Synthesis and Evaluation of Terpolymers Consist of Methacrylates with Maleic Anhydride and Methacrylic Morpholine and Their Amine Compound as Pour Point Depressants in Diesel Fuels

Long-chain alkyl (i.e., tetradecyl, hexadecyl, and octodecyl) methacrylate (MC), maleic anhydride (MA), and methylamidemorpholine (MCNR2) were used in this study to prepare a series of MC–MA–MCNR2 terpolymers and their amine compounds (MC–MA–MCNR2–a) to obtain efficient pour point depressants (PPDs) for diesel fuel. The MC–MA–MCNR2 and MC–MA–MCNR2–a terpolymers were successfully synthesized and then characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR), and gel permeation chromatography (GPC). The effects of the addition of the PPDs on the solid point (SP) and cold filter plugging point (CFPP) of diesel fuel were also investigated. Furthermore, the interactions between the additives and wax crystals were elucidated through differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and rheological mechanics. Results indicate that all of the terpolymer PPDs significantly improved the performance of 0# diesel fuel samples at low temperature. PPDC2 displayed the best performance in decreasing the SP and CFPP of diesel fuel by 19 and 11 °C, respectively. In addition, DSC analysis showed that the terpolymer PPDs reduced the temperature of paraffin precipitation of diesel fuel. However, POM analysis showed that addition of the PPDs did not prevent wax precipitation completely but merely shifted the precipitation toward a lower temperature. Moreover, the addition of the terpolymer PPDs remarkably decreased the viscosity of diesel fuel.