Metallic nanoparticle production utilizing a supercritical carbon dioxide flow process

Metallic nanoparticles of palladium and silver ranging in size from 1 to 15 nm were produced entirely within carbon dioxide by spraying a carbon dioxide carrier solution containing CO2-soluble metal precursors into a CO2 receiving solution containing a reducing agent (NaBH(OAc)3 or H2) and fluorocarbon thiol stabilizing ligands. The process uses the benign solvent CO2 while also allowing for the production of nanoparticles with a limited number of chemical components. Particles were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS).     

A novel method for enzymatic asymmetric reduction of ketones in a supercritical carbon dioxide/water biphasic system

A novel method to enable asymmetric reduction of ketones by an alcohol dehydrogenase from Geotrichum candidum in a supercritical carbon dioxide and water biphasic system is described. The addition of sodium bicarbonate improved the reactivity up to a practical level while retaining excellent enantioselectivity.     

On-line multidimensional chromatography using supercritical carbon dioxide

A two-dimensional chromatographic separation is described which makes use of the unusual properties of supercritical carbon dioxide mobile phase. This solvent has the property of giving a separation of polycyclic aromatic hydrocarbons (PAH) on amine-bonded columns similar to that given by usual normal-phase solvents, and on octadecylsilane-bonded columns similar to that given by usual reversed-phase solvents. Packed columns were used, arranged so that they could be switched in or out of the solvent flow. Polycyclic aromatic hydrocarbon mixtures isolated from coal tar were fractionated according to number of aromatic carbon atoms on an amine-bonded column, and these fractions were trapped on an octadecysilane-bonded column. They were subsequently eluted according to the polarity of the individual compounds. Separations from fractions containing 16 and 18 aromatic carbon atoms are shown.     

Dispersion of organic pigments using supercritical carbon dioxide

This research describes dispersion of organic pigments using supercritical fluids. With low surface tension and high diffusivity of fluids in supercritical states, aggregated particles may be effectively wetted and swelled to form the primary constituent of the dispersing solution by volume. In this paper, the conditions of temperature and pressure are used to control the density of supercritical carbon dioxide subject to PGMEA as cosolvent for dispersing organic powder in a solution. As shown from measurement with a laser scattering particle analyzer, the average diameter of phthalocyanine green 36 with the haloid structure can be significantly reduced to 93.5 nm; for aminoanthraquinone red containing and amino group (-NH(2)) and phthalocyanine blue 15:6 with symmetry benzene and inner hydrogen bond, the mean particle sizes are 178.5 and 188.7 nm, respectively, using supercritical CO(2). Additionally, the transmittance of UV light is used to confirm the dispersing performance in this study.     

Efficient synthesis of isoindoles using supercritical carbon dioxide

Bicyclopyrroles were efficiently converted to the corresponding isoindoles by a retro Diels-Alder reaction in supercritical carbon dioxide. By adding ethylene gas as an oxygen scavenger, the isoindole yield was further improved.     

The improved Kolbe-Schmitt reaction using supercritical carbon dioxide

A comparative analysis of the reactions between sodium phenoxide and CO₂ under the gaseous and supercritical conditions has demonstrated the preferential effect of supercritical conditions for promoting the reactivity of CO₂. A significant increase in product yield was obtained in supercritical CO₂ compared to reactions undertaken in gaseous CO₂.     

超临界CO_2萃取甾醇的研究(1)

本文用超临界ＣＯ＿２对高酸价麦胚油进行选择住萃取，结果表明，萃取温度和压力不同时，萃取物中甾醇的含量不同．且甾醇混合物主要为β－谷甾醇和菜籽甾醇。萃取物的酸价也明显高于高酸价麦胚油。     

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.     

Novel direct reduction of diaryl ketones to diarylmethanes using supercritical 2-propanol

We found that diaryl ketones reduce directly to diaryl alkanes under supercritical 2-propanol. This method was applied to one-pot synthesis of anthracene from anthraquinone derivatives by the addition of sulfur in excellent yields.     

Asymmetric synthesis using hydrolytic enzymes in supercritical carbon dioxide

The use of hydrolytic enzymes in supercritical carbon dioxide (scCO₂), an environmentally friendly solvent with many uses, is an attractive approach to asymmetric synthesis: several examples are reviewed here.     

