Excess Molar Enthalpies Research Articles

Activity coefficients at infinite dilution of organic solutes in the ionic liquid PEG-5 cocomonium methylsulfate at T = (313.15, 323.15, 333.15, and 343.15) K: Experimental results and COSMO-RS predictions

Activity coefficients at infinite dilution γ13∞ have been determined for 25 polar and non-polar organic solutes (alkanes, cycloalkanes, alk-1-enes, alk-1-ynes, aromatic compounds, alcohols, and ketones) in the ionic liquid PEG-5 cocomonium methylsulfate with gas–liquid chromatography at four different temperatures, T=(313.15, 323.15, 333.15, and 343.15)K. Packed columns with phase loadings of 0.28 and 0.34 ionic liquid mass fraction in the stationary phase were employed to obtain γ13∞ values at each temperature investigated. Speed of sound, density, and refractive index values have also been measured for the pure ionic liquid at P=0.1MPa and T=(303.15, 313.15, 323.15, 333.15, and 343.15)K. The uncertainties in the sound speeds, densities, and refractive indices are estimated to be values of 0.9m·s−1, 0.00003g·cm−3, and 0.00002, respectively. Partial molar excess enthalpies at infinite dilution ΔH1E,∞ were calculated for the solutes from the temperature dependency of the γ13∞ values for the temperature range of this study. The uncertainties in the determinations of γ13∞ and ΔH1E,∞ values are 5% and 10%, respectively. Selectivity values at infinite dilution S12∞ for hexane/benzene, cyclohexane/benzene, hexane/hex-1-ene, and hexane/ethanol separations have been calculated. These have been compared against values obtained from COSMO-RS predictions.

Thermodynamic and Topological Studies of 1-Ethyl-3-methylimidazolium Tetrafluoroborate + Pyrrolidin-2-one and 1-Methyl-pyrrolidin-2-one Mixtures

Excess molar enthalpies, HE of 1-ethyl-3-methylimidazolium tetrafluoroborate (1) + pyrrolidin-2-one or 1-methyl pyrrolidin-2-one (2) binary mixtures at 298.15 K, densities, ρ, and speeds of sound, u, data of the same mixtures at (293.15, 298.15, 303.15, and 308.15) K have been measured over entire mole fraction range. The observed densities and speeds of sound data have been utilized to determine their excess molar volumes, VE, and excess isentropic compressibilities, κSE. The topology of the constituents of mixtures (graph theory) has been employed to calculate the VE, HE, and κSE of ionic liquid mixtures. The analysis of the measured data in terms of graph theory suggests that investigated (1 + 2) mixtures are characterized by interactions forming a 1:1 molecular complex, and VE, HE, and κSE values calculated by graph theory are close to the experimental ones.

Topological investigations of binary mixtures containing 1-ethyl-3-methylimidazolium tetrafluoroborate and anilines

The densities, ρ, speeds of sound, u of 1-ethyl-3-methylimidazolium tetrafluoroborate (i)+aniline or N-methylaniline or 2-methylaniline (j) binary mixtures at 293.15, 298.15, 303.15, and 308.15K and excess molar enthalpies, HE of the same mixtures at 298.15K have been measured over entire mole fraction using DSA-5000 and 2-Drop microcalorimeter respectively. Excess molar volumes, VE and excess isentropic compressibilities, κSE values have been predicted by utilizing the measured densities and speeds of sound data. The Graph theory which deals with the topology of the constituents of mixtures has been applied to predict (i) state of components of ionic liquid mixture in their pure and mixed state; (ii) nature and extent of interactions existing in mixtures; and (iii) VE, HE and κSE values. The analysis of VE data in terms of Graph theory suggests that while 1-ethyl-3-methylimidazolium tetrafluoroborate is characterized by electrostatic forces of attraction and exists as monomer; aniline or N-methylaniline or 2-methylaniline exists as associated molecular entities. Further, (i+j) mixtures are characterized by interactions between nitrogen and fluorine atoms of 1-ethyl-3-methylimidazolium tetrafluoroborate with nitrogen and hydrogen atoms of aniline or N-methylaniline or 2-methylaniline to form 1:1 molecular complex. The IR studies also support this view point. The VE, HE and κSE values predicted by Graph theory compare well with the experimental values.

