 381.19K and 26.72mol% (1-butanol) and 377.55K and 53.34mol% (isobutanol), respectively. The VLE measurements were correlated by the van Laar, Wilson and NRTL models for which the binary interaction parameters are reported. The results show that the measurements of two binary systems provide a good agreement with the calculated values acquired by the Wilson and NRTL models, respectively. The thermodynamic consistency of the VLE measurements was checked using the traditional area test and the direct test methods.

Measurement and Correlation of Isobaric Vapor–Liquid Equilibrium for Binary Systems of 1-(Ethoxymethoxy)-2-methyl-propane with Isobutyl Alcohol or 1-Butanol at 101.33 kPa

Experimental vapor–liquid equilibrium (VLE) data for binary systems of 1-(ethoxymethoxy)-2-methyl-propane (EMMP) with isobutyl alcohol and 1-butanol at 101.33 kPa was measured. The measurements of saturated vapor pressure for EMMP were also measured. The experiment was performed by an improved Rose still. A minimum boiling azeotrope was found about the binary system containing 1-butanol for which the azeotropic temperature and composition are 389.64 K and 75.92 mol% (1-butanol) at 101.33 kPa. The VLE measurements were correlated by the Wilson, nonrandom two-liquid, and universal quasichemical models for which the results showed that the measurements had a good correlation by using three models about two binary systems, respectively. The thermodynamic consistency of the VLE measurements was checked by the traditional area test and the direct test methods.

Vapour-liquid equilibria for (water + ethanol + fructose): Experimental data and thermodynamic modelling

Fructose (1,3,4,5,6-pentahydoxyhex-2-one) is an important sugar in the global market because of its unique characteristics when compared to other sugars, which makes fructose economically attractive, even though it is not easily produced. Crystalline fructose may be produced by crystallization of its aqueous solution, with the addition of ethanol as anti-solvent. After the separation of the crystals, the recovery of (ethanol+water+fructose) mother-liquor becomes feasible. Then, a distillation step may recover ethanol, and vapour-liquid equilibrium (VLE) data for (water+ethanol+fructose) mixtures are consequently necessary, despite not being available in the literature. In this work, VLE results for (water+ethanol) and (water+ethanol+fructose) were determined using a modified ebulliometer based on vapour recirculation. VLE measurements for (water+ethanol) were used to verify the thermodynamic consistency applying the Global Area Test developed by Redlich-Kister-Herington. Group contribution activity coefficient models were selected and evaluated to predict VLE for the ternary system. S-UNIFAC, A-UNIFAC and mS-UNIFAC models were tested. mS-UNIFAC demonstrated the best results, with average absolute relative deviation between experimental data and values calculated from the model of 0.1%, 3.6%, 3.0% and 3.6% for mole fraction of ethanol vapour when 0, 10.3, 20.7 and 31.0mass percent of fructose were used.

The Henry Coefficient of CO2 in the MEA-CO2-H2O System

The Henry Coefficient of CO2 is a fundamental property and crucial for the accurate simulation of the absorption and desorption of CO2 in MEA solutions related to post combustion capture (PCC). The free CO2 concentration in amine solutions is very small and is difficult to be measured since it reacts with the solution. The “N2O analogy” is traditionally applied to estimate the physical solubility of CO2 based on the assumption that the two gases behave similarly in amine solutions. We propose a direct way to determine Henry Coefficient of CO2 in MEA solutions as an alternative to N2O analogy. The method only requires vapor liquid equilibrium measurements of the MEA-CO2-H2O system. Based on the total MEA concentration, loading and known equilibrium constants the free CO2 can be computed which allows the determination of the Henry Coefficient. A 6-parameter polynomial is used to approximate the Henry Coefficient as a function of the total MEA concentration and total CO2 concentration at 40 oC.

