Phase Equilibrium Data Research Articles

Transferable Anisotropic Mie Potential Force Field for Alkanediols.

The development of force fields for polyfunctional molecules, such as alkanediols, requires a careful account of different average intramolecular conformations for gas states compared to dense liquid states, where intra- and intermolecular hydrogen bonds compete. In the present work, the transferable anisotropic Mie (TAMie) potential is extended to 1,n-alkanediols. Using the convention that intramolecular nonbonded interactions up to and including the third neighbor are excluded, all force field parameters developed previously for 1-alcohols were transferred to 1,5-pentanediol and beyond, with good agreement with experimental phase equilibrium data. To obtain trans-gauche ratios of 1,2-ethanediol and 1,3-propanediol that are consistent with experimental results, the propensities for intra- and intermolecular hydrogen bonds had to be balanced. This was achieved by parameterizing the intramolecular dihedral energy functions governing the O-C-C-O and O-C-C-C angles while intramolecular charge-charge interactions were active. All partial charges belonging to a functional group are collected in a charge group and all interactions among two charge groups are evaluated even if they are separated by less than three bonds. With this approach, it is possible to apply the nonbonded parameters from 1-alcohols to alkanediols without further refinement. The agreement with experimental phase equilibrium and shear viscosity data is of similar quality as for the 1-alcohols and the trans-gauche ratio agrees with literature results from spectroscopic measurements and ab initio calculations.

Thermodynamic Modeling of the Au-Ge-X (X = In, Sb, Si, Zn) Ternary Systems.

In this study, the CALPHAD approach was employed to model the thermodynamics of the Au-Ge-X (X = In, Sb, Si, Zn) ternary systems, leveraging experimental phase equilibria data and previous assessments of related binary subsystems. The solution phases were modeled as substitutional solutions, and their excess Gibbs energies were expressed using the Redlich-Kister polynomial. Owing to the unavailability of experimental data, the solubility of the third elements in the Au-In, Au-Sb, and Au-Zn binary intermetallic compounds was excluded from consideration. Additionally, stable ternary intermetallic compounds were not reported in the literature and, thus, were not taken into account in the present thermodynamic calculations. Calculations of liquidus projections, isothermal sections, and vertical sections for these ternary systems have been performed, aligning with existing experimental findings. These thermodynamic parameters form a vital basis for creating a comprehensive thermodynamic database for Au-Ge-based alloys, which is essential for the design and development of new high-temperature Pb-free solders.

Phase equilibrium data prediction and process optimizationin butadiene extraction process

In response to the lack of reliable physical parameters in the process simulation of the butadiene extraction, a large amount of phase equilibrium data was collected in the context of the actual process of butadiene production by acetonitrile. The accuracy of five prediction methods, UNIFAC, UNIFAC-LL, UNIFAC-LBY, UNIFAC-DMD, and COSMO-RS, applied to the butadiene extraction process was verified using partial phase equilibrium data. The results showed that the UNIFAC-DMD method had the highest accuracy in predicting phase equilibrium data for the missing system. COSMO-RS predicted multiple systems showed good accuracy. And a large number of missing phase equilibrium data were estimated using the UNIFAC-DMD method and COSMO-RS method. The predicted phase equilibrium data were checked for consistency. The NRTL-RK and UNIQUAC thermodynamic models were used to correlate the phase equilibrium data. Industrial device simulations were used to verify the accuracy of the thermodynamic model applied to the butadiene extraction process. The simulation results showed that the average deviations of the simulated results using the correlated thermodynamic model from the actual values were less than 2% compared to that using the commercial simulation software Aspen Plus and its database. The average deviation was much smaller than that of the simulations using the Aspen Plus database (>10%), indicating that the obtained phase equilibrium data are highly accurate and reliable. The best phase equilibrium data and thermodynamic model parameters for butadiene extraction are provided. This improves the accuracy and reliability of the design, optimization and control of the process, and provides a basis and guarantee for developing a more environmentally friendly and economical butadiene extraction process.

