Progress in Supercritical CO2 Microemulsions with Hydrocarbon Surfactants

Supercritical CO2 (sc-CO2) is an attractive alternative to conventional solvents. Unfortunately, it is a poor solvent for high molecular weight and hydrophilic substances. One potential way to solve this problem is to solubilize these insoluble substances within microemulsions in sc-CO2. Hydrocarbon surfactants are very suitable to form microemulsions for industrial applications, as they are far less expensive and less toxic than fluorinated surfactants. A great many works have indicated that common hydrocarbon surfactants generally can not form microemulsions in sc-CO2, so the structure design of surfactants becomes necessary. In this work, the methods are introduced to study the formation, determination and evaluation of microemulsions in sc-CO2. The principles of designing hydrocarbon surfactants are reviewed, especially those based on the CO2-philic characteristic and the surface activity of surfactants. The effects of cosurfactants on the formation of microemulsions in sc-CO2 are described and the sc-CO2 microemulsions formed by common hydrocarbon surfactants with cosurfactants are reviewed. Finally, the effects of mixed surfactant, especially the hydrocarbon surfactants, on the formation of microemulsions in sc-CO2 are introduced.