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We present an explicit molecular-based interpretation of the thermodynamic phase equilibrium underlying gas solubility in liquids, through rigorous links between the microstructure of the dilute systems and the relevant macroscopic quantities that characterize their solution thermodynamics. We apply the formal analysis to unravel and highlight the molecular-level nature of the approximations behind the widely used Krichevsky-Kasarnovsky [J. Am. Chem. Soc. 57, 2168 (1935)] and Krichevsky-Ilinskaya [Acta Physicochim. 20, 327 (1945)] equations for the modeling of gas solubility. Then, we implement a general molecular-based approach to gas solubility and illustrate it by studying Lennard-Jones binary systems whose microstructure and thermodynamic properties were consistently generated via integral equation calculations. Furthermore, guided by the molecular-based analysis, we propose a novel macroscopic modeling approach to gas solubility, emphasize some usually overlook modeling subtleties, and identify novel interdependences among relevant solubility quantities that can be used as either handy modeling constraints or tools for consistency tests. [ABSTRACT FROM AUTHOR]

Highlights • Measuring the diffusion coefficient of COS in [emim][Tf 2 N]. • Investigation of COS solubility in [emim][Tf 2 N]. • Investigation of SO 2 solubility in [emim][Tf 2 N]. • Modeling the COS and SO 2 solubility in [emim][Tf 2 N]. Abstract The diffusivity and solubility of carbonyl sulfide at temperatures from (313.15 to 353.15) K and pressures up to about 1.0 MPa and also the solubility of sulfur dioxide at the same temperatures and low pressures ranges in ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl) sulfonylimide ([emim][Tf 2 N]) were experimentally investigated. The solubility was measured using a volumetric-base static apparatus and acid gas diffusivity was obtained using the Semi-infinite volume method with low initial pressure. Using the solubility data, Henry's law constants at different temperatures, and the partial molar thermodynamic properties of solution, that is, Gibbs energy, enthalpy, and entropy were calculated. The solubility data were correlated using 1) the generic Redlich – Kwong (GRK) cubic equation of state approaches and 2) the extended Henry's law combined with the Pitzer's virial expansion for the excess Gibbs energy. Finally using solubility data regression has been done with the generic Redlich – Kwong (GRK) cubic equation of state, the precision of experimental solubility data has been inspected via thermodynamic consistency test. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Solubilities of nonpolar gases in 2,5-DMTHF at 101.32 kPa and (273.15–303.15) K were measured. • The methods SPT, Perturbation, UNIFAC and COSMO-RS for solubility were tested. • New UNIFAC interaction parameters to predict solubilities are proposed. • L-J (12,6) potential parameters for 2,5-DMTHF were obtained from SPT model. Abstract The solubilities of gases in liquids are interesting, not only from a practical point of view, but also because they provide a rigorous touchstone to test the structural models on the liquid state. In this work the solubilities of 13 nonpolar gases, He, Ne, Ar, Kr, Xe, H 2 , D 2 , N 2 , CH 4 , C 2 H 4 , C 2 H 6 , CF 4 , and SF 6 , in 2,5-dimethyltetrahydrofuran at five temperatures between (273.15 and 303.15) K and 101.32 kPa partial pressure of gas were measured and the associated thermodynamic functions were calculated. Correlation of data has been made and the capacity of prediction of several typical molecular models of liquids, namely, SPT model, perturbation theory, UNIFAC and COSMO-RS, specifically applied to gas solubilities, has been checked. [ABSTRACT FROM AUTHOR]

Highlights • Measuring the solubility of CO 2 in aqueous sulfolane solution. • Determination of Henrys law constant for the CO 2 solubility in aqueous sulfolane solution. • Modeling of CO 2 solubility in aqueous sulfolane solution. Abstract New experimental data are presented for the solubility of carbon dioxide in aqueous sulfolane (SFL) solution, an important solvent with applications in a variety of chemical industries. Solvent mixtures of (SFL + H 2 O) studied in this work contain the composition range x SFL = (0.0999–0.9313), temperatures from (303.15 to 353.15) K, with step 10 K, and total pressures up to 1.3 MPa. Solubility data and Henry's law constants of CO 2 solubility in pure SFL, pure H 2 O and mixed (SFL + H 2 O) are reported on mole fraction base. Results show that, CO 2 solubility in mixed solvents increases with increasing pressure and gas-free mole fraction of SFL and also decrease with increasing temperature. A model based on the Gibbs excess energy of mixed solvent was used to correlate the obtained experimental data. The correlated values, with an average and maximum relative percent deviation of 1.78% and 7.55% from the obtained experimental data, show that the model is able to represent the experimental data with good correlative accuracy. [ABSTRACT FROM AUTHOR]

