Synthesis of Interface-Targeting Polyether Ester Demulsifiers and Investigation of the Mechanism of Rapid Demulsification of O/W Emulsions at Room Temperature

This study addresses the problems of strong temperature dependence, low demulsification efficiency, and long treatment time for oil-in-water (O/W) emulsions in the petroleum industry. Using polyethylene glycol/polyethylene glycol monomethyl ether (PEG/mPEG) as the hydrophilic polyether backbone, a novel amphiphilic polyether ester–amide demulsifier PEOSu-C18 was designed and synthesized by succinic acid esterification and terminal modification with octadecyl amide to introduce hydrophobic octadecyl-amide segments at polymer chain ends. The linear polyether-ester backbone supplies interfacial adsorption capacity, while terminal long-chain octadecyl hydrophobic segments provide effective interfacial displacement and hydrophobic interactions. Demulsifier dosage, temperature, time, and pH were systematically studied for oil-removal performance. PEOSu-C18 achieved an oil-removal efficiency above 98% within 30 min at a low dosage of 100 mg/L. It maintained excellent performance over a wide temperature range (30–60 °C) and possessed favorable salt tolerance, which can cut the energy and time costs of traditional demulsification. PEOSu-C18 was characterized via FTIR and 1H NMR. Its demulsification mechanism was explored by dynamic interfacial tension, Zeta-potential, and optical microscopy. Results reveal that PEOSu-C18 rapidly migrates to the oil–water interface, competes with and displaces negatively charged kaolinite particles through steric hindrance and hydrophobic interaction, breaks the rigid interfacial film, and accelerates oil-droplet coalescence. This work provides an efficient, rapid, and energy-saving demulsifier with promising prospects for complex oilfield-produced-fluid treatment.