THE INCORPORATION OF A FLUORINATED ETHER FUNCTIONALITY INTO A POLYMER OR SURFACTANT TO ENHANCE CO2-SOLUBILITY

A repeating fluorinated ether functional group, (hexafluoropropylene oxide)n, can enhance the solubility of compounds in dense carbon dioxide. A perfluorinated alkylpolyether which incorporates hexafluoropropylene oxide AS the repeating unit, F(CF3CFCF2O)nC2F5, forms the most CO2-soluble polymers observed to date. The liquid-liquid dew point locus at 295 K of a poly(hexafluoropropylene oxide) (MW = 13,000)/carbon dioxide system was found to increase steadily with polymer concentration over the 1 - 10 wt % range, reaching a saturation pressure of only 17 MPa at 10 wt %. CO2-soluble surfactants were also made by replacing the hydrocarbon carboxylate tails of CO2-insoluble surfactants with perfluoroalkylpolyether carboxylates. Nonionic surfactants, poly(hexafluoropropylene oxide) carboxylic acid (MW = 2,500) and hydroxyaluminum bis[poly(hexafluoropropylene oxide) carboxylate] (MW = 5,000), and an anionic surfactant, sodium poly(hexafluoropropylene oxide) carboxylate (MW = 2,500), exhibited complete miscibility with CO2 at 313 K at pressures above 16 MPa. Despite the high bulk viscosity of the polymeric fluorinated oil (7,000 mPa-s at 293 K) and the associative thickening potential of hydroxyaluminum disoaps, no increases in solution viscosity, relative to pure CO2, greater than 10% were detected.