Excess Molar Enthalpies Research Articles

Excess molar enthalpy measurement and modelling of (oxygenated compounds + hydrocarbon) mixtures: Binary and ternary mixtures containing 2-(2-methoxyethoxy)ethanol, 1-hexene and cyclohexane at (298.15 and 313.15) K

NEW measurements and modelling data of excess molar enthalpy HE at atmospheric pressure and temperatures of (298.15 and 313.15) K using a quasi-isothermal flow calorimeter are presented in this work for the ternary system diethylene glycol monomethyl ether glycol (2-(2-methoxyethoxy)ethanol) + 1-hexene + cyclohexane and the corresponding binary systems over the whole composition range. All the binary and ternary systems present an endothermic behaviour at the chosen temperatures. The experimental data of the binary and ternary systems were correlated using the modified Redlich-Kister equation, NRTL and UNIQUAC models.

Infinite dilution activity coefficients and thermodynamic properties of selected organic solutes and water dissolved in 1, 6-hexanediol

The experimental activity coefficients (γ13∞) and gas-to-liquid partition coefficients (KL) at infinite dilution for 34 organic solutes and water were determined in 1.6-hexanediol (HDO) by the gas–liquid chromatography technique (GLC) in the temperature range from (323.15 to 353.15) K. Fundamental thermodynamic functions such as excess partial molar enthalpy (ΔHiE,(∞)), excess partial molar Gibbs energy, (ΔGiE,∞) and entropy, (TrefΔSiE,∞) at infinite dilution were calculated from experimental values of γ13∞. Reported data were discussed in terms of solvent-solute interactions, heat effects and mixing spontaneity. Selectivity (Sij∞) and capacity (kj∞) related to different separation problems were calculated from γ13∞ data and compared to the literature values for selected ionic liquids (ILs), deep eutectic solvents (DESs) and industrial solvents. New data reported in this study suggest that HDO may be proposed as an alternative solvent for the separation of alkanes-pyridine and alkanes-thiophene systems. Furthermore, it was found that adding a hydrogen bond acceptor to HDO enhances its performance as a separation solvent.

Application of dicyanamide-based ionic liquid in separation of binary mixtures based on gamma infinity data measurements

In this research, the activity coefficients (γ13∞) at infinite dilution of 61 solutes were experimentally determined in the 1-(4-methoxy-4-oxobutyl)-3-methylimidazolium dicyanamide, [(C3COOMe)MIM][DCA]. The data were obtained using the gas-liquid chromatography technique (GLC). The experiment was carried out at a wide temperature range of (318.15 to 368.15) K, in 10 K intervals. The studied solutes included polar and non-polar compounds, as alkanes, alkenes, and alkynes, as well as aromatic hydrocarbons, alcohols, water, ethers, ketones, acetonitrile, pyridine, 1-nitropropane, thiophene, and esters. Density, ρ, measurements for a range of temperatures (298.15–368.15) K, in 10 K intervals, for the chosen ionic liquid (IL) were undertaken at pressure, p = 101 kPa. Values of the gas-liquid partition coefficients, KL at infinite dilution, as well as the basic thermodynamic functions, such as partial molar excess Gibbs energy, enthalpy and entropy at infinite dilution were calculated from the experimental data measurements. The values of selectivity and capacity for the three chosen separation problems as heptane/thiophene, heptane/pyridine and heptane/1-nitropropane were calculated from γ13∞ values and compared to literature data for dicyanamide-based, ILs. The results from the study indicate that [(C3COOMe)MIM][DCA] has attractive capacity for all of the studied separation cases. These measurements allow to verify the possibility of use of investigated ionic liquid as an entrainer in liquid-liquid extraction.

Experimental data and modeling for excess enthalpies of 2-Pentanol with n-alkanes (C7–C9) at T = (293.15, 298.15 and 303.15) K

Excess molar enthalpies, HE, for the binary mixtures of 2-pentanol with n-alkanes(n-heptane, n-octane, and n-nonane) have been determined at three different temperatures T = (293.15, 298.15 and 303.15) K and normal atmospheric pressure over the entire composition range using a Calvet microcalorimeter. All mixtures show endothermic mixing with the maximum values of the excess enthalpies occurring in the n-alkane-rich region. The HE data are smoothed using Redlich–Kister equation. The applicability of the Treszczanowicz–Benson, ERAS,Renon–Prausnitz and Chen–Bagley models to correlate HE of studied mixtures is tested, and the agreement between experimental and theoretical results is satisfactory. Each model includes a self-association equilibrium constant that represents hydrogen bonding and an adjustable parameter that reflects physical interactions.

