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.     

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).     

Addition of modifier in supercritical fluid chromatography using a microbore reciprocating pump

Summary Solubilities of polar analytes in supercritical CO₂ can be enhanced by the addition of polar modifiers. The addition of modifier into an SFC system using a low cost reciprocating pump has been studied. Two different mixing chambers were evaluated for mixing the supercritical CO₂ with modifier. It appeared that a mixing chamber with a packed bed was enough to reduce baseline noise from the modifier pump. Results from the effect of pressure and temperature with various modifier flow rates were obtained. High percentages of modifier (>15%) at a low CO₂ pressure (2000 psi) caused baseline instability. In addition, different I.D. columns were tested with the system and the effect of modifier compressiblity on detector noise was also studied. Several pharmaceutical compounds were separated to demonstrate system performance.     

Amine functionalised metal organic frameworks (MOFs) as adsorbents for carbon dioxide

Three different porous metal organic framework (MOF) materials have been prepared with and without uncoordinated amine functionalities inside the pores. The materials have been characterized and tested as adsorbents for carbon dioxide. At 298 K the materials adsorb significant amount of carbon dioxide, the amine functionalised adsorbents having the highest CO₂ adsorption capacities, the best adsorbing around 14 wt% CO₂ at 1.0 atm CO₂ pressure. At 25 atm CO₂ pressure, up to 60 wt% CO₂ can be adsorbed. At high pressures the CO₂ uptake is mostly dependent on the available surface area and pore volume of the material in question. For one of the iso-structural MOF pairs the introduction of amine functionality increases the differential adsorption enthalpy (from isosteric method) from 30 to around 50 kJ/mole at low CO₂ pressures, while the adsorption enthalpies reach the same level at increase pressures. The high pressure experimental results indicate that MOF based solid adsorbents can have a potential for use in pressure swing adsorption of carbon dioxide at elevated pressures.     

Supercritical fluid extraction of Kava lactones from Kava root and their separation via supercritical fluid chromatography

Summary Seven Kava lactones were extracted from Kava root using both pure and 15% ethanol modified CO₂. Most of the Kava lactones were extracted employing 100% CO₂ with an efficiency greater than 90% relative to conventional solvent extraction using organic solvents. Extraction efficiency did not increase significantly when using 15% ethanol-modified CO₂ as an extraction fluid. Separation of extracted Kava lactones was obtained using various packed columns and methanol-modified CO₂. An optimized separation was achieved using either an amino or protein C₄ column at 125 atm and 80°C. Semi-preparative separation of Kava lactones was also obtained using two columns connected in series.     

Preparation and Characterization of PVDF‐HFP Membrane

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) microporous membrane was prepared by supercritical CO₂ extraction of dibutyl phthalate (DBP) template from PVDF‐HFP/DBP film. The effects of extraction conditions such as pressure, temperature, and extraction time on extraction efficiency and the porosity of membrane were studied. The extraction efficiency of DBP and size stability of polymer membrane during extraction was compared with those of solvent extraction process. The structure of the resulting membrane was characterized by scanning electron microphotograph (SEM), X‐ray diffraction (XRD) and differential scanning calorimeter (DSC). With increasing the extraction temperature, pressure and time, the extraction efficiency and the porosity increased. Maximum extraction efficiency is obtained at extraction pressure and temperature higher than 18 MPa and 75°C, respectively. The porosity of membranes depended on the extraction efficiency and shrinkage ratio of membranes. Compared with solvent extraction, supercritical CO₂ extraction of the film generated the membrane with more uniform structure and higher porosity.     

