Fluid Phase Equilibria最新文献

The micellar properties of octyltrimethylammonium bromide (C₈TAB) in both water and aqueous solutions of 1,2-propanediol have been investigated using accurate measurements of density, sound velocity, and surface tension in the temperature range between 293.15 and 308.15 K. The critical micelle concentration, CMC, the ionization degree, β, the standard thermodynamic parameters of micellization: free energy, Δ_micG°, enthalpy, Δ_micH°, entropy, Δ_micS° and the free energy of transfer, Δ_trG°, of the surfactant octyltrimethylammonium bromide in both water and 1,2 propanediol aqueous solution were evaluated from the experimental results.

The CMC of the surfactant increases as the concentration of 1,2-propanediol increases, while the temperature does not exert important changes within the range considered.

The value of the micellization thermodynamic parameters suggests that adding 1,2-propanediol makes the micellization process less favorable.

The thermodynamic functions of transfer were calculated. The values of the free energy of transfer are small and positive and increase as the diol concentration increases confirming that the transfer of the surfactant from the bulk into the micelle is less favorable.

The present work deals with the evaluation of the partial molar volumes at infinite dilution (${\overline{v}}_i^{\infty }$) of n-components systems based on the dependence of the experimental density (ρ) on composition without involving binary systems. To do this, the multicomponent solution is interpreted by defining the component (1) as the solvent and the mixture of the remaining (n-1) components as the pseudocomponent (2n), characterized by the inner mole fraction $x_i^o$. After the analysis of the concept of infinite dilution, equations are derived that allow evaluating the partial molar volumes at infinite dilution of the pseudocomponent (${\overline{v}}_{2n}^{\infty }$), based on both the dependence of ln ρ $\left(x_{2n}\right)$ and the apparent molar volume ${\varphi }_{v_{2n}}\left(x_{2n}\right)$. Then, on the basis of experimental evidences about the linear variation of ${\overline{v}}_{2n}^{\infty }$ on $x_i^o$, the relationship between ${\overline{v}}_i^{\infty }$ and ${\overline{v}}_{2n}^{\infty }$ was established.

The applicability of the derived expressions was verified in 36 different cases corresponding to 11 ternary systems in the temperature range of 293.15 ≤ T/K ≤ 323.15.

Furthermore, the invariance of the partial molar volume at infinite dilution of the (n-1) components with the proportion in which they are mixed is verified.

The phase transitions of calcium chloride between various hydrates and solid–liquid phase transitions are common in many natural and industrial processes. Recent studies have revealed some discrepancies in investigating the hydration and deliquescence of calcium chloride using different methods. In this study, water vapor sorption analysis and Raman measurements on CaCl₂·2H₂O and CaCl₂·6H₂O and their dehydration products were conducted. The results indicate two possible hydration sequences from lower hydrates to deliquescence at 298.15 K: (1) Hydration of the monohydrate to the dihydrate, followed by the formation of β-CaCl₂·4H₂O, ending with its deliquescence at 18.5 % RH; (2) Hydration of the monohydrate to the dihydrate, followed by the formation of α-CaCl₂·4H₂O and of the hexahydrate, ending with its deliquescence at 29 % RH. It was observed that the transition from pure dihydrate to β-CaCl₂·4H₂O occurs spontaneously, instead of hydration to the thermodynamically stable α-CaCl₂·4H₂O. The latter phase is only formed in the presence of crystal seeds of α-CaCl₂·4H₂O that remained after dehydration. Additionally, direct deliquescence of β-CaCl₂·4H₂O and thus absence of hydration to hexahydrate at 298.15 K is reported for the first time, which could be explained by the more similar lattice structure of CaCl₂·2H₂O (orthorhombic) and β-CaCl₂·4H₂O (monoclinic) than α-CaCl₂·4H₂O (triclinic). Apart from that, an explanation for the observed transformation sequence is proposed, considering the impact of the enhanced solubility of β-CaCl₂·4H₂O compared to the α-CaCl₂·4H₂O. The resulting water to salt ratio below six may contribute to the absence of CaCl₂·6H₂O formation. A Raman spectrum of CaCl₂·H₂O not reported previously is also provided.

