Heat Of Solution Data Research Articles

Vapor–liquid activity coefficients for methanol and ethanol from heat of solution data: application to steam–methane reforming

This paper presents equations and curves to calculate vapor–liquid phase equilibria for methanol and ethanol in dilute aqueous solution as a function of temperature, using activity coefficients at infinite dilution. These thermodynamic functions were originally derived to assess the distribution of by-product contaminants in the process condensate and the steam-system deaerator of a hydrogen plant [Paper ENV-00-171 presented at the NPRA 2000 Environmental Conference, San Antonio, TX, 10–12 September 2000], but have general applicability to other systems as well. The functions and calculation method described here are a necessary piece of an overall prediction technique to estimate atmospheric emissions from the deaerator-vent when the process condensate is recycled as boiler feed water (BFW) make-up. Having such an estimation technique is of particular significance at this time because deaerator-vent emissions are already coming under regulatory scrutiny in California [Emissions from Hydrogen Plant Process Vents, Adopted 21 January 2000] followed closely elsewhere in the US, and eventually worldwide. The overall technique will enable a permit applicant to estimate environmental emissions to comply with upcoming regulations, and a regulatory agency to evaluate those estimates. It may also be useful to process engineers as a tool to estimate contaminant concentrations and flow rates in internal process streams such as the steam-generating system. Metallurgists and corrosion engineers might be able to use the results for materials selection.

Effects of pressure and temperature on the solubility of monosodium L-glutamate monohydrate in water

The solubility of monosodium L-glutamate monohydrate (MSG.H2O) in water was measured at pressures in the range of 0.10-300MPa and 298.15K. The density of MSG solution at high concentrations and heat of solution at saturated concentration were also measured at atmospheric pressure. The solubility, ms, increased with increasing pressure and the pressure coefficient, Θp, [≊(∂ In ms,∂ p)T] at 0.10 MPa was (2.0 ± 0.1) × 10-10Pa-1. It agrees well with (2.1 ±0.2)× 10-10 Pa-1 thermodynamically estimated using the partial molar volume, the activity coefficient of the solute in solution, and the molar volume of the crystal. The excellent agreement at 0.10MPa gives us confidence in the solubility data at higher pressures. The heat of solution data and other pertinent values were used to calculate the temperature coefficient of solubility, ΘT [≊ (∂ In ms/∂(1/T))p], by a thermodynamic equality. The resulting ΘT compares well with the data directly measured by Ogawa.

Quantitative relationship between solubility, initial dissolution rate and heat of solution of chiral drugs.

The aim of this study was to clarify the quantitative relationship between solubility, initial dissolution rate and heat of solution of racemic compound and its enantiomers. Propranolol, propranolol HCl, tyrosine, and tryptophan were used as typical chiral drugs. The heat of solution of chiral drug was measured by an isothermal microcalorimeter and the heat of fusion was measured by a DSC. The free energy difference for the dissolution of drug was calculated from the solubility and initial dissolution rate data. The free energy difference and enthalpy difference of the dissolution between the racemic compound and enantiomer of propranolol, propranolol hydrochloride, tyrosine, and tryptophan were obtained by the solubility, initial dissolution rate and heat of solution data. A good linearity was observed in the free energy difference and the enthalpy difference for the dissolution of them, except for propranolol HCl data. By considering the dissociation in solution, the data of propranolol HCl followed the regression line. The free energy difference of the dissolution was linearly dependent on the enthalpy difference for the racemic compound and its enantiomers. The results fit the theoretical equation. It could be possible to estimate the solubility of chiral insoluble drug from the thermal data.