Thermodynamics of amine mixtures. Systems formed by alkyl-amine and ether, or N,N-dialkylamide, or ethanenitrile

Abstract Systems of the type linear primary or secondary amine + cyclohexane, or + polar compound (namely, linear or cyclic monoether, + 1,4-dioxane, + N,N-dialkylamide, or + ethanitrile) have been investigated using literature data, and by means of DISQUAC. Interaction parameters for the contacts amine/ether, amine/amide and amine/nitrile are provided. For a given contact, the QUAC interchange coefficients remain practically constant along each homologous series. A similar trend has been encountered in other many previous studies. DISQUAC correctly describes excess molar enthalpies, H m E , and vapour-liquid and solid-liquid equilibria of the studied mixtures and improves calculations on H m E from the UNIFAC (Dortmund) model. The experimental data have been used to determine the enthalpy of the interactions between unlike molecules, which are stronger in systems with N,N-dialkylamides or ethanenitrile than in mixtures with ethers. On the other hand, it is shown that H m E values of amine + C6H12 mixtures are closely related to the amine self-association, and that interactions between molecules of the polar compounds are determinant on H m E results of the mixtures amine + fixed polar compound or of the systems fixed amine + polar compound (no linear monoether). Structural effects are relevant in the di-n-butylamine + linear ether systems. The application of the Flory model reveals that orientational effects are rather weak in the investigated solutions. This is in agreement with previous studies on this type of mixtures using the ERAS model.

Thermodynamics and selectivity of separation based on activity coefficients at infinite dilution of various solutes in ionic liquid [DMIM][Tf2N

The activity coefficients at infinite dilution (γi∞) is an important thermodynamic parameter for ionic liquids. By analyzing and calculating them, the possibility of ionic liquids as extractants can be estimated. The infinite dilution activity coefficients of 32 kinds of organic solutes (eg. alkyl benzenes, acetonitrile, tetrahydrofuran, n-alkanes, ethyl acetate, etc.) in ionic liquid 1-decyl-3-methylimidazole bis (trifluoromethylsulfonyl)imide [DMIM][Tf2N] were measured by gas chromatography (GLC) at six temperatures: 313.15 K, 323.15 K, 333.15 K, 343.15 K, 353.15 K, 363.15 K. Calculated some basic thermodynamic parameters such as the partial molar excess enthalpies at infinite dilution (H-iE,∞) , Gibbs free energies (G-iE,∞) and entropies (TrefS-iE,∞) were calculated at a reference temperature Tref = 298.15 K. At 323.15 K, the selectivity (Sij∞) of n-hexane (i)/benzene (j), cyclohexane/benzene, and capacity factor (kj∞) at infinite dilution of benzene have been determined. The results were analyzed in comparison to literature data for alkylimidazolium ionic liquids with [Tf2N]−.

The influence of the ionic liquids functionalization on interaction in binary systems with organic solutes and water – Thermodynamic data of activity coefficients at infinite dilution

In this work, the effect of IL’s functionalization of the interaction of IL with organic solutes and water at infinite dilution has been investigated. Based on the experimental activity coefficients at infinite dilution, (γ13∞) the possibility of using ionic liquids (ILs) in different separation processes, such as aliphatic from aromatic hydrocarbon (heptane/benzene, or cyclohexane/benzene), desulfurization and denitrification of model fuel (heptane/thiophene and heptane/pyridine) were investigated based on the experimental study of the activity coefficients at infinite dilution. The (γ13∞) values were determined for more than fifty different solutes including alkanes, cycloalkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, ethers, ketones, thiophene, acetonitrile, pyridine, 1-nitropropane and water in two ionic liquids: 4-(3-cyanopropyl)-4-methylmorpholinium tricyanomethanide, [Mo1,3CN][TCM] and 4-(3-hydroxypropyl)-4-methylmorpholinium tricyanomethanide, [Mo1,3OH][TCM]. The experiment was performed using inverse gas–liquid chromatography at a wide temperature range from T = (308.15 to 358.15) K. From the experimental data, the partial molar excess Gibbs energy (ΔG1E,∞), enthalpy (ΔH1E,∞) and entropy (Tref ΔS1E,∞) at infinite dilution were determined. The gas–liquid partition coefficients of the solutes, KL were also calculated. Finally, two the values of two factors important from separation point of view: selectivity (S12∞) and capacity (k2) at infinite dilution for few separation problems as hexane/benzene, cyclohexane/benzene, heptane/thiophene, and heptane/pyridine were calculated from γ13∞ and compared to literature values for other ionic liquids taken from available literature. Moreover, physicochemical properties of pure IL including liquid density and dynamic viscosity data, important from the technological point of view was determined at a wide temperature range.

