Vapor–liquid–liquid Equilibrium Research Articles

Computer Simulation of Three-Phase Equilibria for Some Water/n-Alkane Binary Systems.

In this work, the vapor-liquid-liquid equilibrium (VLLE) of the water/n-pentane, water/n-hexane, water/n-octane, and water/n-decane binary systems is calculated by computer simulation using the NVT-Gibbs ensemble (in the version of three simulation boxes) combined with the configurational bias Monte Carlo method. The combination of both methods, the molecular potential models used, and the simulation details allowed us to calculate the triphasic equilibrium properties of the systems studied: the densities of the three phases in equilibrium, their compositions, and potential energies. In previous works, these simulations were not carried out at a temperature range nor water/n-alkanes systems simulated in this work, probably because they are highly nonideal systems; so, to the best of our knowledge, this is the first time that this phenomenon is studied in detail. The results from VLLE simulations of the water/n-pentane system for temperatures from 343.2 to 435 K, the water/n-hexane system for temperatures from 373.11 to 473.15 K, the water/n-octane system for temperatures from 310.9 to 500 K, and for the water/n-decane system for temperatures from 374.15 to 525 K are reported here. The temperature range was selected in concordance with the experimental data available for an adequate study of the VLLE simulation results. The subcritical densities (vapor and liquid rich in n-alkane phases) at various temperatures fit well with the scaling law and the law of rectilinear diameters, allowing the estimation of upper critical end point temperature and density of the VLLE. The simulation results show a good prediction with experimental data reports in the literature.

Assessment and modeling of the isobaric vapor-liquid-liquid equilibrium for water + cyclopentyl methyl ether + alcohol (ethanol or propan-1-ol) ternary mixtures

The three-phase equilibria of water + cyclopentyl methyl ether (CPME) + ethanol or propan-1-ol ternary mixtures are explored from experimental determinations and theoretical modeling at a constant pressure (101.3 kPa), and over 350 K to 356 K. Experimental measurements are performed in a modified Guillespie phase equilibria dynamic cell, which includes an ultrasonic homogenizer. The reliability of the measured three-phase equilibria is validated by employing the Wisniak's L/W thermodynamic consistency test. The measured vapor-liquid-liquid equilibria (VLLE) data at 101.3 kPa are accurately predicted from the phase stability restriction coupled with the multiphase equilibrium criteria. The application of this combined approach is showcased as a thermodynamical tool to explore all possible phase equilibria regions (i.e., one-, two-, and three-phase), providing a robust representation of the multiphase equilibria. Both phase stability and the corresponding multiphase equilibria are calculated using the SAFT-VR-Mie EoS model (statistical associating fluid theory of variable range employing a Mie potential equation of state), where the association and polar nature of pure components and their binary interactions are explicitly considered.No ternary azeotropy is detected within the experimental range of stable VLLE for the water + CPME + ethanol ternary mixture, although the theoretical extrapolation of the experimental conditions using the SAFT-VR-Mie EoS suggests its existence. For the case of the water + CPME + propan-1-ol ternary mixtures, a stable VLLE with a heterogeneous ternary azeotrope is detected from the interpolation of the experimental determinations.The predicted heterogeneous ternary azeotrope supports use of the CPME as a potential entrainer candidate for dehydration of bio-alcohols (e.g., ethanol or propan-1-ol) as well as implying that the distillate products, bio-alcohols (ethanol or propan-1-ol) + CPME mixtures can be directly used as a renewable fuel without the need of additional separation stages.

Vapor-liquid-liquid equilibrium (VLLE), density, and viscosity of the ternary mixtures of normal hexane, water and bitumen at T=185–210°C and at P= 2.5 MPa

