PDF Publication Title:
Text from PDF Page: 032
describe a process where propylene is converted to propylene oxide directly using a silver catalyst, where addition of CO2 enhances the efficiency of conversion. 2.9. Summary: gaseous reactants in CO2 Clearly, carbon dioxide exhibits some significant advantages as a solvent in systems where one or more of the reactants is a gas under typical operat- ing conditions. In such cases, operation in a liquid solvent almost always sets up a situation where the reaction is controlled by diffusion of the gas through the gas-liquid interface. Consequently, use of CO2 as the solvent can produce (at suitable pressure and tem- perature conditions) a single-phase substrate-gaseous reactant–CO2 mixture and hence, eliminate transport resistance owing to the presence of the gas–liquid interface. This, in turn, can render the reaction more efficient and potentially lead to lower energy usage, smaller processes and less waste. In addition, it is clear that use of CO2 as the solvent exhibits special advantages in certain reactions where oxygen is em- ployed as reactant—because CO2 will not oxidize, no solvent-based oxidation waste products will be produced in CO2-based systems. Further, when hy- drogen and oxygen are used together in a process (as in Baiker’s [114] and Beckman’s [14] work), use of CO2 as the solvent can greatly enhance the safety of the process. Despite the successes noted in the litera- ture, there are some interesting avenues of research in the general area of ‘use of gaseous reactants in CO2’ that have not been pursued, yet should be. First, a minority of the papers published on use of H2 , O2 and/or CO in CO2 -based reaction systems em- ploy a two-phase mixture in which to conduct the re- action; researchers opt instead to raise the pressure to a point where a single phase forms. Because CO2 usu- ally swells organic liquids extensively, conducting the reaction in a two-phase mixture could eliminate the transport resistance owing to gas diffusion into the liq- uid phase while permitting use of relatively low oper- ating pressures. In many cases, if one simply knew the phase behavior of the gas/CO2/substrate mixture, one could predict those conditions where high (enough) concentrations of gaseous reactant would exist in the lower, substrate-rich phase. Use of lower pressures renders both equipment design and utilities require- ments less stringent and is thus a ‘green’ advantage. In addition, operation in a two-phase mixture would al- low use of air as an oxidant without a slow build-up of nitrogen in the mixture. Finally, as in the case for hy- drogenations, use of a two-phase mixture would allow for heat transfer via liquid boiling and condensation. Another significant point to be made regarding heterogeneous catalysis in CO2 -based systems is that elimination of the transport resistance owing to gas–liquid diffusion may not render the reaction kinetically controlled, as one must also account for liquid–solid transport and pore diffusion within the catalyst. Typically, the effect of pore diffusion on the control of the reaction is mitigated by employing smaller catalyst particles, but this solution is not al- ways practical at larger scales. In addition, it is often easier to operate using a fixed bed of catalyst rather than a slurry of particles. Because CO2 is a low vis- cosity fluid, it may be possible in some situations to move from a slurry of particles to a fixed bed without sacrificing rate. Finally, a number of researchers have shown that one can design catalysts that are soluble in CO2 and hence one can operate without any transport constraints despite employing gaseous reactants and catalysts. However, recovery of a homogeneous (and typically valuable) catalyst from CO2 is not a trivial problem and its solution is required to allow ho- mogenous reactions in CO2 to be both green and economically viable. Naturally, one solution is to design catalysts that are relatively non-toxic and whose activity is high enough such that recovery is not necessary (as is the case currently with ethylene polymerization catalysts). In the case of all catalysts (homogeneous and heterogeneous), the effect of the presence of CO2 on catalyst deactivation (perhaps through the formation of CO during hydrogenation) is an area that merits further scrutiny. 3. Polymerization and polymer processing 3.1. Introduction Polymerization and polymer processing in/with CO2 exhibits some interesting yet seemingly contra- dictory trends. Some of the most successful commer- cial processes that employ CO2 as solvent involve polymeric substrates, yet the vast majority of polymers E.J. Beckman / J. of Supercritical Fluids 28 (2004) 121–191 151PDF 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 (Standard Web Page)