Thermodynamics of N-Isopropylacrylamide in Water: Insight from Experiments, Simulations, and Kirkwood–Buff Analysis Teamwork

The behavior of thermoresponsive polymer poly(N-isopropylacrylamide) (PNiPAM), an essential building block in the design of smart soft materials, in aqueous solutions has attracted much interest, which contrasts with our knowledge of N-isopropylacrylamide (NiPAM) monomer. Strikingly, the physicochemical properties of aqueous NiPAM are similarly rich, and their understanding is far from being complete. This stems from the lack of accurate thermodynamic data and quantitative model for atomistic simulations. In this joint study, we have probed the thermodynamic behavior of aqueous NiPAM by experimental methods, molecular dynamics (MD) simulations, and Kirkwood-Buff (KB) analysis at ambient conditions. From the partial molar volumes and simultaneously correlated osmotic coefficients, with excess partial molar enthalpies of NiPAM in water, the concentration and temperature dependence of KB integrals was determined. For the purpose of this work, we have developed and employed a novel NiPAM force field, which not only reproduces KB integrals (Gij) and adequately captures macroscopic thermodynamic quantities but also provides more accurate structural insight than the original force fields. We revealed in the vicinity of NiPAM the competing effect of amide hydration with interaction between nonpolar regions. This microscopic picture is reflected in the experimentally observed NiPAM-NiPAM association, which is present from highly dilute conditions up to the solubility limit and is evidenced by G22. From intermediate concentrations, it is accompanied by the existence of apparent dense-water regions, as indicated by positive G11 values. The here-employed KB-based framework provided a mutually consistent thermodynamic and microscopic insight into the NiPAM solution and may be further extended for ion-specific effects. Moreover, our findings contribute to the understanding of thermodynamic grounds behind PNiPAM collapse transition.

Volumetric and Viscosimetric Measurements for Methanol + CH3–O–(CH2CH2O)n–CH3 (n = 2, 3, 4) Mixtures at (293.15–303.15) K and Atmospheric Pressure: Application of the ERAS Model

Densities, $$\rho$$, and kinematic viscosities, $$\nu$$, have been determined at atmospheric pressure and at 293.15–303.15 K for binary mixtures formed by methanol and one linear polyether of the type CH3–O–(CH2CH2O)n–CH3 (n = 2, 3, 4). Measurements on $$\rho$$ and $$\nu$$ were carried out, respectively, using an Anton Paar DMA 602 vibrating-tube densimeter and an Ubbelohde viscosimeter. The $$\rho$$ values were used to compute excess molar volumes, $$V_{{\text{m}}}^{{\text{E}}}$$, and, together with the $$\nu$$ results, dynamic viscosities ($$\eta$$). Deviations from linear dependence on mole fraction for viscosity, $$\Delta \eta$$, are also provided. Different semi-empirical equations have been employed to correlate viscosity data. Particularly, the equations used are the: Grunberg–Nissan, Hind, Frenkel, Katti–Chaudhri, McAllister and Heric. Calculations show that better results are obtained from the Hind equation. The $$V_{{\text{m}}}^{{\text{E}}}$$ values are large and negative and contrast with the positive excess molar enthalpies, $$H_{{\text{m}}}^{{\text{E}}}$$, available in the literature, for these systems. This indicates that structural effects are dominant. The $$\Delta \eta$$ results are positive and correlate well with the difference in volumes of the mixture compounds, confirming the importance of structural effects. The temperature dependences of $$\eta$$ and of the molar volume have been used to calculate enthalpies, entropies and Gibbs energies, $$\Delta G^{*}$$, of viscous flow. It is demonstrated that $$\Delta G^{*}$$ is essentially determined by enthalpic effects. Methanol + CH3–O–(CH2CH2O)n–CH3 mixtures have been treated in the framework of the ERAS model. Results for $$H_{{\text{m}}}^{{\text{E}}}$$ are acceptable, while the composition dependence of the $$V_{{\text{m}}}^{{\text{E}}}$$ curves is poorly represented. This has been ascribed to the existence of strong dipolar and structural effects in the present solutions.

