The vapour pressure behaviour and the association of N-methylethylamine,diethylamine and their N-deuterioanalogues in mixtures with n-hexane

The vapour pressure isotherms of mixtures of N-methylethylamine and N-methyl(N-²H)ethylamine with n-hexane have been measured between 273 and 323 K. The vapour pressure isotherms of mixtures of diethylamine and (N-²H)diethylamine with nhexane between 293 and 353 K have also been measured. In addition, the vapour pressures of the pure amines have been determined down to 228 or 243 K. As evidenced by the small values for the Wilson coefficients, the activity coefficients, the Gibbs free energies and the data derived from the theory of ideal associated solutions, the association of diethlamine is very weak; that of N-methylethylamine is not much larger. The observations on the vapour pressure isotope effect of the two amines and their N-deuterioanalogues are compatible with this interpretation. The normal effect is smaller for diethylamine, with ratios P_D/P_H of 0.972–0.997 between 243 and 323 K, than for N-methylethylamine with values of 0.965–0.991, and the partial pressure quotients calculated for mixtures of the two compounds with n-hexane show the transition from the normal to the inverse effect on low dilution. The data for the N-deuterioanalogues and their mixtures with n-hexane suggest a somewhat greater energy of the deuterium bonds.     

The vapour pressure,orthobaric volumes,and critical constants of tetramethylsilane

The vapour pressure and orthobaric molar volumes of tetramethylsilane have been messured from 373 K to the critical temperature, and the critical temperature (IPTS-68: T^{o = 448.64 K}), critical pressure (p^{c = 2821 kPa}), and critical molar volume (V_m^c = 361 cm³ mol^?1) have been determined.     

Vapour-liquid equilibria. I. An apparatus for isothermal total vapour pressure measurements: Binary mixtures of ethanol and t-butanol with n-hexane, n-heptane and n-octane at 313.15 K

A static apparatus for the determination of total vapour pressure isotherms of mixtures is described. The apparatus works without a null manometer, and degassing of samples is done without freezing. VLE data for six binary mixtures of ethanol and t-butanol with n-hexane, n-heptane and n-octane are reported and compared with literature data. References to other VLE data obtained using this apparatus are also given.     

Thermodynamics of liquid propane + cyclopropane

The vapour pressure differences between a mixture of (propane + cyclopropane) and cyclopropane and between propane and cyclopropane have been measured simultaneously with the absolute vapour pressure of cyclopropane. This was done at 13 temperatures between 175 K and 210 K, as a function of composition. The mixtures show small positive deviations from Raoult's law. The excess molar Gibbs energy (G_m^E) has been calculated from the vapour pressure data fitted to the equation G_m^E/(RTx₁x₂ = (−0.2490±0.0072)+(81.8±1.4)/T. The estimated value of the excess molar enthalpy (H_m^E) for the equimolar composition, in the same temperature range is 170 ± 4 J mol⁻¹. The results were interpreted using Deiters' equation of state.     

Vapour pressure of C60 by a transpiration method using a horizontal thermobalance

A horizontal thermal analysis system was adopted for the measurement of vapour pressure of C₆₀ using the vapour transport technique. The experimental precautions taken in order to ensure measurement of equilibrium vapour pressure by the transpiration method are described. The equilibrium nature of these measurements was ensured by the existence of plateau regions in the isothermal plots of apparent vapour pressure as a function of flow rate of the carrier gas. To verify the applicability of this TG based transpiration method, vapour pressure of CsI was measured to be log(p/Pa)=11.667±0.013−(9390±0.078)/T (K) over the range 737–874 K yielding a value of 195.6 kJ mol⁻¹ for the third-law enthalpy of sublimation, ΔH⁰_sub,298 of CsI, the value which compares well with the literature data. The vapour pressure measurements on C₆₀ over the range 789–907 K could be represented by log(p/Pa)=9.018±0.061−(7955±0.280)/T(K). Third-law treatment of the data yielded a value of 183.5±1.0 kJ mol⁻¹ for ΔH⁰_sub,298 of C₆₀ which is in good agreement with some of the other vapour pressure measurements in the literature, if subjected to third-law processing using the same set of free energy functions reliably reported in the literature.     