Solid State Characterization of Dehydroepiandrosterone

Three polymorphs (forms I–III), a monohydrate (form S2), and three new solvates [4:1 hydrate (form S1), monohydrate (form S3), and methanol half‐solvate (form S4)] were isolated and characterized by X‐ray powder diffractometry (XRPD), IR spectroscopy, differential scanning calorimetry (DSC), hot stage microscopy, solution calorimetry, and their dissolution rates. A new polymorph, designated as form V, melting at 146.5–148°C, was observed by hot stage microscopy. Our results indicate that only forms I and S4 exhibit reproducible DSC thermograms. Five of the isolated modifications undergo phase transformation on heating, and their DSC thermograms are not reproducible. Interpretation of DSC thermograms was facilitated by use of hot stage microscopy. The identification of each modification is based on XRPD patterns (except forms S3 and S4, for which the XRPD patterns are indistinguishable) and IR spectra. In the IR spectra, a significant difference was observed in the OH stretching region for all seven modifications. In a purity determination study, 5% of a contaminant modification in binary mixtures of several modifications could be detected by use of XRPD. To obtain a better understanding of the thermodynamic properties of these modifications, a series of increasing heating rates and different pan types were used in DSC. According to Burger's rule, forms I–III are monotropic polymorphs with decreasing stability in the order form I > form II > form III. The melting onsets and heats of fusion for forms I–III are 149.1 °C, 25.5 kJ/mol; 140.8 °C, 24.6 kJ/mol; and 137.8 °C, 24.0 kJ/mol, respectively. For form III the heat of fusion was calculated from heat of solution and DSC data. In the case of form S1 the melting point, 127.2°C, was obtained by DSC using a hermetically sealed pan. The relative stabilities of the six modifications stored under high humidity conditions were predicted to be, on the basis of the heat of solution and thermal analysis data, form S2 > form S3 > form S1 > form I > form II > form III. However, the results of the dissolution rate determination were inconsistent with the heat of solution data. The stable form I shows a higher initial dissolution rate than the metastable form II and unstable form III. All modifications were converted into the stable monohydrate, form S2, during the dissolution study, suggesting that the moisture level in solid formulations should be carefully controlled.

Thermodynamics of aqueous gallium chloride. Heats of solution and dilution at 25°C

The heat of solution of GaCl3 and heats of dilution of single GaCl3 solutions in water and of mixed GaCl3−HCl solutions in HCl solutions (with a fixed HCl concentration of 0.1337 mol-kg−1 HCl) up to 4 mol-kg−1 GaCl3 were measured at 25°C. While in the acid solutions hydrolysis is suppressed to below 0.5% of total gallium concentration, the measurements in water allow evaluation of the effect of hydrolysis on the relative enthalpy. The Pitzer interaction model for excess properties of aqueous electrolytes was used to interpret the change in relative enthalpy with concentration. Pitzer parameters were derived by statistical inference using ridge regression. Their physical significance is supported by the heat of solution data. The measurements yield the following results for standard heats of formation and Pitzer parameters for the relative molar enthalpy at 25°C: $$\begin{gathered} H_{GaCl_3 }^ \circ = - 722 kJ - mol^{ - 1} ; \beta _{L,GaCl_3 }^0 = - 1.52 \times 10^{ - 3} kg - mol^{ - 1} - K^{ - 1} ; \hfill \\ \beta _{L,GaCl_3 }^1 = 1.21 \times 10^{ - 2} kg - mol^{ - 1} - K^{ - 1} ; C_{L,GaCl_3 } = - 1.42 \times 10^{ - 4} kg^2 - mol^{ - 2} - K^{ - 1} ; \hfill \\ H_{GaOHCl_2 }^ \circ = - 492 kJ - mol^{ - 1} ; H_{Ga(OH)_2 Cl}^0 = - 706 kJ - mol^{ - 1} ; \hfill \\ \end{gathered} $$ With these parameters the overall variance in the partial molar heat of solution at infinite dilution, extrapolated from the present experiments, is minimized to 0.35 kJ2-mol−2, while the experimental apparent molar heats of dilution are reproduced on average within 2.7 kJ-mol−1.

Calculation of the thermodynamic driving force in crystallization from solution

The dependence of the thermodynamic driving force for crystallization on the degree of supercooling δ T is given by the differential heat (partial molar enthalpy increment) of solution divided by RT 2 . For sparingly soluble nonelectrolytes the differential heat of solution may be obtained directly from the slope of a logarithmic plot of solubility versus 1/ T, but for more soluble substances the variation of activity coefficient with concentration should be taken into account. For nonelectrolytes this dependence may be estimated from the thermodynamic properties of pure solute, using a series expansion for the activity coefficient. Highly soluble electrolytes require a more precise treatment, but adequate activity or heat of solution data are found in the literature for most systems of interest. Examples of calculations with different degrees of approximation are presented.

Systematics of ovidic actinide compounds

This paper gives an updated review of recent developments in the field of ovidic actinide compounds, especially with respect to evisting systematics. It is shown that there is some success in evtending the number of evisting ovidation states, e.g. of curium to curium(V), as well as the hope of clarifying open vuestions on the possible evistence of octavalent plutonium in Li v PuO 6 mived ovides or of divalent americium fluoride, stabilived by incorporation in the fluorite structure of BaF 2 (SrF 2). The fluorite lattice in ovidic systems of An(Ac — Cm) can undergo a lot of changes, both in anionic and cationic sublattices. E.m.f. measurements in such systems as well as heat of solution data on actinide sesvuiovides and ordered perovskites give a good picture of the thermodynamic stabilities. Magnetic measurements of 5f 1 and 5f 3 ovidic compounds demonstrate a clear relationship between the transition temperature of magnetic ordering and the shortest An-An distance in the compound. No ordering evists if it is larger than about 450 pm. Despite a lot of new data being available many vuestions still remain open, e.g. those on the stability regions for actinide sesvuiovides, the influence on self-irradiation effects of high ovidation states or of phase evuilibria in most AnO 1.5-AnO 2+ v fluorite phases, e.g. for the AmO 1.5-UO 2 + v system.

