Partial Molar Excess Enthalpies Research Articles

Thermodynamic study of heptane + secondary, tertiary and cyclic amines mixtures. Part IV. Excess and solvation enthalpies at 298.15 K

Partial molar enthalpies and excess enthalpies H E of binary mixtures of heptane + secondary and tertiary n-alkyl, primary cycloalkyl, and secondary (hetero)cyclic amines have been determined at 298.15 K by isothermal titration calorimetry in the whole composition range. All mixtures showed positive H E values which decrease with increasing amine size in each category, and decrease in the order cyclic primary > cyclic secondary > linear primary [1] > secondary > tertiary when comparing amines of similar size in different categories. From partial molar enthalpies at infinite dilution and known enthalpies of vaporization, the solvation enthalpies have been calculated either for heptane in amines and for amines in heptane. These quantities, together with their cavitational and interactional terms obtained applying the scaled particle theory, are discussed to get insight into the types and relative strength of solute–solvent interactions and into their effects on molecular structure features such as branching and cyclization.

Solubilities of Phenylphosphinic Acid, Methylphenylphosphinic Acid, Hexachlorocyclotriphosphazene, and Hexaphenoxycyclotriphosphazene in Selected Solvents

Phenylphosphinic acid (PPA), methylphenylphosphinic acid (MPPA), hexachlorocyclotriphosphazene (HCCP), and hexaphenoxycyclotriphosphazene (HPCCP) were prepared and characterized by elemental analysis, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. Using a static analytical method, the solubilities of PPA, MPPA, HCCP, and HPCCP were measured in ten solvents and correlated with an empirical equation. The calculated results showed good agreement with the experimental data. Furthermore, using the Scatchard−Hildebrand model, activity coefficients have also been calculated and compared with the experimental values. The partial molar excess enthalpies at infinite dilution were also predicted.

Determination of activity coefficients at infinite dilution of water and organic solutes (polar and non-polar) in the Ammoeng 100 ionic liquid at T = (308.15, 313.5, 323.15, and 333.15) K

Activity coefficients at infinite dilution ( γ 13 ∞ ) have been determined for 27 solutes, viz. water and organic compounds ( n-alkanes, cycloalkanes, 1-alkenes, 1-alkynes, aromatics, alcohols, and ketones) in the ionic liquid Ammoeng 100, by gas–liquid chromatography at four different temperatures, T = (308.15, 313.15, 323.15, and 333.15) K. Columns with different phase loadings (20 to 24)% of the ionic liquid in the stationary phase were employed to obtain γ 13 ∞ values at each temperature investigated. Partial molar excess enthalpies at infinite dilution ( Δ H 1 E , ∞ ) were calculated for the solutes from the temperature dependency relationship of the ln ( γ 13 ∞ ) values for the temperature range in this study. The uncertainties in the determinations of the γ 13 ∞ and Δ H 1 E , ∞ values are 6% and 10%, respectively. Selectivity values at infinite dilution ( S ij ∞ ), have been computed from the γ 13 ∞ values to assess the potential candidacy of the Ammoeng 100 ionic liquid for the separation of alkane/alcohol mixtures. The results from this study have been compared to those available for several ionic liquids from previous investigations.

Activity coefficients at infinite dilution of organic solutes in the ionic liquid 1-butyl-3-methylimidazolium hexafluoroantimonate using gas–liquid chromatography at T = (313.15, 323.15, and 333.15) K

Activity coefficients at infinite dilution were determined for 27 solutes: n-alkanes, alk-1-enes, alk-1-ynes, cycloalkanes, alkylbenzenes, alcohols, and ketones in the ionic liquid 1-butyl-3-methylimidazolium hexafluoroantimonate, [BMIM][SbF 6], by gas–liquid chromatography at three different temperatures, T = (313.15, 323.15, and 333.15) K. The results are compared to published data on related compounds. The partial molar excess enthalpy values at infinite dilution were calculated from the experimental data over the same temperature range. Selectivities and capacities at infinite dilution were calculated for the hexane/benzene and methanol/benzene systems from experimental infinite dilution activity coefficients and compared to the literature values for related ionic liquids, as well as to data on industrial molecular solvents.

