Considering the increasing demand for energy and the upward trend in oil prices, there has been a growing emphasis on the utilization of new compounds with higher efficiency for enhancing crude oil recovery in recent years. Accordingly, Gemini surface active ionic liquids (GSAILs) have emerged as effective surfactants with unique properties. Traditional anionic surfactants, like sodium dodecyl sulfate (SDS), have also been known with hight interfacial activity. This study investigates the simultaneous effects of a benzimidazolium cationic GSAIL, [C4benzim-C6-benzimC4][Br2], and SDS on the interfacial tension (IFT) reduction of crude oil–water system at temperature of 298.2 K. The results demonstrate remarkable synergistic effects of the mixture in reducing the IFT up to 97.6% compared to the linear contribution of surfactants. An ultra-low IFT of 0.16 mNˑm−1 was achieved with an optimum GSAIL mole fraction of 0.4 molˑdm−3, attributed to the attractive interaction between the cationic GSAIL and anionic SDS. This could be important in enhanced oil revcovery (EOR) from economic and environmental points of view.
