Measurement of heat capacities of ionic liquids by differential scanning calorimetry

Heat capacities for nine ionic liquids (IL) have been determined with the “three-step” method using two different differential scanning calorimeters (DSC). In addition, the heat capacities of these ionic liquids have been studied by the modulated-temperature differential scanning calorimetry (MDSC™). The measurements cover a temperature range from 315 to 425 K.     

Isobaric specific heat capacity of water and aqueous cesium chloride solutions for temperatures between 298 K and 370 K at p = 0.1 MPa

There has been some controversy regarding the uncertainty of measurements of thermal properties using differential scanning calorimeters, namely heat capacity of liquids. A differential scanning calorimeter calibrated in enthalpy and temperature was used to measure the isobaric specific heat capacity of water and aqueous solutions of cesium chloride, in the temperature range 298 K to 370 K, for molalities up 3.2 mol · kg⁻¹, at p = 0.1 MPa, with an estimated uncertainty (ISO definition) better than 1.1%, at a 95% confidence level. The measurements are completely traceable to SI units of energy and temperature.The results obtained were correlated as a function of temperature and molality and compared with other authors, obtained by different methods and permit to conclude that a DSC calibrated by Joule effect is capable of very accurate measurements of the isobaric heat capacity of liquids, traceable to SI units of measurement.     

Heat capacities of aqueous solutions containing diethanolamine and N-methyldiethanolamine

In this work, we present new results for heat capacities of aqueous mixtures of diethanolamine with N-methyldiethanolamine over the temperature range (303.2 to 353.2) K with a differential scanning calorimeter. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the (DEA + MDEA + water) systems were investigated. For the binary system, (DEA + MDEA), heat capacities of nine concentrations were also measured. A Redlich–Kister-type equation for representing excess molar heat capacity was applied to correlate the measured C_p of aqueous alkanolamine solutions. For a total of 176 data points for the (DEA + MDEA + water) system, the overall average absolute percentage deviation of the calculations are 16.5% and 0.2% for the excess molar heat capacity and the molar heat capacity, respectively. The heat capacities presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.     

New experimental heat capacity and enthalpy of formation of lithium cobalt oxide

The heat capacity of LiCoO₂ (O3-phase), constituent material in cathodes for lithium-ion batteries, was measured using two differential scanning calorimeters over the temperature range from (160 to 953) K (continuous method). As an alternative, the discontinuous method was employed over the temperature range from (493 to 693) K using a third calorimeter. Based on the results obtained, the enthalpy increment of LiCoO₂ was derived from T = 298.15 K up to 974.15 K. Very good agreement was obtained between the derived enthalpy increment and our independent measurements of enthalpy increment using transposed temperature drop calorimetry at 974.15 K. In addition, values of the enthalpy of formation of LiCoO₂ from the constituent oxides and elements were assessed based on measurements of enthalpy of dissolution using high temperature oxide melt drop solution calorimetry. The high temperature values obtained by these measurements are key input data in safety analysis and optimisation of the battery management systems which accounts for possible thermal runaway events.     

Heat capacities of the mixtures of ionic liquids with methanol at temperatures from 283.15 K to 323.15 K

The molar isobaric heat capacities of (methanol + 1-hexyl-3-methylimidazolium tetrafluoroborate) and (methanol + 1-methyl-3-octylimidazolium tetrafluoroborate) mixtures have been determined over the temperature range from 283.15 K to 323.15 K within the whole composition range. The excess molar heat capacities of investigated mixtures have been fitted to the Redlich–Kister equation at several selected temperatures. Positive deviations from the additivity of molar heat capacities have been observed in both examined systems. The results obtained have been discussed in terms of molecular interactions in binary mixtures.     

Excess molar heat capacities for (decan-1-ol + n-heptane) at temperatures from (290 to 318) K. Experimental results and theoretical description using the ERAS model

The isobaric specific heat capacities were measured for (decan-1-ol + n-heptane) mixtures within the temperature range from (290.91 to 318.39) K by means of a differential scanning calorimeter. The results are explained in terms of self-association of alkanols and non-specific interactions between decan-1-ol and n-heptane. The experimental excess molar heat capacities were compared with those calculated with the aid of the ERAS model.     

