Fluid Phase Equilibria最新文献

Shale oil/gas reserves are a major focus for current and future oil/gas exploration. The nanopores in shale vary in size and shape, greatly affecting the phase behavior and multiphase flow of reservoir fluids. Understanding the fluid phase behavior in nanopores is crucial for enhancing the shale oil/gas recovery efficiency. Numerous studies have explored the impact of pore sizes on phase behavior, while relatively few studies have been conducted on the influence of pore shapes on phase behavior. This paper develops a novel two-phase flash algorithm for confined fluids considering the effect of pore size and shape at specified volume and temperature. The proposed algorithm performs well under varying overall molar densities and temperatures. The results confirm that confined fluids in nanopores exhibit distinct phase behaviors compared to bulk fluids. Specifically, at a specified molar density, the dew and cricondentherm point temperatures rise in nanopores, the bubble point temperature decreases. Liquid-phase equilibrium pressure, vapor-phase saturation, and heavy component concentrations in both phases are lower in nanopores, while liquid-phase saturation and light component concentrations in both phases are higher. As pore size decreases and polygon sides of the pore cross-section increase, the phase behavior diverges further from bulk fluids. Polygons with more than 10 sides behave similarly to circular pores. The effects of nanopore cross-sectional shape on the phase behavior of fluids are different near the dew point and bubble point. This effect of the dew point temperature peaks at around 2 nm, while its influence gradually diminishes for the bubble point. As pore radius increases, the shape effect on capillary pressure, equilibrium pressure, and vapor composition peaks at 2 nm, but diminishes for saturation of vapor and liquid phases and liquid composition.

Thermodynamic properties of homogeneous fluids in the metastable and unstable regions are needed to describe confined fluids, interfaces, nucleating embryos and estimate critical mass flow rates. The most accurate equations of state (EoS) called multiparameter EoS, have a second, non-physical Maxwell loop that renders predictions unreliable in these regions. We elaborate how information from the stable region can be used to reconstruct the metastable and unstable regions. For a simple interaction potential, comparison to results from molecular simulations reveals that isochoric expansion of the pressure from stable states reproduces simulation results in the metastable regions. By constructing a dome that extends above the critical point, we obtain an extrapolated pressure from multiparameter EoS that is free of second Maxwell loops. A reconstructed EoS is developed next, by integrating the extrapolated pressure from a stable state to obtain the Helmholtz energy. The consistency of the reconstructed EoS is gauged by computing phase equilibrium densities, pressures, and enthalpies of evaporation, which are in reasonable agreement with experimental values. Combined with density gradient theory, the reconstructed EoS yields surface tensions of water, carbon dioxide, ammonia, hydrogen and propane that deviate, on average, 4.4%, 1.6%, 6.0%, 0.7% and 5.4% from experimental values respectively. The results reveal a potential to develop more accurate extrapolation protocols, which can be leveraged to obtain prediction of metastable properties, surface properties or used as constraints in fitting multiparameter EoS.

Aqueous Two-Phase Systems (ATPSs) constitute extractive media with applicability for the removal of a wide range of solutes, such as antioxidants or pharmaceuticals, and can be designed in a non-toxic and environmentally friendly manner. Nevertheless, prior to their general use at large scale, their liquid-liquid equilibria (solubility curves and tie-line compositions) need to be thoroughly determined.

In this work, 6 solubility curves were obtained for novel aqueous ternary systems containing choline salts (choline chloride, choline bicarbonate, choline (2R,3R)-bitartrate and choline di-hydrogen citrate) and either ethyl lactate (EL) or polyethylene glycol (PEG), at 298.15 K and 0.1 MPa. Moreover, 3 tie-line compositions were successfully determined for the system {ethyl lactate (1) + choline (2R,3R)-bitartrate (2) + water (3)}. Then, this novel ATPS was applied in the removal of three common pharmaceutical pollutants from aqueous media (acetaminophen, amoxicillin and salicylic acid). In these partition studies, salicylic acid and acetaminophen were effectively extracted to the top phase, with the highest partition coefficients ($K=9\pm 2)$ being obtained for salicylic acid in the longest tie-line (length of 0.8816). Acetaminophen achieved the most promising results ($K=2.2\pm 0.1$) in the shortest tie-line (length of 0.6192).