Solubility measurement of methane in triethylene glycol aqueous solutions (90,95,98 wt.% triethylene glycol) from 298 to 323 K and 0.17 to 2.5 MPa

Limited phase equilibria data exists for the methane + water + triethylene glycol system. In this work, new phase equilibrium data were measured for this system for a temperature range of 298 to 323 K and a pressure range of 0.17 to 2.5 MPa. These data add to the information that is required in the design of TEG contactor units since they normally operate over a temperature and pressure range of 283 to 329 K, and 2 to 10 MPa respectively. The data were measured using a static synthetic apparatus. The measured data were modelled in Apen Plus V12.1 using the Cubic Plus Association equation of state. The model correlation yielded a satisfactory description of the measured data since the maximum absolute average relative deviation in pressure was 4.30 %.

Thermodynamic assessment of the Cr–Si binary system

A thermodynamic evaluation of the Cr–Si system was performed concerning the latest experimental phase diagram and with the aid of first-principles calculations. The thermodynamic parameters for the Gibbs energy of pure Cr were modified based on the new experimental value of 1861 °C for the melting point of pure Cr, which was previously reported as 1907 °C in the SGTE database. The Gibbs energy descriptions of the Cr3Si and Cr5Si3 phases were revised using Cr3(Cr,Si)- and (Cr,Si)5Si3-type two-sublattice models to reproduce the latest experimental results of their solubility composition ranges, that is, Cr3Si extending toward the Cr-rich side and Cr5Si3 extending toward the Si-rich side from the stoichiometry. The CrSi and CrSi2 phases were considered line compounds with no solubility range, and the solubility of Cr in the Si phase was ignored. A set of self-consistent thermodynamic parameters for the Cr–Si system was obtained using the CALPHAD technique. The phase diagrams calculated using the optimized parameters showed reasonable agreement with the latest phase equilibrium data and thermodynamic property data in the literature, including the enthalpy of mixing, formation enthalpy, and chemical potential diagrams of Cr and Si in the equilibrium phases.

Phase Equilibrium Data and Storage Capacity of the Ethane Gas Hydrate in the Presence of 1,4-Dioxane and Polyvinylpyrrolidone

Phase Equilibrium Data and Storage Capacity of the Ethane Gas Hydrate in the Presence of 1,4-Dioxane and Polyvinylpyrrolidone

Thermodynamic optimization of KCl-LiCl-LaCl3 with ionic two-sublattice model for liquid

The pyroprocessing technology can reduce nuclear waste by recovering uranium from spent nuclear fuels. To fully take advantage of this technique, it is crucial to have a better understanding of the thermodynamic behavior evolution of the eutectic KCl-LiCl electrolyte with the accumulation of impurities such as lanthanides. The present study carries out thermodynamic modeling for the KCl-LiCl-LaCl3 system and its binary subsystems using the CALPHAD (CALculation of PHAse Diagrams) approach for the first time to predict the liquidus temperatures of KCl-LiCl eutectic as a function of LaCl3 content. Three possible ionic two-sublattice models have been implemented to describe the liquid phase for comparison. Model 1 only involves simple cations and anions. Model 2 and 3 consider short-range ordering in the liquid and introduce species K2LaCl5 and LaCl63-, respectively. It was demonstrated that from the thermodynamics point of view, Model 1 is sufficient to reproduce both phase equilibria and enthalpy of mixing data, whereas Models 2 and 3 seem redundant and increase the number of parameters, which may further lead to poor extrapolation behavior towards multicomponent systems. To achieve better agreements with experimental phase equilibria data and estimated enthalpy of mixing data using the surrounded-ion model, three ternary parameters were optimized for the KCl-LiCl-LaCl3 system. The resultant calculations can well reproduce the experiments and provide insights into the liquidus temperature variation as the mole fraction of LaCl3 increases in the electrolyte.

