In this work, we analyze the predictive performance of the CPA- and SAFT-type families and their polar extensions in capturing the effects of like-unlike interactions on vapor–liquid equilibria and thermophysical properties of mixtures containing polar compounds with non-polar partners. To elucidate the roles of the dipolar segment and binary interaction parameters in describing these properties, several complementary analyses were conducted. Based on these findings, a new parameterization strategy was introduced to reduce the dimensionality of the parameter estimation problem for polar equations of state while preserving predictive capability. In addition, a flexible SQLite-based database of curated thermophysical property data was developed and made available to facilitate future model development and validation.
Pentaerythritol esters of carboxylic acids of various structures have been synthesized. Saturated vapor pressures have been determined using gas chromatography and transpiration methods, and based on the obtained data, an equation for calculating saturated vapor pressures of pentaerythritol esters has been proposed. Vaporization enthalpies of the investigated esters have been calculated from the saturated vapor pressures. A comparison of various methods for predicting vaporization enthalpies of pentaerythritol esters has been performed.
The interaction of the cyclic peptide G4CP2 (βA-RYFFDMWY) with zwitterionic DOPC liposomes was investigated as a minimal membrane model by combining spectroscopy, calorimetry, and enhanced-sampling molecular dynamics. G4CP2 was originally reported as a functional inhibitor of the transcription factor GAL4 and was selected here to provide a physicochemical, membrane-focused characterization of this biologically validated cyclic scaffold. UV-Vis titrations showed hypochromic effects upon lipid addition, while steady-state fluorescence quenching (including synchronous fluorescence) confirmed membrane association without large spectral shifts, suggesting predominantly interfacial binding environments for the Trp reporter. Circular dichroism indicated no major change in spectral shape, with a progressive increase in signal magnitude with lipid concentration consistent with an increasing membrane-associated fraction. Isothermal titration calorimetry revealed micromolar binding with an endothermic enthalpy compensated by a strongly favorable entropy contribution, indicating an entropy-driven association regime. DLS and TEM showed no major vesicle disruption under the tested conditions. To provide a molecular interpretation, reweighted free-energy surfaces were reconstructed from OPES simulations along peptide insertion depth and tilt, and the resulting ensemble was projected onto hydration, aromatic insertion, headgroup contacts, and conformational descriptors. The simulations indicated a broad low-free-energy basin consistent with multiple interconverting membrane-associated microstates and supported an ensemble shifted toward deeper interfacial association characterized by stronger dehydration and aromatic engagement. Overall, the combined experimental-computational data provide a coherent thermodynamic and structural picture of how an aromatic-rich cyclic peptide associates with a zwitterionic bilayer through heterogeneous interfacial states.
Accurate thermodynamic models of nonideal fluids are essential tools. Beyond the need for better predictive capabilities, their rigorous, thermodynamically-consistent implementation and use within property calculation workflows are a strict prerequisite to obtain physically meaningful and interpretable results. This article identifies inconsistencies in the original property calculation framework of the well-established Lee–Kesler model and proposes a thermodynamically-consistent, ready-to-use approach. In addition to the theoretical proof and discussion on consistency, a numerical analysis is presented to provide empirical evidence for the theoretical findings. The magnitude of errors are evaluated and depicted within a wide state space, using the example of CO2 as modeled substance.
