CO2 -expanded liquids

Liu, J.C., Anand, M. and Roberts, C.B. (2006) Synthesis and extraction of beta-D-glucose-stabilized Au nanoparticles processed into low-defect, wide-area thin-films and ordered arrays using CO2-expanded liquids. Langmuir, 22 (9), 3964-3971. 

Building on earlier work in these laboratories (8) we have overcome the typical mass transfer limitations of phase transfer catalysis for propylene oxidation by the use of 3-component liquid phases based on CO2 expanded liquids (CXLs). For the application to oxidations by aqueous H2O2, the organic component of the CXL is chosen because it is miscible with both dense CO2 and water. In this way, homogeneous systems are produced which decrease mass-transfer limitations and intensify chemical reactions. Previous reports using CXL systems have shown that they enhance the oxidation of the substrate and improve the selectivity at moderate reaction temperatures and pressures (3, 8, 9). 

Unconventional solvents include supercritical CO2 (scCOiX CO2-expanded liquids, " ionic liquids, fluorous liquids, and liquid polymers. The advantages and disadvantages of each are summarized in Table I. 

Chamblee, T.S., Weikel, R.R., Nolen, S.A., Liotta, C.L and Eckert, C.A., Reversible in situ acid formation for 0 -pinene hydrolysis using CO2 expanded liquid and hot water. Green Chem., 2004,6(8), 382-386. 

Precipitation/Crystallization to Produce Nano- and Microparticles Because fluids such as C02are weak solvents for many solutes, they are often effective antisolvents in fractionation and precipitation. In general, a fluid antisolvent may be a compressed gas, a gas-expanded liquid, or a SCF. Typically a liquid solution is sprayed through a nozzle into CO2 to precipitate a solute. As CO2 mixes with the liquid phase, it... 

Gas-expanded liquids (GXLs) are emerging solvents for environmentally benign reactive separation (Eckert et al., op. cit.). GXLs, obtained by mixing supercritical CO2 with normal liquids, show intermediate properties between normal liquids and SCFs both in solvation power and in transport properties and these properties are highly tunable by simple pressure variations. Applications include chemical reactions with improved transport, catalyst recycling, and product separation. 

H2 and then CO2 pressure were applied, forming a GXL. The fluorinated catalyst then partitioned off of the fluorinated silica support and into the CO2-expanded organic phase. The reaction was assumed to occur in the expanded liquid phase in which reactants (styrene, hydrogen) and catalyst (fluorinated Wilkinson s catalyst) are homogeneously present. After the reaction was completed, the pressure was released and the catalyst then partitioned back onto the silica surface. 

This expanded liquid EOS model in conjunction with the regular solution theory model predicted the solute solubilities of naphthalene and phenanthrene in toluene with CO2 reasonably well at both high and low pressures (56). 

Solid carbon dioxide can be manufactured by expanding liquid CO through an adiabatic throttling valve. If CO2 is available for the process as a saturated liquid at 800 psia and the expansion reduces the pressure to 14.7 psia, how many pounds of solid carbon dioxide are produced per pound of liquid CO2 ... 

Hou et al. [22] compared reaction selectivity and conversion for the Wacker oxidation of 1-hexene in four different reaction systems (without solvent, or using SCCO2, IL or CO2-IL as solvent). The conversions in all reaction systems were similar. The selectivity in the CO2- based expanded liquid was significantly higher, and was found to increase with pressure. The higher selectivity of this system can be explained by partial dissolution of a reactant in the CO2 gas phase, which leaves less reactant in contact with catalyst in the liquid phase, decreasing isomerization. An enhanced mass transfer in the C02-expanded liquid may also lead to reduced isomerization. Recycling experiments were performed for supercritical CO2 and CO2 -t IL. The catalyst was stable in both systems, but more stable in the latter. The conclusion that can be drawn is that not only is selectivity enhanced, but also catalyst stability. 

Chanfreau, S., Cognet, R, Camy, S. and Condoret, J.-S. (2008) Electrocarboxylation in supercritical CO2 and C02-expanded liquids. Journal of Supercritical Fluids, 46,156-162. 

Supercritical CO2, near-critical water, and C02-expanded liquids are tunable benign solvents that offer exceptional opportunities as replacements for hazardous solvents. They generally exhibit better solvent properties than gases and better transport properties than liquids. They offer substantial property changes with small variations in thermodynamic conditions, such as temperature, pressure, and composition. They also provide wide-ranging environmental advantages, from human health to pollution prevention and waste minimization. 

When pressurised liquid CO2 expands, gaseous and solid CO2 form as a result. Solid CO2 is known as dry ice and available on the market as snow, slices, pellets, nuggets and blocks... 

Methane Methanol Oxides of Mn, Co, Pd, Mo, Cr, V, Cu 25-250 1-69 Continuous, homogeneous or heterogeneous catalyst CO2 mixed with perfluorinated compounds (expanded liquid) 139... 

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