Higher Solvency Azeotropes and Mixtures

The low solvency of PFCs for most nonhalogenated materials has traditionally limited their applicahility. However, the formation of PFC/hydrocarhon (HC) azeotropes and PFC/HC mixtures has improved the solvency and subsequently enhanced the applicability of PFCs in numerous industrial processes. 

One azeotropic mixture is currently available for evaluation in experimental quantities. The azeotrope L-12862 is composed of 90 wt % PFC and 10 wt % 2,2,4-trimethylpentane. The physical properties of this material are given in Table 

This azeotrope exhibits improved hydrocarbon solubility characteristics and retains the excellent halogenated solubility characteristics of PFCs. Because an azeotrope maintains identical vapor and liquid composition at its boiling point, it will act as a single substance, facilitating its recovery via distillation and containment via condensation.  

When more organic solvent power is needed, nonazeotropic mixtures of PFCs and HCs are also available. They are formulated to take advantage of the inerting ability of the PFCs and therefore do not have flash points. Although most hydrocarbons do not exhibit appreciable solubility in PFCs, numerous useful PFC/HC combinations do exist. Some PFC/HC mixtures exhibit complete miscibility and are thus limited only by flash points and flammability. To develop a mixture, the HC solvent(s) can be selected to provide the required solvency properties and substrate compatibility, then an appropriate PFC inerting solvent can be selected. Table 6.6 lists PFC/HC mixtures that have no flash point at the indicated concentrations. Some of these mixtures, or their recipes, are being offered on an experimental basis for evaluation purposes. 

Although these materials do not have flash points using standard ASTM test procedures, it is possible that they have flammable limits in air. For example, L-12862 has no flash point, but it does become flanunable in air between concentrations of 2.7 and 11.5 vol %. Several common materials exhibit this type of behavior. 1,1,2 Trichloroethylene does not have a flash point and is shipped as a nonflanunable material, but shows flammability limits between 12.5 

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