Phase Behavior Research Articles

An empirical model for predicting saturation pressure of pure hydrocarbons in nanopores

Due to the confinement and strong adsorption to the pore wall in meso‑ and nano pores, fluid phase behavior in the confined media, such as the tight and shale reservoirs, can be significantly different from that in the bulk phase. A large amount of work has been done on the theoretical modeling of the phase behavior of hydrocarbons in the confined media. However, there are still inconsistencies in the theoretical models developed and validations of those models against experimental data are inadequate.In this study, we conducted a comprehensive review of experimental work on the phase behavior of hydrocarbons under confinement and analyzed various theoretical phase-behavior models. Emphasis was given to the modifications to the Peng-Robinson equation of state (PR EoS). Through the comparative analysis, we developed a modified alpha-function in PR EoS for accurate prediction of the saturation pressures of hydrocarbons in porous media. This modified alpha-function accounts for the pore size and was derived based on the regression results through minimizing the deviation between the experimentally measured and numerically calculated saturation pressure data. Meanwhile, the thermodynamic properties of propane were calculated in the bulk phase and in the nanopores. Finally, we validated the newly developed model using the experimental data in synthesized mesoporous materials and real reservoir rocks.By applying the modified PR EoS, a more accurate representation of the experimentally measured saturation pressure data in confined nanopores was achieved. This newly developed model not only enhanced the accuracy of the predictions but also provided valuable insights into the confinement effects on the phase behavior of hydrocarbons in nanopores. Notably, we observed significant changes in the properties of propane within confined nanopores, including suppressed saturation pressure and fugacity, indicating a greater tendency for the gas to remain in the liquid phase. Enthalpy of vaporization was found to increase highlighting increased difficulty in transitioning from liquid to gas phase under confinement. Additionally, the new model predicts an increased gas compressibility factor in the nanopores suggesting a close resemblance of ideal gas due to the counterbalance between the attractive and repulsive forces. To validate the model, new datasets containing saturation pressures of propane and ethane under a wide range of temperatures and pore sizes were employed. The newly developed model was further applied to the experimental data obtained in real rock samples (sandstones, limestones, and shales). Interestingly, it was observed that the phase change in these samples predominantly occurred in the smallest pores. This finding highlights the importance of considering the pore size distribution when studying the phase behavior of hydrocarbons in a capillary medium even if the rock has high permeability.This study provided a simple and easy-to-implement modification to the PR EoS for accurate prediction of the phase behavior of petroleum fluids under confinement. The newly developed model for calculating saturation pressures of hydrocarbons demonstrates improved accuracy in representing experimental data compared to the previous models, while offering a more straightforward and simplified approach.

Profoxydim in Focus: A Structural Examination of Herbicide Behavior in Gas and Aqueous Phases.

This study investigates the chemical structure of profoxydim, focusing on its E-isomer, the main commercial form. The research aimed to determine the predominant tautomeric forms under various environmental conditions. Using proton and carbon-13 NMR spectroscopy alongside theoretical modeling, we examined tautomers and their conformers in different solvents (MeOD, DMSO, CDCl3, benzene) to mimic gas and aqueous phases. The findings reveal that the enolic form dominates in the gas phase, while the ketonic form prevails in aqueous environments, providing key insights into the herbicide's environmental behavior. We also observed an isomeric transition from E to Z under acidic conditions, which could affect profoxydim's reactivity in natural environments. The theoretical calculations indicated that in acidic conditions, the E and Z forms are nearly degenerate, with the E form remaining dominant in neutral environments. Additionally, QSAR models assessed the toxicity of various tautomers, revealing significant differences that could impact bioactivity and environmental fate. This research offers crucial insights into the structural dynamics of profoxydim, contributing to cyclohexanedione chemistry and the development of more effective herbicides.

An Overview of Interactions between Goat Milk Casein and Other Food Components: Polysaccharides, Polyphenols, and Metal Ions.

