Supercritical Ethane Research Articles

High pressure phase equilibrium measurements of long chain alcohols in supercritical ethane

High pressure phase equilibrium measurements of long chain 1-alcohols (1-decanol through 1-docosanol) in supercritical ethane and their prediction are presented. The data were measured in a high pressure view cell above the melting points of these alcohols, i.e. between 308 and 356 K, and with 1-alcohol mass fractions ranging from 0.0173 to 0.648. The results show a linear relationship between the phase transition pressure and the system temperature. The phase transition pressure increases with increasing molecular mass of 1-alcohol at constant temperature and composition. Furthermore, a linear relationship exists between the phase transition pressure and the number of carbon atoms of the 1-alcohol, making it easy to predict phase transition by simple interpolation within the experimental boundaries. Additionally, the state-of-the-art sPC-SAFT EOS model, as now typically included in process simulators, is unable to predict the phase equilibria, although it tends to give better results than the classic Peng Robinson EOS.

Understanding the Relative Effectiveness of Alkanethiol Ligands in Dispersing Nanoparticles in Supercritical Carbon Dioxide and Ethane

There is considerable interest in developing a nonfluorous capping ligand that is effective in dispersing nanoparticles in supercritical carbon dioxide. To augment the experimental search for such a molecule, a simulation protocol is developed, involving atomistic molecular dynamics simulations, which captures the relevant physical phenomena related to the effectiveness of capping ligands in stabilizing nanoparticle dispersions, evidenced by a consistency with empirical observation. The method is used to determine why the cheap and benign alkanethiol ligands are effective in supercritical ethane and several organic solvents but not in supercritical CO2 at convenient conditions of temperature and pressure; n-dodecanethiol is used as the representative ligand. We conclude that the ineffectiveness of the alkanethiol ligands in CO2 is primarily because they cannot compensate for the quadrupolar interactions which account for a substantial portion of the cohesive energy of bulk CO2, which is lost to the CO2 mo...

Phase behaviors for the supercritical ethylene + 1-hexene + hexane + polyethylene systems at elevated temperatures and pressures

Phase behaviors of binary, ternary and quaternary polymer solution systems of ethylene, 1-hexene, hexane and polyethylene (PE) were investigated. Three types of nearly monodispersed polyethylene ( PE15k : M ¯ w = 15.4 × 10 3 g mo l − 1 ; M ¯ w / M ¯ n = 1.17 , PE17k : M ¯ w = 17.2 × 10 3 g mo l − 1 ; M ¯ w / M ¯ n = 1.12 , PE108k : M ¯ w = 108 × 10 3 g mo l − 1 ; M ¯ w / M ¯ n = 1.32 ) were used. Measurements were carried out with a synthetic-type apparatus at temperatures as high as 473 K, using PE weight fractions ranging from 0.019 to 0.123 and ethylene weight fractions ranging from 0 to 0.102. As for the 1-hexene + hexane + PE and the ethylene + 1-hexene + hexane + PE systems, the ratios of the weight fractions of 1-hexene to hexane were kept constant at 1.0. Lower critical solution temperature (LCST)-type phase behavior was observed for each system measured. The liquid–liquid (LL) phase boundaries of the 1-hexene + PE and the 1-hexene + hexane + PE systems were slightly higher than those of the hexane + PE systems depending on 1-hexene concentration. On the other hand, the phase boundaries of the ethylene + 1-hexene + PE and the ethylene + 1-hexene + hexane + PE systems were quite similar to those of the ethylene + hexane + PE system. The LL phase boundaries were correlated and predicted by the Sanchez–Lacombe equation of state (S–L EOS) using binary interaction parameters. The characteristic parameters of the S–L EOS for 1-hexene were determined by correlating the vapor pressure of 1-hexene and the LL phase boundaries of the 1-hexene + PE system. The correlated results approximately reproduced the experimental results, although a slight deviation was observed in the region where the concentration of polymer is high. Moreover, the predicted LL boundaries for the 1-hexene + hexane + PE, the ethylene + 1-hexene + PE and the ethylene + 1-hexene + hexane + PE systems approximated the experimental results.

