Viscosities of moderately concentrated solutions of polyethylene in ethane,propane, and ethylene

The viscosities of moderately concentrated solutions of low-density polyethylenes in ethane, propane, and ethylene have been measured at low shear rate in the temperature range of 150–250°C and in the pressure range of about 15000–30000 psi. Within the precision of the measurements, the relative viscosity is independent of pressure over the range investigated but increases as the solvent is changed from propane through ethane to ethylene. The activation energy for the relative viscosity in ethane varies from about 0.5 to 2.5 kcal/mole as the concentration changes from 5 to 15 g/dl. Effects of polymer concentration and molecular weight on solution viscosity in ethane at 150°C have been determined, and all of the data can be represented by a single straight-line plot of the logarithm of relative viscosity versus the intrinsic viscosity (in p-xylene at 105°C) times concentration. This simple relation is valid over wide ranges of polymer concentration and molecular weight and over more than two orders of magnitude of relative viscosity. The solution viscosities of the polyethylenes in the three supercritical fluid solvents used appear surprisingly low at first sight. This behavior is partly a result of the low solvent viscosities but also might mean that the polymer has an abnormally low segmental friction factor compared to that in solutions under more familiar conditions.     

High-pressure phase equilibria of systems carbon dioxide + n-eicosane and propane + n-eicosane

In this work we investigated the phase equilibrium behavior of the binary asymmetric systems propane (C3) + n-eicosane (C20) and carbon dioxide (CO₂) + n-eicosane (C20). We used a variable-volume view cell for obtaining fluid–fluid equilibrium (FFE), solid–fluid equilibrium (SFE) and solid–fluid–fluid equilibrium (SFFE) experimental data. We modeled the phase equilibria of both systems using the Peng–Robinson Equation of State for describing the fluid phases and an expression for the fugacity of pure solid n-eicosane with parameters fit to reproduce the pure n-eicosane melting line. We performed the phase equilibrium calculations by implementing path-following methods for tracking entire solid–fluid (SF) and solid–fluid–fluid (SFF) equilibrium curves for binary asymmetric mixtures. This made it possible to obtain complete isoplethic lines or complete three-phase equilibrium lines in single runs. Although the model is relatively simple, it is able to grasp the complex observed behavior for the systems studied here.     

High pressure phase equilibria of ethyl esters in supercritical ethane and propane

The high pressure phase equilibria of ethyl esters (ethyl decanoate/caprate, ethyl dodecanoate/laurate, ethyl tetradecanoate/myristate and ethyl hexadecanoate/palmitate) in supercritical ethane and propane have been measured in the temperature ranges 311–358 K (T_R = 1.02–1.17) and 376–409 K (T_R = 1.02–1.11), respectively. The measurements were conducted in a high pressure view cell for ethyl ester mass fractions between 0.015 and 0.65. The results show a generally linear relationship between the phase transition temperature and pressure. No temperature inversions or three phase regions were observed. An increase in hydrocarbon backbone length leads to an increase in phase transition pressure. For ethane as supercritical solvent, this increase is linear. For propane as supercritical solvent, the nature of the increase was not quantified as the magnitude of the increase would be significantly influenced by the experimental measurement error as the observed increase is not very large. Comparison of the phase behaviour of ethyl esters with methyl esters shows very little difference, yet the phase transition pressure of ethyl esters in supercritical ethane and propane is significantly lower than those of the corresponding acids. The phase transition pressure of ethyl esters in ethane and propane is also lower than those in carbon dioxide.     

Prediction of Solubility of Cholesterol in Supercritical Solvents

In this study the solubility of cholesterol was calculated in two supercritical pure solvents (carbon dioxide and ethane) as binary systems, and four supercritical solvent/co-solvent systems as ternary systems (cholesterol/carbon dioxide/methanol, cholesterol/ethane/acetone, cholesterol/ethane/hexane, cholesterol/ethane/propane) in various temperatures by SRK, PR, and SAFT equations of state. Pure molecular parameters of SAFT equation of state were obtained by fitting vapor pressure and liquid density data. Also the molecular parameters of cholesterol were obtained by fitting the solubility data of binary systems in one temperature, then they were used for the same system in other temperatures and for ternary systems with the same solvent. Results show that the SAFT equation of state can predict the trend and amount solubility of cholesterol in supercritical solvents much better than the other equations of state.     

