What is a Supercritical Fluid SCF

Technically, a SCF is a gas but not a vapor. The term gas refers to any phase which will conform in volume to the space available [9]. A vapor is defined as a gas whose temperature is less than the critical temperature [9]. This was the definition proposed by Thomas Andrews [12] in 1869 and is still generally, but not universally [10], accepted today. In practice, however, the terms gas and vapor are often used interchangeably. 

The conditions under which a compound is investigated are often described in terms of reduced temperature (7 ) and reduced pressure (pr), defined as the actual values of Tand p divided by and Pc, respectively (eqs 1.1-1 and 1.1-2). The law of corresponding states as introduced by van der Waals [14] implies that compounds behave similarly under the same values of the reduced variables. This allows valuable comparison of different compounds under various conditions, but deviations can be substantial in close proximity to the critical point. 

It is quite common to refer to the somewhat ill-defined region where such changes are noticable as the near-critical region. The synonym para-critical may be occasionally found in older literature. Technically, the near-critical region extends all around the critical point, but the expression is commonly used to refer to the nonsupercritical section only. The very similar expression compressible region refers to the area around the critical point in which the 

The possibility of using SCFs as tunable solvents not only for extraction (SFE) but also for chemical reactions (SFR) is one of the many interesting features associated with their application in modem synthesis. Before we discuss the many potential benefits in detail (Section 1.1.3), it seems appropriate to give a brief introduction to some practical aspects of the use of SCFs on a laboratory scale. 

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Why would you want to do supercritical fluid cleaning In fact, what is a supercritical fluid (SCF) Is it a supercold, mysterious fluid that physicists study What is it good for What can you dissolve in it organics, salts, particles, resins Why not just use water and add a little detergent These are some of the questions which have been discussed by authors in previous chapters and are reviewed in this chapter. 

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