Determination Of Vapor Pressure Research Articles

Infrared Spectroscopic and Physical Properties of Methanol Ices—Reconciling the Conflicting Published Band Strengths of an Important Interstellar Solid

Infrared spectroscopic observations have established the presence of solid methanol (CH3OH) in the interstellar medium and in solar system ices, but the abundance of frozen CH3OH cannot be deduced without accurate band strengths, optical constants, and reference spectra. In this paper we identify disagreements, omissions, and gaps in the literature on infrared (IR) intensities of methanol ices, including unaddressed concerns that reach back several decades. New spectra are presented with intensity measurements aided by new data on the index of refraction and density of solid CH3OH. The result is that the large discordant results from different laboratory groups can now be reconciled. Multiple ices have been used to determine, apparently for the first time, IR intensities of H2O + CH3OH mixtures of accurately known composition for use with observations of interstellar ices. Also for the first time, measurements on CH3OH ices with different thicknesses have allowed us to report both near-IR band strengths and optical constants for two near-IR features used by planetary scientists. We have used our new IR results to determine vapor pressures of solid CH3OH and have compared them to measurements made with a quartz-crystal microbalance. Thermal annealings of methanol ices have been carried out and phase changes in the solid state examined. Comparisons of our results to earlier work are presented where possible, and electronic versions of our new results are made available.

Determination of vapor pressure, evaporation enthalpy and polarity of imidazolium-based ionic liquids

Determination of vapor pressure, evaporation enthalpy and polarity of imidazolium-based ionic liquids

Assessment of the Equivalence of Methods for the Determination of the Vapor Pressure of Oil and Oil Products

Current regulatory documents in Russia establish the need for testing laboratories to determine such parameters as saturated vapor pressure using the Reid method, air saturated vapor pressure, total vapor pressure of crude oil. In analytical practice, appropriate reference materials are used for measurement quality control, method validation, metrological traceability establishment, and other purposes. In addition, the calculation of various vapor pressure equivalents using correlation equations (DVPE – dry vapor pressure equivalent, RVPE – Reid vapor pressure equivalent, etc.) is regulated by appropriate methods for determining vapor pressure. Vapor pressure is a method-dependent parameter; so many producers of reference materials use interlaboratory experiment as a way to establish a certified value. Thus, when conducting an interlaboratory experiment in the process of certification of reference materials, it was revealed that laboratories can incorrectly interpret the obtained experimental data – consider values of the air saturated vapor pressure, total vapor pressure and even calculated vapor pressure equivalents as the Reid vapor pressure. To solve this problem, the authors of this work set the goal of assessing the equivalence of methods for determining the vapor pressure of oil and oil products used in testing laboratories in order to identify the key characteristics of the stated methods and assess their equivalence. The article discusses methods the vapor pressure determination using an automatic vacuum chamber and a Reid bomb. Various matrices of reference materials (hydrocarbons, gasoline, commercial oil, gas condensate) were investigated, and the calculated vapor pressure equivalents were obtained and compared. It was shown that the air saturated vapor pressure, dry vapor pressure equivalent, Reid vapor pressure equivalent, and total vapor pressure cannot be equated to the saturated vapor pressure values determined by the Reid method. A comparative assessment of methods for determining the vapor pressure of oil and oil products used in testing laboratories can be of assistance to developers of regulatory documents for oil, gas condensate, and motor gasoline, revealing the need to separate the requirements for vapor pressure parameters of the considered objects of analysis and providing empirical material.

A graphical derivation and statistical evaluation of simplified polynomials to determine vapour pressure deficit for use in ultra-low power microcontroller applications

