Experimental Vapor-liquid Equilibrium Data Research Articles

Vapor-liquid equilibrium data for the binary system isopropanol+water at 60 kPa and 80 kPa

In this work, experimental Vapor-Liquid Equilibrium (VLE) data for the Isopropanol + Water system under vacuum conditions at 60 kPa and at 80 kPa, for which no experimental evidences have been found in the literature, are reported. The experimental investigation of the isobaric equilibrium has been carried out by GASP at the Process Thermodynamics laboratory (PT lab) of Politecnico di Milano by employing an all-glass dynamic recirculation still. The collected experimental data, together with those already available in the literature at other conditions, have been used for the evaluation of the thermodynamic model that best fits the data. Four different models have been considered and their performances have been checked through the calculation of the Absolute Average Deviation (AAD%). The lowest AAD% has been found for the UNIFAC model only for isobaric data, not for the isothermal points. The regression tool available in Aspen Plus® V14 has been used to fit the binary interaction parameters of the NRTL activity model.

Experimental isochoric apparatus for bubble points determination: Application to CO2 binary mixtures as advanced working fluids

Carbon dioxide binary mixtures are increasingly considered as working fluids in transcritical power cycles, due to the capability to perform liquid-phase compression even at high environmental temperatures. However, a robust thermodynamic model is essential for optimal and reliable design conditions. It is widely recognised that fine-tuning the equation of state with experimental vapour-liquid equilibrium data of the mixture significantly enhances its reliability.In this work, a new apparatus dedicated to vapour-liquid equilibrium measurements of mixtures is presented. The proposed method consists of a constant-volume system, where bubble points are identified from the divergence of slope of the isochoric lines between the two-phase and liquid regions, in the temperature-pressure plane. The temperature and pressure limits of the apparatus are 503 K and 25 MPa.Bubble points of CO2 binary mixtures with hexafluorobenzene (C6F6) and n-pentane (C5H12) have been measured and compared with previous literature data for validation purposes. Then, the CO2 mixture with octafluorocyclobutane (c-C4F8) is experimentally studied, addressing a literature gap in bubble point data. The data are used to calibrate the thermodynamic model, leading to affordable design conditions of the power cycle compared to the non-optimised thermodynamics scenario, in a concentrated solar power tower plant.

Energy-saving extractive distillation system using o-xylene as an entrainer for the high-purity separation of dimethyl carbonate/methanol azeotrope

The pressure-swing distillation traditionally used in the industry for separating dimethyl carbonate/methanol (DMC/MeOH) commonly suffers from high energy consumption and challenges in achieving high-purity separation due to the existence of pinch zone. Hence, energy-saving extractive distillation system is explored to achieve the high-purity separation of DMC/MeOH azeotrope. With the analyses of isovolatility and residue curve maps based on Wilson model calibrated by vapor–liquid equilibrium experimental data, an extractive distillation process using O-Xylene (OX) as the most suitable entrainer were modeled and experimentally validated. Furthermore, design, optimization, and comparison of an extractive distillation process and a pressure-swing distillation process for producing 10000 t DMC/a are investigated. It is demonstrated that the extractive distillation process presents significant economic and emission advantage, specifically with 34.66 % and 26.95 % reductions in operating cost (OC) and in total annual cost (TAC) respectively, as well as 42.53 % reduction in CO2 emissions. This work should provide a feasible and promising approach to energy saving, low-carbon, and high-purity separation of DMC/MeOH azeotrope.

Separation of n-propanol - n-propyl acetate azeotropic system by extractive distillation with ionic liquids: COSMO-RS prediction, experimental investigation and quantum chemical calculation

