Experimental Vapor Research Articles

The electronic structure of ionic liquids based on the TFSI anion: A gas phase UPS and DFT study

The valence bands of [EMIM][TFSI], [DEME][TFSI] and [PYR1,4][TFSI] gas-phase ion pairs have been investigated using ultraviolet photoelectron spectroscopy (UPS). The photoelectron spectra are interpreted by using several density functional and ab initio calculation methods. Although the experimental vapor phase spectra are similar, the different calculation methods make different predictions about the HOMO molecular state of the ion-pairs of the ionic liquids. The HOMO state of the [DEME][TFSI] ion-pair is due to the TFSI anion, while in [EMIM][TFSI] it is due to the EMIM cation. However, it is difficult to make conclusive assignments for the [PYR1,4][TFSI] ionic liquid. All calculation methods predict the LUMO to be of cationic origin in all the studied ion-pairs.

Experimental vapour pressures of eight n-alkanes (C17, C18, C20, C22, C24, C26, C28 and C31) measured at ambient temperatures

We present direct room-temperature vapour pressure measurements for eight semi-volatile n-alkanes of atmospheric importance. Measured vapour pressures range from 8.4 ± 1.6 × 10−3 Pa for C17, to 1.7 ± 0.6 × 10−8 Pa for C31. The new measurements for C17–C18 are in reasonable agreement but at the lower end of values in the literature; the new measurements for C28 and C31 are one-to-two orders of magnitude higher than most literature values, but six orders of magnitude higher than the lowest values in the literature. Our measurements are suitable for atmospheric aerosol modelling and interpretation of environmental measurements, interpolated in carbon number where necessary, and extrapolated over temperatures relevant to the atmospheric boundary layer using the Clausius-Clapeyron equation with literature values of the enthalpy of vaporisation.

Imidazolium-based ionic liquids containing FAP anion: Thermodynamic study

New experimental vapor pressures and vaporization enthalpies of the ionic liquids (ILs) [C2mim][FAP], [C4mim][FAP] , and [C6mim][FAP] with [FAP] = tris(pentafluoroethyl)trifluorophosphate have been measured by the Langmuir method combined with the Quartz Crystal Microbalance. Linear dependence of vaporization enthalpies on alkyl chain length was observed. Gas-phase enthalpies of formation of ILs were calculated by quantum chemistry. Solution enthalpies of ILs available from the literature were used for calculation the aqueous enthalpy of formation of the ∆fHom(FAPaq−) anion in combination with quantum-chemical results. These results will facilitate chemical engineering calculations of processes involving ILs.

A five-parameter cubic equation of state for pure fluids and mixtures

A five parameter cubic equation of state, named 5PGDN is presented for the prediction of thermodynamic properties of pure fluids and mixtures. A new alpha function is proposed with two compound specific parameters which are estimated by matching experimental saturation vapor pressure data at two fixed temperatures Tr=0.5,0.7. We have cast three of the five parameters in terms of the remaining two parameters. The 5PGDN uses the critical temperature, the critical pressure, the critical compressibility factor, and two parameters of the alpha function to calculate thermodynamic properties such as saturated vapor pressure, liquid and vapor density, enthalpy of vaporization, sound velocity, heat capacity at constant pressure and volume. The 5PGDN is further used for the prediction of bubble point pressure and vapor mole fraction of several binary mixtures. The accuracy of 5PGDN is demonstrated by comparing results with the Patel-Teja (PT), Haghtalab-Kamali-Mazloumi-Mahmoodi (HKM1) and Ghoderao-Dalvi-Narayan (4PGDN1) equations of state.

Isothermal Vapor–Liquid Equilibrium Measurements for Alcohol + Water/n-Hexane Azeotropic Systems Using Both Dynamic and Automated Static-Synthetic Methods

