Vapor Pressure Measurements Research Articles

Polymorphism and thermophysical properties of l- and dl-menthol

The thermodynamic properties, phase behaviour, and kinetics of polymorphic transformations of racemic (dl-) and enantiopure (l-) menthol were studied using a combination of advanced experimental techniques, including static vapour pressure measurements, adiabatic calorimetry, Tian-Calvet calorimetry, differential scanning calorimetry (DSC), and variable-temperature X-ray powder diffraction. Several concomitant polymorphs (α, β, γ, and δ forms) were observed and studied. A continuous transformation to the stable α form was detected by DSC and monitored in detail using X-ray powder diffraction. A long-term coexistence of the stable crystalline form with the liquid phase was observed. The vapour pressure measurements of both compounds were performed using two static apparatus over a temperature range from 274 K to 363 K. Condensed-phase heat capacities were measured by adiabatic and Tian-Calvet calorimetry in the wide temperature interval from 5 K to 368 K. Experimental data of l- and dl-menthol are compared mutually as well as with available literature results. The thermodynamic functions of crystalline and liquid l-menthol between 0 K and 370 K were calculated from the calorimetric results. The thermodynamic properties in the ideal-gas state were obtained by combining statistical thermodynamics and quantum chemical calculations based on a thorough conformational analysis. Calculated ideal-gas heat capacities and experimental data on vapour pressure and condensed-phase heat capacity were treated simultaneously to obtain a consistent thermodynamic description. Based on the obtained results, the phase diagrams of l-menthol and dl-menthol were suggested.

Vapor pressure measurements of AgBr by the Knudsen effusion method

The vapor pressure of silver bromide (AgBr) liquid was measured by the Knudsen effusion method. The ratio of the vapor species of silver bromide was calculated from the literature Hildenbrand and Lau, Pankratz [3,6], and the vapor pressures were calculated on the basis of the ratio. As reported in the literature Hildenbrand and Lau [3], we considered the vapor species to be monomers (AgBr) and trimers (Ag3Br3). The partial pressures of AgBr [pmonomer(Pa)] and Ag3Br3 [ptrimer(Pa)] were respectively fitted by the following linear equations over the temperature range 829.9–929.9 K:lnpmonomer= -(23590 ± 519) / T + 25.22 ± 0.59,ln(ptrimer) = -(19449 ± 509) / T + (20.42 ± 0.58).The total vapor pressure of silver bromide [ptotal(Pa)] fitted the following linear equation:ln(ptotal) = -(21653 ± 529) / T + (23.72 ± 0.60).

Validation of the MELCOR input model for a CANDU PHWR containment analysis by benchmarking against integrated leakage rate tests

Abstract In an effort to overcome limitations when validating a code input model for the containment of a nuclear power plant, two integrated leakage rate tests (ILRTs) performed at a CANDU 6 plant were simulated with a MELCOR input model consisting of 51 control volumes. Leakages were assumed to occur at the volumes enclosed within the containment wall. The initial conditions were set to the measurements at the time when the atmosphere stabilization phase was started. The analysis was then carried out until the end of the main test phase. The analysis results show reasonable agreement with the measurements of temperature and vapor pressure, whereas they show deviations with regard to pressure and local temperatures in the middle and lower regions. In addition, a sensitivity analysis of the effects of the heat structure model and the manner by which thermodynamic variables can be lumped was carried out. This study revealed that the ILRT is useful for validating the containment input model. However, available data with which to verify the appropriateness of modeling flow paths and heat structures are limited. Based on the insights obtained, we suggest that an elaborate ILRT be carried out during the commissioning stage with more detailed test provisions and analysis methods to allow this specific application.

A review on physicochemical measurements by headspace gas chromatography. Studies of vapour-liquid equilibria.