Abstract In this work, GC-sPC-SAFT (Group Contribution Simplified Perturbed Chain Statistical Associating Fluid Theory), and GC-PPC-SAFT (including the polar term related to dipole and quadrupole interactions) equations of state (EoS) were applied in order to correlate thermophysical properties of ionic liquids (ILs), and to predict CO 2 and CH 4 solubilities in ILs. Previous works from literature proposed an equation in which the parameters for the pure components were estimated from density data, obtaining a correlation of the IL's molecular parameters as a linear function of the molecular weight, and the associative parameters were "transferred" from 1-alkanols. This work proposes four strategies to parameterize ILs from [C n -mim][BF 4 ], [C n -mim][PF 6 ] and [C n -mim][NTf 2 ] families with GC-sPC-SAFT, including the usage of group contribution (GC) methods for ILs, speed of sound in the pure IL parameterization, and reevaluating the association parameters. The model parameters were obtained fitting simultaneously density and speed of sound experimental data at several temperatures, decreasing deviations between experimental and calculated values for these properties with 2B, 3B and 4C schemes. The obtained ILs' parameters were used to predict the solubility of CO 2 and CH 4 in them. The results obtained in this work with the proposed strategy are able to predict the solubility of gases with high accuracy in a purely predictive way, avoiding the usage of binary interaction parameters, and being compatible with GC methods, and show that both use of speed of sound data and estimation of the association parameters are the key for successful predictions, mainly the use of speed of sound data in the IL parameterization. [ABSTRACT FROM AUTHOR]

Abstract A algorithm coupled with modified Patel-Teja equation of state and Chen-Guo hydrate model is developed to conduct vapor-liquid-semiclathrate multiphase flash calculation for TBAB containing systems. To quantitatively describe the gas consumption ability of semiclathrate slurry, a new concept, i.e., the apparent liquid phase, is introduced. The Patel-Teja equation of state (PT EOS) combined with a Debye-Hückel electrostatic term is chosen to describe the fugacity of TBAB in aqueous solution and calculated gas solubility in aqueous phase. The Chen-Guo hydrate model is extended to calculate the fugacity of TBAB in semiclathrate phase. Several parameters in Chen-Guo model for TBAB are retuned by correlating phase equilibrium data. A mathematical approach based on the secant iteration is successfully applied to solve flash calculation. Results from flash calculations are in satisfactory agreement with experimental data reported in other literature. This new algorithm provides an extended range of calculations for semiclathrate phases, such as amounts of semiclathrate formed, and then, the contributions of absorption and hydration upon separation performance can be quantitatively described. In addition, multistage separation are simulated using this flash algorithm. The effects of TBAB concentration of solution, initial gas liquid volume ratio, temperature, and pressure on separation efficiency are systematically discussed from the perspective of thermodynamics and mass balance. [ABSTRACT FROM AUTHOR]

Despite the long history behind the experimental determinations of gas solubility and the consequent wealth of experimental data for binary systems we are still confronted with lingering issues regarding their reliability, the approximations behind their modeling, and the consistency among resulting solvation quantities. In the present effort we discuss cautiously these issues through the thermodynamic scrutiny of the coexistence phase equilibrium equations involving sparingly soluble species according to the recently proposed rigorous molecular-based solvation formalism [Chialvo: Fluid Phase Equilibria https://doi.org/10.1016/j.fluid.2017.10.031 and Journal of Chemical Physics, 148 (2018)]. We address the fundamentals underlying the isothermal-isobaric phase equilibria associated specifically with the solubility of carbon dioxide in aqueous systems, their thermodynamic limit of stability, as well as the link between the latter and the microstructure of the pair of incipient phases. Moreover, we show how the resulting equilibrium phase composition can provide relevant solvation quantities to test the thermodynamic consistency of the experimental data. Finally, we illustrate the arguments explicitly through the analysis of experimental evidence from a few selected sources in the literature, and discuss the implications behind the findings. [ABSTRACT FROM AUTHOR]

In this communication, a thermodynamic consistency test is performed on the isothermal solubility of hydrogen in alkenes and vapor-liquid equilibrium data for systems containing hydrogen and alkenes. The improved Peng-Robinson equation of state was used for this purpose. The fugacity coefficient of each component and compressibility factor of liquid and vapor phases were calculated by this equation of state. Thermodynamic consistency tests have been performed by rewriting the Gibbs-Duhem equation in terms fugacity coefficient and using the area test method. The results showed that most of the equilibrium data of the liquid phase were consistent, but for the vapor phase less than one-half of the data was consistent. [ABSTRACT FROM AUTHOR]

