Home About us Contact
|
Home About us Contact | ||
|
|
||
CO2 Pressure (co2 + pressure)
Selected AbstractsConversion of carbon dioxide to cyclic carbonates using diimine Ru(II) complexes as catalystsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2009Mahmut Ulusoy Abstract Cationic diimine Ru(II) complexes were synthesized and tested as catalysts for the formation of cyclic organic carbonates from CO2 and liquid epoxides (propylene oxide, epichlorohydrine, 1,2-epoxybutane and styrene oxide) which served as both reactant and solvent. The reaction rates not only depended on the type of ligand, but also on reaction conditions such as temperature, pressure, base, the epoxide substrates and the use of an additional solvent. Reaction rates in terms of turnover frequencies up to 4050 molproduct molcat.,1 h,1 at 99% selectivity were achieved by optimizing the diimine ligand as well as the reaction temperature and CO2 pressure. Consistent with CV measurements, the electron donating group on the p -position of the aryl ring accelerated the reaction rate. Copyright © 2008 John Wiley & Sons, Ltd. [source] Copolymerization of Cyclohexene Oxide with CO2 by Using Intramolecular Dinuclear Zinc CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2005Youli Xiao Abstract The intramolecular dinuclear zinc complexes generated in situ from the reaction of multidentate semi-azacrown ether ligands with Et2Zn, followed by treatment with an alcohol additive, were found to promote the copolymerization of CO2 and cyclohexene oxide (CHO) with completely alternating polycarbonate selectivity and high efficiency. With this type of novel initiator, the copolymerization could be accomplished under mild conditions at 1 atm pressure of CO2, which represents a significant advantage over most catalytic systems developed for this reaction so far. The copolymerization reaction was demonstrated to be a living process as a result of the narrow polydispersities and the linear increase in the molecular weight with conversion of CHO. In addition, the solid-state structure of the dinuclear zinc complex was characterized by X-ray crystal structural analysis and can be considered as a model of the active catalyst. On the basis of the various efforts made to understand the mechanisms of the catalytic reaction, including MALDI-TOF mass analysis of the copolymers' end-groups, the effect of alcohol additives on the catalysis and CO2 pressure on the conversion of CHO, as well as the kinetic data gained from in situ IR spectroscopy, a plausible catalytic cycle for the present reaction system is outlined. The copolymerization is initiated by the insertion of CO2 into the ZnOEt bond to afford a carbonate,ester-bridged complex. The dinuclear zinc structure of the catalyst remains intact throughout the copolymerization. The bridged zinc centers may have a synergistic effect on the copolymerization reaction; one zinc center could activate the epoxide through its coordination and the second zinc atom may be responsible for carbonate propagation by nucleophilic attack by the carbonate ester on the back side of the cis -epoxide ring to afford the carbonate. The mechanistic implication of this is particularly important for future research into the design of efficient and practical catalysts for the copolymerization of epoxides with CO2. [source] Enhanced Stabilization of Reverse Micelles by Compressed CO2CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005Dong Shen Dr. Abstract The effect of compressed CO2 on the solubilization capacity of water in reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in longer chain n -alkanes was studied at different temperatures and pressures. It was found that the amount of solubilized water is increased considerably by CO2 in a suitable pressure range. The suitable CO2 pressure range in which the solubilization capacity of water could be enhanced decreased with increasing W0 (water-to-AOT molar ratio). The microenvironments in the CO2 -stabilized reverse micelles were investigated by UV/Vis adsorption spectroscopy with methyl orange (MO) as probe. The mechanism by which the reverse micelles are stabilized by CO2 is discussed in detail. The main reason is likely to be that CO2 has a much smaller molecular volume than the n -alkane solvents studied in this work. Therefore, it can penetrate the interfacial film of the reverse micelles and stabilize them by increasing the rigidity of the micellar interface and thus reducing the attractive interaction between the droplets. However, if the CO2 pressure is too high, the solvent strength of the solvents is reduced markedly, and this induces phase separation in the micellar solution. [source] Sorption and permeation behavior for CO2 in NH3 -plasma-treated and untreated polystyrene membranesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Y.-S. Yang Abstract In our preceding work, the simultaneous deviation from the conventional dual-mode sorption and mobility model was observed in a case of CO2 in polystyrene (PS) membrane (glass transition temperature of pure polymer = 95°C) at 60 and 70°C. The plasticization effect of sorbed CO2 on both the sorption and diffusion processes tends to be brought about in glassy polymer membranes near the glass transition temperature. The behavior was simulated based on the concept that only one population of sorbed gas molecules of plasticizing ability to the polymer should exist. In the present work, the sorption and permeation behavior for CO2 in NH3 -plasma-treated and untreated PS membranes at 40°C was investigated, where NH3 -plasma treatment was executed at plasma discharge powers of 40, 80, 120, and 160 W for an exposure time of 2 min. The sorption isotherm could be described by the sorption theory of Mi et al. (Macromolecules 1991, 24, 2361), where the glass transition temperature is depressed by a concentration of sorbed CO2 of plasticizing ability. NH3 -plasma treatment on PS membrane had little influence on the sorption behavior of CO2 at plasma discharge powers up to 160 W. The mean permeability coefficients were somewhat increased only at a discharge power of 160 W. At CO2 pressures below 0.9 MPa, the pressure dependencies of mean permeability coefficients for CO2 in both NH3 -plasma-treated and untreated PS membranes at 40°C could also be simulated on the basis of the concept that only one population of sorbed gas molecules of plasticizing ability should exist. At CO2 pressures above 0.9 MPa, however, a plasticization action of sorbed CO2 had much more influence on the diffusion process rather than on the sorption one, and such a combined concept underestimated the mean permeability coefficient. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1798,1805, 2007 [source] | ||||||||||