Fluid Phase Equilibria (v.307, #1)

► Densities of HFC-245fa and HFC-236fa were measured via a vibrating tube densimeter. ► Experimental data were obtained ranging from 293 to 373 K and up to 70 MPa. ► The data of HFC-245fa were correlated to a Tait equation with an AAD of 0.0096%. ► The data of HFC-236fa were correlated to a Tait equation with an AAD of 0.031%.Densities of 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) have been measured for temperatures from 293 to 373 K and pressures up to 70 MPa, with a high-pressure vibrating tube densimeter system in the liquid state. The system was calibrated using water and vacuum via the method of Lagourette et al. The uncertainty in the density measurement was estimated to be ±0.6 kg m−3. The experimental results were correlated to a Tait equation. The average absolute percentage deviations of measurement results from the correlations of HFC-245fa and HFC-236fa are 0.0096% and 0.031%, respectively.
Keywords: Density; Data; Vibrating tube; HFC-245fa; HFC-236fa;

Phase equilibrium measurements of structure II clathrate hydrates of hydrogen with various promoters by Alondra Torres Trueba; Laura J. Rovetto; Louw J. Florusse; Maaike C. Kroon; Cor J. Peters (6-10).
► We report phase equilibrium measurements of organic clathrate hydrates with hydrogen. ► The organics studied are furan, 2,5-dihydrofuran, tetrahydropyran, 1,3-dioxolane and cyclopentane. ► The organics form structure II hydrates with water. ► The organics act as promoter materials in mixed clathrate hydrates with hydrogen. ► The size and geometry of the organic compound determine the stability of the clathrate hydrate.Phase equilibrium measurements of single and mixed organic clathrate hydrates with hydrogen were determined within a pressure range of 2.0–14.0 MPa. The organic compounds studied were furan, 2,5-dihydrofuran, tetrahydropyran, 1,3-dioxolane and cyclopentane. These organic compounds are known to form structure II clathrate hydrates with water. It was found that the addition of hydrogen to form a mixed clathrate hydrate increases the stability compared to the single organic clathrate hydrates. Moreover, the mixed clathrate hydrate also has a much higher stability compared to a pure hydrogen structure II clathrate hydrate. Therefore, the organic compounds act as promoter materials. The stabilities of the single and mixed organic clathrate hydrates with hydrogen showed the following trend in increasing order: 1,3-dioxolane < 2,5-dihydrofuran < tetrahydropyran < furan < cyclopentane, indicating that both size and geometry of the organic compound determine the stability of the clathrate hydrates.
Keywords: Clathrate hydrate; Structure II; Hydrogen; Cyclopentane; Furan; 2,5-Dihydrofuran; Tetrahydropyran; 1,3-Dioxolane; Phase equilibrium;

Comparison of solubility isotherms of benzamide in supercritical carbon dioxide at 318 K.Display Omitted► We determined the solubility of benzamide in supercritical carbon dioxide with and without cosolvent for the first time, using a flow-type apparatus. ► The cosolvent effect for the three investigated cosolvents is: ethanol > acetone > glycol. The strong attractive molecular interactions between ethanol and benzamide could enhance the solubility by up to 11 times. ► The correlated results using two density-based models show satisfactory agreement with the experimental data.The experimental equilibrium solubility of benzamide in supercritical carbon dioxide was measured at temperatures between 308 K and 328 K and for pressures from 11.0 MPa to 21.0 MPa using a dynamic flow method. The effects of three cosolvents – ethanol, acetone and ethylene glycol, were investigated at a cosolvent molar concentration of 3.5%. The results showed that the solubility was enhanced by the presence of the three cosolvents, and ethanol exhibited the highest cosolvent effect. The solubility data in the absence and presence of cosolvents were correlated by two density-based models. The calculated results showed satisfactory agreement with the experimental data.
Keywords: Solubility; Benzamide; Supercritical carbon dioxide; Cosolvent;

