High-efficiency purification of alkali-surfactant-polymer flooding produced water by ultrasonication-ionic liquids combination: Performance and separation mechanism

Abstract

Alkali-surfactant-polymer (ASP) flooding produced water exhibits high emulsification, high viscosity, and low interfacial tension of emulsified oil. This type of oilfield wastewater poses numerous challenges, including difficulties in oil–water separation, turbidity removal during purification, and unqualified reinjection treatment indicators. In this study, molecular dynamics simulations were used to analyze the high stability of ASP flooding produced water. A novel method for ultrasonic-assisted ionic liquid treatment of ASP flooding produced water is proposed. Short-time ultrasonic treatment was utilized to destabilize the oil–water interface and create favorable conditions for ionic liquid purification. After 4 min of ultrasonic treatment, the addition of 340 mg·L^-1 of [C₁₆MIm]Br or [C₁₆MIm]Cl to simulated produced water achieved turbidity removal efficiencies of 98.9 % and 98.6 %, and oil removal efficiencies of 97.9 % and 97.4 %, respectively. The flocs and suspended substances in the treated water were analyzed through instrumental characterization. From a microscopic perspective, the purification mechanism was elucidated, revealing that the synergistic effect of ultrasonic-assisted ionic liquid demulsifier and flocculation is the key to achieving effective purification. Meanwhile, the preliminary ultrasonic treatment can reduce the dosage of ionic liquid by 10 %, which has high economic benefits. This study provides unique ideas and solutions for the advancement of treatment technology for highly emulsified oily wastewater, especially ASP flooding produced water, and has important reference significance for the research on the purification mechanism of ultrasonic-assisted ionic liquids.