Determination Of Vapor Pressure Research Articles

Vapour pressure of water over saturated solutions of tartaric acid, sodium hydrogen tartrate, sodium tartrate, potassium tartrate, calcium tartrate, barium tartrate, citric acid, disodium hydrogen citrate, sodium citrate, and potassium citrate at temperatures from 277 K to 317 K

Vapour pressures of saturated aqueous solutions of tartaric acid, sodium hydrogen tartrate, sodium tartrate, potassium tartrate, calcium tartrate, barium tartrate, citric acid, disodium hydrogen citrate, sodium citrate, and potassium citrate were determined in the temperature range (277 to 317) K using an electronic hygrometer. Only for tartaric acid, sodium tartrate, potassium tartrate and citric acid was it possible to compare the determined vapour pressures with the isoteniscopic results available in the literature. The measured vapour pressures allow the determination of water activities and molar enthalpies of vaporization of solutions at saturation conditions and osmotic coefficients if the solubilities of these compounds in water are known.

Vapor pressure by DSC: extending ASTM E 1782 below 5 kPa

In 1996, American Society for Testing and Materials (ASTM) Method E 1782–96, Standard Test Method for Determining Vapor Pressure by Thermal Analysis received final approval and was published as a standard method. For vapor pressure measurements by DSC, the method requires use of hermetic-type sealable pans with a single pinhole ≤125 μm (50–75 μm recommended) in the center of the lid. Pinholes of this size produce generally acceptable results over the 5 kPa to 2 MPa operational pressure range of the method. However, as the minimum recommended pressure is approached, boiling endotherms become increasingly broad. Recent efforts using larger pinholes (175–375 μm) have shown improved peak sharpness and elimination of leading edge curvature when pinhole size is increased as pressure is reduced. This need for increased pinhole diameter at lower pressures is consistent with orifice selections used in effusion studies. Optimization of pinhole size as a function of pressure may extend the practical operational range of ASTM E 1782 to permit rapid vapor pressure determination to at least 0.2 kPa.

Oliver Cecil Simpson

Oliver Cecil Simpson

The vapour pressure of water over saturated solutions of sodium sulfate, calcium bromide, ferric chloride, zinc nitrate, calcium nitrate, and lithium nitrate at temperatures from 278.15 K to 323.15 K

Vapour pressures of saturated aqueous solutions of Na 2SO 4,CaBr 2,FeCl 3,Zn(NO 3) 2,Ca(NO 3) 2, and LiNO 3 were determined in the temperature range from 278 K to 323 K using an electronic hygrometer with an electrolyte sensor and compared with literature data. Water activities, osmotic coefficients, and molar enthalpies of vapourization and solution at saturation point were evaluated from the determined vapour pressures.

A Study of the Physico-chemical Behavior of Diacetyl in Hydroalcoholic Solution With and Without Added Catechin and Wood Extract

The interactions of diacetyl and ethanol in model solutions were studied in order to improve understanding of the changes in flavor perception that occur during both alcoholic beverage processing and consumption. A gradual reduction was demonstrated in the activity and partition coefficients of diacetyl as the ethanol concentration in aqueous solutions increased. From a sensory point of view, this fact would be expected to cause an increase in the diacetyl sensory thresholds. The expected diacetyl sensory thresholds were calculated based on experimental determination of the diacetyl vapor pressure in ethanol–water solutions at different ethanol concentrations. These sensory thresholds were not measured but merely obtained by theoretical interpolations. No significant variations in the activity coefficients of diacetyl were observed in the presence of catechin. Conversely, the dissolution of wood extract at 40% ethanol caused a significant decrease in diacetyl vapor pressure. The addition of catechin and wood extract to 40% ethanol–water solution contributed to the interactions of ethanol and water measured by DSC analysis.

Thermodynamic Properties and Ideal-Gas Enthalpies of Formation for Methyl Benzoate, Ethyl Benzoate, (R)-(+)-Limonene, tert-Amyl Methyl Ether, trans-Crotonaldehyde, and Diethylene Glycol

Ideal-gas enthalpies of formation of methyl benzoate, ethyl benzoate, (R)-(+)-limonene, tert-amyl methyl ether, trans-crotonaldehyde, and diethylene glycol are reported. The standard energy of combustion and hence standard enthalpy of formation of each compound in the liquid phase has been measured using an oxygen rotating-bomb calorimeter without rotation. Vapor pressures were measured to a pressure limit of 270 kPa or the lower decomposition point for each of the six compounds using a twin ebulliometric apparatus. Liquid-phase densities along the saturation line were measured for each compound over a range of temperature (ambient to a maximum of 548 K). A differential scanning calorimeter was used to measure two-phase (liquid + vapor) heat capacities for each compound in the temperature region ambient to the critical temperature or lower decomposition point. For methyl benzoate and tert-amyl methyl ether, critical temperatures and critical densities were determined from the DSC results and corresponding critical pressures derived from the fitting procedures. Fitting procedures were used to derive critical temperatures, critical pressures, and critical densities for each of the remaining compounds. The results of the measurements were combined to derive a series of thermophysical properties including critical temperature, critical density, critical pressure, acentric factor, enthalpies of vaporization (restricted to within ±50 K of the temperature region of the experimentally determined vapor pressures), and heat capacities along the saturation line. Wagner-type vapor-pressure equations were derived for each compound. All measured and derived values were compared with those obtained in a search of the literature. Recommended critical parameters are listed for each of the compounds studied. Group-additivity parameters, useful in the application of the Benson gas-phase group-contribution correlations, were derived.

