| Supercritical CO2 microemulsion is new scientific area that combines the supercritical CO2 and microemulsion. It not only has the advantages of green solvent, but alsogreatly expand the capacity of supercritical CO2 fluid dissolving high polar molecules and high molecular weight molecules. Since the microemulsion has special structure, which contains a nonpolar continuous CO2 phase, a polar core (typically water) and dynamic aggregates of surfactant molecules surrounding core dispersed in the continuous phase, it has many new features. Hence, the microemulsion technique was widely used in supercritical CO2 extraction, preparation of nanostructured materials and chemical reaction. In this paper, we study the supercritical CO2 microemulsion that contains no fluorine non-ionic hydrocarbon surfactant (LS-mn series?TMN-6?DYNOL-604) and investigate the structure regulation parameters that have great influence on microemulsion. Moreover, the molecular dynamics (MD) simulations were performed based on LS-36 system and LS-45 system. The MD simulations can expand the study to microscopic scale. The main work and results were as follows:1. A series of experiments to test the c?c and W0 of five commercially available nonionic hydrocarbon surfactants (LS-36, LS-45, LS-54, DYNOL-604 and TMN-6) at different conditions were performed. The results suggest that the structure of surfactant, which mainly contains the PO groups, EO groups and branched chain, plays an important role in determining the c?c. The surfactants with more hydrophilic groups, such as EO group and hydroxyl, tend to lead a higher c?c. The ability to load water of the surfactant/CO2 ternary systems is related to the categories and concentration of surfactants, the pressure and temperature required to stable the system are also involved.2. The study of Wo demonstrate that the solubility of surfactant in CO2 is in favour of reverse micelles to load water at lower pressure, while high surfactant concentration and the strong hydrogen bond between hydrophilic structure of surfactant and water can be dominant in determining the ability of the system for solubilizing water athigher pressure.3. Sample analysis was used in MD simulation to examine the relationship between computing time and concentrations of surfactant & water molecules. Many of the simulations were carried out at the conditions derived from the experimental data of Han's group. The results are in good agreement with the experimental data. The simulation results show that dynamic exchange between different molecular inside and outside of the microemulsion exist in all the computation time.4. The influence of factors on surfactant aggregation process was studied. The factors include:temperature, surfactant concentration, W0 and categories of surfactant. The radial distribution function was also used to test the radius of water droplet, and be mutually complementary to the sample analysis. The results indicate that the interaction forces between water molecules increase with the decreasing of temperature. The size of water core is also increase with the decreasing of temperature. It is also found that the microemulsion system with more water molecules can form larger water cluster and catch more surfactants.5. The solubilization properties of IL in scCO2 microemulsion based on LS-mn were investigated. The experimental results show that the LS-54 system has the strongest ability to dissolve the IL, and LS-36 is relatively weak under the same conditions.The solubility of IL in microemulsion system was enhanced with the increase of Wo. In addition, the amount of ethanol added to the system will reduce the cloud point pressure on the solubility of IL.6. The solubilization properties of AgNO3 in scCO2 microemulsion based on LS-36 were investigated. The experimental results show that the solubility of AgNO3 in microemulsion system was enhanced with the increase of W0. The increase of surfactant concentration has no effect on solubilization of AgNO3. |
PDF Full Text Request