During the preparation of n-propyl acetate (NPAC), an azeotropic mixture of NPAC and n-propanol (NPA) will form inevitably, which is difficult to separate by ordinary distillation. In this work, COSMO-RS model was applied to screen appropriate ionic liquids (ILs) to separate the binary azeotrope of NPAC - NPA. 1-decyl-3-methylimidazolium acetate ([DMIM][Ac]), 1-octyl-3-methylimidazolium acetate ([OMIM][Ac]), and 1-hexyl-3-methylimidazolium acetate ([HMIM][Ac]) were selected as entrainers based on solvent capacity and selectivity. The vapor–liquid equilibrium (VLE) data of the binary system (NPA - NPAC) and the ternary system (NPA - NPAC - IL) were measured at atmospheric pressure. The thermodynamic consistency of VLE data was verified by van Ness test and Wisniak's L-W test. The NRTL (non-random two liquids) model was used to correlate the VLE experimental data and obtained good applicability. The experimental results demonstrated that all three ionic liquids can improve the relative volatility of NPAC to NPA, and the separation effect is more obvious with the increase of ionic liquid content. The separation performance order of three ionic liquids follows: [HMIM][Ac] > [OMIM][Ac] > [DMIM][Ac]. Finally, ESP analysis, mutual penetration analysis, and IGMH analysis plus QTAIM topological analysis were used to explore the mechanism of separation. The analysis results indicate that the interaction between ionic liquids and NPA is stronger than that between ionic liquids and NPAC. In addition, the stronger interaction between [DMIM][Ac] and NPA is due to their strong hydrogen bond (HB) interactions.

Vapor-liquid equilibrium measurement for carbon dioxide (CO2)+propylene (R1270) binary mixture at temperatures from subcritical to supercritical

CO2-based binary mixtures have good performance and environmental friendliness, which are considered a good choice for working fluid in cooling and power cycles. Analyzing the properties of the vapor-liquid equilibrium is used to calculate the enthalpy and entropy of the dew and bubble point, which are fundamental parameters of thermodynamics. In this study, we measure the vapor-liquid equilibrium experimental data of CO2-propylene mixture by static thermostatic analysis experimental system. The working fluids in this state are repeatedly collected from the equilibrium cell to the gas chromatograph by the two electromagnetic capillary samplers to analyze the molar fractions. The maximum pressure deviation and maximum relative pressure deviation of the saturation vapor pressure of propylene are -0.004 MPa and -0.38%, respectively. We measure 5 sets of isotherms from 283.73 to 323.72 K, two of which are supercritical temperatures (313.73 K and 323.72 K). The pressure is up to about 6.4 MPa. The standard experimental uncertainties of mole fractions, pressure, and temperature are within 0.004, 0.002 MPa, and 0.06 K, respectively. The association model (the Peng-Robinso equation incorporating the Wong-Sandler mixing rule and the Non-Random Two-Liquid model) is used to fit the obtained vapor-liquid equilibrium data. The value of the average absolute relative deviation of pressure (AARDp) and the average absolute deviation of vapor phase molar fractions of component 1 (AADy1) is 0.29 % and 0.0062, respectively. The relative volatility under the five isotherms is also calculated, and most of the experimental data were within ± 5 % deviation.

Vapor-Liquid Equilibrium in the Acetic Acid-Ethanol-Ethyl Acetate-Water Quaternary System: Critical Literature Review and Thermodynamic Consistency of the Experimental Data

This study presents a critical review of the experimental vapor-liquid equilibrium (VLE) data for the quaternary acetic acid-ethanol-ethyl acetate-water system and its subsystems that are reported in the literature. The thermodynamic consistency of the VLE data were verified using two integral tests: the Redlich–Kister test and the direct integration of the Gibbs–Duhem equation. The VLE data were correlated using the NRTL equation for further integration. Additionally, the reliable value of the integral derived from the direct integration of the Gibbs–Duhem equation for multicomponent systems under isothermal-isobaric conditions was estimated. This integral can be used for testing the thermodynamic consistency of experimental VLE data.

Vapor-liquid phase equilibria behavior prediction of binary mixtures using machine learning

Basic thermodynamic data plays an important role in chemical applications. However, the traditional acquisition of thermodynamic data through experiments is laborious. Thermodynamic data prediction is considered as an alternative to the experiments, especially when qualitative analysis is needed prior to experimental studies. In this work, we report a successful machine-learning based approach to predict the fundamental thermodynamics characteristics of vapor–liquid equilibrium (VLE). A new dataset of the VLE experimental data of 210 binary mixtures with screened descriptors was constructed. The obtained results show that the VLE characteristics of the target system can be fully revealed by machine learning methods and random forest has more excellent predictive ability on the VLE behavior than the neural network. This work provides a new approach to the prediction of VLE data and useful information for the mechanistic study on the VLE phenomenon.

