Temperature Dependence Of Vapor Pressure Research Articles

Vapor pressure and normal boiling point predictions for pure methyl esters and biodiesel fuels

Temperature dependent vapor pressures of the methyl esters of fourteen fatty acids that are commonly present in biodiesel fuels were predicted by the Antoine equation and a group contribution method. The predicted boiling points of these esters up to a pressure of 100 mmHg were within ±1.0% of reported data for these two methods. Normal boiling points were determined from both the predicted vapor pressure and a correlation equation and the prediction errors were less than 5 K comparing to available published data. The vapor pressure and normal boiling points of 19 real-world biodiesel fuels were predicted and compared with reported data where available. The prediction errors of normal boiling points were less than 1.0%, and the predicted vapor pressures were also observed to closely match the reported data among the methyl esters of soybean oil, rapeseed oil and tallow. The predicted results showed that, except for coconut and butterfat, most of the methyl esters of the vegetable oils and animal fats had a normal boiling point in the range of 620–630 K. A sensitivity analysis indicated that the variation of fatty acid composition and the uncertainty of the normal boiling point of C18:2 were the main factors that affected the predicted normal boiling points of the biodiesel fuels.

Statistical Mechanical Study of Thermodynamic Properties of a Family of Fullerites from C36 to C96 in the Equilibrium with Their Vapors

The temperature dependence of saturated vapor pressure of fullerites C36–C96 and their thermodynamic properties along with the sublimation curves up to the spinodal are calculated. The saturated vapor pressures along all the range of temperatures are approximated by logP sat = A − (B/T) − CT. The coefficient A practically does not depend on the number of atoms in the molecule (varying only by 2.2%), B increases noticeably while C decreases from the C36 to the C96, both of them by approximately two. The isothermal bulk modulus B T and the shear modulus C44 vanish at the spinodal points.

Supramolecular stabilization of host molecules within [MPy4(NCO)2]·2Py (M = Cu, Cd) clathrates

Thermodynamic stability and the crystal structure of two clathrates from the series [MPy4(NCO)2]·2Py (M = Cu, Cd; Py = pyridine) have been studied. The molecules of unstable complexes trans-[MPy4(NCO)2] were shown to exist in the bulk phases of the clathrates. The tetragonal distortion, caused by the elongation of two Cu-N(Py) bonds, of the coordination octahedron of the complex molecule was observed in the Cuclathrate. The dissociation of the clathrates is accompanied with a simultaneous decomposition of the host complexes to produce bipyridine complexes. The enthalpy, entropy and Gibbs energy changes of the dissociation processes have been calculated from the temperature dependencies of pyridine vapor pressure over the clathrates determined with a tensimetric method.

Thermodynamics of the intermediate phases in the Mg–B system

The high temperature vaporization thermochemistry of the intermediate phases in the B-rich portion of the Mg–B phase diagram (above 80% at. B) has been extensively studied by Knudsen Effusion-Mass Spectrometry (KEMS) and Knudsen Effusion-Weight Loss (KEWL) techniques. The temperature dependence of the Mg vapor pressures in equilibrium over the binary alloys in the composition range 87.5–95.2 and 95.2–100%at. B (corresponding to the two biphasic regions MgB 7+MgB 20 and MgB 20+β-B, respectively) has been measured in the temperature range 1162–1467 K. The enthalpy changes of the decomposition reactions for MgB 7 and MgB 20 are presented together with previously determined data for the Mg-richest phases MgB 2 and MgB 4 and a self-consistent set of formation enthalpies for all the four Mg–B phases has been derived. The proposed experimental formation enthalpies, Δ f H 298 0 , are MgB 2: −41.1±2.2, MgB 4: −29.9±2.0, MgB 7: −20.3±1.5, MgB 20: −8.5±0.6 kJ/mol atoms. Using the present and literature data the Mg–B thermodynamic description has been newly assessed using Thermo-Calc software and the whole phase diagram redrawn. Good agreement was obtained between the calculated results and the experimental data.

