Homogeneous extraction for sustainable separation of emulsified oily wastewater by using CO2 switchable solution

Recontamination or the difficult recovery of additives are the serious obstacle to separate emulsified oily wastewater, which may cause many health and ecological problems. Herein, the sustainable separation of emulsified oily wastewater was proposed by homogeneous extraction based on CO 2 switchable solution, where there was no pollution caused by additives. Here, CO 2 switchable solution is the bicarbonate solution that was prepared with the switchable solvent and water upon CO 2 . In terms of treating emulsified oily wastewater, the CO 2 switchable solution investigated exhibits the best effects on separating diesel oil or crude oil- emulsified wastewater, compared with flocculation and solvent extraction . Moreover, it was also applied in separating oily wastewater emulsified by hexadecyl ammonium bromide (CTAB) or emulsifier OP-10. After treated with CO 2 switchable solution [DMCHAH][HCO 3 ] (bicarbonate solution of N,N-Dimethylcyclohexylamine) upon N 2 /65 °C, the obvious oil-water phase separation was observed in oily wastewater. Then the oil was obtained and the [DMCHAH][HCO 3 ] was recovered after bubbling CO 2 into the oil phase. By detecting interface tension and microscopy images of oily wastewater, it is concluded that the separation of oily emulsified wastewater is caused by expansion behavior and the coalescence of emulsified oil droplets, which is induced by the reversible transformation from [DMCHAH][HCO 3 ] with hydrophilicity to DMCHA (N,N-Dimethylcyclohexylamine) with hydrophobicity . The sustainable treatment may provide a greener and economical approach for separating oil wastewater.