Vapor Pressure, Heat Capacity, and Density along the Saturation Line: Measurements for Benzenamine, Butylbenzene,sec-Butylbenzene,tert-Butylbenzene, 2,2-Dimethylbutanoic Acid, Tridecafluoroheptanoic Acid, 2-Butyl-2-ethyl-1,3-propanediol, 2,2,4-Trimethyl-1,3-pentanediol, and 1-Chloro-2-propanol

This paper reports measurements made within DIPPR2 Project 821 for the 1995 Project Year. Vapor pressures were measured to a pressure limit of 270 kPa or lower decomposition point using a twin ebulliometric apparatus for the nine compounds listed in the title. Liquid-phase densities along the saturation line were measured for each compound over a range of temperatures (ambient to a maximum of 523 K). A differential scanning calorimeter was used to measure two-phase (liquid + vapor) heat capacities for each compound in the temperature region ambient to the critical temperature or lower decomposition point. Where possible, the critical temperature and critical density for each compound were determined experimentally. The results of the measurements were combined to derive a series of thermophysical properties including critical temperature, critical density, critical pressure, acentric factor, enthalpies of vaporization (restricted to within ±50 K of the temperature region of the experimentally determined vapor pressures), enthalpies of fusion if solid at 310 K, solubility parameters, and heat capacities along the saturation line. Vapor-pressure representations were derived for each compound. All measured and derived values were compared with those obtained in a search of the literature. Recommended critical parameters are listed for each of the compounds studied except 1-chloro-2-propanol. The compounds studied were benzenamine, butylbenzene, sec-butylbenzene, tert-butylbenzene, 2,2-dimethylbutanoic acid, tridecafluoroheptanoic acid, 2-butyl-2-ethyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, and 1-chloro-2-propanol.

A comparative method for developing vapor pressure curves based on evaporation data obtained from a simultaneous TG–DTA unit

In the present study, a novel method for determining vapor pressure values for the construction of vapor pressure–temperature curves is introduced. These calculations are based on evaporation data, which are obtained from thermogravimetric experiments. The technique as advocated by Price and Hawkins focused on adapting the Langmuir equation for evaporation to obtain vapor pressure values for volatile organic substances. In practice, it was discovered that such calculations produce unrealistic values of the vaporization coefficient, α. Hence, a comparative method, which eliminates the need for the inclusion of this vaporization coefficient factor, is developed in the present study. This method is based on the ratio of the Langmuir equations for a reference material and the sample under investigation. The proposed method also possesses the potential for calculations that will determine the molecular weights for unknown materials.

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.

Determination of structural, thermodynamic and phase properties in the Na 2S–H 2O system for application in a chemical heat pump

Structural, thermodynamic and phase properties in the Na 2S–H 2O system for application in a chemical heat pump have been investigated using XRD, TG/DTA and melting point and vapour pressure determinations. Apart from the known crystalline phases Na 2S·9H 2O, Na 2S·5H 2O and Na 2S a new phase Na 2S·2H 2O has been proven to exist. Na 2S· 1 2 H 2 O is not a phase but a 3:1 mixture of Na 2S and Na 2S·2H 2O, presumably stabilised by very slow dehydration kinetics. The vapour pressure–temperature equilibria of the sodium sulphide hydrates have been determined and a consistent set of thermodynamic functions for these compounds has been derived. XRD measurements indicate the topotactic character of the transitions between the hydration states.

Halogenated methyl-phenyl ethers (anisoles) in the environment: determination of vapor pressures, aqueous solubilities, Henry's law constants, and gas/water- (Kgw), n-octanol/water- (Kow) and gas/n-octanol (Kgo) partition coefficients.