► Significant synergism in interfacial tension reduction is achieved with α Triton  > 0.3. ► The highest degree of synergism (40.6%) is appropriate to the lowest used interfacial tension. ► The attractive interaction parameter finds its maximum absolute value at α  ≈ 0.5. ► An alternative variation for interaction between surfactants is revealed at the interface. ► A correlation is introduced for the interaction parameter in the sense of ease of applications.Equilibrium interfacial tension measurements at 25.0 °C of the toluene + water system with two widely used surfactants, octylphenol decaethylene glycol ether (Triton X-100) and cetyl trimethyl ammonium bromide (CTAB) having concentrations much lower than their CMC were performed. According to the obtained parameters from the Szyszkowski equation, Triton has higher adsorption tendency than of CTAB. The results obtained for surfactants mixtures are analyzed by the theory of non-ideal interactions in binary mixtures (NIBMs) and the interfacial composition and the interaction parameter in the mixed adsorbed monolayer are determined. The attractive interaction shows a maximum value at nearly equal surfactants bulk mole fraction. The synergism is achieved for Triton bulk mole fractions of 0.30 and higher, and the highest degree of synergism (40.6%) is found for the bulk mole fraction of 0.52 with the lowest investigated constant interfacial tension of 28.0 mN m−1. A correlation was developed for variation of the interaction parameter with bulk mole fraction.
Keywords: Interfacial tension; Synergism; Interaction parameter; NIBM theory;

► In this paper, we study the vapour–liquid equilibrium for 2-butanone + n-hexane, 2-butanone + n-heptane and 2-butanone + 2,2,4-trimethylpentane. ► The sensitivity of azeotropes to changes in pressure have been study for these systems. ► Data reduction with Wilson, NRTL and UNIQUAC models has carried out. ► Pressure-swing distillation is not much more attractive to separate these azeotropic mixtures.Consistent isobaric vapour–liquid equilibrium data have been measured for 2-butanone + n-hexane, 2-butanone + n-heptane, and 2-butanone + 2,2,4-trimethylpentane at two different pressures. All binary systems present a minimum boiling azeotrope at both pressures, and show that the azeotropic compositions are weakly dependent on pressure. The equilibrium data were correlated using the Wilson, NRTL, and UNIQUAC models for which the parameters are reported.
Keywords: Vapour–liquid equilibria; 2-Butanone; n-Hexane; n-Heptane; 2,2,4-Trimethylpentane;

► Density, viscosity, surface tension, heat stability and heat capacity of a new IL are determined. ► LLE data were measured for [3-mebupy]C(CN)3 and an aromatic + aliphatic hydrocarbon. ► The LLE data were modeled with the NRTL model.Several physical properties were determined for the ionic liquid 3-methyl-N-butylpyridinium tricyanomethanide ([3-mebupy]C(CN)3): liquid density, viscosity, surface tension, thermal stability and heat capacity in the temperature range from (283.2 to 363.2) K and at 0.1 MPa. The density and the surface tension could well be correlated with linear equations and the viscosity with a Vogel–Fulcher–Tamman equation. The IL is stable up to a temperature of 420 K.Ternary data for the systems {benzene +  n-hexane, toluene +  n-heptane, and p-xylene +  n-octane + [3-mebupy]C(CN)3} were determined at T  = (303.2 and 328.2) K and p  = 0.1 MPa. All experimental data were well correlated with the NRTL model. The experimental and calculated aromatic/aliphatic selectivities are in good agreement with each other.
Keywords: Thermodynamic data; Liquid–liquid equilibria; Ionic liquid; NRTL model;

► New experimental liquid–liquid equilibrium data have been reported. ► The data have been modeled using two recent thermodynamic models. ► Performance of the models has been verified and compared. ► Relevant model parameters have been reported for the studied systems.Experimental measurements have been performed for liquid–liquid equilibria in aqueous systems containing 1-pentanol and sodium nitrate at temperatures of 298.15 and 308.15 K and at atmospheric pressure. The results have been modeled using the extended UNIQUAC model and also a modified version of this model. Relevant model parameters have been adjusted using the experimental data. Both models are capable of correlating the experimental data with an average deviation of less than 0.8 weight percent, with the modified model producing slightly better results. The predictive nature of the models has also been verified.
Keywords: Mixed solvent electrolyte solution; Liquid–liquid equilibrium; Extended UNIQUAC model; 1-Pentanol; Sodium nitrate;