Remediation of Soils Contaminated with Total Petroleum Hydrocarbons and Polycyclic Aromatic Hydrocarbons: Extraction with Supercritical Ethane

In this work two natural certified soils were extracted with supercritical ethane. One sample was polluted with total petroleum hydrocarbons (THP−soil) and the second one with polycyclic aromatic hydrocarbons (PAH−soil). The extraction studies were carried out using a high-pressure experimental device constructed in our laboratory. The extraction conditions for the TPH−soil were 27.1 MPa and 308.15 K, whereas those for the PAH−soil were 23.7 MPa and 308.15 K. Four independent extractions were performed on each test soil varying the volume of solvent: 10, 20, 30, and 40 L. Infrared spectroscopy was used to quantify the hydrocarbons in the residues after supercritical extraction of the TPH−soil, whereas high-performance liquid chromatography was employed, with a photodiode array detector and a fluorescence detector, to analyze seven polycyclic aromatic hydrocarbons (PAHs) in the residues after supercritical extraction of the PAH−soil. The extraction results show that there is a reduction of hydrocarbons of 76% using 10 L of ethane while the reduction is 90% using 40 L of ethane for the TPH−soil sample. For the sample of PAH−soil there is a reduction greater than 80% for the concentration of six of the seven PAHs studied. Naphthalene behaves as a refractory compound; hence, it presents the lowest reduction in concentration.

Swelling of Ionic and Nonionic Surfactant Micelles by High Pressure Gases

The influence of different solvent environments on the size, shape, and characteristics of surfactant micelles of Pluronic F127 and CTAB was investigated by small-angle neutron scattering (SANS). SANS experiments were undertaken on dilute micellar surfactant solutions of F127 and CTAB that between them were exposed to liquid and supercritical carbon dioxide, liquid propane, ethane, and heptane under various pressures and temperatures. Swelling of the surfactant micelles could be directly related to the solubility of the solvents within the micelles, especially within their cores. Carbon dioxide produced the largest swelling of the Pluronic F127 micelles, compared to propane and ethane, which mirrors the solubility of the gases in the PPO core of the micelles. Conversely, the extent of swelling of the cores of CTAB micelles was greater with propane compared to carbon dioxide, which again relates to the solubility of the solvents in the alkane core of the CTAB micelles.

Thermodynamic modeling of liquid–fluid phase equilibrium in supercritical ethylene + copolymer + co-solvent systems using the PC-SAFT equation of state

Copolymers are important in the manufacture of new polymeric materials with specific characteristics. For linear polymers, thermodynamic models based on the thermodynamic perturbation theory are interesting, since this theory regards the association between monomers. In this work, cloud points of mixtures of copolymers (PEH, PEP, PEAA and PEVA) (PEP: poly(ethylene-co-propylene); PEAA: poly(ethylene-co-acrylic acid); PEH: poly(ethylene-co-1-hexene); PEVA: poly(ethylene-co-vinyl acetate)), a supercritical fluid ( C 2) and co-solvents (C 1, C 2, C 3, nC 4, 1C 4, 1C 6, AA, VA, He, N 2, CO 2) (C 1: methane; C 2: ethane; C 2: ethylene; C 3: propane; nC 4: n-butane; 1C 4: 1-butene; 1C 6: 1-hexene; AA: acrylic acid; VA: vinyl acetate; He: helium; N 2: nitrogen; CO 2: carbon dioxide) were modeled using the PC-SAFT equation of state (Perturbed Chain-Statistical Associating Fluid Theory) with a one-type van der Waals mixing rule by fitting one single interaction parameter. Pure component parameters for the supercritical fluid and co-solvents were obtained by regression of vapor pressure and density data of saturated liquid, while pure component parameters for polymers that compose the copolymers were obtained by regression of pure liquid PVT data. Binary interaction and pure component parameter estimation was performed by using the modified maximum likelihood method. Relative deviations between the calculated and experimental cloud points show that the PC-SAFT model had an excellent performance.

Recent advances in organometallic alkane and noble gas complexes

Abstract Fast time-resolved infrared (TRIR) spectroscopy has been useful for studying the reactions of a wide range of organometallic alkane and noble gas complexes at ambient temperature following irradiation of metal carbonyl precursor complexes. The reactivity of organometallic alkane and xenon complexes decreases both across and down groups V, VI, and VII, and for a given metal/ligand combination the alkane and xenon complexes have similar reactivities. Systematic studies of reactivity have produced long-lived Re complexes which have allowed such complexes to be characterized using NMR spectroscopy. A new approach using liquid propane at low temperature as a solvent to monitor the interaction of such weakly coordinating ligands with transition-metal centers is outlined. TRIR studies monitoring the coordination and activation of methane and ethane in supercritical methane and liquid ethane solvents at room temperature are also reviewed.

