Supercritical fluid extraction phase diagram

Equilibrium phase diagrams for one or more solutes in supercritical CO2 and other solvents can be very complicated. Relatively little equilibrium information has been published this lack coupled with the cost of high-pressure equipment and the difficulties of scaleup have to date limited the commercial applications of supercritical fluid extraction. 

The third instrumental approach is the use of supercritical fluid extraction (SEE). A supercritical fluid is a substance at a temperature and pressure above the critical point for the substance. (You may want to review phase diagrams and the critical point on the phase diagram in your general chemistry text.) Supercritical fluids are more dense and viscous than the gas phase of the substance but not as dense and viscous as the hquid phase. The relatively high density (compared with the gas phase) of a supercritical fluid allows these fluids to dissolve nonvolatile organic molecules. Carbon dioxide, CO2, has a critical temperature of 31.3°C and a critical pressure of 72.9 atm this temperature and pressure are readily attainable, making supercritical CO2 easy to form. Supercritical CO2 dissolves many organic compormds, so it can replace a variety of common solvents supercritical... 

Both in Supercritical Fluid Extraction (SFE) and Supercritical Fluid Chromatography (SFC), solutes are quite often solids, as many natural products are. In these cases, the phase diagrams can be very complicated, since crystallization and fluid phase equilibria overlap. 

The properties and physical chemistry of liquid and supercritical carbon dioxide have been extensively reviewed (Kiran and Brennecke, 1992), as have many fundamentals and applications for separation, chromatography, and extraction (McHugh and Krukonis, 1994). The phase diagram for pure C02 is illustrated in Figure 1.1. Due to its relatively low critical point, C02 is frequently used in the supercritical state. Other common supercritical fluids require higher temperatures and pressures, such as water with Tc = 374.2 °C and Pc = 220.5 bar, while propane (Tc = 96.7 °C and Pc = 42.5 bar) and ethane (Tc = 32.2 °C and Pc = 48.8 bar) have lower critical pressures but are flammable (McHugh and Krukonis, 1994). 

PCB phase diagrams with carbon dioxide Effect of temperature and pressure on extraction of PCB and polyaromatic hydrocarbons Combination of solid-phase carbon trap with supercritical fluid chromatography for PCB, pesticides, polychlorodibenzo-p-dioxins and polychlorofurans... 

The use of inverse micelles and microemulsions of AOT in supercritical or near supercritical fluids as extractants for valuable hydrophilic substances such as proteins continues to develop. FT-IR studies of the pressure dependence of the water core structure in various parts of the phase diagrams of such systems have been described (89). 

PHASE EQUILIBRIA. A useful solvent for supercritical extraction, especially in food processing, is carbon dioxide, which has a critical point of 31.06 C and 73.8 bars (1070 Iby/in. ). The phase diagram for pure COj (Fig. 20.16) shows the equilibrium regions of solid, liquid, and gas and the conditions under which a supercritical fluid exists. In the supercritical region there is no distinction between liquid and gas and no phase transition from one to the other the supercritical fluid acts like a very dense gas or a light, mobile liquid. 

The extraction of thermodynamic data from phase diagrams together with an analysis of accuracy and precision is considered by Anderson and Chatterjee and this section is followed by a discussion of the properties of volatile phases. The properties of supercritical solutions are reviewed by Holloway, and this is followed by a chapter on metamorphic solutions by Eugster and a review of studies of fluid inclusions is given by Touret. 

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