Preparation of acrylate-modified cationic flocculant by polymer reaction and its performance in treating oilfield-produced water

Introducing a lipophilic group into a cationic polymer flocculant can effectively improve the flocculation performance for treating oilfield-produced water. Copolymerization of acrylate and cationic monomers is the most commonly used method; however, the acrylate content in the copolymer is limited by its solubility in water. In this study, a polymer reaction method was proposed to introduce a suitable acrylate into a cationic polymer to improve flocculation performance. Acrylate was introduced into the copolymer (PDD) of methacryloyloxyethyltrimethylammonium chloride (DMC) and diallylamine (DAA) via the reaction between acrylate and the secondary amine in PDD. The effects of the acrylate type, amount of acrylate introduced, and reaction conditions on the flocculation performance of the product were investigated. The experimental results showed that the hydroxy-terminated acrylate-modified PDD exhibited considerably better performance than PDD, especially the hydroxyethyl acrylate (HEA)-modified PDD (PDD-HEA). When the dosage was 20 mg/L, the oil removal of PDD-HEA was 95.8 %, which was 1.5 times higher than that of PDD. The introduction of HEA can improve the ability of PDD to aggregate oil droplets, but it causes curling of the PDD molecular chain and weakens its bridging and flocculation ability. Therefore, a higher amount of HEA introduced does not necessarily lead to a better performance of the PDD-HEA. The most suitable modification degree of the structural units in PDD was 3.3 %. This study provides new insights into the synthesis and properties of hydrophobically modified cationic polymer flocculants and is helpful for the development of flocculants for oilfield-produced water treatment.