Supercritical Ethane Research Articles

Organic Matrix and Solution Photochemical Studies of (Allyl)dicarbonyl(cyclopentadienyl)molybdenum Compounds

Photolysis of fresh samples of the η3-allyl compounds [(η5-C5H5)Mo(CO)2(η3-C3H5)] or [(η5-C5H5)Mo(CO)2(η3-C3H4CH3)] in a Nujol matrix at ca. 90 K at a wavelength greater than 400 nm was found by IR spectroscopy to cause conversion of the endo rotamer to the exo rotamer. Photolysis of exo enriched samples of [(η5-C5H5)Mo(CO)2(η3-C3H5)] at wavelengths of between 360 and 400 nm reversed the photoconversion leading to an exo to endo conversion. At higher energies photochemical CO loss was also observed. In the case of the 2-methylallyl derivative, a photoproduct believed to be [(η5-C5H5)Mo(H)(CO)(η4-C4H6)] was observed along with CO loss. Time-resolved IR studies of the flash photolysis of [(η5-C5H5)Mo(CO)2(η3-C3H5)] in n-heptane confirm both endo to exo rotamer conversion and CO loss. Under these conditions, the species formed after CO loss is probably [(η5-C5H5)Mo(CO)(n-heptane)(η3-C3H5)]. When [(η5-C5H5)Mo(CO)2(η3-C3H5)] was dissolved in supercritical ethylene and photolyzed, [(η5-C5H5)Mo(CO)(C2H4)(η3-C3H5)] was formed. A mechanism involving two distinct excited states is proposed to account for the photoreversible endo/exo transformations.

Size-Dependent Solubility of Thiol-Derivatized Gold Nanoparticles in Supercritical Ethane

It is shown that alkane thiol-capped gold nanoparticles can be dissolved in supercritical ethane. Importantly, the solubility was found to be dependent on the core diameter thus allowing separation by size. Nanoparticles with a core diameter less than 1.7 nm were soluble in the supercritical fluid.

Pulse Radiolysis Studies of Solvated Electrons in Supercritical Ethane with Methanol as Cosolvent

Pulse radiolysis has been used to study the solvated electron in supercritical ethane with methanol as a cosolvent. These measurements give information about the liquid structure of the cosolvent in these systems. The results show that at temperatures below 110 °C, there are high local concentrations of alcohol molecules (clusters), which are capable of solvating an electron. The agglomeration number of methanol clusters depends on mole fraction of alcohol at a fixed temperature. Addition of salts increases the size of methanol clusters.

Experimental data for the extraction of Peace River bitumen using supercritical ethane

An apparatus was constructed capable of providing extraction data over a wide range of temperatures and pressures using a semi-batch extractor packed with a mixture of bitumen and sand. The results of the extraction of Peace River bitumen using supercritical ethane show that the quantity of recovered bitumen increased when the operating temperature was decreased or the pressure increased. Analysis of the extracted samples showed that the composition, viscosity and SARA fractions were lighter than the feed, had lower viscosities and were free of asphaltenes. The amount by which these properties changed was influenced by changes in the extraction conditions and at what time the samples were obtained during the extraction process.

ChemInform Abstract: Radiolytically Induced Formation and Optical Absorption Spectra of Colloidal Silver Nanoparticles in Supercritical Ethane.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Demixing Pressure Measurements of Aerosol-OT in Ethane + Alcohol Solvent Mixtures

The demixing pressures (dew point pressures) for sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in supercritical ethane + alcohol cosolvent mixtures were measured in a variable-volume view cell. The alcohols studied include methanol, 1-propanol, 1-octanol, and benzyl alcohol. The temperatures studied ranged from 40 to 100 °C with overall alcohol mass fractions ranging from 0 to 0.07. The demixing pressures for AOT (1.6 mass %) in supercritical ethane with methanol, 1-propanol, and 1-octanol were found to linearly increase with temperature. The demixing pressure was found to decrease with increasing alcohol concentration at constant temperature. The differences between methanol and propanol were resolved by calculation of the demixing solvent densities. The addition of 1-octanol decreased the demixing pressure slightly less than the addition of 1-propanol (for 3 mass % cosolvent). For benzyl alcohol as the cosolvent, the demixing pressure increased with increasing cosolvent concentration and showed a very nonlinear dependence on temperature at the highest benzyl alcohol concentration studied.

