Phase Equilibria Of Mixtures Research Articles

Experimental results for the vapor–liquid equilibria of (formaldehyde + 1,3,5-trioxane + methanol + salt + water) systems and comparison with predictions

The salt effect on the vapor–liquid phase equilibrium (VLE) of solvent mixtures is of significant interest in the industrial production of 1,3,5-trioxane. Experimental data for the VLE of quinary systems (formaldehyde + 1,3,5-trioxane + methanol + salt + water) and their ternary subsystems (formaldehyde + salt + water), (1,3,5-trioxane + salt + water), and (methanol + salt + water) were systematic measured under atmospheric pressure. The salts considered included KBr, NaNO 3 , and CaCl 2 . The extended UNIFAC model was used to describe the VLE of the salt-containing reactive mixtures. The model parameters were determined from the experimental VLE data of ternary systems or obtained from the literature, and then were used to predict the VLE of systems (1,3,5-trioxane + KBr + water), (methanol + KBr + water), (formaldehyde + KBr + water), and (formaldehyde + 1,3,5-trioxane + methanol + salt + water) with salt = KBr, NaNO 3 , and CaCl 2 . The predicted results showed good agreements with the measured results. Furthermore, the model was used to uncover the salt effect on the VLE of these multi-solvent reactive systems.

Predictions of thermodynamic properties and phase equilibria of refrigerant systems with COSMO approaches

The knowledge of the phase equilibrium of refrigerant mixtures is crucial for the optimization of the production processes of refrigerant molecules, and the design of energetic systems (heat pumps, Organic Rankine Cycles, …). In this work, different predictive thermodynamic models (COSMO-RS and COSMO-SAC-dsp) have been used to determine the phase behavior of mixtures of refrigerants involving alkanes, fluorinated and chlorinated compounds. The COSMO-RS model leads to rather satisfactory predictions of the vapor-liquid equilibria of mixtures and is able to capture the azeotropic behavior for most systems. However, the original COSMO-SAC model as well as the COSMO-SAC 2010 version lead to unsatisfactory predictions of VLE for these systems, as they are unable to predict the azeotropic behavior in alkane + refrigerants. By combining COSMO-SAC with a dispersion term (COSMO-SAC dsp model) and readjusting the universal parameter for the F atom, it is possible to get very satisfactory predictions of similar accuracy as COSMO-RS. In order to predict the phase behavior at high pressure, the COSMO-SAC-dsp model can be combined with the Peng-Robinson equation of state and the MHV1 mixing rule. Excellent predictions of relative volatilities can be obtained with this approach over wide temperature and pressure ranges. COSMO calculation can also be used to predict saturated liquid densities, vaporization enthalpy and boiling points of pure refrigerants.

Wide-ranging prediction of phase behavior in complex systems by CP-PC-SAFT with universal kij values. I. Mixtures of non-associating compounds with [C2mim][EtSO4], [C4mim][MeSO4], and [C2mim][MeSO3] ionic liquids

This study shows that the inter-relations between critical constants can explain various phenomena occurring in the ionic liquids (IL) systems, such as the higher solubility of aromatic compounds and the differences between solubilities in the specific ILs. Indeed, as the critical constants get more remote, the systems become more asymmetric, increasing thus the immiscibility gaps. The Critical Point-based Perturbed-Chain Statistical Association Fluid Theory (CP-PC-SAFT) EoS rigorously obeys the Tc and Pc of ordinary substances. Moreover, its high precision in modelling the liquid phase properties yields realistic estimations of the imaginary critical constants of ILs. Such features attach an enhanced predictive capacity to this model, even while neglecting the complex chemical background of ILs. Although the substantial disagreements between different sources allow examining the general truthfulness of predictions rather their quantitative precision, it is demonstrated that using the universal value of k12 = 0.027 obtained for just one of the VLE datasets, CP-PC-SAFT realistically predicts various phase equilibria in mixtures of non-reacting gases, n-alkanes, aromatic hydrocarbons, ethers, ketones and haloalkanes with the considered ILs. The accuracies of these predictions are comparable with the widely implemented COSMO-RS approach. However, unlike it, CP-PC-SAFT can be applied for estimating high-pressure phase equilibria and it provides accurate predictions of volumetric data of mixtures in the particularly wide range of conditions.