A thermodynamic method to check the consistency of phase equilibrium data developed by the authors and applied to several situations by different researchers is analyzed to determine the effect of the equation of state employed to correlate the data on the final response of the consistency test. The consistency test method, in fact, uses an equation of state to correlate the equilibrium data and to calculate some properties such as volume, fugacity and compressibility factor. After these properties are determined the Gibbs-Duhem equation is applied to determine data consistency. If the data fulfill the Gibbs-Duhem equation the data are considered to be consistent and if the data do not fulfill de Gibbs-Duhem equation the data are of doubtful thermodynamic consistency. The equation of state dependency of the method has been recognized by the authors and other researchers but discussion of the real effects of the equation of state used on the results of the consistency method has not been presented. This work demonstrates that after a good and accurate thermodynamic model is used to correlate the data, the consistency test can be considered equation-of-state independent. [ABSTRACT FROM AUTHOR]

Solubility and permeability of gases in glassy polymers have been considered with the aim of illustrating the applicability of thermodynamically-based models for their description and prediction. The solubility isotherms are described by using the nonequilibrium lattice fluid (NELF) (model, already known to be appropriate for nonequilibrium glassy polymers, while the permeability isotherms are described through a general transport model in which diffusivity is the product of a purely kinetic factor, the mobility coefficient, and a thermodynamic factor. The latter is calculated from the NELF model and mobility is considered concentration-dependent through an exponential relationship containing two parameters only. The models are tested explicitly considering solubility and permeability data of various penetrants in three glassy polymers, PSf, PPh and 6FDA-6FpDA, selected as the reference for different behaviors. It is shown that the models are able to calculate the different behaviors observed, and in particular the permeability dependence on upstream pressure, both when it is decreasing as well as when it is increasing, with no need to invoke the onset of additional plasticization phenomena. The correlations found between polymer and penetrant properties with the two parameters of the mobility coefficient also lead to the predictive ability of the transport model. [ABSTRACT FROM AUTHOR]

In this work, aqueous 1-allyl-3-methylimidazolium formate ([Amim][HCOO]) was studied as a potential sorbent for CO2 separation. The density and viscosity of aqueous [Amim][HCOO] were measured at temperatures ranging from 293.15 to 333.15 K at atmospheric pressure. The solubility of CO2 and CH4 in dry [Amim][HCOO] as well as the CO2 solubility in aqueous [Amim][HCOO] were measured at pressures up to 1.8 MPa and temperatures of 298.2, 313.2, and 333.2 K. The results showed that the density and viscosity of aqueous [Amim][HCOO] as well as the CO2 solubility in aqueous [Amim][HCOO] decreased upon increasing the water concentration and temperature. The viscosity was very sensitive to the water concentration. The experimental density and viscosity of aqueous [Amim][HCOO] were fitted to semiempirical equations, and the excess molar volume and viscosity deviations were calculated to investigate the interaction between the [Amim][HCOO] ionic liquid and water. The experimental vapor-liquid equilibrium was represented with the nonrandom two-liquid and Redlich-Kwong model. The model parameters can be further implemented into Aspen Plus software to conduct process simulations. [ABSTRACT FROM AUTHOR]

In this study, simple molecular-weight-based correlations for the CP-PC-SAFT parameters for [Cnmim][NTf2] ionic liquids have been developed. These correlations allow a nearly precise modeling of densities, including at elevated pressures and at temperatures up to ~400 K, as well as accurate predictions of the isobaric heat capacities, velocities of sound, and compressibilities. The accuracy of these predictions is superior to that of ePC-SAFT. The available data reveal that solubilities of gases are directly related to their critical temperatures. As the critical temperatures increase, the gas-IL systems become more symmetric, and the solubilities increase. The intrinsic robustness of the CP-PC-SAFT model, along with its agreement with the pure-compound critical temperatures, give this model the capability to accurately predict VLE in [Cnmim][NTf2] systems of various gases, such as CO, O2, CH4, Kr, N2O, H2S, SO2, R134a, R1234ze(E), and CO2, without prior consideration of any mixture data or adjustment of binary parameters. At the same time, the entirely predictive implementation of the model poses unavoidable compromises in its accuracy. In particular, it overestimates LLE in the system R134a-[C6mim][NTf2] and substantially underestimates the extent of phase splits in CO2 solutions above ~50 bar. The latter flaw can be corrected by implementing a universal set of binary adjustable parameters. Similar accuracy of modeling can also be achieved with this set of binary parameters and with their zero values in the cases of additional CO2-[NTf2-] IL systems. [ABSTRACT FROM AUTHOR]