High-pressure vapor-liquid equilibrium of hydrogen and diesel components: Maximum likelihood implicit estimation of equation-of-state binary parameters

Due to increasing environmental requirements and efforts to improve fuel quality, hydro-processing has attained worldwide importance as a critical oil refining operation. Hydro-processing involve hydrogenation of oil fractions and subsequent separations at high-temperature, high-pressure and high hydrogen fugacity. Thus, effective thermodynamic modeling of hydro-processing systems allows accurate vapor and liquid property calculation to solve mass-energy hydro-processing balances. In this work, experimental data of high-pressure vapor-liquid equilibrium of binary systems consisting of hydrogen and Diesel hydrocarbons were compiled and used to statistically calibrate classical cubic equations-of-state and variants with different alpha functions. To accomplish this, the Maximum Likelihood Principle was used to conduct the implicit estimation of binary interaction parameters of hydrogen and each one of 22 hydrocarbons (paraffin, naphthenic and aromatic hydrocarbons) typical of Diesel fractions. Several statistical estimators were used to evaluate the estimated parameters as well as to test the insertion of a second binary interaction parameter or temperature dependence. In general, the FT Equation-of-State – i.e., the Peng-Robinson Equation-of-State using Fu & Tan alpha function for hydrogen – attained the best adherence to data and this adherence is improved by using two binary interaction parameters per pair or imposing temperature-dependence on the binary interaction parameter.

Separation of near-boiling mixtures (acetic acid and water) enhanced by ionic liquid

Acetic acid aqueous solution is a common and typical near-boiling mixture in the petroleum, chemical, polymer, pharmaceutical and food industries. Because of the large number of ideal plates for separating acetic acid and water by ordinary distillation, the energy consumption and production cost are high. Designable ionic liquids (ILs) and deep eutectic solvents (DESs) are environmentally-friendly entrainers for extractive distillation. Many azeotropic systems enhanced by adding ILs or DESs have been studied, but the near-boiling water/acetic acid system is rarely discussed.In this study, an IL 1,2,3-trimethylimidazolium dimethylphosphate ([TMIM]+[Me2PO4]−) with easy synthesis, low production cost and good thermal stability was employed as the rectification entrainer for water/acetic acid system, while the DESs were easy to react in acetic acid aqueous solution and was abandoned. First, the relative volatility of water (1) and acetic acid (2) at the more difficult separation point (x1′ = 0.9) was measured using a modified Othmer still at 101.32 kPa. When the mole fraction of entrainers was 0.071, these relative volatilities were 2.80 (n,n-dimethylformamide), 2.88 (1-methyl-2-pyrrolidinone), 4.82 ([TMIM]+[Me2PO4]−) respectively. The separation performance of [TMIM]+[Me2PO4]− was 67% higher than that of 1-methyl-2-pyrrolidinone. Then, the effect of [TMIM]+[Me2PO4]− concentration on the relative volatility was investigated. The relative volatility was dramatically increased from 1.60 to 6.85 with 0–0.103 mol fraction of [TMIM]+[Me2PO4]− and was 4.28 times that in an IL-free system. After that, isobaric vapor–liquid equilibrium (VLE) data of water + acetic acid, water + [TMIM]+[Me2PO4]− and water + acetic acid + [TMIM]+[Me2PO4]− ([TMIM]+[Me2PO4]− at ∼ 5, 15, and 25 mass%) systems were determined at 101.32 kPa. Also, Based on the chemical theory and Hayden–O’Connell method, the binary energy parameters of the NRTL (Non-Random-Two-Liquid) model for these systems were regressed and the predicted values were found to fit the experimental VLE data quite well..For the first time, we have found that [TMIM]+[Me2PO4]− as an entrainer is superior to conventional volatile solvents for water/acetic acid distillation in terms of performance, which provides more choices and imagination for industry. At the same time, it promotes understanding of the influence of IL structure on water/acetic acid separation performance, and is also an important inspiration for the distillation of other near-boiling systems.