Excess Molar Volumes, Excess Molar Enthalpies, and Excess Isentropic Compressibilities of Binary Mixtures Containing N-Methyl-2-Pyrrolidone and Isomeric Xylenes at 308.15 K

Excess molar volumes, excess molar enthalpies and speeds of sound of 1-methyl pyrrolidin-2-one + o- or m- or p-xylene binary mixtures have been measured over the entire composition range at 308.15 K. The speed of sound data were used to determine the excess isentropic compressibilities. It is observed that while the values of the excess molar enthalpies for the investigated mixtures are positive, the values of the excess molar volumes and excess isentropic compressibilities are negative over the entire composition range. The measured thermodynamic data have been analyzed in terms of Graph, Prigogine–Flory–Patterson, and the Sanchez and Lacombe theories. It is observed that Graph theory correctly predicts the signs and magnitudes of the excess molar volumes, excess molar enthalpies, and excess isentropic compressibilities of the studied mixtures. However, the excess molar volumes, excess molar enthalpies and excess isentropic compressibilities predicted by Prigogine–Flory–Patterson and Sanchez and Lacombe theories are of same sign.

Accurate Measurements of Infinite Dilution Activity Coefficients Using Gas Chromatography with Static-Wall-Coated Open-Tubular Columns

Wall-coated open-tubular (WCOT) columns provide higher column efficiency and lower solute interfacial adsorption effect than packed columns. However, previous efforts used to measure the infinite dilution activity coefficient (γ(∞)) via a chromatographic technique have used packed columns, because the low carrier gas flow rate (U) and the small stationary phase amount (n(2)) in WCOT columns raise large errors. By rationally revising the γ(∞)-calculation equation for static-wall-coated open-tubular column, we observed that U and n(2) are not necessarily needed and the resulting error could be reduced, and WCOT column gas chromatography subsequently became a superior method for the accurate γ(∞) determination. In this study, we validate our revised γ(∞)-calculation equation by measuring γ(∞) in an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate system, in which 55 organic compounds covering a wide range of functional groups were used as probe solutes and their γ(∞) values in the ionic liquid were determined at 40.0, 50.0, and 60.0 °C. Experimental error analysis shows that our revised equation remarkably reduces the error compared to the common γ(∞)-calculation equation. Our data is consistent with previously reported values obtained via other techniques, which further proves the credibility of our revised equation. The accurately determined γ(∞) values can be directly used to calculate the partial molar excess enthalpy, selectivity, and capacity, which will benefit for the rapid screening of solvents (especially ionic liquids) in separation approaches.

Vapor–Liquid Equilibrium, Excess Molar Enthalpies, and Excess Molar Volumes of Binary Mixtures Containing Methyl Isobutyl Ketone (MIBK) and 2-Butanol, tert-Pentanol, or 2-Ethyl-1-hexanol

Phase equilibrium and calorimetric measurements provide complementary data that are vital for process models. The combined use of vapor–liquid equilibrium (VLE) data and excess enthalpies (HE) makes the thermodynamic model more reliable in extrapolation outside the conditions of the measurement. This is important during the tight time schedule of process development. In this work, phase equilibrium and excess enthalpies of binary mixtures were measured by using three apparatuses. Two types of VLE runs were conducted by using a circulation still of the Yerazunis-type and by using Agilent headspace sampler with a gas chromatograph (HS-GC). A SETARAM C80 calorimeter equipped with a flow mixing cells was taken into use for excess enthalpy measurements. New data of phase equilibrium, excess molar enthalpy, and excess molar volume were obtained for industrially relevant binary mixtures of methyl isobutyl ketone (MIBK) with alcohols (2-butanol, tert-pentanol, 2-ethyl-1-hexanol). Excess enthalpy data at 298.15 K are well in line with equilibrium data obtained in the range of (294 to 368) K. Azeotropic behavior was observed in the MIBK + tert-pentanol system. The experimental data were used for the optimization of Wilson and Redlich–Kister equation parameters.