Determination of vapor pressures and enthalpies of vaporization of 1,2-alkanediols

Molar enthalpies of vaporization of 1,2-ethanediol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, and 1,2-octanediol were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. The measured data sets were successfully checked for internal consistency. A large number of the primary experimental results on temperature dependences of vapor pressures have been collected from the literature and have been treated uniform in order to derive vaporization enthalpies at the reference temperature 298.15 K. This collection together with the experimental results reported here has helped to resolve some contradictions which have been met in the available literature.

Thermodynamic properties of multifunctional oxygenates in atmospheric aerosols from quantum mechanics and molecular dynamics: dicarboxylic acids.

Ambient particulate matter contains polar multifunctional oxygenates that partition between the vapor and aerosol phases. Vapor pressure predictions are required to determine the gas-particle partitioning of such organic compounds. We present here a method based on atomistic simulations combined with the Clausius-Clapeyron equation to predict the liquid vapor pressure, enthalpies of vaporization, and heats of sublimation of atmospheric organic compounds. The resulting temperature-dependent vapor pressure equation is a function of the heat of vaporization at the normal boiling point [deltaHvap(Tb)], normal boiling point (Tb), and the change in heat capacity (liquid to gas) of the compound upon phase change [deltaCp(Tb)]. We show that heats of vaporization can be estimated from calculated cohesive energy densities (CED) of the pure compound obtained from multiple sampling molecular dynamics. The simulation method (CED) uses a generic force field (Dreiding) and molecular models with atomic charges determined from quantum mechanics. The heats of vaporization of five dicarboxylic acids [malonic (C3), succinic (C4), glutaric (C5), adipic (C6), and pimelic (C7)] are calculated at 500 K. Results are in agreement with experimental values with an averaged error of about 4%. The corresponding heats of sublimation at 298 K are also predicted using molecular simulations. Vapor pressures of the five dicarboxylic acids are also predicted using the derived Clausius-Clapeyron equation. Predicted liquid vapor pressures agree well with available literature data with an averaged error of 29%, while the predicted solid vapor pressures at ambient temperature differ considerably from a recent study by Bilde et al. (Environ. Sci. Technol. 2003, 37, 1371-1378) (an average of 70%). The difference is attributed to the linear dependence assumption thatwe used in the derived Clausius-Clapeyron equation.

Solvation and hydration characteristics of ibuprofen and acetylsalicylic acid.

Ibuprofen and acetylsalicylic acid were studied by thermoanalytical methods: sublimation calorimetry, solution calorimetry, and with respect to solubility. Upon measuring the temperature dependences of the saturated vapor pressure, enthalpies of sublimation, DeltaH(0) (sub), as well as the entropies of sublimation, DeltaS(0) (sub), and their respective relative fractions in the total process were calculated. The Gibbs energy of solvation in aliphatic alcohols as well as the enthalpic and entropic fractions thereof were also studied and compared with the respective properties of model substances and other nonsteroidal antiinflammatory drugs (benzoic acid, diflunisal, flurbiprofen, ketoprofen, and naproxen). In all cases, enthalpy was found to be the driving force of the solvation process. Correlations were derived between Gibbs energy of solvation in octanol, DeltaG(Oct) (solv), and the transfer Gibbs energy from water to octanol, DeltaG(0) (tr). Influence of mutual octanol and water solubilities on the driving force of partitioning is discussed. An enthalpy-entropy-compensation effect in octanol was observed, and consequences of deviation from the general trend are also discussed.

Thermodynamics of Sublimation, Crystal Lattice Energies, and Crystal Structures of Racemates and Enantiomers: (+)- and (±)-Ibuprofen

