Uber die Thermodynamik der Verdampfung von Scandium(III)-fluorid

On the thermodynamics of vapourization of scandium(III) fluoride The vapourization behaviour of solid ScF₃ was studied by the KNUDSEN effusion method. ScF₃ vapourizes congruently with practically stoichiometric composition in a high vacuum at temperatures from 1300 to 1600°K. Within the temperature ranges 1336–1400K and 1440–1528°K the vapourization was found to obey the equations respectively, assuming monomeric ScF3 to be the predominant gaseous species. By considering literature data for the vapourisation behaviour of AlF₃(s) and LaF3(s) the content of SC₂F₆ (g) in the saturated vapour over SeF₃ (s) was estimated to be approximately 0.3% at 1368 ° K. Second an Third Law calculations were performed using known and estimated thermodynamic data for ScF₃(g) and ScF₃(s), respectively, and the enthalpies and the enthalpies and entropies of vapourization at 298.15 ° K were obtained (data see “Inhaltsübersicht”). A. critical discussion of the experimental and theoretical results allowed to conclude that vapour pressures of ScF₃(s), which were determined by others within were found to be three to four orders of magnitude higher than the vapour pressures determined in this work where are are less probable.     

Gas chromatographic determination of vapour pressure and related thermodynamic properties of monoterpenes and biogenically related compounds

The (subcooled) liquid vapour pressure, heat of vapourization and gas-liquid heat capacity difference of monoterpenes and biogenically related compounds were determined by a gas-liquid chromatographic method based on Kovats retention indices. Compared to those used in previous studies using the same method, these compounds are structurally diverse and have relatively low boiling points. Despite of this and even though the difference in activity coefficients in the chromatographic column stationary phase between the test and reference compounds were ignored, results for vapour pressure compare favorably with experimental literature data. The results indicate that the method can be improved by introducing temperature dependent activity coefficients, preferably based on a physicochemical model for gas-liquid partitioning.     

Vapour pressures and enthalpies of vapourization of a series of the γ-lactones

Vapour pressures and the molar enthalpies of vapourization of the γ-lactones (γ-valerolactone, γ-hexanolactone, γ-heptanolactone, γ-nonanolactone, and γ-decanolactone) have been determined by the transpiration method. These results together with a large number of experimental data from the literature have been checked for internal consistency. This collection has been used for development of group-additivity procedure for prediction of vapourization enthalpies of lactones.     

Zusammenhänge zwischen Dampfdruck,Verdampfungsenthalpie und Oberflächenspannung aprotonischer Lösungsmittel

A relationship has been found between the equilibrium vapour pressurep _eq and the enthalpy of vapourization ΔH _vp of aprotic solvents of the form—RT ln (V _m ·p _eq/RT)=(1?k) ΔH _vp whereV _m is the molar volume of the solvent andk has a value of 0,43 at 25 °C. This relationship allows a calculation of enthalpies a vapourization from the vapour pressure at a given temperature or vice versa and has been tested for a large number of solvents. An extension of a model previously devised to calculate the changes in the basic thermodynamic functions associated with the creation of cavities of molecular dimensions in liquids, to holes ofmacroscopic dimensions predicts a relationship between surface tension σ and vapour pressure or enthalpy of vapourization of aprotic solvents of the form $$\begin{gathered} \sigma = - RT\ln (V_m \cdot p_{eq} /RT)/\sqrt[3]{{36\pi N_L \cdot V_m ^2 }} = \hfill \\ = (1 - k)\Delta H_{vp} /\sqrt[3]{{36\pi N_L \cdot V_m ^2 }} \hfill \\ \end{gathered} $$ which is remarkably well fulfilled for a variety of aprotic solvents.     

Solid—liquid equilibrium and the structure of solutions of highly polar aromatic compounds

Saturated vapour pressures of 11 binary three phase solid—liquid—vapour systems have been measured. The solubility data of six polar compounds in hydrocarbons have also been reported. Solutes forming no intermolecular hydrogen bonds have been considered. The solutes discussed dimerize in inert solvents.     

Effect of small amounts of methanol on the vapour—liquid equilibrium for the water-formaldehyde system

The total vapour pressures of three mixtures of the water-methanol-formaldehyde system have been measured over the range of temperatures 55–95°C. The formaldehyde composition was in the range 34–44 wt.%, while that of methanol was <1 wt.%. These measurements were carried out with the aim of demonstrating that, for studying the vapour—liquid equilibrium for the water—formaldehyde system, it is necessary to eliminate methanol to a greater extent than is usual.The experimental results compare favourably with those calculated by a predictive thermodynamic model which explains nonideality in the liquid phase in terms of chemical forces for the binary systems water—formaldehyde and methanol—formaldehyde and in terms of physical forces (Wilson equation) for the binary system water—methanol.The proposed model was also utilized in bubble-point calculations for the binary system methanol-formaldehyde and for the ternary system over a large range of compositions. The results were compared with literature data.     

