Vapor-liquid Equilibrium Research Articles

Study on characteristics of wet compression-absorption refrigeration cycle with CO2-ionic liquid mixture

The novel wet compression-absorption (WCA) refrigeration cycle with CO2-ionic liquid mixture can bring a new solution for the development and promotion of CO2 in the refrigeration field, but the depressurization mechanism of this cycle still needs further research. Based on the vapor-liquid equilibrium data of CO2-[emim][Tf2N] mixture, the p-h diagrams of CO2-[emim][Tf2N] mixture with the specific global CO2 mole fraction were first calculated and constructed. The cycle flow of WCA refrigeration cycle with CO2-[emim][Tf2N] mixture was plotted on the diagram, the cycle characteristics and depressurization mechanisms of this cycle were analyzed. The results show that there is a temperature slip in the CO2-ionic liquid mixture during the absorption/desorption process. Both strengthening the effectiveness of cooling measures and increasing the proportion of ionic liquid in the mixture can further reduce the operating pressure at the high-pressure side, but the latter may cause a reduction in the cycle refrigeration performance and energy efficiency. For the WCA refrigeration cycle with CO2-ionic liquid mixture, it is crucial to equip an internal heat exchanger, which can significantly improve the corresponding refrigeration capacity and energy efficiency. This study can provide important references for the design and optimization of WCA refrigeration system using a CO2-ionic liquid mixture.

Modeling H2S solubility in aqueous MDEA, MEA and DEA solutions by the electrolyte SRK-CPA EOS

In this study, an electrolyte cubic plus association equation of state (e-CPA EOS) has been proposed to predict the vapor–liquid equilibrium of (H2S) in aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA). This EOS is composed of repulsive forces, short-range interactions, short-range ionic interactions, association term, long-range ionic interactions, and Born term. The Soave– Redlich– Kwong EOS is used as a non-electrolyte part. A new iterative procedure based on the Jacobi method is introduced to obtain the compositions of all species in the liquid phase. The genetic algorithm (GA) is used to find the optimal values of binary interaction coefficients between molecules and ions. Compared with experimental data, the e-CPA EOS model successfully describes the vapor–liquid equilibrium of H2S in the aqueous solutions of MEA, DEA, and MDEA. The average absolute deviations for 313 data of MEA-H2S-H2O, 156 data of DEA-H2S-H2O, and 145 data of MDEA-H2S-H2O systems were obtained as 8.20 %, 8.04 %, and 9.41 %, respectively. In addition, for some similar cases, the capability of the e-CPA EOS was compared with the Clegg–Pitzer, N-Wilson-NRF, e-NRTL, and e-CTS models. The results indicated that the e-CPA EOS has less error than the four other models.

Measurement of Isobaric Vapor-Liquid Equilibrium for Binary System β- Caryophyllene + Linalool and Eugenol + Linalool at 30 and 60 kPa

Measurement of Isobaric Vapor-Liquid Equilibrium for Binary System β- Caryophyllene + Linalool and Eugenol + Linalool at 30 and 60 kPa

A New Excess Free Energy Mixing Rule for Representing Vapor-Liquid Equilibria of Mixed Refrigerants

A New Excess Free Energy Mixing Rule for Representing Vapor-Liquid Equilibria of Mixed Refrigerants

Theoretical analysis of the three-stage phase transition process of alkane droplet under supercritical conditions

With the development of heavy-duty diesel engines, the in-cylinder ambient conditions of the diesel engine are well above critical points of the main components of the diesel fuel. Therefore, significant changes arise in the phase transition process of the liquid fuels. However, the entire phase transition process of the liquid fuels in such supercritical environments is not well understood compared with that under subcritical conditions. In this work, A high-pressure transient droplet evaporation model was presented for the theoretical analysis of phase transition processes of the heptane/dodecane/hexadecane-nitrogen binary system under supercritical conditions. Analysis of the thermodynamic pseudo-trajectories reveals that the alkane droplets will undergo a three-stage phase transition process when the ambient condition is much higher than the critical point of alkanes, including classical two-phase mode, transitional two-phase mode, and supercritical single-phase mode. The evaporation dominates the phase transition process in the classical two-phase mode, and the transition from classical two-phase modes to transitional two-phase modes occurs when gas-liquid interfaces deviate from the global thermal equilibrium. In transitional two-phase modes, a gas-liquid interface still exists and separates the liquid phase and vapor phase, but with a questionable adoption of vapor-liquid equilibrium. The transition from the transitional two-phase mode to the supercritical single-phase mode occurs when the thermodynamic state of the binary mixture in the interface reaches the critical mixing state. We distinguished the phase states for the whole phase transition process according to the thermodynamic analysis of binary systems. Analogous to the immiscible interface in classical two-phase mode, a miscible boundary layer containing supercritical fluids exits between the liquid core and gas in the initial period of the supercritical single-phase mode. The pseudo-boiling phenomenon occurs in this boundary layer.

