Optimal surfactant/cosurfactant structures for microemulsion systems

摘要

This dissertation proposes optimized surfactant structures for consurfactant-free microemulsion systems for Enhanced Oil Recovery (EOR) processes. In addition, the dissertation shows the effect of ethylene oxide (EO) and propylene oxide (PO) moieties on the molecular areas and the interfacial tension behavior of molecules at the interface. Middle phase microemulsions play a major role in EOR processes, and the phase behavior of surfactant/brine/hydrocarbon systems is a key factor in interpreting the performance of oil recovery by low interfacial tension processes. In most surfactant formulations involving microemulsions, a cosurfactant is generally required in combination with a primary surfactant for several purposes. However, on a theoretical basis, a cosurfactant is not a necessary requirement for microemulsion formation. Surfactant structures have a significant effect on cosurfactant requirements of the system. After examining the phase behavior of several industrially feasible surfactants using temperature, salinity, cosurfactant concentrations, EO numbers, and PO numbers as variables, the following series of surfactants are found to form cosurfactant-free microemulsion systems at low temperatures with acceptable solubilization parameters: ethoxylated or propoxylated $Csb{14}$ Guerbet alcohol sulfates; and ethoxylated and/or propoxylated $Csb{13}$ alcohol sulfates. In addition, several industrial alcohols and isomerically pure alcohols, which have a general structure of $Csb4Hsb9 O(EO)sb{m}(PO)sb{n}H$, are examined for their cosurfactant properties. Two surfactants, $Csb{13}O (EO)sb2 (PO)sb2 SOsb3 Na$ and $Csb{13}O (PO)sb2 (EO)sb2 SOsb3 Na$, are also examined. Results show that the number and the sequence of EO and PO units significantly affect the molecular areas and the interfacial tension behavior of these molecules at the water/oil interface.