Reverse Micelle Supercritical Fluid Separations

Abstract

Initial results are presented showing the potential applications of reverse micelle supercritical fluid solvents in separation processes. The formation of reverse micelles in supercritical nalkane continuous phases is described. Phase diagrams obtained from view-cell studies of micellar and microemulsion phases formed in supercritical fluids are reported and shown to be strongly dependent on pressure. The solubility of AOT in ethane and propane over a range of pressures shows behavior typical of solids in supercritical fluids. The maximum water-to-surfactant ratio (W_O) increased dramatically in both ethane and propane systems as pressure was increased. At 300 bar W_O = 4 for ethane at 37 'C and W_O = 12 for propane at 103 _*C. The initial use of supercritical fluids containing reverse micelles for the extraction of solutes from an aqueous phase, and as mobile phases in chromatography, is described.     

Hematite and iron carbonate precipitation-coexistence at the iron–montmorillonite–salt solution–CO2 interfaces under high gas pressure at 150 °C

The hydrothermal reactivity of swelling clays has relevant implications on the geological storage of radioactive waste and greenhouse gases because the clay geo-materials have been proposed as engineered or natural barriers due to their low permeability in confined systems and their high capacity to sequester ions. In the present study, the iron–montmorillonite–salt solution–CO₂ interactions were investigated under high gas pressure (200 bar) at 150 °C.Various chemical processes were characterized at the solid–fluid interfaces such as the dissolution of montmorillonite fine particles and oxidative-dissolution of elemental iron. The ionic supersaturation of solution and possibly the surface complexation in the system produced the precipitation of hematite nanoparticles (< 200 nm) after 15 days of solid–fluid contact. The hematite nanoparticles dispersed and/or coagulated on the clay matrix caused a stable red coloration of the montmorillonite composite. We assume that initial dissolved oxygen was progressively consumed in this closed-stirred system favouring the presence of divalent iron (in-situ change of redox conditions) and then leading the surface precipitation of iron carbonate nanocrystals (< 500 nm) after 60 days of solid–fluid contact. Thus, an atypical mineral coexistence of hematite–iron carbonate was observed in our system. A qualitative comparison with the blank experiment, i.e. at the same P–T conditions, but without CO₂ injection, suggested that the carbon dioxide increased the hydrothermal reactivity of montmorillonite because the hematite and iron carbonate formation were not observed after the same reaction time.     

Selective oxidation of propane and ethane on diluted Mo–V–Nb–Te mixed-oxide catalysts

Te-free and Te-containing Mo–V–Nb mixed oxide catalysts were diluted with several metal oxides (SiO₂, γ-Al₂O₃, α-Al₂O₃, Nb₂O₅, or ZrO₂), characterized, and tested in the oxidation of ethane and propane. Bulk and diluted Mo–V–Nb–Te catalysts exhibited high selectivity to ethylene (up to 96%) at ethane conversions <10%, whereas the corresponding Te-free catalysts exhibited lower selectivity to ethylene. The selectivity to ethylene decreased with the ethane conversion, with this effect depending strongly on the diluter and the catalyst composition. For propane oxidation, the presence of diluter exerted a negative effect on catalytic performance (decreasing the formation of acrylic acid), and α-Al₂O₃ can be considered only a relatively efficient diluter. The higher or lower interaction between diluter and active-phase precursors, promoting or hindering an unfavorable formation of the active and selective crystalline phase [i.e., Te₂M₂₀O₅₇ (M = Mo, V, and Nb)], determines the catalytic performance of these materials.     

Generalizing Binary Solubility Data for Low-Volatile Liquids in Supercritical Fluids

Experimental data on the binary solubilities of a large number of low-volatile liquids in supercritical solvents (carbon dioxide and propane) are generalized by the entropy method of the similarity theory over wide temperature and pressure ranges. Two groups of similar systems are revealed which correspond to different entropy ranges of the pure solvent. The mechanism of the dissolution of liquids in supercritical fluids was found to be mainly physical.     

Phase equilibria of long chain n-alkanes in supercritical ethane: Review,measurements and prediction

The available sets of data for the phase equilibrium of long chain n-alkanes with 10 or more carbon atoms in supercritical ethane were studied to determine if the phase equilibrium pressure can be predicted from the number of carbon atoms and system temperature. It has previously been shown that for the phase equilibria of heavy n-alkanes in supercritical propane there exists, at constant temperature and mass fraction, a linear relationship between the number of carbon atoms and the bubble/dew point pressure. Published data in the temperature range 310–360 K was obtained from a literature survey and, where required, additional data was measured using a high-pressure equilibrium cell. It was found that linear relationships exist and that these relationships can be used to predict the phase equilibrium pressure within 4% of experimental values.     

