Extraction of polychlorinated biphenyl with supercritical carbon dioxide, sulfur hexafluoride and subcritical water

In the extraction of spiked PCB from soil, three extracting fluids were investigated: supercritical carbon dioxide (CO2), supercritical sulfur hexafluoride (SF6) and subcritical water. Among the tested fluids SF6 appeared to be appropriate especially for the extraction of low polar PCB. CO2 and water were found to be suitable for the quantitative extraction of all PCB. Water was judged as the best because of its low price, good availability and environmental safety.     

Determination of Microcystins in Cyanobacteria by Supercritical Fluid Extraction and Liquid Chromatography‐Tandem Mass Spectrometry

Abstract

A method for the detection of microcystins (microcystin LR, RR, and YR) in cyanobacteria by supercritical fluid extraction (SFE) and liquid chromatography‐mass spectrometry (LC/MS) has been developed. Supercritical fluids for the analytical extraction of nonvolatile, higher molecular weight compound, and microcystins from cyanobacteria were investigated. The microcystins included in this study are sparsely soluble in neat supercritical fluid CO₂. However, the microcystins was successfully extracted with a ternary mixture (90% CO₂, 9.5% methanol, 0.5% water) at 40°C and 250 atm. The polar carbon dioxide‐aqueous methanol fluid system gave high extraction efficiency for the extraction of the polar microcystins from cyanobacteria. The microcystins were determined by liquid chromatography‐tandem mass spectrometry (LC/MS/MS).     

Heat of Adsorption of Pure Sulfur Hexafluoride on Micro-Mesoporous Adsorbents

The isotherms and the isosteric heats of adsorption of pure SF₆ were measured on two microporous zeolites (NaX and Silicalite), one mesoporous alumina, and two activated carbons (BPL and PCB) at 305 K. The adsorption isotherms were Type I by Brunauer classification. The PCB carbon adsorbed SF₆ most strongly and the alumina adsorbed SF₆ most weakly. The adsorption of SF₆ on the other three materials were comparable in the low pressure region despite their drastic differences in the physicochemical properties. The heat of adsorption of SF₆ on the silicalite and the alumina remained practically constant over a large range of coverage. The heat of adsorption of SF₆ increased with increasing adsorbate loading on the NaX zeolite in the high coverage region. The heat of adsorption of SF₆ on the activated carbons decreased with increasing adsorbate loading before leveling off in the high coverage region.     

On-Line coupling of supercritical fluid extraction with high performance liquid chromatography

Supercritical fluid extraction was coupled directly with high performance liquid chromatograph. The system was evaluated for direct injection of supercritical CO₂ and modified supercritical CO₂ at high pressure and temperature onto a HPLC system with varying mobile phase compositions and flow rates. Injection of 9 μL supercritical CO₂ onto the HPLC using methanol/water mobile phases from 100% methanol to 80% with a flow of 1.0 mL/min did not adversely affect the baseline of UV detector. However at higher percentages of water, CO₂ solubility in the mobile phase decreased and caused baseline interferences on the UV detector. At higher HPLC mobile phase flow rates, supercritical CO₂ was injected to higher percentages of water without any effect on the UV baseline. Also, increasing the extraction pressure or modifier concentration did not change the results. Separations of polynuclear aromatic hydrocarbons and linear alkenebenzene sulfonate test mixtures were obtained using on-line SFE/HPLC interfaced system.     

Pressurized Solvent Extraction of Paulownia Bark Phenolics

Paulownia bark is mostly utilized jointly with wood, but the possibility of a separate valorization through the pressurized extraction of bark bioactives has been assessed. Subcritical water extraction and supercritical CO₂ extraction are green technologies allowing shorter times than conventional solvent extraction under atmospheric shaken conditions. Subcritical water extraction was carried out at temperatures ranging from 140 to 240 °C and supercritical CO₂ extraction was performed at different pressures (10, 20 and 30 MPa), temperatures (35, 45 and 55 °C) and ethanol concentrations (0, 10 and 15% (w/w)). Subcritical water extraction under a non-isothermal operation during heating up to 160 °C (19 min) provided extraction yields up to 30%, and the extracts contained up to 7% total phenolics with an ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging capacity equivalent to 35% the activity of Trolox, whereas at 240 °C, the yield decreased to 20%, but the phenolic content reached 21%, and the antiradical activity was equivalent to 85% of Trolox. Supercritical CO₂ extraction at 30 MPa, 45 °C and 30 min reached a global yield of 2% after 180 min of extraction, but the product showed very low antiradical capacity. Gallic acid, vanillic acid, vanillin and apigenin were the major phenolic compounds found in the extracts.     

