Molar Enthalpies Of Vaporization Research Articles

Are ionic liquids pairwise in gas phase? A cluster approach and in situ IR study

In this work, we discussed the vaporization and gas species of ionic liquids (ILs) by a cluster approach of quantum statistical thermodynamics proposed by R. Luwig (Phys. Chem. Chem. Phys., 10, 4333), which is a controversial issue up to date. Based on the different sized clusters (2-12 ion-pairs) of the condensed phase, the molar enthalpies of vaporization (ΔvapH, 298.15 K, 1bar) of four representative ILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][NTf2]) 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([Emmim][NTf2]) 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) and ethylammonium nitrate ([EtAm][NO3]), were calculated. The predicted ΔvapH were increased remarkably; even the values of [EtAm][NO3] were larger than 700 kJ mol(-1) when the charged isolated ions were assumed to be gas species. However, the ΔvapH were close to experimental measurements when the gas species assumed to be anion-cation pairwise, indicating that the different conformational ion-pairs can coexist in the gas phase when the IL is evaporated. Particularly for the protic IL, [EtAm][NO3], even the neutral precursor molecules by proton transfer can occur in gas phase. In addition, it's found that the effect of hydrogen bonds on the vaporization cannot be negligible by comparing the ΔvapH of [Emim][NTf2] with [Emmim][NTf2]. The in situ and calculated IR spectra provided the further proof that the ions are pairwise in gas phase.

Building Blocks for Ionic Liquids: Vapor Pressures and Vaporization Enthalpies of Alkoxy Derivatives of Imidazole and Benzimidazole

The design of physical solvents for applications such as CO2 capture has been an important research area as great emphasis is being placed on reducing greenhouse gas emissions. In gas treating with physical solvents, one of the most important solvent properties needed for efficient process operation is a low vapor pressure (≪100 Pa) at ambient temperature. We have identified alkoxy-functionalized imidazoles and benzimidazoles as candidates that can meet this criterion. Vapor pressures of alkoxy derivates of imidazole and benzimidazole have been determined as a function of temperature by the transpiration method. From these data, the molar enthalpies of vaporization (ΔlgHm) were calculated. The measured data sets were successfully checked for internal consistency by comparison with vaporization enthalpies of the parent species—dimethyl ethers of ethylene glycol, diethylene glycol, and triethylene glycol. We observe that for species with the same number of atoms in the side chain [e.g., 1-butylimidazole and 1-(2-methoxyethyl)-imidazole], replacing every third methylene group with an ether oxygen reduces vapor pressure by 50–75%.

A Review on Prediction Methods for Molar Enthalpies of Vaporization of Hydrocarbons: The ELBA Method as the Best Answer

A review on prediction methods for molar enthalpies of vaporization at T = 298.15 K of hydrocarbons is presented. A new method is proposed and compared with six of the most common used ones from the literature. This new method, the extended Laidler bond additivity (ELBA), was applied to the prediction of standard molar enthalpies of vaporization of hydrocarbons (alkanes, alkenes, alkynes, polyenes, poly-ynes, cycloalkanes, cycloalkenes, benzene compounds, biphenyl compounds, and polyphenyl compounds) at T = 298.15 K. A total of 260 experimental standard molar enthalpies of vaporization at T = 298.15 K were used for the parameters optimization. Comparison between the experimental values and those calculated using ELBA led to an average absolute difference of 0.35 kJ mol−1, corresponding to an average relative error of 0.92%. In addition, this new method proves to be better than the ones used for comparison with an independent set of 83 experimental standard molar enthalpies of vaporization at T = 298.15 K.

Density and Surface Tension of Ionic Liquids [H2N–C2mim][PF6] and [H2N–C3mim][PF6

Two amino functionalized ionic liquids 1-(2-aminoethyl)-3-methylimidazolium hexafluorophosphate, [H2N–C2mim][PF6], and 1-(3-aminopropyl)-3-methylimidazolium hexafluorophosphate, [H2N–C3mim][PF6], were synthesized and characterized. The density and surface tension of these ionic liquids were measured from (293.15 to 343.15) K. Their values decreased with increasing temperature. The physical properties such as coefficient of thermal expansion, molecular volume, standard molar entropy, lattice energy, and molar enthalpy of vaporization were estimated using experimental data. The critical temperature of the ionic liquids was estimated using Eötvos equations. The values were then used to estimate the boiling temperature of the ionic liquids according to methods of Rebelo. The interstice model was used to predict the thermal expansion coefficient of the ionic liquids, α, and the result was in very good agreement with the experimental value. In addition, the parachor method was used to predict the physical properties of the ionic liquids [H2N–Cnmim][PF6] (n = 4, 5, 6).