Activity coefficients at infinite dilution of organic solutes in the ionic liquid, methyl(trioctyl)ammonium thiosalicylate, [N1888][TS] by gas–liquid chromatography at T = (303.15, 313.15, and 323.15) K

In this work, activity coefficients at infinite dilution ( γ 13 ∞ ) have been obtained for 19 polar and non-polar organic solutes in the form of n-alkanes, cycloalkanes, 1-alkenes, 1-alkynes, aromatic compounds, and ketones in the ionic liquid methyl(trioctyl)ammonium thiosalicylate by gas–liquid chromatography at three different temperatures, i.e. T = (303.15, 313.15, and 323.15) K. Two columns with different phase loadings of the ionic liquid in the stationary phase (25% and 30%) were employed to obtain γ 13 ∞ values at each temperature investigated. Partial molar excess enthalpies at infinite dilution ( Δ H 1 E, ∞ ) were calculated for each of the solutes from the temperature dependency of the γ 13 ∞ values for the temperature range in this study. Selectivity values at infinite dilution ( S ij ∞ ) were computed from the γ 13 ∞ values to screen the potential candidacy of the ionic liquid for the separation of n-hexane/benzene mixtures. The results from this study have been compared to those available for several other classes of ionic liquids and commercial solvents employed in solvent-enhanced industrial separation processes.

An enthalpic approach to delineate the interactions of cations of imidazolium-based ionic liquids with molecular solvents

We present a systematic investigation on the enthalpic assessment of the interactions operating between the cation and anion of four imidazolium ionic liquids with aqueous and various nonaqueous solvents. Accurate experimental information gathered with the help of an isothermal titration calorimeter at 298.15 K has been analyzed for excess partial molar enthalpy of the ionic liquid, H(IL)(E), in terms of hydrophobic and solvation effects. The variations in the limiting excess partial molar enthalpy of the ionic liquid, H(IL)(E, ∞), have been correlated with solvent properties. We have quantified the enthalpic effects due to dissociation of ionic liquids in very dilute solutions and to clathrate formation with the increasing concentration of ionic liquid. A change in enthalpic behavior from endothermic to exothermic is observed on increasing the carbon chain length attached to the imidazolium ring. The solvent reorganization around the cationic species has been unraveled by employing the ionic liquid interaction parameters called as H(IL-IL)(E) deduced from the H(IL)(E) data. The apparent relative molar enthalpy, φ(L), derived from H(IL)(E) data has been examined in the light of the specific ion interaction theory as advanced by Pitzer with accurate results.

Activity coefficients at infinite dilution of organic solutes in the ionic liquid trihexyl(tetradecyl)phosphonium tetrafluoroborate using gas–liquid chromatography at T = (313.15, 333.15, 353.15, and 373.15) K

Activity coefficients at infinite dilution have been measured by gas–liquid chromatography for 27 organic solutes (n-alkanes, 1-alkenes, 1-alkynes, cycloalkanes, aromatics, alcohols, and ketones) in the ionic liquid trihexyl(tetradecyl)phosphonium tetrafluoroborate [3C 6C 14P][BF 4]. The measurements were carried out at four different temperatures viz. T = (313.15, 333.15, 353.15, and 373.15) K. From the experimental data, partial molar excess enthalpy values at infinite dilution were calculated for the experimental temperature range. The selectivity values for the separation of n-hexane/benzene, cyclohexane/benzene, and methanol/benzene mixtures were determined from the experimental infinite dilution activity coefficient values. These values were compared to those available in the literature for other ionic liquids and commercial solvents, so as to assess the feasibility of employing [3C 6C 14P][BF 4] in solvent-enhanced industrial separations.

Measurements of Activity Coefficients at Infinite Dilution for Organic Solutes and Water in the Ionic Liquid 1-Butyl-1-methylpiperidinium Thiocyanate

The activity coefficients at infinite dilution (γ13∞) for 33 solutes: alkanes, alkenes, alkynes, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, ethers, ketones, and water in the ionic liquid, 1-butyl-1-methylpiperidinium thiocyanate ([BMPIP][SCN]), were determined by gas−liquid chromatography over the temperature range (318.15 to 358.15) K. The partial molar excess enthalpies at infinite dilution values (ΔH1E,∞) were calculated from the experimental γ13∞ values, obtained over the temperature range. The selectivities for heptane/benzene, cyclohexane/benzene, and heptane/thiophene separation problems were calculated from the γ13∞ and compared to the literature values for other ionic liquids with thiocyanate-based anion or with a butyl-methyl-substituted cation.