Halogenated methyl-phenyl ethers (methoxybenzenes, anisoles) are ubiquitous organics in the environment although they are not produced in industrial quantities. Modelling the fate of organic pollutants such as halogenated anisoles requires a knowledge of the fundamental physico-chemical properties of these compounds. The isomer-specific separation and detection of 60 of the 134 possible congeners allowing an environmental fingerprinting are reported in this study. The vapor pressure p0(L) of more than 60 and further physico-chemical properties of 26 available congeners are given. Vapor pressures p0(L), water solubilities S(L)W, and n-octanol/water partition coefficients Kow were determined by capillary HR-GC (High Resolution Gas Chromatography) on a non-polar phase and by RP-HPLC (Reversed Phase High Performance Liquid Chromatography) on a C18 phase with chlorobenzenes as reference standards. From these experimental data the Henry's law constants H, and the gas/water Kgw and gas/n-octanol Kgo partition coefficients were calculated. We found that vapor pressures, water solubilities, and n-octanol/water partition coefficients of the halogenated anisoles are close to those of the chlorobenzenes. A similar environmental fate of both groups can, therefore, be predicted.

The formation of chloride adducts in the detection of dinitro-compounds by ion mobility spectrometry

The formation of chloride adducts by dinitro-alkanes in the gas phase has been studied by ion mobility spectrometry. Special emphasis was placed on the association of chloride with 2,3-dimethyl-2,3-dinitrobutane (DMNB), a prospective taggant for plastic explosives, but the reactions of chloride with 1,4-dinitrobutane (DNB) and with 2,3-dimethyl-2,4-dinitropentane (DMDNP) were also studied briefly. The thermal stabilities of the chloride adducts as shown by the effect of temperature on the mobility spectra were found to decrease in the order DNB·Cl − > DMDNP·Cl − > DMNB·Cl −. The equilibrium Cl − + DMNB = DMNB·Cl − was set up in the drift tube and by monitoring the drift time of the single peak due to the equilibrium mixture of Cl − and DMNB·Cl − as the DMNB concentration was varied, the equilibrium constant was determined. Measurement of the equilibrium constant at a series of temperatures gave ΔH 0 = −92.1 ± 3.1 kJ mol −1 and ΔS 0 = −92.1 ± 7.4 J K −1 mol −1 for the association. The enthalpy change for the formation of the most stable of the dinitro adducts, DNB · Cl −, is estimated to be 20 kJ mol −1 more negative than that for the DMNB adduct. The order of the stabilities of the chloride complexes is consistent with the number of very acidic hydrogen atoms on the carbon atoms in positions α to the nitro groups viz. DNB, 4; DMDNP, 2; DMNB, 0. The determined vapor pressures of DMNB and DNB over the respective ranges −20 to +50 °C and −10 to +30 °C respectively, are described by the equations log P = 19.82 ± 0.09 − (4 878 ± 26)/T (K) and log P = 18.08 ± 0.29 − (4 274 ± 81)/T (K), where P is the vapor pressure in parts per billion by volume, T is temperature in kelvin, and the quoted uncertainties are the standard errors.

Comparison of methods employing gas chromatography retention data to determine vapour pressures at 298 K

Validity of five models suggested for expressing the relationship between vapour pressures and GC retention times measured on a non-polar capillary column were tested on a common set of compounds [five homologous series of the type H–(CH 2) n –Y, where Y denotes Cl, Br, CHO, OCOCH 3 and COOCH 3, and n varies from 6 to 14]. Standard methods of statistical analysis, as well as vapour pressure values obtained independently from direct vapour pressure measurements were used as validity criteria. For the 40-compound data set examined, the methods provided vapour pressures agreeing within 9.2–24.7% (average absolute percent error) with direct experimental data.

Determination of vapor pressure of low-volatility compounds using a method to obtain saturated vapor with coated capillary columns.

The vapor pressures of O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX), O-isobutyl S-2-diethylaminoethyl methylphosphonothiolate (RVX), and 2,4-dinitrotoluene (2,4-DNT) were determined with the gas saturation method in temperatures ranging from -12 to 103 degrees C. The saturated vapor was generated using a fused-silica column coated with the compound. This column was placed in a gas chromatograph, and the vapor pressure was determined directly from the detector signal or by sampling on Tenax tubes that were subsequently analyzed. From the linear relationships obtained by plotting log P vs 1/T, the enthalpies of vaporization (deltaHvap) and the vapor pressures at selected temperatures were determined. The vapor pressure of VX at 25 degrees C was 0.110 Pa and the deltaHvap 77.9 kJ x mol(-1). The corresponding results for RVX were 0.082 Pa and 76.6 kJ x mol(-1). The vapor pressure of 2,4-DNT at 72 degrees C (melting point) was determined to 6.0 Pa, and the enthalpies of the solid and the liquid state were 94.2 and 75.3 kJ x mol(-1), respectively. Using capillary columns to generate saturated vapors has three major advantages: short equilibrium time, low consumption of sample, and safe handling of toxic compounds.

