Research On The Thermodynamic Characteristics Of Reverse Micelle In Supercritical Carbon Dioxide

A review has been accomplished for the advances in techniques with reverse micelle in supercritical carbon dioxide (SCCO2), including studies on surfactants soluble in SCCO2, methods used to research reverse micelle in SCCO2 and applications of the technology in various fields.A variable-volume high pressure view cell apparatus has been designed and built for measuring cloud points by visul observation, which can operate at temperature and pressure under 333.15K and 40MPa. Experimental cloud points were determined for the carboxylic acid form of perfluoropolyether (PFPE) and the ammonium carboxylate of perfluoropolyether (PFPE-NH4) in SCCO2. The research was carried at temperature 308.15K, 313.15K, 323.15K, 333.15K and the mass ratios of PFPE and PFPE-NH4 to CO2 was (0.42 -18.84) ×10-2and (1.20~20.23 ) × 10-2,respectively. Both polymers studied in this work exhibited a lower critical solution temperature (LCST) phase behavior in CO2. At a fixed mass ratio, the cloud point pressure (density) increased with temperature increasing. At a fixed temperature, the cloud point pressure (density) increased with mass ratios increasing at first then became constant when the mass ratio exceeded some special values. The constant of cloud point pressure was called upper critical soluble pressure (UCSP). The turning of mass ratios for PFPE and PFPE-NH4 are between (6.16-7.74) ×10-2and (9.32-11.68) ×10'2 respectively.The solubility of PFPE and PFPE-NH4 in pure CO2 were related by chemical association model. The average relative error for PFPE and PFPE-NH4 was 60.90% and 7.01% respectively, and the maximum of the relative error for PFPE and PFPE-NH4 is 376.02% and 41.67%. The chemical association model can be used to calculate the mass ratio before the turning.In addition, methyl orange was used as solvatochromic probe to prove the existence of a water domain in the supercritical carbon dioxide microemulsion formed by PFPE-NH4. It was proved that reverse micelle can not exist when W0 was less than 8.3 and was formed when W0 was 12.5. The maximum of W0 in the microemulsion formed by PFPE-NH4 was between 18.8 and 25. Temperature has little impact on the stable of the micelle.