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.     

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.     

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.     

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.     

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.     

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.     

Apparent molar volumes and apparent molar heat capacities of aqueous magnesium nitrate,strontium nitrate,and manganese nitrate at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar volumes V_ϕ and apparent molar heat capacities C_p,ϕ were determined at the pressure 0.35 MPa for aqueous solutions of magnesium nitrate Mg(NO₃)₂ at molalities m = (0.02 to 1.0) mol · kg⁻¹, strontium nitrate Sr(NO₃)₂ at m = (0.05 to 3.0) mol · kg⁻¹, and manganese nitrate Mn(NO₃)₂ at m = (0.01 to 0.5) mol · kg⁻¹. Our V_ϕ values were calculated from solution densities obtained at T = (278.15 to 368.15) K using a vibrating-tube densimeter, and our C_p,ϕ values were calculated from solution heat capacities obtained at T = (278.15 to 393.15) K using a twin fixed-cell, differential, temperature-scanning calorimeter. Empirical functions of m and T were fitted to our results, and standard state partial molar volumes and heat capacities were obtained over the ranges of T investigated.     

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.     

The standard molar enthalpy of formation,molar heat capacities,and thermal stability of anhydrous caffeine

The constant-volume energy of combustion of crystalline anhydrous caffeine (C₈H₁₀N₄O₂) in α (lower temperature steady) crystal form was measured by a bomb combustion calorimeter, the standard molar enthalpy of combustion of caffeine at T = 298.15 K was determined to be −(4255.08 ± 4.30) kJ · mol⁻¹, and the standard molar enthalpy of formation was derived as −(322.15 ± 4.80) kJ · mol⁻¹. The heat capacity of caffeine in the same crystal form was measured in the temperature range from (80 to 387) K by an adiabatic calorimeter. No phase transition or thermal anomaly was observed in the above temperature range. The thermal behavior of the compound was further examined by thermogravimetry (TG), differential thermal analysis (DTA) over the range from (300 to 700) K and by differential scanning calorimetry (DSC) over the range from (300 to 540) K, respectively. From the above thermal analysis a (solid–solid) and a (solid–liquid) phase transition of the compound were found at T = (413.39 and 509.00) K, respectively; and the corresponding molar enthalpies of these transitions were determined to be (3.43 ± 0.02) kJ · mol⁻¹for the (solid–solid) transition, and (19.86 ± 0.03) kJ · mol⁻¹ for the (solid–liquid) transition, respectively.     

Apparent molar volumes and apparent molar heat capacities of aqueous solutions of isomeric butanols at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar heat capacities C_{p, φ}and apparent molar volumesV_φ were determined for aqueous solutions of 1-butanol, 2-butanol (both R andS isomers), isobutanol (2-methyl-1-propanol), and t -butanol (2-methyl-2-propanol) at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa. The molalities investigated ranged from 0.02 mol · kg ^− 1to 0.5 mol · kg ^− 1. We used a vibrating-tube densimeter (DMA 512P, Anton Paar, Austria) to determine the densities and volumetric properties. Heat capacities were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Provo, UT, U.S.A.). The results were fit by regression to equations that describe the surfaces (V_φ, T, m) and (C_p,φ, T, m). Infinite dilution partial molar volumesV₂^o and heat capacities C_p,2^owere obtained over the range of temperatures by extrapolation of these surfaces to m =  0.     

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.     

Apparent molar volumes and apparent molar heat capacities of aqueous solutions ofN,N- dimethylformamide andN,N- dimethylacetamide at temperatures from 278.15 to 393.15 K and at the pressure 0.35 MPa

Apparent molar heat capacities C_{p, φ}and apparent molar volumesV_φ were determined for aqueous solutions of N, N - dimethylformamide andN , N - dimethylacetamide at temperatures from 278.15 to 393.15 K and at the pressure 0.35 MPa. The molalities investigated ranged from 0.015 mol ·kg ^− 1to 1.0 mol · kg ^− 1. We used a vibrating-tube densimeter (DMA 512P, Anton PAAR, Austria) to determine the densities and volumetric properties. Heat capacities were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, U.S.A.). The results were fit by regression to equations that describe the surfaces (V_φ,T , m) and (C_{p, φ}, T, m). Infinite dilution partial molar volumes V₂^oand heat capacitiesC_p,2^o were obtained over the range of temperatures by extrapolation of these surfaces to m =  0.     