Phase equilibria of binary and ternary polymer solutions using modified UNIQUAC-based local composition model

In the present research, a modification on UNIQUAC activity coefficient model was done based on the local composition concept. The model was applied for binary and ternary systems containing different polymers and protic solvents. The newly modified model was compared with several local composition models such as Wilson, NRTL, UNIQUAC, polymer-NRTL, UNIQUAC-LBY and UNIQUAC-DMD in vapor–liquid. Also, comparison of the model with NRTL, UNIQUAC and UNIQUAC-LBY was done for liquid–liquid equilibrium data. In the presented model, a Freed-FV term was added to activity coefficient expression to consider the free volume effects in the mixture. Also, new surface and volumetric structural parameters were applied for studied alcoholic and aqueous solutions. AARD % of the new model (known as M-UNIQUAC-LBY model) was 1.98% for 28 vapor–liquid equilibrium data set (314 data points) of binary polymer–solvent systems. Moreover, RMSD % of 14 studied liquid–liquid systems in equilibria (155 tie-lines) was equal to 10.6431. The results of presented model were superior to previously presented ones in both VLE and LLE. Therefore, it can be successfully utilized to predict phase equilibria in mixtures, which contain pertinent components for industrial applications.

Solid–Liquid Phase Equilibrium and Phase Behaviors for Binary Mixtures Composed of Tripalmitoylglycerol (PPP), 1,3-Dipalmitoyl-2-oleoyl-glycerol (POP), and 1,2-Dioleoyl-3-palmitoyl-glycerol (POO)

The crystallization and melting behaviors of binary tripalmitoylglycerol (PPP)/1,2-dioleoyl-3-palmitoyl glycerol (POO), tripalmitoylglycerol (PPP)/1,3-dipalmitoyl-2-oleoyl glycerol (POP), and 1,3-d...

Phase Equilibrium of Reaction Mixtures for the Production of Epichlorohydrin in the Presence of Solvents

An alternative solvent for the production of epichlorohydrin via the epoxidation of allyl chloride with an aqueous hydrogen peroxide solution over a heterogeneous catalyst based on a granulated titanium-containing zeolite has been selected. The problem of replacing toxic methanol with other solvents, which provide, in particular, a simplification of the separation flowsheet, has been solved. Five water–allyl chloride–epichlorohydrin–solvent–heavily boiling fraction five-component systems have been studied (methanol, ethanol, propanol-1, propanol-2, and butanol-1). A thermodynamic topological analysis of phase equilibrium diagrams and an assessment of the possibility and feasibility of separating the mixtures via a method based on a combination of distillation and splitting have been conducted. The most promising solvent for the allyl chloride epoxidation reaction is propanol-2.

Phase Equilibrium of Binary Mixture for the (propylene oxide + 1-pentanol) System at Several Temperatures

Phase Equilibrium of Binary Mixture for the (propylene oxide + 1-pentanol) System at Several Temperatures

THE DEVELOPMENT OF A BASIC PROCESS SCHEME FOR THE PREPARATION OF ISOAMYL ACETATE

The article reports the development of a technological scheme for isoamyl acetate preparation on the basis of kinetic data, vapor-liquid and liquid-liquid equilibrium data. A review of isoamyl acetate production methods was made. At present most of the methods are based on esterification reaction, which takes place in the presence of homogenous and heterogeneous catalysts. Heterogeneous catalysis is preferred because of absence the catalyst separation problem. In the first part of the work vapor-liquid and liquid-liquid equilibrium simulation was made. NRTL and UNIQUAC models were used to calculate phase equilibrium of a quaternary reaction mixture. It was proved by comparison of deviations of the calculated temperature and vapor mole fractions from the experimental values that NRTL is the best model for the considered mixture phase equilibrium calculations. This model was used in further calculations of distillation and liquid-liquid splitting. The choice of the technological scheme is based on the use of the principle of both distillation and liquid phase separation and the recycling of substances in the system. The difficulty in isolating pure isoamyl acetate as a product is due to the presence of four binary azeotropes and two triple ones in the system. When developing and selecting a technological scheme, the possibility of obtaining maximum conversions of the reactants was taken into account. Besides, when designing and calculating the scheme, an assumption was made about infinite separating ability of separation distillation columns. To check operating efficiency of the scheme in real conditions, a verification calculation was made to determine the minimum and working reactor volume. The minimum and working reactor volume calculation was based on the Langmuir-Hinshelwood-Hougen-Watson model for the kinetics of the esterification reaction. The selection of constructive and operating parameters of the scheme, at which high quality of isoamyl acetate is achieved, was made.

The interaction of lipid-liganded gold clusters (Aurora ™) with lipid bilayers.

