Isobaric Molar Heat Capacities Research Articles

Thermodynamic Evaluation of Novel 1,2,4-Triazolium Alanine Ionic Liquids as Sustainable Heat-Transfer Media

Ionic liquids, which are widely recognized as environmentally friendly solvents, stand out as promising alternatives to traditional heat-transfer fluids due to their outstanding heat-storage and heat-transfer capabilities. In the course of our ongoing research, we successfully synthesized ionic liquids 1-ethyl-4-alkyl-1,2,4-triazolium alanine [Taz(2,n)][Ala], where (n = 4, 5); in this study, we present comprehensive data on their density, surface tension, isobaric molar heat capacity, and thermal conductivity for the first time. The key thermophysical parameters influencing the heat-transfer process, such as thermal expansibility, compressibility, isochoric heat capacity, and heat-storage density, were meticulously calculated from experimental data. Upon comparison with previously reported ionic liquids and commercially utilized heat-transfer fluids, [Taz(2,n)][Ala] demonstrated superior heat-storage and heat-transfer performance, particularly in terms of heat-storage density (~2.63 MJ·m−3·K−1), thermal conductivity (~0.190 W·m−1·K−1), and melting temperature (~226 K). Additionally, the presence of the alanine anion in [Taz(2,n)][Ala] provides more possibilities for its functional application.

Geraniol and hydrophobic geraniol:thymol eutectic mixtures: Structure and thermophysical characterization

The properties of essential oils as food preservatives are well-established. These components have also been used as neoteric solvents to prepare eutectic mixtures. Their high capacity to dissolve poorly water-soluble substances makes them particularly interesting in the biotechnology industry. To implement them, it is essential to determine the structural and chemical-physical properties, as well as develop models to predict the behaviour under any operational condition. Herein, pure geraniol and geraniol/thymol mixtures are studied. Nuclear magnetic resonance experiments and molecular dynamics are used to evaluate the fluid structure. In addition, seven thermophysical properties are measured and correlated. The experimental densities, surface tensions, and viscosities were lower than 952 kg m–3, 33 mN m–1, and 36 mPa s, respectively. These values were adequate for the industrial application of these mixtures. PC-SAFT equation of state well predicted the density with an average deviation of 0.13 %, and the isobaric molar heat capacity with a deviation of 6.9 %. Greater compaction was observed at higher thymol molar ratios and dispersive interactions were predominant. Depending on the composition, geraniol was both an acceptor and donor of hydrogen bonds; conversely, thymol acted as a donor. The article provides the necessary knowledge to be able to use these mixtures and design new ones, as ecological solvents in different applications including those in the agri-food sector.

Thermomagnetic Models for the Improved Rosen–Morse Oscillator

ABSTRACTThis study solves the radial Schrödinger wave equation (RSWE) with the improved Rosen–Morse (IRM) potential constrained by an electromagnetic field. Energy eigenvalues are derived using the parametric Nikiforov–Uvarov method and Pekeris approximation. The internal partition function, isobaric molar heat capacity formula, and magnetization model are then deduced from the equation governing pure vibrational energy states. These analytical models are applied to several pure substances, specifically Br2 (X 1Σg+), BrF (X 1Σ+), ICl (X 1Σg+), and P2 (X 1Σg+) molecules. Numerical approximations of the energy eigenvalues for these molecules closely match their exact values. The isobaric molar heat capacity expression yields mean percentage absolute deviations of 1.6585%, 0.9162%, 1.2193%, and 0.7232% when compared against experimental data for Br2 (X 1Σg+), BrF (X 1Σ+), ICl (X 1Σg+), and P2 (X 1Σg+), respectively. These results align well with other heat capacity models in existing literature.