Choline chloride + phenylacetic acid-based deep eutectic solvents are studied. Their most relevant experimental physicochemical properties at different mixing ratios together with the CO2 solubility data obtained in wide pressure and temperature ranges are reported. The presented materials exhibit a significant CO2 capture performance with low corrosion effect when compared with the most common amine-based CO2 capture agents. Detailed rheological measurements are carried out and various models are applied to describe the dynamic flow behavior of the solvents. The CO2 absorption mechanism is evaluated by studying the behavior of the liquid gas and interface. Due to the advantages of low cost, nontoxicity, and favorable physical properties, these solvents are an environmentally promising alternative for effective CO2 capture technological applications. [ABSTRACT FROM AUTHOR]

New experimental results are presented for the solubility of methane in two single solvents (hexane and a petroleum benzine) at temperatures of about (273, 283, and 293) K and pressures up to about 10 MPa. The solubility of methane (in terms of moles of methane per kilogram of solvent at given temperature and pressure) is rather similar in both solvents. The experimental results are evaluated to determine Henry’s constant and the partial molar volume of methane in those solvents. A thermodynamic model, based on the extended Henry’s law, which accounts for interactions in both liquid and gaseous phases, is applied to correlate the experimental results. [ABSTRACT FROM AUTHOR]

Solubility and permeability of gases in glassy polymers have been considered with the aim of illustrating the applicability of thermodynamically-based models for their description and prediction. The solubility isotherms are described by using the nonequilibrium lattice fluid (NELF) (model, already known to be appropriate for nonequilibrium glassy polymers, while the permeability isotherms are described through a general transport model in which diffusivity is the product of a purely kinetic factor, the mobility coefficient, and a thermodynamic factor. The latter is calculated from the NELF model and mobility is considered concentration-dependent through an exponential relationship containing two parameters only. The models are tested explicitly considering solubility and permeability data of various penetrants in three glassy polymers, PSf, PPh and 6FDA-6FpDA, selected as the reference for different behaviors. It is shown that the models are able to calculate the different behaviors observed, and in particular the permeability dependence on upstream pressure, both when it is decreasing as well as when it is increasing, with no need to invoke the onset of additional plasticization phenomena. The correlations found between polymer and penetrant properties with the two parameters of the mobility coefficient also lead to the predictive ability of the transport model.

An experimental study of the solubility and of the thermodynamic properties of solvation, between temperatures (303 and 343) K and at pressures close to atmospheric, of 2-methylpropane (isobutane) in several ionic liquids based on the bis(trifluoromethylsulfonyl)imide anion and on 1-alkyl-3-methylimidazolium cations, [C n C 1 Im][NTf 2 ], with alkyl side-chains varying from two to ten carbon atoms is presented. The isobutane solubility increases with increasing size of the alkyl side-chain of the cation in the ionic liquid and decreases with increasing temperature (as typical of an exothermal dissolution process). The mole fraction solubility of isobutane varies from 0.904 · 10 −2 in [C 2 C 1 Im][NTf 2 ] at T = 343 K to 1.002 · 10 −1 in [C 10 C 1 Im][NTf 2 ] at T = 303 K. The values measured in this work are compared to the behaviour of n-butane in the same ionic liquids published in a previous study (Costa Gomes et al. , 2012). Isobutane was found to be significantly less soluble than n-butane in all the ionic liquids. The differences found are interpreted in relation to the molecular structures obtained by molecular dynamics simulations for the solutions of n-butane and isobutane in the studied [C n C 1 Im][NTf 2 ] ionic liquids. [ABSTRACT FROM AUTHOR]

Abstract: The use of the concepts of the nonextensive thermodynamics allows reconsidering the equilibrium of bubble solubilization and more commonly of gaseous aggregates in supersaturated solutions of gas. The introduced relations are general and include as particular cases the equations usually used to describe these phenomena. These equations are discussed. Especially, we specified the domain of application of Kelvin’s relation which was illustrated by the solubility of gases in fogs and clouds. Various possibilities of thoughts on the behavior of the gaseous aggregates and nano-systems are proposed. Thus, the introduced relations permit to consider the presence of gaseous aggregates in equilibrium with the solution even for under-saturated solution. Nonextensive thermodynamics admits the notion of negative pressure at the inner of confined phases (solid or liquid). [Copyright &y& Elsevier]