High pressure multi-component vapor-liquid equilibrium data and model predictions for the LNG industry

Accurate simulations of scrub columns in liquefied natural gas (LNG) plants are challenging, requiring frequent solution of the non-linear equations governing vapor-liquid equilibrium (VLE), material, and energy balances for multi-component mixtures. Reliable fluid property predictions at high pressures and low temperatures are thus crucial; however, no high-quality multi-component VLE data at conditions relevant to the LNG scrub column are available to test commonly-used equations of state (EOS). Here we report VLE measurements at pressures to 9MPa and temperatures from (203 to 273)K for mixtures containing CH4, C2H6, C3H8, iC4H10, nC4H10 and/or N2. Far from the mixture’s critical point, the GERG-2008 EOS predictions were more accurate than the Peng-Robinson EOS predictions. Above 7MPa both EOS under-predicted the liquid phase’s methane content and over-predicted its butane content by 10–50 times the experimental uncertainty. Rowland et al.’s recent revision of the GERG model reduced the maximum deviations by (17–35)%. Further optimizations should improve the constituent binary departure functions and hence improve the description of multicomponent VLE data, particularly at conditions relevant to LNG production.

A milliliter-scale setup for the efficient characterization of isothermal vapor-liquid equilibria using Raman spectroscopy

Experimental vapor-liquid equilibrium data are of major importance for the chemical industry. However, the measurement of vapor-liquid equilibrium data still requires significant experimental effort. Therefore, we present a novel setup and measurement procedure for the rapid determination of isothermal vapor-liquid equilibria using only milliliter samples. The compositions of both liquid and vapor phases are analyzed using Raman spectroscopy. The measurement setup is successfully validated by reproducing vapor pressures of four pure substances and binary vapor-liquid equilibrium data of methyl tert-butyl ether (MTBE) and 2,2,4-trimethylpentane (iso-octane) at T = 318.1 K as test system from literature. The vapor pressures of MTBE, ethanol, iso-octane and toluene agree with literature data within the measurement uncertainties. The measured binary vapor-liquid equilibrium data are modeled using the PCP-SAFT equation of state. Phase equilibrium data calculated from PCP-SAFT are compared to experimental data from literature. The data deviate by less than 1% in terms of pressure and vapor phase composition for given temperature and liquid phase composition demonstrating the reliability of the presented setup for vapor-liquid equilibrium measurements.

Vapor–Liquid Equilibrium Measurements for Carbon Dioxide + Cyclohexene + Squalane at High Pressures Using a Synthetic Method

Growing interest in the study of production conditions in the presalt led to the need to study complex systems at high pressures and temperatures, such as up to 70 MPa and up to 393 K. The aim of this work is to obtain vapor–liquid equilibrium data at high pressures and temperatures for hydrocarbon systems with carbon dioxide (CO2). To obtain these data, an experimental setup and procedure using a synthetic cell were designed. Experimental data of the binary system CO2 + cyclohexene (C6H10) and CO2 + squalane (C30H62) over a range of temperature between 303 and 398 K and the ternary system CO2 + C6H10 + C30H62 at various temperatures (318–393 K) and compositions are reported. It is noteworthy that the reported measurements in this work were not studied in the literature, and experimental data may contribute to industrial and scientific interests. The phase behavior of the system was also described using the Soave–Redlich–Kwong equation of state together with Mathias–Copeman alpha function. Interaction par...

Isothermal vapor-liquid equilibria, excess molar volume and the deviation of refractive indices for binary mixtures of 1-butanol, 1-hexanol, 3-methyl-1-butanol and butyl acetate

Experimental vapor-liquid equilibrium (VLE) data and mixture properties are reported toward developing a process for the separation of the traditional ABE (acetone + butanol + ethanol) fermentation. Isothermal VLE measurements at 343.2 K were performed by using headspace gas chromatography (HSGC) for binary systems {1-butanol + 3-methyl-1-butanol}, {1-butanol + 1-hexanol}, {butyl acetate + 3-methyl-1-butanol}, {butyl acetate + 1-hexanol} and {3-methyl-1-butanol + 1-hexanol}. The experimental VLE binary data were correlated using the Wilson, NRTL and UNIQUAC activity coefficient model equation. In addition, a digital vibrating tube densimeter and precision digital refractometer were used to determine the excess molar volume (VE) and the deviation of the refractive indices (ΔR) for the same binary systems at 298.2 K. The Redlich-Kister equation was employed to show that the determined VE and ΔR data were well correlated.