Thermodynamics of alkanone + aromatic hydrocarbon mixtures

Linear alkanone or cyclohexanone+aromatic hydrocarbon mixtures have been studied using DISQUAC and the Kirkwood–Buff formalism. The aromatic compounds considered are: benzene, toluene, 1,4-dimethylbenzene, 1,2,4-trimethylbenzene and ethylbenzene. Vapour–liquid equilibria (VLE), molar excess Gibbs energies, GmE, molar excess enthalpies, HmE, and isobaric molar excess heat capacities, CpmE, of the binary systems studied are well represented by DISQUAC. There is a good agreement between experimental HmE values of related ternary mixtures, and DISQUAC predictions obtained by means of binary interaction parameters only DISQUAC improves very meaningfully UNIFAC results on HmE, CpmE, properties which are closely related to the molecular structure of the mixture components. The enthalpy (HintCO-S) of the ketone–aromatic hydrocarbon interactions has been evaluated. These interactions become weaker when the alkanone size increases in mixtures with a given aromatic hydrocarbon, or when the aliphatic surface of the alkylbenzene is increased in systems with a given ketone. Steric effects are more relevant in 1,4-dimethylbenzene mixtures than in those with ethylbenzene. The application of the Kirkwood–Buff formalism to mixtures including toluene or ethylbenzene shows that orientational effects, related to ketone–ketone interactions, exist in solutions with the shorter 2-alkanones. Such effects are weakened when the chain length of the 2-alkanone increases. The opposite behaviour is observed when increasing the aliphatic surface of the alkylbenzene in systems with a given 2-alkanone. The cyclohexanone+benzene mixture shows a structure close to random mixing.

Excess molar enthalpies for binary mixtures of 1,2-dichloroethane with ethers at 298.15 K and atmospheric pressure

Excess molar enthalpies, HE, for the binary mixtures of 1,2-dichloroethane (1,2-DCE) with diethyl ether (DEE), methyl 1,1-dimethylethyl ether (MTBE), diisopropyl ether (DIPE), 1,3-dioxolane (1,3-DIOXO), 1,4-dioxane (1,4-DIOXA), tetrahydropyran (THP), ethylene glycol dimethyl ether (EGDME), diethylene glycol dimethyl ether (DEGDME), and diethylene glycol diethyl ether (DEGDEE), have been measured at 298.15K and atmospheric pressure, using a Setaram Tian-Calvet C80 microcalorimeter. All the binary systems investigated are characterized by exothermic mixing over the entire composition range, except for 1,2-DCE+DIPE which presents a S-shape HE behavior. The experimental HE data have been fitted to the Redlich–Kister polynomial equation.

Interactions of volatile organic compounds with the ionic liquids 1-butyl-1-methylpyrrolidinium tetracyanoborate and 1-butyl-1-methylpyrrolidinium bis(oxalato)borate

