Solid Liquid Phase Equilibrium Research Articles

Determination and molecular simulation of ternary solid–liquid phase equilibrium of succinic acid + maleic acid + water from 283.15 K to 333.15 K

This study used the isothermal saturation gravimetric method to examine the solid–liquid phase equilibrium relationships composed of succinic acid + maleic acid + water spanning from 283.15 K to 333.15 K. The experimental data were utilized for the purpose of plotting the equilibrium phase diagrams of ternary systems in the studied temperature range. There were three crystalline regions in each isothermal ternary phase diagram, two saturation boundary curves, and a co-saturation point. To broaden the use of data from binary and ternary phase equilibrium measurements, Wilson and NRTL models were utilized for correlation and expectation, while relative average deviation (RAD) and root mean square deviation (RMSD) were utilized to evaluate the computational exactness. The results show that the theoretically calculated values were found to be in near agreement with the experimental values, and both models were able to obtain more precise theoretical data under different experimental conditions. In addition, molecular simulation was employed to elucidate the interaction between succinic acid, maleic acid, and water. This study provides accurate and reliable data for the separation of succinic acid and maleic acid mixture in water. These findings can be utilized to make sense of the dissolvability conduct of succinic acid and maleic acid in aqueous solution.

Estimating the phase diagrams of deep eutectic solvents within an extensive chemical space

Assessing the formation of a deep eutectic solvent (DES) necessitates a solid-liquid equilibrium phase diagram. Yet, many studies focusing on DES applications do not include this diagram because of challenges in measurement, leading to misidentified eutectic points. The present study provides a practical approach for estimating the phase diagram of any binary mixture from the structural information, utilizing machine learning and quantum chemical techniques. The selected machine learning model provides reasonably high accuracy in predicting melting point (R2 = 0.84; RMSE = 40.53 K) and fusion enthalpy (R2 = 0.84; RMSE = 4.96 kJ mol−1) of pure compounds upon evaluation by test data. By pinpointing the eutectic point coordinates within an extensive chemical space, we highlighted the impact of the mole fractions and melting properties on the eutectic temperatures. Molecular dynamics simulations of selected mixtures at the eutectic points emphasized the pivotal role of hydrogen bonds in dictating mixture behavior.

N-Alkylisoquinolinium bromides and α,ω-alkanediols: Eutectic systems with co-crystal formation

This research focuses on ionic liquids (ILs), specifically N-alkylisoquinolinium bromides with various chain lengths: octyl, decyl, dodecyl, and hexadecyl. The study covers the synthesis and thermophysical characterisation of these compounds, as well as crystal structure determination for all excluding N-decylisoquinolinium bromide ([i-QuinC10][Br]). The obtained thermophysical parameters were compared with the literature data and also within the extended homologous series.The solid–liquid phase equilibria (SLE) in mixtures of ILs with certain α,ω-alkanediols (1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol) were investigated. As a result of SLE studies, eutectic mixtures capable of acting as eutectic phase-change materials - ePCMs - were determined. Additionally, a self-organization phenomenon was observed between specific pairs, leading to the formation of co-crystals (solid-complex phase). All binary mixtures with [i-QuinC8][Br] formed a simple eutectic system, while in the case of [i-QuinC10][Br], the formation of a non-congruent melting compound was observed in the systems with 1,8-octanediol and 1,10-decanediol. Among the systems with [i-QuinC12][Br], congruent melting compounds were observed for mixtures with 1,8-octanediol, 1,10-decanediol and 1,12-dodecanediol, while a simple eutectic was recorded for 1,6-hexanediol. IL [i-QuinC16][Br] co-crystalised only with 1,12-dodecanediol, while with other diols formed simple eutectic systems. Calorimetric analysis (DSC) and crystal structure determination (X-ray diffraction) were used to characterize the obtained supramolecular compounds.As a result, a series of ePCMs with melting points ranging from 295 K to 343 K are presented, with the {[i-QuinC12][Br] + 1,10-decanediol} system showing the highest enthalpy of melting (173.5 J·g−1). The found features and correlations between structure and properties imply the necessity for additional investigation, indicating the potential for a new generation of compounds with customizable physicochemical properties.

