Extraction of Organic Compounds from Ionic Liquids using Supercritical Fluids

Extraction of Organic Compounds from Ionic Liquids using Supercritical Fluids 

For viability as a means of separation it is important that the desirable phase behavior in IL-CO2 systems does not become disrupted by a third component representing the solute. Blanchard and Brennecke [15] performed a systematic study on the recovery of organic solutes from [BMIM][PF6] with SCCO2 and demonstrated the 

At higher IL concentrations it is not possible to induce a liquid-liquid separation by the addition of CO2, i.e., no LCEP is observed [17]. This complex phase behavior has certain implications for the use of these biphasic systems as reaction/separation media. If large concentrations of reactants and products are present, relative to the IL itself, an additional liquid phase might occur. A liquid-liquid phase split may then be detrimental in homogeneously catalyzed reactions, introducing additional mass-transport limitations. 

High concentrations of CO2 in the IL may enhance the solubility of reactant gases and this may explain, at least partly, observations that the presence of CO2 appears to overcome mass-transport limitations [25], The solubility of hydrogen as a reactant gas in ILs has been determined in the presence of compressed CO2 very recently [26], Indeed, a remarkable increase in concentration of the hydrogen at constant H2 partial pressure has been observed with increasing CO2 pressure. These data could be correlated with an increase in hydrogenation efEciency for the iridium-catalyzed asymmetric hydrogenation of imines. 

In general, however, the effect of different gas solubilities in different ILs on reaction rates is stiU difEcult to predict. 

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