Excess Molar Enthalpies Research Articles

A combined experimental and computational investigation of excess molar enthalpies of (nitrobenzene + alkanol) mixtures

Excess molar enthalpies (HmE) for the binary mixtures of {(nitrobenzene+ethanol), 1-propanol, 2-propanol, 1-butanol and 2-butanol} have been measured over the entire composition range at ambient pressure (81.5kPa) and temperature 298K 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. The excess molar enthalpies (HmE) are positive for all {nitrobenzene (1)+alkanol (2)} mixtures over the entire composition range.A state-of-the-art computational strategy for the evaluation of excess partial molar enthalpies at infinite dilution was followed at the M05-2X/6-311++G∗∗ level of theory with the PCM model. The experimental excess partial molar enthalpies at infinite dilution have been compared to the computational data of the ab initio in liquid phase. Integrated experimental and computational results help to clarify the nature of the intermolecular interactions in {nitrobenzene (1)+alkanol (2)} mixtures. The experimental and computational work which was done in this study complements and extends the general research on the computation of excess partial molar enthalpy at infinite dilution of binary mixtures.

Modeling of thermodynamic properties of an oxygenate + aromatic hydrocarbon: Excess molar enthalpy

Excess molar enthalpy (HmE) have been measured at 303.15K for 1-propanol+benzene or toluene or o- or m- or p-xylene mixtures using flow micro calorimeter. The HmE versus x1 plots are skewed toward y-axis showing maxima at x1≈0.3. At (x1=0.5) HmE vary in the order: toluene<benzene<m-xylene<p-xylene∼o-xylene. The excess volume data have also been interpreted in terms of Graph-theoretical approach and Prigogine–Flory–Patterson theory. It has been observed that while PFP theory fails to predict the HmE values for these systems in the composition range x1<0.5, agreement with experimental values is reasonably good thereafter. The HmE values calculated by Graph theory compared well with the corresponding experimental values.

Excess molar enthalpies for binary mixtures of n-propanol, acetic acid, and n-propyl acetate at 313.15 K and atmospheric pressure

Excess molar enthalpies, HE, for the binary mixtures of acetic acid (AcOH)+n-propanol (n-PrOH), acetic acid (AcOH)+n-propyl acetate (n-PrOAc), and n-propanol (n-PrOH)+n-propyl acetate (n-PrOAc) have been measured at 313.15K and atmospheric pressure using the Setaram C80 calorimeter. The experimental results are presented and correlated with the Redlich–Kister polynomial equation and its modified version. Modeling of the excess enthalpies has been performed using the UNIFAC and NRTL models.

Oxygenated Compounds + Hydrocarbon Mixtures in Fuels and Biofuels: Excess Enthalpies of Ternary Mixtures Containing 1-Butoxybutane + Propan-1-ol +1-Hex-1-ene, or Heptane, or 2,2,4-Trimethylpentane at (298.15 and 313.15) K

New experimental excess molar enthalpy data (376 points) of the ternary systems 1-butoxybutane + propan-1-ol +1-hex-1-ene, or heptane, or 2,2,4-trimethylpentane and the corresponding binary systems at (298.15 and 313.15) K at atmospheric pressure are reported. A quasi-isothermal flow calorimeter has been used to make the measurements. All of the binary and ternary systems show endothermic character at both temperatures. The experimental data for the binary systems have been fitted using the rational equations.

Thermodynamic investigations of 1-ethyl-3-methylimidazolium tetrafluoroborate and cycloalkanone mixtures

The densities, ρ, speeds of sound, u, and heat capacities, (CP)mix, for binary 1-ethyl-3-methylimidazolium tetrafluoroborate (1) + cyclopentanone or cyclohexanone (2) mixtures within temperature range (293.15–308.15 K) and excess molar enthalpies, HE, at 298.15 K have been measured over the entire composition range. The excess molar volumes, VE, excess isentropic compressibilities, \( \kappa_{\text{S}}^{\text{E}}, \) and excess heat capacities, \( C_{\text{P}}^{\text{E}}, \) have been computed from the experimental results. The VE, \( \kappa_{\text{S}}^{\text{E}} \), HE, and \( C_{\text{P}}^{\text{E}} \) values have been calculated and compared with calculated values from Graph theory. It has been observed that VE, \( \kappa_{\text{S}}^{\text{E}} \), HE, and \( C_{\text{P}}^{\text{E}} \) values were predicted by Graph theory compare well with their experimental values. The VE, \( \kappa_{\text{S}}^{\text{E}}, \) and HE thermodynamic properties have also been analyzed in terms of Prigogine–Flory–Patterson theory.

