Abstract: Three imidazole-based hydrophobic ionic liquids ([bmim]PF6, [hmim]PF6 and [omim]PF6) were synthesized using oil bath. The effects of extraction time, the amount of ionic liquids, pH value and the length of alkyl chain of the imidazole hydrophobic ionic liquids on the extraction of oilfield wastewater were investigated using these three ionic liquids. Test results showed that the extraction equilibrium could be reached within 20 min, good treating performance could be obtained at a wastewater to ionic liquid volume ratio of 5 and a wastewater pH value of 3 by using [bmim]PF6 ionic liquid. The treating performance was enhanced with the increase of the hydrophobic of the ionic liquid. [bmim]PF6 ionic liquid could be regenerated and reused for several times, the average COD removal rate of the regenerated ionic liquid was about 80%.

Key words: oilfield waste water, removal rate, ionic liquids