► We calculated chemical and phase equilibrium for hydration of ethylene to ethanol. ► We used PRSV2 equation of state, UNIQUAC model, and Wong–Sandler mixing rules. ► Vapor–liquid hydration achieves higher conversions than vapor-phase hydration. ► No reactive azeotrope exists for ethylene–water–ethanol at 200 °C. ► The reactive phase diagram exhibits a critical point at 200 °C and 155 atm.Due to the economics of the ethylene market and the subsidized production of fermentation-based ethanol in some countries, use of the ethylene hydration process to make ethanol has been steadily declining. The economics of this process might improve by combining the reaction and separation in a reactive distillation column, whose conceptual design requires a study of the combined chemical and phase equilibrium (CPE) of the reacting system. In this work, the Peng–Robinson–Stryjek–Vera equation of state was combined with the UNIQUAC activity coefficient model through the Wong–Sandler (WS) mixing rules in order to correlate the available experimental data for the vapor–liquid equilibria (VLE) of the ethylene–water, ethylene–ethanol, and ethanol–water binary systems at 200 °C. The interaction energies of the UNIQUAC model and the binary interaction coefficient of the WS mixing rules were used as the fitting parameters. From the optimum values of these parameters, both the VLE and the combined CPE of the ethylene–water–ethanol ternary system were predicted at 200 °C and various pressures. At this temperature, the catalytic activity of a H-pentasil zeolite has already been reported to exhibit a maximum for ethylene hydration, and also the experimentally measured two-phase region of the ternary system is sufficiently wide. By means of the reactive flash method, the chemical equilibrium compositions of the liquid and vapor phases were determined for several pressures, and the equilibrium conversion and the vapor fraction were calculated as functions of the ethylene to water feed mole ratio. It turns out that the vapor–liquid mixed-phase hydration of ethylene achieves equilibrium conversions much higher than those computed for a vapor-phase reaction that would hypothetically occur at the same conditions of pressure and feed mole ratio. It was found that the reactive phase diagram of the ternary system exhibits a critical point at 200 °C and 155 atm.
Keywords: Synthetic ethanol; Petrochemical ethanol; Fuel ethanol; Ethylene hydration; Chemical equilibria; Vapor–liquid equilibria;

Molecular dynamics study of selective adsorption of PCB on activated carbon by Bjørnar Jensen; Tatiana Kuznetsova; Bjørn Kvamme; Åge Oterhals (58-65).
► 4 ns MD study of selective PCB adsorption on activated carbon. ► Realistic graphitic mesoporous AC structure created. ► Ab initio approach used to assign partial charges and modify dihedral potential. ► Impact of molecular planarity on PCB adsorption quantified. ► Strong short-range interactions shown to favor planar adsorption.The selectivity of PCB adsorption from fish oil onto activated carbon (AC) was investigated by means of molecular dynamics to determine the importance of molecular planarity. PCB congeners 77 and 118 were selected for comparison purposes due to pronounced differences in mean adsorption efficiency and molecular geometry; triolein, a triacylglycerol of oleic acid (C18:1), was used as the representative fish oil component. Graphitic carbon structure was set up to serve as activated carbon model. Molecular force fields employed in the simulations combined short-range parameters from the OPLS with partial atomic charges obtained via quantum chemical calculations using DFT/B3LYP/6-31**G+ and Solvation Model 6. We modified the dihedral angle potential between the PCB aromatic rings and applied Schrödinger's Jaguar package to evaluate the required force field constants. Our complete system comprised a number of PCB molecules dissolved in triacylglycerol that overlaid and filled the pores of an AC structure. The production run of 4 ns provided strong indications that smaller pores will be conductive to better selectivity though also resulted in certain doubts concerning the estimation and assignment of partial atomic charges on the activated carbon. The majority of PCB molecules trapped in pores were attached via cl–AC “bonding”, leaving the main part of the PCB molecule free to interact with triolein. The cl–AC adsorption energy was found to surpass the energy criteria conventionally used for hydrogen bonds. Planar orientation assumed by a PCB molecule in a very energetically favored position on top of the graphite sheet clearly supported the π-cloud overlap hypothesis.
Keywords: Molecular dynamics; Activated carbon; PCB; Adsorption;

