Bio-based surfactants are increasingly important as an alternative to traditional petro-based surfactants owing to their renewable feedstocks and various applications in many industrial fields such as enhanced oil recovery (EOR). In this study, a new bio-based zwitterionic surfactant with strong interfacial activity at high temperature up to 120 °C was developed through the modification of the methyl oleate derived from renewable non-edible oils. The synthetic route was optimized to promote the conversion rate of quaternization by precisely controlling and timely monitoring the residues of intermediates, and the interfacial activity of the final product was greatly improved after the optimization. This work consolidated our hypothesis that the removal of the residual intermediates of amidation and promotion of the conversion rate of quaternization certainly contributed to enhancing the interfacial activity of the final product, and it will facilitate the design of a sustainable alternative to petro-based chemicals used in EOR.

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).

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