Interactions of volatile organic compounds with two ionic liquids (ILs) 1-butyl-1-methylpyrrolidinium tetracyanoborate [BMPYR][B(CN)4] and 1-butyl-1-methylpyrrolidinium bis(oxalato)borate [BMPYR][BOB] were explored through systematic GLC retention measurements. Infinite dilution activity coefficients γ1∞ and gas–liquid partition coefficients KL of 30 selected solutes in [BMPYR][B(CN)4] and [BMPYR][BOB] were determined at five temperatures in the range from (318.15 to 353.15)K and from (333.15 to 373.15)K, respectively. Partial molar excess enthalpies and entropies at infinite dilution were derived from the temperature dependence of the γ1∞ values. The Linear Free Energy Relationship (LFER) solvation model was used to correlate successfully the KL values. The LFER correlation parameters and excess thermodynamic functions were analyzed to disclose molecular interactions operating between the ILs and the individual solutes. Among other ILs, [BMPYR][B(CN)4] was identified as a very weakly cohesive solvent medium, in contrast to [BMPYR][BOB] which appears to be fairly cohesive IL close in this respect to [BMPYR][DCA] examined recently. Both [BMPYR][B(CN)4] and [BMPYR][BOB] are capable of interacting specifically through all modes (lone electron pairs, dipolarity/polarizibility, and hydrogen bonding) with solutes of complementary capabilities. Their hydrogen bond basicity and ability to interact with lone electron pairs are appreciable but distinctly lower than those of [BMPYR][DCA]. The proton donating capability of these ILs is weak, but still traceable, and stems undoubtedly from unsubstituted hydrogen atoms on the pyrrolidinium ring of their cation. The selectivities of [BMPYR][B(CN)4] and [BMPYR][BOB] for separation of aromatic hydrocarbons and thiophene from saturated hydrocarbons rank among [BMPYR] ILs the lowest and medium, respectively. The selectivity of [BMPYR][B(CN)4] is comparable to that of sulfolane, but this IL surpasses it roughly three times in the capacity. [BMPYR][B(CN)4] and [BMPYR][BOB] could also serve as efficient entrainers in separations of other non-petrochemical azeotropic systems of industrial importance by extractive distillation. In particular, we have identified [BMPYR][B(CN)4] as a very convenient separation agent for (methanol+dimethyl carbonate) mixture.

Activity Coefficients of Organic Solutes at Infinite Dilution in the Ionic Liquids. 2. Organic Solutes in 1-Hexyl-3-methylimidazolium Nitrate and Gas–Liquid Partitioning and Interfacial Adsorption Using Gas–Liquid Chromatography

This paper reports activity coefficients at infinite dilution for a series of organic solutes in the ionic liquid 1-hexyl-3-methylimidazolium nitrate by gas–liquid chromatography at different temperatures between 313.15 and 363.15 K. The contribution of gas–liquid partitioning and interfacial adsorption to the retention mechanism was estimated by changing the loading of ionic liquid in stationary phase, and the influence of different loading of ionic liquid on the experimental values of activity coefficients at infinite dilution was discussed. The partial molar excess enthalpies at infinite dilution and the solubility parameters of ionic liquid were also calculated from the experimental values of activity coefficients at infinite dilution.

Activity coefficients at infinite dilution and physicochemical properties for organic solutes and water in the ionic liquid 1-(2-methoxyethyl)-1-methylpiperidinium trifluorotris(perfluoroethyl)phosphate

This work is continuation of our systematic study of activity coefficients at infinite dilution, γ∞ of different organic solutes and water in the ionic liquids. New data of γ∞ were determined for 62 solutes, including alkanes, alkenes, alkynes, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, ethers, ketones, esters, 1-nitropropane, butanal, acetonitrile, and water in the ionic liquid 1-(2-methoxyethyl)-1-methylpiperidinium trifluorotris(perfluoroethyl)phosphate by inverse gas chromatography at the temperature range from (318.15 to 368.15)K. The basic thermodynamic functions, namely partial molar excess Gibbs free energies, ΔG1E,∞, enthalpies, ΔH1E,∞ and entropies, ΔS1E,∞ at infinite dilution were calculated from the experimental γ∞ values obtained over the temperature range. Additionally the gas–liquid partition coefficients, KL were determined. Results are compared to previously investigated ionic liquids with the same cations or anions. Values of the selectivity and capacity at infinite dilution for heptane/benzene, heptane/thiophene, and heptane/methanol extraction problems were calculated from experimental γ∞ values to verify the possibility of investigated ionic liquid as an entrainer in liquid–liquid extraction.