Molecular simulations of the competitive adsorption among alkane molecules have been extensively investigated; however, the cascading effects induced by such competitive adsorption have not yet been explored in sufficient depth. In this study, a methyl-modified quartz slit-pore model was constructed to simulate the competitive adsorption and spatial distribution of methane, propane, and n-dodecane through molecular dynamics (MD) simulations. The results indicate that n-dodecane preferentially adsorbs on the methylated quartz surfaces, while methane is mainly distributed at the pore center, leading to a significant enrichment of heavy hydrocarbons in the confined fluids compared with the bulk fluids. Phase behavior calculated using the modified Peng–Robinson equation of state (PR EOS) which addresses the impact of adsorbed molecules under confined conditions reveals that when only confinement effects are considered, the phase envelope shrinks toward the lower-left region; however, when heavy-hydrocarbon enrichment within nanopores is also taken into account, the envelope shifts toward the lower-right region. The coupling between these two effects results in a deviation of phase transition pressures from conventional expectations, with the extent of pressure reduction depending on the degree of heavy-hydrocarbon enrichment. The key novelty lies in demonstrating that adsorption-induced compositional redistribution, which is generally neglected in conventional confined-fluid EOS formulations, should be explicitly incorporated into thermodynamic modeling of confined multicomponent hydrocarbon systems. The proposed framework provides a basis for extending conventional phase-equilibrium models to account for adsorption-driven compositional redistribution in nanoporous systems, offering new opportunities for developing next-generation thermodynamic models for confined fluids.
Pesticides are extensively used in agriculture, hygiene management, and public health, making accurate knowledge of their physicochemical properties essential for safe and effective application. Vapor pressure is a key property governing the evaporation behavior of pesticides; however, experimental determination of vapor pressure for low−volatility pesticide compounds is often challenging and resource-intensive. In this study, vapor pressures of representative pesticide compounds spanning a wide range of volatilities were evaluated using all-atom molecular dynamics (MD) simulations based on vapor−liquid coexistence models. Vapor pressures were calculated from vapor-phase densities obtained at elevated temperatures and extrapolated to ambient conditions using the Clausius−Clapeyron equation. The simulated vapor pressures were compared with available experimental data from the literature. Although the MD-predicted vapor pressures do not quantitatively agree with experimental values, the relative ordering of vapor pressures among the investigated compounds is generally consistent with experimental observations. These results indicate that, while quantitative prediction of vapor pressure remains challenging, MD simulations provide a useful framework for comparative evaluation of vapor pressures and relative volatility among pesticide compounds. Overall, this study demonstrates that MD-based vapor–liquid coexistence simulations can serve as a complementary tool for assessing vapor-pressure trends when reliable experimental data are limited. The observed discrepancies are likely associated with the current limitations of the molecular force field employed in this study. Therefore, the present study provides insight into the applicability and limitations of this methodology for predicting vapor-pressure behavior of low-volatility pesticide compounds.
The monomer fraction, X, or the molecular fraction of a component’s molecules not participating in hydrogen bonding, is an explicitly calculable quantity in the SAFT thermodynamic framework. Researchers have long proposed the measurement of X using FTIR spectroscopy and incorporating these data into parameterisation algorithms to overcome parameter degeneracy issues, particularly for polar, solvating species. This work looks to address the lack of monomer fraction data, and indeed the lack of an unbiased approach to its generation, by drawing on spectral processing techniques well-established in the spectroscopic literature. Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) is investigated as an approach to generate monomer fraction data in solvating mixtures. MCR-ALS resolves spectra for different compositions into statistically significant spectral and concentration profiles, which can be physically interpreted to justify a full range of hydrogen bond interactions, while approximating monomer fraction under appropriate assumptions. This overcomes the inherent bias and spectral ambiguity associated with curve fitting approaches used in previous thermodynamic studies of monomer fractions. The method was benchmarked against published ethanol/n-hexane data before application to ethanol/acetone. An apparent acetone monomer/free-carbonyl fraction was estimated across the composition range, while the expected low fraction of ethanol monomers could not be elucidated from the instrument noise and signal processing. An initial assessment of polar-SAFT models to simultaneously predict phase equilibrium and monomer fraction with previously published parameter sets highlighted valid approaches for incorporating these data in model parameterisation and development in future work.