Solubility of propylene gas in octane and various polar solvents

Propene gas solubilities at 101.3 kPa pressure are reported in n-octane, chlorobenzene, acetone, acetic acid, ethyl acetate, n-butanol, N-N-dimethyl formamide (DMF) and ethylene glycol for a range of temperatures. These data, along with data from the literature, were used to show the qualitative effects of unsaturation of the gas component on the solubility in various solvents ranging from non-polar to highly polar and associated solvents. This involved a comparison, when data were available, of the solubilities of ethane, ethylene and acetylene, then of butane, isobutane, isobutylene, trans-2-butene and 1,3-butadiene as well as of propane and propene (propylene). The differences in solubilities could be explained using solubilities expressed as a molecular interaction parameter (mip) and by identifying several different types of molecular interactions. For associating solvents these effects can be summarized as follows: mip of acetylene > mip of ethylene > mip of ethane, also mip of propylene > mip of propane and mip of butadiene > mip of isobutylene≥ mip of trans-2-butylene > mip of butane > mip of isobutane.     

Solubility of ethylene in several polar and non-polar solvents

Solubilities of ethylene at atmospheric pressure and temperatures ranging from ?9°C to 70°C are reported in solvents ranging from the non-polar ones, heptane, dodecane, carbon tetrachloride, carbon disulfide and chlorobenzene to the highly polar ones, isopropanol, butanol and ethylene glycol. A useful relation was observed between ethylene solubilities in non-polar solvents and those of methane, ethane and propane, along with the corresponding energy of vaporization at the normal boiling for those gases. In the highly polar solvents on the other hand, hydrogen bonding (H-bonding) factors were found more useful in relating solubilities in one hydrogen bonding solvent to those in other hydrogen bonding solvents.     

Solubility of propane in isomers of hexane and other non-polar solvents

Solubilities of propane at atmospheric pressure and for temperatures ranging from —15°C to 70°C are reported for a variety of solvents including hexane and the branch-chained hexane isomers, for cyclohexane, perfluorohexane, benzene, ethylbenzene, metaxylene, carbon tetrachloride and carbon disulfide. These data, along with data from the literature, are used in comparing solubility behavior of propane and the other paraffin gases in a range of solvents. While predictions of gas solubilities even in non-polar solvents are still somewhat uncertain, it appears possible to estimate the solubilities of methane, ethane, propane or butane by extrapolation of known solubilities of these gases in a range of solvents. It is also possible to predict the temperature coefficient of solubility in solvents, such as benzene, which yield regular solutions.     

Supercritical CO2 extraction of turmerones from turmeric and high-pressure phase equilibrium of CO2 + turmerones

This work studies the enrichment of turmeric α-β-Ar turmerone using supercritical fluid extractions followed by solid–liquid column partition fractionation. The high-pressure vapor–liquid phase equilibrium of the α-β-Ar turmerone with carbon dioxide was also examined. The purity of α-β-Ar turmerone was increased from 67.7% in extracted oil up to 91.8% in enriched oil, as determined by HPLC analysis. An equilibrium apparatus that comprises two vibrating tube densitometers was then adopted to obtain vapor and liquid equilibrium data for this asymmetric system of α-β-Ar turmerone and carbon dioxide mixture at 313.15 K and 333.15 K. Pressures ranged from 2.82 MPa to 20.80 MPa. Experimental data at elevated pressures were successfully correlated with theoretical methods of Peng–Robinson, Soave–Redlich–Kwong and Patel–Teja equations of state, individually combined with quadratic, Panagiotopoulos–Reid and Adachi–Sugie mixing rules.     

Oxidation of ethane on high specific surface SmCoO3 and PrCoO3 perovskites

An adapted sol–gel method allowed synthesizing SmCoO₃ and PrCoO₃ oxides with high specific surface (ca. 28 m² g⁻¹) and a relatively clean perovskite phase at 600 °C, a temperature much lower than the one required in ceramic methods. The perovskites were investigated as catalysts for the oxidation of ethane in the temperature range 300–400 °C. Both catalysts were very active: ethane was activated already at 300 °C, i.e., 100 °C below the temperatures previously reported for perovskites. The main product was CO₂ on both catalysts, but on PrCoO₃ oxidehydrogenation (ODH) to ethylene was observed already at 300 °C, with the low selectivity. Even so, this was quite unusual for simple perovskites, and for such a low temperature. TPR data showed that praseodymium decreases the reducibility of Co³⁺ in the perovskite, what could explain the observed ODH, and suggest it proceeds via a Mars–van Krevelen mechanism. Kinetic study showed a similar apparent activation energy for both catalysts (ca. 80 kJ/mol), but a difference in the nature of the participating oxygen species: while on PrCoO₃ both adsorbed and lattice species contribute to the reaction, on SmCoO₃ contribution of adsorbed species is practically negligible, due to its very high oxygen lability. The results show that these simple perovskites may be promising catalysts for ethane oxidation at relatively low temperatures.     