Isobaric (vapor + liquid) equilibria for 2-methylthiophene with n-heptane, 2,2,4-trimethylpentane, n-nonane and n-decane at 90.00 kPa

Isobaric vapor-liquid equilibrium (VLE) data for the four systems n-heptane+2-methylthiophene, 2,2,4-trimethylpentane+2-methylthiophene, n-nonane+2-methylthiophene, n-decane+2-methylthiophene were measured at 90.00kPa with a modified Rose-Williams still. Gas chromatography equipped with a flame ionization detector was used to analyze composition of the samples from the vapor-liquid equilibrium systems. All the VLE measurements passed the thermodynamic consistent test using the Herington method and the Van Ness test. The azeotropic behavior was found in the 2,2,4-trimethylpentane+2-methylthiophene system. The experimental data were correlated by the Wilson and NRTL activity coefficient models and also compared with the original UNIFAC predictive model. The corresponding parameters for the three models were obtained. The results exhibited that the measured data got agree well with the calculated values using the Wilson, NRTL and original UNIFAC models.

Feasibility of thermal separation in recycling of the distillable ionic liquid [DBNH][OAc] in cellulose fiber production

The objective of this work was to explore the feasibility of 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) recovery from water solution by thermal separation. The evaporation behavior of pure [DBNH][OAc] was first studied using low pressure distillation in the pressure range of 0.5–2kPa. The dew points of the distillation products from [DBNH][OAc] were measured in the pressure range of 0.5–15kPa and modeled using an Antoine equation. Measurements for vapor liquid equilibrium (VLE) of water+[DBNH][OAc] system were carried out using a static total pressure method. The temperature range for the VLE measurement was 303–353K. The results showed negative deviation from the Raoult’s law. The NRTL activity coefficient model was used to correlate the VLE data. The experiments of [DBNH][OAc] product recovery from a solution containing 80wt.% water were performed using a pilot-scale agitated thin-film evaporator. The performance of the evaporation system was analyzed as a function of the feed flow rate, the evaporator jacket temperature and the operating pressure. The analyses results indicated that the [DBNH][OAc] product with small water content (5–11.7wt.%) was achieved by low pressure evaporation in a single stage.

Phase Equilibria for the Hydroesterification of 10-Undecenoic Acid Methyl Ester

This paper investigates phase equilibria of interest for the hydroesterification of 10-undecenoic acid methyl ester with methanol and carbon monoxide to dodecanedioic acid dimethyl ester in a solvent system composed of methanol and n-dodecane. Carbon monoxide solubilities were measured in 10-undecenoic acid methyl ester, dodecanedioic acid dimethyl ester, and a mixture of methanol/dodecanedioic acid dimethyl ester at 363 and 393 K and at pressures up to 15 MPa. Vapor–liquid equilibrium measurements in the systems methanol/10-undecenoic acid methyl ester, methanol/dodecanedioic acid dimethyl ester, n-dodecane/10-undecenoic acid methyl ester, n-dodecane/dodecanedioic acid dimethyl ester, and 10-undecenoic acid methyl ester/dodecanedioic acid dimethyl ester were performed at temperatures between 342 and 437 K and at pressures of 2 or 80 kPa. The measured data were accurately modeled using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT).

Measurement and correlation of ternary vapor-liquid equilibria for methanol + glycerol + fatty acid methyl ester (methyl laurate, methyl myristate, methyl palmitate) systems at elevated temperatures and pressures

The phase behaviors for three ternary systems (methanol + glycerol + methyl laurate/methyl myristate/methyl palmitate) were studied at elevated temperatures (about 493.0 K, 523.0 K) and pressures by a flow-type method. The results demonstrated that the mole fractions of methanol in liquid phase increase and the mole fractions of glycerol and FAME decrease with increasing pressure. The influences of FAME molecular chain length on mutual solubility between methanol, glycerol and FAME in vapor phase were discussed. The experimental data were regressed by Redlich-Kwong-Soave equation of state (RKS EOS), RKS EOS combined with Boston and Mathias function (RKS-BM EOS) and Redlich-Kwong-Soave Aspen equations of state (RKS-Aspen EOS) with van der Waals (vdW) mixing rule. The correlated results with RKS-Aspen EOS are more accurate than other EOSs. The vapor-liquid equilibria (VLE) experimental data can be employed for designing the methanol process and phase separation in biodiesel production technology.