Vapor Pressures and Vaporization Enthalpy of 2-Ethoxyphenol

The saturated vapor pressures were measured for samples of mole fraction purity of 0.9998 of 2-ethoxyphenol over the temperature range (380.221 to 486.033) K by comparative ebulliometry. Replicate measurements were performed to estimate precision measures for all measured data. The experimental data were correlated by means of the multiresponse maximum likelihood method, and overall measures of data reproducibility are given. The Antoine and the Frost–Kalkwarf-type equations were used. Variance–covariance parameters were reported for the Antoine equation. The calculation of molar enthalpy of vaporization from saturated vapor data is discussed, and values of the calculated molar enthalpy of vaporization are reported. The value of vaporization enthalpy at normal boiling temperature is compared with literature data and corresponding values obtained by predictive methods.

Calorimetric study of 2′-methylacetophenone and 4′-methylacetophenone

Values of the condensed phase standard (p=0.1MPa) molar enthalpy of formation for 2′- and 4′-methylacetophenones were derived from the standard molar energies of combustion, in oxygen, at T=298.15K, measured by static bomb combustion calorimetry. The values of the standard molar enthalpy of vaporization, at T=298.15K, were measured by Calvet microcalorimetry. Combining these two values, the following enthalpies of formation in the gas phase, at T=298.15K, were then derived: 2′-methylacetophenone, –(115.7±2.4)kJ·mol−1, and 4′-methylacetophenone, –(122.6±2.4)kJ·mol−1. Substituent effects are discussed in terms of stability and compared with other similar compounds. The value of the standard molar enthalpy of formation for 3′-methylacetophenone was estimated from isomerization schemes.

Experimental redetermination of the gas-phase enthalpy of formation of ethyl 2-thiophenecarboxylate

The condensed phase standard (p°=0.1MPa) molar enthalpy of formation of ethyl-2-thiophenecarboxylate was derived from the remeasured standard molar energy of combustion, in oxygen, at T=298.15K, by rotating bomb combustion calorimetry and the standard molar enthalpy of vaporization, at T=298.15K, remeasured by Calvet microcalorimetry. Combining these two values, the following enthalpy of formation in the gas phase, at T=298.15K, was then derived for ethyl-2-thiophenecarboxylate: −(277.7±2.9)kJ·mol−1. The calculated gas-phase enthalpy of formation of the title compound, through the G3(MP2)//B3LYP approach was found to be 278.9kJ·mol−1, in excellent agreement with the experimental measured value.

Vapour pressures and enthalpies of vaporization of aliphatic esters

Molar enthalpies of vaporization of n-alkyl formates (with alkyl groups C5–C8), n-alkyl propanoates (with alkyl groups C5–C8) and n-pentyl acetate were obtained from the temperature dependence of the vapour pressure measured by the transpiration method. A large number of the primary experimental results on temperature dependences of vapour pressures have been collected from the literature and have been treated uniformly in order to derive vaporization enthalpies at the reference temperature 298.15K. The available data were successfully checked for internal consistency.

Standard entropy, surface excess entropy, surface enthalpy, molar enthalpy of vaporization, and critical temperature of bis(trifluoromethanesulfonyl)imide-based ionic liquids

The density and surface tension of several bis(trifluoromethanesulfonyl)imide-based ionic liquids (ILs) 1-methyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([MPI][TFSI]), 1,2-dimethyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([DMPI][TFSI]), 1-ethyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([EPeI][TFSI]), and 1-ethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide ([EPrI][TFSI]) were measured at temperatures from 293.15 to 353.15K and atmospheric pressure. The values of thermal expansion coefficient and surface excess entropy were estimated by extrapolation. In terms of Glasser's semiempirical relation of ILs, the standard molar entropy and the lattice energy of ILs were estimated. Using Kabo's and Sugden's methods, the molar enthalpy values of vaporization of the IL, Δ1gHm°(298 K), and Parachor were estimated. The thermal expansion coefficients of the bis(trifluoromethanesulfonyl)imide-based hydrophobic ILs were estimated by the interstice model and they are in good agreement with experimental values. This indicated that the interstice model is reasonable and may be applied to estimate the coefficient of thermal expansion of ionic liquids.

Experimental and computational thermochemistry of 6,7-dihydro-4(5H)-benzofuranone

The standard (p=0.1MPa) molar enthalpy of formation of 6,7-dihydro-4(5H)-benzofuranone was measured, at T=298.15K, by static bomb calorimetry and the standard molar enthalpy of vaporization, at T=298.15K, was obtained using Calvet microcalorimetry. These values were combined together to derive the standard molar enthalpy of formation of the title compound in gaseous phase, at T=298.15K, −(226.0±2.8)kJ·mol−1. [Display omitted] Additionally, density functional theoretical calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets and also other higher-level ab initio quantum calculations have been performed.