Aqueous solutions of sodium acetate (CH₃COONa) and potassium acetate (CH₃COOK) are considered effective alternative heat exchange media for frost-free air–source heat pumps (FFASHPs) owing to the low corrosiveness, low viscosity, and low cost. Equilibrium vapor pressure is the most crucial property that characterizes freezing point and latent heat transfer. However, studies on this property, especially in subzero temperature ranges are scarce. This study was conducted to experimentally investigate the equilibrium vapor pressure of CH₃COONa and CH₃COOK solutions. The developed apparatus and procedures were based on the static method, and validated by evaluating the vapor pressure of distilled water, n-heptane, and calcium chloride (CaCl₂) aqueous solution. Their average absolute deviations were within 1.94%. As the temperature increased from 263 to 328 K and solute concentration increased from 9.27 to 33.81 wt%, 124 data points of the vapor pressure of the CH₃COONa and CH₃COOK solutions were obtained, ranging from 0.2759 to 13.2608 kPa. Modified Antoine equation and ion interaction (Pitzer) model were established for correlation of the experimental data. The average absolute deviations of the CH₃COONa and CH₃COOK solutions produced by Antoine equation were 2.08 and 2.48%, respectively. Those produced by Pitzer model further decreased to 1.36 and 1.45% due to the import of osmotic coefficient and the accuracy improvement. Furthermore, according to the experimental and calculation results, the vapor pressure of the CH₃COONa solution was lower than that of the CH₃COOK solution. Therefore, under the same antifreezing conditions, the CH₃COONa solution facilitates latent heat absorption from ambient air, while the CH₃COOK solution is conducive to achieve regeneration. The results of this study provide foundational data for the vapor pressure of the two solutions and can promote their application in FFASHPs.

We use molecular dynamics simulations to study liquid droplets and bridges inside crystalline pores having triangular, square, hexagonal, and circular cross-sections of varying dimensions. The role of wettability is also investigated by varying solid-fluid interaction strengths. We analyze the stability of liquid droplet or bridge, the density distribution within a droplet or bridge, and the propensity of liquid to occupy corners of polygonal cross-sections of pores. The solid-fluid interfacial free energies calculated from Monte Carlo simulations and a thermodynamic model are used to estimate the free energy change of liquid occupying the corners of a pore. Liquid droplets and liquid bridges are observed for weakly and strongly attractive nanopores, respectively. Both droplets and bridges are unstable inside nanopores having the largest cross-sectional dimension smaller than 10 molecular diameters. Both the liquid configurations are more unstable inside nanopores having hexagonal cross-sections. The propensity of liquid to occupy the corners of a polygonal cross-section of a nanopore decreases with decrease in the number of sides of the polygon.

As a result of strong molecule–molecule and molecule–wall interactions, phase behavior in confined fluids differs significantly from that in bulk fluids. Asphaltene precipitation is a challenging issue for both conventional and unconventional (nano-scale) porous media. In this study, a new model based on cubic-plus-association equation of state (CPA-EOS) was developed for studying phase behavior of asphaltenic crude oil and asphaltene precipitation in nanoporous media. The developed model considers confinement phenomena including shift in the critical properties of components, high capillary pressure, and adsorption/desorption of fluid components on rock surface. For this purpose, necessary modifications were performed on both the EOS and phase equilibria calculations. The developed model was then used to analyze two-phase (vapor–liquid) and three-phase (vapor–liquid–asphaltene) behavior in confined systems. Results demonstrated that confinement phenomena shrink the two-phase envelope and shift the critical point of the mixture. It is also shown that instability of asphaltene in the solution is higher in nanoporous media and increases with reducing pore size. Therefore, the amount of precipitated asphaltene in nanoporous media is higher than that in conventional systems. As adsorption of components with higher molecular weights is more than that of low-molecular weight compounds, the crude oil sample is enriched with lighter components and hence, due to adsorption, bubble point pressure increases, upper branch of dew point curve shifts downward and its lower branch shifts upward, and asphaltene instability increases. Neglecting confinement phenomena results in overestimation or underestimation of saturation pressures as well as asphaltene upper and lower onset points and the proposed model can be of high importance in predicting the extent of asphaltene precipitation during natural depletion or solvent injection in tight oil reservoirs.

