Vapour pressures of n-hexane determined by comparative ebulliometry

The vapour pressures of n-hexane have been measured using comparative ebulliometry with water as the reference fluid. The measurements cover the temperature and pressure range (315.7 K, 41.1 kPa) to (504.0 K, 2876.8 kPa) and join smoothly with results selected from the literature to provide consistent results down to (289.7 K, 13.8 kPa). The combined data set have been described by a Wagner style equation with a fractional standard deviation of 4.2 · 10⁻⁵ in the vapour pressure. The critical pressure p_c was treated as an adjustable parameter and the value of p_c = 3027 kPa was calculated from the smoothing equation using a selected critical temperature of T_c = 507.49 K. The calculated normal boiling temperature is T_b = 341.866 K and an extrapolation to the triple-point temperature T_tp = 177.87 K predicts a triple-point pressure of p_tp = 1.23 Pa.     

Measurement and correlation of the ( p, ρ, T) relation of sulphur hexafluoride (SF 6). II. Saturated-liquid and saturated-vapour densities and vapour pressures along the entire coexistence curve

Comprehensive and accurate measurements of the saturated-liquid and saturated-vapour densities together with the vapour pressure of pure sulphur hexafluoride were carried out from the temperature T =  224 K (triple-point temperature T_t =  223.555 K) to 0.033 K below the critical temperature ( T_c =  318.723 K). Typical values of the total uncertainties of the measurements are: ⩽ ± 0.01 percent for the vapour pressures,⩽ ± 0.015 percent for the saturated-liquid densities, and⩽ ± 0.016 percent for the saturated-vapour densities. The values for the critical density and the critical pressure ( ρ_c =  742.26 kg · m ^− 3, p_c =  3.7550 MPa) and the isothermal compressibilities in the critical region close to the phase boundary have also been determined from these measurements. Comparisons with experimental results of previous workers are presented. Using the new values of this work, new correlation equations for the vapour pressure, the saturated-liquid density, and the saturated-vapour density have been established.     

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.     

Thermodynamic study of the sublimation of crystalline tris(1,1,1-trifluoro-2,4-pentanedionate)ruthenium(III) and tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)ruthenium(III)

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of two crystalline ruthenium complexes: tris(1,1,1-trifluoro-2,4-pentanedionate)ruthenium(III) {Ru(tfacac)₃}, between T =  350.20 K and T =  369.17 K and tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)ruthenium(III) {Ru(hfacac)₃} between T =  299.15 K and T =  313.14 K. From the temperature dependence of the vapour pressure of the crystalline compounds, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. By using an estimated value for the heat capacity differences between the gas and the crystal phases the standard, p^o =  10⁵Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T =  298.15 K, were derived:     

Thermodynamic study on the sublimation of 1,2-diphenylethane and of 3-phenylpropiolic acid

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline compounds: 1,2-diphenylethane (bibenzyl), between T =  289.16 K and T =  303.20 K, and of 3-phenylpropiolic acid between T =  329.15 K and T =  343.15 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation at the mean temperature of the experimental range were derived by the Clausius–Clapeyron equation. From these results the standard, p^o =  10⁵Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T =  298.15 K, were calculated:     

Thermodynamic study on the sublimation of 3-phenylpropionic acid and of three methoxy-substituted 3-phenylpropionic acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following compounds: 3-phenylpropionic acid, between T =  305.17 K and T =  315.17 K; 3-(2-methoxyphenyl)propionic acid, between T =  331.16 K and T =  347.16 K; 3-(4-methoxyphenyl)propionic acid, between T =  341.19 K and T =  357.15 K; 3-(3,4-dimethoxyphenyl)propionic acid, between T =  352.18 K and T =  366.16 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation Δ_cr^gH_m^owere derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. On the basis of estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p ^∘  =  10⁵Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T =  298.15 K, were derived:     

Measurements of the critical parameters for {xNH3 + (1 − x)H2O} with x = (0.9098, 0.7757, 0.6808)

Measurements of the critical parameters for {xNH₃ + (1 ? x)H₂O} with x = (0.9098, 0.7757, 0.6808) were carried out by using a metal-bellows variable volumometer with an optical cell. The expanded uncertainties (k = 2) in temperature, pressure, density, and composition measurements have been estimated to be less than 3.2 mK, 3.2 kPa, 0.3 kg · m^?3, and 8.8 · 10^?4, respectively. In each mole fraction, the critical temperature T_c was first determined on the basis of the intensity of the critical opalescence. The critical pressure p_c and critical density ρ_c were then determined as the point at which the meniscus disappears on the isotherm at T = T_c. The expanded uncertainties (k = 2) in the present critical parameters have also been estimated. Comparisons of the present values with the literature data as well as the calculated values afforded using the equation of state are also presented.     