Intermolecular Interactions in Ternary Glycerol–Sample–H2O: Towards Understanding the Hofmeister Series (V)

We studied the intermolecular interactions in ternary glycerol (Gly)–sample (S)–H2O systems at 25 °C. By measuring the excess partial molar enthalpy of Gly, \(H_{\mathrm{Gly}}^{\mathrm{E}}\), we evaluated the Gly–Gly enthalpic interaction, \(H_{\mathrm{Gly}\mbox{--}\mathrm{Gly}}^{\mathrm{E}}\), in the presence of various samples (S). For S, tert-butanol (TBA), 1-propanol (1P), urea (UR), NaF, NaCl, NaBr, NaI, and NaSCN were used. It was found that hydrophobes (TBA and 1P) reduce the values of \(H_{\mathrm{Gly}\mbox{--}\mathrm{Gly}}^{\mathrm{E}}\) considerably, but a hydrophile (UR) had very little effect on \(H_{\mathrm{Gly}\mbox{--}\mathrm{Gly}}^{\mathrm{E}}\). The results with Na salts indicated that there have very little effect on \(H_{\mathrm{Gly}\mbox{--}\mathrm{Gly}}^{\mathrm{E}}\). This contrasts with our earlier studies on 1P–S–H2O in that Na+, F− and Cl− are found as hydration centers from the induced changes on \(H_{\mathrm{IP}\mbox{--}\mathrm{IP}}^{\mathrm{E}}\) in the presence of S, while Br−, I−, and SCN− are found to act as hydrophiles. In comparison with the Hofmeister ranking of these ions, the kosmotropes are hydration centers and the more kosmotropic the higher the hydration number, consistent with the original Hofmeister’s concept of “H2O withdrawing power.” Br−, I− and SCN−, on the other hand, acted as hydrophiles and the more chaotropic they are the more hydrophilic. These observations hint that whatever effect each individual ion has on H2O, it is sensitive only to hydrophobes (such as 1P) but not to hydrophiles (such as Gly). This may have an important bearing towards understanding the Hofmeister series, since biopolymers are amphiphilic and their surfaces are covered by hydrophobic as well as hydrophilic parts.

Measurements of activity coefficients at infinite dilution of organic compounds and water in isoquinolinium-based ionic liquid [C 8iQuin][NTf 2] using GLC

New isoquinolinium ionic liquid has been synthesized from N-octylisoquinolinium bromide as a substrate. The specific basic characterization of the new compound by NMR spectra, elementary analysis and water content is presented. The activity coefficients at infinite dilution, γ 13 ∞ for 37 solutes viz. alkanes, alkenes, alkynes, cycloalkanes, aromatic hydrocarbons, alcohols, ethers, ketones, and water in the ionic liquid N-octylisoquinolinium bis{(trifluoromethyl)sulfonyl}imide [C 8iQuin][NTf 2], were determined by gas–liquid chromatography at the temperatures from (328.15 to 368.15) K. The partial molar excess enthalpies at infinite dilution values Δ H 1 E , ∞ were calculated from the experimental γ 13 ∞ , obtained over the temperature range. The selectivity for the n-hexane/benzene, cyclohexane/benzene and n-heptane/thiophene separation problems were calculated from the γ 13 ∞ and compared to the other ionic liquids with bis{(trifluoromethyl)sulfonyl}imide anion, NMP and sulfolane, taken from the recent literature. The chosen ionic liquid demonstrates that it is possible to separate different organic compounds with the average selectivity and capacity.

Activity coefficients at infinite dilution of organic solutes in the ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate

Infinite dilution activity coefficients γ 1 ∞ and gas–liquid partition coefficients K L of 30 selected hydrocarbons, alcohols, ketones, ethers, esters, haloalkanes, nitrogen- and sulphur-containing compounds in the ionic liquid (IL) 1-ethyl-3-methylimidazolium methanesulfonate [EMIM][MeSO 3] were determined by gas–liquid chromatography at five temperatures in the range from 318.15 to 353.15 K. Relative contribution of adsorption at gas–liquid interphase to the overall solute retention, as examined by varying sample size and IL loading in the column, was found negligible. Partial molar excess enthalpies and entropies at infinite dilution were derived from the temperature dependence of the γ 1 ∞ values. The linear free energy relationship (LFER) solvation model was used to correlate successfully the K L values. The LFER correlation parameters and excess thermodynamic functions were analyzed to disclose molecular interactions operating between the IL and the individual solutes. Comparison to [EMIM][NO 3] studied previously revealed [MeSO 3] − anion to have still greater hydrogen bond basicity than that found for [NO 3] −. In addition, similarly to [EMIM][NO 3], promising potential of [EMIM][MeSO 3] for applications in solvent-aided separation processes was identified, the selectivities of [EMIM][MeSO 3] for separation of aromatic hydrocarbons and thiophene from saturated hydrocarbons ranking among the highest ever observed with ILs or molecular solvents.