This paper presents a study on the vapor-liquid-liquid equilibrium (VLLE) of a ternary system consisting of normal-hexane (n-C6) as a solvent, water (H2O), and Mackay River bitumen. The study was conducted at temperatures ranging from 185 to 210 °C and a pressure of 2.5 MPa. The solvent/steam and solvent/bitumen ratios were varied to understand the effect of solvent (n-C6) on the phase behavior and the thermophysical properties of the associated phases. The co-injected solvent with steam is often reported as the concentration of solvent in the solvent/steam mixture. Two concentrations of n-C6 in n-C6/water mixture, including mole fractions of 0.01 and 0.05 (i.e., 6.85 and 27.70 vol.%), were considered to examine the effect of the co-injected solvent with steam. Also, two different mole fractions of n-C6 in the mixture of bitumen/n-C6 at 0.7 and 0.4 (37.45 and 14.61 vol.%), respectively, were considered to examine the effect of solvent solubility in bitumen. In addition to the VLLE study, the viscosity and density of the two distinct liquid phases, hydrocarbon-rich oleic and water-rich aqueous phases, were measured and reported. The results from the experiment infer that the concentration of n-C6 co-injected with steam does not significantly affect the equilibrium phase concentrations and thermophysical properties. However, the mixture showed liquid-liquid equilibria (LLE) instead of the vapor-liquid-liquid equilibria (VLLE) when the concentration of n-C6 in bitumen/solvent mixture was less than the equilibrium solubility of n-C6 in the hydrocarbon-rich phase at that operating condition. Furthermore, the results suggest that the presence of bitumen in equilibrium with n-C6 and H2O has no significant effect on the concentration of n-C6 in the vapor phase when compared with the n-C6/H2O binary mixture. Thermodynamic modelling of the VLLE data was performed using the cubic plus association equation of state (CPA EoS). The matching parameters were obtained by tuning the two-phase data, and those parameters were used in predicting the VLLE data. The model was also used to construct the phase regions of the solvent/bitumen/water system on the ternary diagram at different temperatures and pressures. Different phase regions were determined by phase stability analysis. The findings provide insight into steam/solvent condensation behavior with applications to the solvent-aided thermal recovery of bitumen from oil sands.

Artificial Neural Networks (ANNs) for Vapour-Liquid-Liquid Equilibrium (VLLE) Predictions in N-Octane/Water Blends

Blends of bitumen, clay, and quartz in water are obtained from the surface mining of the Athabasca Oil Sands. To facilitate its transportation through pipelines, this mixture is usually diluted with locally produced naphtha. As a result of this, naphtha has to be recovered later, in a naphtha recovery unit (NRU). The NRU process is a complex one and requires the knowledge of Vapour-Liquid-Liquid Equilibrium (VLLE) thermodynamics. The present study uses experimental data, obtained in a CREC-VL-Cell, and Artificial Intelligence (AI) for vapour-liquid-liquid equilibrium (VLLE) calculations. The proposed Artificial Neural Networks (ANNs) do not require prior knowledge of the number of vapour-liquid phases. These ANNs involve hyperparameters that are used to obtain the best ANN model architecture. To accomplish this, this study considers (a) R2 Coefficients of Determination and (b) ANN training requirements to avoid data underfitting and overfitting. Results demonstrate that temperature has a major influence on ANN vapour pressure predictions, while the concentration of octane, the naphtha surrogate having, in contrast, a lesser effect. Furthermore, the ANN data obtained allows the calculation of octane-in-water and water-in-octane maximum solubilities.

Vapor-liquid-liquid equilibria of binary and ternary aqueous systems containing C6-hydrocarbons

BackgroundTo develop process for separating water and C6-hydrocarbons, the vapor-liquid-liquid equilibrium (VLLE) data of the related mixtures are fundamentally important. MethodsThe isothermal vapor-liquid-liquid equilibrium (VLLE) data were measured for the binary and the ternary aqueous mixtures containing C6 hydrocarbons (benzene, n-hexane, and cyclohexane) at temperatures from 343 K to 383 K by using a modified static-type apparatus equipped with a visual cell. The VLLE data were correlated with the NRTL-HOC and the UNIQUAC-HOC models, respectively. Significant findingsIn addition to literature data, the experimental results of the binary systems reveal the temperature and molecular structure effects on the saturated compositions in three coexistent phases. The experimental ternary VLLE properties form a basis to verify the prediction by using the determined parameters of constituent binaries and also to modify the values of the binary parameters for improving the ternary VLLE calculations. The findings of this study offer new phase equilibria data for model development and process design for the related separation units.

Phase Behavior of Carbon Dioxide + Isobutanol and Carbon Dioxide + tert-Butanol Binary Systems