Casein is among the most abundant proteins in milk and has high nutritional value. Casein's interactions with polysaccharides, polyphenols, and metal ions are important for regulating the functional properties and textural quality of dairy foods. To improve the functional properties of casein-based foods, a deep understanding of the interaction mechanisms and the influencing factors between casein and other food components is required. This review started by elucidating the interaction mechanism of casein with polysaccharides, polyphenols, and metal ions. Thermodynamic incompatibility and attraction are the fundamental factors in determining the interaction types between casein and polysaccharides, which leads to different phase behaviors and microstructural types in casein-based foods. Additionally, the interaction of casein with polyphenols primarily occurs through non-covalent (hydrogen bonding, hydrophobic interactions, van der Waals forces, and ionic bonding) or covalent interaction (primarily based on the oxidation of proteins or polyphenols by enzymatic or non-enzymatic (alkaline or free radical grafting) approaches). Moreover, the selectivity of casein to specific metal ions is also introduced. Factors affecting the binding of casein to the above three components, such as temperature, pH, the mixing ratio, and the fine structure of these components, are also summarized to provide a good foundation for casein-based food applications.

Effect of cosolvents on the phase separation of polyelectrolyte complexes.

Evidence is shown that cosolvent mixtures control the coacervation of mixtures of oppositely charged polyelectrolytes. Binary and ternary solvent mixtures lead to non-monotonic solubility as a function of the average dielectric constants of the solvent mixtures. These data are rationalized by considering both electrostatic-driven phase separation and solvophobic-driven phase separation using group contribution effects on solubility parameters. These estimates are introduced into an effective Flory-Huggins interaction parameter within the framework of Voorn-Overbeek theory with variable dielectric constants and temperature dependences. Despite its simplicity, the model recovers salient experimental observations not only on their coacervate stabilities, but also on their lower critical solution temperature behaviors. These observations highlight the importance of weak van der Waals interactions in determining the phase behaviors of polyelectrolyte complexes relative to electrostatic correlations.

Study on the condensate gas phase behavior in Nano-porous media

The pore size in shale has reached the nanoscale. The phase behavior of fluids in nanopores deviates from classical theory, making conventional phase theory inapplicable to shale reservoirs. It is thus of great significance to clarify the phase behavior at the nanometer pore scale in shale. Based on the shale reservoir in the Kaybob of the Duvernay shale, Canada, 6 nm and 10 nm cubic model systems were constructed, and a microscopic physical model was prepared included pathways at 10 nm, 40 nm, 500 nm, and micrometer scale. The fluid phase behavior in nanopores was studied using molecular simulations and nanofluidic chip experiments. The results show that during the retrograde condensation process, the condensate gas in small-scale pores condenses first and is less likely to evaporate as the pressure decreases. The conclusions drawn are: (1) In nanopores, the dew point pressure of condensate gas is higher than that of the bulk phase, and the smaller the scale of nanopores, the higher the dew point pressure. (2) The volume ratio of condensate in nanopores is higher, increasing as pore size decreases. (3) The condensation rate of condensate in nanoporous media varies slowly with pressure drop; During evaporation, the condensation rate of condensate in small pores varies more slowly with pressure drop compared to the bulk phase but is faster in large pores.

Device-based 24-hour movement behaviours in adult phase III cardiac rehabilitation service-users during the COVID-19 pandemic: a mixed-methods prospective observational study

Purpose To examine changes in device-based 24-hour movement behaviours (MB), and facilitators and barriers to physical activity (PA) and exercise, during remotely-delivered cardiac rehabilitation (RDCR). Materials and methods This prospective observational study used wrist-worn GENEActiv accelerometers to assess MB of 10 service-users (63 ± 10 years) at the start, middle, and end of three-months of RDCR. Barriers and facilitators to PA and exercise were explored through self-report diaries and analysed using content analysis. Results At start, service-users were sedentary for 12.6 ± 0.7 h · day−1 and accumulated most PA at a light-intensity (133.52 ± 28.57 min · day−1) – neither changed significantly during RDCR. Sleep efficiency significantly reduced from start (88.80 ± 4.2%) to the end (86.1 ± 4.76%) of CR, with values meeting health-based recommendations (≥85%). Barriers to RDCR exercise included exertional discomfort and cardiac symptoms, and reduced confidence when exercising alone. Setting meaningful PA goals, self-monitoring health targets, and having social support, facilitated PA and exercise during RDCR. Conclusions Our RDCR programme failed to elicit significant changes in MB or sleep. To increase the likelihood of successful RDCR, it is important to promote a variety of exercise and PA options, target sedentary time, and apply theory to RDCR design, delivery, and support strategies.