Study on Thermodynamic Properties of Ionic Liquid N-Butyl-3-methylpyridinium Bis(trifluoromethylsulfonyl)imide

An air- and water-stable hydrophobic ionic liquid N-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide ([c43mpy][NTf2]) was synthesized and characterized. Density, surface tension, dynamic viscosity, and electrical conductivity of the IL were measured and calculated from (278.15 to 353.15) K. The glass transition temperature and decomposition temperature were determined by the differential scanning calorimetry and thermogravimatric analysis. The physicochemical properties like molecular volume, standard molar entropy, lattice energy, parachor, molar enthalpy of vaporization, interstice volume, thermal expansion coefficient, interstice fraction, etc. of the IL were estimated by the reported empirical and semiempirical equations. The dynamic viscosity and electrical conductivity data of the IL were described by Vogel–Fulcher–Tamman and Arrhenius equations, respectively. Then, the relationship between the molar conductivity and dynamic viscosity of this IL was expressed through the Walden rule.

Density, Surface Tension, and Refractive Index of Ionic Liquids Homologue of 1-Alkyl-3-methylimidazolium Tetrafluoroborate [Cnmim][BF4] (n = 2,3,4,5,6)

The values of density, surface tension, and refractive index were measured for a classic series of air and water stable ionic liquids (ILs) based on tetrafluoroborate, [Cnmim][BF4](n = 2,3,4,5,6)(1-alkyl-3-methylimidazolium tetrafluoroborate) in the temperature range of (298.15 to 338.15 ± 0.02) K. In terms of Glasser’s theory, the standard molar entropy and lattice energy of the ILs were calculated. Using Kabo’s method, the molar enthalpy of vaporization of the IL, ΔlgHm0 (298 K), was estimated. According to the interstice model, the thermal expansion coefficient of ILs [Cnmim][BF4] (n = 2,3,4,5,6), α, were calculated, and in comparison with experimental value, their magnitude order is in good agreement. To test this new concept of ionic parachor, [BF4]− was chosen as a reference ion and its individual value of ionic parachor was determined in terms of extrathermodynamic assumption. Then, using ionic parachor of [BF4]−, the ionic parachors for all corresponding imidazolium cations, [Cnmim]+, were calcula...

Building Blocks for Ionic Liquids: Vapor Pressures and Vaporization Enthalpies of 1-(n-Alkyl)-benzimidazoles

Vapor pressures of 1-(n-alkyl)-benzimidazoles with chain lengths from methyl to pentyl (C1–C5) have been determined as a function of temperature by the transpiration method. From these data, the molar enthalpies of vaporization (Δ1gHm) were calculated, and a linear correlation with the number of carbon atoms was found. At a given temperature, 1-n-alkylbenzimidazole vapor pressures were found to decrease with the increasing length of alkyl chain, and the fused ring system was found to lower vapor pressures and increase heats of vaporization relative to the corresponding 1-n-alkylimidazoles.

Energetic Study Applied to the Knowledge of the Structural and Electronic Properties of Monofluorobenzonitriles

The present work reports an energetic and structural study of 2-fluoro-, 3-fluoro-, and 4-fluorobenzonitrile. The standard molar enthalpies of formation, in the condensed phase, of the three isomers were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K. The standard molar enthalpies of vaporization or sublimation (for 4-fluorobenzonitrile), at T = 298.15 K, were measured using high-temperature Calvet microcalorimetry. The combination of these two parameters yields the standard molar enthalpies of formation in the gaseous phase. The vapor-pressure study of the referred compounds was performed by a static method, and the enthalpies of phase transition derived from the application of the Clarke and Glew equation. Theoretically estimated gas-phase enthalpies of formation, basicities, proton and electron affinities, and adiabatic ionization enthalpies were calculated from the G3MP2B3 level of theory. In order to evaluate the electronic properties, the geometries were reoptimized at MP2/cc-pVTZ level, and the QTAIM and NICS were computed. On the basis of the donor-acceptor system, another approach for evaluating the electronic effect for these compounds, using the NBO is suggested. The UV-vis spectroscopy study for the three isomers was performed. The intensities and the band positions were correlated with the thermodynamic properties calculated computationally.

Express thermo-gravimetric method for the vaporization enthalpies appraisal for very low volatile molecular and ionic compounds

An express method for the determination of vaporization enthalpies of extremely low volatile molecular and ionic liquids has been developed using a commercially available TGA. All experimental parameters (mass loss rate, temperature range, and purge gas flow) crucial for reliable measurements were carefully studied using the reference molecular compounds (n-hexadecane, di-butyl phthalate, methyl and ethyl stearate) with the reliable data. Optimal experimental conditions were recommended. Molar vaporization enthalpies of the low volatile reference molecular compounds were reproduced under optimal conditions better than 2kJmol−1. Test measurements with the extremely low volatile ionic liquid [C2mim][NTf2] have revealed an agreement with the reliable data already available in the literature within ±3kJmol−1. The experimental conditions recommended in this work allow a quick appraisal of vaporization enthalpies of very low volatile materials within 8h at a reasonable level of accuracy.