In recent years, the dramatic increase of greenhouse gases concentration in atmosphere, especially of carbon dioxide, determined many researchers to investigate new mitigation options. Thermodynamic studies play an important role in the development of new technologies for reducing the carbon levels. In this context, our group investigated the phase behavior (vapor–liquid equilibrium (VLE), vapor–liquid–liquid equilibrium (VLLE), liquid–liquid equilibrium (LLE), upper critical endpoints (UCEPs), critical curves) of binary and ternary systems containing organic substances with different functional groups to determine their ability to dissolve carbon dioxide. This study presents our results for the phase behavior of carbon dioxide + n-butanol structural isomers binary systems at high-pressures. Liquid–vapor critical curves are measured for carbon dioxide + isobutanol and carbon dioxide + tert-butanol binary systems at pressures up to 147.3 bar, as only few scattered critical points are available in the literature. New isothermal vapor–liquid equilibrium data are also reported at 363.15 and 373.15 K. New VLE data at higher temperature are necessary, as only another group reported some data for the carbon dioxide + isobutanol system, but with high errors. Phase behavior experiments were performed in a high-pressure two opposite sapphire windows cell with variable volume, using a static-analytical method with phases sampling by rapid online sample injectors (ROLSI) coupled to a gas chromatograph (GC) for phases analysis. The measurement results of this study are compared with the literature data when available. The new and all available literature data for the carbon dioxide + isobutanol and carbon dioxide + tert-butanol binary systems are successfully modeled with three cubic equations of state, namely, General Equation of State (GEOS), Soave–Redlich–Kwong (SRK), and Peng–Robinson (PR), coupled with classical van der Waals mixing rules (two-parameter conventional mixing rules, 2PCMR), using a predictive method.

The experimental investigation of the vapor-liquid-liquid and solid-liquid phase equilibrium for (difluoromethane + octafluoropropane) mixture

In this work, the solid-liquid equilibrium (SLE) and vapor-liquid-liquid equilibrium (VLLE) were studied in a cryogenic mixture of difluoromethane (R32) + octafluoropropane (R218). The SLE was measured by a calorimetric method, while the VLLE was measured by a vapor-phase recirculation method for this binary mixture at temperatures ranging from 203.150 to 237.151 K. This binary mixture does not show the common eutectic behavior, and the temperatures of the liquidus line were invariable at different mole fraction. The experimental VLLE data was analyzed by the polynomial and the rectilinear diameter methods to obtain the second liquid phase compositions coexisting in equilibrium. Both methods show good agreement with the experimental data. The liquid phase split was observed below the upper critical end point (UCEP), which is 237.791 K based on the polynomial methods. Beside, a solid-liquid-liquid equilibrium (SLLE) of R32 + R218 was inferred based on the experimental data, which is utilized to explain the unusual experimental data in mixed refrigerants.

VLLE of binary aqueous systems containing 2-butanol, isobutanol, or tert-amyl alcohol

Isothermal vapor-liquid-liquid equilibrium (VLLE) data were measured for water + 2-butanol, water + isobutanol, and water + tert-amyl alcohol at temperatures from 323.12 K to 373.16 K. A modified static-type apparatus equipped with a visual cell was used in the present study. The experimental results confirm that homogeneous azeotrope forms in water + 2-butanol and heterogeneous azeotrope forms in water + isobutanol and in water + tert-amyl alcohol. The VLLE data of the investigated binary systems were correlated well with the NRTL and the UNIQUAC models.

Phase equilibrium measurements and correlation for {tetrafluoromethane (R14) + propane (R290)} system

In this work, a study on the (vapour + liquid) equilibrium (VLE) and (vapour + liquid + liquid) equilibrium (VLLE) for the tetrafluoromethane (R14) + propane (R290) system was carried out using an apparatus based recirculation method at temperatures ranging from (173.150–212.470) K. The uncertainties of the composition, temperature, and pressure were less than 0.005, 5 mK and 2% or 0.0008 MPa, respectively. All of the experimental data were correlated by the Peng–Robinson equation of state (PR EoS) with the Modified Huron–Vidal second-order (MHV2) mixing rule involving the non-random two-liquid (NRTL) activity coefficient model. The results show good agreement with the experimental data, and the maximum root mean square deviations for (R14 + R290) system are Rp =0.0239 MPa, Rx = 0.009, respectively.

Modelling low pressure LLE and VLE of methanol/alkane mixtures with a modified Peng-Robinson EoS and the Huron-Vidal mixing rules

