Solid Phase Equilibria Research Articles

Solid–liquid phase equilibria in the aqueous system containing the chlorides of potassium, ammonium, and calcium at 298.2, 323.2, and 348.2 K

In order to obtain the crystalline forms of the salts of the potassium, ammonium, calcium coexisting chloride system, the phase equilibria relationship of quaternary system K+, NH4+, Ca2+//Cl–-H2O at 298.2, 323.2, and 348.2 K was studied by isothermal dissolution equilibrium method. The solubility and density of equilibrium liquid phases of the system were experimentally determined; X-ray powder diffractometer was used to determine the compositions of the equilibrium solid phase at the quaternary invariant point. It is found that the quaternary system is a complex system at these three temperatures. The phase diagram at 298.2 K consists of three invariant points, seven univariate curves and five crystalline phase regions, forming the solid solutions (NH4Cl)x(KCl)1–x and (KCl)x(NH4Cl)1–x; while at 323.2 and 348.2 K the phase diagram consists of five invariant points, eleven univariate curves and seven crystalline phase regions, the double salts (KCl·CaCl2) and (2NH4Cl·CaCl2·3H2O), solid solutions (KCl)x(NH4Cl)1–x and (NH4Cl)x(KCl)1–x were formed. Among them, the crystalline phase region of solid solution (KCl)x(NH4Cl)1–x is the largest at three temperatures, indicating that it is the easiest to crystallize in this system. Comparing the phase diagrams of the quaternary system at 298.2, 323.2, and 348.2 K, it can be seen that the crystalline form of CaCl2 changes with the increase of temperature: CaCl2·6H2O at 298.2 K, CaCl2·2H2O at 323.2 and 348.2 K. From 323.2 to 348.2 K, the crystalline phase regions of (KCl·CaCl2) and (2NH4Cl·CaCl2·3H2O) increased gradually.

Separation and extraction of NH4Br and (K,NH4)2SO4 from 1-Bromooctane production wastewater by crystallization method

This work provides a method for the separation and extraction of bromine salts from bromine-containing wastewater by crystallization. Wastewater from the production of 1-Bromooctane is rich in potassium and bromine salts. This will allow for the recycling of chemical resources in this aqueous salt system. Based on the need for the process design of the new method, the solubility phase equilibrium of the quaternary K+,NH4+//SO42-,Br-–H2O system at 298.15 K and 323.15 K was investigated in this paper by using the isothermal dissolution equilibrium method, and the dry basis phase diagrams were plotted using the experimental data. And the equilibrium solid phase composition was determined by X-ray diffraction. At 298.15 K, the dry phase diagram of the quaternary system K+,NH4+//SO42-,Br-–H2O consists of three invariant points and five crystalline regions (K2SO4, (NH4)2SO4, (K,NH4)2SO4, (K,NH4)Br, (NH4,K)Br). At 323.15 K, there is one invariant point in the phase diagram of this quaternary system and three crystalline regions((K,NH4)2SO4, (K,NH4)Br, (NH4,K)Br). The (K,NH4)Br crystallization zone grows while the (NH4,K)Br crystallization zone decreases with increasing temperature, according to comparisons of the dry basis phase diagrams of this quaternary system at different temperatures. Crystallization zones of solid solution (K,NH4)2SO4 replaced the K2SO4 and (NH4)2SO4 single salt crystallization zones at the same time. The Pitzer model was used to calculate the solubility of this quaternary system at 298.15 K. The results showed that the experimental values were in good agreement with the calculated values. Based on the theoretical analysis of the dry phase diagram of the quaternary system K+,NH4+//SO42-,Br-–H2O, a process route for salt extraction using bromine-containing wastewater generated from the production of 1-Bromooctane was proposed and designed. The new process was experimentally verified to be technically feasible to obtain NH4Br with 99.01 % purity and (K,NH4)2SO4. The process has significant advantages, such as production safety, low input costs and no three-waste emissions.