Pressure dependence of excess enthalpy for (benzene + cyclohexane) mixture near the critical locus at T = (558.2, 563.2 and 573.2) K and p = (3 to 15) MPa

The pressure dependences of excess molar enthalpies HmE of the (benzene+cyclohexane) mixture at constant temperatures and compositions were measured near the critical locus, using a twin flow type mixing calorimeter. The measurement states are as follows; temperature T=(558.2, 563.2, and 573.2)K, mole fraction of benzene x=(0.119 to 0.916), and pressure range p=(3 to 15)MPa. The composition dependences of HmE at constant pressures and at each temperature were calculated from the pressure dependences of HmE. All pressure dependences of HmE have two peaks except at x=0.916. The pressure dependences at x=0.916 have one peak, and the curve at T=573.2K has a shoulder near p=5MPa. From the detailed consideration with respect to the phase behaviour near the critical locus for this mixture, two peaks should exist in the pressure dependences of HmE at T=558.2K and x=0.916, but the second peak cannot be detected because the peak width is too narrow. The composition dependences of HmE near the critical locus were skewed or S-shaped ones, which are ascribed as the characteristic behaviour in the vicinity of the critical locus.

Framework for correlating the effect of temperature on nonelectrolyte and ionic liquid activity coefficients

A power‐law expression is proposed for correlating the temperature dependence of infinite‐dilution activity coefficients ( ) for nonelectrolyte solute–solvent binary pairs and for pairs including an ionic liquid: , where θij = 0 for Lewis–Randall ideal solutions, θij = 1 for classic enthalpy‐based Scatchard–Hildebrand regular solution and van Laar models, and −5 &lt; θij &lt; 5 for most real binaries. The exponent θij is a function of partial molar excess enthalpy ( ) and entropy ( ) such that . Real binaries are classified into seven types corresponding to distinct domains of and θij. The new method provides a framework for correlating phase‐equilibrium driven temperature effects for a wide variety of chemical and environmental applications. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3675–3690, 2014

Excess enthalpy for the (benzene + cyclohexane) mixture over a wide range of temperature and pressure

A twin flow type of mixing calorimeter was constructed for measuring excess enthalpies of fluid mixtures over wide temperature and pressure ranges. The precision of the calorimeter was tested with (water+ethanol) mixture. The excess molar enthalpies HmE for the (water+ethanol) mixture at temperatures T=(423.2 and 523.2)K and pressure p=5.00MPa and at T=523.2K and p=15.00MPa are in good agreement with the literature values. The HmE values for the (benzene+cyclohexane) mixture were measured using this calorimeter over the temperature range from T=298.2K to T=573.2K and the pressure range from p=5.00MPa to p=25.00MPa. All HmE values are positive and all mole fraction dependencies of HmE are almost symmetrically parabolic. The maximum values of the mole fraction dependence of HmE decrease with increasing temperature and are independent of the pressure, except for the conditions at T=(498.2 and 523.2)K and p=5.00MPa whose states are near the critical point of benzene. The maximum values of HmE of these states were greater than the values expected from the curve representing the temperature dependence of other maximum values of the mole fraction dependence of HmE.

Measurement and Correlation of Excess Molar Enthalpy of Binary Mixtures Containing Butyl Acetate + 1-Alkanols (C1–C6) at 298.15 K

Excess molar enthalpies, ∆H m E , for the binary mixtures of butyl acetate + 1-alkanols, namely (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol), were measured over the whole range of composition at 298.15 K using a Parr 1455 solution calorimeter. The excess partial molar enthalpies, ∆H m, E , were calculated from the experimental excess molar enthalpies using the Redlich–Kister polynomial equation. The sign of ∆H m E for all systems are positive because of the disruption of hydrogen bonding and dipole–dipole interactions in the alkanols and esters, respectively. The magnitude of the ∆H m E values increases with increasing alkyl chain length. The behavior of ∆H m E was analyzed in terms of the length of the alkanol chain, the nature and type of intermolecular interactions and the balance between positive and negative effects on deviations from ideality. The experimental excess molar enthalpy data have also been correlated using the Redlich–Kister and SSF equations and two local composition models (UNIQUAC and NRTL).

