Oil aerated flocs formation assisted by a flocculant for heavy oil produced water treatment

Air flotation cyclone is a potentially efficient method to improve the treatment efficiency of heavy oil produced water in offshore fields. For its practical application, it is of great significance to develop a flocculant that can flocculate air bubbles and oil droplets together to form oil aerated flocs. In this paper, a novel flocculant capable of rapidly forming oil aerated flocs was prepared and the formation conditions and mechanism of oil aerated flocs were investigated. Firstly, copolymer (PDAMPE-NH) was synthesized by free radical solution copolymerization of N-(3-dimethylaminopropyl) methacrylamide (DPM), diallylamine (DAA) and block polyether macromonomer (PEP) as the monomers. Then, the molecular weight of PDAMPE-NH was increased by using polyethylene glycol diacrylate (PEG-DA) as a chain extender. Finally, the target flocculant DA was obtained by protonating the tertiary amine group in the copolymer with formic acid. The protonated tertiary amine group in DA can capture oil droplets, and the polyether group in DA can capture air bubbles. When the DA dosage was 500 mg/L and bubble size was in range of 20 μm to100 μm, the oil aerated flocs were formed, and the oil content of heavy oil produced water reduced from 7250 mg/L to less than 100 mg/L within 90 s. Microscopic observation found that there were three stages for oil aerated flocs formation and the formation of oil-coated bubbles was the key step. The reported results can provide a reference for the fast treatment of heavy oil produced water in offshore fields.