Kinetic Phase Behavior of Binary Mixtures of Tri-Saturated Triacylglycerols Containing Lauric Acid

Kinetic Phase Behavior of Binary Mixtures of Tri-Saturated Triacylglycerols Containing Lauric Acid

Phase behavior of the carbon dioxide/toluene/poly(ethylene glycol) ternary system

The phase behavior of a carbon dioxide (CO2)/toluene (Tol)/poly(ethylene glycol) (PEG) ternary system was investigated in this study to consider the effect of the polymer species on the phase diagram. Measurements were performed using a synthetic method combined with laser displacement and turbidity measurements. Bubble points (vapor–liquid phase separation) were determined from changes in the piston displacement and cloud points (liquid–liquid (LL) phase separation) were determined from changes in the turbidity. The phase boundaries of the CO2 mass fractions ranging from 0.113 to 0.496 were measured by varying the Tol/PEG mass ratio. The homogeneous phase area decreased when the mass ratio of PEG to Tol increased and/or the temperature decreased. These changes in the LL phase-separation behavior were explained by referring to the free volume fraction and solubility parameter estimated using the Sanchez–Lacombe equation of state. The free volume integral fraction could explain the phase diagram, but not the solubility parameter; the effect of polymer species on the Px phase diagram of the ternary system was explained by considering specific interactions between dissimilar components. These results could promote a comprehensive understanding of the phase diagram of CO2/organic solvent/polymer systems and aid the prediction of phase behavior.

Production of Distinct Fibrillar, Oligomeric, and Other Aggregation States from Network Models of Multibody Interaction.

Protein aggregation can produce a wide range of states, ranging from fibrillar structures and oligomers to unstructured and semistructured gel phases. Recent work has shown that many of these states can be recapitulated by relatively simple, topological models specified in terms of multibody interaction energies, providing a direct connection between aggregate intermolecular forces and aggregation products. Here, we examine a low-dimensional network Hamiltonian model (NHM) based on four basic multibody interactions found in any aggregate system. We characterize the phase behavior of this NHM family, showing that fibrils arise from a balance between elongation-inducing and contact-inhibiting forces. Complex oligomers (including annular oligomers resembling those thought to be toxic species in Alzheimer's disease) also form distinct phases in this regime, controlled in part by closure-inducing forces. We show that phase structure is largely independent of system size, and provide evidence of a rich structure of minor oligomeric phases that can arise from appropriate conditions. We characterize the phase behavior of this NHM family, demonstrating the range of ordered and disordered aggregation states possible with this set of interactions. As we show, fibrils arise from a balance between elongation-inducing and contact-inhibiting forces, existing in a regime bounded by gel-like and disaggregated phases; complex oligomers (including annular oligomers resembling those thought to be toxic species in Alzheimer's disease) also form distinct phases in this regime, controlled in part by closure-inducing forces. We show that phase structure is largely independent of system size, allowing generalization to macroscopic systems, and provide evidence of a rich structure of minor oligomeric phases that can arise from appropriate conditions.

Soft and Deformable Thermoresponsive Hollow Rod-Shaped Microgels.

Depending on their aspect ratio, rod-shaped particles exhibit a much richer 2D and 3D phase behavior than their spherical counterparts, with additional nematic and smectic phases accompanied by defined orientational ordering. While the phase diagram of colloidal hard rods is extensively explored, little is known about the influence of softness in such systems, partly due to the absence of appropriate model systems. Additionally, investigating higher volume fractions for long rods is usually complicated because non-equilibrium dynamical arrest is likely to precede the formation of more defined states. This has motivated us to develop micrometric rod-like microgels with limited sedimentation that can respond to temperature and reversibly reorganize into defined phases via annealing and seeding procedures. A detailed procedure is presented for synthesizing rod-shaped hollow poly(N-isopropylacrylamide) microgels using micrometric silica rods as sacrificial templates. Their morphological characterization is conducted through a combination of microscopy and light scattering techniques, evidencing the unconstrained swelling of rod-shaped hollow microgels compared to core-shell microgel rods. Different aspects of their assembly in dispersion and at interfaces are further tested to illustrate the opportunities and challenges offered by such systems that combine softness, anisotropy, andthermoresponsivity.