Abstract: Different ionic liquids (ILs) have been checked as potential ammonia absorbents at near-ambient temperatures and atmospheric pressure. In a first stage, the task-specific ILs 1-2(-hydroxyethyl)-3-methylimidazolium tetrafluoroborate [EtOHmim][BF4], choline bis(trifluoromethylsulfonyl)imide [choline][NTf2], tris(2-hydroxyethyl)methyl-ammonium methylsulfate [MTEOA][MeOSO3] and 1-(2-hydroxyethyl)-3-methylimidazolium dicyanamide [EtOHmim][DCA] were selected as potential high-capacity ammonia solvents by quantum-chemical COSMO-RS analysis. Then, they were experimentally tested considering both thermodynamic and kinetic aspects. Absorption kinetics was described by a phenomenological diffusion model. The desorption curves were also obtained. Finally, an efficiency criterion based on absorption–desorption cycles was established to simultaneously consider the kinetics and thermodynamics of the phenomena for the solvent selection. As a result, we propose a set of ILs with adequate properties to be used as absorbents for ammonia separation. [Copyright &y& Elsevier]

Abstract: Foaming constitutes one of the most important industrial activities in polymer engineering to produce efficient thermal insulating materials. In particular, rigid insulating boards are produced worldwide on a large scale using blowing agents which eventually are released in the environment where they adversely impact the natural friendly stratospheric ozone layer. Concomitantly, the chemicals used as blowing agents contribute to the creation of the unfriendly tropospheric ozone layer generating the disastrous green house effect around our planet. The traditional foaming intermediates currently named freons, like chlorofluorocarbons (CFCs) currently used as blowing agents as well as the hydrochlorofluorocarbons (HCFCs) often considered as alternative blowing agents, must be banned from industrial processes and new (friendly) foaming agents have to be suggested and evaluated in terms of both easy engineering and environmental neutrality. Undoubtedly thermodynamics plays a major role in assessing the effective capability of those chemicals. Some CFCs still accepted and other possible simple gases like carbon dioxide and nitrogen have been considered. The in-depth thermodynamic investigation has been made possible thanks to new experimental developments to determine gas solubility in polymers and associated swelling as well as the thermodynamic properties of (gas+polymer) systems, including the thermophysical properties of polymers under gas sorption. Pertinent data have been generated for such properties over extended T and p ranges. [Copyright &y& Elsevier]

Abstract: In this work, a modified perturbed hard sphere chain (PHSC) equation of state has been applied to the calculation of acid gas (CO2, H2S) solubility in ionic liquids. The proposed equation of state is a combination of the PHSC equation of state and a polar term. The polar contribution is based on the segment approach which is expected to give accurate results for long chain molecules such as ionic liquids. By using polar and association terms, the specific interactions between molecules have been taken into account. The calculated results for ionic liquid densities are in good agreement with the experimental data, and average deviation between calculated and experimental data is less than 0.14%. The solubility of CO2 and H2S in various ionic liquids has been correlated using just one temperature-dependent binary interaction parameter over wide ranges of temperature and at pressures ranging from 0.1 to 100MPa. For binary systems, absolute average deviations of calculated gas solubilities are less than 2.4%. The capability of the proposed model has then been assessed by prediction of solubility behavior for the ternary H2S/CO2/[C4mim][PF6] system. [Copyright &y& Elsevier]

Abstract: A thermodynamic model based on the electrolyte NRTL activity coefficient equation and PC-SAFT equation-of-state is developed for CO2 solubility in aqueous solutions of NaCl and Na2SO4 with temperature up to 473.15K, pressure up to 150MPa, and salt concentrations up to saturation. The Henry''s constant parameters of CO2 in H2O and the characteristic volume parameters for CO2 required for pressure correction of Henry''s constant are identified from fitting the experimental gas solubility of CO2 in pure water with temperature up to 473.15K and pressure up to 150MPa. The NRTL binary parameters for the CO2–(Na+, Cl−) pair and the CO2–(Na+, SO4 2−) pair are regressed against the experimental VLE data for the CO2–NaCl–H2O ternary system up to 373.15K and 20MPa and the CO2–Na2SO4–H2O ternary system up to 433.15K and 13MPa, respectively. Model calculations on solubility and heat of solution of CO2 in pure water and aqueous solutions of NaCl and Na2SO4 are compared to the available experimental data of the CO2–H2O binary, CO2–NaCl–H2O ternary and CO2–Na2SO4–H2O ternary systems with excellent results. [Copyright &y& Elsevier]