<p style="margin: 0cm 0cm 0pt; text-align: justify; line-height: normal;"><span style="font-family: 'Times New Roman','serif'; font-size: 12pt; mso-ansi-language: EN-GB;" lang="EN-GB">Headspace gas chromatography (HS-GC) is a powerful technique for the analysis of volatile compounds. It has found broad applications for quantitative and qualitative analyses of various samples as well as for physicochemical measurements. This paper briefly reviews the basic physicochemical applications of HS-GC including vapour pressure measurements and studies of vapour-liquid equilibria in multicomponent systems. A special attention is paid to methodological aspects of these measurements. The advantages and limitations of HS-GC in this field as well as typical applications are also pointed out.</span></p>

On Particularities of the Vapor Pressure Measurements of Refractory Substances at Very High Temperatures

Vapor pressure measurements of refractory materials at very high pressure remain relevant for constructing adequate equations of state up to the domain of a critical point. In the present paper, an attempt is made to provide a reliable physical ground for the experimental method based on a laser-induced evaporation into the buffer gas, which was used by a number of researchers since the end of 1970s. It is shown that there is a low pressure limit (of roughly 0.1 bar) intrinsically inherent for this kind of measurements. A developed mathematical model is used for interpretation of some controversial or not sufficiently explained experimental results. The model also provides some hints, which could help make more reliable vapor pressure measurements in the future.

Reconciled thermophysical data for anthracene

Anthracene (CAS RN: 120-12-7) is recommended as a primary standard for sublimation enthalpy measurements and it is also frequently used for testing apparatus for vapour pressure measurements. Two recent recommendations by ICTAC for sublimation enthalpy at 298.15 K obtained by extrapolation can be found in the literature. However, no recommended vapour pressure equation and sublimation enthalpy as a function of temperature were reported. The following steps were performed to develop recommended sublimation pressure and enthalpy data for anthracene in the temperature range in which the calibrations are typically performed: (i) analysis and reconciliation of the literature values on vapour pressures and examination of their thermodynamic consistency with related thermal properties; (ii) new extensive vapour pressure measurements in the temperature range (343–373) K; (iii) calculation of ideal-gas thermodynamic properties combining statistical thermodynamics and quantum chemistry methods, and (iv) multi-property correlation of selected vapour pressure and thermal data. The quality and range of available data needed for the multi-property correlation allowed to establish the recommended sublimation pressure equation in the temperature range (200–373) K while at higher temperatures and for the liquid phase only tentative data are provided. Recommended values at 298.15 K are (0.91 ± 0.09) mPa for sublimation pressure and (101.01 ± 0.52) kJ·mol−1 for sublimation enthalpy; the recommended enthalpy of sublimation at 0 K is (104.4 ± 0.9) kJ mol−1. Based on the recommended sublimation pressures, super cooled liquid vapour pressures required for environmental modeling were also calculated.

Volatility and thermodynamic stability of vanillin

Vanillin is a naturally occurring phenolic aldehyde that is world-wide known for its flavouring properties. This work reports an extensive experimental and computational study of its thermodynamic properties. The vapour pressures of crystalline and liquid phases of vanillin were measured in the following temperature ranges T = (321.0–350.7) K and (324.9–382.3) K respectively, using a static method based on diaphragm capacitance gauge. Additionally, the crystalline vapour pressures were also measured in the temperature interval T = (303.1–325.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization, at selected reference temperatures, were derived from the vapour pressure measurements. The enthalpies of vaporization and of sublimation, at T = 298.15 K, were also determined using Calvet microcalorimetry and the standard (p° = 105 Pa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, was calculated and compared with the values estimated by employing quantum chemical calculations. To analyse the thermodynamic stability of vanillin, the standard Gibbs energies of formation in crystalline and gaseous phases were calculated. The molar enthalpy of fusion determined using DSC is compared with indirect results determined using Calvet microcalorimetry and vapour pressure measurements.

Online gas- and particle-phase measurements of organosulfates, organosulfonates and nitrooxy organosulfates in Beijing utilizing a FIGAERO ToF-CIMS