Electrochemical reduction of CO2 at metal-porphyrin supported gas diffusion electrodes under high pressure CO2

Electrochemical reduction of CO₂ at metal-meso-tetraphenylporphyrin (TPP) supported gas diffusion electrodes (GDEs) under CO₂ at atmospheric pressure and 20 atm was carried out. At Co- and Fe-TPP supported GDEs that are comparatively active in the electrochemical reduction of CO₂ under atmospheric CO₂, the current efficiencies for the reduction of CO₂ increased up to 97.4 and 84.6%, respectively, by an increase in CO₂ pressure. At Cu- and Zn-TPP supported GDEs that showed low activity under atmospheric CO₂, the current efficiencies for CO₂ reduction increased up to 50.5 and 65.8%, respectively, under 20 atm CO₂. At these active metal-TPP supported GDEs, the potential of CO₂ reduction shifted positively by an increase in CO₂ pressure. These results indicate that the increase in concentration of CO₂ in the electrolyte solution caused by high pressure enhanced the electrocatalytic activity of metal-TPPs for CO₂ reduction.     

Chromatographic investigation of the effect of dissolved carbon dioxide on the glass transition temperature of a polymer and the solubility of a third component (additive)

The effect of dissolved carbon dioxide on the glass transition temperature of a polymer, PMMA, has been investigated using molecular probe chromatography. The probe solute was iso-octane, and the specific retention volumes of this solute in pure PMMA and mixtures of PMMA with CO₂ were measured over a temperature range of 0 to 180°C and CO₂ pressures from 1 to 75 atm. The amount of CO₂ dissolved in the polymer was calculated from a model fit to previously published solubility data determined chromatographically. Classical van't Hoff-type plots were used to determine the glass transition temperature of CO₂-impregnated PMMA from low pressure up to 46 atm of CO₂. Solvent-induced plasticization was observed with the glass transition temperature decreasing by about 40°C. At some pressures, glass transitions at low temperatures could not be determined from the van't Hoff plots because of the proximity of the polymer glass transition temperature to the gas–liquid transition temperature for CO₂. For these pressures, a new method was developed to determine the glass transition composition. The glass transition pressure was then calculated from the measured composition and temperature using an isotherm model. In every case, the glass transition temperature decreased linearly with increasing concentration of CO₂ in the polymer. However, at higher compositions, the glass transition pressure decreased with increasing composition and decreasing temperature. The observed retention volume of iso-octane with PMMA in a glassy state was correlated with an adsorption model developed from a theory for liquid–solid chromatography derived by Martire. This model accurately described the observed decrease in retention of iso-octane by adsorption on the surface of glassy PMMA with increasing concentration of CO₂ dissolved in the polymer. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2537–2549, 1998     

Nitric Acid-Air Diffusion Coefficient: Experimental Determination Using a Diffusion Cell

Abstract

Trace gaseous nitric acid was generated using a diffusion cell. The determination was made by collection in cellulose filters coated with K₂CO₃ and measuring the concentration by ion chromatography. The measured HNO₃-air diffusion coefficient was 0.0404±0.0010 cm²/s (n=21) for T=298.15 K and P=1 atm. Their dependence with the temperature, over the range from 297.15 K to 318.15 K, could be expressed by D = 10^?4.7773.T^1.366 (R²=0.9467).     

Water and Carbon Dioxide: A Unique Solvent for the Catalytic Polymerization of Ethylene in Miniemulsion

The catalytic polymerization of ethylene is performed in water pressurized with CO₂. The size of the initial monomer droplets and of the resulting polymer particles can be varied by simply changing the CO₂ pressure. Furthermore, at identical ethylene partial pressure, the polymerizations performed in the presence of CO₂ are significantly faster than in its absence. Thus, the combination of CO₂ and water is a promising green solvent for catalytic emulsion polymerizations.     

Antioxidant potential and phytochemical composition of extracts obtained from Phyllanthus phillyreifolius by different extraction methods

Abstract

Phyllanthus phillyreifolius (Euphorbiaceae), poorly studied plant species, was fractionated using conventional and high pressure extraction techniques such as supercritical fluid and pressurized liquid extractions. Lipophilic substances were extracted with n-hexane and supercritical CO₂ with or without co-solvent ethanol, meanwhile higher polarity fractions were recovered with acetone and 70% ethanol. Antioxidant potential was assessed by various chemical assays, which revealed that 70% ethanol was the most effective solvent for recovery of antioxidants. UPLC-MS phytochemical analysis of hydrophilic extracts confirmed geraniin as the main constituent of P. phillyreifolius. Other quantitatively important compounds were phyllanthusiin D and elaeocarpusin. Three isomers of tocopherol (α, β and γ) were quantified by HPLC in lipofhilic extracts. Generally, the results from this study revealed high antioxidant potential of P. phillyreifolius; consequently the plant may be considered as a promising source of antioxidants for functional foods, nutraceuticals and pharmaceutical formulations.     

