Sublimation Vapor Pressures Research Articles

Theoretical Prediction of the Sublimation Behavior by Combining Ab Initio Calculations with Statistical Mechanics

We develop a theoretical model to predict the sublimation vapor pressure of pure substances. Moreover, we present a simple monoatomic molecule approximation, which reduces the complexity of the vapor pressure expression for polyatomic gaseous molecules at a convincing level of accuracy, with deviations of the Arrhenius prefactor for NaCl and NaF being 5.02% and 7.08%, respectively. The physical model is based on ab initio calculations, statistical mechanics, and thermodynamics. We illustrate the approach for Ni, Cr, Cu (metallic bond), NaCl, NaF, ZrO2 (ionic bond) and SiO2 (covalent bond). The results are compared against thermodynamic databases, which show high accuracy of our theoretical predictions, and the deviations of the predicted sublimation enthalpy are typically below 10%, for Cu even only 0.1%. Furthermore, the partial pressures caused by gas phase reactions are also explored, showing good agreement with experimental results.

Phase Transitions Equilibria of Five Dichlorinated Substituted Benzenes.

This work reports an experimental study aiming to determine the thermodynamic properties of five chlorinated compounds with environmental impact. The vapor pressures of the crystalline phases of three isomers of dichlorobenzoic acid (2,4-, 2,5-, and 2,6-) and 2,6-dichlorobenzonitrile were measured at several temperatures using the Knudsen effusion technique. Another technique (a static method based on capacitance diaphragm manometers) allowed the measurement of the vapor pressures of both the crystalline and liquid phases of 2,4-dichlorobenzonitrile between 303.0 and 380.0 K. This latter technique also enabled the measurement of sublimation vapor pressures of 2,6-dichlorobenzonitrile over a larger range interval of temperatures, T = 328.7 and 391.8 K. The standard molar enthalpy, entropy, and Gibbs energy of sublimation (for all the compounds studied) and vaporization (for 2,4-dichlorobenzonitrile) were derived, at reference temperatures, from the experimental vapor pressure results. The temperatures and enthalpies of fusion and the isobaric heat capacities of the five crystalline-substituted benzenes were determined using differential scanning calorimetry. The contributions of the three substituents (-COOH, -CN, and -Cl) to the sublimation thermodynamic properties of the compounds studied were discussed.

Study on the volatility of four benzaldehydes

This work reports the experimental determination of relevant thermodynamic properties of four benzaldehydes. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of syringaldehyde, 3,4,5-trimethoxybenzaldehyde, 4-(dimethylamino)benzaldehyde and of the liquid phase of veratraldehyde were determined using a static method based on capacitance diaphragm manometers. Additionally, the sublimation vapor pressures of the four compounds were also determined at different temperatures, using the Knudsen mass-loss effusion method. The experimental results allowed accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization for the benzaldehydes studied, at reference temperatures, allowing phase diagram representations of the (p,T) results, in the neighborhood of the triple point of the four compounds. Their temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the ones obtained indirectly through vapor pressure measurements. Using high-precision drop calorimetry, the standard isobaric molar heat capacities of the four crystalline benzaldehydes were determined at 298.15 K. The enthalpy of the intermolecular hydrogen bond OH…O in the crystalline phase of syringaldehyde was estimated.

Thermodynamic Stability of Fenclorim and Clopyralid.

The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (p,T) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.

Absolute chemical potentials for complex molecules in fluid phases: A centroid reference for predicting phase equilibria.

Solid-fluid phase equilibria are difficult to predict in simulations because bound degrees of freedom in the crystal phase must be converted to free translations and rotations in the fluid phase. Here, we avoid the solid-to-fluid transformation step by starting with chemical potentials for two reference systems, one for the fluid phase and one for the solid phase. For the solid, we start from the Einstein crystal and transform to the fully interacting molecular crystal. For the fluid phase, we introduce a new reference system, the "centroid," and then transform to gas phase molecules. We illustrate the new calculations by predicting the sublimation vapor pressure of succinic acid in the temperature range of 300 K-350 K.

Vapor pressure of nine perfluoroalkyl substances (PFASs) determined using the Knudsen Effusion Method.

Sublimation vapor pressures of nine pure perfluoroalkyl substances, including Ammonium perfluoro(2-methyl-3-oxahexanoate) (GenX), 1H,1H,2H,2H-Perfluoro-1-decanol (8:2 FTOH), 1H,1H,2H,2H-Perfluoro-1-dodecanol (10:2 FTOH) and C6 to C11 perfluorocarboxylic acids (PFCAs), were measured using the Knudsen technique at near ambient temperatures. Melting temperatures and fusion enthalpies of these compounds were also measured using differential scanning calorimetry. The vapor pressure of GenX ammonium salt is comparable to that of the much higher molecular weight perfluoroundecanoic acid. GenX ammonium salt also did not show actual melting behavior but instead decomposed at around 470 K. The measured near ambient temperature sublimation vapor pressures of the PFCAs and FTOHs were compared with some earlier reported liquid phase vapor pressures obtained at higher temperatures, and reasonable agreement exists between the data obtained in the different studies. The sublimation enthalpies of the PFCAs indicate that the contribution to the sublimation enthalpy of the CF2 group in the alkyl chain is comparable to that of the CH2 group in the corresponding non-fluorinated analogues, even though the PFCAs show consistently higher vapor pressures than do the corresponding carbon number alkanoic acids.