Phase-equilibrium calculations for solutions of poly(ethylene-co-vinyl acetate) copolymers in supercritical ethylene using a cubic equation of state

The cubic equation of state proposed by Sako, Wu and Prausnitz (SWP-EOS) is used to calculate the phase equilibrium for quasibinary solutions of poly(ethylene-co-vinyl acetate) copolymers (EVA) in supercritical ethylene. The copolymer is considered to be polydisperse with respect to molecular weight and, additionally, with respect to chemical composition. Equations for the cloud-point curve and for the shadow curve are derived with the aid of continuous thermodynamics incorporating both kinds of polydispersity by the use of a bivariate distribution function. The calculations are performed for EVA+ethylene systems with different averages of molecular weight and chemical composition of the copolymer at five temperatures (393–473 K). The binary interaction parameter is found to be a function of the temperature and of the chemical composition of the copolymer but to be independent of the molecular weight. Predictions of cloud-point curves and shadow curves of EVA+ethylene systems that were not included in parameter fit are very successful.

Local Density Augmentation in Supercritical Solvents: Electronic Shifts of Anthracene Derivatives

Fluorescence spectroscopy is used to measure local density augmentation in solutions of anthracene, 9-cyanoanthacene, 9,10-dichloroanthracene, and 9,10-diphenyl-anthracene in the supercritical solvents ethane, carbon dioxide, and fluoroform. For this purpose, the relationship between density and spectral shift is calibrated using dielectric continuum models of solvatochromism together with data in the gas phase and in liquid solutions. This approach, and the uncertainties inherent in it, are discussed in detail. The effective local densities (ρeff) deduced from the emission shifts in all of these solute/solvent combinations are comparable at temperatures near to the critical point (Tc+5 K or T/Tc = 1.02). Density enhancement factors ρeff/ρ increase with decreasing bulk density (ρ), reaching values of 5−6 at the lowest bulk densities observable. Density augmentation, the difference between the local and bulk densities (Δρeff ≡ ρeff − ρ) reaches a maximum at densities of ∼0.6 times the critical density (ρc)...

Radiolytically Induced Formation and Optical Absorption Spectra of Colloidal Silver Nanoparticles in Supercritical Ethane,

Colloidal silver nanoparticles were synthesized in supercritical ethane at 80 °C and 80−120 bar, with methanol as cosolvent. Solvated electrons, produced by a pulse of 20 MeV electrons, reduced the silver ions. The time-resolved technique of pulse radiolysis was employed to characterize the reduction products and colloidal metallic particles. The absorption spectra of small silver clusters (Ag2+, Ag3+, Ag42+, etc.) were detected at short times after the pulse. Colloidal metallic silver particles were identified by their characteristic plasmon absorption at 1−10 s after the pulse. Colloidal particles are stable for hours in supercritical ethane. The particles are less than 10 nm in diameter. Their size was determined using transmission electron microscope after precipitation from the solution.

Ion Mobilities in Supercritical Ethane, Xenon, and Carbon Dioxide

The mobility of positive ions was measured in supercritical ethane, xenon, and carbon dioxide as a function of pressure at several temperatures. In supercritical CO2 the mobility of negative ions was also measured. Radii of the moving clusters were calculated with a hydrodynamic compressible continuum model that takes the enhancement in density and viscosity near the ions into account. The results show that positive ions move with a large solvation shell. Changes in size of this shell occur as a function of temperature and pressure. The largest radii at each temperature are found to occur at the pressure corresponding to the maximum in the isothermal compressibility. For positive ions the first solvation shell is totally filled under all conditions.