Molar heat capacities for (2-methyl-2-butanol + heptane) mixtures and cyclopentanol at temperatures from (284 to 353) K

Isobaric specific heat capacities were measured for (2-methyl-2-butanol + heptane) mixtures and cyclopentanol within the temperature range from (284 to 353) K, and for 2-methyl-2-butanol in the (284 to 368) K temperature interval by means of a differential scanning calorimeter. The excess molar heat capacities were calculated from the experimental results. For the temperature range from (284 to 287) K, the excess molar heat capacity is S-shaped with negative values in the 2-methyl-2-butanol rich region and with small negative values at low alcohol concentrations at temperatures from (295 to 353) K. The excess molar heat capacities are positive for all compositions under test at temperatures from (288 to 294) K. The results are explained in terms of the influence of the molecular size and configuration of the alkanols on their self-association capability and of the change in molecular structure of the (2-methyl-2-butanol + heptane) mixtures. The differences between the temperature dependences of the heat capacities of the mixtures studied are qualitatively consistent with results obtained by Rappon et al. [M. Rappon, J.M. Greer, J. Mol. Liq. 33 (1987) 227–244; M. Rappon, J.A. Kaukinen, J. Mol. Liq. 38 (1988) 107–133; M. Rappon, R.M. Johns, J. Mol. Liq. 40 (1989) 155–179; M. Rappon, R.T. Syvitski, K.M. Ghazalli, J. Mol. Liq. 62 (1994) 159–179; M. Rappon, R.M. Johns, J. Mol. Liq. 80 (1999) 65–76; M. Rappon, S. Gillson, J. Mol. Liq. 128 (2006) 108–114].     

Deuterium isotope effect on molar heat capacities and apparent molar heat capacities in dilute aqueous solutions: A multi-channel heat-flow microcalorimeter study

The molar heat capacities of chloroform, dichloromethane, methanol, acetonitrile, acetone, dimethyl sulfoxide, benzene, dimethylformamide, toluene, and cyclohexane, as well as their deuterated isotopologues, were measured using a multi-channel heat conduction TAM (Thermal Activity Monitor) III microcalorimeter. In addition, the apparent molar heat capacities of some of the associated dilute aqueous solutions (0.0039 < solute mole fraction, x_i < 0.0210) were also measured. A temperature drop method from (298.15 to 297.15) K at 0.1 MPa was employed. The corresponding heat capacities were determined from the integration of the measured heat flow. The heat capacity results are shown to be in good to very good agreement with the available literature values. In addition, good correlations were obtained for the effect of isotopic substitution on both molar heat capacity and apparent molar heat capacity in aqueous solutions. These correlations should be useful in the prediction of the molar heat capacities or the apparent molar heat capacities of other deuterated compounds. Since these measurements were conducted with ampoules, the effects of heat of condensation and/or vapor space on the accuracy of the heat capacity determinations are discussed. The overall results from this study demonstrate the utility of a multi-channel heat conduction microcalorimeter in obtaining good reproducibility and good accuracy for molar heat capacities as well as apparent molar heat capacities from simultaneous samples.     

Density,speed of sound,heat capacity,and related properties of 1-hexanol and 2-ethyl-1-butanol as function of temperature and pressure

The speeds of sound in 1-hexanol and 2-ethyl-1-butanol have been measured over the temperature range from (293.15 to 318.15) K and at pressures up to 101 MPa. The densities have been measured within the temperature range from (283.15 to 343.15 or 353.15) K under atmospheric pressure. For the measurements, a pulse-echo-overlap method and a vibrating tube densimeter have been used. Additionally, in the case of 2-ethyl-1-butanol, the isobaric heat capacities from T = (293.15 to 323.15) K at atmospheric pressure have been measured by means of a DSC calorimeter. The experimental results are then used to calculate the densities and isobaric heat capacities as a function of temperature and pressure by means of a numerical integration technique. The effects of pressure and temperature on these and the related properties are discussed. Densities are correlated by means of the Tait equation.     

(Liquid + liquid) phase equilibrium and critical behavior of binary solution {heavy water + 2,6-dimethylpyridine}

The (liquid + liquid) coexistence curves, the isobaric heat capacities per unit volume and the turbidities for the binary solution of {heavy water + 2,6-dimethylpyridine} have been precisely measured. The values of the critical exponents were obtained, which confirmed the 3D-Ising universality. It was found that the critical temperature dropped by 5.9 K and the critical amplitude of the coexistence curve significantly increased as compared to the binary solution of {water + 2,6-dimethylpyridine}. The complete scaling theory was applied to well describe the asymmetric behavior of the diameter of the coexistence curve as the heat capacity contribution was considered. Moreover, the values of the critical amplitudes of the correlation length and the osmotic compressibility were deduced, which together with the critical amplitudes of the coexistence curve and the heat capacity to test universal amplitude ratios.     