Solid-liquid phase equilibrium and thermodynamic properties analysis of 1,3,5-tribromobenzene in sixteen kinds of organic mono-solvents

Solid-liquid equilibrium solubility of 1,3,5-Tribromobenzene (m-TBB) in 16 pure solvents, including ethyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, acetone, 2-butanone, cyclohexanone, 1,2-dichloroethane, chloroform, cyclohexane, toluene, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) were determined by gravimetric method at different temperatures. The solubility of m-TBB increases gradually with the increase of temperature. The order of solubility of m-TBB in alkanes solvents is: chloroform > 1,2-dichloroethane > cyclohexane. The order of solubility of m-TBB in esters solvents is: amyl acetate > butyl acetate > propyl acetate > ethyl acetate > methyl acetate > ethyl formate. The order of solubility of m-TBB in ketones solvents is: cyclohexanone > 2-butanone > acetone. The order of solubility of m-TBB in other solvents is: THF > toluene > DMA > DMF. The KAT-LSER model was selected to explore the solvent effect of m-TBB in the tested solvents. Four thermodynamic models, i.e., the modified Apelblat model, the λh model, the NRTL model and the Wilson model, were selected for correlate the solubility data of m-TBB in 16 mono-solvents. The RAD and the RMSD values of NRTL model were all less than 1.67 × 10-2 and 3.82 × 10-4, respectively. All the four theoretical models can correlate the solubility data of m-TBB well in the selected solvents. The dissolution process of m-TBB were calculated based on the Wilson model. The dissolution process of m-TBB is endothermic, entropy increase and spontaneous. The entropy contributes more to Gibbs free energy.

Solid–Liquid Phase Equilibrium: Alkane Systems for Low-Temperature Energy Storage

The thermal characterization of two binary systems of n-alkanes that can be used as Phase Change Materials (PCMs) for thermal energy storage at low temperatures is reported in this work. The construction of the solid–liquid binary phase diagrams was achieved using differential scanning calorimetry (DSC) and Raman spectroscopy. The solidus and liquidus equilibrium temperatures were determined using DSC for thirty-nine different samples, three for the pure n-alkanes and the remaining for binary mixtures at selected molar compositions and used to acquire the corresponding solid–liquid phase diagrams. The two binary systems of n-octane/n-decane (C8/C10) and n-decane/n-dodecane (C10/C12) are characterized by a eutectic behavior at low temperatures. The eutectic temperature for the system C8/C10 was found at 211.95 K and the eutectic composition appeared at the molar fraction xoctane = 0.87. For the system C10/C12, the eutectic temperature was found at 237.85 K, and the eutectic composition appeared for the molar fraction xdecane = 0.78. This work aims to fulfill the lack of available data in the existing literature, considering the potential application of these systems for low-temperature thermal energy storage. Raman spectroscopy was used to complement the DSC data for the construction of the solid–liquid phase equilibrium diagrams, enabling the identification of the solid and liquid phases of the system. Additionally, the liquidus curve of the phase diagram was successfully described using a modified freezing point depression curve as fitting equation, the absolute root mean square deviation for the data correlation of the C8/C10 and C10/C12 systems being 2.56 K and 1.22 K, respectively. Ultimately, the fitting procedure also enabled a good prediction of the eutectic point for both studied systems.

Solid-liquid phase equilibrium and thermodynamic model of ternary system (NH4+ //SO42−, H2PO4−–H2O) from 313.15 to 343.15 K