Thermodynamic differences between ibuprofen (IBP) racemate and the (+)-enantiomer were studied by X-ray diffraction, thermoanalysis, and crystal energy calculations. The thermodynamic functions of sublimation (as a measure of crystal lattice energy) were obtained by the transpiration method. The sublimation enthalpies (ΔHsub) of (±)-IBP and (+)-IBP are 115.8±0.6 and 107.4±0.5kJ·mol−1, respectively. Using the temperature dependency of the saturated vapor pressure, the relative fractions of enthalpy and entropy of the sublimation process were calculated, and the sublimation process for both the racemate and the enantiomer was found to be enthalpy driven (62%). Two different force fields, Mayo et al. (M) and Gavezzotti (G), were used for comparative analysis of crystal lattice energies. Both force fields revealed that the van der Waals term contributes more to the packing energy in (+)-IBP than in (±)-IBP. The hydrogen bonding energy, however, contributes at 29.7 and 32.3% to the total crystal lattice energy in (+)-IBP and (±)-IBP (M), respectively. Furthermore, different structure fragments of the IBP molecule were analyzed with respect to their contribution to nonbonded van der Waals interactions. The effect of the C─H distance on the van der Waals term of the crystal lattice energy was also studied. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association

Vapor Pressure over KI–CoI2Melts

The vapor pressure in the KI–CoI2 system is determined by isobaric boiling point measurements. Calculated vapor pressure isotherms of the KI–CoI2 system show negative deviations from linearity. The vapor composition over pure CoI2 is determined, and the temperature-dependent vapor pressure of CoI2 is assessed. The boiling point of pure CoI2 is found to be 1160 K.

Thermodynamics of solutions III: comparison of the solvation of (+)-naproxen with other NSAIDs

Naproxen was studied by classical thermoanalytical methods, namely sublimation calorimetry, solution calorimetry and the solubility method. Temperature dependence of a saturated vapor pressure was obtained and the sublimation enthalpy, Δ H sub 0, and entropy, Δ S sub 0, and their relative fraction of the total process were calculated. These parameters yielded for naproxen were compared to the respective data of other naphthalene derivatives. The crystal lattice energy of naproxen was calculated by two force fields (Gavezzotti et al. and Mayo et al.) and compared to the experimental data. Contributions of different motifs of the naproxen molecule to the total packing energy were analyzed. The Gibbs energy of solvation as well as enthalpic and entropic terms thereof in aliphatic alcohols have been studied for naproxen, and compared to model substances and other non-steroid anti-inflammatory drugs (benzoic acid, diflunisal and flurbiprofen). The major driving force of the solvation process is the enthalpy. The respective contributions of the specific and the non-specific solvation interactions in terms of absolute and relative values have been investigated.

Thermodynamics of Solutions IV: Solvation of Ketoprofen in Comparison with other NSAIDs

The present work discusses the characteristics of solvation (Gibbs energy, enthalpic and entropic terms of Gibbs energy) for ketoprofen together with other nonsteroidal antiinflammatory drugs (NSAIDs) in aliphatic alcohols. Ketoprofen was studied by classical thermoanalytical methods of sublimation calorimetry, solution calorimetry, and solubility. Temperature dependence of the saturated vapor pressure was determined, and the sublimation enthalpy, ΔHsub0, and sublimation entropy, ΔSsub0, as well as their respective relative fractions in the total process were calculated. The parameters yielded for ketoprofen were compared with the respective literature data of other benzophenone derivatives. The Gibbs energy of solvation as well as enthalpic and entropic terms thereof in aliphatic alcohols were also studied for ketoprofen and compared with the properties of model substances and other NSAIDs (benzoic acid, diflunisal, flurbiprofen, and naproxen). In all cases, the major driving force of the solvation process is enthalpy. Correlations were derived between Gibbs energy of solvation in octanol, ΔGsolvoct, and the transfer Gibbs energy from water to octanol, ΔGtr0. © 2003 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2502–2511, 2003

Saturated Vapor Pressure and Crystal Structure of Bis-(2-imino-4-pentanonato)copper(II)

A comprehensive study of copper(II) bis-ketoiminate including tensimetric analysis of sublimation and structure solution has been carried out. The temperature dependence of saturated vapor pressure over Cu(ki)2 crystals derived by the flow method is expressed by the equation lnP(atm)} = 25.31-13750/T, ΔHsubl = -114.2 ± 1.3 kJ· mole-1,Δ Ssubl =210.2 ± 3.0> J· mole-1 · K-1. Crystal data for CuO2N2C10H16: a=15.143(3), b=16.681(8), c=13.795(32) A, space group Ccca, Z=12, dcalc = 1.47 g/cm3, R=0.029. The structure is molecular and consists of crystallographically independent Cu(ki)2 complexes of two types, one with a cis structure and the other with a cis–trans disordering. The copper atom has a plane square environment of two oxygen and two nitrogen atoms. In the cis isomer, Cu–O 1.938 and Cu–N 1.895 A; in the disordered complex, all four Cu–O(N) distances are 1.901 A.