Phase equilibria in the NiO-ZnO-SiO2 and PbO-NiO-ZnO-SiO2 systems

Experimental investigation and thermodynamic modeling of the phase equilibria in the (PbO)-NiO-ZnO-SiO2 system has been undertaken to characterize Ni behavior in high-Zn slags. Phase equilibria data at 790–1700 °C were obtained through equilibration of synthetic mixtures in sealed silica ampoules or Pt-Ir / Au foils, rapid quenching, and electron probe X-ray microanalysis. Phase equilibria and liquidus isotherms of the NiO-ZnO-SiO2 system in the tridymite/cristobalite SiO2, monoxide (Ni,Zn)O, zincite (Zn,Ni)O, olivine (Ni,Zn)2SiO4 and willemite (Zn,Ni)2SiO4 phase fields were measured and the extent of the 2-liquid immiscibility gap over cristobalite was determined. Additional solid solutions: larsenite Pb(Zn,Ni)SiO4 and melilite Pb2(Zn,Ni)Si2O7 were measured in the PbO-NiO-ZnO-SiO2 system. It was found that NiO partially substitute ZnO in larsenite and melilite and may form a complete range of solubility in barysilite Pb8(Zn,Ni)Si6O21. New data were used for developing a thermodynamic database to describe the Pb/Cu-containing complex system for characterizing Ni behavior in Zn-containing slags.

Prediction of Phase Equilibrium Conditions and Thermodynamic Stability of CO2-CH4 Gas Hydrate

With the large-scale promotion and application of CO2 flooding, more and more engineering problems have emerged. Due to the high CO2 mole fraction, the associated gas of CO2 flooding very easily forms solid hydrates, compared to conventional natural gas. This has resulted in production decline or shutdown. Understanding the phase equilibrium conditions for hydrate formation in production fluids is crucial for hydrate prevention and control. In this study, accurate predictions of CO2-CH4 mixed gas hydrate formation conditions were performed using theoretical models. The temperature and pressure ranges for hydrate formation were calculated for different CO2 mole fraction, ranging from −11.5 °C to 20.85 °C and from 0.81 MPa to −28.1 MPa, respectively. Based on the calculated phase equilibrium data, a multi-parameter empirical model was developed using polynomial fitting. The calculation errors for the multi-parameter empirical model were 3.09%. The multi-parameter empirical model established in this study can avoid complex thermodynamic equilibrium calculations and has the advantages of simplicity, high accuracy, and wide coverage of downhole conditions. Based on the calculated phase equilibrium data, the dissociation enthalpy of CO2-CH4 hydrate below and above the freezing point of water was calculated. The results showed that an increase in CO2 mole fraction led to an increase in hydrate dissociation enthalpy and enhanced thermodynamic stability, making hydrate prevention more challenging. Our work can contribute to the optimization of CO2 production fluid treatment processes and the development of hydrate prevention and control technologies.

Prediction of ionic liquid solubilities in supercritical CO2 + co-solvent systems using Peng–Robinson equation of state with accurate critical temperature

Supercritical fluid deposition (SCFD) using supercritical carbon dioxide (CO2) to impregnate substrates with ionic liquids (ILs) has attracted considerable attention for the preparation of porous-supported ILs. Because ILs are generally insoluble in pure CO2, it is essential to estimate the solubilities of ILs in supercritical CO2 + co-solvent systems for developing the SCFD process. In this study, a methodology was developed to predict the solubility of ILs in supercritical CO2 with co-solvents using the corresponding binary phase-equilibrium data. For the prediction, the binary interaction parameters for the Peng–Robinson equation of state (PR-EoS) were determined using the correlations to each phase-equilibrium system (i.e., IL + CO2, CO2 + co-solvent, and IL + co-solvent). The predictive model using the PR-EoS, which included a re-determined critical temperature as a pure component parameter of ILs, could reproduce the effects of the temperature, pressure, and co-solvent concentration on the IL solubilities in the supercritical fluid phase without any fitting parameters for the ternary systems. The average absolute relative deviations based on the logarithmic scale for the predictions were <23 %, indicating that the methodology was acceptable for describing the IL solubilities in the supercritical CO2 + co-solvent system.