Temperature effect on spectrum of solvated electron formed in a mixture of supercritical ethane

The spectral shift of the solvated electron in MeOH/C 2H 6 mixture has been studied using pulse radiolysis. The spectral shift can be explained in terms of the size of methanol clusters formed in the solution. With increasing temperature at constant mole fraction of MeOH, the spectral maximum shifts towards lower energy. The width at red side increased with increasing temperature, however, there is no significant changes in the blue side of the spectra with temperature.

Solvent Clustering around Pyrazine Ions in the High-Compressibility Region of Supercritical Ethane

Pyrazine and methylpyrazine attach electrons reversibly in supercritical (SC) ethane in the interesting region near critical densities. Very rapid shifts in the attachment equilibrium occur over ve...

Fluid−Liquid Transitions of Poly(ethylene-co-octene-1) in Supercritical Ethylene Solutions

Fluid−liquid pressures are measured and correlated with two SAFT equations of state for poly(ethylene-co-octene-1) solutions in supercritical ethylene at temperatures up to 180 °C. These cloud-point pressures are found to depend strongly on the molecular weight of the polymer and the branch density but weakly on the polymer concentration in the range from 0.05 to 0.15 polymer weight fraction. EO solutions in ethylene are found to exhibit U-LCST behavior.

Fractionation of Peace River Bitumen Using Supercritical Ethane and Carbon Dioxide

The purpose of this work was to provide valuable data for the use of supercritical fluids in both surface and in situ bitumen and heavy oil recovery operations. Experiments were conducted using a semibatch extractor packed with a mixture of bitumen and sand, and the experiments were performed such that thermodynamic equilibrium governed the extraction process. Experimental temperatures and pressures were varied in order to observe their impact on the ability of supercritical ethane and carbon dioxide to recover oil from the bitumen-sand mixture. The results showed that ethane consistently outperformed carbon dioxide in terms of its ability to extract oil from the bitumen-sand mixture. In all cases, supercritical ethane produced yields that were much greater than those obtained with supercritical carbon dioxide. Analysis of the extracted material revealed that the bitumen extracted using ethane was much heavier and contained a wider range of hydrocarbons.

Temperature dependence of solute vibrational relaxation in supercritical fluids: experiment and theory

Vibrational lifetime ( T 1) data for the asymmetric CO stretching mode of W(CO) 6 in supercritical ethane and carbon dioxide as a function of temperature at various fixed densities are compared to a recent extended hydrodynamic theory [1]. In ethane at the critical density, as the temperature is raised, T 1 initially becomes longer, reaching a maximum ∼70 K above the critical temperature. T 1 decreases with further increase in temperature. The theory is able to reproduce this behavior nearly quantitatively without free parameters. At high density in ethane and in CO 2, the inverted temperature dependence is not observed, in agreement with theoretical calculations.

SANS Study of Polymer−Supercritical Fluid Solutions: Transitions from Liquid to Supercritical Fluid Solvent Quality

Phase behavior and small-angle neutron scattering (SANS) measurements are reported for poly(ethylene-co-1-butene) (PEB) dissolved in pentane, pentane plus ethane, and supercritical ethane to pressures of 2000 bar and temperatures of 130 and 150 °C. The solution microstructure and solvent quality are probed using the high-concentration isotopic labeling technique at the mixture critical concentration to determine the variation of intra- and intermolecular correlations on approach to the phase boundary with isothermal changes in pressure. The SANS results for the three solutions show that the intramolecular radius of gyration remains close to the unperturbed value over the entire pressure range investigated. However, the intermolecular correlation length changes dramatically as the phase boundary is approached and is approximately 3 times larger in ethane as compared to pentane even at 1000 bar from the phase boundary. The intermolecular correlation length data suggest that ethane is a poorer quality solvent than pentane at conditions close to the phase boundary even though both solvents have similar mass densities.