Vapor-liquid equilibrium data for the carbon dioxide and oxygen (CO2 + O2) system at the temperatures 218, 233, 253, 273, 288 and 298 K and pressures up to 14 MPa

Accurate thermophysical data for the CO2-rich mixtures relevant for carbon capture, transport and storage (CCS) are essential for the development of the accurate equations of state (EOS) and models needed for the design and operation of the processes within CCS. Vapor-liquid equilibrium measurements for the binary system CO2 + O2 are reported at 218, 233, 253, 273, 288 and 298 K, with estimated standard uncertainties of maximum 8 mK in temperature, maximum 3 kPa in pressure, and maximum 0.0031 in the mole fractions of the phases in the mixture critical regions, and 0.0005 in the mole fractions outside the critical regions. These measurements are compared with existing data. Although some data exists, there are little trustworthy literature data around critical conditions, and the measurements in the present work indicate a need to revise the parameters of existing models. The data in the present work has significantly less scatter than most of the literature data, and range from the vapor pressure of pure CO2 to close to the mixture critical point pressure at all six temperatures. With the measurements in the present work, the data situation for the CO2 + O2 system is significantly improved, forming the basis to develop better equations of state for the system. A scaling law model is fitted to the critical region data of each isotherm, and high accuracy estimates for the critical composition and pressure are found. The Peng-Robinson EOS with the alpha correction by Mathias and Copeman, the mixing rules by Wong and Sandler, and the NRTL excess Gibbs energy model is fitted to the data in the present work, with a maximum absolute average deviation of 0.01 in mole fraction.

Reference Quality Vapor–Liquid Equilibrium Data for the Binary Systems Methane + Ethane, + Propane, + Butane, and + 2-Methylpropane, at Temperatures from (203 to 273) K and Pressures to 9 MPa

A specialized cell designed for vapor liquid equilibrium (VLE) measurements at cryogenic temperatures and high pressures was used to measure new (p,T,x,y) data for binary mixtures of methane + ethane, + propane, + 2-methylpropane (isobutane), and + butane from (203 to 273) K at pressures up to 9 MPa. A literature review of VLE data for these binary mixtures indicates that a significant number have large uncertainties; however, because estimates of uncertainties in measured phase compositions are often not quantified sufficiently, it can be difficult for equation of state (EOS) developers to identify which data sets are of poor quality. Robust quantitative uncertainties were estimated for the VLE data acquired in this work, which allowed the identification of literature data sets that should not be included in future EOS development. The new data were compared with the predictions of the Peng–Robinson (PR) EOS and the Groupe European de Recherche Gaziere (GERG-2008) multiparameter EOS. The former describes the new data measured at low pressures within experimental uncertainty but deviates systematically from the data as the bubble point pressure is increased; for the binary mixtures containing either of the butanes, the maximum relative deviation of the data from the PR EOS amounted to nearly 10 % of the methane liquid mole fraction. The GERG-2008 EOS was better able to describe the new high-pressure data for the CH4 + C3H8 system than the PR EOS. However, for both the CH4 + C4H10 mixtures, the GERG EOS deviated from these data by an amount twice as large as the PR EOS because of ambiguity about which VLE literature data sets should be used in model development. The new data resolve these ambiguities and should facilitate the development of improved EOS as needed, for example, in simulations of low temperature natural gas separation processes.

Vapor–liquid equilibrium data for the carbon dioxide and nitrogen (CO2 + N2) system at the temperatures 223, 270, 298 and 303 K and pressures up to 18 MPa

A new setup for the measurement of vapor–liquid phase equilibria of CO2-rich mixtures relevant for carbon capture and storage (CCS) transport conditions is presented. An isothermal analytical method with a variable volume cell is used. The apparatus is capable of highly accurate measurements in terms of pressure, temperature and composition, also in the critical region. Vapor-liquid equilibrium (VLE) measurements for the binary system CO2 + N2 are reported at 223, 270, 298 and 303 K, with estimated standard uncertainties of maximum 0.006 K in the temperature, maximum 0.003 MPa in the pressure, and maximum 0.0004 in the mole fractions of the phases. These measurements are verified against existing data. Although some data exists, there is little trustworthy data around critical conditions, and our data indicate a need to revise the parameters of existing models. A fit made against our data of the vapor–liquid equilibrium prediction of GERG-2008/EOS-CG for CO2 + N2 is presented. At 223 and 298 K, the critical region of the isotherm are fitted using a scaling law, and high accuracy estimates for the critical composition and pressure are found.

