Enthalpies Of Dilution Research Articles

Tuning Wetting-Dewetting Thermomechanical Energy for Hydrophobic Nanopores via Preferential Intrusion.

Heat and the work of compression/decompression are among the basic properties of thermodynamic systems. Being relevant to many industrial and natural processes, this thermomechanical energy is challenging to tune due to fundamental boundaries for simple fluids. Here via direct experimental and atomistic observations, we demonstrate, for fluids consisting of nanoporous material and a liquid, one can overcome these limitations and noticeably affect both thermal and mechanical energies of compression/decompression exploiting preferential intrusion of water from aqueous solutions into subnanometer pores. We hypothesize that this effect is due to the enthalpy of dilution manifesting itself as the aqueous solution concentrates upon the preferential intrusion of pure water into pores. We suggest this genuinely subnanoscale phenomenon can be potentially a strategy for controlling the thermomechanical energy of microporous liquids and tuning the wetting/dewetting heat of nanopores relevant to a variety of natural and technological processes spanning from biomedical applications to oil-extraction and renewable energy.

PH dependent physicochemical signatures of amino acids in aqueous buffers: Thermodynamic analysis

The physicochemical signatures such as apparent molar volume (V2,Φ), isoentropic compressibilities (KS,2,φ), and dilution enthalpies of a series of amino acids (AAs) glycine (Gly), L-alanine (Ala), DL-α-amino-n-butyric acid (ABA), L-valine (Val) and L-leucine (Leu) have been measured at various pH values (pH = 2, 5 7 and 9) at a buffer molality of 0.1 mol kg−1 of water at 298.15 K. The data obtained from high sensitivity densimeter and sound analyser along with ultrasensitive isothermal titration calorimetry has been analyzed to evaluate the values of standard partial molar quantities such as for volume at infinite dilution (V2,m0), compressibility KS, 2,m0 and dilution enthalpy (ΔdilH0) of the AAs together with standard partial molar quantities of transfer of these solutes from water to aqueous buffer systems at these pH values. The linear correlation of V2,m0 for this series of AAs against number of carbon atoms in their alkyl chain has been used to evaluate the contribution of zwitterionic end groups (NH3+, COO–), the CH2 group, and other parts of alkyl chains of the AAs to the overall value of V2,m0. The results of standard partial molar transfer properties on volumes, compressibilities and enthalpies of dilution from water to aqueous buffer systems at various pH values have been connected and explained in terms of ion-polar, ion-hydrophilic, hydrophobic-hydrophobic and ion-hydrophobic interactions of the participating groups. These thermodynamic signatures when compared at different pH values suggest that at electrostriction of water dominates at pH 2. Such physicochemical properties of constituents of proteins such as amino acids have not been reported earlier. Thus, the results demonstrate that the interaction of individual amino acid residues with the buffer components does not lead to significant change in their physicochemical properties thereby permitting their use in obtaining mechanistic insights into systems of biological interest consisting of these constituents.

Modeling of dilution enthalpies within implicit-solvent models for electrolytes

This work deals with the calculation of dilution enthalpies for strong aqueous electrolyte solutions when their thermodynamic properties are described within implicit-solvent models. The solution is modeled as a collection of charged hard spheres in a continuum solvent. A new general expression is obtained that accounts for the variation of the solution permittivity, of the size of the ions, and of the specific volume of the solution, with temperature and concentration. This expression is used to compute the enthalpies of LiCl aqueous solutions at temperatures in the range of 25∘C to 100∘C for concentrations up to 6 mol kg−1. The mean spherical approximation (MSA) model with implicit continuum solvent is employed to describe the thermodynamic properties of these solutions.