Temperature dependence of limiting activity coefficients, Henry's law constants, and related infinite dilution properties of C4–C6 isomeric n-alkyl ethanoates/ethyl n-alkanoates in water. Measurement, critical compilation, correlation, and recommended data

Infinite dilution activity coefficients (γ1∞) of C4–C6 isomeric n-alkyl ethanoates/ethyl alkanoates, namely ethyl ethanoate, propyl ethanoate, ethyl propanoate, butyl ethanoate, ethyl butanoate in water were measured at several temperatures in the range from (273 to 361)K. Most measurements were carried out by the inert gas stripping method, although other three headspace gas chromatography techniques were also employed. A comprehensive critical review is further presented of literature data on γ1∞, infinite dilution partial molar excess enthalpies (H¯1E,∞) and heat capacities (C¯p,1E,∞) of these aqueous solutes. For each ester, the data measured in this work together with those reported previously in the literature were correlated with a suitable model equation providing adequate simultaneous description of the equilibrium measurements and the calorimetric information. As a result, a recommended temperature dependence of γ1∞ of superior accuracy was established. The consistency of recommended γ1∞(T) with literature data on mutual solubilities of esters and water was also demonstrated. Analogous recommendations were derived also for the temperature dependence of Henry's law constants (KH). The variation with temperature and ester molecular structure of γ1∞, KH, and related energetic functions of ester dissolution and hydration was overviewed and briefly discussed. Furthermore, the performance of five predictive approaches to estimate γ1∞(T) of the aqueous esters was tested.

Thermodynamics and activity coefficients at infinite dilution for organic solutes, water and diols in the ionic liquid choline bis(trifluoromethylsulfonyl)imide

The activity coefficients at infinite dilution, γ13∞, for 63 solutes, including alkanes, cycloalkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, water, thiophene, ethers, ketones, esters, aldehyde, acetonitrile, pyridine and 1-nitropropane and 6 diols in the ionic liquid (IL) choline bis(trifluoromethylsulfonyl)imide, [N1112OH][NTf2] were determined by (gas+liquid) chromatography at six temperatures in range of (318.15 to 368.15)K and at three temperatures for diols in the range of (388.15 to 418.15)K. The thermodynamic functions at infinite dilution as partial molar excess Gibbs free energy, ΔG1E,∞, enthalpy ΔH1E,∞, and entropy term TrefΔS1E,∞ were calculated from the experimental γ13∞ values obtained over the temperature range. The density of [N1112OH][NTf2] was measured within temperature range (313.15 to 353.15)K. The (gas+liquid) partition coefficient KL was calculated for all solutes. The values of selectivity and capacity for a few separation problems as hexane/benzene, cyclohexane/benzene, heptane/thiophene at T=328.15K were calculated from γ13∞ and compared to literature values for similar ionic liquids, N-methyl-2-pyrrolidinone (NMP), and sulfolane. In comparison with the former measured ammonium-based ILs and the morpholinium-based ILs, the [N1112OH][NTf2] shows average selectivity for the separation of aromatic hydrocarbons, or sulfur compound from aliphatic hydrocarbons, and very high selectivity for pyridine/heptane separation. New data show that [N1112OH][NTf2] IL may be proposed as an alternative solvent for the separation of sulfur or nitrogen compounds from alkanes.

Activity coefficients at infinite dilution of organic solutes in the ionic liquid 1-butyl-3-methylimidazolium methyl sulfate

Activity coefficients at infinite dilution (γi∞) and (gas+liquid) partition coefficients (KL) for organic solutes: alkanes, alkenes, alkyl benzenes, acetonitrile, acetone, tetrahydrofuran, ethyl acetate, and chloromethanes in the ionic liquid (IL) 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][CH3SO4]) have been measured by the (gas+liquid) chromatographic method in the temperature range of (313.15 to 363.15)K. The values of the partial molar excess enthalpies at infinite dilution (H‾iE,∞) were derived from the temperature dependence of the γi∞ values. The entropies (TrefS‾iE,∞) and Gibbs free energies (G‾iE,∞) of organic solutes in [BMIM][CH3SO4] at a reference temperature Tref=298.15K were also calculated from the γi∞ values. The solubility parameters of the IL [BMIM][CH3SO4] were also determined by the regular solution theory (RST). The linear free energy relationship (LFER) analysis of the results was performed to disclose molecular interactions operating between the IL and the individual solutes.