Lipid bilayers of different phospholipid compositions have been prepared, in the form of vesicles, or of supported lipid bilayers, and doped with Aurora™ at 0.1 mol%. Aurora™ consists of an Au55 gold nanoparticle (about 1.4 nm in diameter) capped with triphenylphosphine ligands and a single diglyceride (distearoyl glycerol) ligand. Gold nanoparticles have been incorporated in the past inside liposomes, or grafted onto their surfaces, with diagnostic or therapeutic aims. Including the gold nanoparticles in a stable form within the lipid bilayers has serious technical difficulties. We have tested the hypothesis that, because of the diglyceride ligand, Aurora™ would allow the easy incorporation of gold nanoclusters into cell membranes or lipid bilayers. Our results show that Aurora™ readily incorporates into lipid bilayers, particularly when they are in the fluid phase, i.e. the state in which cell membranes exist. Calorimetric, fluorescence polarization or fluorescence confocal microscopy concur in showing that bilayer-embedded Aurora™hardly changes the physical properties of the bilayers, nor does it perturb the phase equilibrium in lipid mixtures giving rise to lateral phase separation in the plane of the membrane. Atomic force microscopy shows, in fluid bilayers, well-resolved particles, 1.2-2.9 nm in height, that are interpreted as single Aurora™conjugates. Cryo-transmission electron microscopy allows the clear observation of lipid bilayers with an enhanced contrast due to the Aurora™ gold nanoparticles; the single particles can be resolved at high magnification. Our studies support the applicability of Aurora™ as a membrane-friendly form of nano-gold particles for biological research or clinical applications.

Effects of molecular complexation on phase equilibria in mixtures of urea/polyethylene glycol derivatives and electrochemical performance of urethane based polymer electrolyte membranes for solid-state lithium ion battery

Phase diagram approach has been extended to the determination of phase diagram of a binary pair of urea with polyethylene glycol (PEG) in order to providence guidance to the formulation window of isotropic polymer electrolyte membranes (PEMs) with emphasis on the electrochemical performance. Effect of molecular weight of PEG on solid-liquid phase diagrams of its mixtures with urea has been demonstrated experimentally and theoretically. The observed change of eutectic, immiscibility loop, azeotrope type phase diagrams with increasing PEG molecular weight (or decreasing chain-ends) has been analyzed in the context of the combined Flory-Huggins (FH) theory of liquid-liquid demixing and phase field (PF) theory of crystal solidification. This rich phase behavior has been captured via the variation of crystalline-crystalline interaction strength of the combined FH-PF free energies. Subsequently, the phase diagram of poly (ethylene glycol) diacrylate (PEGDA)/urea was constructed in the framework of the aforementioned FH-PF theory. The incorporation of urea not only dissociates lithium cation from its salt, but also enhances the ionic conductivity of urea-modified polymer electrolytes dramatically. However, small molecule hydrophilic urea was found to be electrochemically unstable in the charge/discharge cycling test. To alleviate such shortcoming, urea (or urethane) linkage was imparted into the network chains by synthesizing PEG-bis(carbamate dimethacrylate) (PEGBCDMA) and subsequently photopolymerizing in the presence of SCN plasticizer and LiTFSI salt to afford the ion conductive PEM network. The as-synthesized PEGBCDMA based PEM consisting of PEGBCDMA/SCN/LiTFSI (20/40/40 ratio by weight) turned out to be completely amorphous and transparent before and after photo-crosslinking. The incorporation of urethane linkages in the PEM network exhibited enhanced ionic conductivity, improved thermal stability, and superior tensile properties with improved capacity retention during charge/discharge cycling, suggesting potentials for application in solid-state lithium ion battery.

Membrane Materials with Semi-Interpenetrating Networks Based on Poly(4-methyl-2-pentyne) and Polyethyleneimine

Disubstituted polyacetylene poly(4-methyl-2-pentyne) (PMP) exhibits one of the highest levels of gas/vapor permeability and selectivity of C3+ recovery from mixtures with permanent gases among known polymers. In this study, semi-interpenetrating networks based on compatible mixtures of PMP and thermally crosslinked polyethyleneimine (PEI) have been obtained to enhance the resistance of PMP to organic solvents. Investigation of the phase equilibrium of PMP and PEI mixtures by optical interferometry has revealed that PMP dissolves up to 30 vol % PEI at room temperature. The fact of thermal crosslinking of PEI is confirmed by IR data. The influence of the proportion of crosslinked PEI on the gas permeability, solubility, and swelling in organic solvents of the films prepared from PMP mixtures with PEI has been examined. Having the PEI content higher than 20 vol %, the films are resistant to organic solvents for at least 14 days. Moreover, with an increase in the proportion of PEI, the degree of swelling of the films is substantially reduced. The increase in stability can be explained by the retention of PMP macromolecules in the crosslinked PEI matrix, which probably reduces the swelling of the films and impedes the extraction of linear PMP macromolecules from the polymer network. The ideal O2/N2, CO2/N2, and CO2/CH4 selectivities increase with a growth in the PEI proportion.