Thermodynamics of the ion association of potassium cobalt(III) bis(1,2-dicarbollide) in acetonitrile, methanol and dimethyl sulfoxide

The molar conductivities, Λ, of dilute solutions of potassium cobalt(III) bis(1,2-dicarbollide) (K[COSAN]) in methanol (MeOH), acetonitrile (MeCN) and dimethyl sulfoxide (DMSO) were determined at different temperature ranges. The data were analysed in the frame of Barthel’s low-concentration chemical model (lcCM) to obtain the limiting molar conductivities,Λ∞, and standard association constants, KAo, of K[COSAN]. To confirm the ion association of oppositely charged ions K+ and [COSAN]–, molecular dynamics (MD) simulations were performed, in which the values of KAo from the potential of the mean force between the pair of particles (ions) were determined. From temperature dependence of KAo, the thermodynamic parameters for ion association, namely standard free enthalpy ΔGAo, enthalpy ΔHAo, and entropy ΔSAo, were estimated. The dilution enthalpies of concentrated solutions of K[COSAN] in organic solvents were also determined by using isothermal titration calorimetry (ITC). Our experimental results show that K+ and [COSAN]– ions form ion pairs in all the investigated solvents. Ion association is most pronounced in MeOH and MeCN and the least expressed in DMSO, the process is endothermic and is accompanied by an increase in entropy. The agreement between the calculated values of KAo and the thermodynamic parameters obtained by conductivity and MD simulations follow the same trend.

Dilution enthalpies of the binary systems (LiBO2 + H2O) and (LiB5O8 + H2O) and the ion interactions at 308.15 K

Microcalorimeter measured the dilution enthalpies of the binary systems (LiBO2 + H2O) and (LiB5O8 + H2O) at 308.15 K and 0.1 MPa. Based on the Pitzer theory of electrolytes, their apparent molar enthalpies and the Pitzer single electrolyte parameters at 308.15 K were carried out by fitting the experimental data for the first time. Moreover, the calculated apparent molar enthalpies of LiBO2 and LiB5O8 aqueous solution according to the Pitzer ion-interaction model were consistent well with the experimental values, manifesting the high reliability of this study.

Phase Equilibria and Thermodynamic Properties of Phases in the H2O–Gd(NO3)3 System

Solid–liquid equilibria in the system H2O–Gd(NO3)3 were measured from –20 to 70°C using the isothermal saturation method. The Pitzer–Simonson–Clegg thermodynamic model was implemented to obtain the temperature dependence of Gd(NO3)3⋅6H2O solubility constant, to calculate salt solubility and to construct a phase diagram of the system from eutectic point to hydrate melting. Thermochemical properties of gadolinium nitrate aqueous solutions, such as dilution enthalpies and heat capacities, were assessed also. The model has shown to be reliable for phase equilibria calculation from –35 to 90°C and from 0 up to ~15 mol % of salt as well as the thermodynamic properties of Gd(NO3)3 aqueous solutions at room temperature and around it.

Temperature-dependent enthalpy parameters of the molecular interaction for urea and tetramethylurea as solutes in formamide, ethylene glycol and water

Enthalpies of dilution of urea (U) solutions in formamide (FA), ethylene glycol (EG) and water were measured calorimetrically in the temperature range between (288.15 and 318.15) K. Based on the results obtained, the enthalpy-homotactic coefficients of pairwise (h22) and triplet (h222) interactions between the solvated U molecules were computed and compared with the similar data for the respective solutions of tetramethylurea (TMU). An analysis was done of how temperature influences the solvophilic and solvophobic effects manifested in the h22 and h222 parameters for U and TMU in the studied organic solvents with a spatial H-bonding network.

Explanation and Exploration of the Isothermal Titration Curve for the NaCl + Na2SO4 + H2O System at 298.15 K and 102.2 kPa.

