Liquid heat capacity of the solvent system (piperazine + n-methyldiethanolamine + water)

A new set of values for the heat capacity of aqueous mixtures of piperazine (PZ) and n-methyldiethanolamine (MDEA) at different concentrations and temperatures are reported in this paper. The differential scanning calorimetry technique was used to measure the property over the range T = 303.2 K to T = 353.2 K for mixtures containing 0.60 to 0.90 mole fraction water with 15 different concentrations of the system (PZ + MDEA + H₂O). Heat capacity for four concentrations of the binary system (PZ + MDEA) was also measured. A Redlich–Kister-type equation was adopted to estimate the excess molar heat capacity, which was used to predict the value of the molar heat capacity at a particular concentration and temperature, which would then be compared against the measured value. A total of 165 data points fit into the model resulted in a low overall average absolute deviation of 4.6% and 0.3% for the excess molar heat capacity and molar heat capacity, respectively. Thus, the results presented here are of acceptable accuracy for use in engineering process design.     

Volumetric and viscometric behaviour of the binary systems of N-methyldiethanolamine and diethanolamine with 1-butyl-3-methylimidazolium acetate at various temperatures

In the present work, density and viscosity of two binary mixtures of N-methyldiethanolamine (MDEA) and diethanolamine (DEA) with 1-butyl-3-methylimidazolium acetate ([bmim][acetate]) are measured. The experiments were carried out at atmospheric pressure and at T = (293.15 to 343.15) K for density and from 293.15 K to 353.15 K for viscosity over the whole range of mole fraction. Using the density and viscosity results, several physical and thermodynamic properties such as excess molar volumes (V^E), coefficients of thermal expansions (α), viscosity deviation (Δη),molar activation entropy (ΔS), molar activation enthalpy (ΔH) and molar activation Gibbs free energy (ΔG) for these binary mixtures are calculated.The experimental results of the density and viscosity for the pure systems as well as the binary systems show a decrease with increasing temperature as expected. The results of density measurements show that over all ranges of temperatures investigated the density of the pure components show the following trend: DEA > [bmim][acetate] > MDEA. Therefore, in the binary mixtures of the (MDEA + [bmim][acetate]), the density of the mixture reduces with decreasing concentration of the ionic liquid and for the (DEA + [bmim][acetate]) mixture the density of the blend enhances to reduce the concentration of the ionic liquid. Moreover, the calculated excess molar volumes show a positive deviation from ideality for the two binary mixtures. The behaviour of change of viscosity against concentration for the (MDEA + [bmim][acetate]) system is different from the (DEA + [bmim][acetate]) mixture so that for the first system the value of the viscosity rises with increasing [bmim][acetate] mole fraction, but in the second system there is a minimum viscosity point in the DEA-rich region.     

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.     

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.     

Volumes,heat capacities,and compressibilities of the mixtures of acetonitrile and 2-methoxyethanol

Heat capacities and speed of sound of (acetonitrile + 2-methoxyethanol) mixtures at 298.15 K and the densities of the same mixtures at T = (308.15 and 318.15) K were determined over the whole composition range. The excess of molar volume and isobaric heat capacity of the mixture, the partial molar volumes and heat capacities of both components of the mixture as well as the adiabatic and isothermal coefficients of compressibility and their excess were calculated from the obtained experimental data. The internal pressure of the examined system was also calculated. The results of investigations were analyzed and discussed. The behavior of the analyzed functions is similar to that observed in the case of the mixtures of acetonitrile with some aprotic solvents examined earlier.     

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.     

Apparent molar heat capacities and apparent molar volumes of Pr(ClO4)3(aq), Gd(ClO4)3(aq), Ho(ClO4)3(aq), and Tm(ClO4)3(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa

Acidified aqueous solutions of Pr(ClO₄)₃(aq), Gd(ClO₄)₃(aq), Ho(ClO₄)₃(aq), and Tm(ClO₄)₃(aq) were prepared from the corresponding oxides by dissolution in dilute perchloric acid. Once characterized with respect to trivalent metal cation and acid content, the relative densities of the solutions were measured at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa using a Sodev O2D vibrating tube densimeter. The relative massic heat capacities of the aqueous systems were also determined, under the same temperature and pressure conditions, using a Picker Flow Microcalorimeter. All measurements were made on solutions containing rare earth salt in the concentration range 0.01 ⩽ m/(mol · kg⁻¹) ⩽ 0.2. Relative densities and relative massic heat capacities were used to calculate the apparent molar volumes and apparent molar heat capacities of the acidified salt solutions from which the apparent molar properties of the aqueous salt solutions were extracted by the application of Young's Rule. The concentration dependences of the isothermal apparent molar volumes and heat capacities of each aqueous salt solution were modelled using Pitzer ion-interaction equations. These models produced estimates of apparent molar volumes and apparent molar heat capacities at infinite dilution for each set of isothermal V_φ,2 and C_pφ,2 values. In addition, the temperature and concentration dependences of the apparent molar volumes and apparent molar heat capacities of the aqueous rare earth perchlorate salt solutions were modelled using modified Pitzer ion-interaction equations. The latter equations utilized the Helgeson, Kirkham, and Flowers equations of state to model the temperature dependences (at p=0.1 MPa) of apparent molar volumes and apparent molar heat capacities at infinite dilution. The results of the latter models were compared to those previously published in the literature.Apparent molar volumes and apparent heat capacities at infinite dilution for the trivalent metal cations Pr³⁺(aq), Gd³⁺(aq), Ho³⁺(aq), and Tm³⁺(aq) were calculated using the conventions V₂^∘(H⁺(aq)) ≡ 0 and C_p2^∘(H⁺(aq)) ≡ 0 and have been compared to other values reported in the literature.     

Excess enthalpy,density, and heat capacity for binary systems of alkylimidazolium-based ionic liquids + water

Experimental measurements of excess molar enthalpy, density, and isobaric molar heat capacity are presented for a set of binary systems ionic liquid + water as a function of temperature at atmospheric pressure. The studied ionic liquids are 1-butyl-3-methylpyridinium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. Excess molar enthalpy was measured at 303.15 K whereas density and heat capacity were determined within the temperature range (293.15 to 318.15) K. From experimental data, excess molar volume and excess molar isobaric heat capacity were calculated. The analysis of the excess properties reveals important differences between the studied ionic liquids which can be ascribed to their capability to form hydrogen bonds with water molecules.     

Density,speed of sound and refractive index of (n-hexane + cyclohexane + 1-hexanol) atT = 298.15 K

Densities, speeds of sound and refractive indices have been measured for (n -hexane  +  cyclohexane  +  1-hexanol) and its corresponding binaries atT =  298.15 K. In addition, ideal isentropic compressibilities were calculated from the speeds of sound, densities, and literature heat capacities and cubic expansion coefficients. The excess molar volumes and excess isentropic compressibilities, and deviations of the speed of sound and refractive index are correlated by polynomials and discussed.The Nitta–Chao model was used to estimate binary and ternary excess molar volumes, and several empirical equations were also used to calculate the excess and deviation properties.     

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 enthalpies and excess molar heat capacities of (2-butanone + cyclohexane,or methylcyclohexane,or benzene,or toluene,or chlorobenzene,or cyclohexanone) atT = 298.15 K

Excess molar enthalpies of (2- butanone  +  cyclohexane, or methylcyclohexane, or toluene, or chlorobenzene, or cyclohexanone) and excess molar heat capacities of (2- butanone  +  benzene, or toluene, or chlorobenzene, or cyclohexanone) were measured atT =  298.15 K. Aliphatic systems were endothermic and the chlorobenzene system was exothermic. On the other hand, the toluene system changed sign to be S-shaped similar to the benzene system reported by Kiyohara et al. The values of excess molar enthalpies of the present mixtures were slightly larger than the corresponding mixtures of cyclohexanone already reported. Excess molar heat capacities of aromatic systems were characteristically S-shaped for the mixture containing aromatics. The values of the present mixtures were less than the corresponding mixtures of cyclohexanone. The mixture (2-butanone  +  cyclohexanone) was endothermic forH_m^E and negative for C_p,m^E.     

Heat capacities of the mixtures of ionic liquids with acetonitrile

Isobaric specific heat capacities were measured for {1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF₄) + acetonitrile (MeCN)} and {1-methyl-3-octylimidazolium tetrafluoroborate (OMIMBF₄) + acetonitrile} within the whole range of composition and temperatures from (283.15 to 323.15) K. The excess molar heat capacities were calculated from the experimental results and satisfactorily fitted to Redlich–Kister type polynomials for several selected temperatures. Negative deviations from the additivity of molar heat capacities were observed within the whole composition range of (HMIBMF₄ + MeCN) and (OMIMBF₄ + MeCN). The results obtained have been interpreted in terms of interactions between ionic liquids and acetonitrile.     