A PC-SAFT model for hydrocarbons II: General model development

This is the second paper in a series which describes the development of a general PC-SAFT hydrocarbon model. In instalment I, a new treatment of aromaticity was included in the PC-SAFT equation of state by mapping aromatic π-π attractions onto a dipolar free energy. In this paper we include this aromatic-polar map into the development of a generalized thermodynamic model for hydrocarbons. The characterization model incorporates heteroatom polarity as well as aromaticity. The minimum level of input to the model is boiling point, molecular weight, and specific gravity. If a specific molecular structure is known, the model formalism accommodates inclusion of various aromatic and heteroatom functional groups. We demonstrate by comparison to pure component properties of defined hydrocarbon molecules that the new approach is of nearly quantitative accuracy. We also demonstrate how the use of the polarity contributions allows for accurate prediction of non-idealities in mixture phase equilibria.

Synthesis and Characterization of Diethyl Citrate and Phase Equilibria in Mixtures with Ethanol and Water

In this work, diethyl citrate (DEC) was synthesized and isolated for further physicochemical characterization and phase equilibria study. The synthesis was performed via partial esterification of citric acid with ethanol, and the final product was separated from the resulting mixture using a pH-controlled solvent extraction method. Characterization using 1H NMR and 13C NMR spectroscopy confirmed the presence of both DEC isomers with few impurities. Results indicate that a 6:5 molar ratio of the symmetric to the nonsymmetric ester structures was attained during synthesis. Thermogravimetric analysis and differential scanning calorimetry allowed us to measure, for the first time, glass transition temperature (228 K) and decomposition temperature (493 K) of diethyl citrate. Additionally, P–x data for the vapor–liquid equilibrium of the binary mixtures diethyl citrate + ethanol and diethyl citrate + water were collected at 308 K using an accurate dynamic device. Data were regressed to generate binary interacti...

Unified presentation and comparison of various formulations of the phase stability and phase equilibrium calculation problems

In this paper we present general formulations of the phase-equilibrium and phase-stability problems for multicomponent mixtures and verify that these formulations generalize the problems of phase-equilibrium and phase-stability at constant volume, temperature, and mole numbers (VTN-flash), at constant internal energy, volume, and mole numbers (UVN-flash), and at constant pressure, temperature, and mole numbers (PTN-flash). Furthermore, we develop a numerical method for solving the general formulation of phase-equilibrium problems. This algorithm is based on the direct minimization of the objective function with respect to the constraints. The algorithm uses a modified Newton-Raphson method, along with a modified Cholesky decomposition of the Hessian matrix to generate a sequence of states with decreasing values of the objective function. The algorithm was implemented in C++ and using generic programing we have a single, portable solver for all three flash formulations. Properties of the algorithm are shown on phase-equilibria problems of multicomponent mixtures in different specifications and with different levels of difficulty. Complexities and numerical performance of the individual flash formulations are discussed.

Distinctive Features of the Phase Equilibrium of Mixtures of C1-C3 Hydrocarbons and Nitrogen

Study of the phase equilibrium of natural gas components plays an important role in the designing of LNG plants. Since the problems of equilibrium in two-phase vapor-liquid systems of natural gas hydrocarbons have been extensively studied, investigations are currently focused on multiphase systems of hydrocarbons in mixtures with inorganic substances such as water, carbon dioxide, hydrogen sulfide, hydrogen, and nitrogen. This article dwells on the phase equilibrium of binary mixtures of methane, ethane, and propane with nitrogen. Depending on the ratio of the components and the thermobaric parameters, mixtures of these hydrocarbons with nitrogen may exist as mixtures of mutually soluble components or mixtures of only partially soluble components. The areas of existence of three-phase liquid-liquid-gas system were determined by calculation. The results obtained hold great importance for LNG process design and modernization.

