Characteristics and mechanism of rapid demulsification of highly stable oil-in-water emulsions at ambient temperature by functionalized metal-organic framework crystal materials

Achieving rapid demulsification of highly stable oil-in-water (O/W) emulsions with elevated water-to-oil ratios (＜100:1) at ambient temperatures poses a significant challenge in treating petroleum wastewater emulsions. Consequently, developing demulsifiers capable of lowering reaction temperatures, disrupting the oil-water phase equilibrium at high water-to-oil ratios, and exhibiting resistance to acids, alkalis, and salts is particularly crucial for addressing oil pollution issues in coastal regions. To address this objective, this study designed and synthesized a metal-organic framework crystal material-grafted hydroxypropyltrimethyl ammonium chloride chitosan (M-HACC) demulsifier, whose performance was subsequently evaluated. Results demonstrate that this demulsifier rapidly breaks high water-to-oil ratio (1000:1) emulsions at ambient temperature (30–35℃), achieving 99.0% demulsification efficiency within 30 min. For cationic CTAB-stabilized O/W emulsions, the efficiency reaches 99.0%. The demulsification efficiency of this demulsifier remains unaffected by acidic or alkaline conditions and high salinity. Within the pH range of 2–12, demulsification efficiency reaches 86.0 ± 4.0%, with optimal performance (99.0%) observed at pH = 7. Even at salinities ranging from 10 to 50 g/L, demulsification efficiency still achieves 95.0 ± 2.0%. Analysis of demulsification properties before and after grafting HACC indicates that M-HACC contains abundant oxygen-containing functional groups and positively charged moieties. At the oil-water interface, the emulsifying agent disrupts the interfacial film through hydrogen bonding and electrostatic attraction, ultimately achieving rapid demulsification and separation of highly stable O/W emulsions. The synthesized M-HACC demulsifier provides a rapid and effective solution to oil pollution in coastal waters.