Effect of Silica Nanoparticles on the Performance of Polysulfone Membranes for Olefin‐Paraffin Separation

The separations of ethylene/ethane and propylene/propane using polysulfone‐silica nanocomposite membranes were studied. Silica nanoparticles were prepared via sol‐gel method and the membranes by phase inversion. Characterization by Fourier transform spectroscopy and scanning electron microscopy indicated a good distribution of silica nanoparticles in the polymer matrix and also a good compatibility between the two phases. The performances of the prepared membranes in ethylene‐ethane and propylene‐propane separation were evaluated. The results showed the increments in gas permeability and selectivity by silica. Higher silica contents increased the solubility coefficient and reduced the diffusion coefficient of gases. The plasticization pressure of polysulfone was increased by incorporating the silica nanoparticles in polymer.     

Simple three parameter equations for correlating liquid phase compositions in subcritical and supercritical systems

Two Chrastil type expressions have been developed to model the solubility of supercritical fluids/gases in liquids. The three parameter expressions proposed correlates the solubility as a function of temperature, pressure and density. The equation can also be used to check the self-consistency of the experimental data of liquid phase compositions for supercritical fluid–liquid equilibria. Fifty three different binary systems (carbon-dioxide + liquid) with around 2700 data points encompassing a wide range of compounds like esters, alcohols, carboxylic acids and ionic liquids were successfully modeled for a wide range of temperatures and pressures. Besides the test for self-consistency, based on the data at one temperature, the model can be used to predict the solubility of supercritical fluids in liquids at different temperatures.     

Supercritical Fluid Extraction of Ethylene Oxide from Its Aqueous Solution

The mutual solubility of ethylene oxide and supercritical carbon dioxide was studied at T = 308 K in the pressure range P = 4.2–20 MPa, and the phase distribution of ethylene oxide in the water–ethylene oxide–supercritical carbon dioxide system was investigated at T = 308 and 323 K and P = 7.3–20.0 MPa.     

Experimental cloud points for polybutadiene + light solvent and polyethylene + light solvent systems at high pressure

The hydrogenation of unsaturated heavy compounds is conventionally carried out in the presence of two fluid phases, because the immiscibility in the binary subsystem ‘hydrogen + heavy substrate’ cannot be overcome by adding a standard solvent. Using a supercritical or quasicritical solvent allows the hydrogen and the unsaturated heavy substrate to dissolve into a single phase. To select the operating conditions of a supercritical reactor, it is necessary to determine the phase boundaries of the subsystems ‘solvent + hydrogen’ and ‘solvent + heavy compound’. In this work, we measured cloud points for binary systems made of polybutadiene (PB) or polyethylene (PE) and a light solvent, i.e., propane or dimethyl ether (DME) or diethyl ether (DEE). The temperature range studied was from 50 to 160 °C for ‘PB + DME’ and ‘PB + Propane’ and from 100 to 190 °C for ‘PB + DEE’ and ‘PE + DEE’. We found that in PB-containing binary systems, at the ranges of conditions of the experiments, the minimum pressure required to guarantee homogeneity, at any temperature, is below 200 bar for DEE, below 300 bar for DME and in the order of 500 bar when using propane as solvent. Our data for ‘PE + DEE’ indicate the need for a minimum pressure of about 240 bar to keep the system within a single phase. The results from this work and from the literature suggest that the use of binary solvent mixtures may be convenient to carry out the supercritical hydrogenation of PB.     

Phase equilibria of linear saturated high molecular mass acids in supercritical ethane

High-pressure phase equilibria of the ethane/acid homologous series for linear saturated acids with between 10 and 22 carbon atoms are investigated. Measurements for ethane with decanoic, undecanoic, dodecanoic, tetradecanoic, hexadecanoic, octadecanoic and docosanoic acid were conducted between 308 and 353 K in the acid mass fraction range of 0.016–0.68. Higher phase transition pressures were measured at higher temperatures and no three-phase regions, or indications thereof, were observed. The measurements revealed that as the number of carbon atoms increased, so the phase transition pressure increased linearly, prompting the compilation of a set of linear pressure–carbon number plots. The observed phase transition pressures for the ethane/acid systems are also lower than that of the CO₂/acids systems, suggesting that ethane is an alternative supercritical solvent to or co-solvent with CO₂ for processes involving high molecular mass acids.