Synthesis of nano-hybrid polymethacrylate-carbon dots as pour point depressant and combined with ethylene-vinyl acetate resin to improve the cold flow properties of diesel fuels

The application of nanoparticles in terms of improving the cold flow properties of diesel fuels attracted more and more attention, and the composite technology of pour point depressant could further improve the cold flow properties of diesel fuels. A new type of nano-hybrid pour point depressant (PPD) was created in this study by copolymerising surface-modified carbon dots with tetradecyl methacrylate, which demonstrated good cold flow properties for diesel fuels (ΔSP = 21 °C, ΔCFPP = 9 °C). Besides, the ethylene-vinyl acetate (EVA) resin was also tested as a novel class of PPD to improve the cold flow properties of diesel fuels and exhibited excellent effect (ΔCFPP = 13 °C) on reducing the cold filter plugging point of diesel fuels. Thus, the combined technology of these two type of PPDs was used to further improve the cold flow properties of diesel fuels. The results indicated that the composite PPDs showed a great decrease in both solid point and cold filter plugging point of diesel fuels at a dose of 1500 ppm (ΔSP = 30 °C, ΔCFPP = 20 °C), which indicates better performance than achieved by either of them alone. In addition, polynomial and quadratic function fitting models are established to describe how the two main factors affect the cold flow properties of diesel fuels, and the fitting effects are well. In the end, using a differential scanning calorimeter, polarised optical microscope and rheological analysis, the paraffin crystallisation and morphology of wax crystals for diesel fuels before and after treatment with PPDs were studied, and the mechanism of heterogeneous nucleation and crystallisation of paraffin induced by PPD was proposed to explain the effects of nano-hybrid PPD, EVA resin and combined PPDs.