Crystallization of bisphenol a polycarbonate induced by supercritical carbon dioxide

Supercritical carbon dioxide readily induces crystallization in bisphenol A polycarbonate. Crystallization begins within one h of exposure to the CO₂ at temperatures and pressures as low as 75°C and 100 atm. The degree of crystallinity increases sharply as the CO₂ pressure is raised from 100 to 300 atm but levels off thereafter. This behavior is likely due to a minimum in the T_g of the polycarbonate/CO₂ mixture owing to the opposite effects of the pressure on the T_g of the polymer and on the equilibrium weight fraction of CO₂ absorbed. Percent crystallinities of over 20%, comparable to that achieved using acetone or other organic liquids, have been obtained after 2 h exposure to supercritical CO₂. Since polycarbonate degasses quickly and quantitatively at ambient temperature and pressure, the high T_g of bisphenol A polycarbonate can be regained in the crystallized material without further vacuum treatment.     

Titanocene dichloride/KI: an efficient catalytic system for synthesis of cyclic carbonates from epoxides and CO2

Titanocene dichloride (Cp₂TiCl₂)/KI was developed to be an efficient catalytic system for the cycloaddition of CO₂ to epoxides to synthesize relevant cyclic carbonates from epoxides and CO₂. Various influencing factors on the coupling reaction, such as co‐catalyst, temperature, CO₂ pressure and reaction time, were investigated. The optimal reaction conditions were KI as co‐catalyst, 150 °C reaction temperature, 12 atm CO₂ pressure and 4 h reaction time using THF as solvent for the synthesis of propylene carbonate in 98% yield. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of carbonates directly from 1 atm CO2 and alcohols using CH2Cl2

We introduced here a new one-pot, general procedure for the preparation of dialkyl carbonates from alcohols in a straightforward fashion under 1 atm pressure of CO₂ using Cs₂CO₃ and CH₂Cl₂ as key reagents.     

Facilitated transport of CO2 through polyethylenimine/poly(vinyl alcohol) blend membrane

Polyethylenimine (PEI)/poly(vinyl alcohol) (PVA) blend membranes were prepared for the facilitated transport of CO₂. The polymeric carrier PEI was retained in the blend membrane by the entanglement with PVA chains. The CO₂ permeance decreased with an increase in CO₂ partial pressure in feed gas, whereas the N₂ permeance was nearly constant. This result clearly showed that only CO₂ was transported by the facilitated transport mechanism. The CO₂ and N₂ permeabilities increased monotonically with the PEI weight percent in the blend membrane, whereas the selectivity of CO₂ over N₂ showed a maximum. The selectivity increased remarkably with increasing heat-treatment temperature of the membrane. The highest selectivity obtained reached more than 230 when the CO₂ partial pressure was 0.065 atm. The prepared membrane was stable.     

Improvement of CO2/CH4 separation characteristics of polyimides by chemical crosslinking

Uncrosslinked and crosslinked polyimides and copolyimides have been synthesized in order to increase selectivity without an unacceptable loss in permeability. The goal was to reduce undesirable effects caused by CO₂ induced swelling in CO₂/CH₄ separation processes by stabilizing the polyimide structure with crosslinks. In the polymerization reaction 6FDA (4,4′-(hexafluoroisopropylidene)diphthalic anhydride) was used as dianhydride monomer and mPD (m-phenylene diamine) and DABA (diamino benzoic acid) were used as diamine monomers. With copolyimides containing strong polar carboxylic acid groups (i.e. 6 FDA–mPD/DABA 9:1) reduced plasticization was seen up to a pure CO₂ feed pressure of 14 atm, presumably due to hydrogen bonding between the carboxylic acid groups. By chemical crosslinking of the free carboxylic acid groups of the 6FDA–mPD/DABA 9:1 with ethylene glycol, the swelling effects due to CO₂ can be reduced at least up to a pure CO₂ feed pressure of 35 atm. With increasing degree of crosslinking, increasing CO₂/CH₄ selectivity was found because of reduced swelling and polymer chain mobility. By using ethylene glycol as a crosslinking agent, CO₂ permeability was not significantly lowered because the reduced chain mobility was compensated by the additional free volume caused by the crosslinks.     

