Brenda H. Hutton

Investigation of AOT reverse microemulsions in supercritical carbon dioxide

Abstract Bis(2-ethylhexyl) sodium sulphosuccinate (AOT) was successfully solubilised in supercritical carbon dioxide (scCO2), with ethanol or pentanol as co-solvent. Three molecular spectroscopic probes: methyl orange (MO), 8-hydroxy-1,3,6-pyrenetrisulphonic acid trisodium salt (HPTS), and riboflavin (RF) were used to examine the solubilisation characteristics of the water/scCO2 microemulsions formed with AOT. MO was extracted at various operating conditions, although the wavelength of its solvatochromic absorption maximum was not indicative of bulk water properties. Instead, the spectral results imply that MO may be located at the surfactant/water interface. The highly water-soluble dye HPTS was unable to be extracted into scCO2/AOT/water systems, suggesting that the water in the reverse micelle core was not as polar under supercritical conditions as those at ambient conditions. Finally, RF was extracted into the supercritical phase (40°C, 175 bar) with pentanol co-solvent, with an apparent enhanced uptake compared with the value at 40°C and ambient pressure in bulk water. This appears to be due to the presence of microcrystals dispersed in the supercritical phase.

AOT reverse microemulsions in scCO2 — a further investigation

Abstract The solubility of riboflavin (RF), potassium ferricyanide (K 3 Fe(CN) 6 ) and polar components from yeast extract (YX) in a sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) modified supercritical carbon dioxide (scCO 2 ) system was investigated. The results from RF solubility studies indicate that the microemulsion phase formed by AOT contains a polar core with an effective static dielectric constant of 20±5. Although this core is not indicative of bulk water, the overall improvement in polarity from pure scCO 2 is approximately a factor of 10. K 3 Fe(CN) 6 , a highly ionic compound, could not be solubilised into the modified supercritical fluid, indicating that the core was not sufficiently polar to dissolve highly ionic compounds. Finally, successful extraction of polar compounds from YX demonstrated the potential industrial applications of AOT-modified scCO 2 .