Isothermal vapor–liquid equilibria of binary mixtures containing (methanol, or propan-1-ol, or water, or acetonitrile) and 1-ethyl-3-methylimidazolium thiocynate ionic liquid: Measurements and modeling

Ionic liquid vapor–liquid equilibrium (VLE) measurements were performed on binary systems for1-ethyl-3-methylimidazolium thiocynate [EMIM][SCN] (2) + {methanol, or propan-1-ol or water or acetonitrile}(1) at range temperatures between 273.15 and 363.15 K. Experiments were undertaken at pressures between 15 Pa and 255 kPa using a static device. The reported data were successfully correlated by means of two models, namely NRTL or COSMO-RS, and the PC-SAFT equation of state. While results obtained in this study indicate that the phase behavior of systems involving the ionic liquid and alcohols, water or acetonitrile can be accurately described by these three models, it was found that experimental data may be represented with higher accuracy with PC-SAFT than NRTL and COSMO-RS models.

Vapor–Liquid Equilibrium for Ethyl Acetate + Acetonitrile with Acetate-Based Ionic Liquids as Entrainers at 101.3 kPa and Analysis of the Separation Mechanism

Vapor–Liquid Equilibrium for Ethyl Acetate + Acetonitrile with Acetate-Based Ionic Liquids as Entrainers at 101.3 kPa and Analysis of the Separation Mechanism

Vapor–Liquid Equilibrium for Acetonitrile + Ethanol with Imidazole-Based Ionic Liquids as Entrainers at 101.3 kPa

Vapor–Liquid Equilibrium for Acetonitrile + Ethanol with Imidazole-Based Ionic Liquids as Entrainers at 101.3 kPa

Selective Vapor Condensation for the Synthesis and Assembly of Spherical Colloids with a Precise Rough Patch.

Patchy particles occupy an increasingly important space in soft matter research due to their ability to assemble into intricate phases and states. Being able to fine-tune the interactions among these particles is essential to understanding the principles governing the self-assembly processes. However, current fabrication techniques often yield patches that deviate chemically and physically from the native particles, impeding the identification of the driving forces behind self-assembly. To overcome this challenge, we propose a new approach to synthesizing spherical colloids with a well-defined rough patch on their surface. By treating polystyrene microspheres with vapors of a good solvent, here an acetone-water mixture, we achieve selective polymer corrugation on the particle surface resulting in a chemically similar yet rough surface patch. The key step is the selective condensation of the acetone-water vapors on the apex of the polystyrene microparticles immobilized on a substrate, which leads to rough patch formation. We leverage the ability to tune the vapor-liquid equilibrium of the volatile acetone-water mixture to precisely control the polymer corrugation on the particle surface. We demonstrate the dependence of patch formation on particle and substrate wettability, with the condensation occurring on the particle apex only when it is more wettable than the substrate, which is consistent with Volmer's classical nucleation theory. By combining experiments and molecular dynamics simulations, we identify the role of the rough patch in the depletion interaction-driven self-assembly of the microspheres, which is crucial for designing programmable supracolloidal structures.

