General Aspects of Supercritical Fluids as Mass Separating Agents

1 General Aspects of Supercritical Fluids as Mass Separating Agents 

Separation processes with supercritical gases, called supercritical fluid extraction (SFE), is a group of separation processes that applies supercritical fluids (SCFs) as separating agents in the same way as other separation processes, such as liquid-liquid extraction or absorption, make use of liquid solvents. In these processes, the solvent is a supercritical component or a supercritical mixture of components [1-3]. 

SCFs may be used in the same way as other ordinary solvents taking into account their different properties and behaviors. Supercritical fluids can replace liquids solvents in many processes, such as extractions from solids (leaching), countercurrent multistage separations, chromatographic separations, and others, provided the solvent properties of the SCFs are adequate. 

SFE must be seen in comparison to separation processes which are well known, widely used, and sufficiently well understood. These processes comprise the various forms of distillation (rectification), evaporation, crystallization, liquid-liquid extraction, liquid-solid extraction, and stripping. SFE is used only if there are major advantages apparent at an early point of decision. 

In synthetic chemistry, SFE can be attractive as an alternative to conventional methods for purification of reaction products such as vitamins, pharmaceuticals and many other high-value products [4], Its technical use is currently mainly restricted to applications in food industry for extraction from natural products and in some cases for the fractionation of the products [5]. This chapter therefore focuses on these types of production and purification processes, but all the methodologies discussed may be readily adapted to synthetic applications. Equipment for carrying out separation processes of various sizes is available from coimnercial suppliers, and is described in more detail in Chapter 2.1 and elsewhere [1]. 

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