Apparent molar volumes and apparent molar heat capacities of aqueous tetrahydrofuran,dimethyl sulfoxide, 1,4-dioxane,and 1,2-dimethoxyethane at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

We determined apparent molar volumes V_? at 278.15 ? (T/K) ? 368.15 and apparent molar heat capacities C_p,? at 278.15 ? (T/K) ? 393.15 at p = 0.35 MPa for aqueous solutions of tetrahydrofuran at m from (0.016 to 2.5) mol · kg^?1, dimethyl sulfoxide at m from (0.02 to 3.0) mol · kg^?1, 1,4-dioxane at m from (0.015 to 2.0) mol · kg^?1, and 1,2-dimethoxyethane at m from (0.01 to 2.0) mol · kg^?1. Values of V_? were determined from densities measured with a vibrating-tube densimeter, and values of C_p,? were determined with a twin fixed-cell, differential, temperature-scanning calorimeter. Empirical functions of m and T for each compound were fitted to our V_? and C_p,? results.     

Apparent molar volumes and apparent molar heat capacities of aqueous lead nitrate at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar volumes V_φ and apparent molar heat capacities C_p,φ were determined for aqueous solutions of lead nitrate [Pb(NO₃)₂] at m=(0.02 to 0.5) mol · kg⁻¹, at T=(278.15 to 393.15) K, and at the pressure 0.35 MPa. Our V_φ values were calculated from densities obtained using a vibrating-tube densimeter, and our C_p,φ values were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter. Our results were fitted to functions of m and T and compared with results from the literature.     

Apparent molar volumes and apparent molar heat capacities of aqueous adonitol,dulcitol, glycerol,meso-erythritol,myo-inositol,d-sorbitol,and xylitol at temperatures from (278.15 to 368.15) K and at the pressure 0.35 MPa

Apparent molar volumes V_ϕ were determined for aqueous adonitol, dulcitol, glycerol, meso-erythritol, myo-inositol, d-sorbitol, and xylitol at temperatures from (278.15 to 368.15) K and at the pressure 0.35 MPa, and apparent molar heat capacities C_p,ϕ of the same solutions were determined at temperatures from (278.15 to 363.15) K at the same pressure. Molalities m/(mol · kg⁻¹) of the solutions were in the range (0.02 ⩽ m ⩽ 3.2) for adonitol, (0.02 ⩽ m ⩽ 0.15) for dulcitol, (0.02 ⩽ m ⩽ 5.0) for glycerol, (0.02 ⩽ m ⩽ 3.0) for meso-erythritol, (0.02 ⩽ m ⩽ 0.5) for myo-inositol, (0.02 ⩽ m ⩽ 2.0) for d-sorbitol, and (0.02 ⩽ m ⩽ 2.7) for xylitol. A vibrating tube densimeter was used to obtain solution densities and a fixed-cell temperature scanning calorimeter was used to obtain heat capacities. Values of V_ϕ and C_p,ϕ for these sugar alcohols are discussed relative to one another and compared to values from the literature, where available.     

Apparent molar volumes and apparent molar heat capacities of aqueous barium nitrate at temperatures from (278.15 to 393.15) K and at the pressure 0.35 MPa

Apparent molar volumes V_φ and apparent molar heat capacities C_p,φ were determined for aqueous solutions of barium nitrate Ba(NO₃)₂ at molalities m=(0.0025 to 0.2) mol · kg⁻¹, at T=(278.15 to 393.15) K, and at the pressure 0.35 MPa. Our V_φ values were calculated from densities obtained using a vibrating-tube densimeter, and our C_p,φ values were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter. Our results were fitted to functions of m and T and compared with values from the literature.     