Effect of glucose–citric acid deep eutectic solvent on the vapor–liquid equilibrium of an aqueous ethanol solution

Objectives. To study the effect of a deep eutectic solvent (DES) based on glucose and citric acid on the vapor–liquid equilibrium of an aqueous solution of ethanol.Methods. A qualitative and quantitative analysis of the conditions of vapor–liquid equilibrium in an ethanol–water–DES ternary mixture was performed based on the open evaporation method and the measurement of TPxy data using a Świętosławski ebulliometer. Since the volatility of the DES is negligible in comparison with that of water and ethanol, the composition of the vapor phase was measured by means of Karl Fischer titration. The conditions of vapor–liquid phase equilibrium were modeled using the UNIFAC model.Results. The open evaporation method was used to determine the curves of residual concentrations for the ethanol–water–DES mixture at various DES concentrations and compositions (glucose–citric acid ratios). TPxy data was obtained for the mixture produced by adding 30 wt % DES to an aqueous solution of ethanol at atmospheric pressure. Studies show that DES based on glucose and citric acid has a significant effect on the relative volatility of ethanol in aqueous solution, leading to the disappearance of the azeotropic point. This effect is due to only the presence of glucose. Citric acid does not change the composition of the equilibrium phases, but rather increases the solubility of glucose in aqueous ethanol solutions. This is especially important at high ethanol concentrations, since glucose is poorly soluble in ethanol.Conclusions. Addition of DES based on glucose and citric acid to an aqueous solution of ethanol leads to the disappearance of the azeotropic point. DES can thus be considered as a promising entrainer for extracting ethanol from aqueous solutions using extractive distillation. Modeling of the conditions of vapor–liquid equilibrium in the ethanol–water–DES system using the UNIFAC model showed a satisfactory level of accuracy. The error in the calculated data increases with increasing the glucose concentration, while remaining acceptable for practical use.

Experimental measurements and correlation of vapor–liquid equilibrium data for the difluoromethane (R32) + 1,3,3,3-tetrafluoropropene (R1234ze(E)) binary system from 254 to 348 K

In this study, we present new experimental data of vapor–liquid equilibrium for the binary system difluoromethane (R32) + 1,3,3,3-tetrafluoropropene (R1234ze(E)), measured at 273.14 and 363.32 K and at pressure ranging from 0.1568 to 4.3553 MPa. A “static-analytic”-type apparatus is used to do the measurements, with sampling of the equilibrium phases via capillary sampler (ROLSI®). We used three different models to correlate the data: 1) the Peng–Robinson cubic equation of state combined with the NRTL excess free energy model and Wong-Sandler mixing rules, 2) Helmholtz energy model like the one incorporated in REFPROP 10.0 software and 3) Predictive PPR78 model for which the new group parameter of R32 was adjusted. All of the three models show a very good agreement with the experimental data except for temperature higher that R32 critical temperature.

Vapor-liquid equilibrium and thermodynamic properties of saturated argon and krypton from Monte Carlo simulations using abinitio potentials.

Vapor-liquid equilibria and thermodynamic properties of saturated argon and krypton were calculated by semi-classical Monte Carlo simulations with the NpT + test particle method using abinitio potentials for the two-body and nonadditive three-body interactions. The NpT + test particle method was extended to the calculation of second-order thermodynamic properties, such as the isochoric and isobaric heat capacities or the speed of sound, of the saturated liquid and vapor by using our recently developed approach for the systematic calculation of arbitrary thermodynamic properties in the isothermal-isobaric ensemble. Generally, the results for all simulated properties agree well with experimental data and the current reference equations of state for argon and krypton. In particular, the results for the vapor pressure and for the density and speed of sound of the saturated liquid and vapor agree with the most accurate experimental data for both noble gases almost within the uncertainty of these data, a level of agreement unprecedented for many-particle simulations. This study demonstrates that the vapor-liquid equilibrium and thermodynamic properties at saturation of a pure fluid can be predicted by Monte Carlo simulations with high accuracy when the intermolecular interactions are described by state-of-the-art abinitio pair and nonadditive three-body potentials and quantum effects are accounted for.

Crystallization risk of aromatic compounds in LNG production. Part II: The solubility of p-xylene in methane-rich mixtures down to cryogenic temperatures

New measurements of solubility of solid p-xylene in solvents methane and (90%mol/mol)methane + (10%mol/mol)ethane have been carried out using a cryogenic apparatus and adopting a static-analytic method for temperatures from 273 K down to 128 K at nominal pressures of 3 and 6 MPa. Measured solid-liquid and solid-vapor equilibria have been compared to literature values of solubility of solid p-xylene in methane-rich phases and to modeling results obtained by coupling a cubic equation of state and a model for the solid phase. Results confirm the conclusions reported in our previous study of this system that evidenced of a non-monotonic variation of the solubility of p-xylene with temperature when crossing the critical region of the solvent and that binary interaction parameters regressed on vapor-liquid equilibrium can be used for predicting the solubility at cryogenic conditions.

