The existence of fine oil droplets that are difficult to coalesce greatly reduces the oil–water separation efficiency of alkali‒surfactant‒polymer (ASP) flooding-produced water. In order to improve the oil–water separation efficiency and promote the reinjection of ASP-produced water, a novel cationic graft copolymer CDC was obtained by ultrasonically assisted copolymerization of chitosan and dimethyl diallyl ammonium chloride under the initiation of cerium ions. The copolymer CDC was characterized by FT-IR, XRD, TGA and SEM, and it was confirmed that the grafting reaction proceeded successfully. The flocculation effect of copolymer CDC on ASP-produced water (Nan 4–8, pH = 7.83; Sanyuan-6, pH = 9.95) was investigated. Copolymer CDC has better oil removal rate (90.5%) and light transmittance (95.25%) to Nan 4–8 produced water compared with Sanyuan-6-produced water. It has a better oil removal effect when the initial pH of produced water is 6–7 and the temperature is 30 °C. After the addition of CDC, the large-diameter oil droplets in produced water will coalesce and separate. It may be that under weak acid or neutral conditions, the electrostatic attraction of produced water is enhanced, compressing the double electron layer of oil droplets, and destroying the stability of oil droplets. In addition, the hydrophobic effect of –CH=CH 2 in CDC molecules increases the hydrophobic association between molecules and increases the probability of oil droplet collision during the flocculation process.
The existence of fine-sized oil drops that are difficult to coalesce greatly decreases the separation efficiency of produced water from alkali, surfactant, and polymer flooding technology (ASP) containing oil-in-water emulsions. To improve oil–water separation efficiency, a silica-supported polyether polysiloxane quaternary ammonium (abbreviated as PPQA@SiO2) demulsifier was synthesized. The supported demulsifier possesses a rough surface structure and large surface area. In addition, it displays high thermal stability. It was applied for treating the produced water from ASP flooding. The effects of dosage, treatment temperature and treatment time on the oil removal efficiency from ASP produced water were investigated. Owing to the synergetic effect of demulsification and adsorption, the supported demulsifier exhibited an oil removal greater than 92% within 50 min at the initial oil concentration of 300 mg L−1, which is much higher than that of a commercial demulsifier SA001 (40.33%). Furthermore, the demulsification mechanism was explored from the perspective of the zeta potential, mean diameter and size distribution of the oil droplets. The high oil removal efficiency establishes PPQA@SiO2 as a promising candidate for oil–water separation from the ASP flooding produced wastewater.
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