SURFACE ACTIVITY AND PHASE BEHAVIOUR OF POTASSIUM HEPTYLENE DECYL SUCCINATE / WATER BINARY SYSTEM

The surface activity of potassium heptylene decyl succinate (PHDS) at water-air interface was studied. The obtained results showed a very good correlation between the surface activity of PHDS and concentration of surfactant solutions and temperature of the system. The phase behaviour and structure of aggregates in PHDS)/water binary system were investigated. The phase diagram of the PHDS/water binary system was obtained depending on the concentration of components and temperature of the system. It was established that due to the double hydrocarbon chain of the PHDS molecule, the lamellar liquid crystalline phase exists across a wide range of the phase diagram. It was shown that upon the addition of water, the cross-sectional area of the PHDS molecules in lamellar liquid crystals is changed insignificantly. This result was associated with the invariability of the distance of the lipophilic layers of formed lamellar liquid crystals by PHDS molecules. On the basis of video-enhanced microscopic studies, it was established that in two-phase region of the phase diagram, lamellar liquid crystals coexist with water in the form of vesicles.

Effect of High-Pressure Torsion Temperatures on the Precipitation and Properties of Cu-Cr Alloy.

This study examines the impact of high-pressure torsion (HPT) processing at various temperatures on the precipitation behavior of Cu-Cr alloys. The introduction of defects through HPT is observed to promote the precipitation of Cr atoms. Unlike the traditional large-scale precipitation that typically occurs around 400 °C, HPT can induce the precipitation of solute atoms even at room temperature. Furthermore, the temperature at which HPT is performed significantly influences the behavior of the precipitated phase during subsequent aging, ultimately affecting the alloy's overall properties. At elevated temperatures (ETs) and room temperature (RT), Cr atoms tend to aggregate, forming Guinier-Preston (GP) zones or precipitates, which coarsen into incoherent precipitates after annealing. In contrast, when HPT is conducted at liquid nitrogen temperature (LNT), Cr atoms are retained in their original positions, leading to the formation of uniformly distributed, high-density small precipitates post-annealing. This phenomenon results in superior properties for HPT-LNT-treated samples, evidenced by a microhardness of 191.8 ± 3.2 HV and an electrical conductivity of 84.6 ± 1.8% IACS.

The Time-Varying Characteristics of Relative Permeability in Oil Reservoirs with Gas Injection

Relative permeability is a critical parameter in reservoir numerical simulation and production prediction, intimately associated with reservoir architecture and fluid property. During gas injection development, substantial alterations in reservoir properties and fluid phase behavior induce dynamic changes in relative permeability. Clearly characterizing the time-varying features of relative permeability is very useful for an understanding of how gas injection influences fluid mobility within the reservoir and enhances recovery rates. In this paper, core displacement experiments are firstly conducted to obtain the characteristics of the relative permeability of oil and gas under various development stages and displacement conditions, further delineating the comprehensive shifts in reservoir properties at different gas injection stages. Subsequently, a novel reservoir numerical simulation method is proposed that considers the spatial and temporal segmentation of relative permeability curves in the reservoir simulation. Finally, a practical application is presented to clarify the effects of injection and production parameters on the development performance of gas flooding oil reservoirs. The results show the following: (i) Significant time-varying characteristics of relative permeability occur throughout gas injection development, in the early stages of gas injection, where most of the reservoir is at the gas injection front, and a rightward shift in relative oil and gas permeability indicates that gas injection promotes oil mobility. Conversely, in the later stages of gas injection, as the reservoir reaches the trailing edge of gas injection, the change trend in relative oil and gas permeability reverses, shifting leftward, thereby exacerbating the gas breakout phenomena. (ii) Increasing the rate of gas injection causes relative oil and gas permeability to move leftward, effectively enhancing the gas volume sweep coefficient and microscopic oil displacement efficiency at lower injection speeds while reducing development performance at higher injection speeds. (iii) An increase in gas injection pressure causes relative oil and gas permeability to shift rightward, and although it reduces residual oil saturation and enhances microscopic oil displacement efficiency, it also intensifies gas breakout phenomena and lowers the gas volume sweep coefficient. This paper provides theoretical guidance and technical support for the design of gas injection strategies, optimization of injection and production parameters, and production forecasting.