The Søreide–Whitson (S&W, 1992) equation of state framework for gas–water–brine phase equilibria is widely used in reservoir simulation; published updates since have addressed individual gases rather than the framework as a whole. This work presents updated kijAQ(T) and embedded salinity Δkij(T,m) correlations for eight gases (CH4, C2H6, C3H8, n-C4H10, CO2, H2S, N2, H2), developed from approximately 2000 pointwise-regressed BIP values. The correlations retain the original S&W water alpha function and are backward-compatible with existing simulator implementations; only the BIP correlation coefficients need updating.Freshwater kijAQ correlations are fitted to freshwater data only, and salinity effects are represented through an additive Δkij(T,m) term fitted to reproduce modern Sechenov models for each gas. This two-stage approach provides functionally independent freshwater and brine components while remaining drop-in compatible with the original framework. Investigations into both replacing the S&W water alpha function with a higher-accuracy form and adopting a modular gamma-phi salting-out framework found that solubility predictions are indistinguishable when the BIP is refitted: the kij absorbs upstream model differences, supporting the simpler embedded approach.The framework is extended to hydrogen for underground storage applications, and H2S salting-out support is added for the first time.
The solubility of (+)-usnic acid ((+)-UA) in ten pure solvents and five binary mixed solvents was determined over the temperature range of 283.15–323.15 K. The experimental data for pure solvents were correlated using the modified Apelblat, λh, Wilson and NRTL models, while the General Solubility model (GSM) and the Jouyban-Acree (JA) model were additionally applied to binary solvent systems. The solubility of (+)-UA increased monotonically with temperature and the mass fraction of good solvent, and the Wilson model provided the most accurate overall correlation. The KAT-LSER model was then employed to evaluate solvent effects. The analysis showed that solvent-solvent cohesive energy density significantly hindered the dissolution process, while dipolarity/polarizability exerted only a moderate influence. Molecular simulations, including intramolecular hydrogen-bond analysis and molecular electrostatic potential (MEP) surfaces, were carried out to explore hydrogen-bond interactions among the enol-keto tautomers of (+)-UA. Strong intramolecular hydrogen bonding was found to favor compact conformations and to reduce solvent accessibility, whereas tautomers with more exposed polar regions exhibited enhanced solvation capability. Free-energy calculations further suggested that the dissolution behavior reflects a balance between intramolecular stabilization and solute-solvent interactions. In addition, thermodynamic analysis based on activity coefficients derived from the Wilson model indicated that both the mixing and dissolution processes were spontaneous and mainly driven by entropy.
This study examines the thermodynamic behavior of binary systems containing the green solvent γ-valerolactone (GVL) and p-xylene or o-xylene. The measurements of the isobaric vapor-liquid equilibrium (VLE) were performed at 50.0 kPa and 70.0 kPa; furthermore, the excess molar enthalpies (HE) were determined at 298.15 K for the binary mixtures. The experimental HE results were positive across the entire composition range, suggesting that the addition of non-polar aromatic rings disrupts the self-interactions of the polar lactone in GVL. The absence of azeotropic behavior in these systems allows for a straightforward distillation process. We confirmed the consistency of the VLE data through Van Ness and L–W thermodynamic tests. The correlation of the experimental data was performed using a simultaneous regression of VLE and HE employing the Wilson, NRTL, and UNIQUAC activity coefficient models. Experimental data were compared with predictions from the UNIFAC and UNIFAC-DMD group contribution models and the COSMO-RS quantum chemical model. COSMO-RS with the TZVPD-FINE parameterization level displayed better predictive accuracy than all other models studied and its validity was further confirmed through retrospective testing on several additional GVL-containing binary mixtures, including toluene, ethylbenzene, water, and alcohols.
Although PR-EOS-based phase-equilibrium calculations and binary interaction parameter (kij) correlations have been widely used for CO₂–hydrocarbon systems, most existing correlations were developed primarily from pure n-alkane or simple model-solvent data and therefore have limited reliability for real heavy oils with complex pseudocomponent characteristics. The novelty of this work lies in systematically extending a standard PR EOS, van der Waals mixing-rule, and Rachford–Rice flash-calculation framework to CO₂– heavy oil systems by developing a kij correlation calibrated and validated using phase-equilibrium data that include real crude oils. The proposed correlation explicitly incorporates the reduced temperature of CO₂ (Tri) and the acentric factor of the oil pseudocomponent (ωj), thereby representing the temperature dependence and molecular asymmetry of CO₂–heavy oil mixtures without introducing excessive model complexity. A total of 414 phase-equilibrium data points, covering 7 CO₂–hydrocarbon binary systems and 10 CO₂–crude oil systems, were compiled from the literature; 279 data points were used for parameter regression and 135 independent data points were reserved for validation. The results show that the proposed kij correlation provides improved predictive performance for CO₂–crude oil phase-equilibrium calculations, particularly for real crude oil systems, within the validated temperature range of 293.15–373.15 K and pressure range of 1.55–18.90 MPa.