Thermodynamic Properties of Moldy-Musty Contaminants of Wine

This paper reports thermodynamic properties of phase transitions of 2,4,6-trichloro and 2,4,6-tribromo anisoles and of 2,4,6-tribromophenol. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of the three compounds were measured, respectively, in the temperature ranges T = (297.1 to 368.3) K, T = (330.7 to 391.7) K, and T = (336.5 to 401.7) K, using a static method based on capacitance diaphragm manometers. Moreover, the sublimation vapor pressures of 2,4,6-tribromophenol were also measured in the temperature interval (307.2 to 329.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies, and Gibbs energies of sublimation and of vaporization, at reference temperatures, were derived from the experimental results as well as the (p,T) values of the triple point of each compound. The temperatures and molar enthalpies of fusion of the three benzene derivatives were determined using differential scanning calorimetry and were compared with...

Volatility and chemical stability of chromium, molybdenum, and tungsten hexacarbonyls

The sublimation vapor pressures of three metallic (group 6) hexacarbonyls, Cr(CO)6, Mo(CO)6, and W(CO)6, were measured using the Knudsen mass-loss effusion method. The standard (po = 0.1 MPa) molar enthalpies, entropies, Gibbs energies, and heat capacity difference between the gas and solid state, at T = 298.15 K, were derived from the experimental results combined with selected literature ones covering a wide range of temperature. The temperatures and molar enthalpies of fusion of those compounds were measured using differential scanning calorimetry. The thermodynamic stability of the hexacarbonyls was evaluated taking into account the standard Gibbs energies of formation in the crystalline and gaseous phases. Gas-phase absolute entropies, heat capacities, and enthalpies of formation of the three compounds studied as well as the bond distances M–C and C–O were calculated.

Simplified calculation of solubility of solid solutes in supercritical carbon dioxide by EoS models

Equations of State (EoSs) have been widely used in calculating solubility of solutes in supercritical carbon dioxide (SCCO2). However, the traditional EoS models, need the data of sublimation vapor pressure and critical parameter of solutes, which are difficult to obtain, and the calculation procedure is also complicated. In this study, simplifications and approximations were made towards combinations of three EoSs (Soave-Redlich-Kwong, Peng-Robinson, and modified Esmaeilzadeh-Roshanfekr) and five mixing rules (Huron-Vidal, van der Waals one and two, modified covolume-dependent, and Wong-Sandler) to overcome the above limitations. After simplifications and approximations, the modified models have been reduced into two groups, including two and three parameter models. At last, the models in the work of Yazdizadeh et al. (2012) and four semi-empirical models (Chrastil, Valle and Aguilera, Sung and Shim, and Sparks) were used for comparison, and comparative analysis suggests that the new models in this work are better.

Review of Sublimation Thermodynamics of Polycyclic Aromatic Compounds and Heterocycles

This review details sublimation vapor pressure and thermodynamic data on 85 polycyclic aromatic compounds and heterocycles from the early 1900s through 2012. These data were collected using a variety of vapor pressure measurement techniques, from effusion to gas saturation to inclined-piston manometry. A brief overview of each measurement technique is given; these methods yield reproducible sublimation vapor pressure data for low volatility organic compounds such as polycyclic aromatic compounds and heterocycles. Several conclusions can be drawn from this literature survey, specifically that there remains a dearth of data on the sublimation thermodynamics (and fusion thermodynamics) of heteroatomic high molecular weight aromatic compounds, inhibiting a holistic understanding of the effect of specific heteroatoms and substituent position on the thermodynamics of these compounds. However, we can clearly see from the data that there are a variety of potential intermolecular interactions at work that generally tend to increase the enthalpy of sublimation and decrease the vapor pressure of a substituted polycyclic aromatic compound/polycyclic heterocycles versus its parent compound.

Deviations from ideal sublimation vapor pressure behavior in mixtures of polycyclic aromatic compounds with interacting heteroatoms

Despite the relatively small atomic fraction of a given heteroatom in a binary mixture of polycyclic aromatic compounds (PAC), the presence of heteroatoms can significantly impact mixture vapor pressure behavior over a wide range of temperatures. The vapor pressures of several binary PAC mixtures containing various heteroatoms show a range of behavior, from practically ideal behavior following Raoult’s law to significant deviations from ideality depending on the heteroatoms present. Mixtures were synthesized using the quench-cool technique with equimolar amounts of two PAC, both containing heteroatoms such as aldehyde, carboxyl, nitrogen, and sulfur substituent groups. For some mixtures, deviation from ideality is inversely related to temperature, though in other cases we see deviation from ideality increasing with temperature, whereas some appear independent of temperature. Most commonly we see lower vapor pressures than predicted by Raoult’s Law, which indicates that the interacting heteroatoms prefer the solid mixture phase as opposed to the vapor phase. Although negative deviations predominate from Raoult’s Law, the varying mixtures investigated show both higher and lower enthalpies and entropies of sublimation than predicted. In each mixture, a higher enthalpy of sublimation leads to higher entropy of sublimation than predicted, and vice versa.

