Synthesis of chemical grafting pour point depressant EVAL-GO and its effect on the rheological properties of Daqing crude oil

The alkali-catalyzed alcoholysis of polyethylene vinyl acetate (EVA) was used to obtain the product ethylene-vinyl alcohol copolymer (EVAL), and the grafting product poly(ethylene-vinyl alcohol)-graphene oxide (EVAL-GO) was prepared in the form of chemical grafting by utilization of the groups on the surface of GO and EVAL through the esterification reaction. The products were analyzed by Fourier transform infrared (FTIR), 1 H nuclear magnetic resonance (NMR) and Thermogravimetric (TG). The rheological properties of the oil sample and changes in the morphology of wax crystals were characterized by Advanced Hybrid Rheometer and polarized optical microscopy (POM) respectively. The degree of alcoholysis of EVAL reached 74.51%, and the grafting rate of EVAL-GO (0.5%) was 36.18%. Reduction of pour point and gel point of nanocomposite treated crude oil was 12 °C and 4 °C from undoped crude oil at the optimum additive concentration of 1000 mg/kg. Moreover, it decreased the viscosity and yield value of virgin crude oil by 99.5% and 78.3%, respectively. From the morphological analysis, it was indicated that EVAL-GO could make the wax crystals form sphere-like crystals, and the increased void space promoting more liquid oil to be released thus significantly improving the low-temperature fluidity of Daqing waxy crude oil.