Comments on “Solubility measurement and correlation of 2-phenyl-1H-indole in fourteen mono organic solvents from 289.05 K to 338.55 K”

Abstract A polemic is given regarding the thermodynamic properties reported in the published paper. The authors' calculated infinite dilution activity coefficients and infinite dilution partial molar excess enthalpies of 2-phenyl-1H-indole are found to be inconsistent with the Wilson model curve-fit parameters reported in the paper.

Characterization of the solubilizing ability of short-chained glycol-grafted ammonium and phosphonium ionic liquids

Abstract Infinite dilution activity coefficients and gas-to-liquid partition coefficients are reported for >40 organic solvents dissolved in (2-methoxyethyl) triethylphosphonium bis(trifluoromethylsulfonyl)imide, (2-methoxyethyl)tributylphosphonium bis(trifluoromethylsulfonyl)imide, and (2-methoxyethyl)triethylammonium bis(trifluoromethylsulfonyl)imide in the temperature range from 323.15 K to 373.15 K. Experimental values were determined using the method of inverse gas chromatography. Measured infinite dilution activity coefficients are used to calculate the partial molar excess Gibbs free energy, enthalpy and entropy associated with dissolution of the organic solutes into the three ionic liquid solvents. Abraham model correlations for solute transfer into each ionic liquid solvent have also been determined from the measured infinite dilution activity coefficient data.

Measurements of Activity Coefficients at Infinite Dilution for Organic Solutes in the Ionic Liquids N-Ethyl- and N-Octyl-N-methylmorpholinium Bis(trifluoromethanesulfonyl)imide. A Useful Tool for Solvent Selection.

In recent years, many papers describing ionic liquids (IL) as promising solvents in separation techniques have been published. The conscious choice of appropriate ionic liquid as absorption media in effective extraction of selected types of analytes requires deeper understanding of the analyte−IL interactions. Therefore, intensive research is conducted to determine the values of activity coefficient at infinite dilution, which allows us to characterize the nature of these interactions. Based on the inverse gas chromatography retention data, activity coefficients at infinite dilution of 48 different organic compounds in the ionic liquids N-ethyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide [C2C1Mor][TFSI] and N-octyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide [C8C1Mor][TFSI] were determined. The measurements covered a broad range of volatile organic compounds, including n-alkanes, n-alkenes, n-alkynes, alcohols, aldehydes, ketones, aromatic compounds and common polar solvents, representing different types of interactions. Activity coefficients at infinite dilution were measured in the temperature range from 313.15 to 363.15 K. The excess partial molar enthalpies and entropies at infinite dilution were determined. Selectivity at infinite dilution was also calculated for exemplary separation processes in the hexane/benzene system. The obtained results were analyzed and compared with literature data for ionic liquids containing the same anion [TFSI]¯ and different cations. The study results indicate that some potential applications of the investigated ionic liquids in separation problems exist.

Effect of molecular structure on excess molar enthalpy of amine-based carbon dioxide absorbent and water

Amine-based carbon dioxide absorbent has the characteristics of high selective absorption rate and strong absorption capacity and occupies the leading position in the carbon dioxide absorption process. The absorption performance of amine carbon dioxide absorbents is directly related to their thermodynamic properties. Accordingly, for the selection of new absorbents, the important thermodynamic properties such as the excess molar enthalpy of the system must be determined first. In this paper, the excess molar enthalpies for amine-based carbon dioxide absorbents in water were measured with C-80 calorimeter at atmospheric pressure. With the experimental data in this work and the literature data, the relationship between the molecular structure and excess molar enthalpy of amine-based carbon dioxide absorbent was studied.