Isothermal (vapor ＋ liquid) equilibrium measurements and correlation of the binary mixture 3,3,3-trifluoropropene (R1243zf) ＋ isobutane (R600a) at temperatures from [formula omitted] to [formula omitted] K

The restrictions set by the F-gas Regulation and the Kigali Amendment to the Montreal Protocol have pushed an extensive research into alternatives for fluorinated greenhouse gases in air conditioning and refrigeration. Hydrofluoroolefins (HFOs) are emerging as promising substitutes for hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) in HVAC and refrigeration. Amongst these, R1243zf raised interests as low-GWP substitutes for R134a. The pursuit of low GWP refrigerants has also led to the examination of hydrocarbons (HCs), like propane (R290) and isobutane (R600a), due to their efficiency, low charge, and affordability, despite their flammability. The mixtures of R1243zf and isobutane could be of interest for medium temperature heat pump applications. Moreover, blending HFOs with HCs usually leads to azeotropic mixtures. While HCs benefit of a wide range of data and reliable Equations of State (EoS), HFOs, and in particular their mixtures, lack comprehensive information. This study reports vapor–liquid equilibrium (VLE) measurements for the 3,3,3-trifluoropropene (R1243zf) + isobutane (R600a) binary system in the temperature range between 283.15 K and 323.15 K. The measurements have been carried out by means of a vapor-recirculation apparatus combined with gas-chromatographic analysis. This work reports 53 experimental data with an expanded uncertainty (k=2) of 0.003 mol mol−1. The reported data, along with the data available in the literature, have been used to developed two new mixture models based on the Helmholtz free energy EoS, both leading to a significant improvement in the VLE prediction, with RMSE values lower than 0.005 mol mol−1 for both the liquid and the vapor phase composition.

Superancillary Equations for the Multiparameter Equations of State in REFPROP 10.0

Superancillary equations have been developed for the recommended (by NIST) multiparameter equations of state (EOS) for all 147 pure fluids in NIST REFPROP 10.0. These superancillary equations represent the orthobaric densities and saturation pressure of the EOS as a function of temperature by Chebyshev expansions to an accuracy better than the iterative calculations in REFPROP and are hundreds to thousands of times faster to evaluate than a full iterative solution of Maxwell’s criteria. The C++ code required to develop and test the superancillary equations is provided as open-source material. The methodology is straightforwardly extensible to new multiparameter EOS, establishing a new paradigm for the evaluation of vapor–liquid equilibria for pure fluids.

Analysis of Vapor–Liquid Equilibrium in Ternary Systems for an Adequate Planning of Their Experimental Determination and Correlation

Analysis of Vapor–Liquid Equilibrium in Ternary Systems for an Adequate Planning of Their Experimental Determination and Correlation

Study on separation of methanol and dimethyl carbonate azeotropic system with deep eutectic solvents

Dimethyl carbonate (DMC) is an important diesel and gasoline additive that is also a low-toxic and environmentally friendly chemical raw material. However, it will form an azeotrope with methanol (MeOH) during the actual chemical production process. Therefore, separating high-purity DMC from the azeotrope is of significance. In extractive distillation, deep eutectic solvents (DESs) have demonstrated superior separation performance as green extractants. This study calculated the σ-profiles of DMC, MeOH, and DESs by the COSMO-SAC model to examine the most appropriate DES for the MeOH and DMC separation. Eventually, DES1(1:2 choline chloride (ChCl): malonic acid (MA)), DES2(1:2 ChCl: urea), DES3(1:2 ChCl: glycerol (G)), DES4(1:2 ChCl: ethylene glycol (EG)), DES5(1:2 ChCl: pyruvic acid (PA)) were designated as preferred extractants. The vapor pressures of five DESs at different temperatures were determined using a thermogravimetric analyzer, while their critical properties, normal boiling points, and acentric factors were predicted. The vapor–liquid equilibrium (VLE) data measured for DMC + MeOH + DESs ternary systems at 101.3 kPa showed that the addition of 15 mol % of any of the five DESs could successfully break the azeotrope and DES2 achieved a higher degree of separation in the MeOH-DMC binary azeotrope compared to the other DESs evaluated. The binary interaction parameters between MeOH/DMC and DESs were calculated through the NRTL (Non-Random Two-Liquid) model, and the fitting results were found to be consistent with the experimental data. The mechanism of the MeOH-DMC separation by DES2 was elucidated through quantum chemical (QC) calculations. The improved independent gradient model (IGMH) and the theory of atoms in molecules (AIM) demonstrated that the stronger interaction between DES2 and MeOH molecules is the key for DES2 to break the azeotrope of the system.