Apparent molar volumes and apparent molar heat capacities of aqueous urea, 1,1-dimethylurea,and N,N′-dimethylurea at temperatures from (278.15 to 348.15) K and at the pressure 0.35 MPa

Apparent molar volumes V_ϕ and apparent molar heat capacities C_p,ϕ were determined for aqueous solutions of urea, 1,1-dimethylurea, and N,N′-dimethylurea. Measurements were made at molalities m = (0.02 to 6.0) mol · kg⁻¹ for urea, at m = (0.01 to 1.6) mol · kg⁻¹ for 1,1-dimethylurea, and at m = (0.01 to 8.0) mol · kg⁻¹ for N,N′-dimethylurea. Experimental temperatures ranged from (278.15 to 318.15) K for both urea and 1,1-dimethylurea, and from (278.15 to 348.15) K for N,N′-dimethylurea. All measurements were conducted at the pressure p = 0.35 MPa. Density measurements obtained with a vibrating-tube densimeter were used to calculate V_ϕ values. Heat capacity measurements obtained with a twin fixed-cell differential temperature-scanning calorimeter were used to calculate C_p,ϕ values. Functions of m and T were fitted to the results and were compared with the literature values. The “structure making/structure breaking” aspects of urea in water are discussed. Comparisons are made between the different urea compounds, and the effects of the methyl-group additions are outlined.     

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.     

Partial molar heat capacities and volumes of transfer of some saccharides from water to aqueous sodium chloride solutions at T=298.15 K

Partial molar heat capacities (C^o_p,2,m) and volumes (V^o_2,m) of seven monosaccharides, namely, d(−)-ribose, d(−)-arabinose, d(+)-xylose, d(+)-glucose, d(+)-mannose, d(+)-galactose, and d(−)-fructose; five disaccharides, namely, sucrose, d(+)-cellobiose, d(+)-maltose monohydrate, d(+)-lactose monohydrate, d(+)-trehalose dihydrate, and one trisaccharide, d(+)-raffinose pentahydrate, have been determined in NaCl(aq), m = (1.0, 2.0, and 3.0) mol·kg⁻¹ at T=298.15 K from volumic heat capacity and density measurements employing a Picker flow microcalorimeter and a vibrating-tube densimeter, respectively. These data were combined with the earlier reported C^o_p,2,m and V^o_2,m values in water to calculate the corresponding partial molar properties of transfer (Δ_trC^o_p,2,m and Δ_trV^o_2,m) from water to aqueous sodium chloride solutions at infinite dilution. These transfer parameters are positive, and the values increase with the concentration of sodium chloride for all the saccharides. Transfer parameters have been discussed in terms of solute-cosolute interactions on the basis of a cosphere overlap model. Pair and higher-order interaction coefficients have also been calculated from transfer parameters.     

Thermodynamic characterization of the mixture (1-butanol + iso-octane): Densities,viscosities, and isobaric heat capacities at high pressures

The densities at high pressures of 1-butanol and iso-octane were measured in the range (0.1 to 140) MPa at seven different temperatures, from (273.15 to 333.15) K, and their mixtures were measured in the range (0.1 to 50) MPa at four different temperatures, from (273.15 to 333.15) K. The measurements were performed in a high-pressure vibrating tube densimeter. The pressure–volume–temperature behavior of these compounds and their mixtures was evaluated accurately over a wide range of temperatures and pressures. The data were successfully correlated with the empirical Tamman–Tait equation. The experimental data and the correlations were used to study the behavior and the influence of temperature and pressure on the isothermal compressibility and the isobaric thermal expansivity.Also, the isobaric heat capacities were measured over the range (0.1 to 25) MPa at two different temperatures (293.15 and 313.15) K for the pure compounds and their mixtures. The measurements were performed in a high-pressure automated flow calorimeter. The excess molar heat capacities were assessed for the mixture and a positive deviation from the ideality was obtained.