The aim of this work has been to derive and statistically evaluate the accuracy of second-order and third-order polynomials to determine vapour pressure deficit (VPD). These polynomials take air temperature and relative humidity measurements to determine VPD without the use of an exponential function, as proposed by F W Murray in 1967. Replacing the exponential function with a 2nd or 3rd order polynomial may be beneficial in ultra-low power microcontroller-based measurement applications where; code size, memory usage and power requirements are critical design drivers. However, oversimplification may impact precision. This work presents alternative 2nd order and 3rd order equations that have been derived from a Murray equation dataset where VPD isothermal datasets were plotted against relative humidity. These linear relationships allow y = mx + c analysis where, (i) ‘c’ can be set to zero with a offset in the relative humidity data, and, (ii) ‘m’ can be derived from a 2nd of 3rd order polynomial where ‘m’ = f(T) and is derived using Excel-based fitting of the gradients from the isothermal datasets. The resulting ‘m’ = f(T) 2nd and 3rd order polynomials presented R 2 values of 0.998 04 and 0.999 98 respectively. A Bland-Altman statistical assessment was performed, where the Murray equation (reference) dataset is plotted against the difference between the reference and polynomial datasets using the same air temperature and relative humidity inputs. The difference datasets presented 2-sigma (95% confidence interval) variances for the 2nd and 3rd order polynomials as <±0.1 kPa and <±0.01 kPa respectively. The 2nd and 3rd order polynomials also resulted in a bias values of <0.0037 kPa and <0.0013 kPa respectively. These results suggest that a 3rd order polynomial equation could be used to determine VPD in ultra-low-power microcontroller measurement applications, with minimal impact on VPD measurement precision.

Thermodynamic assessment of RuO4 oxide

RuO4 oxide appears much less stable than RuO2(s) in the Ru–O binary system with a melting point close to room temperature and a certain propensity to vaporize or decompose at low temperatures. Ab initio simulations in the framework of density functional theory (DFT) on RuO4(s) are performed to analyze the cubic and monoclinic structures and to evaluate the heat capacities at low temperatures. Then, a critical evaluation of thermodynamic data from calorimetry and vapor pressure determinations - was carried out coupled with ab-initio calculations to propose new thermodynamic data: the entropy.S° (RuO4, s, cubic, 298K) = 132.7 J·K−1mol−1 and formation enthalpy.ΔfH° (RuO4, s, cubic, 298K) = −252.4 ± 5.5 kJ mol−1.

A comparative study of experiments and theories on steady-state evaporation of water

A precise description of energy and mass transport across the liquid-vapor interface of water is central in disciplines spanning from climatology to seawater desalination. We present a critical assessment of six recent experimental data sets that report temperature jumps, vapor pressures, and evaporation rates during steady-state evaporation of water. The experimental data were used to test available theories. Three state-of-the-art theories that take the resistance of the liquid-vapor interface into account were compared; statistical rate theory, non-equilibrium thermodynamics, and kinetic theory of gases. Statistical rate theory appears to under-predict the difference between the saturation pressure and the actual pressure of the vapor phase. Interface transfer coefficients for water compatible with non-equilibrium thermodynamics theory were determined. These coefficients predict the right order of magnitude of the evaporation fluxes from the different data sets. However, inconsistencies between the different data sets and indications of systematic measurement errors were identified during the determination and evaluation of these coefficients. The condensation coefficient in kinetic theory of gases computed from the experimental data span two orders of magnitude. All three theories were found to depend much on a precise determination of the conditions at the interface, in particular on the difference between the vapor phase pressure and the saturation pressure. Already a shift of 1–5 Pa changes the predicted evaporation rates significantly. For certain experiments, a change of 2 Pa modifies the evaporation rate predicted by statistical rate theory by one order of magnitude. Overall, we show that determination of vapor pressures to a higher accuracy (<0.3 Pa) is needed to enhance the understanding of evaporation mechanisms and which theory to use.

Journey of a molecule from the solid to the gas phase and vice versa: direct estimation of vapor pressure of alkaline-earth metalorganic precursors for atmospheric pressure vapor phase deposition of fluoride films.