Abstract. A time-of-flight chemical ionization mass spectrometer (CIMS) utilizing the Filter Inlet for Gas and Aerosol (FIGAERO) was deployed at a regional site 40 km north-west of Beijing and successfully identified and measured 17 sulfur-containing organics (SCOs are organo/nitrooxy organosulfates and sulfonates) with biogenic and anthropogenic precursors. The SCOs were quantified using laboratory-synthesized standards of lactic acid sulfate and nitrophenol organosulfate (NP OS). The variation in field observations was confirmed by comparison to offline measurement techniques (orbitrap and high-performance liquid chromatography, HPLC) using daily averages. The mean total (of the 17 identified by CIMS) SCO particle mass concentration was 210 ± 110 ng m−3 and had a maximum of 540 ng m−3, although it contributed to only 2 ± 1 % of the organic aerosol (OA). The CIMS identified a persistent gas-phase presence of SCOs in the ambient air, which was further supported by separate vapour-pressure measurements of NP OS by a Knudsen Effusion Mass Spectrometer (KEMS). An increase in relative humidity (RH) promoted partitioning of SCO to the particle phase, whereas higher temperatures favoured higher gas-phase concentrations. Biogenic emissions contributed to only 19 % of total SCOs measured in this study. Here, C10H16NSO7, a monoterpene-derived SCO, represented the highest fraction (10 %) followed by an isoprene-derived SCO. The anthropogenic SCOs with polycyclic aromatic hydrocarbon (PAH) and aromatic precursors dominated the SCO mass loading (51 %) with C11H11SO7, derived from methyl naphthalene oxidation, contributing to 40 ng m−3 and 0.3 % of the OA mass. Anthropogenic-related SCOs correlated well with benzene, although their abundance depended highly on the photochemical age of the air mass, tracked using the ratio between pinonic acid and its oxidation product, acting as a qualitative photochemical clock. In addition to typical anthropogenic and biogenic precursors the biomass-burning precursor nitrophenol (NP) provided a significant level of NP OS. It must be noted that the contribution analysis here is only representative of the detected SCOs. There are likely to be many more SCOs present which the CIMS has not identified. Gas- and particle-phase measurements of glycolic acid suggest that partitioning towards the particle phase promotes glycolic acid sulfate production, contrary to the current formation mechanism suggested in the literature. Furthermore, the HSO4⋅H2SO4- cluster measured by the CIMS was utilized as a qualitative marker for acidity and indicates that the production of total SCOs is efficient in highly acidic aerosols with high SO42- and organic content. This dependency becomes more complex when observing individual SCOs due to variability of specific VOC precursors.

Development of the Knudsen effusion methodology for vapour pressure measurements of low volatile liquids and solids based on a quartz crystal microbalance

The principle of operation, concepts and recent developments of the Knudsen effusion methodology for the vapour pressure measurement of ionic liquids and other low volatile liquids and solids are presented. A new version of a Knudsen effusion apparatus, coupled with a quartz crystal microbalance, which is used for a reliable measurement of the mass flow from a Knudsen effusion cell, is described in detail. In the new system, designed and optimized for the vapour pressure measurement of ionic liquids, it is possible to measure the vapour pressure of small samples using very short effusion time over a wide temperature range. This apparatus allows the vapour pressure measurements using step-temperature and continuous-temperature modes that have the advantage of reducing the measurement time interval and minimize the effect of a sample degradation. A significant number of improvements on the performance and capability for the vapour pressure measurements of ionic liquids has been implemented: in situ temperature control of the vacuum chamber for a better stability of background signal; a new design of a stainless steel effusion cell to decrease the reactivity and sample decomposition; dual temperature control ensuring a positive temperature gradient between bottom and top of the cell in order to avoid the ionic liquids condensation on the effusion cell lid and significantly improved stability of the time frequency derivative at high temperatures; Installation and test of a mass flow tube, on the top of the outlet of the cell lid oven block in order to increase the mass sensitivity coefficient of QCM. The tests and benchmarking concerning the measurement of vapour pressures of ionic liquids performed with [C2mim][NTf2] indicate that the described Knudsen effusion apparatus and methodology is able to produce reproducible and reliable experimental vapour pressure data with an accuracy and quality similar than the achieved in the measurements with low volatile solids. The effect of the improvements on the performance of the Knudsen effusion apparatus was tested and evaluated by the comparison of the vapour pressure results of 1,3,5-triphenylbenzene and 1-ethyl-3-methylimidazolium with the available literature data.