Henry’s Law Constants and Infinite Dilution Activity Coefficients of Propane, Propene, Butane, 2-Methylpropane, 1-Butene, 2-Methylpropene, trans-2-Butene, cis-2-Butene, 1,3-Butadiene, Dimethyl Ether, Chloroethane, and 1,1-Difluoroethane in 2-Methylphenol, 3-Methylphenol, and 4-Methylphenol

Henry’s law constants and infinite dilution activity coefficients of propane, propene, butane, 2-methylpropane, 1-butene, 2-methylpropene, trans-2-butene, cis-2-butene, 1,3-butadiene, dimethyl ether, chloroethane, and 1,1-difluoroethane in 2-methylphenol, 3-methylphenol, and 4-methylphenol in the temperature range of (290 to 340) K were measured by a gas stripping method, and partial molar excess enthalpies and entropies were evaluated from the activity coefficients. A rigorous formula for evaluating the Henry’s law constants from the gas stripping measurements was used for the data reduction of these highly volatile mixtures. The estimated accuracies are about 2 % for the Henry’s law constants and 3 % for the infinite dilution activity coefficients. The Henry’s law constants followed the order of increasing Henry’s law constant with decreases in the normal boiling point temperature of the liquefied gas except for polar gases. The activity coefficients of the solutes in 2-methylphenol were smaller than those in 3-methylphenol and 4-methylphenol, and the activity coefficients of solutes in 3-methylphenol had similar values to those in 4-methylphenol.

Gas-liquid chromatography measurements of activity coefficients at infinite dilution of hydrocarbons and alkanols in 1-alkyl-3-methylimidazolium bis(oxalato)borate

The activity coefficients at infinite dilution, γ i ∞ for various solutes: alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols in the ionic liquids 1-butyl-3-methylimidazolium bis(oxalato)borate [BMIM][BOB] and 1-hexyl-3-methyl-imidazolium bis(oxalato)borate [HMIM][BOB] have been determined by gas-liquid chromatography at the temperatures ranging from 308 to 348 K. The partial molar excess enthalpies at infinite dilution H i E , ∞ of the solutes in the ionic liquids were also derived from the temperature dependence of the γ i ∞ values. The selectivities for the hexane/benzene, cyclohexane/benzene and hexane/hexene separation problems were calculated from experimental infinite dilution activity coefficient values and compared to the other ionic liquids, taken from the recent literatures.

Study of the Hyflon AD80 perfluorinated copolymer by inverse gas chromatography

The perfluorinated copolymer of tetrafluoroethylene and perfluoromethoxydioxole, Hyflon® AD80x, is investigated by inverse gas chromatography. C5–C13n-alkanes are used as sorbates, for which the specific retention volume, the solubility coefficient at infinite dilution, and the excess thermodynamic functions are calculated in the temperature range 30–115°C. The solubility coefficients of the hydrocarbons in the studied polymer are shown to be lower than those in amorphous Teflons AF1600 and AF2400, a finding that is consistent with the difference between the glass-transition temperatures of these polymers. The correlation between excess partial molar enthalpies and critical volumes of n-alkanes testifies that the upper limit for the size of the free-volume element in this polymer is 613 A3. Mixing of n-alkanes with Hyflon AD80 is thermodynamically disadvantageous (\( \bar G_1^{E,\infty } \) > 0) and becomes even less advantageous with an increase in the size of hydrocarbon molecules. Excess entropy mainly contributes to the high values of excess free energy, thus indicating a higher order in the system containing the glassy polymer than that in systems in which the polymer occurs in the rubberlike state.

A reversal from endothermic to exothermic behavior of imidazolium-based ionic liquids in molecular solvents

In this communication, we present an interesting reversal in the enthalpic behavior from endothermic to exothermic on increasing the carbon chain length attached to the imidazolium ring in the imidazolium-based ionic liquids. A systematic investigation is presented on the excess partial molar enthalpy, H IL E directly measured using isothermal titration calorimeter at 298.15 K for the interactions operating between cation and anion of four imidazolium ionic liquids with aqueous and various non-aqueous solvents. This reversal behavior is analyzed in terms of hydrophobic and solvation effects.

