Supercritical fluid technology homogenization

Herkley C. Homogeneous catalysis in supercritical carbon dioxide. In Sun Y-P, ed. Supercritical Fluid Technology in Materials Science and Engineering. New York Marcel Dekker, 2002 189-226. 

Finally, it should be stated that ethyl lactate is a novel ecofriendly solvent for potential applications in supercritical fluid technology, as a cosolvent of carbon dioxide. Ethyl lactate can be readily dissolved in CO2 in the amounts usually employed for supercritical extraction processes (15-20 wt% or lower). Additionally, at the typical temperatures employed (35-70°C) the ethyl lactate -1- CO2 system presents homogeneous (single) phase at relative low pressures. 

Earlier, no emphasis was given to homogeneous catalysis in supercritical fluids, albeit the technique per se is now well established in extraction technology (e. g., for coffee, tea, hops, spices, and natural flavors). Incorporated in homogeneous catalyst processes [58-60], supercritical conditions can dramatically change the solubility profile of solvents and the reactivity of certain chemicals. 

Catalysis in a single fluid phase (liquid, gas or supercritical fluid) is called homogeneous catalysis because the phase in whieh it occurs is relatively uniform or homogeneous. The catalyst may be molecular or ionic. Catalysis at an interface (usually a solid surface) is ealled heterogeneous catalysis-, an implication of this term is that more than one phase is present in the reactor, and the reaetants are usually concentrated in a fluid phase in contact with the eatalyst, e.g., a gas in contact with a solid. Most catalysts used in the largest technological processes are solids. The term catalytic site (or active site) deseribes the groups on the surface to which reactants bond for catalysis to occur the identities of the catalytic sites are often unknown because most solid surfaces are nonuniform in structure and eomposition and difficult to characterize well, and the active sites often constitute a small minority of the surface sites. 

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