Experimental measurement of equilibrium vapour pressure of H2O/KCOOH (potassium formate) solution at high concentration

This paper presents the measurement of the equilibrium vapour pressure of H2O/KCOOH solution with a concentration in salt from 60 to 80% in the temperature range from 5 to 75 °C typical for desiccant application. The experimental measurements were performed in a VLE apparatus instrumented with a pressure gauge having a maximum uncertainty (k = 2) within ±35 Pa and a platinum resistance thermometer having a maximum uncertainty (k = 2) within ±0.05 K. A set of 40 experimental data points on H2O/KCOOH equilibrium vapour pressure was fully reported and compared with the unique other set of experimental data (Beyer and Steiger, 2010) available in the open literature and also with the estimation of a referenced chemical engineering property database (Aspen Plus®): a reasonable agreement was found in both the cases. A best-fitting regression model based on present set of data was also reported: the mean absolute percentage deviation between experimental and calculated data is 1.1%.

Measurement of Vapor Pressures and Melting Properties of Five Polybrominated Aromatic Flame Retardants

While vapor pressure is among the most important properties used in the environmental fate assessment of organic contaminants, measured vapor pressures exist only for a few representatives of the group of novel brominated flame retardants (BFRs). To expand on this limited set of data, the vapor pressures of five BFRs—1,2,4,5,-tetrabromo-dimethylbenzene (TBX), 1,2,3,4,5-pentabromo-6-methyl-benzene (PBT), 1,2,3,4,5-pentabromo-6-ethyl-benzene (PBEB), 2,3,4,5,6-pentabromo-phenol (PBP), and 1,3,5-tribromo-2(2,3-dibromopropoxy)-benzene (TBP-DBPE)—were measured in the temperature range 322.7–367.7 K with the gas saturation method. Enthalpies of sublimation or vaporization were determined from the slopes of semilogarithmic plots of measured vapor pressure against reciprocal temperature. The melting temperature and enthalpy of fusion were measured using differential scanning calorimetry. From these experimental data, the vapor pressures and subcooled liquid vapor pressures at 298.2 K, pi° and pi°,sl, respectively,...

Vapor pressure measurement of liquid dessicants at low temperatures by a novel technique.

Due to non-condensable gas under conditions of vacuum and low temperatures, it becomes difficult to obtain precise vapor pressures of typical liquid desiccants by an experiment. Usually, non-condensable gas is removed by a traditional degassing method (degassing after prepared solutions - DPS), in which prepared liquid desiccants are circularly frozen and non-condensable gas is pumped out. However, the solvent of liquid desiccants could greatly evaporate during traditional degassing processes. Concentrations of the prepared liquid desiccants could be greatly deviated from those of the prepared liquid desiccants. Accordingly, measured vapor pressures usually greatly deviate from those corresponding to the concentrations of the prepared liquid desiccants. Moreover, it becomes very difficult to determine new concentrations of the prepared liquid desiccants after degassing, precisely. To overcome the challenges for precise measurements of typical liquid desiccants, a novel technique is developed in this context. The new method is called DSSPS (degassing solvents and solutes before preparing solutions - DSSPS), in which degassed solvent and solute is weighted respectively, and then, is mixed as measured solutions. Thus, concentrations of the measured solutions could be determined easily and precisely. Vapor pressures of LiCl-H2O desiccants are measured by the new method at a range from 218K to 258K and with the mass fractions of solutions from 5% to 20%. Totally, 35 sets of vapor pressure are measured. Then, the data is correlated based on Antoine equation.The ARD% (Absolute Relative Deviation - ARD) of equation is from 0.04% to 3.21% and AARD% (Average Absolute Relative Deviation - AARD) is 1.73%. So, the new method could be used to measure vapor pressure of aqueous solutions at vacuum and low temperatures precisely. The average error between experimental data and the results calculated by EES (Engineering Equation Solver - EES) is within 15.2%, and its maximum error is 35.46%. Vapor pressure data in this context also provides important reference for development of a precise calculation model.

Vapor pressures and thermophysical properties of selected ethanolamines

A thermodynamic study of three ethanolamines, 2-(diethylamino)ethanol, 2-(ethylamino)ethanol and 2-(isopropylamino)ethanol, reporting the measurements of vapor pressure, liquid phase heat capacities, and phase behavior is presented in this work. The vapor pressures were measured using a static method in the temperature interval 238–343 K. After a critical assessment of literature data, selected experimental data were correlated using the Cox equation. The liquid phase heat capacities were measured in the temperature range 265–355 K using Tian-Calvet calorimetry and the phase behavior was investigated using differential scanning calorimetry (DSC) starting from 183 K. For 2-(ethylamino)ethanol and 2-(isopropylamino)ethanol, two monotropically related crystalline forms were identified. To our knowledge, vapor pressure and heat capacity for 2-(isopropylamino)ethanol and phase behavior data for 2-(ethylamino)ethanol and 2-(isopropylamino)ethanol are reported for the first time in this work.