Amine volatility in CO 2 capture

Amine volatility is a key screening criterion for amines to be used in CO 2 capture. Excessive volatility may result in significant economic losses and environmental impact. It also dictates the capital cost of the water wash. This paper reports measured amine volatility in 7 m MEA (monoethanolamine), 8 m PZ (piperazine), 7 m MDEA (n-methyldiethanolamine)/2 m PZ (piperazine), 12 m EDA (ethylenediamine), and 5 m AMP (2-amino-2-methyl-1-propanol) at 40–60 °C with lean and rich loadings giving CO 2 partial pressures of 0.5 and 5 kPa at 40 °C. The amine concentrations were chosen to maximize CO 2 capture capacity at acceptable viscosity. At the lean loading condition (where volatility is of greatest interest), the amines are ranked in order of increasing volatility: 7 m MDEA/2 m PZ (6/2 ppm), 8 m PZ (8 ppm), 12 m EDA (9 ppm), 7 m MEA (31 ppm), and 5 m AMP (112 ppm). The apparent amine partial molar excess enthalpies in these systems were estimated to range from ∼10 to 87 kJ/mol of amine.

Activity coefficients at infinite dilution of organic solutes in N-alkylpyridinium bis(trifluoromethylsulfonyl)imide ([C nPY][NTf 2], n = 2, 4, 5) using gas–liquid chromatography

The activity coefficients at infinite dilution, γ i ∞ for both polar and non-polar solutes in the ionic liquids N-alkylpyridinium bis(trifluoromethylsulfonyl)imide ([C n PY][NTf 2], n = 2, 4, 5) have been determined by gas–liquid chromatography using the ionic liquid as the stationary phase. The measurements were carried out at the temperatures from (303 to 353) K. The partial molar excess enthalpies at infinite dilution H i E, ∞ of the solutes in the ionic liquids were also derived from the temperature dependence of the γ i ∞ values. The values of the selectivity for the hexane/benzene and cyclohexane/benzene separation problems were calculated from experimental infinite dilution activity coefficient values and compared to the other ionic liquids, taken from the recent literatures.

Excess Molar Enthalpies of Benzyl Alcohol + Alkanols (C1−C6) and Their Correlations at 298.15 K and Ambient Pressure

Excess molar enthalpies, HmE, for the binary mixtures of benzyl alcohol + methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol, and hexan-1-ol were measured over the entire range of composition at 298.15 K and ambient pressure using a Parr 1455 solution calorimeter. From the experimental results the excess partial molar enthalpies, HiE, and excess partial molar enthalpies at infinite dilution, HiE,∞, were calculated. While the excess molar enthalpies are negative for the methanol mixture, those for ethanol, propan-1-ol, butan-1-ol, pentan-1-ol, and hexan-1-ol mixtures are positive over the entire range of composition of benzyl alcohol. The experimental data were correlated by the Redlich−Kister equation and the two thermodynamics models (Wilson and nonrandom two-liquid, NRTL).

Measurements of Activity Coefficients at Infinite Dilution in Solvent Mixtures with Thiocyanate-Based Ionic Liquids Using GLC Technique

The activity coefficients at infinite dilution, gamma13(infinity) for 34 solutes--alkanes, cycloalkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, water, thiophene, ethers, and ketones--in the ionic liquid 1-butyl-4-methylpyridinium thiocyanate, [BMPy][SCN], and in 1-butyl-1-methylpyrrolidinium thiocyanate, [BMPYR][SCN], were determined by gas-liquid chromatography at the temperature range from 298.15 to 368.15 K. The partial molar excess enthalpies at infinite dilution values, DeltaH1E,infinity, were calculated from the experimental gamma13(infinity) values obtained over the temperature range. The selectivities for the n-heptane/benzene, cyclohexane/benzene, and n-heptane/thiophene separation problems were calculated from the gamma13(infinity). Obtained values were compared to the literature values for the other ionic liquids, NMP, and sulfolane.

Determination of Activity Coefficients at Infinite Dilution of 35 Solutes in the Ionic Liquid, 1-Butyl-3-methylimidazolium Tosylate, Using Gas−Liquid Chromatography

The activity coefficients at infinite dilution, γ13∞, for hydrocarbon solutes, alcohols, water, thiophene, ethers, and ketones in the ionic liquid 1-butyl-3-methylimidazolium tosylate (p-toluenesulfonate), [BMIM][TOS], have been determined by gas−liquid chromatography at temperatures T = (338.15, 348.15, 358.15, and 368.15) K. The selectivity values have been calculated at T = 338.15 K, and the results indicate that the ionic liquid [BMIM][TOS] should be considered as a solvent for separation of aromatic sulfur compounds from alkanes. The partial molar excess enthalpy values at infinite dilution ΔH1E∞, determined in this work, together with the values γ13∞ have been discussed in terms of intermolecular interactions and compared to results of related systems obtained earlier by us and from the literature.