Prediction of Physicochemical Properties of Valine Ionic Liquids [Cnmim][Val] (n = 2, 3, 4, 5, 6) by Empirical Methods: 2

A new ionic liquid [C3mim][Val] (1-propyl-3-methylimidazolium valine) was synthesized and characterized by 1H NMR. To avoid the influence of trace water in the ionic liquid (IL), the standard addition method (SAM) was employed; the density and surface tension of the [C3mim][Val] were determined over the temperature range of 303.15–333.15 K (±0.05 K). The experimental density, surface tension, and parachor values at 298.15 K are in good agreement with that predicted by Tong et al. [J. Tong et al., Ind. Eng. Chem. Res.2011, 50, 2418–2423]. Based on the experimental data for [C3mim][Val], a series of physicochemical properties—the molecular volume (Vm), surface tension (γ), refractive index (nD), molar enthalpy of vaporization (ΔlgHm0), the thermal expansion coefficient (α) values, the standard molar entropy (S0), and the molar polarization (Rm)—for the homologue of [Cnmim][Val] (n = 2, 4, 5, 6) were estimated using the empirical methods. The estimated results are consistent with one of Tong’s estimations, in terms of the experimental data for [C2mim][Val].

Waring and Riedel Functions for the Liquid–Vapor Coexistence Curve

There exists a minimum in the Waring function, psi(T) = -d(ln p)/d(1/T), and in the Riedel function, alpha(T) = d(ln p)/d(In T), in the liquid-vapor coexistence curve for most fluids. By analyzing National Institute of Standards and Technology data for the molar enthalpy of vaporization and the compressibility variation at the liquid-vapor phase change of 105 fluids, we find that the temperatures of these minima are linearly correlated with the critical temperature, T-c. Using reduced coordinates, we also demonstrate that the minima are well-correlated with the acentric factor. These correlations are used for testing four well-known vapor pressure equations in the Pitzer corresponding states scheme.

Vapor–Liquid Equilibria of Glycerol, 1,3-Propanediol, Glycerol + Water, and Glycerol + 1,3-Propanediol

Vapor–liquid equilibria of two compounds, glycerol (or 1,2,3-propanetriol) and 1,3-propanediol, and two mixtures, glycerol + water and glycerol + 1,3-propanediol, were determined using a static apparatus. The obtained pressure values range from 6 Pa to 45 kPa for the compounds and from (32 to 163) kPa for the mixtures. From the temperature dependence of the vapor pressures, the molar enthalpies of vaporization at the mean temperature of the experimental range were derived from the Clausius–Clapeyron equation. From these results the standard enthalpies of vaporization at T = 298.15 K were calculated. The experimental data of the mixtures were correlated using the nonrandom two-liquid (NRTL) model.

Thermochemistry of some methoxypyridines

The standard (po=0.1MPa) molar enthalpies of formation, at T=298.15K, for the liquids 2-methoxypyridine, 4-methoxypyridine and 2,6-dimethoxypyridine were determined by static bomb combustion calorimetry. The standard molar enthalpies of vaporization, at T=298.15K, were measured by Calvet microcalorimetry. The standard (po=0.1MPa) molar enthalpies of formation of the three compounds studied, in the gaseous phase, at T=298.15K have been derived from the corresponding standard molar enthalpies of formation in the liquid phase and the standard molar enthalpies of vaporization, yielding ((−42.7±1.9), (−18.2±1.8) and (−233.5±1.8))kJ·mol−1, for 2-methoxypyridine, 4-methoxypyridine and 2,6-dimethoxypyridine, respectively.

Estimation of Physicochemical Properties of 1-ethyl-3-methylimidazolium Thiocyanate Ionic Liquid Using Density and Surface Tension

The density and surface tension of the ionic liquid (IL) [C2mim][SCN] (1-ethyl-3-methylimidazolium thiocyanate) were measured in a temperature range from (298.15 to 338.15) K. In terms of Glasser's semiempirical relation theory of ILs, the standard molar entropy and lattice energy of the homologous series of ILs [Cnmim][SCN] of the IL were estimated at 298 K, respectively. Using Kabo's method and Rebelo's method, the molar enthalpy of vaporization of the IL, H(298), at 298 K and, H(Tb), at hypothetical normal boiling point was estimated, respectively. According to the interstice model, the thermal expansion coefficient of the IL was calculated and in comparison with experimental value, it is in good agreement.In terms of semiempirical method, physicochemical properties molecular volume Vm, parachor P, surface tension r, thermal expansion coefficients a, of the homologue of [Cnmim][SCN] (n = 3, 4) were predicted.