Modeling of the Vapor-Liquid Equilibria Properties of Binary Mixtures for Refrigeration Machinery

The presence of both critical and azeotropic states in the vapor-liquid equilibria (VLE) is a very important issue in the chemical and refrigeration engineering. The knowledge of the phase behavior (subcritical phase/supercritical phase) of refrigerant allows designing and optimizing the refrigeration industrials processes. However, it is rare to find data for this information, which poses a great challenge for researchers to develop predictive and correlative thermodynamic models. The present study proposes the computation of the compositions and pressures of critical and azeotropic points of the isothermal VLE as well as the correlation of experimental VLE data. Firstly, experimental data (PTxy) was used to predict the vapor-liquid phase of both critical and azeotropic behaviors and to determine their properties using the relative volatility model. Secondly, the thermodynamic model (PR-MC-WS-NRTL) was applied to correlate the data of the binary refrigerant systems and describe their isothermal (VLE) behavior. The results proved that there is good agreement between predicted values obtained by the developed model and the experimental reference data. The relative error of both critical and azeotropic properties does not exceed 4.3 % for the molar fraction and 7.5 % for the pressure using relative volatility model. On other hand the relative deviation is respectively less than 2.60 % and 2.58 % for the liquid and vapor mole fractions using (PR-MC-WS-NRTL) model. This shows the ability of these models to give a reliable solution to predict and modulate the phase behavior of the binary refrigerant systems.

Isothermal (Vapour + Liquid) Equilibrium Measurements and Correlation of the Binary Mixture {3,3,3-Trifluoropropene (HFO-1243zf) + 2,3,3,3-tetrafluoropropene (HFO-1234yf)} at Temperatures from 283.15 K to 323.15 K

The many constrains introduced by the F-gas Regulation and the Kigali Amendment to the Montreal Protocol have resulted in an intense search for alternatives to fluorinated greenhouses gases for air conditioning and refrigeration purposes (Mota-Babiloni A, Makhnatch P, in Int J Refrig 127:101–110, 2021). With respect to the urge of new low-GWP and low-ODP refrigerants, blends composed of hydrofluoroolefins (HFO) are considered promising possible substitutes to hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) for HVAC&R applications (Sovacool et al., in Renew Sustain Energy Rev 141:110759), but thermophysical properties data for these blends are still scarce (Bell et al., in: J Chem Eng Data, 2021). In the present study, the vapor–liquid equilibrium (VLE) for the binary system (HFO-1243zf + HFO-1234yf), for which just one set of data on the VLE is available to date in literature, has been experimentally studied by means of a vapor recirculation apparatus. The measurements have been performed at isothermal conditions in the range of temperatures between 283.15 K and 323.15 K, while the composition of both the phases in equilibrium has been measured by gas-chromatographic analysis. The experimental VLE data have been correlated by two different equations of state (EoS): the Peng-Robinson (PR) EoS combined with Mathias–Copeman (MC) alpha function and van der Waals (vdW) mixing rules, and the Helmoltz EoS with dedicated binary interaction parameters. Correlated results showed a good agreement with the experimental data for the binary system.

Isobaric Vapor–Liquid Equilibria of Binary Systems Containing Oxygenated Biofuel Compounds (Ethanol + Cyclopentanone, Propyl Butanoate + 4-Methylphenol, Cyclopentanone + Propane-1,2-diol) at Atmospheric Pressure

The isobaric phase equilibrium data for the binary systems of ethanol + cyclopentanone, propyl butanoate + 4-methylphenol, and cyclopentanone + propane-1,2-diol at atmospheric pressure were measured using a modified distillation apparatus. The Herington and Van Ness tests were employed to confirm the thermodynamic consistency of the experimental data. In addition, the Wilson, NRTL, and UNIQUAC models were used to correlate experimental vapor–liquid equilibrium data. The corresponding binary interaction parameters (BIPs) for the three models, which are useful for the modeling and designing separation processes involving biofuel, were obtained using a maximum likelihood objective function. It has been confirmed that when appropriate BIPs are used in each model, the outputs are consistent with each other and with experimental data.