Alternating copolymerization of carbon dioxide and epoxide catalyzed by an aluminum Schiff base–ammonium salt system

The alternating copolymerization of carbon dioxide (CO₂) and cyclohexene oxide (CHO) with an aluminum Schiff base complex in conjunction with an appropriate additive as a novel initiator is demonstrated. A typical example is the copolymerization of CO₂ and CHO with the (Salophen)AlMe ( 1a )–tetraethylammonium acetate (Et₄NOAc) system. When a mixture of the 1a –Et₄NOAc system and CHO was pressurized by CO₂ (50 atm) at 80 °C in CH₂Cl₂, the copolymerization of CO₂ and CHO took place smoothly and produced a high polymer yield in 24 h. From the IR and NMR spectra, the product was characterized to be a copolymer of CO₂ and CHO with an almost perfect alternating structure. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis indicated that an unfavorable reaction between Et₄NOAc and CH₂Cl₂ and a possible chain‐transfer reaction with concomitant water occurred, and this resulted in the bimodal distribution of the obtained copolymer. With carefully predried reagents and apparatus, the alternating copolymerization in toluene gave a copolymer with a unimodal and narrower molecular weight distribution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4172–4186, 2005     

Stripping of photoresist on silicon wafer by CO(2) supercritical fluid

Supercritical CO₂-based fluid is not only being considered as environmentally benign medium for photoresist (PR) removal in electronic device manufacture, but also capable of challenging feature dimensions. Despite many attractive properties, clear supercritical CO₂ has little solvating power for PR. Here, two acetate modifiers were selective to add in the CO₂ and evaluated individual contribution to the overall stripping rate by factorial experiment design, which included four other factors with four level ranges for each one and concluded the best 90% extraction efficiency would be obtained under the optimized parameters: 2.5 min static time, 35 min dynamic time, 1.25 ml ethylacetate spiked, 125 °C oven temperature and 480 atm CO₂ pressure. As analyzing the variances of these contributors to this system, it disclosed that dynamics controlled the stripping mechanism before near 35 min purging but thermodynamics took over after then; and that increasing pressure was more competent for removing PR than increasing temperature. All supercritical extracts were from two commercial PR coated on two substrates and analyzed by UV absorption spectrometry. Removing PR coated on silicon oxide layer was easier than that on Al-Cu alloy one.     

Dual-mode analysis of subatomspheric-pressure CO2 sorption and transport in Kapton H polyimide film

Sorption kinetics and equilibria as well as permeabilities and diffusion time lags for CO₂ in Kapton polyimide film have been studied at temperatures from 35 to 55°C and pressures up to 0.78 atm. The sorption/desorption cycles indicate that the diffusivity of CO₂ increases with increasing local penetrant concentration in the polymer. Both the permeability and time lag decrease with increasing upstream CO₂ pressure. All of these results are described well by theoretical expression based on the dual-mode theory of sorption and transport in glassy polymers.     

Flash photolysis study of the recombination of chlorine atoms in the presence of various inert gases and NO

The recombination of chlorine atoms has been investigated by flash photolysis in the inert gases He, Ne, Ar, N₂, CO₂, CF₄, SiF₄, SF₆, and C₂F₆. The pressure dependence of the reaction has been measured between 0.5 and about 100 atm for He, N₂, and CO₂. Experiments on the NO-catalyzed recombination of chlorine in the presence of He (0.5–100 atm) permitted a determination of the falloff curve of the reaction Cl+NO(+He)→ClNO(+He).