In this work, it is assessed the capabilities and limitations of a simple cubic EoS/GE thermodynamic model to describe the phase equilibria of methanol/alkane mixtures using generalized binary interaction parameters. In first place, the critical properties of the n-alkanes were selected to generalize the parameters of the model by fitting the liquid-liquid equilibria (LLE) of binary mixtures formed by methanol with pentane, heptane and decane respectively. Adequate description of the LLE coexistence curve can be obtained at atmospheric pressure for mixtures with n-alkanes in the 4-10 carbon number range. Also, it is possible to represent the mathematical behavior of the UCST of the methanol alkane series according to literature. Finally, some predictions were made for vapor liquid equilibria (VLE) and vapor-liquid-liquid equilibria (VLLE) conditions at low and high pressure. In general, predictions are unsatisfactory. In some cases, at low pressures, qualitative predictions for the azeotropic behavior can be obtained. In second place, a second set of generalized parameters were obtained by fitting the VLE of binary mixtures formed by methanol with propane, pentane and hexane. Using this new set, the model is capable to reproduce in qualitative way the high-pressure vapor-liquid equilibria of methanol/alkane mixtures between propane and decane. However, for LLE equilibria the results are inadequate from qualitative and quantitative points of view. Based on the results found in this work, it can be established that the selected model is not capable to describe simultaneously the VLE and LLE of methanol/alkane type mixtures reasonably with a single set of binary interaction parameters.

Molecular engineering of sustainable phase-change solvents: From digital design to scaling-up for CO2 capture

• Digital design and experimental validation of phase-change CO 2 capture solvents. • Evaluation of thermodynamics, reactivity, process and sustainability properties. • SAFT-γ Mie predicts entire three-phase envelope for S 1 N/DMCA + H 2 O + CO 2 . • Low regeneration energy, viscosity and vapour losses, high cyclic capacity. • Favourable health and safety performance compared to other solvents. Phase-change solvents promise reduced energetic and environmental footprints for separation systems, including absorption-based CO 2 abatement technologies. The search for efficient phase-change solvents is limited by challenges in vapour-liquid–liquid equilibrium (VLLE) prediction and in sustainability assessment. We overcome these with a digital approach to screen billions of structures and design the novel phase-change solvent S 1 N (N1-cyclohexylpropane-1,3-diamine) and mixture S 1 N/DMCA (N,N-dimethylcyclohexylamine). Screening criteria include thermodynamic and process-related properties, reactivity and sustainability of solvent production and use. VLLE phase envelopes are predicted using the SAFT-γ Mie (Statistical Associating Fluid Theory) equation of state thanks to its transferability to any structure and the implicit modelling of ionic species. Experimental validation confirms the suitability of S 1 N/DMCA for scaling-up, with a cyclic capacity of 1.19 mol CO 2 / kg-solvent, a regeneration energy of 2.3 GJ/ton-CO 2 , and vapour losses and viscosity lower by 10% and 70% than those of other solvents. S 1 N is also safer for plant operation and working personnel.

Isobaric vapor – liquid – liquid equilibrium for water + MTBE + alcohol (ethanol or 1-butanol) mixtures

Vapor – liquid – liquid equilibrium (VLLE) for water + MTBE + ethanol and water + MTBE + 1-butanol ternary systems have been measured in a modified dynamic Guillespie type cell at the isobaric condition of 101.3 kPa and over the temperature range from 325.6 to 328.9 K for water + MTBE + ethanol mixture and from 329.5 to 355.1 K for water + MTBE + 1-butanol mixture. The quality of the measured data is thermodynamically validated by the L/W Wisniak's consistency point- point test. According to the experimental results, the liquid – liquid equilibria are Type I for water + MTBE + ethanol mixture and Type II for water + MTBE + 1-butanol mixture. The VLLE for water + MTBE + ethanol mixture displays heterogeneous ternary azeotrope whereas the water + MTBE + 1-butanol mixture is a zeotropic ternary mixture. The experimental VLLE data for both ternary mixtures are correlated by a modified version of the nonrandom two-liquids (NRTL) activity coefficients model, which incorporates a ternary contribution. This ternary contribution reduces the global average absolute deviation from 5 % to 1.3 % for water + MTBE + ethanol mixture and from 3.1% to 1.9 % for water + MTBE + 1-butanol mixture.The experimental isobaric VLLE data of the ternary mixtures are also accurately modeled by applying the Peng–Robinson Stryjek–Vera equation of state appropriately extended to mixtures employing the modified Huron–Vidal mixing rule with the NRTL activity coefficient model. This model allows directly transferring the experimental excess Gibbs energy function to the EoS model for equilibrium calculation purposes. This theoretical framework shows that experimental VLLE data can be accurately predicted and provide a route to interpolate values of the phase equilibrium.

