scCO2 Phase Research Articles

Transglucosylation of caffeic acid by a recombinant sucrose phosphorylase in aqueous buffer and aqueous-supercritical CO2 media

Polyphenolic compounds, such as caffeic acid, offer many health benefits, but their industrial applications are limited because of their low solubility in water and instability under UV light or heat. In this study, we enzymatically produced caffeic acid glucosides, in both aqueous buffer and aqueous-supercritical carbon dioxide (SC-CO2) media, using a recombinant sucrose phosphorylase (SPase) from Bifidobacterium longum. By using LC/MS/MS analysis, we verified that the enzymatic reaction products were caffeic acid monoglucosides and diglucosides. Under SC-CO2, the amounts of the reaction products from the enzyme reaction were smaller than those in the aqueous reaction medium. However, this is the first report of the transglucosylation of caffeic acid by SPase, and also the first enzymatic reaction with phenolic compounds conducted in a SC-CO2 phase.

Selective hydrogenation of citral catalyzed with palladium nanoparticles in CO2-in-water emulsion

CO2-in-Water (C/W) emulsion was formed by using a nonionic surfactant of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (P123), and palladium nanoparticles were synthesized in situ in the present work. The catalytic performance of Pd nanoparticles in the C/W emulsion has been discussed for a selective hydrogenation of citral. Much higher activity with a turnover frequency (TOF) of 6313 h−1 has been obtained in this unique C/W emulsion compared to that in the W/C microemulsion (TOF, 23 h−1), since the reaction was taking place not only in the surfactant shell but also on the inner surface of the CO2 core in the C/W emulsion. Moreover, citronellal was obtained with a higher selectivity for that it was extracted to a supercritical carbon dioxide (scCO2) phase as formed and thus its further hydrogenation was prohibited. The Pd nanoparticles could be recycled several times and still retain the same selectivity, but it showed a little aggregation leading to a slight decrease in conversion.

VULCAN-SUPPORTED Pt ELECTROCATALYSTS FOR PEMFCs PREPARED USING SUPERCRITICAL CARBON DIOXIDE DEPOSITION

In this study, supercritical carbon dioxide (scCO2) deposition was used to prepare vulcan-supported Pt (Pt/Vulcan) electrocatalysts for proton exchange membrane fuel cells (PEMFCs), and the effects of process variables on the properties of the electrocatalysts were investigated. The two different methods used to reduce the organometallic precursor were thermal reduction in nitrogen at atmospheric pressure and thermal reduction in scCO2. In the former method, the maximum Pt loading achieved was 9%, and this was governed by the adsorption isotherm of the Pt precursor between the scCO2 phase and the Vulcan phase. By using the latter method, higher Pt loadings of 15% and 35% could be achieved. The Pt/Vulcan catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and cyclic voltammetry (CV). The average particle sizes for Pt/Vulcan 9%, 15%, and 35% catalysts were 1.2, 1.3, and 2 nm, respectively. Electrochemical surface areas obtained from CV data were found to vary with the Pt loading.

A Continuous Reactor for the (Chemo)enzymatic Dynamic Kinetic Resolution of Rac-1-Phenylethanol in Ionic Liquid/Supercritical Carbon Dioxide Biphasic Systems

Enzymatic transformations in ionic liquids (ILs)/supercritical carbon dioxide (scCO2) biphasic systems, whereby enzyme molecules are ``immobilized" in the IL phase and substrates/products are transported by the scCO2 phase, are described as a way for carrying out clean synthetic chemical processes to produce pure products. As a model system to study, the ionic liquid butyltrimethyl ammonium (bis(trifluoromethane)sulfonyl imine) ([btma][NTf2]) was assayed for Candida antarctica lipase B (CALB)-catalyzed the kinetic resolution of rac-1-phenylethanol. The suitability of this IL was established from both the activity and stability of the enzyme. A continuous dynamic kinetic resolution (DKR) process in [btma][NTf2])/scCO2 biphasic system was carried out by using simultaneously both immobilized Candida antarctica lipase B in silica gel and silica modified with benzenosulfonic acid groups (SCX) catalysts at 50 ºC and 10 MPa, providing a good yield (78 %) for (R)-1-phenylethyl propionate product with excellent enantioselectivity (ee = 92 %) in continuous operation.

Emulsion copolymerization ofD,L-lactide and glycolide in supercritical carbon dioxide

Biodegradable polyesters were synthesized via an emulsion polymerization in supercritical carbon dioxide (SC-CO2). Copolymers of lactide and glycolide were synthesized in SC-CO2 with stannous octoate as the ring-opening catalyst and a fluorocarbon polymer surfactant as an emulsifying agent. The conversion of lactide and glycolide was monitored with respect to the reaction time and temperature with 1H NMR spectroscopy. The conversion of glycolide surpassed 99% within 72 h for an SC-CO2 phase maintained at 200 bar and 70 °C. Under the same conditions, lactide conversion reached 65% after 72 h of polymerization. Unpolymerized monomer was removed after the reaction by extraction with an SC-CO2 mobile phase. The molecular weights of all the copolymers were measured by gel permeation chromatography. Weight-average molecular weights (Mw) ranged between 2500 and 30,200 g/mol and polydispersity indices ranged from 1.4 to 2.3 for polymerization times of 6 and 48 h, respectively. Although the molecular weight increased significantly during the first 48 h of reaction, there was no significant difference in the Mw for polymerization times of 48 and 72 h. Emulsion polymerization within the benign solvent SC-CO2 demonstrated improved conversion and molecular weight versus polymers synthesized without surfactant. The emulsion polymerization of lactide and glycolide copolymers in SC-CO2 is proposed as a novel production technique for high-purity, biodegradable polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 562–570, 2001

Enhanced product selectivity in the Mizoroki–Heck reaction using a supercritical carbon dioxide–liquid biphasic system

Arylation of ethylene catalysed by Pd complexes bearing triphenyl phosphite ligands proceeds efficiently in a scCO2–liquid biphasic system to give a mixture of arylated products; the selectivity of monoarylated products, styrene derivatives, can be improved by increasing the CO2 pressure, where the monoarylated products are effectively extracted from the liquid reaction phase into the scCO2 phase to prevent over-reactions to diarylated products.

A Distributed Reactivity Model for Sorption by Soils and Sediments. 7. Enthalpy and Polarity Effects on Desorption under Supercritical Fluid Conditions

Mechanisms of phenanthrene desorption from five subsurface materials in supercritical carbon dioxide (SC CO2) were investigated by measuring isotherms in the presence of fixed quantities of a polar cosolvent (methanol) and by calculating desorption enthalpies from the temperature dependence of the isotherms. The addition of 7.4 mol % methanol to the SC CO2 phase resulted in 2−11-fold reductions in Freundlich capacity factors at 120 atm and 50 °C. The capacity reduction greatly exceeded that expected from the 21% increase in phenanthrene solubility accompanying cosolvent addition. Isotherms became more linear at 120 atm and 50 °C upon methanol addition for all sorbents except a shale sample. Solubility and organic carbon-normalized phenanthrene sorption capacities declined with increasing solvent polarity, in the order dry SC CO2 > methanol-amended SC CO2 > aqueous solution, and declined with sorbent organic carbon content. Sorption enthalpies from an ideal gas reference state ranged from −106 to −70 kJ/mo...