Use of Thermodynamically Consistent Phase Equilibrium Data to Obtain a Generalized Padé-Type Model for the Henry’s Constants of Gases in Ionic Liquids

A generalized Padé-type expression is proposed for Henry’s constant of gases in ionic liquids. The constants are determined using an equation of state, and generalized expressions for the Henry’s constants of the gases in the ionic liquids are proposed. The solute gases included in the study were oxygen, hydrogen, and carbon monoxide in three solvent ionic liquids ([MDEA][Cl], [Bmim][PF6], and [Hmim][TF2N]). The Valderrama–Patel–Teja equation of state with the mixing rules of Kwak and Mansoori are employed to correlate the solubility data, to examine the thermodynamic consistency of the experimental data, and to determine the fugacity (fi) for each concentration (xi) of the solute gas in the liquid phase. From these data, the fugacity coefficients (fiL/xi) are determined to obtain Henry´s constant as Hi = lim(fiL/xi) when xi→0. The calculated Henry’s constants are correlated in terms of the temperature and acentric factor of the gases to finally obtain a generalized expression for Henry´s constant, Hi.

Phase Behavior and Phase Equilibria for The Polydisperse Polyethylene + Ethylene + Hexane System at High Pressures and Temperature: Experiments and Correlations

This study aims to provide experimental phase equilibrium and phase behavior data for polydisperse PE + ethylene + hexane system. Polydisperse PE (Mw 30.0 kg/mol, PDI 4.2) was used with feed PE weight fraction, ⱳF,PE, of 0.02 to 0.20. The experiments based on a synthetic method were conducted at 473.2 K using an apparatus consisted of an equilibrium cell equipped with sampling tubes for solvent-rich and polymer-rich phases. The LL phase separation pressure increased by about 1 MPa for 1 wt% increase in ethylene concentration. The weight fraction of PE in solvent-rich phase, ⱳS,PE, decreased as the ⱳF,PE and pressure decreased. Similarly, the weight fraction of PE in polymer-rich phase, ⱳP,PE, also decreased as the ⱳF,PE decreased. The solvent-rich phase contained lower molecular weight fractions of PE, while the polymer-rich phase contained higher molecular weight fractions. These results were correlated and predicted with the Sanchez-Lacombe (S-L) EoS. Finally, the effects of pressure and ⱳF,PEon solvent recovery ratio were investigated with the S-L EoS. The results provided in this study could be used to obtain the higher hexane recovery by controlling the LL separation pressure.

High-pressure phase equilibrium data for systems involving carbon dioxide, globalide, ε-caprolactone, poly(globalide-co-ε-caprolactone) and dichloromethane

High-pressure phase equilibrium data for systems involving carbon dioxide, globalide, ε-caprolactone, poly(globalide-co-ε-caprolactone) and dichloromethane

Crystallization separation of Na2CO3 and Na2MoO4 from the high-salinity ash slag produced by production process of Na2MoO4 based on the theory of phase equilibrium

High-salinity ash slag containing Na2CO3 and Na2MoO4 produced from the production process of Na2MoO4 brings about the resource waste and environmental pollution issues. To realize the resource utilization of these high-salinity ash slag, the phase equilibrium data of the ternary Na2CO3–Na2MoO4–H2O system at 298.15 K and 323.15 K were determined using the isothermal dissolution equilibrium method, and the equilibrium solid phase was determined by X-ray diffraction. By comparing the phase diagrams of the ternary Na2CO3–Na2MoO4–H2O system at 298.15 K, 323.15 K, and 353.15 K, the change rules of the crystallization region were analyzed. The Pitzer and HW models were used to calculate the ionic interaction parameters of θMoO4–CO3 and ψNa–MoO4–CO3, which could be further used to predict the solubility curves of the ternary Na2CO3–Na2MoO4–H2O system. The calculation results were in good agreement with the experimental results. Furthermore, the phase diagrams of the ternary Na2MoO4–Na2CO3–H2O system at 298.15 K and 353.15 K were selected to design a process for the highly-efficient recovery of Na2MoO4·2H2O and Na2CO3·H2O from the high-salinity ash slag. The experimental results showed that the one-way recovery rate of Na2CO3 could reach 92.55%, with a purity of 99.62%, and that of Na2MoO4·2H2O is 45.61%, with a purity of 99.14%. These results were almost consistent with the theoretical calculation results. After multiple cycles, Na2CO3 and Na2MoO4 could be completely recovered.