Robust Inverse Modeling of Growing Season Net Ecosystem Exchange in a Mountainous Peatland: Influence of Distributional Assumptions on Estimated Parameters and Total Carbon Fluxes

AbstractWhile boreal lowland bogs have been extensively studied using the eddy‐covariance (EC) technique, less knowledge exists on mountainous peatlands. Hence, half‐hourly CO2 fluxes of an ombrotrophic peat bog in the Harz Mountains, Germany, were measured with the EC technique during a growing season with exceptionally dry weather spells. A common biophysical process model for net ecosystem exchange was used to describe measured CO2 fluxes and to fill data gaps. Model parameters and uncertainties were estimated by robust inverse modelling in a Bayesian framework using a population‐based Markov Chain Monte Carlo sampler. The focus of this study was on the correct statistical description of error, i.e. the differences between the measured and simulated carbon fluxes, and the influence of distributional assumptions on parameter estimates, cumulative carbon fluxes, and uncertainties. We tested the Gaussian, Laplace, and Student's t distribution as error models. The t‐distribution was identified as best error model by the deviance information criterion. Its use led to markedly different parameter estimates, a reduction of parameter uncertainty by about 40%, and, most importantly, to a 5% higher estimated cumulative CO2 uptake as compared to the commonly assumed Gaussian error distribution. As open‐path measurement systems have larger measurement error at high humidity, the standard deviation of the error was modeled as a function of measured vapor pressure deficit. Overall, this paper demonstrates the importance of critically assessing the influence of distributional assumptions on estimated model parameters and cumulative carbon fluxes between the land surface and the atmosphere.

Isopiestic Determination of the Osmotic and Activity Coefficients of the {hH2SO4 + (1 − h)Al2(SO4)3}(aq) System at T = 298.15 K. 1. Experimental Results at Stoichiometric Ionic Molality Factions h = (0.85777, 0.71534, 0.57337, 0.42985, 0.28593, and 0.14332)

Isopiestic vapor-pressure measurements have been made at 166 compositions of the {hH2SO4 + (1 − h)Al2(SO4)3}(aq) system at the temperature 298.15 K using H2SO4(aq) as the isopiestic reference standard, where h is the stoichiometric ionic molality fraction of H2SO4 in the mixtures that was calculated by assuming complete dissociation of both solutes. These experiments were performed up to the crystallization limits at values of h = (0.85777, 0.71534, 0.57337, 0.42985, 0.28593, and 0.14332) corresponding approximately to h = (6/7, 5/7, 4/7, 3/7, 2/7 and 1/7); the highest achieved molalities are very slightly above or close to the solubility limits because of the very limited tendency of Al2(SO4)3 to form supersaturated solutions when concentrated isothermally at 298.15 K.

Development of an Advanced Knudsen Effusion Mass Spectrometer for Measurements of Vapor Pressures and Determination of Basic Thermodynamic Data

The amount and composition of vapor pressures over a liquid or solid phase are key physical properties. With the temperature dependency of the partial pressures basic thermodynamic data can be derived such as enthalpy, entropy and Gibbs energy of the vaporization reaction as well as their partial and molar mixing values for the condensed phase. Such high precision thermodynamic data are a basis for designing new materials and predict the corrosion resistance and phase stability of new alloys for technical applications especially at high temperatures. The vapor pressure (pi) can be measured by the method of Knudsen Effusion Mass Spectrometry (KEMS) in a high vacuum atmosphere. Therefore, a sample is heated up in a Knudsen Cell. The crucible of the Knudsen Cell is closed with a lid which has a small orifice between 0.1 – 1 mm. At constant temperature the gas phase is in equilibrium with the sample. Due to the mean free path in vacuum, the molecules of the gas atmospheres effuse from the Knudsen Cell only stochastically. The molecules effuse out of the Knudsen Cell and will be ionized and then characterized quantitatively and qualitatively by a mass spectrometer. Thereby the equilibrium between gas phase and condensed phase will practically not be disturbed. With the KEMS method it is possible to measure vapor pressures between 1∙10-7 - 1 mbar. Measurements can be performed between 290 K – 3000 K. A completely new designed experimental device is set up in our laboratory. The aim of the project is to build up a new KEMS apparatus which exceeds the current state of the art of measuring vapor pressures in sensitivity and usability. The focus of the new KEMS-device is a user-friendly operation, compact dimensions and self-explanatory evaluation software. Special designed sample carrier will allow measuring samples highly automatical and determination of high precise thermodynamic data.