Theoretical Study of Thermodynamic Properties of a Family of Fullerites from C36 to C96 in the Equilibrium with Their Vapors

On the basis of the correlative method of the unsymmetrized self-consistent field that yields the account of the strong anharmonicity of the lattice vibrations, it has been calculated the temperature dependence of saturated vapor pressure of higher and smaller fullerites, from C36 up to C96, and their thermodynamic properties along their sublimation curves. We have used the intermolecular potential of Girifalco with parameters recently calculated for these fullerenes. The calculations were accomplished up to the temperature of loss of stability (spinodal point) Ts. We compare our results with available experimental data and with quantities calculated earlier for the magnitudes of the most widespread of the fullerites, the C60. The behavior of some characteristics is considered in their dependence on the number of atoms in the molecule. The saturated vapor pressures up to the spinodal points of the two-phase systems crystal−gas is approximated by the formula log Psat = A − (B/T) − CT, where the last term i...

Thermodynamic study of sodium–iron oxides: Part I. mass spectrometric study of Na–Fe oxides

Vaporization behavior of Na 4FeO 3(s) was thermodynamically studied from 590 to 717 K by means of high temperature mass spectrometry. It was found that Na 4FeO 3(s) decomposed into Na 3FeO 3(s) and released sodium vapor. The temperature dependence of partial vapor pressure of sodium over Na 4FeO 3(s) was measured so that the Gibbs energy of formation of Na 3FeO 3(s) was evaluated as Δ f G°(Na 3FeO 3)=−1168629+338.34× T.

Response modeling methodology (RMM)—a new approach to model a chemo-response for a monotone convex/concave relationship

Modeling the variation of a response in terms of the variation transmitted to it by a related factor (or factors) comprises the bulk of the scientific and engineering research effort. Often, we may reasonably assume that the relationship between the response and the affecting factor (or a linear combination of factors) is monotone convex (concave). To model such a relationship, a new Response Modeling Methodology (RMM) has recently been introduced and shown to represent a natural generalization of many theoretical or empirically-derived models, developed over the years in various scientific and engineering disciplines. In particular, many models of chemistry and chemical engineering fall into this category. In this paper, we demonstrate application of the new methodology to the modeling of a chemical response, and discuss extension to non-monotone relationships. It is shown that some well-known and widely used property correlation equations are indeed special cases of the new model. The allied estimation procedures are applied to some published data sets, related to temperature dependence of vapor pressure and solid heat capacity. We assess the effectiveness of the new approach relative to current models.

Calculation of the Thermodynamic Properties of the Copper-Zinc System from Measured Boiling Point Values

The temperature dependences of the saturated vapor pressure, the enthalpies of vaporization, standard boiling points, enthalpies, entropies, Gibbs energies, and component activities were calculated for liquid alloys of the copper-zinc system from the measured boiling points at various pressures. The calculation results were compared with the previous data obtained for this system by other methods.

On the thermodynamic properties of higher and smaller fullerites

The temperature dependences of the saturation vapor pressure of C96 and C36 fullerites and their properties along the sublimation curves are calculated using a correlation method of unsymmetrized self-consistent field that allows for strong anharmonicity of the lattice vibrations. The calculation is performed in terms of the Girifalco intermolecular potential with parameters recently determined for these fullerenes. Since experimental data on C96 and C36 fullerites are unavailable, the results of our calculations are compared with our results obtained earlier for the most commonly encountered fullerite C60. The specific features in the dependences of the properties of C96 and C36 fullerites on the number of atoms per molecule are revealed.

