A new zwitterionic surfactant with high interfacial activity and high salt tolerance derived from methyl oleate through an eco-friendly aryl-introducing method

Surfactants, that can reduce the interfacial tension between crude oil and formation water to ultra-low, are needed in tertiary oil recovery. A bio-based zwitterionic surfactant, N-phenylpropanaldehyde epoxy acetal octadecanoicamido propyl-N, N-dimethyl hydroxy sulfonate (PADS), was derived from methyl oleate. In the process of synthesizing PADS, a new reactive site was introduced by epoxidizing methyl oleate and then the benzene ring was introduced by acetalization, which was a greener new method of introducing benzene ring into hydrophobic chains of surfactants. PADS was identified by ESI-MS and NMR, and its interfacial activity was measured by interfacial tensiometer. The results showed that PADS possessed excellent interfacial activity and potential for low-dose application. Under alkali-free conditions, it could reduce the interfacial tension between crude oil and simulated formation water to ultra-low in a wide concentration range (0.005–3 g/L). In addition, although the NaCl concentration was 230 g/L in the system, PADS still had good interfacial activity and could maintain ultra-low oil–water interfacial tension. The protocol of epoxidation and acetalization provides a new feasible path to preparing bio-based surfactants with high interfacial activity. Graphical