Isothermal titration microcalorimetry (ITC) is a common and powerful tool in thermodynamics and related fields, and the connection between the solution behavior and raw titration curve is complex, important, and worth studying, so we try to discuss this problem using a complex solid–solid–liquid diagram. Although there are many experimental methods for studying ternary phase diagrams, ITC has been proven to be a simple, universal method at normal temperature and pressure. This method can be extended to investigate phase diagrams of multisalt aqueous solutions and related systems. Here, the phase equilibrium of one common ternary system (NaCl + Na2SO4 + H2O) was determined using the ITC method with the aid of X-ray diffraction measurements. This isothermal and isobaric titration method can be used not only to determine the boundaries of different phase regions by analyzing changes in the slope of the observed heat vs solvent concentration plot but also to provide additional accurate data regarding the solid dissolution enthalpy and the dilution enthalpy. The dissolution enthalpy of 1 mol NaCl (Na2SO4) solid dissolving in water to just form a saturated solution is measured at 1.92 kJ/mol (−15.60 kJ/mol), and the dissolution enthalpy of the mixed solids can be evaluated with these data. The dilution enthalpy is strongly dependent on the solute concentration (0.08–0.23 kJ/mol at the range of concentration studied), and for the same range concentration of a solute, the dilution enthalpy of Na2SO4 is positive and larger than that of NaCl. Therefore, the connection between the observed heat and the microscopic behavior and the separation between the dissolution and dilution data may result in the possibility to gain a clearer understanding about the solution behaviors.

Pyrrolidinium bromide deep eutectic solvents in separation of molecular solutes: Solvent selection for separating industrial mixtures

The separation of molecular solutes utilizing deep eutectic solvents for industrial processes is essential and important for the purpose of green solvent applications. Deep eutectic solvents (DES) based on 1.000:2.002 M ratio of [1-ethyl-1-methylpyrrolidinium bromide + triethylene glycol] and 1.000:2.001 M ratio of [1-ethyl-1-methylpyrrolidinium bromide + diethylene glycol] were used to evaluate their potential in separation of industrial mixtures. The pre-screening of the prepared DESs was based on the activity coefficients at infinite dilution measurements using gas liquid chromatography at different temperatures and at atmospheric pressure. The experimental data was conducted at temperature, T = (313.15–343.15) K. The intermolecular interactions occurring between the solvent and solute were discussed. These were further discussed by computing the excess thermodynamic functions at infinite dilution (enthalpies, ΔH1E,∞, Gibbs free energies, ΔG1E,∞, and entropy term, TrefΔS1E,∞). The effectiveness of the investigated deep eutectic solvents was based on the separation parameters (selectivities and capacity) values. These extraction parameters give a clear indication on how much of solvent would be required for a specific extraction and how selective the solvent is towards solutes to be separated. The results also reveal the ability of the investigated deep eutectic solvents to dissolve the solutes. The investigated deep eutectic solvents (DESs) were found to be useful in separating mixtures comprising (alkane-alcohol and acetone-ethanol). The influence of percentage loading, molar ratio as well as the influence of hydrogen bond donor was discussed.

μFlowCal – High‐Resolution Differential Flow Microcalorimeter for the Measurement of Heats of Mixing

AbstractThis work presents the description, calibration, test and performance evaluation of a new flow microcalorimeter. The μFlowCal is a differential heat conduction, flow microcalorimeter, designed to work in isothermal conditions, in differential mode and in the absence of gas phase, requiring small amounts of sample (200 μL). Both the microcalorimeter and its operational methodology were optimized to measure the heat of mixing of fluids with moderate viscosity and volatility. The microcalorimeter has a sensitivity of 116 μV mW−1 and a level of detection of 170 nW. A very good performance (uncertainty <5 %) was obtained for the selected test processes: enthalpy of dilution of aqueous sucrose solutions and excess enthalpy of binary mixtures of decane‐octanol. The μFlowCal prototype is a new tool in micro‐scale physical chemistry and a step forward concerning signal resolution and sample volume. Nowadays, these are major requirement for the study of novel promising solvents and their mixtures.