Experimental VLE Data of Binary Systems of Ester + Alcohol at 0.6 MPa. Verification using new Association Parameters for the Point– to–Point Test

Experimental data of vapor–liquid equilibria (VLE) are reported for the following binary systems: butyl acetate+ethanol, butyl acetate+1–propanol and butyl acetate+1–butanol at 0.6 MPa. No azeotrope was found in the butyl acetate+1–butanol system at 0.6 MPa. The thermodynamic consistency of the obtained data was analyzed using some equations of state (EOS) in the point–to–point test. The phase behavior was satisfactorily modelled using the Peng–Robinson EOS. The new association parameter of the Hayden–O’Connell method was determined from 144 pure substances and the influence of the second virial coefficient calculations in the point–to–point test was evaluated.

Prediction of the volumetric and vapor-liquid equilibrium properties of CO2-N2-O2-Ar fluid mixtures with a general Helmholtz equation of state

A general equation of state (EOS) explicit in the form of Helmholtz free energy has been developed to predict the pressure-volume-temperature-composition (PVTx) and vapor-liquid equilibrium (VLE) properties of the CO2N2O2-Ar fluid mixtures. The EOS, which uses four mixing parameters, is based on highly accurate EOS for pure CO2, N2, O2 and Ar fluids and contains a simple generalized departure function presented by Lemmon and Jacobsen (1999). Four mixing parameters are fitted from the experimental PVTx and VLE data of binary systems available. Comparison with experimental data available indicates that the EOS can reproduce the PVTx and VLE properties of CO2N2O2-Ar fluid mixtures up to 453 K and 1000 bar within or close to experimental uncertainties. The general EOS can be used to evaluate the change of density and VLE composition from impurities N2, O2 and Ar during the CO2 capture and sequestration process.

Vapour-liquid equilibrium for xylenes + tetrapropylene glycol binary systems: Experimental data and regression

In this study are reported vapour-liquid equilibrium (VLE) data for three binary systems such as xylenes + tetrapropylene glycol (TePG). These data have been measured in the temperature range (310.15 to 538.15) K for the systems involving o-xylene, m-xylene, p-xylene and TePG. The VLE experimental data were determined by using static equilibrium apparatus. The p-T-x data were regressed using the NRTL model with three, five and eight parameters. The results obtained using NRTL with eight parameters presents the smallest relative deviations of the calculated values for vapour pressure and composition compared to experimental values. A comparison was made using the T-x-y diagrams between the data obtained with the NRTL resulted parameters based on experimental VLE data and the data calculated using the UNIFAC predictive model.

New Experimental Vapor-Liquid Equilibria Data and Thermodynamic Modelling for R1234yf/propane/R32 as low-GWP Mixtures in Heat Pump Applications

This paper presents new experimental results for the Vapor – Liquid Equilibria of binary mixtures of R1234yf and propane at 277 and 313 K. The newly collected data are then used, in combination with other existing data retrieved from the literature, to calibrate the Peng-Robinson Equation of State with suitable accuracy for domestic vapour compression heat pump cycles simulations. After calibration, the Equation of State is applied to numerical simulations, in Aspen Plus, aimed at finding the optimal refrigerant composition, among ternary mixtures containing R1234yf, propane and R32. Results identify a Pareto curve where the optimal mixtures (with flammability lower or equal to A2L and GWP < 500) are represented in terms of two contrasting objectives: COP and the volumetric heating effect. Ternary mixtures containing propane and R1234yf respectively in the range 0÷12%mass and 18÷30%mass are Pareto optimal: the mixture with the best COP (2.7% lower than R410A one) is the binary pair R32 = 70% + R1234yf = 30%, a composition very close to the one of the commercial refrigerant R454B. On the other hand, the mixture with the largest volumetric effect (6.5% higher than R410A one) is the ternary blend R32 = 70% + R1234yf = 18% + propane = 12%. This study confirms that is quite challenging to find R410A replacements featuring at the same time reasonable heating capacity and a COP not lower than R410A one.