A Numerical Comparison of Soave Redlich Kwong and Peng-Robinson Equations of State for Predicting Hydrocarbons’ Thermodynamic Properties

Mixture phase equilibrium and thermodynamic properties have a significant role in industry. Numerical analysis of flash calculation generates an appropriate solution for the problem. In this research, a comparison of Soave Redlich Kwong (SRK) and Peng-Robinson (PR) equations of state predicting the thermodynamic properties of a mixture of hydrocarbon and related compounds in a critical region at phase equilibrium is performed. By applying mathematical modeling of both equations of states, the behavior of binary gases mixtures is monitored. The numerical analysis of isothermal flash calculations is applied to study the pressure behavior with volume and mole fraction. The approach used in this research shows considerable convergence with experimental results available in the literature.

Phase equilibrium of a quaternary system: Methanol, ethylene, water and hydrogen peroxide

In this work, we examine, using molecular simulation, the liquid-vapor phase equilibria and atomic-level structure of an ethylene-expanded mixture of methanol, water and hydrogen peroxide as functions of temperature and pressure. The motivation for this study is a recently proposed catalytic process for the epoxidation of ethylene to ethylene oxide in Nb-doped silica nanopores [J. Catal. 336 75 (2016)], where the solvent (methanol) is expanded by the reactant (ethylene) in the presence of the oxidant (hydrogen peroxide in water). Optimal tuning of the reaction conditions can be greatly facilitated by detailed information as to the phase equilibrium and local structure (e.g., hydrogen bonding) of this quaternary mixture. In particular, we focus on the solubility of ethylene in this system as a function of water content. We compare this quaternary system to the recently studied ethylene/methanol/water ternary mixture [Fluid Phase Equilib. 429 275 (2016)]. One major conclusion of this work is that for solutions in which the methanol to water/hydrogen peroxide ratio is greater than 50%, the solubility of ethylene in the quaternary mixture is identical within the statistical error to that of a corresponding ternary mixture, in which hydrogen peroxide is replaced by water. Given that these methanol-rich systems are precisely those of most utility in the epoxidation process, this observation greatly simplifies the phase-equilibrium analysis.

Analysis of the Role of Phase Transformations in the Reproduction of Gas–Liquid Flows is a Possibility to Improve the Standards of Discharge for Multiphase Flows

The influence of the phase transitions in gas–liquid flows on the accuracy of reproduction of the discharge of gas–liquid mixtures under high pressures on test benches is analyzed. An algorithm for the numerical analysis of the phase equilibrium of mixtures of air with various concentrations of an Exxol oil substitute is developed with the use of the equations of state and the fundamental concepts of thermodynamics. The coefficients of binary interaction of the Exxol oil substitute and the main components of air (nitrogen, carbon dioxide, oxygen, and argon) are obtained. The experimental data and numerical results on the saturation of Exxol–air mixtures are presented for various concentrations. It is shown that if we neglect the phase transitions, then the information about the parameters of multiphase flows measured on testing benches becomes significantly distorted.

Phase equilibrium and physical properties of biobased ionic liquid mixtures

Protic ionic liquid crystals (PILCs) obtained from natural sources are promising compounds due to their peculiar properties and sustainable appeal. However, obtaining PILCs with higher thermal and mechanical stabilities for product and process design is in demand and studies on such approaches using this new IL generation are still scarce. In this context, this work discloses an alternative way for tuning the physicochemical properties of ILCs by mixing PILs. New binary mixtures of PILs derived from fatty acids and 2-hydroxy ethylamines have been synthesized here and investigated through the characterization of the solid-solid-[liquid crystal]-liquid thermodynamic equilibrium and their rheological and critical micellar concentration profiles. The mixtures presented a marked nonideal melting profile with the formation of solid solutions. This work revealed an improvement of the PILCs' properties based on a significant increase in the ILC temperature domain and the obtainment of more stable mesophases at high temperatures when compared to pure PILs. In addition, mixtures of PILs also showed significant changes in their non-Newtonian and viscosity profile up to 100 s-1, as well as mechanical stability over a wide temperature range. The enhancement of the physicochemical properties of PILs here disclosed by such an approach leads to more new possibilities of their industrial application at high temperatures.

Phase Equilibrium of Binary Mixture for the (Carbon Dioxide + 1-Phenyl-2-Pyrrolidone) System at High Pressure

Phase Equilibrium of Binary Mixture for the (Carbon Dioxide + 1-Phenyl-2-Pyrrolidone) System at High Pressure