Atmospheric pressure (AP) vapor phase processes such as spatial atomic layer deposition (S-ALD) and AP-metalorganic chemical vapor deposition (AP-MOCVD) are becoming increasingly appealing for their use in a variety of academic and industrial applications. Evaluation of precursor vapour pressures is crucial for their application in AP processes and to this aim the Langmuir equation has been applied as a simple and straightforward method for estimating the vapor pressure and vaporization enthalpy of various metalorganic precursors. Using benzoic acid as a calibration reference, the vapour pressure-temperature curves for several alkaline-earth β-diketonate fluorinated compounds, with molecular formula "M(hfa)2·L" (with M = Mg, Ca, Sr, Ba; Hhfa = 1,1,1,5,5,5-hexafluoroacetylacetone and L = diglyme, triglyme, and tetraglyme) are derived from their termogravimetric curves. Thus, the enthalpy of vaporization of all complexes has been estimated using the Clausius-Clapeyron equation. As a proof of concept, preliminary results on the use of [Mg(hfa)2·2H2O]·2diglyme and [Ca(hfa)2·diglyme·H2O] or [Ca(hfa)2·triglyme] as precursors for AP-MOCVD deposition of MgF2 and CaF2 in the form of thin films are presented. This approach may be used to easily determine vapor pressures of complexes and thus evaluate "a priori" the suitability of a compound as precursor for AP-MOCVD and/or spatial ALD.

Application of the Flash DSC 1 and 2+ for vapor pressure determination above solids and liquids

In this work, we adapted a procedure for vapor pressures determination utilizing a fast scanning chip calorimeter to the case of a stagnant gas phase. The validity of the developed procedure was checked by comparing the vapor pressures determined in this work for several polyaromatic, heteroaromatic, and long-chain compounds with reliable vapor pressure data available in the literature. The results of the comparison show that the commercial Flash DSC 1 and the Flash DSC 2+ (Mettler Toledo, Switzerland) can be used for a reliable appraisal of the vapor pressures in a wide temperature range, which allows using these devices without additional technical changes as a source of comprehensive and internally consistent information about the energy of phase transitions.

Determination of Vapor Pressure, Enthalpy of Vaporization, and Heat Capacity of Methyl 4-tert-Butylbenzoate

Determination of Vapor Pressure, Enthalpy of Vaporization, and Heat Capacity of Methyl 4-<i>tert</i>-Butylbenzoate

Comparability of calibration strategies for measuring mercury concentrations in gas emission sources and the atmosphere

Abstract. A primary mercury gas standard was developed at Van Swinden Laboratory (VSL) to establish an International System of Units (SI)-traceable reference point for mercury concentrations at emission and background levels in the atmosphere. The majority of mercury concentration measurements are currently made traceable to the empirically determined vapour pressure of mercury. The primary mercury gas standard can be used for the accurate and precise calibration of analytical systems used for measuring mercury concentrations in air. It has been especially developed to support measurements related to ambient air monitoring (1–2 ng m−3), indoor and workplace-related mercury concentration levels according to health standards (from 50 ng m−3 upwards) as well as stationary source emissions (from 1 µg m−3 upwards). The primary mercury gas standard is based on diffusion according to ISO 6154-8. Calibration gas mixtures are obtained by combining calibrated mass flows of nitrogen and air through a generator holding diffusion cells containing elemental mercury. In this paper, we present the results of comparisons between the primary gas standard and mercury calibration methods maintained by NPL (National Physical Laboratory in the United Kingdom), a National Metrology Institute (NMI), and the Jozef Stefan Institute (JSI), a Designated Institute (DI). The calibration methods currently used at NPL and JSI are based on the bell-jar calibration apparatus in combination with the Dumarey equation or a NIST (National Institute of Standards and Technology in the United States) reference material. For the comparisons, mercury was sampled on sorbent traps to obtain transfer standards with levels between 2 and 1000 ng with an expanded uncertainty not exceeding 3 % (k=2). The comparisons performed show that the results for the primary gas standard and the NIST reference material are comparable, whereas a difference of −8 % exists between results traceable to the primary gas standard and the Dumarey equation.