Direct dissolution of UO<Subscript>2</Subscript> and in situ extraction by TBP–HNO<Subscript>3</Subscript> and TiAP–HNO<Subscript>3</Subscript> organic solutions at atmospheric pressure

Supercritical CO₂ assisted dissolution of metals and metal-oxides and in situ extraction by TBP (or co-solvent) has been reported in literature. However, in this work, the dissolution and in situ extraction by nitric acid solvates of TBP and alternate solvent TiAP has been reported for g-level UO₂ (essentially PHWR fuel pellet fragments) feeds at atmospheric pressure without requiring supercritical fluids. Encouraging results were obtained.     

Carbon Dioxide Supercritical Fluid Extraction with on-line Fluorescence Detection

Abstract

An HPLC detector was modified to operate as a low pressure on-line supercritical fluid extraction detector. Spectra of CO₂ and fluorene are presented of pressures ranging from 85 to 150 atm. Both the intensity and emission wavelength of fluorene were effected by CO₂ pressure. As pressure increased, the emission intensity also increased and the emission shifted to a shorter wavelength. The intensity of CO₂ emission decreased by increasing pressure. The emission wavelength of CO₂ was unaffected by pressure. A detection limit for fluorene was found to be 5 μg per extraction. The minimal detectable mass was 25 μg (± 8% RSD) per extraction.     

Application of a gas-liquid entraining rotor to supercritical fluid extraction : Removal of iron(III) from water

Supercritical fluid extraction (SFE) of aqueous solutions is often limited by poor mass transport. The performance of a new gas-liquid entraining device was investigated to improve mass transport and thereby increase extraction efficiency. As a test system, iron(III) was extracted from water with a β-diketone chelating agent (HL) and supercritical fluid carbon dioxide. Metal β-diketonate complexes with sufficient solubility in supercritical fluid CO₂ are often poorly extracted from aqueous solutions due to limited mass transport between the water-soluble metal ion and the CO₂-soluble chelating agent. The new entraining device maximizes contact between the ligand-rich CO₂ phase and the metal ion-rich aqueous phase. Iron(III) was extracted from water with the chelating agent 2,2,7-trimethyl-3,5-octanedione (H(tod)) and supercritical fluid CO₂ at 60 °C and 20.8 MPa. With entrainment, 79% of the iron was removed from the aqueous phase. This represents a three-fold increase in iron extraction efficiency over that of a static system.     

The frequency,fluence, and pressure dependence of the absorption of pulsed CO2-laser radiation by SF6 at 140 K

We report measurements of absorption of pulsed CO₂ laser radiation by SF₆ at 140 K. These measurements cover a broad range of fluence (10^?6 to 0.8 J/cm²), SF₆ gas density (2 × 10¹⁵ to 6 × 10¹⁶ cm^?3), and frequency (six CO₂-laser frequencies within the SF₆ v₃ band). We employ two methods of data reduction including one that gives a simple phenomenological function of the three principal independent variables. We conclude that at low fluence a small fraction of the SF₆ molecules absorb the laser radiation and that collisions and higher fluence both increase that fraction. At higher fluence absorption by vibrationally excited molecules becomes increasingly important.     

Some applications of supercritical fluid extraction

Supercritical fluid extraction (SFE) exploits the solvation power of fluids at temperatures and pressures close to their critical point. Use of SFE with supercritical CO₂ is reported for the extraction of caffeine and quinine from various plant materials and of morphine from serum. Results are compared with those obtained by extractions with subcritical methanol and tetrahydrofuran, normal organic Soxhlet extractions and solid-phase extraction.     

Extraction of various additives from polystyrene and their subsequent analysis

Summary The extraction of fifteen polymer additives which are used as antioxidants, uv stabilizers, process lubes, flame retardants, and antistats from eight formulations of polystyrene is demonstrated with supercritical carbon dioxide and compared to traditional dissolution/precipitation extractions. The purpose of the study was two fold: 1) the development of a high performance liquid chromatography method(s) for the additives and 2) the determination of the viability of supercritical fluids for extraction of the additives from polystyrene. Nine of the additives were assayed via reversed phase liquid chromatography while, the remaining six additives could not be assayed in this manner. In order to develop an extraction method for the additives, the effects of static extraction time, CO₂ density, and temperature were first investigated. These preliminary extractions revealed that a static period which afforded an opportunity for the polymer to swell combined with a high CO₂ density and temperature above the polymer glass transition yielded quantitative recoveries of the additives. Triplicate extractions of the various polystyrene formulations matched additive recoveries obtained by the traditional dissolution/precipitation method but the former method was faster and used less organic solvent.     

SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> binary aerogels: Synthesis in new supercritical fluids and study of thermal stability

A comparative analysis of properties of SiO₂–TiO₂ binary aerogels prepared by supercritical drying using different supercritical fluids (isopropanol, hexafluoroisopropanol, methyl tert-butyl ether, and CO₂) has been performed. The use of different supercritical fluids allows preparation of both homogeneous amorphous SiO₂–TiO₂ binary aerogels (by supercritical drying in hexafluoroisopropanol and CO₂) and composite aerogels containing nanocrystalline anatase (by supercritical drying in isopropanol and methyl tert-butyl ether). The thermal treatment of the aerogels at temperatures up to 600°C does not lead to considerable change in the porous structure and phase composition of the aerogels.     

Influence of Metallic Materials on SF<Subscript>6</Subscript> Decomposition Components under Positive DC Partial Discharge

Determination of the influence and mechanism of metallic materials on SF₆ decomposition under direct current (DC) partial discharge is one of the key aspects to improve SF₆ decomposition component analysis (DCA). In this study, three kinds of metallic materials, namely, aluminum, copper, and 18/8 stainless steel, were made into needle–plate electrons, and then used in the SF₆ positive DC partial discharge decomposition experiments. The influences of metallic materials on the five main decomposition components (i.e., CF₄, CO₂, SOF₂, SO₂F₂, and SO₂) were determined by gas chromatography–mass spectrometry. Results showed no significant correlation among the contents of CO₂ for the different kinds of metallic materials. However, the metallic materials considerably influenced the contents of the other four gases. The difference in SF₆ decomposition characteristics for the different metal electrodes was mainly due to the difference in anti-halogenation ability of metals and the passive film. Therefore, the impacts of different metallic materials should be considered when using SF₆ DCA for the condition monitoring and fault diagnosis of DC gas-insulated equipment.     

Estimation of ecotoxicological potential of contaminated sediments based on a sequential extraction procedure with supercritical CO2 and subcritical H2O solvents

Sediment samples were taken from the Tisza–Szamos area and Gödöll lake system. A new sequential extraction scheme in a supercritical extractor using supercritical CO₂, subcritical H₂O, and a subcritical mixture of 90% H₂O and 10% CO₂ as solvents was employed. This procedure provides relevant information about environmentally mobile heavy metal fractions (water-soluble, bicarbonate-forming) of sediments during a reasonably short time (5 h). The environmental mobility of Zn and Cd was found to be the highest among the sediments involved in these investigations. This mobility represents detectable ecotoxicity, which can be tested with the subcritical water extracts. Performance of pollen tube growth (PTG) test and the ecotoxicological stable isotope metabolic assay (ESIMA) was compared. Potential ecotoxicity of aqueous extracts was reliably detectable by PTG test during a relatively short time (1 day).     

FT-IR study on interactions between solutes and entrainers in supercritical carbon dioxide

Fourier transform infrared (FT-IR) spectroscopy has been used to measure the molarities of hydrogen bonding species between carboxylic acids (acetic acid and palmitic acid) and water in supercritical CO₂. The equilibrium constants of dimerization for the carboxylic acids were determined in supercritical CO₂ with octane. Further, the interactions of propanol-d (1- and 2-propanol-d) or xylenol (2,5-, 2,6- and 3,4-xylenol) isomers with acetone in supercritical CO₂ were studied. Experiments were carried out at 308.2–313.2 K and 7.0–20.0 MPa. The molarities of hydrogen bonding species between the carboxylic acids and water in supercritical CO₂ increase with the increasing molarity of water. The carboxylic acids interact more easily with ethanol than water in supercritical CO₂. For supercritical CO₂+carboxylic acid+octane systems, the equilibrium constants between the carboxylic acid monomer and dimer increase with the increasing molarity of octane. The equilibrium constants of the carboxylic acids seem to approach to those in liquid paraffin according to addition of octane in supercritical CO₂. The amount of the interaction species between 1-propanol-d and acetone is larger than that between 2-propanol-d and acetone. The amount of acetone interacting with OH group for 3,4-xylenol is the largest among those for xylenol isomers. These differences among the isomers may be caused by the screen effects of methyl groups around hydroxyl group for the isomers.     

Chemical consequences of electron scavenging by SF6 in radiolysis experiments

Contrary to the usual assumption that it is unreactive, SF₆^? formed by electron attachment is found to undergo rapid bimolecular reactions with molecules (HX) possessing acidic hydrogen, including HCl, HBr, HCO₂H, CH₃CO₂H, H₂S, and HCN. It is clear for many systems that meaningful mechanistic inferences about radiolytic processes occurring in the presence of SF₆ should consider a wide variety of non-scavenging reactions. Appropriate caution should be exercised in any experiment in which SF₆ is used to scavenge and detect low energy electrons. The reaction sequences observed are interesting in that they provide convenient bimolecular pathways for the formation of a variety of anionic dimers of the type XHY^?.     