Modeling the Phase Behavior in Mixtures of Pharmaceuticals with Liquid or Supercritical Solvents

The concept of solubility parameter, which is widely used for the screening of solvents in pharmaceutical applications, is combined with a thermodynamic theory that is able to model systems with large deviations from ideal behavior. The nonrandom hydrogen-bonding (NRHB) theory is applied to model the phase behavior of mixtures of six pharmaceuticals (i.e., ibuprofen, ketoprofen, naproxen, benzoic acid, methyl paraben, and ethyl paraben). The pure fluid parameters of the studied pharmaceuticals were estimated using limited available experimental (or predicted) data on sublimation pressures, liquid densities, and Hansen's solubility parameters. The complex hydrogen-bonding behavior was explicitly accounted for, while the corresponding parameters were adopted from simpler molecules of similar chemical structure or/and fitted to the aforementioned pure fluid properties. In this way, the solubility of the studied pharmaceuticals in liquid solvents was calculated. The average root-mean-square deviation between experimental and calculated solubilities is 0.190 and 0.037 in log(10) units for prediction (calculations without a binary interaction parameter adjustment) and for correlation (calculations using one binary interaction parameter fitted to experimental data), respectively. In addition, using one temperature-independent binary interaction parameter the phase behavior of pharmaceuticals in supercritical CO(2) and ethane was satisfactorily correlated. Finally, preliminary encouraging results are shown concerning two ternary mixtures where the model is able to predict accurately the solubility of pharmaceuticals in mixed solvents based on interaction parameters fitted to corresponding single solvent data.

High pressure phase behavior for the supercritical ethylene + cyclohexane + hexane + polyethylene systems

Phase behavior of binary, ternary and quaternary systems of ethylene, cyclohexane, hexane and polyethylene (PE, M ¯ w = 15.4 × 10 3 ) was investigated. Measurements were carried out at temperatures from 373 to 488 K, PE weight fractions from 0.017 to 0.152, and ethylene weight fractions from 0 to 0.100 with a synthetic-type apparatus. The ratios of the weight fractions of cyclohexane to hexane in the mixtures were kept constant at about 1/9 or 2/8 for the cyclohexane + hexane + PE and the ethylene + cyclohexane + hexane + PE systems. Liquid–liquid phase separation for the cyclohexane + PE binary system did not appear in the range from 373 to 473 K and up to 30 MPa. All other systems exhibited LCST (lower critical solution temperature)-type phase behavior. For the cyclohexane + hexane + PE and the ethylene + cyclohexane + hexane + PE systems, liquid–liquid phase separation temperature increased with increasing concentration of cyclohexane. On the other hand, the liquid–liquid phase separation temperature decreased with increasing concentration of ethylene for the ethylene + cyclohexane + PE and the ethylene + cyclohexane + hexane + PE systems. The liquid–liquid phase boundaries of the cyclohexane + hexane + PE and the ethylene + cyclohexane + PE systems were satisfactorily correlated with the Sanchez–Lacombe equation of state and temperature-dependent binary parameters. Moreover, the predicted results reproduced well the phase boundaries of the ethylene + cyclohexane + hexane + PE system.

Size-Selective Separation of Polydisperse Gold Nanoparticles in Supercritical Ethane

The aim of this study was to use supercritical ethane to selectively disperse alkanethiol-stabilized gold nanoparticles of one size from a polydisperse sample in order to recover a monodisperse fraction of the nanoparticles. A disperse sample of metal nanoparticles with diameters in the range of 1-5 nm was prepared using established techniques then further purified by Soxhlet extraction. The purified sample was subjected to supercritical ethane at a temperature of 318 K in the pressure range 50-276 bar. Particles were characterized by UV-vis absorption spectroscopy, TEM, and MALDI-TOF mass spectroscopy. The results show that with increasing pressure the dispersibility of the nanoparticles increases, this effect is most pronounced for smaller nanoparticles. At the highest pressure investigated a sample of the particles was effectively stripped of all the smaller particles leaving a monodisperse sample. The relationship between dispersibility and supercritical fluid density for two different size samples of alkanethiol-stabilized gold nanoparticles was considered using the Chrastil chemical equilibrium model.

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.

Phase behavior for the supercritical ethylene + hexane + polyethylene systems

The present work investigated the phase behavior for the ethylene + hexane + polyethylene (PE) systems at temperatures from 373 to 473 K, PE weight fractions from 0.01 to 0.13, and ethylene weight fractions from 0 to 0.1 by using a synthetic-type apparatus. Two nearly-monodisperse PE samples having weight-average molecular weights of 15.5 × 10 3 (PE15k) and 108 × 10 3 (PE108k) were used in this work. All the binary hexane + PE and ternary mixtures exhibited lower critical solution temperature-type liquid–liquid phase behavior in the temperature range examined. The phase separation pressures increased with increasing temperature and PE molecular weight. The addition of supercritical ethylene to the hexane + PE solutions dramatically shifted the liquid–liquid phase boundary to lower temperatures and higher pressures, because it acted as a poor solvent for PE. The Sanchez–Lacombe equation of state was used to correlate and predict the phase boundaries. The experimental liquid–liquid phase boundaries for the hexane + PE systems could be correlated satisfactorily with a temperature-dependent binary parameter. By adjusting the binary parameter for ethylene + PE pair, the ternary phase boundaries could also be correlated and predicted satisfactorily.