Critical properties of some aliphatic symmetrical ethers

The critical temperatures T_c and the critical pressures p_c of dihexyl, dioctyl, and didecyl ethers have been measured. According to the measurements, the coordinates of the critical points are T_c = (665 ± 7) K, p_c = (1.44 ± 0.04) MPa for dihexyl ether, T_c = (723 ± 7) K, p_c = (1.19 ± 0.04) MPa for dioctyl ether, and T_c = (768 ± 8) K, p_c = (1.03 ± 0.03) MPa for didecyl ether. All the ethers studied degrade chemically at near-critical temperatures. A pulse-heating method applicable to measuring the critical properties of thermally unstable compounds has been used. The times from the beginning of a heating pulse to the moment of reaching the critical temperature were from 0.06 to 0.46 ms. The short residence times provide little decomposition of the substances in the course of the experiments. The critical properties of the ethers investigated in this work have been discussed together with those of methyl to butyl ethers. The experimental critical constants of the ethers have been compared with those estimated by the group-contribution methods of Wilson and Jasperson and Marrero and Gani. The Wilson/Jasperson method provides a better estimation of the critical temperatures and pressures of simple aliphatic ethers in comparison with the Marrero/Gani method if reliable normal boiling temperatures are used in the method of Wilson and Jasperson.     

Thermodynamic study on the sublimation of succinic acid and of methyl- and dimethyl-substituted succinic and glutaric acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline dicarboxylic acids: succinic acid, between T =  360.11 K and T =  375.14 K; methylsuccinic acid, between T =  343.12 K and T =  360.11 K; 2,2-dimethylsuccinic acid, between T =  350.11 K, and T =  365.11 K; 2-methylglutaric acid, between T =  338.38 K and T =  347.63 K; and 2,2-dimethylglutaric acid between T =  342.18 K and T =  352.66 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds, the standard, p^o =  10⁵Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T =  298.15 K, were derived:     

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.     

Thermodynamic study on the sublimation of six methylnitrobenzoic acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following six compounds: 2-methyl-3-nitrobenzoic acid, between T =  357.16 K and T =  371.16 K; 2-methyl-6-nitrobenzoic acid, between T =  355.16 K and T =  369.16 K; 3-methyl-2-nitrobenzoic acid, between T =  371.16 K and T =  385.14 K; 3-methyl-4-nitrobenzoic acid, between T =  363.21 K and T =  379.16 K; 4-methyl-3-nitrobenzoic acid, between T =  363.10 K and T =  377.18 K; 5-methyl-2-nitrobenzoic acid, between T =  355.18 K and T =  371.08 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p^o =  10⁵Pa, molar enthalpies Δ_cr^gH_m^o, entropies Δ_cr^gS_m^oand Gibbs energies Δ_cr^gG_m^oof sublimation at T =  298.15 K, were derived:     

Thermodynamic study of the sublimation of six aminomethylbenzoic acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following substituted benzoic acids: 2-amino-3-methylbenzoic acid at T between 343.16 K and 357.17 K; 2-amino-5-methylbenzoic acid at T between 345.15 K and 361.16 K; 2-amino-6-methylbenzoic acid at T between 339.17 K and 355.15 K; 3-amino-2-methylbenzoic acid at T between 367.16 K and 381.22 K; 3-amino-4-methylbenzoic acid at T between 363.18 K and 377.16 K; and 4-amino-3-methylbenzoic acid at T between 367.17 K and 383.14 K. The standard, p⁰ =  10⁵Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T =  298.15 K were derived from the temperature dependence of the vapour pressure using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds.     