► We have measured new experimental data on vapour–liquid equilibria at isothermal conditions. ► Three binary and one ternary systems consisting of isooctane + isobutanol + isobutyl methyl ketone were investigated. ► Correlation of data with use of the Wilson and NRTL equation. ► Prediction of phase equilibria in ternary system based on binary data.Vapour–liquid equilibrium data in the three binary 2,2,4-trimethylpentane + 2-methyl-1-propanol, 2-methyl-1-propanol + 4-methyl-2-pentanone, 2,2,4-trimethylpentane + 4-methyl-2-pentanone systems, and in the ternary 2,2,4-trimethylpentane + 2-methyl-1-propanol + 4-methyl-2-pentanone system are reported. The data were measured isothermally at 333.15, 348.15 and 364.15 K covering the pressure range 12–100 kPa. The binary vapour–liquid equilibrium data were correlated using the Wilson and NRTL equations by means of a robust algorithm for processing all isotherms together; resulting parameters were then used for calculation of phase behaviour in the ternary system and for subsequent comparison with experimental data.
Keywords: Vapour–liquid equilibrium; Experimental data; Prediction; Hydrocarbon; Alcohol; Ketone;

► Critical properties of eleven CO2 binary systems are determined and calculated. ► The calculated results show good agreements compared with the experimental data. ► The adjustable parameters λ, k σ and k ɛ were obtained. ► The critical curves all belong to type I at higher temperatures and pressures.A set of variable-volume autoclave with a quartz window was used for the experimental determination of the high-pressure phase equilibria and critical curves. The critical temperatures, pressures, densities and mole volumes in the region near the critical point of CO2 were examined for eleven binary systems of supercritical CO2 (SC CO2) with different kinds of substances (ketone, alkane, ester and alcohol), respectively. The critical curves of the above binary systems were also calculated using an equation of state. The equation consists of a hard body repulsion term and an additive perturbation term, which takes care of the attractive molecular interaction. The calculated data were compared with the experimental data, and yielded good agreements. At the same time, the values of the adjustable parameters, λ, k σ and k ɛ were obtained. The critical curves of the above eleven binary systems at higher temperatures and pressures all belong to type I.
Keywords: Binary systems; SC CO2; Critical curves;

► Estimation methods for hydrocarbon critical temperature, pressure and acentric factor using evaluated physical property data with uncertainties. ► Re-derivation of a simple cubic equation of state (Peng–Robinson) using uncertainties on vapor pressure, acentric factor, critical temperature and critical pressure. ► Development of database of physical properties of interest for the natural gas industry taking into account recommended uncertainties. ► Calculation of pressure–temperature envelopes for prototype gas mixtures taking into account physical property uncertainty.A simple model is proposed to estimate the critical temperature and critical pressure of hydrocarbons in the range of C5–C36 with parameters determined using weighted linear least squares and weighted non-linear least squares taking into consideration the experimental uncertainty in the data as well as in the correlating parameters. The correlation model was parameterized using the normal boiling point and specific gravity at 60 °F. The uncertainties of parameters and associated covariance matrix necessary for error propagation calculations are reported and a comprehensive evaluation of acentric factors uncertainties based on the experimental vapor pressures was conducted. In addition, a simple sensitivity analysis designed to determine how the uncertainty of properties used for calculations based on the equations of state propagate thorough the model and affect the final results. The normal boiling points of two pure components, n-hexane and n-dodecane were calculated using an equation of state and the estimated error in the calculations is presented together with estimated uncertainties for the prototype pressure–temperature envelopes for two binary mixtures of methane–n-hexane and methane–n-dodecane.
Keywords: Error propagation; Errors in physical property models; Estimation of physical properties; Cubic equations of state; Phase envelope calculation; Process simulation;