Vapor- liquid equilibrium for the n-dodecane + phenol and n-hexadecane + phenol systems at 523 K and 573 K

A continuous flow apparatus was applied to measure the phase equilibrium at 523 K and 573 K. The performance of the apparatus was analysed with the determination of vapor pressures of water at the temperatures (T = 453 K and 473 K). The measured water vapor pressures deviated from the literature values less than 1 %. Vapor pressures of n-dodecane, n-hexadecane and phenol were measured at the temperatures (T = 523–623 K) and, the bubble point pressures of n-dodecane + phenol and n-hexadecane + phenol were measured at the temperatures (T = 523 K and 573 K). The measured vapor pressures of the pure components were compared with the literature values. Relative vapor pressure deviated from the literature value less than 2 % for all the measured vapor pressures. The measured vapor pressures value in this work agreed well with the literature, which indicates that the measurement apparatus and the method can produce good-quality data. The measured bubble point pressures for the n-dodecane + phenol and n-hexadecane + phenol systems were modeled with Peng-Robinson and Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equations of state and Non-random Two-liquid (NRTL) activity coefficient model. The measured systems were at first modeled with Peng-Robinson and Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equations of state without binary interaction parameters. Additionally, the parameters were regressed to optimize the performance of the models. The NRTL activity coefficient model described the behaviour of the measured and the literature data better than the equations of state. Furthermore, the Peng-Robinson equation of state resulted in better predictions than PC-SAFT equation of state even without binary interaction parameters regression. Both equations of state modeled the phase equilibrium behaviour of the system well. The n-dodecane + phenol system showed azeotropic behaviour.

Permeability coefficients and vapour pressure determination for fragrance materials.

This study aims to correlate new experimental data relevant to the description of the combined evaporation/permeation process of a perfume applied onto the skin. The vapour pressure data were measured by thermogravimetric analysis (TG-DTA). The Antoine constants and the Clarke and Glew parameters were determined for the same set of fragrance molecules to describe its low vapour pressures at new temperature ranges. The permeability coefficient of a set of 14 fragrance molecules in ethanolic solution was determined by Franz diffusion cell experiments, using porcine skin. The samples were analysed by gas chromatography with a flame ionization detector (GC/FID) and high-performance liquid chromatography with UV visible detector (HPLC/UV). A QSAR model was proposed to correlate the experimental data. The Antoine constants were determined and presented low standard deviations. The Clarke and Glew physically significant parameters were obtained along with its statistical analysis. The fitting is good since the magnitude order is in accordance with the literature, associated with the low correlation between the estimated parameters and low standard deviations. The presented correlation, based on a mixture using only ethanol as solvent, showed better results than previous QSAR models with a standard relative deviation ( of 0.190, a standard error (SE) of 0.397 and a determination coefficient (R2 ) of 0.7786. The dataset is still small compared to larger and more general QSAR models; however, it is much more specific as to the type of solvent and class of materials studied. This work represents an advance for the modelling of the perfume diffusion process since it specifies important properties that until then had been treated in a more general way.

Experimental Method for the Determination of the Saturation Vapor Pressure above Supercooled Nanoconfined Liquids

For sorption studies, the saturation vapor pressure p0 above an adsorbate is of great significance. For example, it is needed for the determination of the pore size distribution, the Laplace pressure, and the chemical potential. Above the bulk triple point, T3bulk, this pressure is identical with the saturation vapor pressure above the bulk liquid. However, below T3bulk, the correct value of p0(T) is controversial. Nanoconfined fluids exhibit a shift of the freezing and melting temperatures in comparison to the bulk state. Thus, the adsorbed fluid is supercooled in a certain temperature range below T3bulk. Here, we show that it is possible to determine the appropriate saturation vapor pressure above the nanoconfined supercooled liquid experimentally. For this purpose, we have performed sorption measurements with liquid argon in nanoporous Vycor glass in the temperature range of the supercooled liquid and at temperatures above the bulk triple point. In order to determine the unknown and temperature-dependent saturation vapor pressure of the supercooled confined adsorbate, p0(T), we use the Kelvin equation relating this quantity to the pore radius, rP(p0), that is independent of temperature. The knowledge of the absolute values for the liquid–vapor surface tension of the supercooled adsorbate, γlv(T), is not required. However, we presuppose that its dependence on the unknown vapor pressure, γlv(p0), is bulk-like. Our results indicate that the saturation vapor pressure above the supercooled nanoconfined liquid corresponds to that above supercooled bulk argon (i.e., to the pressure obtained by an extension of the usual vaporization curve to T < T3bulk). We expect that this method can be used for the determination of p0 above other supercooled adsorbates.

