Surfactant-mediated demulsification: from waste oil processing to potential biomedical emulsion applications

Surfactant-mediated demulsification plays a critical role in diverse industrial and biomedical processes, from crude oil treatment to pharmaceutical emulsion formulation. This study investigates the demulsification performance of three high-hydrophilic – lipophilic balance (HLB) surfactants, such as Tergitol NP-9 (HLB = 12.9), sodium dodecyl sulfate (SDS, HLB = 12), and Tween-80 (HLB = 15) in separating water from waste lubricant oil emulsions. Two waste lubricant samples with distinct viscosities were treated with varying surfactant concentrations to evaluate water separation efficiency (WD%). In the lower-viscosity sample (Sample 1), NP-9 exhibited the highest WD% (91.1% at 275 ppm), followed by SDS (83.5% at 275 ppm) and Tween-80 (49.4% at 125 ppm). In the higher-viscosity sample (Sample 2), NP-9 and SDS efficiencies decreased (72.8% and 69.6%, respectively), whereas Tween-80 performance improved to 64.9%. NP-9 and SDS achieved near-maximum separation within minutes, while Tween-80 required prolonged retention times to hours. Thermal treatment (70 °C for 2 h) had minimal impact on NP-9 and SDS (2-13%) but markedly enhanced Tween-80’s demulsification efficiency (35-100%), suggesting temperature-dependent interfacial interactions. Although all surfactants achieved substantial water removal, the separated aqueous phase did not meet regulatory standards for direct discharge, highlighting the need for post-treatment.