Thermodynamics of vaporization of some alkyladamantanes

The boiling temperature of 1,3-dimethyladamantane was measured by comparative ebulliometry over the pressure range 6  <  (p / kPa)  <  100. The temperature dependencies of saturation vapour pressure and enthalpy of vaporization, and the normal boiling temperature,T_b =  476.53 K, were derived. The enthalpy of vaporization,ΔlgHmo =  (49.21  ±  0.2)kJ · mol ^− 1, was calorimetrically measured atT =  308.15 K. The experimental and calculatedΔlgHmo values were found to agree within the error limits. Densities of the liquid phase were measured at the temperatures (293.15, 298.15, and 303.15) K. The experimental vapour pressures of 1,3-dimethyladamantane and of the previously studied 1,3,5-trimethyladamantane were extrapolated to the regions of the liquid phases from the triple to the critical temperatures.     

Vapor pressures and vaporization enthalpy of codlemone by correlation gas chromatography

The vapor pressure and vaporization enthalpy of codlemone (trans, trans 8,10-dodecadien-1-ol), the female sex hormone of the codling moth is evaluated by correlation gas chromatography using a series of saturated primary alcohols as standards. A vaporization enthalpy of (92.3 ± 2.6) kJ · mol⁻¹ and a vapor pressure, p/Pa = (0.083 ± 0.012) were evaluated at T = 298.15 K. An equation for the evaluation of vapor pressure from ambient temperature to boiling has been derived by correlation for codlemone. The calculated boiling temperature of T_B = 389 K at p = 267 Pa is within the temperature range reported in the literature. A normal boiling temperature of T_B = (549.1 ± 0.1) K is also estimated by extrapolation.     

Thermodynamic properties of 1,2-dihydronaphthalene: Glassy crystals and missing entropy

Measurements leading to the calculation of the standard thermodynamic properties for gaseous 1,2-dihydronaphthalene (Chemical Abstracts registry number [447-53-0]) are reported. Experimental methods include oxygen combustion-bomb calorimetry, adiabatic heat-capacity calorimetry, vibrating-tube densitometry, comparative ebulliometry, and inclined-piston gauge manometry. 1,2-Dihydronaphthalene decomposed significantly when heated to temperatures above T = 480 K. Consequently, the critical temperature, critical pressure, and critical density were estimated. Standard molar entropies, standard molar enthalpies, and standard molar Gibbs free energies of formation were derived at selected temperatures between T = 250 K and 500 K. The standard state is defined as the ideal gas at the pressure p = p^° = 101.325 kPa. Standard entropies are compared with those calculated statistically on the basis of assigned vibrational spectra from the literature for the vapor phase. A large and near constant difference between the entropies calculated statistically and those determined calorimetrically was observed over the entire temperature range studied. Two glass-like features are observed in the heat capacity against temperature curve for the solid state, indicating that the crystals are disordered. A quantitative accounting for the entropy discrepancy is proposed based on possible molecular orientations of 1,2-dihydronaphthalene. Results are compared with experimental values reported in the literature.     

Vapour pressures of selected organic compounds down to 1 mPa,using mass-loss Knudsen effusion method

A recently developed Knudsen effusion apparatus was improved and used for measurements of vapour pressures of selected organic compounds. Calorimetric studies were conducted using a Calvet-type calorimeter, complementing the information obtained for the vapour pressures and facilitating the modelling and analysis of the data.Vapour pressures of benzoic acid, a reference substance, were determined at temperatures between 269 K and 317 K, corresponding to a pressure range from 2 mPa to 1 Pa, extending the range of results available in the literature to lower pressures. Benzanthrone was studied between temperatures 360 K and 410 K (5 mPa–1 Pa) in order to test the apparatus at higher temperatures.Values presented in the literature for the vapour pressure of solid n-octadecane, one of the most promising compounds to be used as “phase change material” for textile applications, were found inconsistent with the triple point of the substance. Sublimation pressures were measured for this compound between T = 286 K and 298 K (2–20 mPa) allowing the correction of the existing values. Finally, vapour pressures of diphenyl carbonate, a compound of high industrial relevance for its use in the production of polycarbonates, were determined from T = 302 K to 332 K (0.02–1 Pa).     

