PDF Publication Title:
Text from PDF Page: 028
pressure on the rate constant was attributed to potential limitations in catalyst solubility in the CO2/propylene mixture—as pressure increased the catalyst solubil- ity should increase, accounting for the observed ef- fect. In a follow-on study published in 1999, Guo and Akgerman employed transition state theory, cou- pled with partial molar volumes calculated using the Peng-Robinson equation of state, to attempt to explain the selectivity increase with increasing pressure. Cal- culations reproduced trends in both temperature and pressure-dependence of the rate and the selectivity. It is not clear whether this work has any ‘green’ rami- fications, as the substrate employed (propylene) is a highly compressible fluid itself, and hence might be expected to solubilize significant quantities of hydro- gen and CO. In this case, addition of CO2 would tend to dilute the reactant concentrations, slowing the rate. On the other hand, if it could be shown that addition of CO2 enhances the concentration of H2 and CO sig- nificantly, then process advantages might be realized. Xiao et al. [107] have also examined homogeneous hydroformylation in CO2. They note, for example, that use of fluorinated aryl phosphine ligands (as part of a rhodium catalyst) leads both to higher solubility in CO2 and higher reaction rates (the latter owing to both electronic affects and solubility limitations of alky- lated phosphine catalysts). Comparison of the rates of hydroformylation of acrylates in CO2 and toluene showed the expected enhancement (in CO2) owing to the considerable increase in solubility of the reactants (CO and H2) in CO2 versus toluene at the same pres- sure. Selectivities remained the same. Here, as in other research on hydrogenation and hydroformylation in CO2, the ‘green’ advantages of the process are sug- gested to be the increased rates owing to the higher solubility of H2 and CO in CO2 versus typical organic solvents, plus the inherently benign nature of CO2 ver- sus other solvents. However, these attributes may be offset by the high pressure required to operate in CO2 (energy and capital requirements will likely be higher) and the increased cost and potential environmental problems owing to the use of fluorinated catalyst lig- ands needed to provide reasonable solubility in CO2. It would be quite useful to explore the use of CO2 as a swelling agent for a liquid hydroformylation sys- tem, where the dilution effect is offset by the enhanced solubility of gaseous reactants in the liquid phase owing to the presence of CO2. Catalysts could still be homogeneous yet not require fluorinated ligands, given that the continuous phase would be primar- ily alkyl-functional substrate (and product). Con- sequently, one could eliminate gas–liquid transport resistance while operating at substantially lower pres- sures than those required for single-phase operation. This indeed might be the process compromise that would provide the ‘greenest’ operation. Note that this is the opposite to what many authors recommend [108]—whereas a single phase is the best option for some processes, in cases where CO2/liquid sub- strate/gas reactive mixtures are being considered, two-phase operation has significant advantages. In- deed, if one could operate a hydroformylation at high space-time yield at lower pressures and temperatures than the current process owing to the presence of CO2, the process would be both green and economically viable. As in the case of hydrogenation, the use of a two-phase (liquid–vapor) system would allow easy heat removal through boiling (and later condensation) of the liquid. 2.7.2. Heterogeneous hydroformylation in CO2 Several research groups have evaluated heteroge- neous catalysis of hydroformylation in CO2; gen- erally, yields were good and selectivities to linear aldehyde excellent. For example, Poliakoff [109] used a rhodium complex (aryl phosphine ligands) immo- bilized on silica—selectivity to linear aldehyde was >90% at 10% alkene (1-octene) conversion. Clearly, use of an immobilized catalyst eases catalyst recovery and re-use issues. Poliakoff found no drop in catalyst activity after 30 h continuous use. Abraham [110] has also examined heterogeneous hydroformylation of propylene, focusing on the design of the catalyst to optimize performance. At first, Abraham’s group focused on support design to try to minimize prod- uct sorption, while more recent work has targeted the design of ‘tethered’ rhodium catalysts to try to achieve the advantages of both homogeneous and heterogeneous catalysts. It is again interesting that researchers have neglected to examine the question ‘under what conditions will the use of CO2 provide better results than when using neat substrate?’ Given that gases, such as CO and hydrogen, are poorly solu- ble in organic liquids, if CO2 will swell the substrate substantially, then conditions may exist where the concentration of hydrogen in the liquid phase (of a E.J. Beckman / J. of Supercritical Fluids 28 (2004) 121–191 147PDF 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)