Study of the solid-phase equilibria in the GeTe-Bi2Te3-Te system and thermodynamic properties of GeTe-rich germanium bismuth tellurides

A set of self-consistent thermodynamic parameters of the GeTe-rich germanium-bismuth tellurides were determined using an electromotive force (EMF) method with a glycerol electrolyte in a temperature range from 300 to 450 K. The solid-phase equilibrium diagram of the GeTe-Bi2Te3-Te system at 400 K was constructed using X-ray diffraction (XRD) and scanning electron miscroscope (SEM) techniques of synthesized electrode alloys, as well as available literature data. It is found that all telluride phases in GeTe-Bi2Te3 pseudo-binary section have a tie-line connection with elemental tellurium. The relative partial thermodynamic functions of GeTe in alloys were calculated using data from EMF measurements of concentration cells relative to the GeTe electrode. These findings together with the corresponding thermodynamic functions of GeTe and Bi2Te3 were used to calculate the relative partial molar functions of germanium in alloys, and also the standard thermodynamic functions of formation and standard entropies of the ternary compounds, namely Ge2Bi2Te5, Ge3Bi2Te6 and Ge4Bi2Te7.

Effect of ZrO2 on the phase relations for CaO-SiO2-TiO2 system related to efficient extraction of titanium from titania-bearing slag

The selective crystallization and phase separation process has been regarded as a promising process for the recycling of titanium from titania-bearing furnace slag, however, the composition modification mechanism still remains unclear due to the lack of fundamental thermodynamic data. In the present work, the influence of ZrO2 addition on the equilibrium phase relations and the 1400 °C isotherm for CaO-SiO2-TiO2 system were experimentally determined by using the high temperature equilibration-quenching technique, and Scanning Electron Microscopy-Energy Dispersive X-ray Spectrometry, and X-ray diffraction analysis. The equilibrium solid phases of rutile (TiO2), perovskite (CaTiO3), and tridymite (SiO2) are determined to be coexisting with the liquid phase. In addition, comparisons of present results with thermodynamic calculation by FactSage show significant discrepancies. The present work is important for enriching the thermodynamic database of titania-bearing slag oxide systems as well as optimizing the selective crystallization and phase separation process.

Determination of solubility of sildenafil citrate in propylene glycol + 2-propanol and N-methyl pyrrolidone + water: Comparing solubilization power of aqueous or non-aqueous mixtures

For identifying the solubilization power of aqueous and non-aqueous solvent mixtures for sildenafil citrate (SLC), its solubility was determined in four mono-solvents of propylene glycol, 2-propanol, N-methyl pyrrolidone and water along with the binary solvent mixtures of propylene glycol + 2-propanol and N-methyl pyrrolidone + water at 293.2 to 313.2 K and at pressure of 85 kPa. Among the neat organic solvents and also water, N-methyl pyrrolidone presented a high solubilization power for SLC (8.66 × 10-2 at 313.2 K) and its aqueous binary mixtures had also a more ability to solubilize the drug in compared with the binary (propylene glycol + 2-propanol) mixtures (with the highest value of 4.96 × 10–4 at 313.2 K). Besides, increasing the solubility of SLC with raising temperature illustrated that its dissolution in the aforementioned mixtures was endothermic. The equilibrium solid phase crystal of SLC was also characterized with X-ray powder diffraction analysis to identify no polymorphic transformation, solvate formation or crystal transition during the whole solvent crystallization process. Moreover, the experimental mole fractions were modelled by used commonly cosolvency models and regressed the model parameters. The back-calculated mole fractions of SLC by cosolvency models shown a better agreement with the experimental data (overall mean percentage deviation (OMPD) ≤ 7.6 %) and Jouyban-Acree model as a function of temperature and solvent compositions had the best performance (MPD of 3.2 %). Furthermore, the solubility data sets of SLC in 7 binary solvent mixtures were collected from the literature and correlated with the Jouyban-Acree model and its derivates, the OMPDs for the back-computed solubility indicating the generally trained models, especially Jouyban-Acree-Abraham model (MPD of 24.2 %), had an acceptable ability in the prediction of SLC solubility and can be useful in the pharmaceutical industry. Finally, apparent thermodynamic properties of Gibbs free energy, standard enthalpy and entropy of the dissolution processes were also investigated.