Measurement and correlation of vapor-liquid equilibria for a binary system containing 1-butyl-3-methylimidazolium tridecafluorohexylsulfonate and carbon dioxide

Using a high-pressure variable-volume view cell, the vapor-liquid equilibria of the binary system CO2 and 1-butyl-3-methylimidazolium tridecafluorohexylsulfonate ([BMIM][TDfO]) were determined. The CO2 mole fraction ranged from 0.104 to 0.952 over a temperature range of 298.2-323.2 K. Both the Peng-Robinson and Soave-Redlich- Kwong equations of state were applied with two different mixing rules to correlate with the experimentally obtained results. Increasing the alkyl chain length in perfluorinated sulfonate anion mother structure from methyl to hexyl markedly increased the CO2 solubility. To investigate the effect of the number of fluorine atoms in the anion on the phase behavior of imidazolium-based ionic liquid, these experimental results were then compared with those reported in previous experimental studies of 1-alkyl-3-methylimidazolium cations-including ionic liquid+CO2 binary system.

Isothermal vapor–liquid equilibrium measurements and assessments of 1,1,1,3,3,3-hexafluoropropane + N,N-dimethylformamide/N-methyl-2-pyrrolidone working pairs for absorption power cycles

To develop novel working pairs for absorption power cycles, this study selected 1,1,1,3,3,3-hexafluoropropane (HFC236fa)+N,N-dimethylformamide (DMF) and HFC236fa+N-methyl-2-pyrrolidone (NMP) systems. In addition, the vapor–liquid equilibrium (VLE) data of the two systems were measured in a temperature range extending from 293.15K to 353.15K and a pressure range of 30–900kPa. The five-parameter non-random two liquid (NRTL) model was chosen to regress the obtained VLE data. The results indicated that the NRTL model was suitable for the regression of the VLE data, and the maximum deviations of the pressure between the experimental and calculated values were 4.06% and 3.83%, and the average relative deviations were 1.55% and 1.90%, respectively. The regressed activity coefficients were both less than 1, which indicated that the two binary mixtures exhibit negative deviations from Raoult’s law. Therefore, the two systems exhibit good affinity. However, the activity coefficient of HFC236fa+DMF is smaller than that of HFC236fa+NMP. Finally, the systems in the literature were compared to this work, and the affinity of the systems was analyzed based on the molecular structure and hydrogen bond.

Isobaric (vapor–liquid) equilibria for binary systems of methanol + 1-(methoxymethoxy)-propane and 1-propanol + 1-(methoxymethoxy)-propane at 101.33 kPa

Isobaric vapor–liquid equilibrium (VLE) data have been measured for methanol+1-(methoxymethoxy)-propane and 1-propanol+1-(methoxymethoxy)-propane systems at 101.33kPa. The two binary systems present two minimum temperature azeotropes at 101.33kPa. Saturated vapor pressure data for the pure component of 1-(methoxymethoxy)-propane used in the VLE calculations was measured. The VLE measurements for two binary systems above were correlated by van Laar, Wilson, and Non-Random Two Liquids (NRTL) models. The corresponding binary interaction parameters for three models were also obtained. By comparing the experimental value with the calculation value, the results showed that the measured data of two binary systems above were well correlated by the Wilson and NRTL models, respectively.

Bubble-Point Measurements of n-Butane + n-Octane and n-Butane + n-Nonane Binary Mixtures

Mixtures of small gaseous hydrocarbons with longer chain hydrocarbons are of interest to the natural gas industry as well as other industries in which separations are critical. In particular, binary mixtures of n-nonane are of interest, because n-nonane was recently incorporated into the GERG-2008 equation of state, but there is little experimental vapor–liquid equilibrium (VLE) data available to support the equation. The bubble-point pressures of four compositions of each of the binary mixtures n-butane + n-octane and n-butane + n-nonane were measured over the temperature range of 270 to 370 K. The data and the expanded uncertainty (at a 95 % confidence level, k = 2) of each point are reported. Additionally, the data are compared to existing literature data for the n-butane + n-octane and the GERG-2008 equation for both systems. This is the first report of vapor–liquid equilibrium measurements on n-butane + n-nonane binary mixtures.