Isothermal vapor–liquid equilibrium measurements (pressure– temperature–liquid and vapor composition) were conducted for water (1) + propan-1-ol (2), n-hexane (1) + butan-2-ol (2), and n-hexane (1) + 2-methyl-propan-1-ol (2) at three temperatures, each using a dynamic moderate pressure equilibrium still. Additionally, pressure–temperature-overall composition measurements for the first two systems were conducted for the intermediate temperatures using a newly automated static-synthetic apparatus to confirm the operability of the automation scheme and to compare the model predictions of the vapor-phase compositions from the processed pressure–temperature–liquid composition data by the static-synthetic method with the experimental vapor compositions measured by the dynamic method. The automation scheme was developed and implemented on the original static total pressure vapor–liquid equilibrium apparatus of Raal et al. (Fluid Phase Equilib. 2011, 310, 156–165) using the LabVIEW graphical programming language. In comparison to the manual operating mode, this scheme improved the efficiency of operation by reducing the man-hours involved and minimized the associated uncertainty with the measurement procedure with respect to liquid composition. Once executed, the control scheme requires approximately 2 days to produce a single 40-data point (pressure–temperature–liquid composition) isotherm and minimizes human intervention to 2–3 h in comparison to a 2-week long measurement procedure in the nonautomated operating mode and in excess of 3 weeks using the dynamic method with analysis by gas chromatography. All experimental data were modeled using the γ–Φ approach with the NRTL and UNIQUAC activity coefficient models and the virial equation of state with the Hayden and O’Connell correlation. For the pressure–temperature–liquid and vapor composition data measured, thermodynamic consistency testing was performed. The data sets passed the point test with 0.01 tolerance and the area test with 10% tolerance. Experimental vapor-phase compositions obtained by phase sampling in the dynamic method compared reasonably well with the predictions from the pressure–temperature–liquid composition data measured by the automated static-synthetic method.

An Atomistic Understanding of the Unusual Thermal Behavior of the Molecular Oxide Tc2O7.

The thermal behavior of Tc2O7 has been investigated by single-crystal X-ray diffraction of the solid state over a range of 80-280 K and by ab initio molecular dynamics (MD) simulations. The thermal expansion coefficient of the solid was experimentally determined to be 189 × 10-6 Å3 K-1 at 280 K. The simulations accurately reproduce the experimentally determined crystal structures and thermal expansion within a few percent. The experimental melting point and vapor pressure for Tc2O7 are unusually high and low, respectively, in comparison to similar molecular solids. Through investigating the structure and the motion of the solid across a range of temperatures, we provide insights into the thermal behavior of Tc2O7.

Natural convection flows due to evaporation of heavier-than-air fluids: Flow direction and validity of using similarity of temperature and vapor density fields

Natural convection driven by evaporation of heavier-than-air fluids from the surface of the heated horizontal and vertical flat plates is studied both experimentally and numerically. The combined buoyancy effects of temperature and vapor density are shown to result in either downward or upward flow depending on the plate temperature and evaporating substance volatility and molar mass. For some substances (e.g., butanol) flow reversals are observed: solutal buoyancy is dominant for low and high temperatures of the heated plate leading to downward flow, whereas at moderate temperatures thermal buoyancy prevails resulting in upward convection. Refractive index fields are measured using Background Oriented Schlieren (BOS). Similarity between the temperature and vapor density fields associated with heat and mass transfer analogy is used to obtain temperature and vapor density fields from experimental data. The validity of this approach is analyzed. Good agreement between experimental temperature and vapor density distributions and numerical simulations is obtained for ethanol vapor, which has Lewis number about 1.8. For butanol vapor, which has Lewis number about 2.5, similarity is violated and temperature and vapor density contributions to refractive index cannot be separated. This is also true for validity of simplified modeling using total expansion coefficient. Similarity is also shown to be violated for hot liquid evaporation from a tank with conductive walls. In this case boundary conditions are dissimilar and upward convective flow of warm clean air near the outer surface of the tank walls is observed, which entrains the heavy vapor.

Vapor Pressure Mapping of Ionic Liquids and Low-Volatility Fluids Using Graded Isothermal Thermogravimetric Analysis

One of the hallmarks of ionic liquids (ILs) and a critical part of their sustainable implementation is their low volatility, although statements in this regard are frequently made in the absence of a critical evaluation. Although it is generally accepted that conventional ILs exhibit significantly reduced vapor pressures relative to common organic solvents, glib statements about ILs having zero volatility can no longer be abided, even if a concrete temperature-dependent vapor pressure, Pvap(T), framework for placement of IL performance has not yet been established. In this communication, Pvap(T) values of 30 illustrative low-volatility fluids—including representative imidazolium-, ammonium-, and pyrrolidinium-based aprotic ILs; examples of protic, polymeric, and di-cationic ILs; as well as deep eutectic solvents (DESs) and glycols—were determined using a simple, convenient, and reproducible isothermal thermogravimetric method. Guided by this “vapor pressure map”, observed trends can be discussed in terms of anion basicity, cation geometry, alkane chain length, hydrogen bonding strength, and van der Waals forces, providing a context for the placement of theoretical and experimental vapor pressures gleaned in future IL and DES studies.