Phase formation in the system Na+,Ca2+,Al3+|| SO42–,HCO3--H2O at 273 K

The article discusses the results of determining possible phase equilibria on geometric images of a five-component mutual water-salt system of sulfates, sodium bicarbonates, calcium and aluminum at 273 K, followed by the construction of its phase complex diagram. The patterns that determine the structure of the phase complex of this system are needed both to obtain scientific data used as reference material, as well as to create optimal conditions for the disposal of liquid waste from industrial aluminum production containing sulfate, bicarbonate salts of sodium, calcium and aluminum. To achieve this goal, we used the translation method, according to which the dimension of the geometric images of the diagram of the original (private) system, when adding a subsequent component to it, increases by one, i.e. the geometric images are transformed. Due to the fact that the studied five-component system consists of five particular four-component systems, the addition of a fifth component to any of them is accompanied by a transformation of the geometric images of all five four-component systems. Transformed geometric images, based on their topological properties, are translated (transferred) to the level of a five-component composition. At the level of a five-component composition, transformed and translated geometric images, observing the Gibbs phase rule, intersect and form geometric images of a given level of component. The study of the phase equilibria of a five-component water-salt mutual system of sulfates, sodium bicarbonates, calcium and aluminum and the construction of its phase complex diagram by the translation method at 273 K showed that it is characterized by the presence of twelve divariant fields, ten monovariant curves and three non-invariant points at this temperature. Based on the data obtained, a complete closed phase diagram of the studied system was constructed for the first time and, for ease of reading, fragmented along the divariant crystallization fields of equilibrium solid phases.

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.

Chemical stability of Pb[(UO2)2O2(OH)2](H2O) and Pb2[(UO2)5O6(OH)2](H2O)2 compounds in aqueous solutions

The chemical stability of Pb[(UO2)2O2(OH)2](H2O) and Pb2[(UO2)5O6(OH)2](H2O)2 compounds in aqueous solutions was studied. The acid-base boundaries of the existence of these compounds in aqueous solutions were established, the hydrolysis products were identified, and the solubility was determined. Based on the data obtained, the equilibrium constants of dissolution reactions, the Gibbs functions of the formation and dissolution of Pb[(UO2)2O2(OH)2](H2O) and Pb2[(UO2)5O6(OH)2](H2O)2, were calculated, the solubility curves of the compounds under study, and the phase diagrams of U(VI) and Pb(II) in saturated aqueous solutions and in equilibrium solid phases were calculated.

Thermodynamic phase equilibria containing sodium, potassium, magnesium, strontium and chloride in underground brine environment and evaporation and salt precipitation behavior of strontium chloride

The isothermal dissolution equilibrium method was employed to study the thermodynamic phase equilibria of the NaCl + KCl + MgCl2 + SrCl2 + H2O system at 298.2 K. The equilibrium solubilities and solid phase compositions of the quinary system at 298.2 K were determined by chemical analysis and X-ray diffraction, and the corresponding stable phase diagrams were drawn. The phase diagram of the quinary system has three invariant points, six solid phase crystallization fields and fifteen solubility curves. In the phase diagram, crystalline area of double salt KCl·MgCl2·6 H2O existed. Moreover, the Pitzer thermodynamic model was utilized to predict the phase equilibria of the quinary system at 298.2 K, and the predicted solubilities agreed well with the experimental values. The results demonstrate that the Pitzer model can accurately describe the thermodynamic properties in the quinary system at 298.2 K. Finally, based on the advantages of rich strontium in underground brine from Longnu Temple brine-bearing structure in Sichuan basin of China, the salt precipitation law of strontium chloride was studied.

THERMODYNAMIC INVESTIGATION OF Ag8GeТe6 AND Ag8GeТe6-xSex SOLID SOLUTIONS BY THE EMF METHOD WITH A SOLID Ag+ Conducting Electrolyte

The thermodynamic properties of Ag8GeTe6 compound and Ag8GeТe6-xSex solid solutions were studied by EMF measurements of the concentration cells concerning to a silver electrode with Ag4RbI5 solid electrolyte in the 300–400 K temperature range. The partial thermodynamic functions of silver in alloys are calculated from the EMF measurements data. Based on the data on solid-phase equilibria in the Ag-Ge-Se-Te system, the potential-forming reactions responsible for these partial molar functions were determined and the standard thermodynamic functions of formation and standard entropies of the Ag8GeТe6 compound and solid solutions of the compositions Ag8GeTe5Se, Ag8GeTe4Se2, Ag8GeTe3Se3, Ag8GeTe2Se4 and Ag8GeTeSe5 were calculated.

Solubility Studies of Sulfates of Copper, Zinc and Cobalt in Phosphoric Acid at 30 ºC

Present study reports the isothermal experiments conducted at 30 ºC to ascertain the solubility of copper, zinc and cobalt sulfates in phosphoric acid. The solubility diagram of CuSO4-H3PO4-H2O system is shown to have one branch, this is equivalent to the discharge of copper sulfate pentahydrate into the equilibrium solid phase. The solubility diagrams of zinc and cobalt sulfates have two branches of salt crystallization, corresponding to the release of hexahydrates and monohydrates of zinc and cobalt with increasing phosphoric acid content, saturated solutions in the ZnSO4-H3PO4-H2O and CoSO4-H3PO4-H2O systems become more viscous and denser, reaching a maximum at the transition point, while these indicators in the CuSO4-H3PO4-H2O system only increase.