Modelling solubility of solids in supercritical fluids using response surface methodology

A Response Surface Methodology approach to correlate the solubility data of solids in supercritical fluids directly to the pressure and temperature is described. Published data for 2,6-dimethylnaphthalene, 2,3-dimethylnaphthalene, phenanthrene and benzoic acid in both supercritical carbon dioxide and supercritical ethylene were correlated by means of quadratic models, with R2 statistics greater than 0.99 at more than a 99.9% confidence level. With the developed quadratic models, the solubility for the above-mentioned solids in both supercritical fluids was predicted with average absolute percentage errors less than 5%. So, this approach to estimate solubility provides a possible guide for saving experimental effort and then giving simple models that could be used for industrial design purposes. © 2000 Society of Chemical Industry

Vibrational Lifetimes and Spectral Shifts in Supercritical Fluids as a Function of Density: Experiments and Theory

Vibrational lifetime and spectral shift data for the asymmetric CO stretching mode of $W(CO)_6$ in supercritical ethane, carbon dioxide, and fluoroform as a function of density at two temperatures are presented, and the lifetime $(T_1)$ measurements are compared to theory. The data and theory are refinements of previous work. Measurements at zero density allow the contribution from solute-solvent interactions to be separated from strictly intramolecular contributions to $T_1$. The results in the polyatomic SCFs are compared to data in Ar. The density functional/thermodynamic $theory^1$ has been extended to include contributions at large wavevector (k). Very good, quantitative agreement between theory and data taken in ethane and fluoroform is achieved, but the agreement for data taken in carbon dioxide, while reasonable, is not as good. The theory uses a variety of input information on the SCF properties obtained from the fluids' equations of state and other tabulated thermodynamic data. The solute-solvent spatial distribution is described in terms of hard spheres. The theory is able to reproduce the data without solute-solvent attractive interactions or clustering in the calculation of the spatial distribution.

Molecular Structure and Phase Diagram of the Binary Mixture of n-Heptane and Supercritical Ethane: A Gibbs Ensemble Monte Carlo Study

Pressure-composition and temperature-composition phase diagrams are computed for the binary mixture of n-heptane and supercritical ethane using four different molecular models of increasing complexity. The ethane and heptane molecules were described using either (i) single-site Lennard−Jonesium (LJ) with fixed well-depth and size parameters, (ii) single-site LJ with temperature-dependent well depths, (iii) chains of methyl and methylene pseudo-atoms interacting via LJ potentials placed at the positions of all carbon nuclei, or (iv) an explicit-hydrogen representation with LJ interaction sites placed both at the carbon nuclei and at the centers of all carbon−hydrogen bonds. For comparison, simulations were also performed for the binary mixture of n-heptane and helium using the pseudo-atom model for the n-heptane molecules. All four models produce phase diagrams for the ethane/n-heptane mixture that are in reasonable agreement with experiment. However, the accuracy of the calculated phase diagrams improves markedly with increasing complexity of the model (and therefore increasing computational requirements). In both the liquid (n-heptane-rich, higher specific density) and supercritical (ethane-rich, lower specific density) phases center-of-mass radial distribution functions appear to show more enhanced structures for the two single-site models than the united-atom and explicit-hydrogen force fields. However, the number integrals of these radial distribution functions are strikingly similar for all models, that is the differences in molecular shape do not lead to a difference in the clustering of the solvent molecules around the solute. In particular, preferential solvation of n-heptane by ethane is not observed in the supercritical phase. Analysis of the contributions of the liquid and the supercritical phases to the decrease of the Gibbs free energy of transfer of n-heptane with increasing pressure suggest that the enhanced solubility of n-heptane in high-pressure supercritical ethane can be attributed to two causes of roughly equal importance: “Pulling” of n-heptane into the supercritical phase by an increased density of ethane that acts as a nonspecific solvent, and “pushing” n-heptane out of the liquid phase by an increased concentration of ethane.

Catalytic Intermolecular Pauson – Khand Reactions in Supercritical Ethylene

Ethylen ist nicht nur das Substrat, sondern auch das Lösungsmittel in der hier vorgestellten katalytischen intermolekularen Pauson-Khand-Reaktion mit endständigen Alkinen [Gl. (1)]. Die 2-substituierten Cyclopentenone wurden in akzeptablen bis hohen Ausbeuten erhalten. Unter diesen Bedingungen genügt ein niedriger CO-Druck (5 atm), damit die Reaktion abläuft.