Experimental Investigation on the Isobaric Molar Heat Capacities of [EMIM][BF4] and [HMIM][Tf2N] with Dissolved R32 or R125

Experimental Investigation on the Isobaric Molar Heat Capacities of [EMIM][BF₄] and [HMIM][Tf₂N] with Dissolved <i>R</i>32 or R125

Effect of alkyl chain length on the thermal properties and toxicity of n-alkyl-ammonium nitrate ionic liquids (n = 2, 3, 4, 5, 6, 8) for energy applications

AbstractThe most currently used ionic liquids (ILs) are protic ionic liquids (PILs), subject to extensive investigation regarding their physical properties. These compounds along with their mixtures with other substances such as salts and solvents, serve as electrolytes in next generation electrochemical smart devices, and emerge as viable candidates to replace conventional Heat Transfer Fluids (HTFs) in various energy applications. Despite the extensive number of studies, important information about this kind of compounds is still unknown, such as the effect of alkyl chain length on thermal and thermophysical properties, as well as toxicity. This work, extending previous studies of our group, summarizes the liquid range, heat capacity and acute toxicity level of six ammonium ILs: specifically, n-alkyl-ammonium nitrate ILs with increasing alkyl chain length (n = 2, 3, 4, 5, 6, 8). For this study, the synthesis of the three ILs with the longest alkyl chain was performed, along with DSC, TGA and toxicity measurements. It was observed that an increase in alkyl chain length resulted in a decrease in short-term thermal stability and an increase in melting temperature, indicating a reduction in the liquid range. A compensation effect between enthalpy and entropy of melting was observed for the studied chain lengths. The isobaric specific and molar heat capacities increase with temperature for all the compounds studied here, and good correlations were obtained between molar heat capacity and the number of carbon atoms in the alkyl chain for every temperature. Finally, most of the ILs are non-toxic, although toxicity increases with alkyl chain length.

Characterization of camphor: thymol or dl-menthol eutectic mixtures; Structure, thermophysical properties, and lidocaine solubility

The low solubility of drugs in aqueous media is a major problem for the pharmaceutical industry. Among the solutions proposed, the use of eutectic mixtures can be highlighted. In them, the components used can also increase the therapeutic advantages of the active principle. In this work, we analyzed the solubility of lidocaine in mixtures of camphor + thymol or dl-menthol. These binary eutectic solvents were also characterized. For all this, several NMR techniques were used and different thermophysical properties (density, speed of sound, refraction index, isobaric molar heat capacity, surface tension, and kinematic viscosity) were measured. The results indicated that the interaction of camphor with thymol was stronger than with dl-menthol, providing a more compact fluid. On the contrary, the steric hindrance was greater in the mixture with dl-menthol, giving rise to a more viscous liquid. Furthermore, the lidocaine was significantly more soluble (up to 540 times) in these mixtures than in water. The lidocaine showed the strongest interactions with thymol molecules, somewhat weaker with dl-menthol, and the weakest were with camphor ones.

Bound-state energy spectrum and thermochemical functions of the deformed Schiöberg oscillator

In this study, a diatomic molecule interacting potential such as the deformed Schiöberg oscillator (DSO) have been applied to diatomic systems. By solving the Schrödinger equation with the DSO, analytical equations for energy eigenvalues, molar entropy, molar enthalpy, molar Gibbs free energy and constant pressure molar heat capacity are obtained. The obtained equations were used to analyze the physical properties of diatomic molecules. With the aid of the DSO, the percentage average absolute deviation (PAAD) of computed data from the experimental data of the 7Li2 (2 3Πg), NaBr (X 1Σ+), KBr (X 1Σ+) and KRb (B 1Π) molecules are 1.3319%, 0.2108%, 0.2359% and 0.8841%, respectively. The PAAD values obtained by employing the equations of molar entropy, scaled molar enthalpy, scaled molar Gibbs free energy and isobaric molar heat capacity are 1.2919%, 1.5639%, 1.5957% and 2.4041%, respectively, from the experimental data of the KBr (X 1Σ+) molecule. The results for the potential energies, bound-state energy spectra, and thermodynamic functions are in good agreement with the literature on diatomic molecules.