Vapour pressure and thermodynamic properties of hexamethyldisilane at 305–387 K

The Swietoslawski's differential ebulliometer has been minimized to be usable for ca. 13 cm³ of liquid. After a performance test with acetone, the vapour pressure of hexamethyldisilane is determined over the temperature range 304.61–386.74 K. The Antoine equation obtained is log₁₀(P/kPa) = 5.97097 − 1319.85/{(T/K) − 52.96} and the normal boiling point is 385.81 K. The present results agree with literature values of Suga and Seki at 287–310 K and Brockway and Davidson at 293–334 K.     

New pressure-density-temperature measurements and new rational equations for the saturated liquid and vapour densities of oxygen

The results of pressure, density, temperature (p, ?, T) measurements in the temperature range from 65 K to 300 K, for pressures up to 7.2 MPa, and for densities from 0.3 mol dm^?3 to 39 mol dm^?3, are presented for pure oxygen. Using the experimental results, new values for the densities of saturated liquid and vapour are evaluated. To check the accuracy of these results, corresponding sets reported in the literature are critically analysed to determine the most reliable p, ?, T set for oxygen. Finally, new equations for the densities of saturated liquid and vapour are developed using a statistical procedure.     

New equipment using a static analytic method for the study of vapour–liquid equilibria at temperatures down to 77 K

A new apparatus designed for the study of vapour–liquid equilibria (VLE) of small molecules at temperatures down to 77 K and pressures up to 40 MPa was built, set-up and used up to 2.8 MPa. It is based on the `static-analytic' method using two pneumatic capillary sampling devices, which allow taking small and reliable in-situ samples and performing direct analyses through gas chromatography. Accurate P, x, y isothermal data obtained for the O₂–N₂ and Ar–N₂ mixtures are well represented by the Soave–Redlich–Kwong equation of state (SRK-EoS). The conclusions which can be drawn from the comparison with literature data are the following: maximum deviations on pressure, temperature and vapour phase composition, between literature experimental data and the calculated ones (using our binary interaction parameters) are not larger than 3.3%, 0.12 K and 4.2%. We also point out inconsistencies in several literature data.     

Thermodynamic properties of saturated and compressed liquid difluorochloromethane

In an isochoric study the thermodynamic behaviour of liquid difluorochloromethane was experimentally investigated. New measurements of (p, ?, T) have been carried out at densities from 0.83 to 1.36 g·cm^?3 (reduced densities from 1.6 to 2.7) and pressures up to 60 MPa. In addition new results for the vapour pressure of liquid difluorochloromethane are reported at temperatures from 312 to 369 K. Saturated liquid densities were obtained from the extrapolation of the isochoric results to the vapour-liquid coexistence curve.     

Precision Evaluation in Kr Adsorption for Small BET Surface Area Measurements of Less Than 1 m2

A volumetric Kr-adsorption apparatus using a precise capacitance manometer has been developed. A specially designed adsorption cell (CVC: constant volume adsorption cell) utilizing a vacuum jacket (Joyner et al., 1949) is adopted to keep the adsorption cell volume constant regardless of the variation in liquid nitrogen level throughout the experiment. Using the CVC, the pressure change in accordance with liquid N₂ supply cycle has been minimized to less than 0.01 Pa compare to about 1 Pa for conventional cell. Time dependent change of the adsorption cell volume and repeatability in its measurements have been demonstrated in detail using helium gas. Good linearity of the BET plot of the Kr adsorption isotherm on several hundred cm² samples are demonstrated in the relative pressure range from 0.05 to 0.35.     

Surface tension for octafluorocyclobutane,n-butane and their mixtures from 233 K to 254 K,and vapour pressure,excess Gibbs function and excess volume for the mixture at 233 K

The surface tensions of octafluorocyclobutane (234 to 267 K), n-butane (238 to 273 K) and of their mixtures (232 to 254 K) have been measured by differential capillary rise; there is a slight minimum in the isotherms near x(c-C₄F₈) ≈ 0.8 but no maximum. The total vapour pressure and density of the liquid mixture were measured at the triple point temperature of c-C₄F₈, 233 K. The mixture displays marked positive azeotropy. The excess Gibbs function and excess volume are both large and positive but the deviation from ideality is insufficient for liquid—liquid immiscibility whose absence was confirmed by visual observation at temperatures down to the solid—liquid phase boundary. All the foregoing are consistent with theoretical expectations based upon the dominant effect of an interaction energy between the unlike components which is smaller than that predicted by the Berthelot geometric mean rule. No inferences can be drawn as to the role of chain flexibility.     

