Preparation and controllable heavy oil viscosity reduction performance of pH-responsive star block copolymers

Abstract

In this study, a series of S-PHEDM star block copolymers of hydrophilic N-hydroxyethyl acrylamide (HEAm) and pH-responsive N,N-dimethylaminoethyl methacrylate (DMAEMA) were synthesized by reversible addition-fragment chain transfer (RAFT) copolymerization for the controllable viscosity reduction of heavy oil. The structures and average molecular weights of the star polymers were characterized by FT-IR spectra, 1H NMR spectra and GPC measurements. The aggregation behavior and oil/water interfacial properties of S-PHEDM were studied using DLS, TEM and IFT measurements in aqueous solutions with various pH values. The properties of heavy oil emulsions formed by S-PHEDM were monitored under different pH conditions using Turbiscan Lab measurements and optical microscopy at ambient temperature, and cyclic regulation of emulsion stability was successfully achieved through regular adjustments of pH values in oil/water mixing systems. Then, S-PHEDM was applied to the field of heavy oil viscosity reduction. Therein, S-PHEDM-2 achieved a degree of viscosity reduction of 99.88% at a dosage of 1000 mg·L−1 for heavy oil (ηapp, 50 °C = 85820 mPa·s) under alkaline conditions. The dehydration rate of the formed emulsion was 25.58% after standing for 1 h. When the heavy oil mixing system was adjusted to acidic, the heavy oil emulsion demulsified rapidly and achieved a dehydration rate of 90.7% within 1 h. The flexible transformation between viscosity reduction and oil–water separation for the heavy oil/water mixing system by adjusting the pH values provided a new idea to enhance efficiency and reduce costs during heavy oil recovery.