Experimental and simulation study on heat and mass transfer characteristics in direct-contact total heat exchanger for flue gas heat recovery

Direct-contact total heat exchange with liquid desiccant produces enormous gains in both sensible and latent heat recovery of low-grade flue gas. Previous studies related to that has tended to focus on the system performance rather than the heat and mass transfer characteristics, which is equally essential to their design, simulation and operation. This paper establishes an experimental system to investigate the heat and mass transfer characteristics in direct-contact total heat exchanger for flue gas total heat recovery. Ceramic structured packing is adopted considering its corrosion and high-temperature resistances; calcium chloride aqueous solution is employed as the coolant and absorbent for its low cost and high latent heat recovery capability. Based on those, the effects of flue gas and solution inlet parameters on the performance indices, including sensible and latent heat recovery capacities, latent heat rate and total heat recovery rate, are tested and analyzed. Coupled heat and mass transfer models between flue gas and solution in this process are developed, which feature the enthalpy of dilution. By combining the models and experimental data, heat and mass transfer coefficients are calculated and fitted. In addition, the effect of packing height on total heat recovery capacity and ratio is investigated through simulations. The results show that the total heat recovery rate of 74.7% can be achieved at packing height to 1.5 m when liquid–gas ratio is 5.172.

Thermodynamic Description of Dilution and Dissolution Processes in the MgCl2-CsCl-H2O Ternary System.

Thermodynamic data on the properties of the water-based electrolyte systems are very valuable for fundamental physical chemistry and for industrial applications. The missing data both on the dilution and dissolution enthalpies for the ternary CsCl−MgCl2−H2O mixed electrolyte system were investigated by means of the calorimetry method. The dilution calorimetry was performed at 298 for the set of solutions from diluted to concentrated at constant ratio Cs+/Mg2+ . The relative partial molar enthalpies, ideal, total, and excess ones were calculated. By means of the dissolution calorimetry, the standard enthalpies of formation, the enthalpies, and entropies for the double salt formation from simple salts were evaluated. The results obtained indicate that entropy as the major factor affecting the formation of the joint compound, both in the liquid and solid phases. These data can be implemented in thermodynamic databases and allow for accurate thermodynamic calculations for the salts extraction from natural water sources and for its possible application as thermochemical energy storage.

On interactions in binary mixtures used in solvent extraction: Insights from combined Isothermal Titration Calorimetry experiments and Molecular Dynamics simulations

Despite its importance, the description of liquid–liquid extraction is made difficult because the link between the experimental methods and the interactions present in the solution is not direct due to the many organisation phenomena that can occur. We propose a new methodology combining microcalorimetric measurements and molecular modelling to better describe the nature and strength of these interactions in these complex fluids by focusing on extractant-diluent mixtures (N,N-dialkylamides + n-alkanes). Enthalpies of dilution were obtained by microcalorimetric measurements at 298 K for each n-dodecane and n-heptane with DEHiBA and for n-dodecane with DEHBA. These results have been compared, thanks to a new method that we present here, to molecular dynamics simulations carried out on these same systems. We especially analyzed the influence of the alkyl branching of the extracting molecules and the role of the diluent. Globally, the excess enthalpy is such that these mixtures are energetically not very different from regular solutions but the detailed balance shows an important attraction between the extractants, which can lead to the formation of macromolecular entities favouring extraction. Calorimetry appears to be a method of choice for linking experiments and molecular modelling in these complex liquid mixtures, and experimental developments could benefit from using it more often, especially to validate force-fields.

Solubility Isotherm Determinations at T = (273.15, 298.15, 323.15, 348.15 and 363.15) K and Thermodynamic Modeling of the H3BO3 + SrCl2 + H2O System

Boron abundantly exists in salt lake brine system as various boron-containing aqueous species or minerals. The phase behavior of boron and other substances (Li, Na, K, Rb, Cs, Mg, Ca, Sr, Cl, S etc.) in the complicated salt brine system during the solar pool process needs to be simulated and predicted by models. Basic experimental data (e.g. solubility, etc.) of simple binary and ternary system are necessary for the model parameterizations. At present, the unavailability of solubility data in the H3BO3 + SrCl2 + H2O ternary system makes the model parameterization difficult. In this paper, we determined the solubility isotherms in the H3BO3 + SrCl2 + H2O ternary system at 273.15 K, 298.15 K, 323.15 K, 348.15 K and 363.15 K. The result show that the isotherms all consisted of the solubility branches H3BO3(cr) and SrCl2⋅nH2O(cr) (n = 6 and 2), and no new phase has been found. Then, a Pitzer–Simonson–Clegg (PSC) model in the ISLEC software package was used to simulate the thermodynamic properties of the H3BO3 + H2O, SrCl2 + H2O, and H3BO3 + SrCl2 + H2O systems, including solubility, water activity, activity coefficients, heat capacity and enthalpy of dilution. With the obtained model parameters, a complete polythermal phase diagram of the H3BO3 + SrCl2 + H2O system was predicted at temperatures from 255 to 373 K. The present work lays the foundation for the future simulations of complicated salt lake brine systems containing H3BO3 and SrCl2.