Vapor-liquid equilibrium of acid gases with imidazolium-based ionic liquids using the UMR-PRU model

The UMR-PRU group contribution equation of state (EoS), which couples the Peng-Robinson EoS with UNIFAC via the Universal Mixing Rules, is extended to pure imidazolium-based ionic liquids (ILs), as well as to their mixtures with CO2 and H2S. The studied ILs consist of alkyl-methylimidazolium cations and tetrafluoroborate, hexafluorophosphate and bis(trifluoromethylsulfonyl)imide anions. The EoS parameters of pure ionic liquids, are determined by fitting experimental vapor pressure and liquid density data. For the extension of UMR-PRU to binary CO2/IL and H2S/IL mixtures, the model parameters are determined by fitting experimental binary vapor-liquid equilibrium data of acid gases with ionic liquids. For comparison, the Peng-Robinson coupled with the conventional van der Waals one-fluid mixing rules (vdW1f) is also applied to the same systems, using adjustable attractive and co-volume cross interaction parameter. It is shown that Peng-Robinson accurately describes pure ionic liquid vapor pressures and liquid densities, while UMR-PRU yields very satisfactory vapor-liquid equilibrium results for binary and ternary mixtures containing ILs and acid gases. Overall, UMR-PRU yields much better results than Peng-Robinson coupled with the vdW1f mixing rules, which indicates the superiority of the UMR mixing rules over the vdW1f ones.

Simulation Study and Sensitivity Analysis of Gamma-Valerolactone Production from Ethyl Levulinate

Gamma-valerolactone (GVL) is emerging as a promising renewable fuel because it can be produced from renewable materials such as biomass. This article presents a conceptual design and simulation of the conversion of ethyl levulinate into GVL biofuel by hydrogenation process using ChemCAD 7.1.2 software. The process simulation method involves selecting a thermodynamic model, defining component chemicals, selecting suitable operating units and identifying operating conditions. The NRTL thermodynamic model was used for the liquid phase modeling and SRK for the vapor phase fugacity calculation. The binary interaction parameter of NRTL thermodynamic model was regressed from experimental vapor-liquid equilibrium (VLE) data. A sensitivity analysis of the effect of feed temperature on the GVL purification distillation column was carried out to obtain the optimum value for the distillation column configuration.

Thermodynamic modeling of adsorption at the liquid-solid interface

Adsorptive separation techniques are significantly energy efficient in comparison to conventional thermal separation techniques such as distillation. Despite extensive research and development activities undertaken for mixed-gas adsorption, the use of adsorption techniques for the separation of multicomponent liquid mixtures is still limited. A major barrier is the lack of accurate adsorption thermodynamic models, which form the scientific foundation of process simulation of such systems, making the translation to industrial scale challenging. In this work, we have rigorously computed the surface excess of adsorption for six binary liquid mixtures on silica gel at 303 K using the frameworks of the generalized Langmuir isotherm (gL) and the adsorbed solution theory (AST). The six binary liquid mixtures were formed by the pair-wise combinations of four components: benzene, 1,2-dichloroethane, cyclohexane, and n-heptane. We have based our calculations by considering simultaneous equilibria of three phases: saturated vapor phase, bulk liquid phase, and adsorbed phase. The composition of the corresponding saturated vapor phase was estimated by the Nonrandom Two-Liquid activity coefficient model and experimental vapor-liquid equilibria data. The activity coefficients of the adsorbed phase, the central issue of multicomponent adsorption thermodynamics, were calculated using the adsorption Nonrandom Two-Liquid activity coefficient model. Devoid of simplifying assumptions, gL and AST provide rigorous thermodynamic frameworks for adsorption equilibria of multicomponent liquid mixtures.

CO2 solubility modelling in Non-Precipitating aqueous solutions of potassium lysinate

Modelling of CO2 solubility in aqueous solutions of potassium lysinate (LysK) is mainly hindered by scarcity of experimental vapor–liquid equilibrium data and lack of chemical equilibrium constants associated to the reaction mechanism for the CO2/LysK/H2O system. Therefore, Kent-Eisenberg (KE) correlation stands out from the literature, being among the most used approaches for the description of the equilibrium CO2 partial pressure at different loadings. In this work, a Kent-Eisenberg-like approach has been developed, enhancing the empirical Kent-Eisenberg with Debye-Hückel activity coefficients in order to guide model calibration with reference to selected experimental data for CO2 solubility in 33.1 and 33.5 %w/w aqueous LysK solution; moreover, the KE edition provides an estimation of the missing equilibrium constants. This information has been embedded in a first thermodynamically sound and predictive Deshmukh-Mather (DM) model (average absolute deviation equal to 7 %) validated against additional experimental data in a wide temperature and concentration range.