Excess molar volumes, excess molar enthalpies and refractive index deviations for binary mixtures of propan-1-ol, butan-1-ol and pentan-1-ol with 2,2,4-trimethylpentane at 298.15 K

Density (ρ), refractive index (nD), and molar excess enthalpy (HE) of binary mixtures of propan-1-ol with 2,2,4-trimethylpentane, butan-1-ol with 2,2,4-trimethylpentane and pentan-1-ol with 2,2,4-trimethylpentane at 298.15K and ambient pressure have been experimentally measured in the whole composition range. Excess molar volumes (VE), deviation of refractive indices (ΔnD), deviations of molar refraction (ΔR) and HE data were correlated with Redlich–Kister equation. Refractive indexes estimates were carried out using several mixing rules. An estimation of density of the binary mixture was performed using the equation suggested by Nakata and Sakurai [35] using the Lorentz–Lorenz refractive index mixing rule with densities and refractive indexes of the pure substances. Wilson and Non Random Two Liquids (NRTL) models were applied for HE correlation. The Prigogine–Flory–Patterson (PFP) and Extended Real Association Solution (ERAS) theories have been used to correlate the excess molar volumes of the mixtures. The behavior of the thermophysical properties was analyzed in terms of the length of the alkanol chain and the balance between positive and negative deviations of the ideality.

Thermodynamics of mixtures containing amines. XI. Liquid + liquid equilibria and molar excess enthalpies at 298.15 K for N-methylaniline + hydrocarbon systems. Characterization in terms of DISQUAC and ERAS models

Liquid+liquid equilibrium (LLE) temperatures have been determined for the N-methylaniline+tetradecane, or +hexadecane systems by the method of the critical opalescence using a laser scattering technique. The coexistence curves have an upper critical solution temperature (UCST) and, due to size effects, are skewed towards high mole fractions of the amine. Excess molar enthalpies, HmE, at 298.15K and atmospheric pressure, have been also measured over the entire mole fraction range, using a Tian–Calvet microcalorimeter, for the mixtures N-methylamine+heptane, +octane, +decane, +cyclohexane, or +toluene. The HmE curves of alkane solutions are characterized by a large maximum and a rather flattened top, which are typical features of systems at temperature close to the UCST. N-methylamine+alkane, +benzene, +toluene or +1-alkanol mixtures have been investigated in terms of the DISQUAC and ERAS models. The corresponding interaction parameters are reported. From the analysis of the experimental data and of the theoretical results, it is shown that: (i) HmE of the studied N-methylamine solutions is mainly determined by the disruption, upon mixing, of the interactions between like molecules; (ii) interactions between isomeric aromatic amines become weaker in the sequence: primary>secondary>tertiary; (iii) for isomeric molecules, interactions between aromatic amines are stronger than between linear amines; (iv) in aromatic amine+aromatic hydrocarbon or +1-alcohol systems, amine-solvent interactions are stronger in the order tertiary<secondary<primary; (v) physical interactions play a dominant role in the investigated mixtures; (vi) DISQUAC and ERAS models provide similar HmE results for systems including alkanes. In the case of mixtures with aromatic hydrocarbons or 1-alkanols, where interactions between unlike molecules are relevant, HmE is better described by DISQUAC; and (vii) the quasichemical interchange coefficients (l=1,3) for the contacts amine/aliphatic; amine/aromatic; amine/cyclic and amine/hydroxyl are the same for systems with aniline, 2-methylaniline, N-methylaniline, or N,N-dimethylaniline.