Simulations and Experiments of the Kinetics of the Electrochemical Double Layer in Ionic Liquids

Ionic liquids are an interesting class of electrolytes both from a fundamental scientific standpoint and from an applications standpoint due to a number of relevant applications like batteries, supercapacitors and solar cells. Even though the constituents of ionic liquids are only ions, the conductivities are known to be pretty low. The suggested reasons for this low conductivity are low mobility due to high viscosity and the existence of most ions as ion pairs. Even though they have low conductivities, their electrochemical potential window and their low to non-existent vapor pressures make them very attractive as electrolytes. Because ionic liquids have no measurable vapor pressure, in-situ X-Ray Spectroscopy (XPS) can be performed directly on the ionic liquids during electrochemical experiments. This is not possible with more conventional electrolytes since any other electrolytic solution would not be conducive to running experiments inside the ultra-high vacuum (UHV) chamber. We have been doing experiments investigating both Faradaic and non-Faradaic aspects of electrochemical experiments on ionic liquids inside the XPS chamber. On the Faradaic side we have recently shown that the reduction of imidazolium based ionic liquids can yield stable carbene species (Aydogan-Gokturk et.al. New Journal of Chemistry 18(2017), 10299-10304 and Aydogan-Gokturk et.al. Electrochimica Acta 234(2017), 37-42) and that gold nanoparticles can be oxidatively synthesized starting from metal electrodes (Camci et.al. ACS Omega, 2(2017), 478-486). On the non-Faradaic front, investigations of the electrochemical double layer revealed that the applied potential has transient effects that are sensed unexpectedly far away from the electrode surface (Camci et.al. Phys. Chem. Chem. Phys. 18(2016)28434-28440). Specifically, our experiments indicate that the effects of the applied potential are felt up to millimeters away from the electrode surface during the transients. These transients can last hundreds of seconds and dominate the response. The current contribution is going to elaborate more on the unexpected electrochemical double layer effects. Even though the electrochemical double layer in electrolytes is well understood since the days of Gouy-Chapman-Stern model development, the double layer in the ionic liquid media is known to be somewhat different. There is a sizable body of recent modeling literature on the electrochemical double layer in ionic liquids. For example, work by Bazant et.al. (Phys. Rev. Lett. 106(2011) 046102), Lee et.al.(Phys. Rev. Lett. 115(2015)106101) and Gavish et.al.(J. Phys. Chem. Lett. 7(2016), 1121-1126) consider continuum type models of various sorts to model the behavior of the anions and the cations in great detail. The results indicate that there is some layering behavior that are either close to the electrode surface or throughout the region between the electrodes. The models used, though very detailed and thorough neglect ion pairing and thermal fluctuations. The effect of ion pairing is a crucial part of the explanation of the low conductivity of ionic liquids. On the other hand, thermal fluctuations are a necessary part of the conventional explanation of the diffuse double layer. In most cases, the models developed predict a layered steady state structure and also predict that the Debye length would be on the order of 10-20 times the size of a monolayer for most cases. Our experiments indicate that the effect of the applied potential is felt way farther away from the electrode in the transient times. We have developed a simpler modeling framework that model diffusion, convection and ion pairing using simple algebraic expressions on a simple grid that is set up. This framework involves setting up a grid between the two electrodes and starting with a homogeneous ionic liquid. At every time step, the algorithm iterates over the grid and treats diffusion, migration and ion pairing separately using simple constructs. Diffusion is simply handled by a random number generator that determine which way the ions will move, if at all. Then, the potential difference between neighboring points of the grid is used to evaluate the electric fields, which is used to then treat migration. Finally, for every position on the grid, a simple chemical equilibrium calculation is employed to solve for the number of ions that pair up. Using this framework to model the behavior of the ionic liquids and tuning the parameters of the simulation based on the results of transient measurements inside the XPS chamber using Squarewave applied potentials, we will report behavior of the electrochemical double layer in ionic liquids and insights about various parameters of ionic liquids such as ion-pairing constants, mobilities and diffusion coefficients. Figure 1

