Water-Diesel Microemulsions Stabilized by an Anionic Extended Surfactant and a Cationic Hydrotrope

Abstract

Alcohol-free microemulsions were formulated using mixtures of extended surfactant (C_12-14-PO₁₄-EO₂SO₄Na), sodium dodecyl benzene sulfonic acid and cationic hydrotropes with equal amounts of water and diesel. The cationic hydrotropes had short hydrocarbon or propylene oxide chain. The formulation included sodium carbonate to convert naphthenic acids in diesel to soaps. The phase behavior at ambient temperature of oil-free mixtures as a function of NaCl concentration was investigated. Visual inspection as well as cross polarizers were used to detect anisotropy. The microemulsion fish phase diagram and solubilization ratios for diesel and brine in the middle phases were determined. The minimum surfactant concentration needed to initiate middle phase formation was 0.10 wt%.

Salinity scans revealed that optimal salinity can be adjusted according to the hydrophilic/lipophilic nature of the hydrotrope used. Interfacial tension measurements using a spinning drop tensiometer showed a minimum value of 0.0015 mN/m between middle phase microemulsion and excess brine and a value of 0.032 mN/m between diesel and brine.

Keywords:

• Cationic and anionic surfactants
• extended surfactant
• middle phase microemulsions
• ultra low interfacial tension

Acknowledgments

The authors would like to thank George Smith and his group (Huntsman Corporation, Houston, Texas) for kindly providing the extended surfactant samples, and Peter Schwab, Evonic Goldschmidt, Germany, for providing us with Variquat samples.

Financial support from the Swedish Research Council is gratefully acknowledged.