Fe3O4@SiO2 functionalized PEG-PPG-PEG triblock copolymer-grafted graphene oxide as novel magnetic nanodemulsifier for water-in-crude oil emulsion separation

The formation of water-in-crude oil emulsions during oil production and refining is a serious problem in oil industry. Chemical demulsification is a crucial and urgent treatment step for such emulsions. In this research, a novel magnetic nanodemulsifier (MND) has been synthesized by grafting graphene oxide nanosheets with poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) triblock copolymer functionalized Fe3O4@SiO2, and characterized by a range of spectroscopic techniques. The prepared MND has an SBET of 534 m2/g, Ms value of 25.05 emu/g, and a positive surface charge of 23.1 mV. Our novel MND has a water contact angle of 58° and oil contact angle of 76.6°, which classifies it as an amphiphilic nanodemulsifier. The measured dynamic IFT for blank water/oil emulsion is 60.5 mN/m, while it is reduced to 13.25 mN/m 600 s after adding MND. The MND can quickly demulsify water/oil emulsions with 100% demulsification rate at 1900 ppm dose, 80 ℃ demulsification temperature and 5 min settling time. The demulsifier is reusable for at least four cycles, can effectively demulsify water/oil emulsions at pH 2–6 with demulsification efficiency between 82.14 % and 99.3 %, and salt water/oil emulsions with 83.21 % and 94.46 % DE for 2000 and 4000 ppm salt content, respectively. A demulsification mechanism was proposed, which showed that the prepared MND could efficiently adsorb at the oil-water interface via hydrogen-bonding with water droplets along the triblock copolymer chains, while the high density and high surface area oleophilic graphene oxide nanosheets contribute to efficient dispersibility of the MND in the oil phase. The MND's spider-like architecture, nano-size, amphiphilic and magnetic properties, high density and high surface area work synergistically to facilitate dispersibility of the MND and promote fast demulsification.