Efficient selection of conventional and phase-change CO2 capture solvents and mixtures based on process economic and operating criteria

The aim of this work is to exploit shortcut models in order to efficiently assess conventional and phase-change solvents and mixtures based on CO2 capture and upstream plant process and economic performance criteria. This is approached by exploiting a previously available shortcut model which is currently suitable only for solvents exhibiting vapor-liquid equilibrium (VLE) behavior. This model is extended to account for solvents which exhibit vapor-liquid-liquid equilibrium (VLLE), phase-change behavior and is implemented in 10 solvents and mixtures, including 2 phase-change solvents. The VLE behavior of conventional solvents and mixtures is represented using models obtained from literature or regressed from experimental data. The VLLE behavior of the phase-change solvents MAPA/DEEA (3-(methylamino)propylamine/2-(diethylamino)ethanol) and MCA (methyl-cyclohexylamine) is modelled through regression curves from experimental data. The performance criteria for solvent assessment include cyclic capacity, solvent flowrate and purchase cost, regeneration duty, net efficiency penalty and lost revenue of power plant from parasitic electricity due to capture. The performance of the phase-change solvents is validated based on literature data, whereas it is superior to that of conventional CO2 capture solvents. The net efficiency penalties of MCA and MAPA/DEEA are approximately between 2.9 and 3.3% points lower than MEA (monoethanolamine), whereas the lost revenue of the power plant due to the capture unit is 47% and 50% lower than MEA, respectively.

A Novel Experimental Procedure to Measure the Bulk Mass Densities and Interfacial Tensions for Mixtures at Vapor–Liquid–Liquid Equilibria

A new experimental methodology has been developed to measure bulk mass densities and interfacial tensions of mixtures at vapor−liquid−liquid equilibria (VLLE). This technique considers the use of a...

Multiphase equilibria of binary and ternary mixtures containing water, propylene glycol methyl ether, and propylene glycol methyl ether propionate

Vapor-liquid equilibrium (VLE) and vapor-liquid-liquid equilibrium (VLLE) data were measured for the binary and ternary systems of propylene glycol methyl ether (PGME) + propylene glycol methyl ether propionate (PGMEP), water + PGMEP and water + PGME + PGMEP using a static-type apparatus equipped with a visual cell under isothermal condition over a temperature range of 318.15 K–363.15 K. The phase equilibrium data of the binary systems are correlated well with the NRTL-HOC and the UNIQUAC-HOC models by using linearly temperature-dependent parameters. However, the ternary VLLE properties are unable to be estimated accurately only by using the parameters determined from the phase equilibrium data of the constituent binaries. The representation of the ternary VLLE properties can be substantially improved as the six model parameters are determined simultaneously from the ternary VLLE data.

Commissioning of the Cryogenic Phase Equilibria Test Stand CryoPHAEQTS

Medium-sized cryogenic applications such as local hydrogen liquefaction or HTS power applications require temperatures below 77 K at some kW cooling power. These conditions are efficiently reached by cryogenic mixed refrigerant cycles (CMRC). The CMRC development relies on physical property data of cryogenic fluid mixtures that is not available for most binary and multi-component systems. The cryogenic phase equilibria test stand CryoPHAEQTS provides precise physical property data of cryogenic fluid mixtures at temperatures from 15 K to 300 K and at pressures up to 150 bar. It also allows flammable mixtures (e.g. containing hydrogen) or oxidizing mixtures (e.g. containing oxygen). Vapor-liquid equilibria (VLE), vapor-liquid-liquid equilibria (VLLE) and the liquidus line of solid-liquid equilibria (SLE) are obtained by direct sampling from the equilibrium cell and analysis by gas chromatography. The equilibrium cell offers optical access by 4 windows to identify the coexisting phases. The cell temperature is set by a pulse-tube cryocooler and a counter-heater. As a unique feature, the specific heat capacity of the vapor phase in equilibrium is measured by the combination of a novel thermal and a Coriolis type flow meter. Having measured both caloric and thermal properties of the mixtures, we can develop new equations of state that cover all thermodynamic state variables. In this talk, we report on the progress in the construction and commissioning of CryoPHAEQTS. Validation of the measurement accuracy is presented by comparison of pure substances measurements against literature data.