Multicomponent Evaporation Characteristics of Biodiesel Sprays

The vapor mass fraction distribution of the multicomponent surrogate of diesel and biodiesel fuel is studied using multicomponent evaporation model at engine-relevant conditions. The numerical model is validated with experimental liquid tip penetration and vapor penetration for diesel and biodiesel. The vapor distribution for a multicomponent surrogate is significantly different than that of single-component fuel. The tetradecane, single-component surrogate for diesel has different vapor mass distribution unlike in multicomponent diesel fuel. The spatial mass fraction distribution profile of biodiesel is found to be the function of volatility differential of the pure components and their proportion in the composition. The vapor mass fraction distribution for biodiesel of palm and soybean is found to be similar to that of their single-component surrogate due to comparable volatility of components of these biodiesels. However, methyl laurate in coconut biodiesel has volatility differential with other components and also has a significant share of 40% to 50% in the coconut biodiesel composition. The change in percentage of methyl laurate in coconut composition is found to have strong impact on vapor distribution. The vapor mass fraction distribution is observed to be affected by the change in the biodiesel composition specifically volatile component.

Measurement and Correlation of Density, Viscosity and Vapor Pressure for Binary Mixtures of a Hydrocarbon Fuel + Dimethoxy Methane

Densities, viscosity and bubble-point vapor pressures for binary mixtures of dimethoxy methane and a hydrocarbon fuel (exo-tetrahydrodicyclopentadiene) were measured over the whole composition range. The excess molar volumes ( $$ V_{\text{m}}^{\text{E}} $$ ) and viscosity deviations (Δη) for the binary systems were calculated from the density and viscosity data. The Antoine equation was fitted with the experimental vapor pressures, and the corresponding parameters were calculated. Positive values of excess molar volumes, negative viscosity deviations and positive deviations from Raoult’s law for the vapor pressures are observed. The three physical properties and the corresponding calculation results provide valuable information on the application and study of mixed liquid hydrocarbon fuels.

On the use of transport properties to discriminate Mie-type molecular models for 1-propanol optimized against VLE data

Parameterization of classical force fields often suffers from highly correlated parameters. In the present work the hypothesis that transport properties such as shear viscosity or self-diffusion coefficient can be used to decouple force field parameters that were fitted to static thermodynamic properties, such as saturation vapor pressure and liquid density is investigated. Here 1-propanol was studied where united-atom sites are described through Mie potentials and point charges. Four models were selected that gave about the same level of agreement with experimental liquid densities and vapor pressures. Shear viscosity and self-diffusion coefficients were evaluated with the aim to discriminate the models. However, the degeneracy of force field parameters observed in the static properties was also observed in the dynamic properties. We conclude that meaningful parameterizations for transferable force fields should simultaneously consider several molecules from a homologous series in order to define a less degenerate optimization problem.

Polarizable Transferable Anisotropic United-Atom Force Field Based on the Mie Potential for Phase Equilibria: Ethers, n-Alkanes, and Nitrogen.

This study proposes a Polarizable Transferable Anisotropic Mie (P-TAMie) force field for ethers and mixtures of ethers with n-alkanes and nitrogen. In our approach, polarizability is accounted for using a charge-on-spring model (also referred to as the Drude model or core-shell model) placed on every united-atom site. Parameters for polarizabilities are obtained from ab initio calculations, without the need to introduce empirical scaling factors. The van der Waals parameters and static partial charges are optimized to minimize deviations to experimental vapor pressure and coexisting liquid density data. Vapor-liquid phase equilibria are calculated using Monte Carlo simulations in the grand canonical ensemble, using a MC scheme with multiparticle moves. Correlation results for pure substances and predictions of mixture behavior obtained from the proposed polarizable force field (P-TAMie) are in good agreement with experimental data. We compare the polarizable force field with an analogous nonpolarizable force field, namely, the Transferable Anisotropic Mie (TAMie) force field, where both force fields share the same intramolecular force field and were parametrized using the same objective function. The comparison should thus single out the role of polarizability in predicting phase equilibria. The comparison of P-TAMie with the nonpolarizable TAMie force field, however, shows very similar results of both models. This study does not include water and aqueous mixtures or other pronounced polar substances.

Estimation of critical point, vapor pressure and heat of sublimation of pharmaceuticals and their solubility in supercritical carbon dioxide

The critical point and vapor pressure of pharmaceuticals are required in the calculation of their solubility in supercritical fluids by using an equation of state. The experimental critical point of many pharmaceuticals are not accessible due to their temperature sensitivity, also the experimental vapor pressure of many pharmaceuticals are not available at temperatures at which the supercritical extraction is usually accomplished. In this study, four group contribution methods are used to estimate the critical point and acentric factor of eight pharmaceuticals. The estimated properties are evaluated in predicting the vapor pressure and enthalpy of sublimation of the pharmaceuticals by using the Peng Robinson equation of state. The most accurate critical points are employed to calculate the solubility of the pharmaceuticals in the supercritical CO2 by using the Peng Robinson equation combined with two mixing rules. The AARD of 7.28% indicates the good performance of the Wong Sander mixing rule.