Measurement and Modeling of Excess Molar Enthalpies of Binary Mixtures Involving Hydrocarbon Components of Fuel

Experimental excess molar enthalpies of binary systems that are constituted by different groups of hydrocarbons, which are 1-hexene, methylcyclohexane, cyclohexane, isooctane, and heptane, are repo...

DCA]-based ionic liquids for the extraction of sulfur and nitrogen compounds from fuels: Activity coefficients at infinite dilution

Some petroleum processes need the removal of low level aromatic-sulfur and nitrogen compounds for many products, which are extremely important according to the new strict environmental regulations to reduce sulfur and nitrogen content compounds in liquid fuels. Thus the new, alternative solvents such as ionic liquids (ILs) have been proposed. ILs reveal a high selectivity and capacity of extraction of sulfur- and nitrogen-compounds from alkanes with little solvent loss during the process. The measurements of activity coefficients γ13∞ at infinite dilution of different solutes in the IL shows the effect of interactions between organic solutes, or water on the interfacial and bulk properties of the IL. The new (3-cyanopropyl)pyridinium dicyanamide, [N–C3CNPy][DCA] and (3-cyanopropyl)methylpyrrolidinium dicyanamide, [N–C3CNMPyr][DCA] were investigated in this work. The data were obtained using the gas-liquid chromatography technique. Measurements were undertaken at six temperatures, in 10 K intervals, in the range of (318.15–368.15) K. The solutes studied included both non-polar and polar compounds, as alkanes, alkenes, alkynes, as well as aromatic hydrocarbons, alcohols, water, ethers, ketones, and esters. The most important solutes used were thiophene, pyridine, and 1-nitropropane. Densities, ρ, measurements for a range of temperatures, T (298.15–368.15) K for the chosen ILs were undertaken at pressure, p = 101 kPa. The gas-liquid partition coefficients, KL at infinite dilution were calculated. The fundamental thermodynamic functions such as partial molar excess Gibbs energy, enthalpy and entropy at infinite dilution were calculated from the experimental data measurements to discuss the interaction between solutes and the ILs. The values of selectivity and capacity for three separation cases, viz. heptane/thiophene, heptane/pyridine, and heptane/1-nitropropane were calculated from γ13∞ values and compared to literature data for dicyanamide-based ILs. The Abraham solvation parameter model was presented for all solutes. The obtained results indicated that [N–C3CNPy][DCA] has large selectivity and capacity values for all three of the separation cases studied.

Thermodynamic study of mixtures containing dibromomethane. II: volumes and enthalpies at 298.15 K

Excess molar volumes, VE, of binary mixtures of dibromomethane (DBM) with n-hexane, n-heptane, n-octane, cyclohexane, tetrachloromethane, dipropyl and dibutyl ether, tetrahydrofuran, and 3-pentanone are determined at 298.15 K in the whole composition range by means of a vibrating tube densimeter. For the same DBM mixtures plus with n-pentane and except with dipropyl ether and 3-pentanone, partial molar enthalpies, Hi, and excess molar enthalpies, HE, are obtained through a heat flow calorimeter and a titration method purposely devised. Both excess properties are positive for cyclohexane, tetrachloromethane, and n-alkanes, the latter exhibiting an increase with increasing number of carbon atoms. Dipropyl and dibutyl ether mixtures exhibit negative VE values, while n-hexane, tetrahydrofuran, and 3-pentanone mixtures show an S-shaped VE curve. Negative HEs are observed only for tetrahydrofuran, whereas dibutyl ether exhibits an S-shaped HE curve. HE results are compared with the predictions of the DISQUAC model. The partial molar volumes at infinite dilution, V°, as well as the enthalpies of solvation, ΔsolvH°, of the examined substances in DBM are evaluated and discussed also considering data on other compounds found in the literature. For V° and ΔsolvH°, a group additivity scheme is proposed to enable the estimation of these properties for other molecules and how much structural peculiarities such as chain length, polarity of groups, and cyclic structures influence their values.