A thermodynamic formulation is developed for coupled precipitation-complexation equilibria in heterogeneous multiligand aqueous systems. The approach is based on a generalized equilibrium equation (GE) that combines hydrolysis, ligand complexation, protonation, and hydroxide precipitation within a unified mass-balance formalism. The coupled equilibria are described through Gibbs-energy relationships constrained by solubility products and dissolved-species distributions. To quantify non-additive stabilization under heterogeneous conditions, a dimensionless synergistic coefficient (SC) is introduced as a thermodynamic descriptor derived from differences in residual dissolved-metal concentrations. In this treatment, SC becomes meaningful only in the presence of a persistent solid phase and therefore reflects stabilization associated with precipitation-controlled equilibria. The approach was applied to representative Co/Ni ascorbate-tartrate systems using literature stability constants corrected to I = 0.1 M through the Davies formalism. The calculations show that mixed-ligand equilibria shift hydroxide precipitation boundaries and generate asymmetric dissolved-metal distributions over defined pH intervals. These results show that non-additive behavior in multiligand systems arises from coupled heterogeneous equilibria governed by simultaneous complexation and precipitation constraints.
Sulfur emissions from the combustion of fossil fuels can have negative impacts on both the environment and human health. Sulfur in fuel oil primarily exists in the form of thiophene compounds; however, traditional hydrodesulfurization technology is not effective for removing these compounds. In this study, a non-hydrodesulfurization method is proposed that employs a mixed solvent system composed of an ionic liquid and supercritical carbon dioxide (ScCO2) to extract and separate thiophenic compounds. The phase equilibrium of thiophene and its interactions with ionic liquid in mixtures of 1‑butyl‑3-methylimidazolium bis(trifluoromethanesulfonyl) imide ([Bmim][Tf2N]) and ScCO2 were investigated using Monte Carlo simulation. Analysis of the thiophene-[Bmim][Tf2N]-ScCO2 ternary system showed that thiophene preferentially associates with the short alkyl chain (C6) and the end of the long alkyl chain (C10) on the cationic imidazole ring and is evenly dispersed around the anion. Phase equilibrium data indicate that CO2 preferentially transfers to the liquid phase under high pressure, while thiophene tends to remain in the liquid phase within the pressure range studied. The results demonstrate that adding ScCO2 to the ionic liquid improves the separation of thiophene, mitigates the limitations inherent to each solvent, and prevents cross-contamination between them.
The absolute vapour pressures of 2-and 3-chloropyridine (measured over liquid samples) and of 2,3-, 2,5-, 2,6-dichloropyridine and 2,3,5-trichloropyridine (measured over solid samples) were determined using the transpiration method. Sublimation enthalpies of the di-and tri-chloropyridines were obtained via solution calorimetry, while their fusion enthalpies were measured by differential scanning calorimetry (DSC). The new thermochemical data were evaluated together with literature values for mono-, di-and tri-chloropyridines using a combination of empirical methods and quantum chemical calculations. The set of benchmark-quality properties for chloropyridines has been recommended for thermochemical calculations.