Vibrational Spectroscopy in Supercritical Fluids: From Analysis and Hydrogen Bonding to Polymers and Synthesis

Supercritical fluids are beginning to be used widely in chemistry. Applications range from extraction and chromatography in analytical chemistry to solvents for reaction chemistry and preparation of new materials. Spectroscopic monitoring is important in much of supercritical chemistry, and vibrational spectroscopy is particularly useful in this context because the vibrational spectrum of a given molecule is usually quite sensitive to the environment of that molecule. Thus, vibrational spectra are excellent probes of conditions within the fluid. In this review, we describe a variety of techniques and cells for IR and Raman spectroscopy in supercritical fluids and illustrate the breadth of applications in supercritical fluids. The examples include: the use of supercritical Xe as a spectroscopically transparent solvent for chemistry and for supercritical fluid chromatography with FTIR detection of analytes; Raman spectroscopy as a monitor for gases dissolved in supercritical CO₂; the effect of solvent density on hydrogen bonding in supercritical fluids and the formation of reverse micelles; IR as a monitor for the supercritical impregnation/extraction of polymers and the reactions of organometallic compounds impreganated into polymers; reactions of organometallic compounds in supercritical fluids; and finally, the use of miniature flow reactors for laboratory-scale preparative chemistry. Overall, our aim is to provide a starting point from which individual readers can judge whether such measurements might usefully be applied to their own particular problems.     

Dry ice-originated supercritical and liquid carbon dioxide extraction of organic pollutants from environmental samples

Packed in a high-pressure vessel and under calculated conditions, dry ice can be used as a source of carbon dioxide for supercritical CO₂ extraction or liquid CO₂ of organic compounds from environmental samples. Coupled with a fluid modifier such as toluene, dry ice-originated supercritical CO₂ (Sc CO₂) achieves quantitative extraction of many volatile organic compounds (VOCs) and semivolatile organic compounds (SOCs) including polycyclic aromatic hydrocarbons (PAHs), n-alkanes, and polychlorinated biphenyls (PCBs) from solid matrices. Compared to contemporary manual or automated supercritical fluid extraction (SFE) technologies, this novel technique simplifies SFE to a minimum requirement by eliminating the need of a high-pressure pump and any electrical peripherals associated with it. This technique is highly suitable to analytical areas where sample preservation is essential but difficult in the sampling field, or where sample collection, sample preparation, and analysis are to be done in the field.     

Valorization of Fermented Shrimp Waste with Supercritical CO2 Conditions: Extraction of Astaxanthin and Effect of Simulated Gastrointestinal Digestion on Its Antioxidant Capacity

Lactic acid fermentation increases the bioactive properties of shrimp waste. Astaxanthin is the principal carotenoid present in shrimp waste, which can be found esterified in the liquid fraction (liquor) after its lactic acid fermentation. Supercritical CO₂ technology has been proposed as a green alternative to obtain astaxanthin from fermented shrimp waste. This study aimed to optimize astaxanthin extraction by supercritical CO₂ technology from fermented liquor of shrimp waste and study bioaccessibility using simulated gastrointestinal digestion (GD) of the optimized extract. A Box–Behnken design with three variables (pressure, temperature, and flow rate) was used to optimize the supercritical CO₂ extraction. The optimized CO₂ extract was obtained at 300 bar, 60 °C, and 6 mL/min, and the estimated characteristics showed a predictive extraction yield of 11.17%, antioxidant capacity of 1.965 mmol of Trolox equivalent (TE)/g, and astaxanthin concentration of 0.6353 µg/g. The experiment with optimal conditions performed to validate the predicted values showed an extraction yield of 12.62%, an antioxidant capacity of 1.784 mmol TE/g, and an astaxanthin concentration of 0.52 µg/g. The astaxanthin concentration decreased, and the antioxidant capacity of the optimized extract increased during gastrointestinal digestion. In conclusion, our optimized supercritical CO₂ process is suitable for obtaining astaxanthin from shrimp by-products after lactic acid fermentation.     

Multiphoton spectroscopy of the gasdynamically cooled SF6: third harmonic generation and dissociation spectrum

The third harmonic generation spectrum originating in the system of the low laying SF₆ vibrational levels has been investigated for the gasdynamically cooled gas (T_rot ? 30 K) using a continuously tuned CO₂-laser. A HF*-luminescence technique has been applied to obtain the SF₆ dissociation spectrum. The spectral features revealed did allow to make an adequate choice of the anharmonicity constants.