Low-temperature gel breaking fracturing fluid for marine hydrate reservoir fracturing and its effect on phase equilibrium of methane hydrates

Hydraulic fracturing has been proven useful for improving the gas production efficiency of low-permeability hydrate reservoirs. However, no specific fracturing fluid system exists for marine hydrate reservoirs. Applying conventional water-based fracturing fluids in low-temperature (<293.2 K) marine hydrate reservoirs can lead to difficulties in gel-breaking and hydrate instability caused by external additives. In this study, we developed two water-based fracturing fluid systems that exhibited good gel-breaking performance at low temperatures (278.2–288.2 K), one comprising ammonium persulfate (APS), ferrous sulfate (FeSO4), and citric acid (CA), the other APS and triethanolamine (TEA). In addition, we investigated the influence of crosslinking and gel-breaking reactions of the fracturing fluids on the methane hydrate phase equilibrium. The breaking time of the APS-FeSO4-CA system at 278.2K, 283.2K, and 288.2K was 30 min, 75 min, and 120 min respectively. On the other hand, the APS-TEA system accomplished the same task in 3 h, 6 h, and 10 h respectively. Furthermore, methane hydrate phase-equilibrium data showed that the fracturing fluid's three states, base fluid (BF), fracturing fluid gel (FFG), and gel-breaking liquid (GBL), all exerted an inhibitory effect on the phase equilibrium, with the hydrate suppression temperature (ΔT) ranging from 0.4 to 1.0 K. The differences in their inhibitory effect were primarily related to the micromorphology of the hydroxypropyl guar gum (HPG) molecules and the number of active hydroxyl (-OH) groups in the solution. Cryo-scanning electron microscopy (SEM) measurements revealed that the micromorphology of HPG in BF, FFG, and GBL transformed from regular ribbon-like structures to 3-D network structures and then to hole-containing, short ribbon-like structures. FFG formed a regular 3-D network structure after adding crosslinking agents to the BF. The ΔT values reversed from FFG < BF to FFG > BF when the HPG concentration increased from 0.3 wt% to 0.5 wt%, possibly due to the difference in the HPG molecules' water adsorption capacity before and after crosslinking. The broken HPG molecules with OH− groups in the solution were transformed into residues after gel-breaking, decreasing the GBL's inhibitory effect. Therefore, our results indicated that micromorphology variations could cause differences in the HPG molecules' water adsorption capacity, ultimately leading to ΔT differences. Based on our findings, the gel-breaking fracturing fluid systems we developed demonstrated potential for optimizing hydraulic fracturing in marine hydrate reservoirs.

Determination of Citronellal-geraniol Phase Equilibrium Data and Distillation Simulation Study based on Aspen Plus Software

Aspen Plus is an efficient, reliable, and scalable large-scale process simulation software suitable for a variety of applications. It boasts excellent computational efficiency, high-quality physical property data, and comprehensive system integration, earning consistent acclaim within the industry. The separation of citronella oil components is increasingly expensive due to their thermal sensitivity and high separation difficulty. This study utilizes gas chromatography to analyze the volatile oil components and investigates the phase equilibrium relationship of citronellal -geraniol system in citronella oil. Experimental phase equilibrium data for the citronellal-geraniol system in citronella oil are obtained to provide the thermodynamic basis for the separation of the citronellal-geraniol system in citronella oil. Aspen Plus process simulation software is used to estimate the physical property parameters of the citronellal-geraniol system and optimize the distillation separation, providing support for the industrial production of high-purity separation of the citronellal-geraniol system.

Thermodynamic assessment of La–Fe–Si systems

The phase equilibria of the La–Fe–Si system were investigated using a combination of experimental and thermodynamic modeling methods. The isothermal cross-section of the La–Fe–Si ternary system in the (Fe, Si)-rich region at 1373 K was experimentally investigated using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Based on the experimental results and literature reports of the La–Fe–Si system, the thermodynamic model parameters of the system were optimized using the CALPHAD method. The intermediate compounds in the La–Si binary system and ternary compounds in the La–Fe–Si ternary system were described via sublattice models. The calculated thermodynamic and phase equilibria data were in good agreement with the experimental data, providing a foundation for the development of a multi-component thermodynamic database for LaFeSi-based alloys.