Interactional behavior of saccharides/derivatives with amoxicillin drug in aqueous medium: Insights from volumetric, calorimetric and spectroscopic studies

The physicochemical studies are significant in understanding the molecular interactions of saccharides and their derivatives with amoxicillin drug in aqueous solution. Therefore, the apparent molar volumes (V2,ϕ), and the limiting standard molar enthalpies of dilution (ΔdilH∞m) of saccharides and their derivatives in (0.001, 0.002, 0.003 and 0.004) mol·kg–1 aqueous solutions of amoxicillin were determined from the precise density, ρ and heat change, q measurements at (288.15, 298.15, 308.15 and 318.15) K under pressure, p = 0.1 MPa. The data were processed to obtain the corresponding transfer volumes (ΔtrV2∞) and enthalpies of dilution of transfer (ΔtΔdilH∞m) of solutes from water into aqueous solutions of amoxicillin. The volumetric expansion coefficients (∂V2∞/∂T)P, their second-order derivatives (∂2V2∞/∂T2)P and heat capacity change (∆dilC∞p,2,m) were also determined. Proton (1H) NMR spectra for mA = 0.02 mol·kg–1 saccharides/derivatives were also recorded in different molalities, mB = 0.001, 0.002, 0.003 and 0.004 mol·kg–1 of amoxicillin solution prepared in solvent {9:1 H2O + D2O}. The NMR results show that the Hc proton of amoxicillin has more activity (acidity) and it interacts more with the solute molecules (saccharide/derivative) than other protons of amoxicillin.

The enthalpies of dilution of some dipeptides in water at 298.15 K

The enthalpies of dilution of glycyl-L-α-alanine, glycyl-L-α-leucine and glycyl-L-glutamine have been measured in water at T = 298.15 K. The experimental results were used to calculate the enthalpic coefficients of the interactions between dipeptides molecules in water based on McMillan–Mayer's model. The values of the interaction parameters were interpreted in terms of the hydrophobic or hydrophilic properties of the amino acid side chins in the examined dipeptide molecules and the influence on their interactions with each other in water.

Dissolution of potassium chloride as a test process for isothermal calorimeters operated in the milli-Watt range

A test and calibration method for isothermal calorimeters equipped with a device for liquid injection and mixing is described. The procedure was developed with special reference to calorimeters operated with heat flow values in the milli-watt range. The investigated reaction was the dissolution of potassium chloride in water at 298 K in the concentration range 56–80 water molecules per KCl entity or molalities of 0.7−1 mol kg−1. The solution enthalpies (ΔsolH) were assessed after electrical calibration and correction for side effects obtained from separate blank measurements. The obtained values were corrected to the state of infinite dilution (ΔsolH∞) at each experimental molality by use of literature values of the relative apparent enthalpy of dilution. The obtained result was 229.6 ± 1.0 J g−1 (n = 16). The solution enthalpy (ΔsolH) as a function of molality in the experimental concentration interval was fitted by a 1-order polynomial resulting in a slope of -12.3 J g−1 mol−1 kg and intercept of 240.5 J g−1. The results are suggested as reference values for validation of calorimeters calibrated electrically or for the purpose of calibration.