Vapor liquid equilibrium prediction of methanol–ionic liquid systems using UNIFAC model to select alternative working fluids of absorption cycle

AbstractThe purpose of this paper is to study the working fluids in absorption cycle containing methanol (CH3OH) as the refrigerant and the imidazolium ionic liquid (IL) as the absorbent. The UNIFAC model was implemented to correlate the published experimental vapor liquid equilibrium data of CH3OH–IL working fluids and 14 new group interaction parameters between CH3OH and ILs were obtained. Method reliability and applicability were evaluated by calculating the vapor pressures of five CH3OH–IL working fluids. The ILs contained 1‐methyl‐3‐methylimidazolium dimethylphosphate ([Dmim][DMP]), 1‐ethyl‐3‐methylimidazolium ethyl sulfate ([Emim][ES]), 1‐ethyl‐3‐methylimidazolium diethylphosphate ([Emim][DEP]), 1‐butyl‐3‐methylimidazolium dibutylphosphate ([Bmim][DBP]), and 1‐ethyl‐3‐ethylimidazolium diethylphosphate ([Eeim][DEP]). The average absolute relative deviations for the vapor pressures between the calculated results and the experimental data were 0.91%, 1.67%, 0.66%, 0.75%, and 2.1%, respectively. Then, the CH3OH–IL systems without experimental data were predicted. Comparisons of the vapor pressure and excess Gibbs function of the studied CH3OH–IL systems, CH3OH‐[Hmim][DEP] (1‐hexyl‐3‐methylimidazolium diethylphosphate) system, as an alternative working fluid, was found to have potential to improve the absorption cycle performance upon more research work.

Effect of boiling on the acidity of hydrothermal solutions

Natural seawater and H2O–NaCl solutions were equilibrated along the two-phase (liquid–vapor) curves between 150 and 390 °C to re-examine the effect of liquid–vapor phase separation on element fractionations between saline brines and vapor phases. The experimental setup allows vapor and brine to be sampled separately at in situ P–T conditions. Experimental vapor pressure is constrained by temperature and the electrolyte concentration of the brines. With increasing temperature, dissolved electrolytes react with increasing temperature to hydroxides and HCl, in both seawater and H2O–NaCl solutions. The extent of hydrolysis is more pronounced in seawater than in H2O–NaCl solutions because seawater contains, in addition to NaCl, a range of other electrolytes capable of hydrolysis. Associated HCl has a great affinity to fractionate to the vapor phase when phase separation occurs. At 365 °C, halite-saturated vapor phases have a pH25 (pH after condensation to 25 °C) of 1.8 (seawater) and 2.8 (H2O–NaCl brines). Our data suggest that boiling of hydrothermal solutions followed by mixing of vapor condensates with seawater can impose pH25 values as acidic as the most acidic natural hydrothermal solutions vented on the ocean floor.

Application of Electrolyte Based Model on Ionic Liquids-Methane Hydrates Phase Boundary

In the current study, the phase behaviour of selected methane (CH4) hydrate-Ionic Liquids (ILs) systems were predicted via Dickens and Quinby-Hunt model. The model chosen is an electrolyte-based model; therefore easily accommodate ILs that are molten salts. The experimental hydrate vapour liquid Equilibrium (HLwVE) data of ILs was extracted from various literature sources for validation of the applied model. The overall predicted results suggested that the studied predictive model found in line with the experimental literature data for almost all the studied systems. The maximum deviation observed from the pyrrolidinium family of IL which also found to less than 0.67 K. Apparently it can be concluded that the selective model could applicable for accurate prediction of thermodynamic hydrate phase boundaries of methane hydrates in the presence of ILs. Since hydrate experimentations are very time-consuming, accurate thermodynamic predictions of hydrate phase are very crucial for exploring various hydrate-based technologies like flow assurance, natural gas recovery and gas storage and transportations.

Experimental Comparison of Construction Material Vapor Permeability in Case of Horizontal or Vertical Sample Position

The paper proposes a device for vapor permeability coefficient determination in case of vertical sample position. The device is a L-type section capacity with a window in upper part of long side of the capacity. A test sample of construction material is positioned vertically and sealed in the window. The capacity has built-in relative air humidity sensors distributed along capacity height. These sensors allow measuring height-average relative air humidity. Experimental vapor permeability coefficient values, obtained by means of the proposed device and by means of well-known wet cup method, have been compared. Rock wool has been used as a test material. As a result, wet cup method has been confirmed for vapor permeability coefficient determination for vertical enclosing structures.