Representation T-V-x des systemes binaires a tension de vapeur non negligeable

The effect of the variableV/m on the appearance of DTA endotherms has been used to obtain quantitative data on theT-V-x representation of the NdAs-As system. The peritectic reaction is NdAs₂ (solid)+vapour ? NdAs (solid)+liquid at 1185 K. At this temperature, the four phases set up a quadrangle in theV/m-x plane. The sides of this quadrangle have been defined by experiment: the vapour phase is composed of 87 mol% As and itsV/m value is 12.2 mm³ mg^?1. The peritectic liquid is composed of 87 mol% As. The eutectic equilibrium at 1080 K appears to be NdAs (solid)+As (solid)+vapour ← liquid It sets up a triangle, inside which the liquid phase is placed. The vapour phase is composed of 100 mol% As, and itsV/m value is 10 mm³ mg^?1. The eutectic liquid is composed of 90 mol% As. Three polythermal sections of the NdAs-As binary system are described for a constant volume.     

An equipment for dynamic measurements of vapour–liquid equilibria and results in binary systems containing cyclohexylamine

A computer-aided equipment for precise measurements of vapour–liquid equilibrium (VLE) data at normal and low pressures using the dynamic method will be introduced. The apparatus consists of a circulation still which allows isothermal and isobaric measurements. The digital measurement and control system is accomplished by a multimeter coupled with a PC via IEEE-card. The quality of the measurement data is demonstrated by a comparison of the measured vapour pressure data of the pure substances toluene, n-octane and cyclohexylamine with the vapour pressure equation of Daubert and Danner. Furthermore, vapour–liquid equilibrium data were measured in the binary systems cyclohexylamine + aniline or water or n-octane. The measured data were regressed according to the activity coefficient models NRTL, UNIQUAC and to the Elliott–Suresh–Donohue-equation of state (ESD-EOS).     

Vapour pressure of diethyl phthalate

Measurements of vapour pressure in the liquid phase and of enthalpy of vaporisation and results of calculation of ideal-gas properties for diethyl phthalate are reported. The method of comparative ebulliometry, the static method, and the Knudsen mass-loss effusion method were employed to determine the vapour pressure. A Calvet-type differential microcalorimeter was used to measure the enthalpy of vaporisation. Simultaneous correlation of vapour pressure, of enthalpy of vaporisation and of difference in heat capacities of ideal gas and liquid/solid phases was used to generate parameters of the Cox equation that cover both the (vapour + solid) equilibrium (approximate temperature range from 220 K to 270 K) and (vapour + liquid) equilibrium (from 270 K to 520 K). Vapour pressure and enthalpy of vaporisation derived from the fit are reported at the triple-point temperature T = 269.92 K (p = 0.0029 Pa, Δ_vapH_m = 85.10 kJ · mol⁻¹ ), at T = 298.15 K (p = 0.099 Pa, Δ_vapH_m = 82.09 kJ · mol⁻¹), and at the normal boiling temperature T = 570.50 K (Δ_vapH_m = 56.49 kJ · mol⁻¹). Measured vapour pressures and measured and calculated enthalpies of vaporisation are compared with literature data.     

Mesures calorimétriques des enthalpies de vaporisation et de sublimation par effusion; mise au point de la technique

The association of an effusion cell to a Tian-Calvet microcalorimeter offers the possibility of measuring, at 298.15 K, energies of vaporisation (or sublimation) of compounds, the vapour pressures of which range from 10⁻⁴ to 100 torr, with a reproducibility of 1%. The following results are obtained for enthalpies of vaporisation [(ΔH_vap)_m] of water (vapour pressure, 23.7 torr at 298.15 K), 43.84±0.29 kJ.mol⁻¹; cyclohexane (vapour pressure, 97.5 torr at 298.15 K), 32.89±0.29 kJ.mol⁻¹; hexamethylphosphotriamide (vapour pressure, 51.10⁻³ torr at 298.15 K), 61.1± 1.7 kJ.mol⁻¹.     

Thermodynamic study of the vaporization of uracil

The vapour pressure of uracil was measured in the temperature range 452–587 K using different techniques and the pressure—temperature equation log P(kPa) = 12.13 ± 0.50 — (6823 ± 210)/T was derived. The thermodynamic functions of gaseous and solid uracil were also evaluated through spectroscopic and calorimetric measurements. The sublimation enthalpy of uracil, ΔH⁰₂₉₈ = 131 ± 5 kJ mole^?1, was derived from second and third law treatment of the vapour data.     