Excess enthalpies for pseudobinary mixtures containing vegetable oils at the temperatures 298.15 K, 353.15 K and 383.15 K

This paper presents excess enthalpies for the following systems containing refined vegetable oils: soybean oil+methanol (at 353.15K/722kPa), soybean oil+ethanol (at 353.15K/687kPa and 383.15K/653kPa), soybean oil+n-hexane (at 353.15K/722kPa and 383.15K/756kPa), soybean oil+propan-2-ol (at 298.15K/998kPa), sunflower oil+methanol (at 353.15K/791kPa), sunflower oil+ethanol (at 353.15K/894kPa and 383.15K/860kPa), sunflower oil+n-hexane (at 353.15K/756kPa and 383.15K/894kPa), sunflower oil+propan-2-ol (at 298.15K/929kPa), rapeseed oil+methanol (at 353.15K/963kPa), rapeseed oil+ethanol (at 353.15K/998kPa and 383.15K/1136kPa), and rapeseed oil+n-hexane (at 353.15K/894kPa and 383.15K/1136kPa). The measurements were carried out with a commercially available isothermal flow calorimeter. The experimental HE values have been correlated using the Redlich-Kister polynomial equation. The results for systems with propan-2-ol and some values of partial molar excess enthalpies at infinite dilution, HiE,∞, obtained in this study have been compared to those available in the literature. The results were also discussed in terms of molecular interactions.

Solubilities of 4-(Hydroxymethyl)-1-oxido-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane in Organic Solvents

A phosphorus flame retardant of 4-(hydroxymethyl)-1-oxido-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane (PEPA) was synthesized by pentaerythritol and phosphorus oxychloride at a certain condition. The structural features of PEPA were investigated with Fourier transform infrared spectroscopy and 1H NMR methods. The thermal behavior of PEPA was carried out with differential scanning calorimetry and thermogravimetric analysis instruments. A static analytic method was used to measure the solubilities of the PEPA in several organic solvents. The measurements were accurately acted in ethyl acetate, acetonitrile, isopropyl alcohol, ethanol, n-propyl alcohol, acetone, methanol, and chloroform at the temperature range from 292.75 K to 333.45 K. Using the Scatchard–Hildebrand methodology, the activity coefficients of the solute have been calculated, and the partial molar excess enthalpies at infinite dilution were also predicted.

Experimental Measurements and Correlations of Excess Molar Enthalpies for the Binary and Ternary Mixtures of (Cyclohexane, 1,4-Dioxane and Piperidine) or (Cyclohexane, Morpholine and Piperidine) at 308.15 K and Atmospheric Pressure

Excess molar enthalpies for the binary and ternary mixtures of (cyclohexane, 1,4-dioxane, and piperidine) and (cyclohexane, morpholine, and piperidine) were measured using a Calvet microcalorimeter at 308.15 K and atmospheric pressure. The empirical equations of Redlich–Kister and Cibulka were used to correlate the experimental excess molar enthalpies for the binary and ternary mixtures, respectively. The capability of artificial neural network algorithm to model these data is also studied.

Isothermal vapour pressures and thermodynamic excess properties of 3,5- and 2,6-dimethylpyridine with cyclohexane. Measurements and prediction

The vapour pressures of liquid mixtures 3,5- and 2,6-dimethylpyridine (or lutidines) with cyclohexane were measured by a static method in the range of 283.15–353.15K. The pure components vapour pressures data and those of corresponding mixtures were correlated using Antoine type equation. Data reduction by Barker's method provides correlation for excess molar Gibbs energy GE.The excess molar enthalpies HE of binary liquid mixtures of 3,5- and 2,6-dimethylpyridine with cyclohexane were measured at 303.15K using a Calvet type microcalorimeter, C80 Setaram.The experimental results, along with our previous data of GE and HE[1,2] are used for estimating interaction parameters in DISQUAC, an extended quasi-chemical group contribution model [3].

