PDF Publication Title:
Text from PDF Page: 057
176 E.J. Beckman / J. of Supercritical Fluids 28 (2004) 121–191 to use a biphasic system (with CO2) to perform green chemistry is that the continuous component of each phase (CO2 and the second component) should either both be environmentally benign (and hence cross-contamination is irrelevant) or should be immis- cible over essentially the entire concentration regime. Thus, only the components of interest (reactants, products) are moving across the phase boundary. Reactions making use of the CO2/water biphasic mixture have long been proposed as green alterna- tives to conventional reactions. Each of these sol- vents is inherently benign, they are immiscible over a broad range of concentrations, and the inevitable cross-contamination that occurs upon phase contact does not require remediation. Eckert et al. [289] first examined the use of a conventional phase transfer cat- alyst in a CO2/water mixture and found that despite the lack of ‘CO2-philic’ ligands, the tetraalkyl ammo- nium bromide was effective at catalyzing the reaction across the interface. While Eckert employed a phase transfer catalyst, Johnston et al. (and later Tumas) enlarged the interfacial surface area through creation of an emulsion [290]. The enhanced surface area in the emulsion greatly enhanced the rate of the model reactions performed by these two groups (see Fig. 6). Beckman and Hancu [33](b) also examined the use of added surfactant to enhance reactivity in a CO2/water biphasic system. Here, CO2 dissolves in aqueous hy- drogen peroxide, forming percarbonate (through two distinct mechanisms). The percarbonate ion (basic conditions are employed) then reacts with an alkene at the interface, forming the epoxide. The addition of surfactant to this system substantially enhanced the reaction rate, as did the addition of a phase trans- fer catalyst. The usual caveat in CO2/water biphasic mixtures is that the low pH can cause problems for some reactions [291]. Quadir et al. [292] used the CO2/water biphasic system in an intriguing way; here CO2 was employed to alter the particle size distribu- tion emanating from an emulsion polymerization in water. The recent intense scientific interest in ionic liquids has created another possible biphasic system for use with carbon dioxide. Ionic liquids are salts (to date, ammonium and phosphonium salts) that exhibit melt- ing temperatures close to or below room temperature. These materials exhibit manageable viscosities and essentially negligible vapor pressures and are hence Fig. 7. Phase behavior of carbon dioxide with the ionic liquid 1-butyl-3-methyl imidazolium hexafluorophosphate [293]. considered potentially benign solvent media. In 1999, Brennecke [293] observed that ionic liquids would ab- sorb large quantities of CO2 at relatively low pressure (mole fractions of ≈0.6 at pressure below 100 bar), yet the amount of ionic liquid dissolved in CO2 was below the detection limit of the instrument employed (and thus below 10−5 mole fraction). As such, the phase behavior of an ionic liquid in equilibrium with CO2 resembles that of a crosslinked polymer in equi- librium with CO2 (Fig. 7). Further, like polymer–CO2 mixtures, the apparent volume change upon mixing for an IL–CO2 mixture is large and negative, such that the volume change upon swelling of the IL is rather small, despite the amount of CO2 absorbed. Further, because CO2 dissolves readily in the ionic liquid, transport across the interface is rapid. A number of researchers have since exploited ionic liquid/CO2 biphasic mixtures as media for green chemistry. Tumas [89] employed CO2 as a reactant in the formation of dimethyl formamide from amines, postulating that the ionic liquid would stabilize the po- lar intermediate in the reaction. Both Cole-Hamilton [294] and Leitner [295] conducted catalytic reactions in an ionic liquid, employing CO2 to both extract products (leaving the catalysts behind) and enhance the solubility of gaseous reactants in the ionic liquid phase. Jessop and Eckert [90] examined asymmetric hydrogenation in an ionic liquid, again where the product is stripped into CO2, leaving the catalyst behind. It would not be surprising to see other such efforts in the future. The previously stated (Section 2) caveats regarding ionic liquids naturally still apply.PDF Image | Supercritical and near-critical CO2 in green chemical synthesis and processing
PDF Search Title:
Supercritical and near-critical CO2 in green chemical synthesis and processingOriginal File Name Searched:
sos.pdfDIY PDF Search: Google It | Yahoo | Bing
NFT (Non Fungible Token): Buy our tech, design, development or system NFT and become part of our tech NFT network... More Info
IT XR Project Redstone NFT Available for Sale: NFT for high tech turbine design with one part 3D printed counter-rotating energy turbine. Be part of the future with this NFT. Can be bought and sold but only one design NFT exists. Royalties go to the developer (Infinity) to keep enhancing design and applications... More Info
Infinity Turbine IT XR Project Redstone Design: NFT for sale... NFT for high tech turbine design with one part 3D printed counter-rotating energy turbine. Includes all rights to this turbine design, including license for Fluid Handling Block I and II for the turbine assembly and housing. The NFT includes the blueprints (cad/cam), revenue streams, and all future development of the IT XR Project Redstone... More Info
Infinity Turbine ROT Radial Outflow Turbine 24 Design and Worldwide Rights: NFT for sale... NFT for the ROT 24 energy turbine. Be part of the future with this NFT. This design can be bought and sold but only one design NFT exists. You may manufacture the unit, or get the revenues from its sale from Infinity Turbine. Royalties go to the developer (Infinity) to keep enhancing design and applications... More Info
Infinity Supercritical CO2 10 Liter Extractor Design and Worldwide Rights: The Infinity Supercritical 10L CO2 extractor is for botanical oil extraction, which is rich in terpenes and can produce shelf ready full spectrum oil. With over 5 years of development, this industry leader mature extractor machine has been sold since 2015 and is part of many profitable businesses. The process can also be used for electrowinning, e-waste recycling, and lithium battery recycling, gold mining electronic wastes, precious metals. CO2 can also be used in a reverse fuel cell with nafion to make a gas-to-liquids fuel, such as methanol, ethanol and butanol or ethylene. Supercritical CO2 has also been used for treating nafion to make it more effective catalyst. This NFT is for the purchase of worldwide rights which includes the design. More Info
NFT (Non Fungible Token): Buy our tech, design, development or system NFT and become part of our tech NFT network... More Info
Infinity Turbine Products: Special for this month, any plans are $10,000 for complete Cad/Cam blueprints. License is for one build. Try before you buy a production license. May pay by Bitcoin or other Crypto. Products Page... More Info
| CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com | RSS | AMP |