A tremendous amount of wastewater containing ammonium salts, mainly NH4H2PO4 and (NH4)2SO4, has been produced in the production of cathode material of lithium iron phosphate (LFP). However, as an important basis for salt separation, the solid–liquid phase equilibrium (SLPE) of these two salts has been investigated by few studies. In this study, SLPE of the ternary system (NH4+ //SO42−, H2PO4−–H2O) from 313.15 K to 343.15 K at 101.2 kPa were investigated by isothermal dissolution method, and the corresponding physicochemical properties (density, viscosity, and pH) of saturated solution were measured. The phase diagram is composed of one invariant point, two univariant curves, and two single-salt crystallization fields for NH4H2PO4 and (NH4)2SO4. Comparing the phase diagrams from 263.15 K to 343.15 K, it is obvious that two single-salt crystallization fields shrink with increasing temperature. And the area reduction of NH4H2PO4 in two salts is more significant. When the temperature drops below 268.15 K, the ice crystallization field would appear. Neither single-salt solid solution, hydrous salt nor double salt was found in the whole temperature range. Furthermore, Pitzer model was successfully applied to describe the SLPE of the ternary system at temperatures from 273.15 K to 343.15 K. The lacking Pitzer-model parameters of mixed electrolytes (θSO4-H2PO4 and ψNH4-SO4-H2PO4) were calculated, and the temperature coefficients of model parameters and dissolution equilibrium constant were obtained. The importance of this study is that it supplies basic data and theoretical references for the separation and resource utilization of two ammonium salts from wastewater in the LFP batteries industry.

Glutaric acid purification by coupled solution crystallization and melt crystallization

The mixed dibasic acids (DBA) is a by-product during adipic acid (ADA) production by oxidation of cyclohexanol or cyclohexanone, which contains large amount of glutaric acid (GA) with ADA and succinic acid (SA). In this work, we have explored the feasibility of the coupled solution crystallization and melt crystallization for the purification of GA. To obtain fundamental thermodynamic properties for the process design, the gravimetric method was used to measure the solubility of the three dibasic acids in water from 293.15 K to 345.15 K at atmospheric pressure. The results showed that GA was the most soluble component while all solubility increased with increasing temperature. Therefore, it is reasonable to concentrate GA in the liquid phase by cooling crystallization. Similarly, the ternary solid-liquid melt equilibrium phase diagram was constructed based on the experimental data of the three binary subsystems (GA-ADA, GA-SA, ADA-SA). It was found that the concentrated GA after solvent evaporation could be purified by melt crystallization efficiently. Thus a coupled solution crystallization and melt crystallization process was designed. With the operated operating parameters, the purity of GA could reach 99.06% by secondary melt crystallization. Overall, the coupled solution crystallization and melt crystallization method to separate DBA has proven to be effective.

Thermodynamics of the solid-liquid phase equilibrium of a binary system: Effect of a chemical reaction in the liquid and epitaxial strain in the solid

We introduce two thermodynamics models of solid-liquid phase equilibrium of a binary system in the presence of (a) a chemical reaction in the liquid involving only one of the binary components and, (b) strain-inducing epitaxial conditions on the solid in addition to the chemical reaction in the liquid. These models show the existence of the counter intuitive behavior that epitaxy may promote recrystallization of the solid in spite of the reaction driving dissolution. The conditions for this recrystallization behavior are determined by the value of the epitaxial lattice matching composition, the temperature and the overall composition of the binary solid-liquid system.

Solid-liquid phase equilibrium and thermodynamic properties analysis of Bazedoxifene acetate in fifteen kinds of mono-solvents