Isothermal vapor–liquid equilibrium and excess molar enthalpies of the binary mixtures furfural + methyl isobutyl ketone, +2-butanol and +2-methyl-2-butanol

Isothermal vapor–liquid equilibria (VLE) of the binary mixture of furfural+methyl isobutyl ketone (MIBK), furfural+2-butanol and furfural+2-methyl-2-butanol were measured at 333, 346 and 353K with three equipment: a static total pressure apparatus, a recirculation still apparatus and a gas chromatograph connected to a headspace sampler (HS–GC). Excess molar enthalpy (hE) was measured for the three binary mixtures at 298.15K by using a SETARAM C80 calorimeter equipped with a flow mixing cell. Gas chromatography–mass spectrometry was employed for the analysis of furfural impurities. A comprehensive consistency analysis was performed for the obtained data. The experimental data were correlated with the NRTL, UNIQUAC and Wilson activity coefficient models. The results were compared with the UNIFAC-Dortmund and COSMO-RS predictive models. All investigated mixtures show positive deviation from Raoult's law.

Elucidation of Ionic Interactions in the Protic Ionic Liquid Solutions by Isothermal Titration Calorimetry

The strong hydrogen-bonded network noted in protic ionic liquids (PILs) may lead to stronger interactions of the ionic entities of PILs with solvents (water, methanol, ethylene glycol, dimethylsulfoxide (DMSO), N,N'-dimethylformamide (DMF)) as compared with those of aprotic ionic liquids (APILs). The PILs used in this work are 1-methylimidazolium tetrafluoroborate, 2-methylpyridinium tetrafluoroborate, and N-methylpyrrolodinium tetrafluoroborate in comparison to 1-butyl-3-methylimidazolium tetrafluoroborate, which is classified as an APIL. In this work, the excess partial molar enthalpy, H(E)IL obtained from isothermal calorimetric titrations at 298.15 K is used to probe the nature of interactions of the PIL cations with solvent molecules against those present in APIL-solvent systems. This work also reports interesting flip-flopping in the thermal behavior of these PIL-solvent systems depending upon the structure of the cationic ring of a PIL. In some cases, these flip-flops are the specific fingerprints for specific PILs in a common solvent environment. The excess partial molar enthalpy at infinite dilution, H(E,∞)IL, of these PILs bears a critical dependence on the solvent properties. An analysis of relative apparent molar enthalpies, ϕL, of the PIL solutions by the ion interaction model of Pitzer yields important information on ionic interactions of these systems.

Experimental study on the calorimetric data of butylacetate with pentanol isomers as important biofuels and correlation treatment at T = 298.15 K

Excess molar enthalpies, , of binary mixtures of butylacetate (common component) + pentanol isomers as important biofuels, namely 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol and 3-methyl-2-butanol, were measured over the whole range of the composition at T = 298.15 K and ambient pressure using a Parr 1455 solution calorimeter. The excess partial molar enthalpies, , were calculated according to experimental excess molar enthalpies and the Redlich–Kister polynomial equation. The extracted data were used to evaluated the so-called intermolecular interaction functions, and . The sign of for all systems are positive and show endothermic behaviour over the entire range of compositions. The values become more positive with the increasing of the branches and steric factors. The experimental excess molar enthalpy data have been also correlated using the Redlich–Kister and SSF equations and two thermodynamic models (Wilson and NRTL). The experimental data have been qualitatively discussed and interpreted on the basis of the polarity, size and shape of alkanols.

Excess molar enthalpies for binary mixtures of cyclopentanone, cyclohexanone, or cycloheptanone with n-nonane at T = 298.15 K and atmospheric pressure

Excess molar enthalpies, HE, for the binary mixtures of cyclopentanone, cyclohexanone, or cycloheptanone with n-nonane were measured at T=298.15K and 0.1MPa, by means of a Setaram Tian-Calvet MS80 microcalorimeter. All the binary systems investigated show endothermic behaviour (positive values) over the whole mole fraction range. The molar excess enthalpies decrease as the size of the cycloalkanone increases. The experimental results of HE are fitted to the Redlich–Kister equation to correlate the composition dependence. The experimental HE data are also used to test the suitability of the Wilson, NRTL, and UNIQUAC models. The correlation of excess enthalpy data in these binary systems using the UNIQUAC model provides relatively the most appropriate results.