Demulsification technology for process-level prevention of oily sludge: Performance study of polyether demulsifiers for polymer-containing produced fluids.

The treatment of produced water from enhanced oil recovery is hindered by the formation of hazardous, polymer-containing oily sludge caused by the electrostatic complexation between cationic reverse demulsifiers and residual partially hydrolyzed polyacrylamide (HPAM). To address this, we designed a series of nonionic polyether demulsifiers with controlled ethylene oxide (EO)-propylene oxide (PO) diblock and EO-PO-EO triblock architectures using tetraethylenepentamine as initiator. The optimized triblock demulsifier T3-H-2 reduces oil-water interfacial tension to 2.4 ± 0.1 mN/m at 1 mg/L and decreases the dilational modulus from 34.1 ± 1.3 to 16.2 ± 0.8 mN/m (at 0.1 Hz). Bottle tests confirm that T3-H-2 (300 mg/L) achieves 99.8 ± 2.5% water separation from water-in-oil emulsions within 90 min and an oil removal efficiency of 95.2 ± 3.8% from oil-in-water emulsions after 24 h. The nonionic polyethers operate via film disruption, not charge neutralization, avoiding HPAM complexation. This yields 91.5 ± 3.6% HPAM retention in the aqueous phase vs. 0.7 ± 0.1% with a cationic demulsifier. The retained HPAM is well-suited for recycling in the preparation of fresh polymer flooding fluids. This work provides a sustainable pathway for treating polymer-containing produced fluids, achieving efficient oil-water separation while preventing hazardous oil sludge formation during produced water treatment.