Solid-liquid phase behaviour of novel kosmotrope/chaotrope binary mixtures involving sarcosine

The concept of deep eutectic solvents (DESs) has been recently applied to osmolytes (kosmotropes or chaotropes), small organic molecules responsible for stabilization of proteins and other biomolecules in various biological systems. In this study the combinations of the kosmotrope sarcosine (Sar) with chaotrope urea (U) or guanidine hydrochloride (G) across various molar ratios was studied experimentally by the differential scanning calorimetry and infrared spectroscopy. Theoretical prediction of thermodynamic interaction terms based on screening of the charge density was used to support interpretation of experimental findings. Phase diagrams were constructed for both Sar-U and Sar-G systems and eutectic behaviour was identified. Neither of the two systems showed depression of the eutectic temperature compared to its ideal solution values, and therefore neither of the systems could be classified as a deep eutectic solvent in the classical sense. The Sar-G system did show at least partial crystallization of its eutectic solution upon cooling. However, the eutectic solution of the Sar-U system remained amorphous at decreased temperatures, and the phenomenon was attributed to be kinetic in nature and originating from strong intermolecular hydrogen bonding interactions of the components. Thus, it was speculated that the role of osmolytes in stabilizing cellular biomolecules might not come from the thermodynamics only.

Diffusiophoresis promotes phase separation and transport of biomolecular condensates

The internal microenvironment of a living cell is heterogeneous and comprises a multitude of organelles with distinct biochemistry. Amongst them are biomolecular condensates, which are membrane-less, phase-separated compartments enriched in system-specific proteins and nucleic acids. The heterogeneity of the cell engenders the presence of multiple spatiotemporal gradients in chemistry, charge, concentration, temperature, and pressure. Such thermodynamic gradients can lead to non-equilibrium driving forces for the formation and transport of biomolecular condensates. Here, we report how ion gradients impact the transport processes of biomolecular condensates on the mesoscale and biomolecules on the microscale. Utilizing a microfluidic platform, we demonstrate that the presence of ion concentration gradients can accelerate the transport of biomolecules, including nucleic acids and proteins, via diffusiophoresis. This hydrodynamic transport process allows localized enrichment of biomolecules, thereby promoting the location-specific formation of biomolecular condensates via phase separation. The ion gradients further impart directional motility of condensates, allowing them to exhibit enhanced diffusion along the gradient. Coupled with a reentrant phase behavior, the gradient-induced enhanced motility leads to a dynamical redistribution of condensates that ultimately extends their lifetime. Together, our results demonstrate diffusiophoresis as a non-equilibrium thermodynamic force that governs the formation and transport of biomolecular condensates.

Dynamic Phase Behavior of Surface-Active Fluorinated Ionic Liquid Epoxidation Catalysts.

We report on the synthesis of amphiphobic fluorinated surface-active ionic liquid (FSAIL) epoxidation catalysts, which show reversible temperature-controlled solubility in water. The solubility of FSAILs containing the catalytically active perrhenate- and tungstate anions was studied in both the aqueous and the substrate phase, showing a significant solubility decrease in both media compared to their non-fluorinated congeners. It was shown that both the epoxide product and the catalyst additive phenylphosphonic acid (PPA) are efficient in transferring the FSAIL catalyst into the organic phase, rendering the reaction homogeneous. The FSAILs were used as catalysts for the epoxidation of olefins using aqueous H2O2 as oxidant, showing an exceptionally high catalytic activity at mild conditions. Catalyst recycling was demonstrated over ten consecutive runs by phase separation and subsequent product distillation.