Stimuli-responsive lyogels are considered to be smart materials due to their capability of undergoing significant macroscopic changes in response to external triggers. Due to their versatile and unique properties, smart lyogels exhibit great potential in various applications such as drug delivery or actuation processes. While Poly-N-isopropylacrylamide (pNIPAM) is widely known as a thermo-responsive material, it also shows significant solvent-responsive swelling behavior. For the systems tested, polar solvents induce strong swelling due to hydrogen bonding with the amide group, nonpolar solvents lead to significant shrinkage of the lyogels. The aim of this study is to investigate and to model this behavior for future application in chemical or biochemical reactors. As a current area of research, incorporating smart lyogel technology into (bio-)chemical reactors facilitates the development of smart reactor systems. Applying thermodynamic modelling with the g^E model COSMO-RS on the monomer or oligomers of pNIPAM, the correlation between solvent-polymer interactions and the degree of swelling can be observed. pNIPAM derivatives exhibit low infinite dilution activity coefficients (IDACs) in polar solvents with large degrees of swelling, while displaying an increase of IDACs in nonpolar solvents. Hydrogen bonds dominate the swelling behavior of lyogels not only in pure solvents but also in mixtures of solvents with varying polarity. Even in mixtures containing high amounts of nonpolar solvents, large degrees of swelling were observed due to the uptake of the polar solvent in the lyogel matrix. This effect can be observed in binary solvent mixtures but also in representative mixtures along an esterification reaction with varying carboxylic chain length of alcohol and carboxylic acids.

We report new experimental data of the ultrasonic measurements in three ionic liquids with triflate anion: 1-ethylpyridinium triflate, 1-butyl-3-methylimidazolium triflate, diethylmethylammonium triflate. The speed of sound was determined in the temperature range of $\left(297\text{–}374\right)K$ and the pressure range of $(0.1\text{–}196.2)\mathrm{MPa}$. In addition, the respective densities in this range were found using the acoustic route. For the first two substances, the effect of pressure-induced solidification is detected. It is shown that the high-pressure data on the sound velocity can be accurately predicted by applying the pressure fluctuation theory-based model using parameters, which requires only the data determined at the ambient atmospheric pressure. In turn, the density can be predicted using the Fluctuation Theory-based Equation of State (FT-EoS), which includes the isothermal nonlinearity parameter, which is argued as related to the frequency of interparticle oscillations. This interdependence is confirmed by the comparative analysis with the respective peak in the low-frequency Raman–Kerr spectrum.

In this study, we investigate the composition-dependent mechanical properties and elastic anisotropies of sII hydrogen hydrates using first-principles method. The evaluation of the elastic moduli and their direction dependency is achieved by computing the second-order elastic constants (SOECs) of the unit lattice. The various trends of elastic constants with the hydrogen composition of the cages introduces variations in the bonding strength, compressibility, stiffness, and shear properties of the structure which are captured by the Poisson's ratio, bulk, Young, and shear moduli, respectively. Elastic properties were found to be significantly influenced by the system's anisotropy, arising from the geometry of the cages and their unique arrangement within the lattice being affected by the increase in the hydrogen occupancy of the cages. The detailed analysis of elastic anisotropies revealed shifts in the strongest and weakest directions of the material with varying the hydrogen content of the cages. The Poisson's ratio captures the anisotropic bonding strengths within the crystal structure with the hydrogen composition of the lattice, explaining the reason behind the existence of strongest and weakest directions in terms of compression, tension, and shear forces. Taken together the established structure-property-composition relations will be useful in the design and optimization of hydrogen sII hydrates for energy storage applications.

In this work, gas liquid chromatography was used to obtain the retention data of volatile organic solvents (here referred as solutes) at different temperatures, T = (313.15 - 353.15) K and at atmospheric pressure. The retention data obtained was used to compute the activity coefficients at infinite dilution. The solvent was prepared by the combination of 1‑butyl‑2,3-dimethylimidazolium chloride and diethylene glycol at 1:2 molar ratio and was used as a stationary phase to evaluate intermolecular interactions of various volatile organic solvents, including (aromatic hydrocarbons, ketones, alkanes, alkenes, alkynes, alcohols, thiophene, acetonitrile and tetrahydrofuran). Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy were utilized to determine any possible shifts when the two compounds were assorted. TGA/DSC 1 was also utilized to determine the thermal stability of the investigated solvent and to confirm that there will be no bleeding on the column loading when operated at T = (313.15 - 353.15) K. The excess thermodynamic properties at infinite dilution including enthalpies, Gibbs free energies and entropy term were computed to further explain the types of interactions occurring between the systems. The activity coefficients at infinite dilution data were used to calculate the separation parameters (selectivity and capacity) to evaluate the feasibility of the solvent in separating the industrial mixtures. Values pertaining to selectiveness and capacity were evaluated and compared to other extracting solvents found in literature for the separation of azeotropic mixtures. The attained activity coefficients at infinite dilution data reveals that the investigated solvent better separate solutes at low temperatures and this is an added advantage when using 1‑butyl‑2,3-dimethylimidazolium chloride to diethylene glycol. In addition, the investigated solvent was found suitable for the extraction of azeotropic mixtures comprising alkanes and alcohols.