Formation of Fluorapatite in the Equilibrium System CaO–P2O5–HF–H2O at 298 K in a Nitrogen Atmosphere

The process of biomineralization of apatite in nature has been studied by scientists from various fields of science for more than a century. Unlike the volcanogenic, hydrothermal, and other types of igneous apatites, the genesis of which is entirely clear, the formation of phosphate ores of marine sedimentary origin is still debatable. Since phosphate concentrations in water bodies are too low for the spontaneous precipitation of solid phosphates, the study of different ways for their concentration is of particular interest. In this work, phase equilibria in the system CaO–P2O5–HF–H2O at 298 K, involving fluorapatite formation, have been studied. Fluorapatite is known to be the most common phosphate mineral and the main source of phosphorus on Earth, playing an important role in the mineralization process of dental tissues in vertebrates. The equilibrium in the system defined above was studied at a low mass fraction of the liquid phase components, i.e., in conditions close to natural. It has been shown that the compounds of variable composition with the fluorapatite structure containing HPO42− ions were formed in the acid region of this system. These compounds are formed at pH ≤ 7.0 and have invariant points with monetite, CaHPO4, and fluorite, CaF2. Stoichiometric fluorapatite was formed at the lowest concentrations of the liquid phase components in a neutral and weakly alkaline medium and had an invariant point with Ca(OH)2. The composition of the resulting equilibrium solid phases was found to be dependent on the Ca/P ratio of the initial components and pH of the equilibrium liquid phase. Fluorite CaF2 was present in each sample obtained in this study.

Enhancing the equilibrium solubility of salicylic acid in aqueous media by using polyethylene glycols 200, 400 and 600 as cosolvents: Correlation and dissolution thermodynamics

The solubility of salicylic acid in three mixtures of polyethylene glycol (PEG) with different molar masses of 200 to 600 g/mole were experimentally determined by a shake flask method at temperature range of (293.15 to 313.15) K under ambient pressure (≈85 kPa). The experimental results indicated that the solubility of salicylic acid enhanced by the introduction of PEGs to the water, and that could be explained with Hansen’s parameters and like-dissolves-like rule. Based on the results, PEG 600 had the best solubilization power, whereas PEG 200 displayed the lowest solubilization power, and generally the solubility decreased with decreasing molar mass of PEG and also decreasing temperature. Moreover, the equilibrium solid phase crystal of salicylic acid is characterized with X-ray powder diffraction analysis to identify no polymorphic transformation, solvate formation or crystal transition during the whole solvent crystallization process. A number of linear and nonlinear cosolvency models including the Jouyban-Acree based models along with the equations of van’t Hoff, the mixture response surface, the combined nearly ideal binary solvent/Redlich-Kister, λh and the modified Wilson-van’t Hoff were challenged to correlate/predict the solubility of salicylic acid in these mixtures. The computed values of the Jouyban-Acree based models presented a good agreement with the experiment data than the others, as a consequent of a low mean percentage deviation (MPD ≤ 15.7%). According to the enthalpy–entropy compensation analysis, there observed slope changes indicating that two mechanisms, enthalpy or entropy controlled the solubility increment depending on the PEG mass fraction in each solution.

Phase Equilibrium and Crystallization Process of the Ternary System KCl-(NH2)2CO-H2O at Different Temperatures

The phase equilibriums of the ternary system KCl-(NH2)2CO-H2O at 303.15 K, 323.15 K, 333.15 K, and 343.15 K were studied using the isothermal dissolution equilibrium method, in which the composition of equilibrium solid phase was determined by Schreinemaker’s wet residue method and X-ray diffraction (XRD) method. It was found that the ternary system is a simple cosaturated system, without the formation of neither double salt nor solid solution. Wilson and NRTL models were employed to correlate in the solubility data of the system at experimental temperatures. The maximum values of RAD and RMSD of the Wilson model were 2.18 × 10−2 and 0.83 and those of the NRTL model were 1.69 × 10−2 and 0.40, respectively. The two models were utilized to forecast solubility data at various temperatures, and the obtained outcomes were in line with the literature data. Based on the experimental solubility data at 343.15 K, the cooling crystallization process of the system was monitored online by focused beam reflectance measurement (FBRM) and particle video microscope (PVM). The crystal products were characterized by XRD, scanning electron microscope (SEM), and energy dispersive spectrometry (EDS). The results showed that the precipitation of (NH2)2CO occurred during the crystallization process, and this was followed by KCl. KCl was formed on the surface of (NH2)2CO crystal. The crystal was a simple mixture containing KCl and (NH2)2CO.