Abstract: The solubility of hydrogen sulfide in a series of 1-(2-hydroxyethyl)-3-methylimidazolium ([HOemim]+)-based ionic liquids (ILs) containing different anions, viz. hexafluorophosphate ([PF6]−), trifluoromethanesulfonate ([OTf]−), and bis-(trifluoromethyl)sulfonylimide ([Tf2N]−) at temperatures ranging from 303.15 to 353.15K and pressures of up to about 1.8MPa was measured by a volumetric based static apparatus. The solubility data were correlated using two models: (1) the Krichevsky–Kasarnovsky equation and (2) the extended Henry''s law combined with the Pitzer''s virial expansion for the excess Gibbs energy. Henry''s law constants (at zero pressure) in mole-fraction and molality scales were obtained at different temperatures by means of these two models. Using the solubility data, the partial molar thermodynamic functions of solution, i.e. Gibbs energy, enthalpy, and entropy were calculated. Comparison showed that the solubility of H2S is greater than that of CO2 in the corresponding ILs studied in this work and that the solubility of both gases increases as the number of trifluoromethyl (–CF3) groups in the anion increases, i.e. the solubility behavior of both gases follows the order [HOemim][Tf2N]≥[HOemim][OTf]>[HOemim][PF6]>[HOemim][BF4]. [Copyright &y& Elsevier]

Abstract: The solubility of carbon dioxide in a series of 1-(2-hydroxyethyl)-3-methylimidazolium ([hemim]+) based ionic liquids (ILs) with different anions, viz. hexafluorophosphate ([PF6]−), trifluoromethanesulfonate ([OTf]−), and bis-(trifluoromethyl)sulfonylimide ([Tf2N]−) at temperatures ranging from 303.15K to 353.15K and pressures up to 1.3MPa were determined. The solubility data were correlated using the Krichevsky–Kasarnovsky equation and Henry’s law constants were obtained at different temperatures. Using the solubility data, the partial molar thermodynamic functions of solution such as Gibbs free energy, enthalpy, and entropy were calculated. Comparison showed that the solubility of CO2 in the ILs studied follows the same behaviour as the corresponding conventional 1-ethyl-3-methylimidazolium ([emim]+) based ILs with the same anions, i.e. [hemim][NTf2]>[hemim][OTf]>[hemim][PF6]>[hemim][BF4]. [Copyright &y& Elsevier]

Free-energy related properties for small molecules in poly(dimethylsiloxane) (PDMS) have been evaluated using a test-particle-insertion method with the excluded volume map sampling (EVMS). The excess chemical potential (solubility) and solvation energy in PDMS at 298 K were calculated for five noble gases (He, Ne, Ar, Kr, Xe) and for five hydrocarbon gases (CH4, C2H6, C3H8, C2H4, C3H6). The bulk configurations of PDMS composed of 8 chains of CH3-(Si(CH3)2-O-)301-Si(CH3)3 were obtained by the molecular dynamics simulation with NPT ensemble. The solubility coefficients obtained by the EVMS method showed a good agreement with the experimental values. The solvation entropy for the respective gas molecule was also evaluated from the solubility enthalpy and the excess chemical potential both of which were calculated during the test-particle-insertion method. The relations of these free-energy related properties with the molecular size based on the Lenard-Jones size parameter or Lenard-Jones force constants are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Small bubbles of nitrogen, methane, or argon with an average radius of 50nm, as measured by scanning electron microscopy, were prepared under atmospheric conditions. The lifetime of the nanobubbles extended to more than two weeks. The total amount of gases in the nanobubble solutions reached 600cm3 per 1dm3 of water, and the liquid density was about 0.988g/cm3. The internal pressure of the nanobubbles was estimated to be 6MPa. The number of nanobubbles was 1.9×1016 bubbles per 1dm3 of water. These findings show that almost no gas samples are dissolved homogeneously in the aqueous solution and that the vast majority is present in the form of nanobubbles, that is, nanobubbles should be thermodynamically unstable. Attenuated total reflectance infrared spectroscopy showed that the surfaces of the nanobubbles contain hard hydrogen bonds that may reduce the diffusivity of gases through the interfacial film. [Copyright &y& Elsevier]