Extraction of Hydrocarbons from Crude Oil Tank Bottom Sludges using Supercritical Ethane

A custom‐built, solvent recirculating, supercritical fluid extraction (SFE) apparatus was used to study the extraction of hydrocarbons from a crude oil tank bottom sludge (COTBS) with supercritical ethane. The SFE experiments were carried out varying the pressure (10 MPa and 17.20 MPa) and temperature (35°C and 65°C). The yield of the extracted hydrocarbon fraction increased with increase in extraction pressure at constant temperature, and decreased with increase in extraction temperature at constant pressure. The maximum extraction yield was obtained at the pressure and temperature conditions that lead to the highest solvent density. The extracted hydrocarbon fraction was a significantly upgraded liquid relative to the original untreated COTBS.

Comments on “Measurement and Modeling of the Solubility of Water in Supercritical Methane and Ethane from 310 to 477 K and Pressures from 3.4 to 110 MPa”

We describe a new flow cell apparatus for measuring the water content of gases up to 120 MPa at 490 K that uses a combination of gravimetric and electrical resistance techniques to determine the solubility of water in the gaseous phase. The new experimental data for the solubility of water in supercritical methane and ethane were obtained with our apparatus spanning pressures from 3.4 to 110 MPa covering a temperature range from 310 to 477 K. We model the experimental results by combining two equations of state; vapor-phase fugacities and fugacity coefficients are calculated with a modified Peng−Robinson equation of state, and aqueous-phase fugacities are calculated using an equation by Wagner and Pruss (J. Phys. Chem. Ref. Data 2002, 31, 387−535) or by a modification of a correlation developed by Saul and Wagner (J. Phys. Chem. Ref. Data 1987, 16, 893−901). We compare the model results with new and existing experimental data and with commercially available simulators. Our model reproduces the experimenta...

Behavior of charged species in supercritical heavy rare gas fluids

Electron mobilities were measured in supercritical (SC) Xe and Kr as functions of pressure and temperature. Ion mobilities, reaction rates of electrons with C 6F 6, O 2 and pyrazine were also measured in SC Xe. Electron mobility is strongly field-dependent and the low-field mobility μ e exhibits a deep minimum at a density just below the critical density. A deformation potential model of the acoustic phonon scattering type can reproduce μ e change in SC Xe and Kr quantitatively. From positive ion mobility values, a hydrodynamic compressible continuum model indicates that the cluster radius goes to a maximum, 1 nm, at 291 K at the pressure of the isothermal compressibility, χ T , peak. The rate constant for the reaction C 6F 6+e −→C 6F 6 – sharply increases up to nearly 10 15 molal s −1 in this pressure region. Pyrazine was found to form neutral clusters in SC Xe prior to electron attachment. These and other data are compared with the observation made in SC ethane.

Interactions between sterically stabilized nanoparticles in supercritical fluids: A simulation study

The authors report a simulation study of the interaction between gold nanoparticles stabilized with both linear and branched alkane chains in supercritical ethane. In agreement with experimental and previous theoretical work, the authors find that increasing solvent density and making ligands more branched make the nanoparticle interaction more repulsive. These findings are analyzed in terms of the extent of the chain interdigitation and chain-solvent interaction energy.

In situ ATR-FT-IR study of the thermal decomposition of diethyl peroxydicarbonate in supercritical carbon dioxide