The vapour pressures of several metal-2,2,6,6-tetramethyl-3,5-heptanedione complexes measured by a Knudsen effusion method

The melting points, vapour pressures and heats of sublimation of the complexes of Ga, In, Y, La, Gd, Fe, Zn, Pb and Li with 2,2,6,6-tetramethyl-3,5-heptanedione are reported for the temperature range below the melting point of 40? to 250?C and pressures from 10 to 10^?2 torr. The measurements were made with an easily constructed Knudsen effusion cell in conjunction with a Mettler thermobalance.     

Excess properties of the hexafluorobenzene—n-hexadecane and hexafluorobenzene—benzene—n-hexadecane systems at 298.15 K

Vapour pressures and excess volumes for the hexafluorobenzene—n-hexadecane system and vapour pressures for the hexafluorobenzene—benzene—n-hexadecane system have been measured at 298.15 K. Thermodynamic consistency of the data has been checked using a Padé approximation for the binary system, and a new expression for the excess Gibbs energy of the ternary system. The new expression compares favourably with others previously proposed in the literature.     

Calculation of high pressure vapour—liquid equilibria for systems containing polar substances with the use of an augmented van der Waals equation of state

An augmented van der Waals equation of state based on a perturbation theory has been applied to the calculation of high pressure vapour—liquid equilibria for systems containing polar substances. The equation of state comprises four terms, which imply the contributions from repulsion, symmetric, non-polar asymmetric, and polar asymmetric interactions. The characteristic parameters of each pure substance have been determined by three methods with the use of vapour pressures and saturated liquid densities. Mixing models for the terms of the repulsion, symmetric, and non-polar asymmetric interactions are the same as used previously. Two types of mixing models based on a three-fluid model and/or a one-fluid model are developed for the polar asymmetric term. The polar asymmetric term has a large effect on the prediction of the vapour—liquid equilibrium. With the introduction of a binary interaction parameter, the equation is found to be useful in correlating the vapour—liquid equilibria for a system containing a polar substance except near a critical region.     

Correlation of gas solubilities in water and methanol at high pressure

A random—nonrandom—mixture equation for the Helmholtz energy of a fluid mixture is shown to correlate the solubility of inert and acidic gases in water and methanol quite accurately at pressures up to 300 bar. Further, the calculated Henry's law constants of the gases in water show good agreement with experimental data.The gas solubility models is a modification of our previous model. It contains three binary interaction parameters, one in the reduced density term and two in the attractive terms. When the nonrandom parameter vanishes the model reduces to the classical mixing rule. The model correlates vapour—liquid equilibria in binary and ternary hydrocarbon—methanol systems quite accurately.The results of the correlation are compared with results obtained using the classical van der Waals quadratic mixing rule. The random—nonrandom model is, in all cases, superior to the van der Waals model. Finally, a comparison of computer time consumption for the two models is given.     

Indirect determination of low vapour pressures using solid-phase microextraction--application to tetrachlorobenzenes and tetrachlorobenzyltoluenes

There is still a gap of reliable vapour pressure data at ambient temperature for low volatile organic substances due to the difficult and time-consuming determination using the classical methods. Static headspace extraction with a solid-phase microextraction (SPME) fibre in combination with gas chromatographic analysis provides an inexpensive tool for the indirect determination of low vapour pressures down to 10(-5) Pa. The procedure consists of two steps: (a) exposure of SPME fibre in the headspace above the test chemical over minutes to hours and (b) desorption and quantification of extracted amount. The calibration was performed using low volatile reference substances with well-known vapour pressures. A good correlation was found between substance uptakes of SPME fibre and vapour pressures. The method was applied, e.g. to tetrachlorobenzenes and to selected tetrachlorobenzyltoluenes with questionable vapour pressures. We obtained values between 0.98 and 13.5 Pa for the former and results between 0.13 and 0.68 mPa for the latter group of congeners. The scope of the method can be extended to substances with even lower vapour pressures, provided that reliable reference data are available.     

Fundamental investigation of thermal properties of rare-earth beta-diketonates

The thermal properties of the rare-earth chelates of Htfa (trifluoroacetylacetone) and Hhfa (hexafluoroacetylacetone) have been investigated. Thermogravimetric curves were obtained by heating samples in the injection chamber of a gas chromatograph, both in an atmosphere of helium, and of helium containing ligand vapour. None of the chelates was completely vaporized in a helium atmosphere at temperatures up to about 240 degrees , but the tfa chelate of Lu and all the hfa chelates were completely vaporized in the atmosphere of helium containing ligand vapour. The vapour pressures and heats of vaporization of these chelates were also measured.     

Application of the Quartic Hard Chain equation of state to polymer mixtures

The Quartic Hard Chain equation of state proposed by Kubic is a simple model for chain-like molecules. This study considers the application of this equation to polymer solutions. The equation was not found to be a useful predictive model because polymer parameters could not be reliably predicted from pure component properties. However, the equation was found to be a useful empirical form for representing polymer solution data. Because the Quartic Hard Chain equation is applicable to the vapour—liquid equilibria of normal fluids, this method is potentially useful for representing high pressure vapour—liquid equilibria in systems with dissolved polymer.     