Flowsheets for hydroxyacetone–phenol binary mixture separation: The use of special distillation methods

Objectives. To study the possibility of hydroxyacetone–phenol binary mixture (a constituent of a mixture of phenol production by the cumene method) separation in flowsheets based on the use of distillation special methods. This is the addition of separating agents to increase the relative volatility of the components of the original mixture, and the variation of pressure in the columns.Methods. A computational simulation in Aspen Plus® was used as the research method. Mathematical modeling of the vapor–liquid equilibrium was carried out using a local compositions model Non-Random Two Liquid. The viability of the latter was confirmed by comparing experimental and calculated on phase equilibrium data, and azeotropic data. The average relative error does not exceed 3%.Results. The dependence of the composition and boiling point of the hydroxyacetone–phenol azeotrope on pressure was determined in a computational experiment (as the pressure increases, the azeotrope is enriched with phenol). The possibility of using a complex of columns operating under different pressures to separate the mixture was shown (the shift of the azeotrope is about 9%). The change in the relative volatility of components of the original mixture in the presence of a high(diethylene glycol) and a low-boiling (acetone) separating agent was investigated. Both solvents are selective agents used in extractive and re-extractive distillation processes. Three technological separation flowsheets containing two distillation columns were proposed.Conclusions. The study established the operation parameters of the columns (number of theoretical stages, feed stages of the original mixture and separating agent, and reflux ratio) and energy consumption (total heat supplied to the columns boiler) of three separation flowsheets ensuring the production of products of a given quality (not less than 0.99 mol fractions). The flowsheet with diethylene glycol is characterized by the lowest energy consumption. It is recommended that complexes of extractive and re-extractive distillation be further optimized. This enables the second product of cumulus production—acetone—to be involved in the technological cycle.

Vapor-liquid equilibrium data and performance analysis on binary mixture of R32 and R1216 for residential air condition system

In order to accurately evaluate the performance of R32 and unsaturated fluorinated olefins (HFOs) binary mixtures in residential air condition (RAC) system, the vapor-liquid phase equilibrium (VLE) data of R32 and R1216 binary mixture has been measured with a liquid phase circulation system in the temperature range from 285 to 315 K. The experimental data were correlated by Peng-Robinson (PR) equation of state with Huron-Vidal (HV) mixing rule and non-random two-liquid (NRTL) activity coefficient model. Maximum deviation of the pressure and the mole fraction was 1.38% and 0.013, respectively. The azeotropic behavior was observed for the R32 and R1216 binary mixture when the mole fraction of R32 was around 0.9. The RAC system with standard refrigeration, heating and variable evaporation temperature operating condition was simulated. The cycle performance of binary mixtures of R32 + R1216, R1234yf and R1234ze(E) at different concentrations was compared. The azeotrope R32/R1216 (molar ratio 0.9/0.1) has an extremely low GWP, the COP, refrigeration/heating capacity per unit volume and condensation pressure close to pure R32, and lower discharge temperature. At the same time, it also has well variable operating conditions performance and can be considered as a drop-in replacement for R32 and R410A in RAC systems.

Phase equilibria and mechanism analysis of separating ethanol from fuel additives by chord chloride-deep electrochemical solvents

There is an azeotropic mixture of ethanol and heptane in the production process of gasoline additives. This work explored the possibility of extracting ethanol from ethanol and heptane with deep eutectic solvents (DESs) to recover components and protect the environment. Three kinds of choline chloride (ChCl)-DESs were synthesized, and then the ternary phase equilibrium data of ethanol, heptane and DESs were measured. The reliability of the data can be verified by the fitting results of the experimental data and the linear equation. In addition, the NRTL model can be correlated with the phase equilibrium results, and the accuracy of the fitted data is determined by the GM/RT surface of GUI-MATLAB. The calculated root mean square deviation shows that the phase equilibrium data has high accuracy. The experimental data show that ChCl-ethylene glycol DES have better ethanol separation results. Then the microscopic mechanism of the separation process was analyzed. The analysis results of electrostatic potential and independent gradient model show that the interaction between DESs and ethanol is mainly hydrogen bond interaction and van der Waals interaction, among which hydrogen bond interaction is the main interaction. In addition, the effect of DES structure on ethanol separation was revealed by the microscopic distribution of molecular dynamics simulation. This work provides a theoretical reference for selecting DESs to separate ethanol-heptane azeotrope.