Regeneration of cobalt-contaminated activated carbon by supercritical carbon dioxide extraction

A mixture of Di-(2-ethylhexyl) phosphoric acid (D2EPHA) and n-hexane or methanol is used as the extractant solution for extracting cobalt from activated carbon using supercritical carbon dioxide extraction technology. In this work, a semi-continuous pilot unit of SFE is employed to conduct the extraction. In order to feed the viscous extractant by HPLC pump, n-hexane or methanol is added as a diluent to reduce the viscosity of the extractant. The amount of cobalt removed along the time course of the extraction is recorded and plotted as an extraction curve. A kinetic model is also established and fit to the extraction curve, and the obtained parameters of the model are used to explain the regeneration mechanism. The effects of temperature ranged from?40 to?80?°C and the effect of the concentration of diluents on the extraction are investigated and discussed based on the established model. It is also found that the removal of cobalt ions reaches a maximum; this varies with the operational conditions and is known as maximum removal efficiency. It is presumed that the maximum removal efficiency is affected by the adsorption kinetics of the extractant and the rate of ion exchange between the extractant and metal ions on the surface of the activated carbon. After increasing the extraction temperature from?60 to?80?°C it is observed that the maximum removal efficiency is greatly increased, presumably resulting from the diminishing competitive adsorption between the extractant and diluents. The established model can help to reveal the extraction mechanism and to promote maximum removal efficiency for regenerating activated carbon without secondary pollution.     

Effect of carbon dioxide concentrations on asymmetric reduction of ketones with plant-cultured cells

Enantioselectivities in asymmetric reduction of ketones were controlled by atmospheric carbon dioxide concentrations: the reaction in high carbon dioxide concentrations under illumination of fluorescent light afforded the corresponding l-alcohol while that in low carbon dioxide concentrations in the presence of glucose under dark conditions gave the antipode, d-alcohol.     

Investigation of carbon dioxide modified supercritical and near supercritical carrier streams for flow injection systems

Since flow injection (FI) is a dilution technique, efforts have been undertaken to minimize online dilution or dispersion. Solutes in supercritical fluids exhibit increased diffusion coefficients which have been shown to decrease dispersion of the sample zone. This work investigates the use of supercritical fluids (or CO₂ modified fluids) as carrier streams for FI. Both a non-reacting tracer and an online chemical reaction were employed to investigate the behavior of solutes in supercritical and near critical systems. Further, these results are compared to those obtained in the system studied with a conventional carrier stream. Plots of peak response vs% CO₂ modifier increase with a sharp break at moderate modifier composition (20–30%). Plots of peak variance vs% CO₂ modifier show decreased variance with increasing % modifier. The system was also optimized with regards to temperature and pressure. The optimized system displayed improved limits of detection and decreased variance relative to 0% CO₂ modifier carrier streams.     

Grafting of glycidyl methacrylate onto polypropylene using supercritical carbon dioxide

Free-radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) films has been studied using supercritical carbon dioxide (SC-CO₂) as a solvent and a swelling agent. As the reaction temperature was below the melting point, PP was modified in the solid phase. The PP film was first soaked with the monomer GMA and benzoyl peroxide (BPO) as an initiator using SC-CO₂ at different experimental conditions of pressure, temperature, and thermal treatment time. After releasing CO₂, film GMA molecules were grafted onto PP in different times. Using this method, the degree of grafting and the morphology could be controlled through the combination of pressure, temperature, and soaking time. FTIR spectra confirmed that GMA had been grafted onto PP and that polypropylene-graft-glycidyl methacrylate (PP-g-GMA) presented a high surface reactivity for conductive polyaniline anchoring. DSC measurements and TG analyses showed that the thermal profiles of the graft copolymer and virgin PP are quite similar and that the graft PP does not exhibit changes in terms of thermal degradation profile and melting temperature, respectively. X-ray data showed that a high degree of grafting leads to a lower degree of crystallinity of polypropylene.     

Epoxidation of olefins with a silica-supported peracid in supercritical carbon dioxide under flow conditions

Anhydrous 2-percarboxyethyl-functionalized silica (2b), a recyclable supported peracid, is a suitable reagent to perform the epoxidation of alkenes 1 in supercritical carbon dioxide at 250 bar and 40 °C under flow conditions. This procedure simplifies the isolation of the reaction products and uses only carbon dioxide as a solvent under mild conditions. The solid reagent 2b can be easily recycled by a reaction with 30% hydrogen peroxide in an acid medium.     

在超临界CO2流体中的化学反应

超临界CO2流体中的化学反应是继超临界流体应用于萃取分离过程之后进一步将其应用于化学反应的新尝试。本文重点综述了超临界CO2流体中的化学反应研究进展, 并对其发展前景作了展望。