Crystallization is widely used for the isolation and purification of active pharmaceutical ingredients (APIs) in the final manufacturing stage. Bazedoxifene (BZD) acetate, classified as a third-generation selective estrogen receptor modulator, is employed in the treatment of postmenopausal osteoporosis. This work reports the equilibrium solubility data of BZD acetate in fifteen different mono-solvents, including methanol, ethanol, n-propanol, i-propanol, n-butanol, ethyl formate, methyl acetate, ethyl acetate, acetone, 2-butanone, cyclohexanone, tetrahydrofuran (THF), 2-methyltetrahydrofurane (2-MeTHF), 1,4-dioxane and acetonitrile (ACN), within the temperature range “T = 283.15–323.15 K” under p = 0.1 MPa. The solubilities of BZD acetate in various solvents increase with increasing temperature. Among the alcoholic solvents, the solubility order is as follows: methanol > ethanol > n-propanol > n-butanol > i-propanol. In esters solvent, the solubility of BZD acetate decreases in the following order: methyl acetate > ethyl acetate > ethyl formate. For ketones solvent, the solubility decreases in the following order: cyclohexanone > acetone > 2-butanone. The maximum value of BZD acetate solubility was 0.011 mol·mol−1 in tetrahydrofuran at T = 323.15 K, but the least data was found in ethyl formate at 283.15 K. Four thermodynamic models, i.e., the Yaws model, modified Apelblat model, λh model, and Wilson model were applied to fit the solubility data of BZD acetate in different solvents. Among them, the Wilson model represents the most accurate fitting outcomes. Finally, the thermodynamic functions of mixing (including enthalpy, entropy, and Gibbs energy) were calculated, and the results indicate a mixing process that is both spontaneous and driven by entropy. The solubility data, correlated models, and derived thermodynamic functions present essential thermodynamic fundamentals for the industrial production of BZD acetate crystallization, facilitating efficient separation and purification.

Solid-liquid phase equilibrium relationship of high salt wastewater of coal chemical industry and mechanism of crystallization and scaling process

Crystallization and scaling problem in the process of falling film evaporation was one of the key problems restricting the evaporation process in near-zero discharge of coal chemical wastewater. We studied the phase equilibrium data of the ternary system Na+, Mg2+//Cl--H2O at 303.15–373.15 K. And, the influencing factors of crystallization and scaling were investigated, the flow characteristics of high-salt wastewater descending film were analyzed and the scaling sites were predicted. Results showed the system was a simple ternary system. Both w(NaCl) and w(MgCl2) were linearly correlated with the temperature. The higher MgCl2 contents, the faster rates of crystallization and scaling; temperature and scaling rate showed a positive correlation; the fitted curve of scaling under different roughness was in accordance with y=ax+b. The flow characteristics in evaporation tubes of four high-salt wastewaters (10% NaCl+9, 11% CaCl2, 10% NaCl+9, 11% MgCl2) were simulated. The risk of precipitation scaling was obtained at 591 mm, 667 mm, 772 mm and 938 mm, which was also verified by falling film evaporation experiments. The phase equilibrium relationship was creatively combined with numerical simulation in this paper. Meanwhile, phase equilibrium data was introduced in the study of crystallization and scaling process. This study provided a theoretical basis for the reasonable control of salt scaling in evaporation process of coal chemical industry. It is benefit to ensure the efficient operation of the evaporator, achieve the recycling of inorganic salt products and maximize economic benefits. The goal of "near-zero discharge" would be achieved eventually.

Thermodynamic Modeling the Solid–Liquid Phase Equilibrium of a Water–Methanol–Potassium Dihydrogen Phosphate Ternary System with a Mixed-Solvent Electrolyte (MSE) Model

The solubility measurement of potassium dihydrogen phosphate (MKP) in a water–methanol system is of great significance for the salting-out crystallization of MKP. The solubility of MKP in the H2O–CH3OH solution was determined by the static equilibrium method in the range of 283.15–343.15 K, and the molar fraction of CH3OH varied from 0.0588 to 0.6923. The mixed-solvent electrolyte model (MSE) was used to regress the experimental results, and new parameters were obtained. Based on it, the thermodynamic model of the H2O–CH3OH–MKP system was established, which is in good agreement with the experimental results, with a relative average absolute deviation of 6.46%. Then, the change in the ion concentration and the activity coefficients in the system were predicted by the thermodynamic model. Finally, the Pixact Crystallization Monitoring (PCM) system and a scanning electron microscope (SEM) were used to observe the crystallization process and the morphology of MKP in the H2O–CH3OH system, respectively.

