Interfacial tension and the behavior of microemulsions and macroemulsions of water and carbon dioxide with a branched hydrocarbon nonionic surfactant |
| |
Authors: | Xi Chen Quoc P Nguyen Keith P Johnston |
| |
Affiliation: | a Department of Chemical Engineering, University of Texas, Austin, TX 78712, United States b Department of Petroleum and Geosystems Engineering, University of Texas, Austin, TX 78712, United States c The Dow Chemical Company, Freeport, TX 77541, United States |
| |
Abstract: | Measurements of interfacial tensions for 2-ethyl-hexanol-(propylene oxide)∼4.5-(ethylene oxide)∼8 (2EH-PO4.5-EO8) at the planar water-CO2 interface and the surfactant distribution coefficient are utilized to explain microemulsion and macroemulsion phase behavior from 24 to 60 °C and 6.9 to 27.6 MPa. A CO2 captive bubble technique has been developed to measure the interfacial tension γ at a known surfactant concentration in the aqueous phase, with rapid equilibration at the water-CO2 interface. The surface pressure (γo − γ) decreases modestly with density at constant temperature as CO2 solvates the surfactant tails more effectively, but changes little with temperature at constant density. The area per surfactant at the CO2-water interface determined from the Gibbs adsorption equation decreases from 250 A2/molecule at 24 °C and 6.9 MPa, to 200 A2/molecule at 27.6 MPa. It was approximately twofold larger than that at the water-air interface, given the much smaller γo driving force for surfactant adsorption. For systems with added NaCl, γ decreases with salinity at low CO2 densities as the surfactant partitions from water towards the W-C interface. At high densities, salt drives the surfactant from the W-C interface to CO2 and raises γ. Compared with most hydrocarbon surfactants, this dual tail surfactant is unusually CO2-philic in that it partitions primarily into the CO2 phase versus the water phase at CO2 densities above 0.8 g/ml, and produces γ values below 1 mN/m. With this small γ, a middle phase microemulsion and a C/W microemulsion were formed at low temperatures and high CO2 densities, whereas macroemulsions were formed at other conditions. |
| |
Keywords: | Microemulsions Emulsions Interfacial tension Surfactant |
本文献已被 ScienceDirect 等数据库收录! |
|