The thermal decomposition of the organic free-radical initiator, diethyl peroxydicarbonate (DEPDC), was monitored by in situ ATR-FT-IR in heptane, and in the green solvent supercritical carbon dioxide (scCO 2) both with and without supercritical ethylene. It was observed that the characteristic peaks of DEPDC at 1802–1803 and 1194–1203 cm −1 decreased significantly upon heating corresponding to the decomposition of DEPDC, while two new intense peaks simultaneously appeared at 1747 and 1262 cm −1 in heptane, and similarly at 1756 and 1250 cm −1 in scCO 2. The changes in the absorbance intensity of the characteristic peaks of the initiator during the decomposition were used for the measurement of the decomposition rate constant ( k d) of DEPDC. It was found that the thermal decomposition of DEPDC at low concentration in either heptane under atmospheric N 2 or scCO 2 under high pressure was via the first-order kinetics of unimolecular decomposition. The activation energy of the thermal decomposition of DEPDC was found to be 115 kJ/mol in heptane from 40 to 74 °C and 118 kJ/mol in scCO 2 from 40 to 60 °C. These new peaks revealed the formation of carboxyl groups contained in the decomposed products, indicating incomplete decarboxylation. During removal of CO 2 after the reaction in scCO 2, the instable intermediate monoethyl carbonate was decarboxylated and converted into the major end product, ethanol.

Solvent Density Effects on the Solvation Behavior and Configurational Structure of Bare and Passivated 38-Atom Gold Nanoparticle in Supercritical Ethane

In exploring the effects of solvent density on the mode and the degree of solvation of the bare and passivated 38-atom gold particle in supercritical ethane, we have extended the molecular dynamics simulations of the system, reported previously,(34) to cover a range of isotherms in the T > T(c) regime, where T(c) is the critical temperature of the solvent. Consonant with our previous observations, the modes of solvation of the bare and the passivated particle, deduced from the radial distribution of the solvent about the metal core center of mass, are found to be vastly different from each other at all solvent densities: while the molecules solvating the bare particle form a well-defined, two-region layer around it, those solvating the passivated particle are loosely dispersed in the passivating layer. For the bare particle, the degree of solvation (vartheta) as a function of solvent density passes through a maximum occurring in the close vicinity of the critical point, consistent with our previous results and in agreement with Debenedetti's theoretical analysis,(22,23) which predicts a solvation enhancement effect in the critical region for systems where the unlike solvent/solute interaction is much stronger than the solvent/solvent interaction. Taking the degree of solvation (vartheta) as a measure of solvent quality, we have investigated how the solvent quality would vary along the solvent-density isotherms. In the solvent-density regime rho > rho(c), the solvent quality is found to be a decreasing function of the density as a result of progressive dominance of the excluded volume effect over the attractive particle/solvent interactions. The particle/solvent affinity is greatly reduced in the presence of the passivating layer, resulting in considerable shrinkage of the good-solvent-quality domain in the supercritical regime. The solvent environment and the presence of the passivating chains produce significant disorder in the equilibrium structure assumed by the nanoparticle core.

Outflow from fractured pipelines transporting supercritical ethylene

This paper describes a methodology for predicting outflow from a rupture in a pipeline transporting supercritical ethylene. Ethylene outflow is of particular interest and is a challenging scenario to model as typical operating temperatures are a few degrees above the critical temperature, 283 K. Thus when the pipe fractures the initial rapid depressurisation induces a number of propagation waves to travel up the pipeline initiating phase changes and fundamentally changing the nature of the outflow problem. The methodology presented is primarily based on an outflow model for compressed volatile liquid outflow as this is demonstrated to be the flow regime upstream of the pipe fracture after a small time interval following pipe fracture. The model is validated using a more complex commercially available pipeline model, PROFES for propane outflow as experimental data at relatively low pressure and short pipes exist in the open literature and has been used to validate the models considered here. Finally the ethylene outflow methodology has been applied to a number of different ethylene pipeline scenarios with a range of operating temperatures, pressures and pipeline diameters of interest to confirm that predicted outflow rates trend as expected.

Measurement and Modeling of the Solubility of Water in Supercritical Methane and Ethane from 310 to 477 K and Pressures from 3.4 to 110 MPa

We describe a new flow cell apparatus for measuring the water content of gases up to 120 MPa at 490 K that uses a combination of gravimetric and electrical resistance techniques to determine the solubility of water in the gaseous phase. The new experimental data for the solubility of water in supercritical methane and ethane were obtained with our apparatus spanning pressures from 3.4 to 110 MPa covering a temperature range from 310 to 477 K. We model the experimental results by combining two equations of state; vapor-phase fugacities and fugacity coefficients are calculated with a modified Peng−Robinson equation of state, and aqueous-phase fugacities are calculated using an equation by Wagner and Pruss (J. Phys. Chem. Ref. Data 2002, 31, 387−535) or by a modification of a correlation developed by Saul and Wagner (J. Phys. Chem. Ref. Data 1987, 16, 893−901). We compare the model results with new and existing experimental data and with commercially available simulators. Our model reproduces the experimental data within 2−6% using one adjustable parameter, indicating that the predictions of the model are equal to or superior to the commercially available simulators.