N-(9-Fluorenylmethoxycarbonyl)-L-aspartic acid (Fmoc-L-aspartic acid) is an important building block in modern solid-phase peptide synthesis and plays a key role in the field of chemistry. To enrich the existing research database of related substances, the solubility of Fmoc-L-aspartic acid in 12 single solvents was determined by static gravity method, and the temperature range was 283.15 K to 323.15 K. Experimental results demonstrated that the solubility of Fmoc-L-aspartic acid rises as temperature elevates across all selected solvent systems. At the same time, two models were used to fit the experimental data, and it was found that the Apelblat model had the highest accuracy. Subsequently, the intermolecular interaction mechanism between Fmoc-L-aspartic acid and solvent was elucidated from the aspect of solvent properties. Further verification indicated that solvent polarity parameter (ET(30)), hydrogen bonding interaction and cohesive energy density serve as the key factors dominating the solvation characteristics of the target compound. In addition, molecular electrostatic potential surface analysis (MEPs) was used to indicate the interaction sites of hydrogen bonds. The solvation property of Fmoc-L-aspartic acid within twelve neat solvents was systematically investigated via Hansen solubility parameters (HSPs), interaction energy and interaction region indicator (IRI) analysis methods.
The pvTx properties of refrigerants are the fundamental parameters for the design and performance optimization of refrigeration equipment. However, experimental data for key mixtures such as R125 + R1234yf, R125 + R1234ze(E), and R143a + R1234yf remain scarce, especially at high pressures. In this work, the pvTx properties of these three mixtures were measured using a high-precision isochoric apparatus. The measurements cover temperature and pressure ranges of 237.02 - 310.17 K and 1.3 - 13.6 MPa, respectively. The average absolute relative deviation (AARD) of the multi-parameter equation of state in REFPROP 10.0 from the experimental data is 0.28% for the R125 + R1234yf mixture, 0.37% for the R125 + R1234ze(E) mixture, and 0.49% for the R143a + R1234yf mixture. The measured pvTx data were correlated using the modified Tait equation, and the AARDs of this equation for the three mixtures are 0.12%, 0.10%, and 0.04%, respectively. The modified Tait equation shows better agreement with experimental data and exhibits no obvious systematic deviations.
Oleyl-capped nanoparticles are generally dispersible in non-polar media and would not be stable with polar solvents. Their dispersibility in water media can however be enabled by the use of auxiliary surfactants, via formation of a bilayer between the surfactant tails and the capping ligands of these hydrophobic nanoparticles. For a detailed assessment of this dispersibility effect, long-range comprehensive molecular dynamics runs were performed on oleyl-capped gold nanoclusters in water. Cetyl trimethyl ammonium bromide (CTAB) is proved as auxiliary surfactant to stabilize these hydrophobic nanoclusters in water. The present simulations results provide an insightful overview about the stabilization of oleyl-capped nanoparticles in aqueous dispersions.
The viscosities of pure liquids at high pressures were calculated with the models coupling Eyring’s absolute rate theory with the equation of state for the square-well chain fluid with variable range (SWCF-VR EOS). Three temperature-independent parameters in the viscosity models were determined based on the molecular parameters of SWCF-VR EOS and the reported viscosity data from the literature. To validate the viscosity model, more than 3000 viscosity data points were used, covering 38 conventional pure liquids, 11 ionic liquids, and one molten polymer. The overall average absolute deviations (AADs) were 3.37% for conventional pure liquids and 4.91% for high-viscosity liquids (ionic liquids and polymer). The slightly larger deviations for the high-viscosity liquids prompted the modification of the viscosity model to better describe their viscosities. By considering the temperature dependency of parameter k2 in the original model, the overall AAD for the high-viscosity liquids is reduced to 3.94%. The viscosities of these liquids were well reproduced with a suitable model. The viscosity model parameters and their combinations of the homologous compounds were regressed to establish the linear correlations expressed in term of the molecular weights. The empirical transferability within the limited homologous families of the models is evidenced by the calculated results based on the correlations. This work reformulated the existing Eyring/SWCF-VR framework by eliminating the need for temperature-dependent parameter fitting. It offers a practical and computationally efficient tool for correlating and predicting high-pressure liquid viscosities, while also providing a pragmatic strategy for the development of viscosity models.