The investigation of crystal structure, thermodynamic properties, and fluorescence properties of three new rare earth coordination compounds

Three new rare earth coordination compounds [REL3Ph]2(RE = Pr(1), Sm(2)); [ErL3Ph]2·4C2H5OH(3); (L = 2,6-dimethylbenzoate, Ph = o-phenanthroline) were synthesized. The crystal structures of the three compounds were measured by X-ray single-crystal diffraction. From the results, we made out that compounds 1–3 were binuclear structures, and 1D chain-like structures could be formed by hydrogen bonding. The thermal degradation data of the compounds and the three-dimentional infrared cumulative spectra of the gaseous decomposed products were obtained by TG/DSC-FTIR technique, and the thermal degradation patterns were explained. The isobaric molar heat capacity of compounds 1 and 2 in the low-temperature region was obtained by the DSC technique and the thermodynamic parameters were derived. The fluorescence spectrum of compound 2 was determined, showing that it had potential application value in the orange-red luminescence region.

Deep Eutectic Solvents Formed by Glycerol and Xylitol, Fructose and Sorbitol: Effect of the Different Sugars in Their Physicochemical Properties.

The search for new eutectic solvents for different applications (extraction, drug formulation, chemical reactions, etc.) is booming thanks to their high solubility capacity and low toxicity. However, it is necessary to carry out a comprehensive physicochemical characterization of these mixtures to understand the molecular behavior at different experimental conditions. In this study, three deep eutectic solvents (DESs) formed by glycerol and xylitol, fructose and sorbitol and water in the molar ratio 1:2:3 were prepared and several physicochemical properties (refractive index, density, surface tension, viscosity, speed of sound, isobaric heat capacity and isentropic compressibility) were measured and analyzed in the 278.15-338.15 K temperature range. The results indicate a linear dependence with temperature for the following properties: surface tension, refractive index, density and isobaric molar heat capacity while viscosity values have been fitted to the Vogel-Fulcher-Tammann equation.

Thermodynamic and Thermal Analyze of N,N-Dimethylformamide + 1-Butanol Mixture Properties Based on Density, Sound Velocity and Heat Capacity Data.

The present paper contains data on the density (ρ), sound velocity (u), and specific heat capacity cp of the mixture of N,N-dimethylformamide + 1-butanol (DMF + BuOH) determined in the entire concentration range of solution and in the temperature range (293.15-318.15) K. The analysis of thermodynamic functions such as isobaric molar expansion, isentropic and isothermal molar compression, isobaric and isochoric molar heat capacity, as well as their excess functions (Ep,mE,KS,mE,KT,mE,Cp, mE,CV, mE) and also VmE was undertaken. The analysis of changes in the physicochemical quantities was based on consideration of the system in terms of intermolecular interactions and resulting changes in the mixture structure. The results available in the literature were confusing during the analysis and became the reason for our decision to thoroughly examine the system. What is more, for a system whose components are widely used, there is very scarce information in the literature regarding the heat capacity of the tested mixture, which was also achieved and presented in this publication. The conclusions drawn from so many data points allow us to approximate and understand the changes that occur in the structure of the system due to the repeatability and consistency of the obtained results.

On the interpretation of the unusual behavior of aqueous-organic mixtures in concentration regions with intersecting isotherms of heat capacity properties

Based on our own and some literature results, we have carried out a detailed analysis of concentration regions of the aqueous-organic mixture in which the temperature dependences of both excess molar heat capacity, CpE, and apparent molar heat capacity of each component, Cp,ϕ,i, are intersected. It is established that the ∂CpE/∂T and ∂Cp,ϕ,w/∂Tderivatives (W is water) for the {(W + hexamethylphosphoramide (HMPA)} and {(W + tert‑butanol (t-BuOH)} mixtures intersect in a rather narrow concentration interval between (0.30 and 0.35) and (0.35 and 0.40) mole fractions of the organic component, respectively. This fact we have interpreted as evidence that the decisive role in the mutually overlapping heat-capacity contributions to CpEresulting in such a situation plays the abnormal change in the isobaric molar heat capacity of W (Cp,w), which has a minimum at T ≈ 308 K, when the temperature increases.