Solid-liquid phase equilibrium of 2, 4-epibrassinolide in binary mixed solvents: Solubility determination, model correlation, preferential solvation and thermodynamic properties

The solubility of 2, 4-epibrassinolide in four binary mixed solvents including (ethanol + water, isopropanol + water, acetone + water, and acetonitrile + water) with numerous compositions was determined at temperature of 283.15 K to 323.15 K by a laser dynamic method. The solubility of 2, 4-epibrassinolide in all four binary solvent mixtures increases with increasing temperature. At a given temperature, it shows a trend of increasing and then decreasing with increasing mole fraction of water. In the same solvent composition, the order of solubility is isopropanol + water > ethanol + water > acetone + water > acetonitrile + water. The experimental solubility data of 2, 4-epibrassinolide was correlated with the modified Apelblat, Van’t Hoff, NRTL, Wilson, and three-suffix Margules model. The preferential solvation mechanism of 2, 4-epibrassinolide in four aqueous solutions was also discussed by IKBI method. Furthermore, the Wilson model was worked to analyze the thermodynamic mixing properties of the solutions, including ΔmixG, ΔmixH and ΔmixS. All ΔmixG values are negative indicating that the mixing process of 2, 4-epibrassinolide in these solvents is spontaneous.

Solid-liquid phase equilibrium for the system ammonium polyphosphate-urea ammonium nitrate-potassium chloride-water at 273.2 K

Based on the dynamic method, a quaternary system of ammonium polyphosphate (APP)-urea ammonium nitrate (UAN, CO(NH2)2-NH4NO3)-potassium chloride (KCl)-H2O and its subsystems (APP-[CO(NH2)2-NH4NO3]-H2O, KCl-[CO(NH2)2-NH4NO3]-H2O and APP-KCl-H2O) were systematically investigated at the temperature of 273.2 K. Each ternary phase diagram contains one invariant point and three crystallization regions. The crystallization regions are: (1) (NH4)3HP2O7, (NH4)4P2O7 and ((NH4)3HP2O7 + (NH4)4P2O7) for APP-[CO(NH2)2-NH4NO3]-H2O diagram; (2) KCl, KNO3 and (KCl + KNO3) for KCl-[CO(NH2)2-NH4NO3]-H2O diagram and (3) (NH4)3HP2O7, KCl and ((NH4)3HP2O7 + KCl) for APP-KCl-H2O diagram. The quaternary phase diagram of APP-[CO(NH2)2-NH4NO3]-KCl-H2O has no quaternary invariant point but includes four solid phase crystallization regions, i.e., (NH4)3HP2O7, (NH4)4P2O7, KNO3 and KCl, in which the KNO3 region occupies the largest area. The maximum total nutrient content (N + P2O5 + K2O) existing as ionic forms in the APP-[CO(NH2)2-NH4NO3]-H2O, KCl-[CO(NH2)2-NH4NO3]-H2O, APP-KCl-H2O and quaternary systems is 44.70%, 32.86%, 45.56% and 46.23% (mass), respectively, indicating that the maximum nutrient content can be reached using raw materials of the corresponding systems to prepare liquid fertilizer. In the quaternary system, the content of NH4+-N ascends with the increase of the total nutrient content, while the contents of NO3--N and CO(NH2)2-N increase with elevated total N. This work can help optimize the operating parameters for the production, storage and transportation of liquid fertilizers.

Experimental analysis and modeling of the molecular architecture influence on the solid-liquid transition of ethylene/1-octene copolymer solvent systems

The knowledge of solid-liquid equilibria of polymer-solvent systems is particularly important for further clarifying and understanding polymer crystallization. The molecular architecture in terms of molecular weight and branching related to the semicrystallinity of the polymer plays a key role in solid-liquid equilibria in polyethylene-solvent systems. Recently, a new thermodynamic model based on the Lattice Cluster Theory and continuous thermodynamics was developed, which can capture the influence of molecular weight distribution and degree of branching on solid-liquid equilibria. The model was applied to ethylene/1-hexene copolymer-solvent systems. However, the experimental database for solid-liquid equilibria of polymer solvent systems, where comprehensive molecular information of the polymer is connected with morphological quantities, e.g., semicrystallinity, and solid-liquid phase equilibria, is scarcely available in the literature. Therefore, herein a concept for this structure-property relationship is developed for ethylene/1-octene copolymer-solvent systems. The experimentally determined structure-property relationships are then used for determining the parameters of the statistical thermodynamics model and for model validation. The thermodynamic model allows the investigation of the transition zone from branching to molecular weight-induced solid-liquid equilibrium in dependence on the polydisperse nature of ethylene/1-octene copolymers.

