ABSTRACT
In its liquid or supercritical state, carbon dioxide (sc−CO2) represents a cheap (~$0.05 kg−1), nontoxic, nonflammable, and environmentally responsible alternative to conventional petrochemical and perchlorinated solvents. At 31.1°C and 73.8 bar, the critical point is readily accessible, and variation of solvent density with temperature and pressure offers a flexibility in solvent power that is not so readily achieved with normal solvents. Many low-molecular-weight and nonpolar materials are soluble in CO2, and it is already used routinely for various commercial processes including decaffeination of coffee [1], supercritical fluid chromatography [2], and as a reaction medium for synthetic
chemistry, e.g., synthesis of fluoropolymers [3]. However, weak intermolecular forces in CO2 result in very low solubility of polar materials and this has prevented its widespread application. Small molecules such as low-molecular-weight (low-MW) alcohols may be employed as entrainers to enhance solvent polarity and, therefore, solubility of polar entities, but success with this approach has been limited and the mechanism is not well understood.