Formation conditions and thermodynamic model predictions of carbon monoxide hydrates by Qiang Sun; Xuqiang Guo; Aixian Liu; Bei Liu (95-99).
► CO–THF hydrate formation pressures are measured at different temperatures. ► We fit complete parameter values of CO required in Chen–Guo hydrate model for the first time. ► Hydrates formation conditions of different systems including CO are predicted by Chen–Guo model. ► The parameter values of CO fitted in this work are acceptable. The applied range of Chen–Guo hydrate model is extended.With a fine accuracy and conciseness, Chen–Guo hydrate model has been widely applied to predict the hydrates formation conditions of different systems, including inhibitor containing systems and salt containing systems. However, the model could not predict the formation condition of carbon monoxide (CO) hydrates as the parameter values of CO required in the calculation are not available. In this work, CO hydrate formation pressures were measured at different temperatures in tetrahydrofuran (THF) solution first, then the parameter values of CO required in Chen–Guo model were fitted completely for the first time. On that basis, the hydrates formation conditions of different systems including CO were predicted by the model to verify the accuracy of the fitted values. The comparison between the predicted results and our experimental data (or literature data) shows that the absolute average deviation percentage (AADP) of structure I hydrates is no more than 1.481%, and the AADP of structure II hydrates is less than 6.796%. It is proved that the fitted parameter values of CO are credible, and Chen–Guo model is capable of predicting the formation conditions of CO hydrates. The experimental results and model modifications extend the applied range of Chen–Guo model and promote the development of CO hydrates thermodynamics research.
Keywords: Carbon monoxide; Hydrate; Tetrahydrofuran; Chen–Guo model;

► Isothermal 30 °C study of heterogeneous equilibria in C12H22O11–Ca(OH)2–H2O system. ► Solubility (liquidus) curves have been determined. ► Two phases C12H22O11·3Ca(OH)2 and C12H22O11·2Ca (OH)2 have been evidenced. ► This work shows that these ternary phases exhibit incongruent solubilities at 30 °C.Solid–liquid equilibria in the C12H22O11–Ca(OH)2–H2O system have been determined at 30 °C. Two phases C12H22O11·3Ca(OH)2 and C12H22O11·2Ca (OH)2 have been evidenced, and solubility (liquidus) curves have been determined. It is thus shown that these ternary phases exhibit incongruent solubilities at 30 °C. These solid phases were characterized using Infrared Spectroscopy (IR), Scanning Electron Microscopy (SEM) and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES).
Keywords: Phase equilibria solid–liquid; Ternary system C12H22O11–Ca(OH)2–H2O; Calcium saccharates;

► Solubility data of LiBr and LiNO3 in alcohols. ► Temperature range is between 298.15 and 338.15 K. ► Solubility products of the salts in pure organic solvent. ► Osmotic coefficients calculated based on Pitzer model.The solubility of lithium bromide and lithium nitrate in solvents methanol, ethanol, 1-propanol, 2-propanol and 1-butanol were measured in the range between 298.15 and 338.15 K using an analytical gravimetric method. An empirical equation was used to fit the experimental solubilities and the Pitzer model with inclusion of Archer's ionic strength was used for the calculation of osmotic coefficients. The experimental data of system pressures (p) for the correlation of LiBr + ethanol, LiBr + 2-propanol at T (298.15–333.15 K) and LiNO3  + ethanol at T (298.15–323.15 K) were obtained from published literatures. Moreover, the parameters of the Pitzer model were re-correlated and were used to predict mean ion activity coefficients. A procedure was also presented to predict the solubility products of salts in pure organic solvent.
Keywords: Solubility; Activity coefficient; Lithium bromide; Lithium nitrate;