A new thermogravimetric application for determination of vapour pressure curve corresponding to average boiling points of oil fractions with narrow boiling ranges

The average boiling point of oil fractions with narrow boiling ranges or pseudo-components is an important parameter in thermodynamic calculations in the fields of process design and environmental protection. The present work provides an experimental approach, involving a method based on the thermogravimetric analysis, for determination of the pressure dependence of average boiling points (or in other words for determination of “the vapour pressure curve corresponding to average boiling points”) of oil fractions with narrow boiling ranges, pre-prepared by distillation. This method can be used for determination of the atmospheric average boiling points (corresponding to atmospheric pressure) of thermally unstable fractions from the pressure dependence curves, obtained from the tests conducted at lower pressures. The method uses the principle of ASTM E1782 “Standard Test Method for Determining Vapor Pressure by Thermal Analysis”, where the material is vaporised at pre-determined pressure from a hermetically sealed capsule through a pinhole using a constant heating rate experiment. The accuracy of the method was evaluated on the basis of the average boiling point values of narrow boiling ranges fractions determined by rectification both at atmospheric pressure and in vacuum (determined as the arithmetic mean of the lower and upper temperature limits of the fraction). The pressure dependence curves of the average boiling points, formed here on the basis of average boiling points obtained in the pressure range from 5 kPa to atmospheric pressure, can be reliably described by the integrated Clausius-Clapeyron equation. To increase the accuracy in determining the atmospheric average boiling points of thermally unstable fractions, obtained in extrapolation from the Clausius-Clapeyron curve of the average boiling points in the tests conducted at lower pressures, a higher number of tests, on the basis of which to conduct the extrapolation, is desirable.

Learning distillation by a combined experimental and simulation approach in a three steps laboratory: Vapor pressure, vapor-liquid equilibria and distillation column

Distillation is one of the most important separation process in industrial chemistry. This operation is based on a deep knowledge of the fluid phase equilibria involved in the mixture to be separated. In particular, the most important aspects are the determination of the vapor pressures of the single compounds and the correct representation of the eventual not ideality of the mixture. Simulation science is a fundamental tool for managing these complex topics and chemical engineers students have to learn and to use it on real case-studies. To give to the students a complete overview of these complex aspects, a laboratory experience is proposed. Three different work stations were set up: i) determination of vapor pressure of two pure compounds; ii) the study of vapor-liquid equilibria of a binary mixture; iii) the use of a continuous multistage distillation column in dynamic and steady-state conditions. The simulation of all these activities by a commercial software, PRO II by AVEVA, allows to propose and verify the thermodynamic characteristics of the mixture and to correctly interpret the distillation column data. Moreover, the experimental plants and the data elaboration by classical equations are presented. The students are request to prepare a final report in which the description of the experimental plants and experimental procedure, the interpretation of the results and the simulation study are critically discussed in order to encourage them to reason and to acquire the concepts of the course.Two different questionnaires each with 7 questions, for the course and for the laboratory, are proposed and analyzed. The final evaluation of the students was strongly positive both for the course as a whole and for the proposed laboratory activities.

Fast scanning calorimetry: Sublimation thermodynamics of low volatile and thermally unstable compounds

Fast scanning calorimetry (FSC) was applied for measurements of the sublimation rates of theophylline, caffeine and anthraquinone as reference compounds. In comparison to conventional vapor pressure determination techniques, this method requires only nano-gram-size samples. The increased surface to volume ratio allows for very high sublimation rates and makes the sublimation process dominant over a possible decomposition. Experimental conditions and data treatment have been elaborated and validated by comparison with reliable literature data. The FSC method “opens a new door” for reliable experimental determination of vapor pressures and sublimation enthalpies for very low volatile and thermally unstable compounds like bio-relevant molecules.

Bioactivity and toxicological study of Amiton and related isomers

Organophosphates are well known to have toxic properties amongst other favorable chemical and physical properties. This holds true for pesticides and especially chemical warfare agents. The present study focusses on the toxicity and bioactivity of nerve agent VG and related isomers which were designed by us in need of nontoxic and non-bioactive surrogate substances for training reasons. A previous study revealed that some of the isomers are ideal model substances for e.g. vapor pressure determination. However, the toxicity and bioactivity data for these new compounds are still missing. Thus, we used the classical Ellman essay to determine the AChE and BuChE toxicity and Vibrio fisheri bacteria to test aquatic toxicity. Additionally, we made use of QSAR-methods to model toxicity data of other species e.g. Daphnia magna. By now we are able to adjust the toxicity in a wide range by choosing proper substituents.

