Ionic liquids and a commercial anionic surfactant in demulsifying crude oil in water emulsion

Crude oily wastewaters generate widely in industries and marine oil spill operations. Crude oily wastewaters contain stable oil in water emulsion (O/W), and their treatment has been challenging. Crude oil has toxic compounds for humans and the environment, and effective treatment requires meeting environmental regulations. This dissertation aimed to investigate effective and environmentally friendly demulsifiers (commercial anionic surfactant and ionic liquids) in demulsifying stable O/W emulsions. Firstly, the O/W emulsification process by ultrasonic homogenization was conducted to optimize the processing parameters and determine the required energy to generate stable emulsion, which is applicable for enhancing crude oil demulsification. The optimum condition to generate stable emulsion was at a power level of 76–80 W, sonication time of 16 min, water salinity of 15 g/L NaCl, and pH of 8.3, which required 60−70 kJ energy. Secondly, the commercial anionic surfactant showed high efficiency (99%) in demulsifying O/W emulsion at the concentration of 900 mg/L in a short shaking time (15 min) at room temperature (25 °C). It could reduce the total extractable petroleum hydrocarbons in the separated water to <10 mg/L without gravity separation and achieve promising demulsification performance at high salinity (36 g/L) and various fresh and weathered oil concentrations. Thirdly, ionic liquid with hydroxyl functional groups on the side chains effectively demulsified O/W emulsion (92%) stabilized by natural emulsifiers (e.g., asphaltenes) at a low concentration (25 mg/L) and room temperature without settling. Hence, the hydroxyl functional group is a suitable substitution for the alkyl group on the ionic liquids side chains to reduce ionic liquid toxicity. It was also found that its potency was highly affected by the emulsion type (stabilized by natural emulsifiers+Tween 20), in which demulsification efficiency reached 61% at the ionic liquid concentration of 50 mg/L and the demulsification temperature of 50 °C at 90 min gravity separation settling time. This indicated the synergistic interaction of natural emulsifiers and Tween 20 and the formation of thicker film at the oilwater interface, which affected the ionic liquid performance. Finally, comparing the performance of three ammonium-based ionic liquids with a distinct side chain (alkyl, ester, and amide) in demulsifying O/W emulsion, it was found that ionic liquid’s side chain and hydrophilicity greatly influenced their performance in the demulsifying O/W emulsion. Substitution of the hydrophobic alkyl group with the hydrophilic amide or ester groups to reduce ionic liquid toxicity improved the ionic liquid potency in the demulsifying emulsion. Ionic liquid with the amide group on the side chain resulted in the highest demulsification efficiency (94%) compared to ionic liquids with the ester (91%) and alkyl (88%) groups at the ionic liquid concentration of 25 mg/L and settling time of 15 min at room temperature, indicating the superiority of the amide group in the demulsifying O/W emulsion.