Mass Spectrometric Studies of Physical, Thermochemical and Reactive Properties of Xenon Fluorides, Xenon Oxides and Xenon Oxyfluorides

Using a reactor with a flowing diffusion cloud coupled to a high-resolution, low-energy electron-impact ionization mass spectrometer, mechanistic, kinetic and thermochemical characteristics of gas-phase reactions with the participation of charged and neutral xenon oxides, xenon fluorides and xenon oxyfluorides have been investigated. Ionization energies for XeF, XeF2, XeF4, XeO3, XeO4, XeOF4 molecules and appearance energies for the ions formed from these molecules were obtained. Based on experimental and reference data, the enthalpies of XeO3 and XeOF4 formation were refined and a number of binding energies in the parent and fragment ions were calculated. For electron-impact ionization, the ionization cross-sections for Xe, XeF2, XeF4 and XeOF4 proved to correlate with a semi-empirical principle of full ionization. Based on the temperature dependencies of saturated vapor pressures for XeO4, XeOF4 and XeO2F2, their enthalpies of evaporation, sublimation and melting were determined. The mechanisms of gas-phase reactions between H atoms and neutral XeF2, XeF4, XeF6, XeO4 and XeOF4 were studied.

Atmospheric nitrogen and sulfur containing compounds for three sites of South Korea

Atmospheric concentrations of gaseous HNO 3, NH 3 and particulates NO 3 − and SO 4 2− were analyzed at three sites, Chunchon, Seoul and Anmyon-do, on the Korean peninsula by filter pack method. The samples were collected over a period of 24 h every Wednesday. At one of the sites, Chunchon, atmospheric SO 2 was measured by using a four-stage filter pack. The annual mean concentrations of HNO 3 and NH 3 in 1998 ranged from 1.67 to 2.94 and from 2.00 to 3.95 μg m −3, respectively. The annual average of SO 2 at Chunchon was 7.32 μg m −3. The annual averages of particulate NO 3 − and SO 4 2− were 4.83–6.10 and 4.88–7.25 μg m −3, respectively. Particulate SO 4 2− showed no distinct seasonal variation while its primary pollutant, SO 2 displayed concentration peak in winter and bottomed out during summer. Consequently, the S(VI)/[S(IV)+S(VI)] ratio increased in a warm and light intensive summer and decreased in the cold and dark winter. This result suggests oxidation reactions were more efficient during the summer than in the winter. HNO 3 showed a summer maximum which resulted from the temperature dependence of vapor pressure and oxidation reaction rates of its related compounds. Atmospheric NH 3 was elevated in the warmer season, which related to an increase in source strength and vapor pressure. On the other hand, particulate NO 3 − and NH 4 + showed either winter peaks or no seasonal variation. These seasonal trends in nitrogen related compounds can primarily be explained by the gas–particle conversion reaction of NH 4NO 3 to NH 3 and HNO 3. This fact is supported by an increase in the ratio of gaseous nitrogen to particulate nitrogen as the ambient temperature rose.

Supercooled Liquid Vapor Pressures of the Polycyclic Aromatic Hydrocarbons

The vapor pressure of the supercooled liquid (PL) for 35 unsubstituted and alkylated polycyclic aromatic hydrocarbons (PAHs) was determined as a function of temperature using a gas chromatographic retention time technique. Pyrene and 1,2-benzanthracene, two compounds with well-established temperature-dependent vapor pressures, served as standard reference compounds. The method was calibrated with nine PAHs for which the vapor pressures at 25 °C are known from measurements relying on gas saturation and gas effusion techniques. Enthalpies of vaporization ΔvapH were also determined. The PL data were evaluated by comparison with several sets of published data and found to be reliable. For most of the investigated PAHs, a strong linear relationship between log PL and molecular mass exists, ranging over more than 9 orders of magnitude. However, PAHs with bulky substituents, such as phenyl- and tert-butyl-groups, have a higher vapor pressure than would be expected on the basis of molecular mass, presumably becau...