Magnetically recyclable polydopamine-polyquaternium modified Fe3O4 nanoparticles for demulsification of asphaltene-rich ASP flooding produced water

The asphaltene-rich alkaline-surfactant-polymer (ASP) flooding produced water has been identified with high interfacial stability and severe secondary emulsification, which poses great difficulties in its demulsification process. This leads to an urgent need to develop targeted and efficient demulsifiers. In this research, a novel polydopamine-polyquaternium modified Fe3O4 (PQA-PDA@Fe3O4) nanoparticle integrates the electrical neutralization, interfacial adsorption and magnetic aggregation functionalities was prepared to dispose this emulsion. Primarily, structural and surface properties of the PQA-PDA@Fe3O4 demulsifier were systemically characterized by a series of analytical techniques, which presents its core-shell, hydrophilic and positively charged characters. When employing PQA-PDA@Fe3O4 to treat the produced water that contained 500 mg/L emulsified oil, a demulsification efficiency of 90.5 % was achieved at 200 mg/L dosage. It was found that the PQA-PDA@Fe3O4 nanoparticles could coalesce the fine oil droplets into large and dense aggregates, as demonstrated by the raised fractal dimension values. By monitoring the interfacial properties (interfacial tension, zeta potential and interfacial film elastic modulus) variations, the demulsification mechanism was further explored. The PQA-PDA@Fe3O4 nanoparticle could spontaneously migrate to the oil/water interface and reassemble a loose interfacial film, thus leading the oil droplets destabilization and aggregation. Notably, the magnetic force between the PQA-PDA@Fe3O4 nanoparticles significantly accelerates the oil droplets aggregation and inhibits the secondary emulsification process, so as to achieve the outstanding demulsification efficiency. Moreover, this PQA-PDA@Fe3O4 nanoparticle exhibited acceptable magnetic recyclability. These results provided an effective and alternative protocol to demulsify the asphaltene-rich ASP flooding emulsions.