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].     

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.     

Experiments and model for the surface tension of (MDEA + [Bmim][BF4]) and (MDEA + [Bmim][Br]) aqueous solutions

The surface tension (γ) of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]), 1-butyl-3-methylimidazolium bromide ([Bmim][Br]), (N-methyldiethanolamine(MDEA) + [Bmim][BF₄]) and (MDEA + [Bmim][Br]) aqueous solutions were measured by using the BZY-1 surface tension meter. The temperature ranged from (293.2 to 323.2) K. The mass fraction of MDEA ranged from 0.35 to 0.45. A thermodynamic equation was proposed to model the surface tension of (MDEA + ionic liquids) (ILS) aqueous solutions and the calculated results agreed well with the experiments. The effects of temperature, mass fractions of MDEA and ILS on the surface tension were demonstrated on the basis of experiments and calculations.     

Excess molar enthalpies and excess molar volumes of (an alkanol + a nitrile compound) atT = 298.15 K andp = 0.1 MPa

Excess molar enthalpies and excess molar volumes at T =  298.15 K andp =  0.1 MPa are reported for (methanol, or ethanol, or 1-propanol  +  1,4-dicyanobutane, or butanenitrile, or benzonitrile). For all the mixtures investigated in this work the excess molar enthalpy is large and positive. The excess molar enthalpy decreases as the carbon chain number of the alkanol species increases from methanol to propanol. The excess molar volumes are both positive and negative. The Extended Real Associated Solution and the Flory–Benson–Treszczanowicz models were used to represent the data. Both these models describe better the excess molar enthalpy than the excess molar volumes of (an alkanol  +  a nitrile compound).     

The partial molar heat capacities of glycine and glycylglycine in aqueous solution at elevated temperatures and atp = 10.0 MPa

Apparent molar heat capacities have been determined for aqueous solutions of glycine at temperatures from 352.09 K to 470.63 K and glycylglycine at temperatures from 352.09 K to 423.15 K. Both systems were investigated at a pressure of 10.0 MPa. Measurements were performed with a differential flow calorimeter that is capable of operation at temperatures  > 723 K and pressures to approximately 40.0 MPa. Partial molar heat capacities at infinite dilution have been calculated from apparent molar values and have been corrected for “relaxation" contributions. The reported partial molar heat capacity values for aqueous glycine and glycylglycine solutions have been modelled using the revised Helgeson, Kirkham, and Flowers semi-empirical equations of state. These models for solutions of glycine and glycylglycine in water have been compared with those previously reported in the literature.     

Excess molar properties for binary systems of alkylimidazolium-based ionic liquids + nitromethane. Experimental results and ERAS-model calculations

Density, isobaric molar heat capacity, and excess molar enthalpy were experimentally determined at atmospheric pressure for a set of binary systems ionic liquid + nitromethane. The studied ionic liquids were: 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylpyridinium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium trifluoromethanesulfonate. Density and heat capacity were obtained within the temperature range (293.15 to 318.15) K whereas excess molar enthalpy was measured at 303.15 K; excess molar volume and excess molar isobaric heat capacity were calculated from experimental data. The ERAS-model was applied in order to study the microscopic mechanisms involved in the mixing process. Although the studied compounds are not self-associated, ERAS-model describe adequately the experimental results if cross-association between both compounds is considered.     

Molar heat capacities of some aqueous (2-amino-2-hydroxymethyl-1,3-propanediol + glycol) systems

A new set of molar heat capacity data for aqueous {2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) + glycol} at (30 to 80) °C and different concentrations (4% to 16% by weight TRIS or 56% to 44% by weight water, in a fixed amount of glycol – 40% by weight) were gathered via reliable measurement method and are presented in this report. The glycols considered were diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (T₄EG), propylene glycol (PG), dipropylene glycol (DPG), and tripropylene glycol (TPG). The 198 data points gathered fit the equation, C_p = C_p,a + B₁m + B₂m² + B₃m³, where C_p and C_p,a are the molar heat capacities of the (TRIS + glycol + water) and (water + glycol) systems, respectively, B_i the temperature-dependent parameters, and m the mole TRIS per kilogram (glycol + water). The overall average absolute deviation (AAD) of the experimental data from the corresponding values calculated from the correlation equation was 0.07%.