Heats of solution and the influence of solutes on the temperature of maximum density of water

The influence of N,N-dimethylformamide, N,N-dimethylacetamide, 2-pyrrolidinone, N-methyl-2-pyrrolidinone, and N-t-butyl-2-pyrrolidinone on the temperature of maximum density (TMD) of water has been investigated. Heats of solution for these compounds and for diethylsulfoxide, tetramethylene sulfoxide, tetramethylene sulfone, dimethyl sulfoxide, and tetrahydrofuran in water at 23°C are also reported. These data, together with published TMD and heat of solution data for other solutes, are used to examine the relationship between the enthalpy change on dissolution of a solute in water and the effect of the dissolved substance on the structure of water as reflected by changes in the temperature of maximum density of the system.

Simultaneous heat and mass transfer from multicomponent condensing vapor‐gas systems

AbstractMulticomponent vapor condensation in the presence of noncondensing gas has been analyzed using numerical solutions to a set of linearized rate equations that describe the simultaneous heat and mass transfer to the condensate film. For specific examples of methanol and water and ethanol and toluene condensing from turbulent air streams in vertical tube and on horizontal tube condensers, it is shown that the alcohol concentrations in both the liquid and gas phases increase as condensation from initially superheated, alcohol‐rich gas phases progresses; the liquid phases also become richer in alcohol. The mass fluxes of the vapors vary with their respective mass transfer coefficients and local concentration driving forces. In the vertical tube condensers, the flux of the alcohols go through maximums. Gas phase saturation is approached as the mixtures cool and the final traces of vapor become more difficult to condense. Interface properties are computed from limited VL equilibrium data, heat of solution data, and a predictive equation. The techniques of solution and analysis have general application to the design of cooler‐condensers in either vertical or horizontal configurations.

Thermodynamic behavior of polymethyl methacrylate solutions

Abstract The Maron theory of polymer solutions was used to examine the available osmotic pressure, light scattering, and heat of dilution data for polymethyl methacrylate (PMMA) in fourteen solvents. No vapor pressure or heat of solution data could be found for these systems. Wherever possible interaction parameters, μ, were evaluated as functions of volume fraction, temperature, and molecular weight, as well as X, the temperature coefficient of μ. The equations deduced allow in some instances the prediction of the vapor pressure behavior of solutions of noncrystalline PMMA and also the heat of mixing of random amorphous polymer with solvent. The data were not sufficient to establish the complete dependence of μ on concentration, molecular weight, and temperature for any PMMA-solvent system.

Hydratationsenthalpie der alkalihalogenid-ionenpaare

It is shown that the enthalpy of hydration of ion pairs can be calculated from heat of solution data on the basis of a cyclic thermodynamic process according to Δ H S = L(O) − Δ H sub 1 − Δ H diss, where Δ H S is the enthalpy of hydration, L(O) the heat of solution (ideal), Δ H sub 1 the enthalpy of sublimation and Δ H diss the enthalpy of dissociation of the ion pair. Data for L(O) and Δ H sub 1 are available in the literature; Δ H diss can be evaluated from the Denison and Ramsay formula. Values of the enthalpy of hydration for the alkaline halides calculated from the above equation are presented and compared with reported values derived from thermodynamic data. Limits and sources of error, and the advantages and disadvantages of the different methods for calculation of the various intermediate quantities involved, are extensively discussed, and their influence on the limits of confidence of the resulting Δ H S values is analysed.

High‐Temperature Energy Relations in the Alkali Borates: Binary Alkali Borate Compounds and Their Glasses

The energy relations existing between the congruently melting compounds Li2O ‐2B2O3, Na2O–2B2O3, Na2O‐4B2O3, and K2O‐4B2O3 and their glasses have been determined for the temperature range 25° to 1100°C. High‐temperature heat‐content, entropy, and heat of solution data are given for both the glasses and the corresponding devitrified materials. A comparison of the heats of fusion of the alkali borates on a gram atom of oxygen basis shows that they follow the order Li > Na > K. The entropy differences between the glass and the corresponding crystalline material have been determined at 25°C. The free‐energy change at 25°C. for the reaction crystal → glass has been calculated for the four compounds.