Vapor pressure determination by thermogravimetry

A method for measuring the vapor pressures of a wide range of materials using a conventional thermobalance and standard sample holders is described. The equipment is calibrated using pure reference materials of known vapor pressure and exploiting the relationship between volatilization rate and vapor pressure based on the Langmuir equation for free evaporation. Enthalpies of vaporization and sublimation can be determined, in some cases, the melting temperature and enthalpy of fusion can be obtained directly from thermogravimetry. Applications to the study of plasticizers and UV absorbers are described. Poor correlation of experimental results with predicted values obtained by molecular modeling is found. The application of modulated temperature thermogravimetry for the determination of enthalpies of sublimation and vaporization is also explored.

Solid–liquid phase transition of Lennard-Jones fluid in slit pores under tensile condition

The effect of equilibrium vapor-phase pressure onto freezing of a simple fluid in a nanopore is examined. We employ a molecular dynamics (MD) technique in a unit cell with imaginary gas phase, which has the benefit of easy determination of equilibrium vapor pressure. The method is shown to give consistent results with those by the grand canonical Monte Carlo (GCMC) method, and to have better feature of smaller degree of hysteresis between freezing and melting. The MD simulations showed liquid–solid phase transitions, at a constant temperature, with the variation in the equilibrium vapor-phase pressure below the saturated one. Thus-determined solid–liquid coexistence lines exhibited significant dependence of the freezing point against small changes in the bulk–phase vapor pressure, which implies the importance of tensile effect on freezing in nanopores. The capillary effect on the shift in freezing point was successfully described by a simple model based on continuum and isotropic assumption, even in a pore as small as 2 nm in width.

Vapor pressures of sulfonylurea herbicides

Vapor pressure values for agricultural chemicals are necessary for estimating volatilization and dissipation through transport in the vapor phase. The low vapor pressures of the sulfonylurea herbicides have presented significant challenges in vapor pressure determination. We have used the Knudsen gas effusion method at elevated temperatures and extrapolated to 25 °C. Along with the Knudsen method, computer calculations using the Grain equation were also used to estimate vapor pressure. The gas saturation method with quantitation by high performance liquid chromatography (HPLC) provided an upper limit that confirmed the low vapor pressures obtained using Knudsen gas effusion and computer calculations. We report the best available experimental results for the vapor pressures of sulfonylurea herbicides. © 2000 Society of Chemical Industry

Critical Point and Vapor Pressure Measurements at High Temperatures by Means of a New Apparatus with Ultralow Residence Times

A new flow method has been employed to obtain critical point and vapor pressure data at high temperatures for four compounds: squalane, toluene, ethylbenzene, and styrene. This new flow method allows the determination of reliable critical points and vapor pressures for thermally unstable or otherwise reactive compounds. The critical point is inferred from other measurements in the critical region. The measurement accuracy is less than that obtained by more conventional methods, but this method has been used where conventional methods fail.

Development and application of very high temperature mass spectrometry. Vapor pressure determinations over liquid refractories

Abstract Existing thermodynamic and vaporization data for liquid refractories are based either on estimates or on data extrapolated from studies on the solids obtained at much lower temperatures. Previously, we have shown that pulsed laser heating, coupled with time-dependent mass spectrometry of the free-expansion vapor plume, can be used for semi-quantitative measurements of vaporization thermochemistry. The present work extends this approach with the development of (a) more direct, and more accurate, methods for determining the system temperature and pressure; (b) improved experimental and theoretical determinations of key parameters such as ionization cross sections; and (c) improved characterization of the gas dynamic expansion and thermal equilibration processes. Example material systems considered include C, SiC, Al2O3, ZrO2—7%Y2O3, and Y2O3 at temperatures and total pressures typically in the range of 3000 to 5000 K and 0.01 to 10 bar, respectively (1 bar = 105 Nm-2).

Determination of cocaine and heroin vapor pressures using commercial and illicit samples.

The establishment of drug vapor pressure reference values provides valuable information in the development of vapor sensing devices for drug detection. The purpose of this work was to determine equilibrium headspace vapor pressures for commercial and illicit drug samples for use in such applications. Samples of cocaine, both free base and hydrochloride forms, and heroin hydrochloride were evaluated. The procedure used to measure the vapor pressures was a modification of a previously published method. Vapor pressure values at 20 degrees C previously reported for cocaine free base range from 0.37 x 10(-7) to 1.20 x 10(-7) Torr. The vapor pressure value determined in this study was 2.96 x 10(-7) Torr. It is likely that the discrepancies are due to differences in experimental conditions, varying sources of samples, and uncertainty in the methodologies. When the values were compared for commercial (99% purity) and illicit (unknown purity) sources of cocaine free base, there were no statistical differences in the projected room temperature (20 degrees C) vapor pressure values. However, the commercial and illicit samples of cocaine hydrochloride did show statistical differences. Although no comparison was made with the vapor pressure values for a pure, commercial sample, the vapor pressures of heroin hydrochloride (81% purity) at various temperatures were determined using the method developed for cocaine and are reported in this paper.