Critical Microemulsion Concentration and Molar Ratio of Water-to-Surfactant of Supercritical CO2 Microemulsions with Commercial Nonionic Surfactants: Experiment and Molecular Dynamics Simulation

Abstract

The critical microemulsion concentration (cμc) and the molar ratio of water-to-surfactant (W0) of supercritical CO2 (scCO2) microemulsion that uses different nonionic hydrocarbon surfactants (LS-36, LS-45, LS-54, DYNOL-604, TMN-6) were examined at temperatures from 35 to 45 °C and pressures up to 19 MPa. The results show that the cμc mainly depends on the structure of the surfactant. The surfactant with more hydrophilic structure, such as the ethylene oxide (EO) group and hydroxyl, tends to produce a higher cμc. In addition, the cμc increases with the increase of the ratio of ethylene oxide (EO) group number to the propylene oxide (PO) group number of the surfactant. The capacity of the microemulsion system to dissolve water, which is characterized by W0, is related to the concentration and structure of surfactant. It is found that a higher solubility of surfactant in CO2 favors the system to dissolve water at lower pressure. At higher pressure, the stronger hydrophilicity of surfactant and the higher sur...