Thermodynamics of solution of proto- and mezoporphyrins in N,N-dimethylformamide

This paper describes the results of thermodynamic study of dissolution of proto- and mesoporphyrins in liquid N,N-dimethylformamide (DMF) at different temperatures. Enthalpies of solution and solubility of protoporphyrin dimethylester (PDE) and mesoporphyrin dimethylester (MDE) in DMF have been obtained from T = (298 to 318) K. Free energies, enthalpies, entropies and heat capacities of solution have been computed from the combination of enthalpic and solubility data via the Gibbs–Helmholtz equation. We have shown that for all blood porphyrins this approach reproduces both free energies of solution and solubility values for the physiological temperature range.     

An experimental setup for isobaric heat capacities for viscous fluids at high pressure: Squalane,bis(2-ethylhexyl) sebacate and bis(2-ethylhexyl) phthalate

A high-pressure flow calorimeter has been used to determine highly accurate isobaric heat capacities for different viscous fluids, squalane (SQN), bis(2-ethylhexyl) sebacate (DEHS) and bis(2-ethylhexyl) phthalate (DEHP) from T = (293.15 to 353.15) K and up to 30 MPa. The experimental device was adapted for viscous liquids at high pressure and it can measure heat capacities with an estimated total uncertainty better than 1%. The isobaric heat capacity values were analysed together with their temperature and pressure dependences. In addition, a fitting equation of the experimental molar isobaric heat capacity for these viscous fluids as a function of temperature and pressure was proposed.     

Standard molar volumes and heat capacities of aqueous solutions of sodium trifluoromethanesulfonate at temperatures up to 573 K and pressures to 28 MPa

Densities and heat capacities of aqueous solutions of sodium trifluoromethanesulfonate (sodium triflate) of concentrations from 0.025 to 0.3 mol · kg⁻¹ were measured with high temperature, high pressure custom-made instruments at temperatures up to 573 K and at pressures up to 28 MPa. Standard molar volumes and standard molar heat capacities were obtained via extrapolation of the apparent molar properties to infinite dilution. The results for volumetric properties are consistent with earlier literature data, but no previous measurements exist for heat capacities of sodium triflate at superambient conditions. The new data were used for calculating the standard molar volumes and heat capacities for the triflate anion and compared with the results for triflic acid that should be essentially identical within the expected error margins. At temperatures above 473 K an effort was made to refine the processing of literature data for HCl(aq), taking into account its partial association, and subsequently to modify the value for Na⁺ ion calculated from the standard thermodynamic values of NaCl(aq) where its ion pairing was already considered. This approach yields reasonable agreement at high temperatures between the values for triflate ion calculated from its salt and those for triflic acid.     

Heat capacity (Cp) and entropy of olivine-type LiFePO4 in the temperature range (2 to 773) K

The heat capacity of olivine-type lithium iron phosphate (LiFePO₄ – LFP) has been measured covering a temperature range from (2 to 773) K. Three different calorimeters were used. The Physical Property Measurement System (PPMS) from Quantum Design was applied in the range between T = (2 and 300) K, a Micro-DSC II from Setaram within the range between T = (283 and 353) K and data between T = (278 and 773) K were measured by means of a Sensys DSC (Setaram) using the Cp-by-step method. Experimental data are given with an error of (1 to 2)% above T = 20 K and up to 8% below 20 K. The data were subdivided into appropriate temperature intervals and fitted using common heat capacity functions. The low temperature results permit the calculation of standard entropies and temperature coefficients of electronic, lattice, as well as magnetic (antiferromagnetic transition at T = 49.2 K) contributions to the heat capacity. The obtained experimental values were compared to results of a recently published first principles phonon study (DFT) and to few available experimental data from the literature.     

