Highly Ca²⁺-Ion-Tolerant Biobased Zwitterionic Surfactant with High Interfacial Activity

Abstract

The wide application of surfactants has a harmful effect on the environment, drawing more attention to the development and application of low-toxicity surfactants. A salt-tolerant and low-toxicity biobased zwitterionic surfactant, N , N -dimethyl- N -[2-hydroxy-3-sulfo-propyl]- N -benzyloxyoctadecanoyl-1,3-propanediamine (SPBOPA), was prepared from the oleic acid extracted from waste oils and anise ether extracted from the tarragon. The final surfactant structure was confirmed using gas chromatography–mass spectrometry (GC–MS), liquid chromatography–mass spectrometry (LC–MS), and 1 H nuclear magnetic resonance (NMR) spectroscopy. The SPBOPA surfactant could reduce the interfacial tension between crude oil and formation brine to ultralow (5.2 × 10 –4 mN/m) at a low dosage without extra alkali. It still had good interfacial properties in NaCl up to 60 g/L, Ca 2+ up to 2000 mg/L, and temperature up to 100 °C. Furthermore, SPBOPA had strong antidilution and antiadsorption properties with low toxicity as demonstrated by the high LD 50 value of >5000 mg/kg·BW. It could also enhance the wetting ability of crude oil surfaces. Meanwhile, it showed a high biodegradability in the environment. All of the results achieved in this work confirmed that the SPBOPA surfactant is a more robust and promising biobased surfactant candidate than traditional surfactants as an eco-friendly surfactant for enhanced oil recovery (EOR).