Pentacene Crystal Growth on Silica and Layer-Dependent Step-Edge Barrier from Atomistic Simulations.

Understanding and controlling the growth of organic crystals deposited from the vapor phase is important for fundamental materials science and necessary for applications in pharmaceutical and organic electronics industries. Here, this process is studied for the paradigmatic case of pentacene on silica by means of a specifically tailored computational approach inspired by the experimental vapor deposition process. This scheme is able to reproduce the early stages of the thin-film formation, characterized by a quasi layer-by-layer growth, thus showcasing its potential as a tool complementary to experimental techniques for investigating organic crystals. Crystalline islands of standing molecules are formed at a critical coverage, as a result of a collective reorientation of disordered aggregates of flat-lying molecules. The growth then proceeds by sequential attachment of molecules at the cluster and then terrace edges. Free-energy calculations allowed us to characterize the step-edge barrier for descending the terraces, a fundamental parameter for growth models for which only indirect experimental measurements are available. The barrier is found to be layer-dependent (approximately 1 kcal/mol for the first monolayer on silica, 2 kcal/mol for the second monolayer) and to extend over a distance comparable with the molecular length.

Experimental measurements and modelling of CO2 solubility in aqueous mixtures of benzylamine and N‐(2‐aminoethyl) ethanolamine

AbstractIn this work, carbon dioxide solubility in N‐(2‐aminoethyl) ethanolamine (AEEA) activated aqueous benzylamine (BZA) solutions are studied using a stirred‐cell reactor in the temperature and pressure range of 313.15–333.15 K and 0.2–219 kPa, respectively. AEEA is a linear diamine with a primary and secondary amine groups, and BZA is a primary cyclic amine. The concentration of the aqueous blends used are (20mass% BZA + 10mass% AEEA), (24mass% BZA + 6mass% AEEA), and (28mass% BZA + 2mass% AEEA). Density and viscosity of unloaded aqueous amine blends are also measured in experimental temperature and concentration ranges and correlated using Joubian–Acree mathematical model. Model‐predicted density and viscosity data are in good agreement with experimental results showing 0.05% and 3.41% AAD, respectively. To correlate experimental vapor–liquid‐equilibrium data, Kent–Eisenberg (KE), artificial neural network (ANN), and soft models are used. Equilibrium constants of monocarbamate formation reaction of BZA and AEEA are regressed as a function of temperature and CO2 loading to fit the experimental data with KE model expression. KE model is also utilized to estimate the pH of CO2 loaded aqueous amine solutions. ANN model is found to predict CO2 solubility with better accuracy (1.56% AAD) in comparison of KE model (8.27% AAD) and soft model (15.5%). The CO2 absorption capacity of (20mass% BZA + 10mass% AEEA) solvent (~0.8 mol CO2/mol amine) is higher than that of monoethanolamine (~0.5 mol CO2/mol amine). Heats of absorption values of (BZA + AEEA) solvents (~25 kJ/mol CO2) predicted from Gibbs–Helmholtz relationship are found to be lower than that of MEA (~87 kJ/mol CO2) and PZ (~66 kJ/mol CO2).

Measurement and correlation of vapor–liquid equilibrium data for binary and ternary systems composed of (−)-β-caryophyllene, p-cymene and 3-carene at 101.33 kPa

Abstract New experimental vapor–liquid equilibrium (VLE) data for three binary systems composed of p-cymene + (−)-β-caryophyllene, 3-carene + (−)-β-caryophyllene, and 3-carene + p-cymene and for the ternary system of (−)-β-caryophyllene + p-cymene + 3-carene were obtained using a modified Ellis equilibrium still over the temperature range from 444.44 to 528.78 K at 101.33 kPa. The compositions of these mixtures were assessed using gas chromatography. The VLE data for the binary systems passed thermodynamic consistency tests based on the Herington method and Van Ness test. The thermodynamic consistency of the ternary system was checked by a Van Ness test. The VLE data for binary systems were correlated using the Wilson, NRTL, and UNIQUAC activity coefficient models with minor deviations. The ternary VLE data were also satisfactorily correlated using the Wilson, NRTL and UNIQUAC models. By comparing the experimental values for the ternary system with the values calculated using the three models, the average absolute deviation of the equilibrium temperature and vapor–phase composition were determined to be less than 0.57 K and 0.0060, respectively. These results indicated excellent agreement of the models with experimental values.