Topological investigations of binary mixtures containing ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate and pyridine or isomeric picolines

The densities, ρ, speeds of sound, u of {1-ethyl-3-methylimidazolium tetrafluoroborate (i)+pyridine or α- or β- or γ-picoline (j)} at T/K=(293.15, 298.15, 303.15, and 308.15) and excess molar enthalpies, HE of the same set of mixtures at T/K=(298.15) have been measured over entire mole fraction range using DSA-5000 and 2-drop microcalorimeter. Excess molar volumes, VE and excess isentropic compressibilities, κSE values have been predicted by utilizing the measured densities and speeds of sound data. It has been observed that VE, HE, and κSE values for the studied mixtures are negative over entire composition. The connectivity parameter of third degree of a molecule, 3ξ (which in turn depends upon its topology) have been applied to predict (i) state of components of ionic liquid mixtures in their pure and mixed state; (ii) nature and extent of interactions existing in mixtures; and (iii) VE, HE, and κSE values. The analysis of VE data in terms of Graph theory (which deals with topology of a molecule) suggest that while 1-ethyl-3-methylimidazolium tetrafluoroborate is characterised by electrostatic forces of attraction and exist as monomer; α- or β- or γ-picoline exist as associated molecular entities. Further, (i+j) mixtures are characterized by interactions between nitrogen and florine atoms of 1-ethyl-3-methylimidazolium tetrafluoroborate with nitrogen and carbon atoms of pyridine or isomeric picolines to form 1:1 molecular complex. The IR studies also support to this view point. The VE, HE, and κSE values predicted by Graph theory compare well with experimental values.

Excess properties and vapour pressure of 2-diethylaminoethylamine + cyclohexane

The vapour pressures of liquid (2-diethylaminoethylamine (2-DEEA)+cyclohexane) mixtures were measured by a static method between (T=273.15 and T=363.15)K at 10K intervals. The excess molar enthalpies HE at 303.15K were also measured. The molar excess Gibbs energies GE were obtained with Barker’s method and fitted to the Redlich–Kister equation. The Wilson equation was also used. Deviations between experimental and predicted GE and HE, by using DISQUAC model, were evaluated. The proximity effect of N atoms produces a decrease of the interactional parameters.

Excess enthalpies of ternary mixtures of oxygenated additives + hydrocarbon mixtures in fuels and bio-fuels: Dibutyl ether (DBE) and 1-butanol and 1-hexene or cyclohexane or 2,2,4 trimethylpentane at 298.15 K and 313.15 K

New experimental excess molar enthalpy data (420 points) of the ternary systems dibutyl ether (DBE) and 1-butanol and 1-hexene at 298.15K and 313.15K, and DBE and 1-butanol and cyclohexane or 2,2,4-trimethylpentane (TMP) at 313.15K at atmospheric pressure are reported. A quasi-isothermal flow calorimeter has been used to make the measurements. All the ternary systems show endothermic character. The experimental data for the ternary systems have been fitted using the Redlich–Kister rational equation. Considerations with respect the intermolecular interactions amongst ether, alcohol and hydrocarbon compounds are presented.

Activity Coefficients at Infinite Dilution of Alkanes, Alkenes, and Alkyl Benzenes in 1-Butyl-3-methylimidazolium Dibutylphosphate Using Gas–Liquid Chromatography

The activity coefficients at infinite dilution, γi∞, for 16 organic solutes, alkanes, alkenes, and alkyl benzenes in the ionic liquid 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]), have been measured by the gas–liquid chromatographic method. The measurements were carried out in the temperature range of (313.15 to 363.15) K. The partial molar excess enthalpies at infinite dilution, HiE,∞, of the solutes in [BMIM][DBP] were also derived from the temperature dependence of the γi∞ values.