The Effects of the Solvent Choice of the Continuous Phase on the Poly(Urea-Urethane) Microcapsules Properties

Xylitol, a natural crystalline polyol, presents a cooling effect due to its negative heat of solution at 35 °C supported by humidity absorption, contributing to a fresh sensation when it dissolves. Since this material is sometimes in a liquid state, it cannot be incorporated in or onto a substrate without being protected. One of the strategies to protect the active substance may be forming a barrier layer at its surface, i.e., microencapsulation. The present work is devoted to studying the effect of continuous phase parameters affecting on encapsulation of xylitol with a poly (urea-urethane) shell through a two-step microencapsulation process. The first step is liquid-liquid dispersion either in toluene or Miglyol 812N, and the second step is microencapsulation by interfacial polymerization. The process can be used to control the size distribution of the microparticles, the thickness, and the chemical nature of the shell, which influences the release rate of the active substance. The choice of the continuous phase solvent (toluene or Miglyol 812N) required some changes in the formulation of the system, especially the HLB of the surfactant mixture, to obtain a stable emulsion with a narrow particle size distribution. The thermo-chemical and morphological characteristics of microparticles were studied by Fourier transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), enthalpy of dilution, and scanning electron microscope (SEM). The microparticle size is governed by the emulsion step and the chemical composition of the organic phase. Most of the thermal properties are related to their porous structure and their chemical shell formation during the interfacial polymerization step.

Thermodynamic properties for the aqueous solutions of cesium borates at 298.15 K and 101 kPa: Experimental and correlation by Pitzer ion-interaction model

As a new-type of liquid mineral resource of cesium including salt lake brine, geothermal water, underground water and seawater, the recovery of cesium is of great significance for its importance strategic purpose in modern industry, and the parameterization of ion-interaction model is essential to understand the ion-interaction of cesium borate solutions. In this paper, the dilution enthalpies on Cs2B4O7 aqueous solutions from 0.03900 to 0.54815 mol·kg−1 and CsB5O8 aqueous solutions from 0.02072 to 0.09889 mol·kg−1 at 298.15 K and 1.325 kPa were determined by the high-precision adiabatic microcalorimeter BT2.15 (Setaram, France), and the dissolution enthalpies for Cs2B4O7·5H2O and CsB5O8·4H2O were measured by the multi-channel microcalorimeter TAM-IV (TA, America). On the basis of experimental dilution enthalpies, the apparent molar enthalpies of Cs2B4O7 and CsB5O8 aqueous solutions were derived, and the diagrams of apparent molar enthalpy against molalities of Cs2B4O7 and CsB5O8 in aqueous solutions were plotted. And then, according to the Pitzer ion-interaction model of apparent molar enthalpy of electrolyte, Pitzer single parameters i.e. FMX (βMX0L, βMX1L, βMX2L and CMXL, M = Cs+, X = [B4O5(OH)4]2− or [B5O6(OH)4]−) were obtained for the first time. The calculated apparent molar enthalpies for Cs2B4O7 and CsB5O8 aqueous solutions agree well with the experiment values, indicating that the single salt parameters obtained for Cs2[B4O5(OH)4] and Cs[B5O6(OH)4] in this work are reliable.

Dilution enthalpies of LiBO2 and LiB5O8 aqueous solutions at 298.15 K and the application of ion-interaction model

The dilution enthalpies of LiBO2 (aq) from 0.0398 to 0.7684 mol·kg−1 and LiB5O8 (aq) from 0.0521 to 0.8067 mol·kg−1 at 298.15 K and 101.325 kPa were investigated using the microcalorimeter BT 2.15. The apparent molar enthalpies on two lithium borates were obtained, and the diagrams of their apparent molar enthalpy against molality for LiBO2 (aq) and LiB5O8 (aq) were also plotted. Considering the constructers of BO2- and B5O8- in aqueous solution are existed as in [B(OH)4]- and [B5O6(OH)4]-, the Pitzer single-salt parameters (βMX(0)L, βMX(1)L, βMX(2)L, CMXL) for LiB(OH)4 and LiB5O6(OH)4 were obtained for the first time. A comparison between the calculated apparent molar enthalpies for LiBO2 (aq) and LiB5O8 (aq) based on Pitzer model and those determined experimentally agree well, which indicate that the Pitzer single parameters of LiB(OH)4 and LiB5O6(OH)4 obtained are reliable.