PVT, saturated liquid density and vapor-pressure measurements of main components of the biofuels at high temperatures and high pressures: Methyl palmitate

PVT, saturated liquid density and two-phase (vapor-pressure) properties of one of the main component of the biofuel (methyl palmitate), produced from a soybean, have been measured. One-phase PVT measurements were made for ten liquid and four vapor isochores between (85.2 and 811.7) kg·m−3over the temperatures range from (300 to 443) K using a constant-volume piezometer technique. The vapor-pressures (PS,TS) of the methyl palmitate were measured in the temperature range from (300 to 501) K. The combined expanded uncertainty of the density, ρ, pressure, P, and temperature, T, measurements at 95% confidence level with a coverage factor of k = 2 is estimated to be 0.1%, (0.15–0.5)% depending on temperature and pressure ranges, and 15 mK, respectively. We have critically assessed all of the reported density data at atmospheric pressure and at high-pressures and vapor-pressures together with the present results for their internal thermodynamic consistence to carefully select primary data to fit reference correlations for ρ0(T) and vapor-pressure PS(T). The measurements were concentrated in the two-phase region to accurately determine vapor-pressures and in the immediate vicinity of the phase-transition temperatures to precisely determine the phase boundary properties (PS,TS,ρS) on the liquid + gas equilibrium curve. The liquid-gas phase transition temperatures (TS) for seven liquid isochores of (711.9, 766.8, 774.5, 782.3, 795.00, 803.40, and 811.70) kg·m−3were accurately obtained using the isochoric (P-T) break point technique. The measured values of the vapor-pressures and saturated liquid densities were fitted to Wagner-type vapor-pressure equation and complete scaling model, respectively. The values of the critical parameters (PC,TC,ρC) were estimated using vapor-pressure and liquid-gas coexistence curve data. The correlation for the density at atmospheric pressure, ρ0(T), together with the present and reported high-pressure density measurements (ρ,P,T) were used to develop two-parametric (c and B) and theoretically based Tait-type equation of state.

Density, Viscosity and Volatility of Binary Mixtures of Isopropyl Ether and exo-Tetrahydrodicyclopentadiene

Measurements of density, viscosity and vapor pressure for binary mixtures of exo-tetrahydrodicyclopentadiene (JP-10) with isopropyl ether are reported at temperatures of (293.15, 298.15, 303.15, 308.15, and 313.15) K over the entire composition range. The excess molar volumes, viscosity deviation and excess Gibbs energies of activation for the binary systems were calculated from the experimental values and fitted with the Redlich–Kister equation. Isopropyl ether was added to enhance the vapor pressure of JP-10. Experimental vapor pressure data were correlated by the Antoine equation. Several semi-empirical equations were used to correlate the viscosity data. The McAllister equation gives relatively satisfactory results for the correlation. The experimental and correlated data could be used in the development of models for mixtures of hydrocarbons with oxygenates.

Vapor Pressure Measurement for the Ternary System of Water, Lithium Bromide, and 1-Ethyl-3-methylimidazolium Acetate

To improve the performance of an absorption system, ionic liquids (ILs) have been chosen as additives to conventional working fluid (lithium bromide aqueous solution) in recent years. In this paper, 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) was added to lithium bromide aqueous solution (mass ratio LiBr/[Emim]Ac = 3) to measure the vapor–liquid equilibrium (VLE) data of the ternary system. The experiment was conducted by means of boiling point method, at temperatures between 303.94 K and 405.41 K and mass fractions of absorbent between 0.20 and 0.60. The experimental data were regressed using an Antoine-type equation, and the average absolute relative deviation (AARD%) between the experimental and calculated values was 0.34%, which showed excellent accuracy and consistency. The experimental ternary system was compared with the conventional LiBr + H2O system and two other ternary systems from the literature; the result revealed that the experimental ternary system had lower vapor pressures, which will ...