Sublimation Vapor Pressures as Evaluated by Correlation-Gas Chromatography

Vapor pressures of the liquid phase obtained by correlation-gas chromatography are used in conjunction with experimental fusion enthalpies to calculate sublimation vapor pressures of a number of compounds including n-alkanes, polyaromatic hydrocarbons, aromatic heterocyclic compounds, and polycyclic hydrocarbons. Vapor pressures at the fusion temperature, Tfus, calculated from vapor pressure equations generated by this technique and obtained by extrapolation, are used to evaluate vaporization enthalpies at Tfus. The sublimation enthalpy at Tfus is obtained from the sum of the experimental fusion enthalpy and vaporization enthalpy. The vapor pressure at Tfus, used as an approximation of the triple-point vapor pressure, combined with the sublimation enthalpy and a heat capacity adjustment is used to calculate sublimation vapor pressures as a function of temperature. Calculated sublimation vapor pressures extrapolated to near ambient temperatures compare with experimental values to within a factor of three.

Raoult's Law and Its Application to Sublimation Vapor Pressures of Mixtures of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous pollutants resulting from incomplete combustion and many fuel processing and storage operations. They are encountered in the environment in man...

Calculation of the solid solubilities in supercritical carbon dioxide using a modified mixing model

The Peng–Robinson equation of state and a modified Huron–Vidal type mixing model with a volume correction term are applied in this study to calculate the solid solubilities of aromatic, fatty acid and heavy alcohol compounds in supercritical carbon dioxide. The UNIFAC activity coefficient model with its optimally fitted binary interaction parameters is used in this study. A volume correction term is employed, and its parameters are correlated as functions of the solid molar volume for both non-polar and polar systems. The effect of the sublimation vapor pressure on the calculation of solid solubilities in supercritical carbon dioxide is examined. The sublimation vapor pressures for heavy compounds are fitted in this study to yield the optimally calculated results of the solid solubility. Reasonable sublimation vapor pressures are obtained and their values are well correlated by the Antoine equation. A generalized calculation model is proposed in this study which gives satisfactory results of the solid solubility in supercritical carbon dioxide for both the binary and ternary systems.

Vapor pressures of organic semiconductors:: α-hexathiophene and α-quaterthiophene

The sublimation vapor pressures of the thin film transistor materials, α-hexathiophene (α-6T) and α-quaterthiophene (α-4T) were measured using the Knudsen effusion method and enthalpies of sublimation were calculated. The criteria for Knudsen cell design to obtain accurate vapor pressures of large organic molecules were examined. A recording microbalance with an accuracy of ±0.1 μg was used in conjunction with a specially designed Knudsen cell. Vapor pressures from 10 −6 to 10 −2 Torr were measured. At low pressures, the mean free path was large even for oligomers with hard sphere diameters of 22 Å, so that Knudsen criteria were fulfilled. The vapor pressure results are used to discuss the observations from previously published physical vapor crystal growth experiments.

The thermodynamic properties of biphenyl

Ideal-gas thermodynamic properties for biphenyl based on calorimetric measurements were determined between 300 and 700 K, well into the range of typical chemical-process temperatures. Experimental methods included adiabatic heat-capacity calorimetry, comparative ebulliometry, inclined-piston manometry, and differential-scanning calorimetry (d.s.c.). The derived values provide a firm basis for the prediction of thermodynamic properties for a large family of molecular structures including many substituted biphenyls—such as polychlorinated biphenyls (PCBs)—as well as polyphenyls of arbitrary size. Results also highlighted ambiguities common in the statistical calculation of thermodynamic properties of polycyclic molecules. Critical-property measurements with a d.s.c. indicated the commonly accepted assessed values to be in error. The biphenyl critical properties serve as a “cornerstone” in group-contribution estimation schemes, which are employed often by engineers in corresponding-states correlations for the estimation of a great variety of physical properties. Thermodynamically consistent sublimation vapor pressures were derived to show which of the many literature values are valid, an essential step in the validation of the many reported PCB vapor-pressure measurements, which are key to environmental-impact considerations.

The interaction of krypton and an exfoliated graphite at 77.4 K

An exfoliated graphite sample was prepared having a significant increase in basal plane area over the original highly ordered pyrolytic graphite crystal. The boundary planes of the expanded sample appeared intact and were highly reflective. The krypton adsorption at 77.4 K was at first linear with P P o , then reached a plateau over the range from 0.45 to 0.65, and then increased uniformly to P P o of 0.99, where p is pressure and p 0 is the sublimation vapor pressure of solid krypton. Each desorption branch initiated from several levels of adsorption decreased only slightly to the lowest pressures measured ( P P o ∼ 0.01 ). A model is proposed in which the adsorption process is concomitant with a contraction between adjoining graphite lamellae.