Theoretical prediction of enthalpies and temperatures of sublimation of organochlorine compounds including pesticides

Crystal lattice energies of several organochlorine compounds—including pesticides, of known crystal structures were calculated on the basis of a model which takes into account electrostatic, dispersive and repulsive interactions—using three different sets of empirical parameters. These characteristics compare reasonably with experimental heats of volatilization, and it was subsequently shown how statistical and classical thermodynamics can be employed to evaluate dependencies of function of states of gaseous and solid compounds on temperature and how enthalpies and temperatures of sublimation at standard pressure, as well as vapour pressurevs. temperature dependencies can be predicted.     

Vapour pressure of binary,three-phase (S-L-V) systems and solubility

Solubilities and vapour pressures along the solid-liquid equilibrium line for systems 2-t-butyl-4-methylphenol+benzene, 2-t-butyl-4-methylphenol+cyclohexane, 2,6-di-t-butyl-4-methylphenol+benzene, 2,6-di-t-butyl-4-methylphenol+cyclohexane and enthalpies of fusion for six phenols have been measured.The effect of specific interactions, leading to association, on solubilities and vapour pressures of 13 binary three-phase systems (S—L—V) has been discussed. Results of solubility prediction from vapour pressure measurements and vice versa are presented.     

A new procedure for consistency testing of binary vapour—liquid equilibrium data

A procedure has been proposed for testing the thermodynamic consistency of low-pressure binary vapour—liquid equilibrium data. The method, employing the idea of local defects due to Mc Dermott and Ellis, is based on the statistical nature of consistency and is systematically formulated using the methods of mathematical statistics. It provides well-defined limits for the test quantities and consequently is superior to all empirically evaluated tests. In addition, the proposed procedure provides an estimate of experimental error and enables any systematic characteristic to be identified. The efficiency of the method developed here has been investigated through Monte Carlo simulations and its applicability to actual vapour—liquid equilibrium data has been demonstrated using a number of examples. A comparison with the methods of Ulrichson and Stevenson and Samuels et al., which also utilize a statistical treatment of the local defects, reveals a serious error involved in both. For the case when credit is placed in the vapour—liquid equilibrium data, the consistency may be used to draw some conclusions on the vapour phase non-ideality. In this respect, minimization of the consistency criterion proposed is shown to lead to the maximum likelihood estimate of the second-cross virial coefficient.     

Vapour—liquid equilibria in binary systems formed by N-Methylpyrrolidone with hydrocarbons and hydroxyl derivatives

The vapour—liquid equilibria (VLE) determined by an ebulliometric total pressure method under isothermal conditions for binary systems formed by N-methylpyrrolidone with hexane (333.25 and 343.15 K), dodecane (393.25 K), cyclohexane (333.25 and 354.15 K), methyl-cyclohexane (354.15 and 373.25 K), benzene (333.25 and 354.15 K), toluene (362.15 and 383.35 K), propylbenzene (352.15 and 373.75 K), butylbenzene (352.15 and 373.75 K), propanol-1 (354.15 K), hexanol-1 (351.75 and 393.35 K) and at 393.55 K for cyclohexanol, 4-methylphenol and 2,4-dimethylphenol are reported. The vapour pressures of the pure substances are given. The least squares analysis of VLE data by means of the Redlich-Kister equation is given.     

Vapour—liquid equilibrium of the systems 1-propanol—2,2,4-trimethylpentane and 2-propanol-n-hexane

The vapour—liquid equilibrium data were measured for the binary systems 2-propanol—n-hexane at 328.21 K and 1-propanol—2,2,4-trimethylpentane at 328.37 K and 348.52 K by using the recirculation still proposed by Berro et al. (1975). The excess volumes for these systems were measured with an Anton Paar densimeter. The reduction of VLE data and analysis of experimental errors were performed. The NRTL temperature-dependence parameters were estimated. The measured VLE data and the activity coefficients were compared with the values predicted by the chemical-reticular group-contribution method (CRG) (Neau and Péneloux, 1979). For both systems satisfactory agreement was found. This proves that the CRG model can be used to predict the vapour—liquid equilibria of alcohol—alkane systems containing branched components.     

Experimental and estimated saturated vapour pressures of aroma compounds

The saturated vapour pressure of d-linalool, 2-nonanone, d-limonene and isoamyl acetate were measured using a static method at different temperatures from 223 to 468 K. From the experimental values, Antoine's constants were determined to enable the calculations of the saturated vapour pressures at a given temperature. The saturated vapour pressure of the four aroma compounds at 298 K were respectively 27, 59, 200 and 733 Pa. These results were compared with those obtained using different estimation methods (Antoine–Grain, Watson, Lee–Kesler, Gomez–Thodos, Grain and Mackay). Gomez–Thodos' model was found to be the most accurate method for the estimation of the saturated vapour pressure of these aroma compounds. The importance of accurate saturated vapour pressures for the calculation of other thermodynamic properties used in the study of vapour–liquid equilibria of aroma compounds is discussed.