Exploration of Large-Scale Application of Efficient and Clean Utilization of Low-Grade Bauxite

In recent years, the rapid development of the domestic alumina industry has greatly accelerated the consumption of high-alumina–silica-ratio bauxite resources in China. The development of an efficient and clean utilization technology applicable to low-grade bauxite in China is not only a requirement for resource and environmental protection, but also a powerful guarantee to maintain the sustainable development of China’s aluminum industry. Based on this, the authors’ team proposed a new process for the treatment of low-grade bauxite ore via a calcification–carbonization method from the perspective of equilibrium solid-phase reconstruction and achieved the first industrial-scale trial run on the basis of existing laboratory research. The results show that the mass fraction of Na2O in bauxite residue can be reduced to 0.95% in the treatment of typical diaspore bauxite, the A/S in the bauxite residue can be reduced to 0.85 after two-time carbonization–alumina dissolution, and the actual alumina dissolution rate can reach 81.32%. The relevant results verified the feasibility and advantages of the calcification–carbonization method in industrial production.

Determination of L-Glutamine Solubility in 12 Pure Solvent Systems from 283.15 to 323.15 K

The mole fraction solubility of L-glutamine in 12 pure solvents (methanol, n-propanol, sec-butanol, 2-butanone, ethanol, acetonitrile, n-butanol, ethyl acetate, n-pentanol, water, n-hexane, and isobutanol) was determined by the static gravimetric method at a temperature range of 283.15–323.15 K under a pressure of 98.8 kPa. The equilibrium solid phase of L-glutamine in the solvent systems was characterized by powder X-ray diffraction analysis. The solubility in the 12 monosolvents was found to increase with absolute temperature. The maximum and minimum values were in water and ethyl acetate, respectively. The empirical solvent polarity parameters (ET(30)), cohesive energy density, and hydrogen bond donor/acceptor (HBD/HBA) tendencies were employed to analyze the solubility behavior and solvent effects. The solubility data were fitted using the modified Apelblat model and the Yaws model, at the same time, the model parameters and data deviation values were calculated. These two solubility models were evaluated using the Akaike Information Criteria and Akaike weights. The results showed that the modified Apelblat model had better correlation results. The solubility data could be used in the preparation and optimization of L-glutamine crystallization processes.

Solubility and Polymorphism of a HOF Monomer N1,N3,N5-Tris(pyridin-4-yl)benzene-1,3,5-tricarboxamide in 12 Neat Solvents at Temperatures from 283.15 to 323.15 K

A gravimetric method is adopted to measure the solid–liquid equilibrium of N1,N3,N5-tris(pyridin-4-yl)benzene-1,3,5-tricarboxamide (TPBTC), a hydrogen-bonded organic framework (HOF) monomer in different solvents (methanol, dichloromethane, isopropanol, n-hexane, acetone, ethanol, 2-butanone, n-butanol, acetonitrile, water, ethyl acetate, and n-propanol). The experiment is carried out at atmospheric pressure, and the experimental temperatures range from 283.15 to 323.15 K. The powder X-ray diffraction analysis was performed on the equilibrium solid-phase characterization of TPBTC in different solvents, and the solid form of solute in equilibrium with different solvents was a mixture of three kinds of crystalline forms and an amorphous form. In the 12 monosolvents, the solubility increased with absolute temperature, and the following order was obtained: 2-butanone > isopropanol > n-propanol > n-butanol > ethyl acetate > acetonitrile > methanol > ethanol > dichloromethane > n-hexane > acetone > water. In the studied temperature range, the maximum and minimum values were recorded for 2-butanone (0.6753 × 10–3 mol/mol at 323.15 K) and water (0.004650 × 10–3 mol/mol at 283.15 K), respectively. The solubility behavior and solvent effects in various solvents were first investigated by the hydrogen bond acceptor tendencies as the main factor then interpreted by solvent polarity, cohesive energy density, and steric effect for some exceptions. In addition, the solid–liquid equilibrium data of TPBTC were correlated with the Yaws model and the Apelblat model. Furthermore, the two thermodynamic models were evaluated using the Akaike Information Criterion and Akaike weights. It can be observed that the Yaws model was more appropriate than the Apelblat model.