Dipolar interactions play an important role for thermodynamic properties of many fluids and accordingly for their modeling. In molecular-based equation of state models, the effect of dipolar interactions is usually described by Helmholtz energy models. There are several Helmholtz energy models for dipolar interactions available in the literature today. In this work, eight dipole contribution models describing the dipole–dipole interactions of fluids were critically assessed by comparing their results with molecular simulation reference data of Stockmayer fluids. Therefore, the dipole contribution models were combined with an accurate Lennard-Jones (LJ) Helmholtz energy model. The following thermodynamic properties were considered in the comparison: vapor pressure, saturated densities, enthalpy of vaporization, surface tension (by using density gradient theory), critical point, second virial coefficient, and thermodynamic properties at homogeneous state points, such as the Helmholtz energy, pressure, chemical potential, internal energy, isochoric heat capacity, isobaric heat capacity, thermal expansion coefficient, isothermal compressibility, thermal pressure coefficient, speed of sound, Joule–Thomson coefficient, and Grüneisen parameter. For the evaluation of the dipole contribution models, molecular simulations for the Stockmayer fluid with the dipole moments of ${\mu }^2/4\pi {ϵ}_0\varepsilon {\sigma }^3=0.5,1,2,3,4,5$ were carried out. The results indicate, that all considered dipole models exhibit some significant weaknesses. Nevertheless, some dipole contribution models are found to provide a robust description for many properties and state ranges. Overall, the deviations of the dipole contribution models from the Stockmayer simulation data are, in most cases, an order of magnitude higher than the deviations of the LJ EOS from LJ simulation data.

Introduction of nanobubble (NB) into liquid can significantly affect the transport properties such as viscosity and diffusivity, being important in the design and optimization of many liquid-related industrial processes. The present paper reports the atomistic insights into influence of porosity (volume fraction of NBs in solution) and temperature on viscosity and self-diffusion coefficient in benzene liquid containing NBs by using molecular dynamics (MD) simulation with the COMPASS force field. We make molecular modeling of NB-containing benzene liquid using the cubic box with porosities increasing from 0 to 24.6% and conduct a series of MD simulations as increasing temperature from 298 to 343 K. Our simulations reveal that as increasing the porosity the viscosity decreases according to the cubic polynomial while the self-diffusion coefficient increases rapidly. When compared with high polar NB aqueous solutions, although the changing tendencies of transport properties are similar, the changing degrees in benzene liquid are clearly higher, indicating that NB creation has a stronger influence on transport properties of non-polar benzene liquid due to the weaker intermolecular interaction. Meanwhile, as increasing temperature, the viscosity decrease while the self-coefficient increases, both according to the Arrhenius equation. Such temperature dependence is similar to aqueous solution, meaning that temperature affects the transport properties of polar and non-polar liquids alike. This work will contribute to developing NB utilization to practical applications.

The significant rise in carbon dioxide (CO₂) emission due to industrial growth is a major global challenge. As a result, there is a need to implement various techniques to reduce and regulate this phenomenon. One such technique involves the utilization of ionic liquids (ILs) as solvents in CO₂ capturing and separation processes, which is already commonly practiced. In this study four advanced intelligent models, Extreme Gradient Boosting (XGBoost), Gradient Boosting (GBoost), Light Gradient Boosting Machine (LightGBM), and Categorical Boosting (CatBoost) have been proposed to predict the solubility of CO₂ in 160 different ILs based on factors such as temperature, pressure, and the chemical structure of the ILs. Findings indicate that the XGBoost model is the most accurate among the four models, with the root mean square error (RMSE) and coefficient of determination (R²) values of 0.014 and 0.9967, respectively. Moreover, the results reveal that increasing pressure, decreasing temperature, and lengthening the alkyl chain all increase the solubility of CO₂ in ILs. Furthermore, pressure and the number of –CH₂ substructure in ILs have the most significant impact on the CO₂ solubility in ILs, respectively. To ensure the XGBoost model's reliability, the model's data has been assessed using the leverage technique. The results show that 92.44 % of the data fell within the valid area, which is a substantial percentage and indicates the model's high reliability. The findings of this study will assist in designing and fine-tuning the chemical structure of ionic liquids specifically for CO₂ capture purposes.