Monte Carlo simulations of squalane in the Gibbs ensemble

We investigate the liquid–vapour coexistence curve of 2,6,10,15,19,23-hexamethyltetracosane (squalane) near the critical point with a new Lennard–Jones parameter set and compare our results to existing simulation data as well as to recent experimental vapour pressure data. Comparison of the liquid–vapour coexistence curve to previous simulation data reveals that this new force field, which includes tail corrections to the truncation of the non-bonded interactions increases the liquid density. We determine the critical temperature to 829 K and 825 K (with roughly 1% error) for two different system sizes, 72 and 108 molecules, and the critical density to 0.211 g/cm³ and 0.228 g/cm³, respectively. We extrapolate experimental vapour pressure data by use of Antoine's law to the temperature range covered by simulation and yield good agreement between simulation and experiment. We note that the vapour pressure in simulation is essentially governed by the ideal vapour pressure.     

Thermodynamic properties of liquid mixtures of carbon monoxide and methane

The equations of state of liquid methane at 125.00 K and of six liquid mixtures of carbon monoxide and methane at 116.30, 120.00 and 125.00 K have been measured from just above the saturation vapour pressure to the freezing pressure of methane. The results show that the excess volume V^E is large and negative at low pressures but becomes less negative as the pressure is increased, being almost zero at the highest pressures. The curve of V^E against the mole fraction x is very asymmetrical at low pressures, but becomes more symmetrical with rising pressure.The effect of pressure on the excess functions G^E, H^E and T·S^E has been calculated. H^E and T·S^E prove to be much more sensitive to pressure than G^E.Conformal solution theory, in the van der Waals one-fluid form, reproduces the experimental results very successfully.     

Liquid–liquid equilibrium data of water with neohexane,methylcyclohexane, tert-butyl methyl ether,n-heptane and vapor–liquid–liquid equilibrium with methane

Liquid–liquid equilibrium (LLE) data for non-aqueous liquid (neohexane [NH], tert-butyl methyl ether [TBME], methylcyclohexane [MCH], or n-heptane [nC₇]) and water have been measured under atmospheric pressure at 275.5, 283.15, and 298.15 K. It was found that TBME is the most water soluble followed by NH, MCH, and nC₇. As the temperature increased, the solubility of the non-aqueous liquids (NALs) in water decreased. The solubility of water in the non-aqueous liquid was found to increase in the following order: MCH < nC₇ < NH < TBME. It was found to increase with increasing temperature. In addition, vapour–liquid–liquid equilibrium (VLLE) data for the above binary systems with methane were measured at 275.5 K and at 120, 1000, and 2000 kPa. It was found that the vapour composition of water and NALs decreased as the pressure increased. The water content in the non-aqueous phase was not a strong function of pressure. The concentration of methane in the non-aqueous phase increased as the pressure increased. Furthermore, the concentration of the methane and NALs in the water phase increased proportionally with pressure. The solubility of methane in water followed Henry's law. It is noted that the measurements were completed prior to the onset of hydrate nucleation.     

Excess Gibbs energies of the ternary system ethanol+N,N-dimethylformamide+cyclohexane at 298.15 K

Vapour–liquid equilibrium (VLE) for the ternary system ethanol (EtOH)+N,N-dimethylformamide (DMF)+cyclohexane (Cy) and for the relevant binary mixtures containing DMF have been determined at 298.15 K by headspace gas chromatographic analysis of the vapour phase directly withdrawn from an equilibrium apparatus. Measurements of liquid–liquid equilibria in both binary DMF+Cy and ternary mixtures have been also carried out. The binary VLE data have been described with different correlation equations. The capabilities of different models of either predicting or reproducing the ternary data have been compared. Excess Gibbs energies G^E as well as activity coefficients γ_i of components have been obtained and briefly discussed. While EtOH+DMF behaves almost ideally with slightly negative G^E-values, both EtOH+Cy and DMF+Cy exhibit large positive deviations. The G^Es of the ternary system are positive with the exception of a narrow region in dilute Cy. The excess entropy and the temperature dependence of G^E and γ_i have been calculated in the whole ternary domain from the known excess enthalpy and heat capacity. The predictions by different equations of the effect of temperature on the mutual solubilities of DMF and Cy as well as on the binodal curve of EtOH+DMF+Cy have been compared with experiment.