Solid-liquid phase equilibrium of adiphenine hydrochloride in twelve pure solvents

The solubility and apparent thermodynamic properties of Adiphenine hydrochloride (ADH) (Form I) in twelve mono-solvents including methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, n-amyl acetate, isopropyl acetate, isobutyl acetate, n-hexanol, n-heptanol, n-octanol, anisole and acetone were reported in this work. The solubility of ADH (Form I) was quantified by the laser monitoring method at atmospheric pressure and the selected temperature ranged from 278.15 K to 323.15 K. In the same solvent, the lower the temperature is, the less the solubility of ADH (Form I) is. A maximum mole fraction solubility of ADH (Form I) existed in n-hexanol (0.2241) at 323.15 K while the minimum mole fraction solubility (1.139 × 10−4) appeared in isopropyl acetate at 278.15 K. The experimental values of solubility were fitted by modified Apelblat model, NRTL model and UNIQUAC model, and it was found that the calculated values of the NRTL model and the modified Apelblat model were closer to the experimental values. The dipolarity/polarizability of the solvent and the acidity of the hydrogen bonds both play a positive role in increasing the solubility of ADH (Form I). The apparent thermodynamic properties of the dissolution process of ADH (Form I) were analyzed by the van't Hoff equation. It can be found that the dissolution process is an entropy-driven endothermic processes.

Modelling the solid–liquid–vapour phase behaviour of n-alkanes in a TPT-1 framework

We study the global phase behaviour of n-alkanes applying Wertheim's first order thermodynamic perturbation theory (TPT1). The molecules are modelled as homonuclear chains comprised of m freely jointed spherical segments interacting via the Lennard-Jones potential. Vega et al. [J. Chem. Phys. 116, 17 (2002)] have shown that the TPT1 is suitable to treat solid phases as well as fluid phases when model chains are considered, but that the adoption of a fully flexible chain model leads to the under-prediction of triple point temperatures and overestimation of the fluid ranges in comparison to experiment. Here, we propose a model in which a different number of segments are used to treat the fluid and the solid phase. The number of segments used to model the molecules in the fluid phase , and the LJ monomer potential parameters σ and ε are taken from published soft-SAFT values, whereas in the case of the solid phase a reduced temperature-dependent effective chain length is determined through a minimisation between theoretical and experimental liquid-solid phase equilibrium data. We refer to this model as effective-solid TPT1 (es-TPT1). We use the model proposed to calculate the solid–liquid–vapour phase diagrams of several n-alkanes and compare with experimental data. In the approach proposed, the conformation of chains in the solid phase is decoupled from the fluid phase, and an excellent description of the melting properties, as well as accurate predictions of the triple point temperatures for the n-alkanes examined is obtained. This simple solution provides an avenue to model the solid–liquid–vapour phase behaviour of other real substances in a TPT1 framework, and hence within the SAFT family of equations.

Insights into the structural features of deep eutectic solvents: the eutectic point as an unicum in their physical properties and the surface tension as a method for its determination

Deep Eutectic Solvents (DESs) are a class of solvents that are increasing their relevance thanks to their environmental-friendly characteristics, to their catalytic properties and to the complexity of their structural features. Formed by simply mixing two H-bond capable substances in solvent-free conditions, the network of interactions between them and between the molecules of the same species lead to a difficult crystal lattice organization, therefore to liquid systems at certain molar ratio of the formers. Solid-liquid phase equilibrium profiles can then be written in order to identify the eutectic point of the mixtures, the minimum in the melting points of the systems.In this work the structural features of a DES mixture at different molar fractions were analysed in order to underline eventual singularities at the eutectic point. Ionic conductivity, viscosity and surface tension measures of the liquids at different molar fractions were analysed. It emerged that the eutectic point is a unicum in the mobility of the charges (as emerged from ionic conductivity activation energies) that is more hampered at the eutectic; the surface tensions showed a minimum correspondent to the same eutectic, indicating a less-structured liquid at this point; viscosity on the contrary didn’t show any singularity in the profiles.The surface tension was then applied as a method for the determination of the eutectic point of different DESs liquids; the technique revealed to be precious for the eutectic point determination of really low-melting point mixtures, taking in account the structural diversity of the eutectic underlined with all the measures.

