Some Applications of Microemulsions

Systems in which one liquid phase is finely dispersed in another under the stabilizing influence of one or more additional components find applications in countless areas. As consumers, we encounter many of these every day. Floor waxes, shaving lotions, beverage concentrates, 

13 Two representations of a portion of the phase diagram for the water-benzene-potassium oleate-pentanol system. The unshaded regions represent homogenous solutions, (a) Redrawn, with permission, from S. Friberg and I. Burasczeska, Prog. Colloid Polym. Sci., 63, 1 (1978). (b) Redrawn, with permission, from C. U. Herrmann, U. Wurz, and M. Kahlweit, In Solution Chemistry of Surfactants, Vols. 1 and 2 (K. L. Mittal, Ed.), Plenum, New York, 1979. 

Numerous methods have been explored to recover at least some of this vast resource. Injection of oil-miscible fluids, gases under high pressure, and steam —either separately or in combination — have all been tried with various degrees of success. This is where microemulsions enter the picture. Under optimum conditions an aqueous surfactant solution — which may also contain cosurfactants, electrolytes, polymers, and so on —injected into an oil reservoir has the potential to solubilize the oil, effectively dispersing it as a microemulsion. 

It is apparent that extrapolating laboratory studies on microemulsions to oil recovery is a formidable task. While laboratory research is conducted with pure solutes, distilled water, and at constant temperature, these are meaningless in the field, where the following applies  

The oil itself is a complex mixture containing surface-active components. 

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Let us now discuss some applications of microemulsions in catalytic processes. It has been shown in [298] that the use of microemulsions instead of organic solvents for electrochemical reactions is advantageous from both economical and ecological reasons. The electrode/fluid interface in microemulsions probably consists of a dynamic layer of surfactant molecules packed more loosely on the electrode than in aqueous solutions. Microemulsions provide good yields of carbon-carbon addition products in reactions catalysed by cobalt complexes when preparing vitamin B 2. Excellent stereo-selective control in microemulsions made with the cationic surfactant cetyl trimethyl ammonium bromide was demonstrated for the catalytic cyclisation of 2-(4-bromobutyl)-2-cycIohexene-l-one to 1-decalone. Electrochemical synthesis may be a viable future approach to environmentally friendly chemical methods. 

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