Dichloromethane: Revision and extension of pρT relationships for the liquid

In spite of the great importance of the PVT data of dichloromethane, only limited information on these data seems to be available in the literature. In this work, we present experimental densities of the liquid dichloromethane over the ranges T = (270 to 330) K and p = (0.1 to 30) MPa using a vibrating tube densimeter, model DMA 512P from Anton Paar with an estimated uncertainty lower than ±0.5 kg · m^?3. The high consistency of our data compared with those measured by other authors allows that all the experimental results have been combined and correlated together with the Tait equation in the temperature and pressure ranges T = (244 to 430) K and p = (0.1 to 101) MPa. From the Tait equation, thermomechanical coefficients as the isothermal compressibility, isobaric expansivity, thermal pressure, and internal pressure were calculated. Some of the measurements of density were made at pressures lower than the critical pressure which enabled us to obtain very reliable values for the density of the saturated liquid within the range T = (270.0 to 330.0) K. These data were combined with other values existing in the literature, which made it possible to extend the information on the saturated liquid density to the range T = (208 to 399) K. From these data, a new equation describing the saturated liquid density of dichloromethane was found covering the entire temperature range between the triple and the critical temperatures. A new equation for the vapour pressure was found by using selected values from the literature covering the entire temperature range between the triple and the critical temperatures.     

Measurements of (p, ρ, T) properties for isobutane in the temperature range from 280 K to 440 K at pressures up to 200 MPa

Measurements of (p, ρ, T) properties for isobutane in the compressed liquid phase have been obtained by means of a metal-bellows variable volumometer in the temperature range from 280 K to 440 K at pressures up to 200 MPa. The volume-fraction purity of isobutane used was 0.9999. The expanded uncertainties (k = 2) of temperature, pressure, and density measurements have been estimated to be less than 3 mK, 1.5 kPa (p ⩽ 7 MPa), 0.06% (7 MPa < p ⩽ 50 MPa), 0.1% (50 MPa < p ⩽ 150 MPa), and 0.2% (p > 150 MPa), and 0.11%, respectively. In region more than 100 MPa at 280 K and 440 K, the uncertainty in density measurements rise up to 0.15% and 0.23%, respectively. The differences of the present density values at the same temperature between two series of measurements, in which the sample fillings are different, are within the maximum deviation of 0.09% in density, which is enough lower than the expanded uncertainty in density. Eight (p, ρ, T) measurements at the same temperatures and pressures as the literature values have been conducted for comparison. In addition, vapour pressures were measured at T = (280, 300) K. Moreover, the comparisons of the available equations of state with the present measurements are reported.     

Hydrogen production from hydrogen sulfide using membrane reactor integrated with porous membrane having thermal and corrosion resistance

Using mathematical model and experimental method, the thermal decomposition of hydrogen sulfide in membrane reactor with porous membrane which has Knudsen diffusion characteristics was investigated. With mathematical model, the effect of characteristics of membrane reactor and operating conditions on H₂ concentration in the permeate chamber, y_H2, which increases at higher reaction temperature, lower pressure and higher ratio of cross-sectional area of the permeate chamber to that of the reactor, was evaluated. The reaction experiments with ZrO₂–SiO₂ porous membrane were carried out under the following conditions: temperature T, 923–1023 K; pressure in the reactor p^R_T, 0.11–0.25 MPa absolute; pressure in the permeate chamber p^P_T, 5 kPa absolute and inlet flow rate of H₂S f⁰_H2S, 3.2×10⁻⁵–1.5×10⁻⁴ mol/s. At p^R_T=0.11 MPa and f⁰_H2S=6.4×10⁻⁵, y_H2 increased from 0.02 at T=923 K to 0.15 at 1023 K. With the experimental condition, p^R_T=0.11, T=1023 K and f⁰_H2S=3.2×10⁻⁵, y_H2 was 0.22. The experimental results were compared with the results of the mathematical analysis. The agreement between both the results is found rather good at a lower reacting temperature, but not so good at a higher reacting temperature.     

Bubble points measurement for (triethyl orthoformate + diethyl malonate)

The bubble points for (triethyl orthoformate + diethyl malonate) at T = (373.15, 383.15, and 393.15) K and at p = 13.33 kPa, measured with an inclined ebulliometer are presented. The experimental results are analyzed using the UNIQUAC equation with the temperature-dependent binary parameters with satisfactory results. Experimental vapour pressures of triethyl orthoformate are also included.