Volumetric, enthalpic and VLE studies of binary mixtures of isomers of butyl chloride with cyclohexane at 298.15 K

Excess molar volumes (VmE), excess molar enthalpy (HmE) and isothermal vapor-liquid equilibrium data for n-, sec- and tert-butyl chloride (A) + cyclohexane (B) systems were measured at 298.15 K. Excess molar Gibbs free energy (GmE) for these systems were calculated by Barker's method. The VmE and HmE for these mixtures follow the sequence: n- > sec- > tert-butyl chloride while it is reverse for GmE. Prigogine-Flory-Patterson theory (PFP) predicts the experimental VmE and HmE data for these systems quite well except for HmE of n-butyl chloride (xA>0.5) mixtures and tert-butyl chloride mixtures for xA<0.5. The activity coefficients γA and γB of the components in binary (A+B) mixtures were also predicted by Singh and Maken activity coefficient model employing limited experimental activity coefficient data.

Activity coefficients at infinite dilution of organic solutes, using novel N-(2′, 3′-epoxypropyl)-N-methyl-2-oxopyrrolidinium chloride ionic liquid by GLC

The activity coefficients at infinite dilution (γ13∞) for 31 solutes, from the following classes of compounds: alkanes, cycloalkanes, alkenes, cycloalkenes, aromatic hydrocarbons, alcohols, ketones, acetonitrile, thiophene and water were determined using an ionic liquid (IL) modified column utilizing gas liquid chromatography. In this work, N-(2′, 3′-epoxypropyl)-N-methyl-2-oxopyrrolidinium chloride IL was used to determine the activity coefficients of organic solutes in the range of temperatures from T = 323.15 K–343.15 K, using 10 K intervals, under atmospheric pressure. From these experimental γ13∞ data, the following thermodynamic properties at infinite dilution, including partial molar excess Gibbs free energies (ΔGiE,∞), enthalpies ΔHiE,∞and entropy TrefΔSiE,∞ were computed. Furthermore, selectivity (Sij∞) and capacity (Kj∞) were also calculated from experimental value of γ13∞ for separation of mixtures such as (heptane/benzene, heptane/thiophene, hexane/benzene, water/butanol and hexane/ethanol) at T = 323.15 K–343.15 K. Generally, the results of this work indicate that the investigated IL has good potential for separating aliphatic solutes from aromatic ones. Specifically, the chosen IL reduces the retention time of most of the solutes used, compared to other reported ILs. Furthermore, the findings of this study suggest that this IL [N(2′,3′-epoxypropyl)-N-methyl-2-oxopyrrolidinium chloride] may be useful for future applications such as separation and purification in petrochemical industries.

Experimental solubility of clotrimazole and some thermodynamic aspects of dissolution in different solvents

Equilibrium solubility of clotrimazole, an important antimycotic drug, was measured between (293.15–313.15) K in four pharmaceutically relevant solvents including buffer pH 2.0, buffer pH 7.4, hexane and 1-octanol. The experimental solubility results were correlated by modified Apelblat and van’t Hoff equations. The compound melting temperature and enthalpy were determined. The activity coefficients at infinite dilution of clotrimazole in each solvent were calculated from experimental data on solubility and thermophysical properties. Substitution aqueous solvents for organic ones leads to lower activity coefficients and higher solubility of the drug. The limiting partial molar excess enthalpies, entropies and Gibbs energies of clotrimazole were evaluated.

Measurement and correlation of the solubility of tin compounds and β-diketimine in selected solvents

The solubility of organotin compounds under inert atmosphere plays a significant role in homogeneous catalysis process; however, no such study has been reported. The solubilities of dimethyltin dichloride (1), stannous chloride (2), β-diketiminato ligand LH (3) (L = HC(CMeNAr)2, Ar = 2,6-Et2C6H3), and tin (II) compound [LSnCl] (4) in six organic solvents were measured using a static analytic method from 268.15 K to 313.15 K under a purified nitrogen atmosphere to select the optimum solvent for a homogeneous reaction and recrystallization. The difference in solubility can be attributed to molecular structure, coordination bonding, and molecular polarity. Six commonly used thermodynamic models were used to correlate the experimental solubility data. Some models show a great correlation with a low value of average absolute deviation (AAD). In addition, the solubility parameter of solute, partial molar excess enthalpies at infinite dilution, and thermodynamic properties were calculated to study the dissolution behavior in more depth.