DETAILED DESCRIPTION As used herein "stable" with regard to foams, dispersions and emulsions means the physical and functional properties of the fluid remain substantially unchanged for a period of time sufficient to permit the desired end use.
As used herein "fluid" refers to solutions, dispersions, emulsions, foams and microemulsions.
It is often difficult to characterize the exact physical state of a fluid while under pressure.
Solutions and microemulsions both appear to be homogeneous and clear, since the droplet or particle size of a microemulsion is too small to scatter light.
Emulsions and foams of fluids under pressure are often indistinguishable because they may not exhibit changes in Theological properties when converting from an emulsion to a foam (see for example Blauer, et al.
(Society of Petroleum Engineers, SPE paper 18214, 1988).
Blauer et al.
note that the fluid is in a foam state if the temperature is greater than the bubble point of the discontinuous phase, and in an emulsion state if less.
However, if the average fluid pressure is greater than the critical pressure of the discontinuous phase, there is no obvious change from liquid to gas.
As used herein the term "compressed fluid", with reference to carbon dioxide, means a supercritical fluid, a near-critical fluid, an expanded liquid or a highly compressed gas, depending on the temperature, pressure and composition.
See, for example, Supercritical Fluids, Encyclopedia of Chemical Technology, 4th Edition, John Wiley and Sons, N.
Y, vol.
23, pp.
453.
The compressed fluid carbon dioxide may be present in the supercritical, compressed gas, near-critical fluid, expanded liquid or liquid states and may be used to prepare the compositions of this invention.
If liquid CO.
sub.
2 is used in the compositions or processes of this invention, the temperature is preferably below about 31.
degree.
C.
If compressed gaseous CO.
sub.
2 is used, the pressure is preferably from about 20 to 75 bar (2 to 7.
6 MPa).
The CO.
sub.
2 may also be used in the supercritical state, i
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Liquid Purification 