Set-up of the cryogenic phase equilibria test stand CryoPHAEQTS

The design of processes using cryogenic fluid mixtures requires fluid property data, which is unavailable today. In particular, this data is crucial to develop cryogenic mixed-refrigerant cycles for high-temperature superconductor (HTS) applications and to further optimize hydrogen liquefaction processes. CryoPHAEQTS, which is currently being built at KIT, will provide physical property data for fluid mixtures in a temperature range of 15–300K and at pressures up to 15 MPa, including also mixtures with either flammable or oxidizing components (e.g. hydrogen, deuterium, oxygen). By direct sampling from an equilibrium cell, vapor-liquid equilibria (VLE) and vapor-liquid-liquid equilibria (VLLE) can be determined using gas chromatography. Solid-liquid equilibria (SLE) are measured using a calorimetric method. The measurement of heat capacities is implemented by combining two different flow measurement principles. In addition, the test stand offers optical access for a future upgrade with an optical measurement system that allows in-equilibrium measurements of both bulk transport properties by dynamic light scattering (DLS) and surface tension by surface light scattering (SLS).

Experimental measurement and assessment of equilibrium behaviour for phase change solvents used in CO2 capture

Phase change solvents are receiving increased attention in the effort to significantly reduce regeneration energy requirements in post combustion CO2 capture processes with chemical absorption. In this study, the phase behavior of various phase change, aqueous amine solutions, was experimentally investigated. A new experimental apparatus was developed and evaluated by determining the CO2 solubility in aqueous monoethanolamine (MEA) solutions at 40, 60 and 80 °C. Subsequently, new experimental data were obtained for aqueous solutions containing N,N-dimethylcyclohexylamine (DMCA), methylcyclohexylamine (MCA) and 2-amino-2-methyl-1-propanol (AMP) at 40, 60 and 90 °C that exhibit phase change behavior. It was observed that the investigated solutions present vapor – liquid equilibrium (VLE) at 40 °C and vapor–liquid-liquid equilibrium (VLLE) at 60 and 90 °C for CO2 partial pressures up to approximately 70 kPa. In addition, screening experiments were performed using sulfolane, which has been previously used for gas sweeting applications, instead of AMP in the DMCA-MCA mixture. However, such system presents relatively low CO2 solubility, compared to the aforementioned (DMCA-MCA-AMP) system and aqueous MEA solutions. Finally, additional screening experiments were performed for two aqueous DMCA – 3-methylaminopropylamine (MAPA) amine solutions at different concentrations.

Toluene/n-Heptane Separation by Extractive Distillation with Tricyanomethanide-Based Ionic Liquids: Experimental and CPA EoS Modeling

This work covers the phase equilibrium characterization of systems containing n-heptane, toluene, and two tricyanomethanide-based ionic liquids (ILs), 1-ethyl-3-methylimidazolium tricyanomethanide ([C2C1im][TCM]) and 1-butyl-4-methylpyridinium tricyanomethanide ([4-C4C1py][TCM]). Aiming at evaluating these ILs for the n-heptane/toluene extractive distillation, the vapor–liquid–liquid equilibria (VLLE) and vapor–liquid equilibria (VLE) were determined by headspace-gas chromatography (HS-GC) in the whole composition range at temperatures from 323.2 to 423.2 K and solvent to feed (S/F) ratios of 1, 5, and 10. Experimental results were modeled with the Cubic Plus Association (CPA) Equation of State (EoS). ILs’ molecular parameters were regressed through density and heat capacity data and further used to describe the binary and ternary mixtures phase equilibria. Extractive distillation with ILs stands as a powerful approach for the dearomatization of liquid fuels, whereas the combination of HS-GC methodology a...

Thermodynamic modeling of VLE and VLLE for the ternary system of 2,3,3,3-tetrafluoroprop-1-ene(R1234yf) + propane (R290) + 1,1,1,2-tetrafluoroethane(R134a) at 253.15 K-313.15 K

The excess Gibbs free energy-equation of state (GEEoS) models is presented based on the Peng-Robinson (PR) EoS combined with the Wong-Sandler (WS) mixing rule and the modified UNIFAC group contribution method (PR-WS-MUNIFAC). The average absolute deviation (AAD) of vapor phase mass fraction and the absolute average relative deviation (AARD) of pressure are 0.0047 and 0.53%, respectively, for R152a + R1234yf; 0.0064、0.0050 and 1.59%, respectively, for R32 + R125 + R134a. The VLE properties of the ternary mixture R1234yf + R290 + R134a as a drop-in replacement for R134a were predicted over the temperature range of (253.15–313.15 K) at 10 K intervals. The vapor–liquid-liquid equilibrium (VLLE) was qualitatively analyzed in theory, and the relevant phase equilibrium diagrams were constructed. The R290 + R134a system has clear characteristics of VLLE near the azeotropic point; the pressure of the upper critical end point (UCEP) is approximately 1.627 MPa. Liquid phase separation also exists in the ternary system of R1234yf + R290 + R134a.