Influence of Methacrylate-benzyl Methacrylate-N-vinyl-2-pyrrolidone as Pour Point Depression on Cold Flow Properties of Diesel Fuel

The addition of benzyl methacrylate–methacrylate copolymers to diesel significantly improves its cold flow properties, but it is always limited by a large dosage. To improve the depressing efficiency further, N-vinyl-2-pyrrolidone (NVP), as a polar nitrogenous compound, was introduced, and a series of methacrylate-benzyl methacrylate-N-vinyl-2-pyrrolidone terpolymers (R1MC-MB-NVP) was synthesized at different molar ratios (1:1:1, 5:1:1, 10:1:1, 15:1:1, and 20:1:1). Those terpolymers were characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), and thermogravimetric analysis (TGA). Their effects on the cold filter plugging point (CFPP) and solid point (SP) of diesel fuel were evaluated. With 2000 ppm of C14MC-MB-NVP (15:1:1), treated diesel has an improved depression on the solid point (SP) by 23 °C, whereas C16MC-MB-NVP (5:1:1) treated diesel indicates an improved reduction on the CFPP by 14 °C. However, combined PPDs (PPDC-6) of C14MC-MB-NVP (15:1:1) and C16MC- MB-NVP (5:1:1) in a mass ratio of 1:4 present the best depressing effects, and the SP and CFPP of diesel treated with 2000 ppm PPDC-6 are decreased by 29 and 15 °C, respectively. Furthermore, the action mechanism of PPDs was studied by polarizing optical microscopy, differential scanning calorimetry, and rheology analysis. Results showed that the introduction of NVP into PPDs not only improves the solubility and dispersity of wax crystals in diesel but also facilitates the formation of hydrogen bonds between PPDs and other polar substances and further disperses wax crystals into wax crystal molecules by the hydrogen bond ability.