Practical Aspects of Reactions in Supercritical Fluids SFRs

2 Practical Aspects of Reactions in Supercritical Fluids (SFRs) 

Inorganic and organic compounds which are frequently used as SCFs are listed, together with leading references for their volumetric behavior, in Tables 1.1-1 and 1.1-2. The listed SCFs include those that are most commonly employed for syntheses and chemical reactions and they are compared in terms of critical parameters, physical properties and approximate cost. For critical parameters and volumetric data of other SCFs, the reader is referred to several reviews [22-26] and the series of contributions by the lUPAC Commission 1.2 on Thermodynamics, Subcommittee on Thermodynamic Data [27-33]. Even more detailed volumetric data for SCFs can be found in two excellent series of monographs the lUPAC Thermodynamic Tables Project [11,34-43] and the Thermodynamic Properties series by the National Standard Reference Data Service of the USSR [44-50]. 

The purity of the SCF is an important consideration in the planning of a synthesis. Low concentrations of impurities can have noticeable effects on the volumetric and phase behavior of SCFs. For example, helium can be present in commercial CO2 because it is sometimes added as a head-gas to ensure nearly-complete delivery of the cylinder contents and this has been found to affect the use of SCCO2 as a solvent for analytical and prepeu-ative purposes [51-53]. The He head-gas is unnecessary if a cooled pump is used for CO2 delivery. 

Purity can also have an effect on the cost of the SCF. The prices in Table 1.1.-1 are typical for research quantities with the purity closest to 99.99 % as of early 

However, for some materials, especially the higher hydrocarbons, the price is highly dependent on the purity and very high purities are prohibitively expensive. For these compounds the price is listed for 99.5 % purity the major contaminants are usually other hydrocarbons of similar molecular weight. 

---