Abstract: The solubility of hydrogen sulphide in three ionic liquids, viz. 1-hexyl-3-methylilmidazolium hexafluorophosphate ([hmim][PF6]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF4]), and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([hmim][Tf2N]), at temperatures ranging from 303.15K to 343.15K and pressures up to 1.1MPa were determined. The solubility values were correlated using the Krichevsky–Kasarnovsky equation and Henry’s constants were obtained at different temperatures. Partial molar thermodynamic functions of solvation such as standard Gibbs free energy, enthalpy, and entropy were calculated from the solubility results. Comparison of the values obtained show that the solubility of H2S in these three ionic liquids was in the sequence: [hmim][BF4]>[hmim][PF6]≈[hmim][Tf2N]. [Copyright &y& Elsevier]

Abstract: Like our previous work with imidazolium- and phosphonium-based ionic liquids, we report diffusivities over a range of viscosities (71–532cP) and develop a predictive diffusivity correlation. Reported are the permeability, solubility, and diffusivity data for nine gases in nine ammonium RTILs liquids at 30°C, as determined with a lag-time technique. The gas solubilities and diffusivities of the ammonium RTILs are of the same magnitude as those for the phosphonium and imidazolium RTILs. The ammonium RTILs used, in this study, included cations with both N-alkyl groups and branched alkyl groups. We also report on ammonium-based RTILs derived from quaternary ammonium surfactants. These surfactants-derived ammonium-based RTILs offer a relatively inexpensive alternative to imidazolium-based RTILs. We compare and contrast the thermodynamic (solubility) and transport (diffusivities) phenomena in the ammonium-based RTILs with both the imidazolium and the phosphonium RTILs in the context of being working fluids in a chemical process. From this comparison came certain “universal” trends for diffusivity in RTILs. Specifically, diffusivity scales roughly with the inverse of the square-root of viscosity and inversely with solute molar volume to the power of 1–1.3. This means that diffusivity, in RTILs, is less dependent on viscosity, and more dependent on solute size than predicted by the conventional Stokes–Einstein model. The gases tested were carbon dioxide, nitrogen, oxygen, methane, ethylene, propylene, 1-butene, butane, and 1,3-butadiene. [Copyright &y& Elsevier]

The thermodynamics based on the interaction of small molecules on a polymer melt surface has been studied by molecular simulations. The melt surface structure of cis-1,4-polyisoprene was constructed using a molecular dynamics simulation technique. The system contained 20 polymer chains and a total of 30,000 carbon atoms. The excess chemical potential and enthalpy terms (average interaction energy between the gas and the polymer) were obtained using a test-particle-insertion method with excluded volume map sampling as a function of the position from the inside to the surface. The thickness of the surface estimated by the density change was 1.3 nm at 373 K. The excess chemical potential showed a minimum and a negative value only at the surface just beyond the position with half of the inside density. These results show the intrinsic properties of the polymer surface which accommodates gas molecules due to adsorption. [ABSTRACT FROM AUTHOR]

Abstract: New experimental results are reported for the solubility of ammonia in liquid mixtures of (water+methanol). Five (gas-free) solvent compositions are considered (mole fraction of methanol of about 0.05, 0.25, 0.5, 0.75, and 0.95). The temperature amounts to about 313K, 353K, and 393K. The solubility pressure ranges up to about 0.1MPa, 0.6MPa, and 1.6MPa, respectively. The molality of ammonia in the solvent mixture of (water+methanol) (the mole fraction of ammonia in the liquid) ranges up to 13molkg−1 (about 0.3). The experimental results are used to determine Henry''s constant of ammonia in the liquid mixtures of (water+methanol). An extension of Pitzer''s molality scale-based model for the Gibbs excess energy (to solvent mixtures) is applied in a thermodynamic model to describe the phase equilibrium. [Copyright &y& Elsevier]

Abstract: This work reports gas solubility data and Henry''s constants for carbon dioxide in pure water and ethanol and in their mixtures. For this purpose, a simple laboratory apparatus containing a glass equilibrium cell was constructed and the methodology consisted basically in injecting and storing the gas into the system at a pre-established pressure and then allow the gas dissolution. The liquid phase compositions were calculated through an iterative procedure considering the validity of Henry''s law for the liquid phase fugacity of the lighter component. The experiments were performed in the temperature range of 288–323K, up to 6atm in pure solvents and at various ethanol–water mixture compositions. From the experimental gas–liquid equilibrium data, P–x diagrams, excess Henry''s constants as well as partial molar enthalpy and entropy of solution have been determined. [Copyright &y& Elsevier]

