Ionic liquid extraction with supercritical carbon

The products - mainly aldehydes and unreacted or isomerized alkene - are simply removed by decantation and filtration, extraction with the aid of an organic solvent immiscible with the ionic liquid or using supercritical carbon dioxide, and distillation. 

Supercritical fluids (e.g. supercritical carbon dioxide, scCCb) are regarded as benign alternatives to organic solvents and there are many examples of their use in chemical synthesis, but usually under homogeneous conditions without the need for other solvents. However, SCCO2 has been combined with ionic liquids for the hydroformylation of 1-octene [16]. Since ionic liquids have no vapour pressure and are essentially insoluble in SCCO2, the product can be extracted from the reaction using CO2 virtually uncontaminated by the rhodium catalyst. This process is not a true biphasic process, as the reaction is carried out in the ionic liquid and the supercritical phase is only added once reaction is complete. 

Use of supercritical fluid extraction (SFE), for a more effective separation of products from ILs Continuous bicycUc process of extraction of sulphur-containing aromatic compounds (SAs) from diesel fuel and gasoline with ionic liquids and reextraction of SAs from ILs with supercritical carbon dioxide (scCOj)... 

Supercritical carbon dioxide (scCOa) can be combined with ionic liquids providing an efficient, simple, and environmentally friendly separation method. For example, methanol is miscible with the ionic liquids and forms one phase. When this phase is saturated with scCOa, the formation of two phases could be observed and the upper phase contains most of the methanol. It should be noted that SCCO2 reduces the viscosity of ionic liquids and could facilitate mass transfer. The scCOa-philic, less polar products are easy to extract from reaction media. 

The most investigated binary ionic liquid systems are mixtures with carbon dioxide (CO2). In 1999, Blanchard et al showed that the solubility of CO2 in imidazolium-based ionic liquids is very high, however, CO2 is not able to dissolve any ionic liquid. Therefore, it was found possible to extract a solute from an ionic liquid using supercritical CO2 without any contamination by the ionic liquid. ... 

In 1999 Blanchard et al. reported a good solubility of carbon dioxide in l-butyl-3-methylimidazolium hexafluorophosphate at high pressures, while the ionic liquid did not dissolve in carbon dioxide. Therefore, supercritical carbon dioxide is suited to extract organic solutes from ionic liquids, and also continuous flow homogeneous catalysis in ionic liquids carbon dioxide systems is possible. First spectroscopic studies show that the anion dominates the interactions with carbon dioxide by Lewis acid-base interactions. However, the strength of carbon dioxide anion interactions did not correlate with carbon dioxide solubility. Thus, strong anion-carbon dioxide interactions were excluded as major cause for the carbon dioxide solubility in ionic liquids. Instead, a correlation of carbon dioxide solubility and the ionic liquid molar volume was observed. Additionally, a significant volume decrease of dissolved carbon dioxide was... 

Selective extraction of organic conqx>unds using green solvents is attractive from economic and environmental points of view. Carbon dioxide and water are two of the cheapest and most environmentally acceptable solvents on the earth. As explained in die introduction section, liquid and supercritical CO2 are able to dissolve non-polar or slighdy polar organic conqiounds. Water is an excellent solvent for ionic conqiounds because of its high dielectric constant (8 =78.5 at 25 °C) which decreases with increasing tenqierature due to the... 

Chapter 8 briefly introduced the concept of supercritical fluids in the context of undersea thermal vents. The supercritical point for water occurs at a temperature of 705°F (374°C) and a pressure of 222.3 bar (atmosphere). Above this temperature, no pressure can condense water to its liquid state. For carbon dioxide (CO2), the critical temperature (88.0°F or 31.1°C) and critical pressure (73.8 bar) are much lower. Above the supercritical point, CO2 behaves as a liquidlike gas liquidlike densities, gaslike viscosities. The solubility properties of supercritical CO2 are mnable by varying temperature and/or pressure. Density and dielectric constant increase with increasing pressure and decreasing temperature. Water and ionic substances are insoluble in supercritical CO2. The ability of supercritical CO2 to dissolve and extract relatively non-polar substances has been known for decades. The range may be extended by adding polar solvents such as methanol or acetone. The addition of surfactants helps to disperse microscopic particles to form colloidal suspensions. Carbon dioxide is nonflammable, nontoxic, and inexpensive. 

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