Isobaric molar heat capacity model for the improved Tietz potential

AbstractIn this study, the improved Tietz potential was used to describe the internal vibration of diatomic molecules. By employing the expression for upper bound vibrational quantum number and canonical partition function of the system, equation for the prediction of constant pressure (isobaric) molar heat capacity of diatomic molecules was derived. The analytical model was used to predict the isobaric molar heat capacity of the ground state CO, BBr, HBr, HI, P2, KBr, Br2, PBr, SiO, and Cl2 molecules. The upper bound vibrational quantum number obtained for the molecules are 85, 100, 21, 21, 115, 301, 89, 157, 110, and 67. The calculated average absolute deviations are 2.3462%, 1.1342%, 2.3350%, 1.9078%, 0.7268%, 2.4041%, 1.7849%, 1.8989%, 2.5209%, and 2.1523% from experimental data. The results obtained are in good agreement with available literature data on gaseous molecules.

Study on the volatility of four benzaldehydes

This work reports the experimental determination of relevant thermodynamic properties of four benzaldehydes. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of syringaldehyde, 3,4,5-trimethoxybenzaldehyde, 4-(dimethylamino)benzaldehyde and of the liquid phase of veratraldehyde were determined using a static method based on capacitance diaphragm manometers. Additionally, the sublimation vapor pressures of the four compounds were also determined at different temperatures, using the Knudsen mass-loss effusion method. The experimental results allowed accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization for the benzaldehydes studied, at reference temperatures, allowing phase diagram representations of the (p,T) results, in the neighborhood of the triple point of the four compounds. Their temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the ones obtained indirectly through vapor pressure measurements. Using high-precision drop calorimetry, the standard isobaric molar heat capacities of the four crystalline benzaldehydes were determined at 298.15 K. The enthalpy of the intermolecular hydrogen bond OH…O in the crystalline phase of syringaldehyde was estimated.

Measurement and correlation of isobaric molar heat capacities of deep eutectic solvents consisting of choline chloride and triethylene glycol

Deep eutectic solvents are environmentally friendly substitutes to room temperature ionic liquids in broad engineering applications like biofuel purification, polymer synthesis, gas capture, and organic extraction. In this work, the isobaric molar heat capacities of deep eutectic solvents consisting of choline chloride and triethylene glycol (in molar ratio of 1: 3, 1: 4, and 1: 5) are investigated by flow method in the temperature from 334.91 K to 364.98 K and pressure from 0.19 MPa to 25.21 MPa. The relative expended uncertainty of measurement system is calculated to be 1.4 % within 95 % degree of confidence. Experimental results show that the isobaric molar heat capacity increases linearly with higher temperature and lower pressure. With choline chloride added in triethylene glycol, the heat capacity decreases linearly with the decreasing of triethylene glycol molar fraction. Finally, the correlation of these binary mixtures is established based on the experimental data with the maximum absolute relative deviation and average absolute relative deviation of 1.01 % and 0.31 %, respectively.

Heat capacity of six glymes in N,N-dimethylformamide + water mixtures. Solvation of glymes

The paper presents the heat capacities of glyme solutions: monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme, in binary solvents N,N-dimethylformamide + water at four temperatures (293.15 K, 298.15 K, 303.15 K, 308.15 K) obtained using differential calorimeter Micro DSC III, Setaram – France. The concentration of glymes was approximately 0.25 mol/kg. On the basis of the obtained experimental results, the apparent isobaric heat capacities of the glymes were calculated. It was noted that the larger the glyme molecule was, the more pronounced the increase in the value of the apparent molar heat capacity function with the increase in water content in the two-component solvent. The observed changes in apparent isobaric heat capacity as a function of the water content in the mixed solvent are discussed in terms of the hydrophobic nature of the glymes. Moreover, it was shown that the apparent molar isobaric heat capacity of the glymes in pure solvents, i.e. in water and in N,N-dimethylformamide, increases linearly with the increase in the number of oxygen atoms in the glyme molecules i.e. with the size of glyme molecules. Furthermore, a linear correlation was observed between the apparent isobaric molar heat capacity and the enthalpic effect of the hydrophobic hydration of the studied glymes at 298.15 K. The results obtained in this paper are compare with the same obtained for selected cyclic ethers.