Abstract: This paper describes the development of a thermodynamic model for predicting solubilities of nine gases (H2, N2, CO, Ar, O2, CH4, C2H4, C2H6, CO2) in battery electrolyte formulations composed of five organic carbonates (cyclic and linear) and lithium salts (LiPF6) between 283 and 363K and <1MPa. The PSRK equation of state by Holderbaum and Gmehling [Fluid Phase Equilib. 70 (1991) 251–265] was combined with the NRTL expression for activity coefficients [H. Renon, J.M. Prausnitz, AIChE J. 14 (1968) 135–144] and used for correlating available gas solubility data. The prediction ability of the PSRK model was tested by correlating gas solubility data in propylene carbonate and predicting the gas Henry''s constants in other carbonates. The PSRK predictions of missing combinations and multicomponent systems and were validated by experimental measurements. The PSRK model is shown to predict gas solubilities in ternary battery formulations with accuracy within 10%. The prediction of gas solubility was also tested using the quantum mechanical/COSMO-RS method by Klamt and Eckert [Fluid Phase Equilib. 172 (2000) 43–72]. The COSMO-RS method did not require any prior experimental information and produced quantitatively correct results for binary gas+carbonate systems. [Copyright &y& Elsevier]

Abstract: New experimental VLE data of CO2–water binary system are reported over a wide temperature range from 278.2 to 318.2K and pressures up to 8MPa. A static-analytic apparatus, taking advantage of two pneumatic capillary samplers, is used. The experimental solubility data generated in this work are in very good agreement with previous data reported in the literature. Three different models have been used to represent the new experimental VLE data. The first thermodynamic model is based on a dissymmetric approach with the Peng–Robinson equation of state including classical mixing rules for the vapour phase and a Henry''s law treatment of the aqueous phase. The second and third thermodynamic models belong to φ–φ approaches: the second model uses the Peng–Robinson equation of state combined with the Wong–Sandler/Huron–Vidal mixing rules, and the third model the SAFT-VR equation of state based on a variable range square-well potential. [Copyright &y& Elsevier]

Abstract: The solubility of carbon dioxide in aqueous solutions of sodium chloride is studied by NVT- and NpT-Gibbs Ensemble Monte Carlo Simulations at 373, 393 and 433K at pressures up to 10MPa. The intermolecular forces are approximated by effective pair potentials (SPC and TIP4P models for water, the EPM2 potential model for carbon dioxide and several pair potentials for sodium chloride). Unlike interactions are estimated applying common combining rules. The simulation results are compared with experimental data. The experimentally observed “salting-out effect” is predicted by the simulation, but the decrease of the solubility of carbon dioxide caused by the presence of salt is overestimated. An improvement is achieved by introducing binary interaction parameters into unlike pair potentials. In some simulations the amount of dissolved sodium chloride was above the solubility limit. In these simulations crystal-like structures were observed in the liquid phase. [Copyright &y& Elsevier]

Extension of well established EoS for fluid mixtures to the description of thermodynamic properties of non-equilibrium glassy polymeric phases is considered and corresponding calculations for pseudo-equilibrium gas content are performed. Results obtained using three different “tangent hard spheres chain” EoS are discussed and compared with experimetnal data for low-pressure gas solubility in glassy polycarbonate. While the overall result allows to conclude that tools developed herein may be confidently used for pure predictions of gas and vapor solubility in polymeric material below the glass transition temperature, interesting differences among the performance of different models were observed which can be attibuted to the different form of interaction potential considered. [Copyright &y& Elsevier]

Natural eruptions in shallow permafrost with formation of large craters reported lately from gas-producing regions of the Russian Arctic may result from pressure buildup in freezing closed zones of gas-saturated unfrozen soil (taliks). Under certain conditions, increasing pressure may lead to hydraulic fracture of the overlying permafrost, with ensuing eruption of talik material and crater formation. The conditions of pore moisture freezing in gas-saturated taliks and related pressure buildup have been modeled by thermodynamic calculations. The model uses elegant equations to provide constraints on the freezing temperature of pore fluids containing dissolved salts and gases, which depends on free gas pressure, composition and contents of dissolved pore gases (methane, carbon dioxide, and their mixtures), and salinity. Pressure increase in these conditions is limited thermodynamically by the onset of gas hydrate formation. • Thermodynamic calculations of freezing of gas saturated talik zone is observed. • The influence of gas pressure and salinity on freezing point of pore water are investigated. • Gas solubility affects phase equilibrium in the system 'ice – gas-bearing water'. • Carbon dioxide have significant effect on freezing process of confined gas saturated talik zone. [ABSTRACT FROM AUTHOR]