Phase Behavior Of Supercritical Carbon Dioxide Microemulsion

In this work, two series of equipments were established to do research on the supercritical fluids. One was for the study of phase behavior, of which a high-pressure volume-variable stainless steel view vessel was the key component. The other was an on-line UV-vis spectrum system, mainly consisting of a special high-pressure sample cell and an UV-vis spectrophotometer. Molecular spectroscopic probes could be used to examine the solubilization characteristics and mcrio-enviroment of the supercritical microemulsion. The quaternary supercritical mixtures of water/ethanol/scCO₂/AOT (the food-grade anionic surfactant Bis (2-ethylhexyl) sodium sulfosuccinate) were studied by measurements of the cloud points and the absorbance of MO as a molecular spectroscopic probe to examine the solubilization characteristics of the supercritical mixture and to confirm the formation of w/c microemulsion. The influences of various factors on the cloud point pressure were measured and discussed in a wide range of change (10⁴5℃, 6-23 MPa) in the supercritical mixture. The cloud-point measurements suggested that the formation of mircoemulsion was possibly dominant in the fluid with higher water content and at lower temperature, while the water preferred to be dissolved into the supercritical continuous phases at lower water content and at higher temperature. Ethanol worked as both co-solvent and co-surfactant in this supercritical fluid. Both of the cloud-point and absorbance measurements showed that when the concentration of ethanol was lower, the ethanol molecules mainly located in the continuous phases;and when it was higher, the ethanol molecules mainly acted as a co-surfactant to construct the water pool. In the both cases the ethanol enhanced the solubility of water. For the first time, the critical microemulsion concentration (cue) was determined to be 0.003⁰.004mol/L of AOT by both cloud-point and UV-Vis Spectroscopy measurements. The critical microemulsion concentration was not changed with temperature in the research temperature region, but it increased slightly with the concentration of water and ethanol.