Heat capacities and electrical conductivities of 1-ethyl-3-methylimidazolium-based ionic liquids

We present the heat capacities and electrical conductivities of five [Emim] 1-ethyl-3-methylimidazolium-based ionic liquids: [Emim][BF₄] (tetrafluoroborate), [Emim][CF₃SO₃] (trifluoromethanesulfonate), [Emim][C₂N₃] (dicyanamide), [Emim][C₂H₅SO₄] (ethylsulfate), and [Emim][MDEGSO₄] (2-(2-methoxyethoxy) ethylsulfate). The heat capacities were measured using a differential scanning calorimeter (DSC) over the temperature ranging from (303.2 to 358.2) K. The electrical conductivities were measured over the temperature ranging from (293.2 to 353.2) K using a commercial conductivity meter. The estimated uncertainties of heat capacity C_p and electrical conductivity σ measurements were ±0.015 kJ · kg^?1 · K^?1 and ±0.001 mS · cm^?1, respectively. The measured C_p and σ are presented as a function of temperature. The temperature dependency of the C_P value was correlated using an empirical equation. A modified version of VTF-type (Vogel–Tamman–Fulcher) equation was used to describe the temperature dependency of σ values. The correlations give satisfactory results. Also, the results of this study are in good agreement with the available literature data. The heat capacities and electrical conductivities presented in this work are in good agreement with the available literature data. The results of this study can be applied to numerous chemical processes, since C_p and σ data are essential information for rational design.     

Speed of sound,density, and heat capacity for (2-methyl-2-butanol + heptane) at pressures up to 100 MPa and temperatures from (293 to 318) K. Experimental results and theoretical investigations

In this paper, some new physicochemical properties of (2-methyl-2-butanol + heptane) are investigated using an acoustic method. Of clear interest to us is the study of the effect of branched structure of alcohol on association in mixtures with heptane and consequently, the effect of temperature and pressure on deviations from ideal solution behaviour. Thus, this work presents experimental properties and theoretical study of (2-methyl-2-butanol + heptane) as functions of temperature and pressure over the entire composition range. The densities and speeds of sound in (2-methyl-2-butanol + heptane) have been measured for temperatures ranging from (293 to 318) K under atmospheric pressure and under elevated pressures up to 101 MPa, respectively. The densities, heat capacities and appropriate excesses of these binaries were calculated for the same temperatures and for pressures up to 100 MPa. The acoustic method was applied in the calculations. The effects of pressure and temperature on the excess molar volume and the excess molar heat capacity of (2-methyl-2-butanol + heptane) are explained in terms of the influence of the molecular size and configuration of the alcohols on their self-association capability, packing effect, and the non-specific interactions between the 2-methyl-2-butanol and heptane basing on the results obtained from the modified ERAS model.     

Liquid heat capacity of the solvent system (piperazine + 2-amino-2-methyl-l-propanol + water)

This report presents a new set of heat capacity data for the system piperazine {(PZ) + 2-amino-2-methyl-1-propanol (AMP) + water (H₂O)}, measured using the differential scanning calorimetry technique, over the temperature range 303.2 K to 353.2 K and at fourteen (14) different concentrations in which the water mole fractions, x₃’s, were fixed at 0.60, 0.70, 0.80, and 0.90. Heat capacity for the binary system {PZ (1) + AMP (2)} at x₁ = 0.05, 0.10, 0.15, and 0.20 were, likewise, measured to generate parameters necessary in the Redlich–Kister-type model, which was used to estimate excess molar heat capacities. Such estimates were then used to predict the values of the molar heat capacity at the corresponding sets of temperature and concentration. The predicted values were subsequently compared against the measured values and the results are satisfactory.     

Thermodynamic and acoustic properties of (heptane + dodecane) mixtures under elevated pressures

The speed of sound in (heptane + dodecane) mixtures was measured over the whole concentration range at pressures up to 101 MPa and within the temperature range from (293 to 318) K. The density of (heptane + dodecane) was measured in the whole composition range under atmospheric pressure and at temperatures from (293 to 318) K. The densities and heat capacities of these binaries at the same temperatures were calculated for pressures up to 100 MPa from the speeds of sound under elevated pressures together with the densities and heat capacities at atmospheric pressure. The effects of pressure and temperature on the excess molar volume and the excess molar heat capacity are discussed.     

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

Activity coefficients at infinite dilution were determined for 24 solutes (n-alkanes, alk-1-enes, alk-1-ynes, cycloalkanes, alkylbenzenes, and alcohols) in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate by gas-liquid chromatography at three different temperatures T = (313.15, 323.15, 333.15) K. The partial molar excess enthalpy values at infinite dilution were calculated from the experimental results over the same temperature range. Selectivities and capacities at infinite dilution for the hexane/benzene and methanol/benzene separation problems were calculated from experimental infinite dilution activity coefficient values. The activity coefficients, enthalpies, selectivities, and capacities are discussed and compared to literature values for other ionic liquids, as well as industrial molecular solvents.