Robust chitosan sponges for highly efficient aggregation-induced demulsification separation of emulsified oil from surfactant-polymer oily sewage

Removing emulsified oil from surfactant-polymer-flooding (SPF) oily sewage is a tough problem during oil field exploitation as the viscosity and emulsification degree of the oily sewage dramatically increased with the addition of surfactant and polymer in the recovery process. Herein, alkylated chitosan (CS-NaOH) sponges with uniform porous structure were prepared by freeze-drying and water bath heating in sodium hydroxide solution. With the superhydrophilicity and negative surface charges, the CS-NaOH sponges exhibited excellent SPF oily sewage separation performance by means of the aggregation-induced demulsification mechanism. Especially, the 3 wt% CS-NaOH sponges showed the SPF oily sewage separation performance with separation efficiency as high as 98.11% and separation flux up to 12,100 L·m⁻²·h⁻¹·bar⁻¹. Furthermore, the acetyl group in the chitosan molecule was converted to amino group through the deacetylation reaction triggered by alkalization, resulting in more intermolecular hydrogen bonds formed in CS-NaOH sponges. Therefore, the CS-NaOH sponges possessed extraordinary stability in comparison to the CS sponges without alkalization treatment, including ultrahigh compressibility, superior fatigue resistance and ranking chemical stability, which provided a guarantee for the subsequent long-term practical application.