Phase supercritical carbon dioxide

SCF cleaning alternative is especially useful for extremely sensitive and complex assemblies. At temperatures above 31°C and pressures above 73 bar, carbon dioxide transforms into a supercritical phase. Supercritical carbon dioxide reveals an extremely low surface tension. Consequently, the wetting of small gaps and complex assembly architectures can be achieved. However, the contamination that should be removed has to be nonpolar, and the compounds should be resistant to high pressures. Due to these basic limitations and the high costs of this cleaning process, this process does not play an important part in the electronic industry. 

Figure 25. SFC separation of some normal alkanes CnH2n+2, according to Maag [60] (capillary column stationary phase superbonded polymethylsiloxane (for details see [60]) mobile phase supercritical carbon dioxide, T = 371 K).

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

Figure 6.2 Influence of colunn internal diaeeter and stationary phase filn thickness on efficiency for open tubular colunns operated at 10 u with supercritical carbon dioxide under low density conditions as the nobile phase. (Reproduced with pemission from ref. 46 and 47. Copyright Dr Alfred Huethig Publishers).

Li S, Varadarajan GS and Stanley H. 1991. Solubilities of theobromine and caffeine in supercritical carbon dioxide correlation with density-based models. Fluid Phase Equilib 68 263-280. 

SAP supported-aqueous-phase scC02 supercritical carbon dioxide... 

Small stationary phase coated fiber exposed to sample, then transferred to inlet Inert gas bubbles through sample vaporized analytes collected on trap and desorbed into GC Supercritical carbon dioxide extracts analytes from liquid and solid samples... 

Brady et al. [52] have discussed pressure-temperature phase diagrams for carbon dioxide polychlorobiphenyls and examined the rate process of desorption from soils. Supercritical carbon dioxide was used to extract polychlorobiphenyls and DDT and Toxaphene from contaminated soils. 

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. 

Borch-Jensen, C., Staby, A. and Mollerup, J. M. Ind. Eng. Chem. Res. 33 (1994) 1574-1579. Phase equilibria of urea-fractioned fish oil fatty acid ethyl esters and supercritical carbon dioxide. 

They achieved fast separation of -blockers in less than 2 min on a short column using supercritical carbon dioxide modified with 20% ethanol and small amount of n-propylamine as the mobile phase. 

Keywords Supercritical carbon dioxide Solubility measurement Homogeneous catalysis Multi-phase catalysis Hydroformylation... 

Gong XY, Cao XJ. (2009) Measurement and correlation of solubility of artemisinin in supercritical carbon dioxide. Fluid Phase Equilibri 284 26-30. 

---