Experimental Study on the Confined Phase Behavior of n-Butane/n-hexane Binary Mixture: The Effect of the Amount of Nanoporous Material at Varying Pore Sizes and Temperatures

Experimental Study on the Confined Phase Behavior of <i>n</i>-Butane/<i>n</i>-hexane Binary Mixture: The Effect of the Amount of Nanoporous Material at Varying Pore Sizes and Temperatures

Deep eutectic solvents and traditional refrigerants in absorption refrigeration cycles using molecular approaches

Absorption Refrigeration Cycles (ARC) represent a sustainable technology capable of effectively producing cold with modest energy consumption from waste heat or renewable sources. However, the right choice of working fluid pair absorbent–refrigerant is essential for the system to work properly. This contribution is devoted to analysing the performance of an ARC using a wide variety of refrigerants in combination with selected deep eutectic solvents (DES) as absorbents. Three choline chloride-based and one ionic liquid (IL)-based DESs as absorbers are combined with sixteen refrigerants. The PC-SAFT equation of state is employed to assess the thermophysical properties. Accurate modelling of the absorption cycle has revealed that the phase behaviour of the working mixture significantly constrains the temperature and pressure range within which the cycle can operate. Idealised ARCs are insufficient for accurately representing the capabilities and limitations of these systems. Of the sixty-four working pair mixtures, only eighteen are suitable for ARCs based on technical and thermodynamics criteria. The Coefficient of Performance (COP) has been updated with additional key performance indicators that consider environmental and safety factors. The maximum values of the COP for this mixture are around 0.92, while many options lie in ranges around 0.60. This comprehensive analysis helps establish a ranking of the best options. The results have shown that the IL-based DES using R227ea or R236ea is the most efficient system among all the systems studied, with performances of 0.92 and 0.74.

Construction of mixed gels of yolk granules and salted ovalbumin driven by pH: phase behavior and calcium bioaccessibility

Mixed gels of egg yolk granules (EYGs) and salted ovalbumin (SO) with different pH values were constructed to design gels of great quality and nutritional properties. However, the formation and dietary properties of mixed gels may be affected by the phase behavior of the mixed protein solution. In this study, the pH was adjusted from 3.0 to 8.0 to tune phase behavior of mixed protein solution before heating. The results demonstrated the presence of a collapsed gel and a dense phase network at pH 3.0 caused by phase separation. As the pH increased and phase separation disappeared, the EYGs-SO gel network showed a filling network structure and then changed to a loose interpenetrating network gel structure with a decreased fractal dimension (from 2.94% to 2.89%). The interpenetrating network improved gel hardness and water-holding capacity. During gelation, the phase separation reduced the gelation transition temperature. The main forces that support EYGs-SO gel were hydrogen and disulfide bonds. Moreover, EYGs-SO showed greater calcium bioaccessibility (7.85% - 8.08%) at pH 3.0, 4.0, and 5.0. In summary, the phase behavior in mixed solution modulates the gelation of mixed gels. The construction of mixed gels also provides ideas and strategies for the value-added utilization of salted egg whites.

Investigation on the structural, elastic, electronic, thermodynamic, and vibrational properties of the full heusler Sc2XAl (X =Cd and Zn): An ab initio study

The structural, mechanical, electronic, thermodynamic, and phonon characteristics of Sc2CdAl and Sc2ZnAl in L21 phase were the main focuses on this investigation. The density of states (DOS) and electronic band spectra signify the metallic behavior of the L21 phase of both materials. The impact of atomic arrangement with respect to the Wyckoff sites on the mechanical stability were additionally studied. The elastic constants of Sc2CdAl and Sc2ZnAl alloys indicated that these alloys convened Born mechanical stability criteria. Using the density functional perturbation theory's first-principle linear response method, complete phonon spectra have been acquired. Moreover, the quasi-harmonic approximation, specific heat capacity at constant volume, the internal free energy, entropy, and vibrational free energy variations of Sc2CdAl and Sc2ZnAl as full Heusler alloys have been utilized in examination the change over the temperature between 0 and 800 K. Both alloys might find application in real industrial applications.