Perturbed-Chain SAFT as a Versatile Tool for Thermodynamic Modeling of Binary Mixtures Containing Isoquinolinium Ionic Liquids

This contribution reports a recapitulation of our experimental and modeling study on thermodynamic behavior of binary systems containing N-alkylisoquinolinium ionic liquids (ILs) based on bis(trifluoromethylsulfonyl)imide anion, [CniQuin][NTf2] (n = 4,6,8). In particular, we report isothermal vapor-liquid equilibrium (VLE) phase diagrams and molar excess enthalpies of mixing (H(E)) for binary mixtures of [C8iQuin][NTf2] IL with various organic solutes including benzene, toluene, thiophene, pyridine, and butan-1-ol. The measured VLE data represented simple homozeotropic behavior with either negative or positive deviations from ideality, depending on polarity of the solute, temperature, and mole fraction of IL. In turn, the obtained data on H(E) were negative and positive for the mixtures containing aromatic hydrocarbons or thiophene and butan-1-ol, respectively, in the whole range of IL's concentration. All of the measured and some previously published data regarding phase behavior of [C8iQuin][NTf2] IL were analyzed and successfully described in terms of perturbed-chain statistical associating fluid theory (PC-SAFT). The methodology used in this work was described by us previously. In general, the proposed modeling results in VLE diagrams, which are in excellent agreement with experimental data. In the case of H(E), the results obtained are good as well but not so satisfactory such as those for VLE. Nevertheless, they seem to be very promising if one take into account the simplicity of the utilized molecular model against significant complexity of IL-based systems. Thus, we concluded that PC-SAFT equation of state can be viewed as a powerful and robust tool for modeling of systems involving ILs.

Thermodynamic properties and vapor–liquid equilibria of associating fluids, Peng–Robinson equation of state coupled with shield-sticky model

Combining Peng–Robinson (PR) equation of state (EOS) with Liu et al.’s association contribution derived from shield-sticky model (SSM), a new cubic-plus-association (CPA) EOS is proposed to describe the thermodynamic properties of pure associating fluids and their mixtures. The CPA-SSM EOS contains five molecular parameters (a0, c1, b, ω and δɛ/k) for the pure associating fluids, while for non-associating fluids it reduces to PR EOS with three molecular parameters (a0, c1, b). The molecular parameters are obtained by fitting the saturated pressures and/or liquid molar volumes at wide temperature ranges. The overall average absolute deviations (AADs) of 58 pure associating fluids and 20 non-associating fluids are 0.74% and 0.54% for saturated vapor pressure, 2.00% and 1.85% for liquid molar volumes respectively. The enthalpies of vaporization for 13 pure associating fluids are well predicted by using these molecular parameters. The molecular parameter b for homologous substances shows a good linear relationship with respect to their corresponding molecular weights. Using one temperature-independent binary adjustable parameter kij, satisfactory results of vapor–liquid equilibria (VLE) for both self- and cross-associating systems are obtained. The overall AADs of the equilibrium temperatures, pressures and vapor phase mole fractions are 1.46K, 1.26kPa and 0.0197 respectively for 25 self-associating systems, and 0.75K, 0.50kPa and 0.0155 respectively for 29 cross-associating systems. Other caloric properties such as the excess molar enthalpies of mixing are also successfully computed. The CPA-SSM EOS proposed has been proved to have comparable accuracy as other models but with much simpler form.

Activity coefficient at infinite dilution measurements for organic solutes (polar and non-polar) in fatty compounds: Saturated fatty acids

The activity coefficients at infinite dilution , γ13∞ (the subscript 1 and 3 correspond to solute and solvent, respectively), for 21 solutes, including alkane, cycloalkane, alkene, aromatic compounds, alcohol, ester, ketone, and halogenated hydrocarbons, in four solvents, that are the saturated fatty acids: capric (decanoic) acid, lauric (dodecanoic) acid, myristic (tetradecanoic) acid, and palmitic (hexadecanoic) acid, were determined by gas–liquid chromatography at temperatures from 314.10K to 358.33K. Comparison with previously published for selected solutes in palmitic (hexadecanoic) acid were also performed. The values of the partial molar excess Gibbs free energy, ΔG13∞, enthalpy, ΔH13∞, and entropy, ΔS13∞, at infinite dilution were calculated from experimental γ13∞ values obtained over the temperature range. Results obtained in this work allow a more accurate description of the real behavior of fatty systems.