Isobaric molar heat capacities of dimethyl carbonate and alkane binary mixtures at high pressures

Isobaric molar heat capacities of dimethyl carbonate and alkane binary mixtures at high pressures

Thermophysical characterization of choline chloride: Resorcinol and its mixtures with water

The study of deep eutectic solvents has increased in recent years. This is because of their great solubility ability and lower toxicity than usual organic solvents. In this work, deep eutectic solvents formed by choline chloride and resorcinol in the mole ratio 1:2 and its mixtures with water, e.g., choline chloride:resorcinol:water 1:2:1.05 (water mass fraction = 0.05) and choline chloride:resorcinol:water 1:2:2.22 (water mass fraction = 0.1), have been studied. Several physicochemical properties (density, speed of sound, isentropic compressibility, refractive index, surface tension, isobaric molar heat capacity, viscosity, and electrical conductivity) have been obtained and analysed at atmospheric pressure in the range of 283.15–338.15 K. The starting temperature for the speed of sound measurements was 308.15 K. The effects of temperature and water inclusion have been evaluated. The obtained results have shown a linear correlation between density, speed of sound, refractive index, surface tension and isobaric molar heat capacity and temperature. Additionally, the viscosity and electrical conductivity data can be adjusted using the Vogel-Fulcher-Tammann equation. Finally, the inclusion of water was analysed to check how the thermophysical properties were modified. These modifications had greater effects on transport properties, viscosity and electrical conductivity.

Isobaric Molar Heat Capacities of Binary Mixtures of Diethyl Carbonate and Methyl Caprate at High Pressures

Isobaric Molar Heat Capacities of Binary Mixtures of Diethyl Carbonate and Methyl Caprate at High Pressures

Thermophysical Study of Pyridinium-Based Ionic Liquids Sharing Ions.

The thermophysical properties of three pyridinium-based ionic liquids sharing ions were measured at several temperatures (278.15-338.15) K and at atmospheric pressure (0.1 MPa). Three ionic liquids were studied: 1-butylpyridinium bis(trifluoromethyl-sulfonyl)imide, 1-hexylpyridinium bis(trifluoromethylsulfonyl)imide, and 1-hexylpyridinium tetrafluoroborate. The following thermophysical properties were measured: density, speed of sound, refractive index, surface tension, isobaric molar heat capacity, kinematic viscosity, and electrical conductivity. The thermophysical properties at atmospheric pressure were correlated with temperature, noting that the starting temperature for the speed of sound measurements depended on the ionic liquid. From these experimental results, some derived properties (isentropic compressibility, molar refraction, and dynamic viscosity) are calculated. These results together with those published previously for 1-butylpyridinium tetrafluoroborate are discussed.

Molar heat capacity of liquid Ti, Al20Ti80 and Al50Ti50 measured in electromagnetic levitation

Temperature dependent isobaric molar heat capacity cP was measured in a containerless way for liquid Ti and two AlTi binary liquid alloys. The technique of electromagnetic levitation was used in combination with laser modulation calorimetry. In all cases, linear temperature dependencies were found: At the corresponding liquidus temperatures, cP equals 49.75(±2.0) J∙K-1mol-1, 57.43(±2.9) J∙K-1mol-1, and 42.60(±2.2) J∙K-1mol-1, for Ti, Al20Ti80 and Al50Ti50, respectively. The respective temperature coefficients amount to -1.67∙10-2J∙K-2mol-1, -2.73∙10-2J∙K-2mol-1, and +7.83∙10-2J∙K-2mol-1. For liquid Ti, there is a good agreement with existing literature data. The results are discussed in relation to the Neumann-Kopp rule.