The paper presents experimentally determined (solid + liquid) phase diagrams in the {LiBr (1) + ionic liquid (2) + water (3)} systems. Interpretation of the results and comparison with the literature data for the {LiBr + water} enables the determination of the influence of the ionic liquid on the LiBr solubility in water. It is known that one of the disadvantages of an aqueous lithium bromide solution is the tendency to crystallize, especially with a higher concentration of lithium bromide in the solution. This is one of the problems in absorption refrigeration technology where the aqueous lithium bromide solution is a working fluid commonly used on an industrial scale. One of the possibilities for improving the properties of this system is the use of an additive increasing the solubility of LiBr in water. In this work, the following ionic liquids (ILs): N-(2-hydroxyethyl)ammonium glycolate, N,N-di(2-hydroxyethyl)ammonium glycolate, N,N-di(2-hydroxyethyl)-N-methylammonium glycolate, and N,N,N-tri(2-hydroxyethyl)-ammonium glycolate were considered as an addition to the conventional system. The (solid + liquid) phase diagrams were determined using the dynamic method. Liquid phase range was determined at the absorber operating temperature, T = 303.15 K, and compared to LiBr + water system.

This study thoroughly investigates the solubility of oxazepam in supercritical carbon dioxide (SC-CO₂) at temperatures of 308, 318, 328, and 338 K and pressures ranging from 12 to 30 MPa. The solubility measurements revealed a mole fraction of oxazepam ranging from 2.50 × 10⁻⁶ to 7.13 × 10⁻⁵, with the highest solubility observed at 338 K and 30 MPa. The solubility data were effectively modeled using semi-empirical density-based models (Mendez-Santiago and Teja (MST), Chrastil, Bartle et al., Kumar and Johnston (K-J), and Alwi-Garlapati), two equations of state (Peng-Robinson and modified-Pazuki) and regular solution models. The K-J model emerged as the best fit for the experimental data, boasting the lowest Average Absolute Relative Deviation (AARD) value of 7.73 %. The Peng-Robinson equation of state outperformed the modified-Pazuki equation, with AARD values of 15.71 % and 18.15 %, respectively. The study's key finding is the low solubility of oxazepam in SC-CO₂, which suggests that supercritical antisolvent techniques could be effectively employed for synthesizing nanoparticles of this pharmaceutical compound. These findings have practical implications as they provide valuable insights for optimizing drug formulation processes and demonstrate the potential of SC-CO₂ in pharmaceutical applications.

The global phase equilibrium behavior of the CO₂+H₂S system is discussed in this work for temperatures ranging from 160 K up to the critical region. Solid phases of CO₂ and H₂S and corresponding equilibria have been modeled by considering either a 4^th-order equation of state (also used for the fluid phases) or a solid fugacity model for the pure components combined with an activity coefficient model (both coupled with a reference equation of state for the fluid phases).

Phase equilibrium calculations have been performed by the minimization of the Gibbs Free Energy of mixing and compared to existing literature data.

The types of pressure-mole fraction phase diagrams that can be encountered in the low-temperature thermodynamic region have been described. The temperature and pressure ranges where the phase behavior of the system changes have been identified and a representative phase diagram is presented for each range.

Lithium-based fluoride salts are one of the leading options as fuel matrix in Molten Salt Reactors. The understanding of their thermodynamic behavior, e.g. chemical stability, activity, as well as heat transfer properties, in the reactor’s environment is crucial for the safety assessment. In this work, the chemical equilibria of lithium fluoride with two important fission products dissolved in the salt matrix, namely barium fluoride and zirconium fluoride, are considered. The phase diagrams of the binary systems