A novel bio-based phase change material of methyl palmitate and decanoic acid eutectic mixture: Thermodynamic modeling and thermal performance

One of the most sustainable methods of energy management is thermal energy storage using renewable phase change materials. Phase change materials (PCMs) with high latent heat can store thermal energy when available and release it effectively when required. In this study, the thermal properties of a set of binary mixtures of methyl palmitate (MP) and decanoic acid (DA) have been evaluated as a new bio-based and renewable PCM. Both phase change materials are obtained from vegetable oil and are biomass-based materials. The results show that the binary eutectic mixture consisting of 30% MP and 70% DA has the desired properties as a PCM for applying as thermal energy storage in the building materials. These features include the convenient melting and freezing temperatures (Tm = 20.19 °C, Tf = 15.08 °C) and the high value of corresponding latent heats (ΔHf =202.3 J.g−1, ΔHm = 201.43 J.g−1). Evaluating other thermo-physical properties of this mixture also confirms its fitness for the PCM role. The composition and melting point of the eutectic point and the solid-liquid phase equilibrium for these mixtures were predicted by several thermodynamic models from which UNIQUAC showed the lowest Average Relative Deviation percentage (ARD%) of 0.29%.

Examination of eutectic phase change materials composed of diols and ionic liquids

This paper presents solid–liquid phase equilibrium studies of binary systems composed of pyridinium chloride monohydrates: hexadecylpyridinium chloride monohydrate, [PyC16][Cl] or dodecylpyridinium chloride monohydrate, [PyC12][Cl] with diols: 1,2-hexanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol and 1,12-dodecanediol. These systems were selected to obtain eutectic mixtures with a high melting enthalpy and lower volatility (thus flammability) than pure diols. Ten eutectic Phase Change Materials (ePCMs) with melting points ranging from 265 K to 333 K (-8 °C to 60 °C) and enthalpies of melting from 125.9 to 212.8 J·g−1 were obtained. Experimental data were then correlated with the Non-Random Two-Liquid (NRTL) equation, and mixtures of eutectic composition were subjected to physicochemical characterisation. Using DSC, the latent heats of pure components and eutectic mixtures were determined, as well as the viscosity and the thermal conductivity of ePCMs was measured as a function of temperature. The final objective of the study was to increase the thermal conductivity of ePCMs by adding carbon nanotubes or expanded graphite, and to characterise the performance of such composite systems. The stability of nanofluids containing no less than 1 wt% SWCNTs and from about 10 wt% EG was confirmed under both isothermal and energy storage operating conditions, i.e. during a series of at least 1000 phase transformations. The addition of an inexpensive EG at 10 wt% increases the thermal conductivity by up to 200 % and reduces the probability of ePCM leakage as the material retains its shape even after melting.

Modeling and Optimization of a Suspension Crystallization Separation Process for para-Xylene Purification

The morphology and DSC methods were used for measuring the crystallization kinetics of para-xylene. Solubility data from DSC experiments were fitted using the activity coefficient model and classical solid–liquid phase equilibrium theory, while the rates of nucleation, growth, aggregation, and breakage (functions of supersaturation) were built from morphological experiments. The particle size distribution was modeled via a population balance equation and validated by experimental data on a suspension crystallization separation process. The effects of the crystallizer operating temperature and residence time on product yield were also investigated; although the rates of nucleation, growth, breakage, and aggregation increase with decreasing temperature and increasing residence time, the breakage and aggregation are dominant at low temperatures and long residence times. Therefore, the crystallization process should be operated at an optimal temperature and residence time. The models built for this work can be used further in additional process design and optimization.