Herein we propose for the first time the utilization of a metal complex for forming water‐in‐supercritical CO2 (scCO2) microemulsions. The water solubility in the metal‐complex‐stabilized microemulsion is significantly improved compared with the conventional water‐in‐scCO2 microemulsions stabilized by hydrocarbons. Such a microemulsion provides a promising route for the in situ CO2 reduction catalyzed by a metal complex at the water/scCO2 interface. 相似文献
Abstract Poor-solvating property of supercritical carbon dioxide (scCO2) has been a great challenge, which limits the use of CO2 as a common “green” solvent. The present report describes that by increasing molar volume (v) and lowering the melting temperature, which lowers cohesive energy density or solubility parameter (δ), it is possible to increase the solubility of metal-based catalysts in scCO2 without using costly fluorinated or tailor-made CO2-philic modifications. We have studied various chlorodistannoxanes (1) and Cu–β-diketonates (2) to support our views. The study of bio-diesel production and transesterification of hindered esters using 1 in scCO2 shows a 2–8-folds rate enhancement coupled with an easier catalyst and product separation than that in organic solvents. The methodology, which works at least within the range of Van der Waals sphere of interactions, can be useful to solubilizing the molecules in scCO2 and carries great opportunity in catalysis as well as in separation science. 相似文献
Liquid or supercritical carbon dioxide has important environmental and economic advantages over petrochemical solvents currently used for industrial processes. However, low solubility in CO2, particularly of polar compounds, is a hurdle to its implementation as an acceptable alternative. These solubility problems have been overcome by employing specialised fluorinated surfactants to stabilise water nano-droplets as water-in-supercritical/liquid CO2 microemulsions. Such novel microemulsions can now facilitate innovative ‘green-and-clean’ applications of carbon dioxide technology. 相似文献
Hydrosilation of poly(methylhydrosiloxane) with a fluorinated olefin in supercritical CO2 (scCO2) using Karstedt's Pt catalyst has been successfully demonstrated; results were compared with those obtained in a subcritical conventional solvent, i.e. toluene. Rates of hydrosilation were found to be dependent on solvent, reactant concentration, and reaction temperature. Levels of hydrosilation were 40–50%, depending on reaction conditions. Gel formation, which was not observed under any conditions in subcritical toluene, occurred in all reactions done in scCO2 and accounted for up to 20 wt.‐% of the final product mix. 相似文献
A number of new fluoroalkyl ether-containing polythiophenes are synthesized via oxidative polymerization in supercritical CO2 (scCO2) and chloroform. In both cases, high-molecular-mass polymers with high yields are prepared. The properties of the polymers synthesized in scCO2, such as molecular mass, polydispersity, conjugation, and UV absorption, are similar to the properties of the polymers obtained in chloroform. All poly(fluoroalkyl ether thiophenes) show solubility in DMF, toluene, THF, chloroform, and acetone. The glass-transition temperatures of the polymers are in the range 58–82°C, and the temperatures corresponding to 10% loss in their weight are in the ranges 248–294 and 260–303°C for poly(fluoroalkyl ether thiophenes) synthesized in scCO2 and chloroform, respectively. All polymers fluoresce in the blue region with emission maxima at 506 to 526 nm. Because of the unique combination of fluoroalkyl and carbonyl groups, poly(fluoroalkyl ether thiophenes) feature good solubility in scCO2, which is a promising alternative solvent for the oxidative polymerization of fluoroalkyl ether thiophenes. 相似文献
Fluoropolymers are used in many technologically demanding applications because of their balance of high-performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids (SCFs). The homogeneous solution homo- and copolymerization of highly fluorinated acrylic, styrenic and olefinic monomers in supercritical carbon dioxide using free radical methods will be discussed [Science, 257 , 945 (1992)]. Detailed decomposition rates and efficiency factors will be presented for azobisisobutyronitrile (AIBN) in supercritical carbon dioxide and will be compared to conventional liquid solvents [Macromolecules, 26 , 2663 (1993)]. Additionally, viscosities of polymer solutions in supercritical CO2 have been measured using a high pressure, falling cylinder viscometer. The results show that the polymer solution viscosities in supercritical CO2 are an order of magnitude lower than with the same polymers in conventional organic solvents. The results from these homogeneous solution polymerization studies has allowed us to also consider heterogeneous polymerizations in a carbon dioxide continuous phase. Conventional emulsion polymerizations of unsaturated monomers are performed in either aqueous or organic dispersion media with addition of surface active agents (surfactants) to stabilize the colloidal dispersion that forms. With free radical initiators that are preferentially soluble in the continuous phase, high rates of polymerization and high molar mass polymers can be obtained simultaneously. Herein we describe an environmentally responsible alternative to aqueous and organic dispersing media for emulsion polymerizations which utilizes supercritical carbon dioxide, in conjunction with molecularly engineered free radical initiators and amphiphilic molecules that are specifically designed to be interfacially active in CO2. Conventional lipophilic monomers, exemplified by methyl methacrylate and styrene, can be polymerized heterogeneously using a fluorinated azo-initiator in supercritical CO2 in the presence of added surfactant to form stable emulsions that result in submicron size particles. Detailed surfactant and initiator syntheses and phase behavior will also be discussed. 相似文献
Cobalt‐mediated radical polymerization (CMRP) of vinyl acetate (VAc) is successfully achieved in supercritical carbon dioxide (scCO2). CMRP of VAc is conducted using an alkyl‐cobalt(III) adduct that is soluble in scCO2. Kinetics studies coupled to visual observations of the polymerization medium highlight that the melt viscosity and PVAc molar mass (Mn) are key parameters that affect the CMRP in scCO2. It is noticed that CMRP is controlled for Mn up to 10 000 g mol−1, but loss of control is progressively observed for higher molar masses when PVAc precipitates in the polymerization medium. Low molar mass PVAc macroinitiator, prepared by CMRP in scCO2, is then successfully used to initiate the acrylonitrile polymerization. PVAc‐b‐PAN block copolymer is collected as a free flowing powder at the end of the process although the dispersity of the copolymer increases with the reaction time. Although optimization is required to decrease the dispersity of the polymer formed, this CMRP process opens new perspectives for macromolecular engineering in scCO2 without the utilization of fluorinated comonomers or organic solvents.