Thermochemical properties of mono- and di-cyano-aromatic compounds at 298.15 K

The solution calorimetry approach was applied for the determination of the sublimation enthalpies for cyano-aromatic compounds. According to this approach, the vaporization/sublimation enthalpies were estimated as a difference between solution (cr/l to the solution) and solvation (gas to the solution) enthalpies in acetonitrile as a solvent. The solvation enthalpy of studied compounds was calculated using the previously developed and tested additive scheme. The solution enthalpies of five cyano-aromatic compounds were measured experimentally for the first time by using solution calorimeter.The new approach for the evaluation of the condensed state enthalpy of formation by using first principles calculations and solution calorimetry technique is proposed. In most cases obtained results are in good agreement with literature values.Apparatus for determination of vapor pressure by using the transpiration method was developed. The experimental setup was tested by measuring the vapor pressure of pure naphthalene. Vapor pressures for 1- and 2-cyano-naphthalenes were measured by using the newly elaborated transpiration setup. Experimental and calculated values of sublimation enthalpies are in good agreements with the most reliable available literature data. Sublimation enthalpy of 9-cyano-anthracene was obtained by solution calorimetry for the first time.

Determination of flash point and Reid vapor pressure in petroleum from HTGC and DHA associated with chemometrics

Flash point (FP) and Reid vapor pressure (RVP) are physicochemical properties of crude oil that are used as safety and environmental parameters. In this paper, we propose a methodology for estimating the FP and RVP for crude oil by means of detailed hydrocarbon analysis (DHA) and high temperature gas chromatography (HTGC) associated with partial least squares (PLS) regression. These techniques were used due to their direct relationship to FP and RVP. We studied 107 crude oil samples (with an API gravity range of 11.4–54.0) collected from a Brazilian sedimentary basin. The curve data derived from these two techniques were merged to better describe the true boiling point curve. Using fusion information drawn from the two chromatographic techniques (DHA and HTGC), we estimated the flash point with an average error of 5.3 °C and a coefficient of determination of approximately 0.9. While the data fusion represents an information gain in the estimation of the flash point, for to estimate the Reid vapor pressure, the HTGC data are sufficient. The PLS regression generated the best Reid vapor pressure results, with an average error of 0.4 kPa and with a coefficient of determination of above 0.99.

An Indirect Method for Vapor Pressure and Phase Change Enthalpy Determination by Thermogravimetry

Vapor pressure is a fundamental property of a pure substance. This property is the pressure of a compound’s vapor in thermodynamic equilibrium with its condensed phase (solid or liquid). When phase equilibrium condition is met, phase coexistence of a pure substance involves a continuum interplay of vaporization or sublimation to gas and condensation back to their liquid or solid form, respectively. Thermogravimetric analysis (TGA) techniques are based on mass loss determination and are well suited for the study of such phenomena. In this work, it is shown that TGA method using a reference substance is a suitable technique for vapor pressure determination. This method is easy and fast because it involves a series of isothermal segments. In contrast to original Knudsen’s approach, where the use of high vacuum is mandatory, adopting the proposed method a given experimental setup is calibrated under ambient pressure conditions. The theoretical framework of this method is based on a generalization of Langmuir equation of free evaporation: The real strength of the proposed method is the ability to determine the vapor pressure independently of the molecular mass of the vapor. A demonstration of this method has been performed using the Clausius–Clapeyron equation of state to derive the working equation. This algorithm, however, is adaptive and admits the use of other equations of state. The results of a series of experiments with organic molecules indicate that the average difference of the measured and the literature vapor pressure amounts to about 5 %. Vapor pressure determined in this study spans from few mPa up to several kPa. Once the p versus T diagram is obtained, phase transition enthalpy can additionally be calculated from the data.