Prediction of azeotropes position of refrigerant mixtures using the PHSC EoS

The work aims is predict the azeotropes' position in refrigerant mixtures using the Perturbed Hard Sphere Chain (PHSC) equation of state (EoS). The vapor-liquid equilibrium (VLE) of seventeen binary refrigerant mixtures has been correlated using two model-adjustable parameters. The results show that the proposed model can calculate the bubble and dew points of binary systems, accurately. The average ARD value of binary VLE calculations has been obtained 1.28 %. The azeotropes pressure and composition of binary mixtures have been predicted using the PHSC EoS with the average ARD values of 1.043 % and 2.23 %, respectively. The maximum relative deviation has been observed for R717+R125 systems with two azeotropes points; ARDx=12.2 %. The performance of the PHSC EoS has been evaluated by predicting the azeotropes position of ternary mixtures. The PHSC EoS results have been compared to three cubic-based EoSs containing the PR-vdW, PR-BM, and PR-MHV2-NRTL models. The results show that the PHSC EoS can predict the ternary VLE data and azeotropes position satisfactory. The relative absolute deviation does not exceed 1.7 % for the azeotropes pressure. The PHSC EoS can be used as a robust and efficient model for the prediction of the azeotropes' position in binary and ternary refrigerant mixtures. Prediction of azeotropic composition helps us to find promising refrigerant candidates in the pre-design stage of the desired apparatus.

Population Balance Equations for Reactive Separation in Polymer Upcycling.

Many polymer upcycling efforts aim to convert plastic waste into high-value liquid hydrocarbons. However, the subsequent cleavage of middle distillates to light gases can be problematic. The reactor often contains a vapor phase (light gases and middle distillates) and a liquid phase (molten polymers and waxes with a suspended or dissolved catalyst). Because the catalyst resides in the liquid phase, middle distillates that partition into the vapor phase are protected against further cleavage into light gases. In this paper, we consider a simple reactive separation strategy, in which a gas outflow removes the volatile products as they form. We combine vapor-liquid equilibrium models and population balance equations (PBEs) to describe polymer upcycling in a two-phase semibatch reactor. The results suggest that the temperature, headspace volume, and flow rate of the reactor can be used to tune selectivity toward the middle distillates, in addition to the molecular mechanism of catalysis. We anticipate that two-phase reactor models will be important in many polymer upcycling processes and that reactive separation strategies will provide ways to boost the yield of the desired products in these cases.

Modelling of pure refrigerant thermodynamic properties and vapor-liquid equilibrium of refrigerant mixtures with the UMR-PRU model

In this work, the UMR-PRU model is extended to refrigerant mixtures. Key properties of pure refrigerants, such as vapor pressure, saturated volume, heat capacity and enthalpy of vaporization are examined with the Peng-Robinson equation of state, to which UMR-PRU reverts for pure components, and appropriate modifications to the attractive and repulsive terms are made. For the extension of UMR-PRU to refrigerant mixtures, four new UNIFAC groups are introduced and binary UNIFAC interaction parameters are fitted to experimental vapor-liquid equilibrium data. The predictive capability of the model is tested in ternary refrigerant mixtures. A comparison is made between UMR-PRU and the REFPROP model, which is currently considered as the state-of-the-art model for refrigerants. The results reveal that UMR-PRU describes the vapor-liquid equilibrium of refrigerant mixtures with similar accuracy as REFPROP. Both models are also employed for performing process simulations of vapor compression refrigeration cycles, yielding very comparable results regarding the COP and mass flowrate of the working fluid.