Numerical Analysis of Sulfamerazine Solubility in Acetonitrile + 1-Propanol Cosolvent Mixtures at Different Temperatures

The current challenges of the pharmaceutical industry regarding the environmental impact caused by its waste have led to the design and development of more efficient industrial processes. In this context, solubility studies are at the core of different processes, such as formulation, preformulation, synthesis, purification, recrystallization, quantification, and quality control. This research evaluates the solubility of sulfamerazine (SMR) in acetonitrile + 1-propanol cosolvent mixtures at nine temperature levels with UV/vis spectrophotometry using the vial-shake method. According to the analysis of the solid phase in equilibrium using differential scanning calorimetry, there were no polymorphic changes. The minimal solubility of SMR was reached in 1-propanol at 278.15 K, and the maximal solubility in acetonitrile at 313.15 K. In all cases, the process was endothermic and dependent on the cosolvent composition, and the solution enthalpy drove the solution process. The solubility data were well correlated with the van’t Hoff, Yalkowsky–Roseman–van’t Hoff, Apelblat, Buchowski–Ksiazczak λh, Yaws, NRTL, Wilson, and modified Wilson models, with the YR model being one of the most attractive because it presented an excellent prediction percentage from four sets of experimental data. The solution process of SMR in acetonitrile + 1-propanol cosolvent mixtures depends on the affinity of SMR for acetonitrile and temperature increase.

Design of a Device and System to Study the Liquid–Solid-Phase Equilibrium Experiment of CO2 in PLNG

Pressurized liquefied natural gas (PLNG) is a new natural gas liquefaction solution proposed in recent years for reducing the construction and operating costs of floating liquefied natural gas (FLNG). For natural gas, the liquefaction temperature is strongly influenced by the pressure; when the pressure increases, the liquefaction temperature of natural gas increases accordingly. The increase in the liquefaction temperature of natural gas leads to a higher solubility of impurities such as carbon dioxide, which means that the pretreatment standards for liquefied natural gas can be reduced. Therefore, the use of PLNG technology can simplify pretreatment plants and significantly reduce construction and operating costs. In order to better apply PLNG technology to FLNG, it is necessary to understand the solubility of carbon dioxide in pressurized LNG and the phase change during liquefaction. To achieve this, experimental setups are needed to simulate the temperature and pressure environment of the LNG to obtain the relevant data and observe the relevant phenomena. After a literature research and analysis of the advantages and disadvantages of previous experimental setups, several improvements are proposed in this paper, and based on this, a visualization device is designed for studying the liquid–solid-phase equilibrium experiment of CO2 in PLNG. The device has a pressure resistance of 20 MPa, a minimum operating temperature of 77 K, and a variable volume function. It is also equipped with a sapphire window to be able to observe the inside of the device. In order to verify the superiority of the device, experiments were conducted using the device to verify the pressure resistance, variable volume, and visualization functions of the device. The experimental results show that the experimental device designed in this paper does have a certain superiority.

Study on Stable Phase Equilibria of Quinary System LiBr–NaBr–KBr–MgBr2–H2O at 298.15 K

According to the composition characteristics of mineral elements in underground brine in the Sichuan basin of China, the complete phase equilibria and phase diagram of the quinary system LiBr–NaBr–KBr–MgBr2–H2O were studied at 298.15 K. Using the experimentally determined solubilities and equilibrium solids, the spatial stereo phase diagram of the quinary system, the dry base projection phase diagrams of the saturated surfaces of the four salts MgBr2·6H2O, KBr, LiBr·2H2O, and NaBr·2H2O, and the corresponding water content diagrams were plotted, respectively. The experimental results show that at 298.15 K, in addition to the four original components, the anhydrous salt NaBr and the double salt KBr·MgBr2·6H2O are formed. The phase diagram of the quinary system at 298.15 K contains 10 univariate curves, three invariant points, and six equilibrium solid-phase crystallization regions (KBr crystallization region, NaBr crystallization region, NaBr·2H2O crystallization region, MgBr2·6H2O crystallization region, LiBr·2H2O crystallization region, KBr·MgBr2·6H2O crystallization region). When MgBr2·6H2O or KBr is saturated, LiBr has a strong salting-out effect on KBr, NaBr, or MgBr2 and NaBr, while when LiBr·2H2O is saturated, MgBr2 has a salting-out effect on KBr and NaBr. All four saturated projection surfaces have MgBr2·6H2O, and NaBr is generated. These phase equilibrium data can provide a theoretical basis to guide underground brine mining and extract useful components.