Impact on Diesel Fuel Crystallization of Alkyl-Methacrylate—Maleic-Anhydride—Methacrylamide Terpolymers Used as Cold-Flow Improvers

Abstract

Alkyl-methacrylate—maleic-anhydride—methacrylamide terpolymers (MR₁—MA—MCNR₂) are some of the most widely used cold flow improvers (CFIs). The crystallization behavior of diesel fuel with added MR₁—MA—MCNR₂ must be studied in order to develop more efficient terpolymers MC₁₄—MA—MCNR₂ was synthesized by the reaction of tetradecyl methacrylate (MC₁₄), maleic anhydride (MA), and methacrylamide (MCNR₂). The diesel fuel was filtered in situ at its cold filter plugging point (CFPP) in a manual CFPP apparatus before and after adding MC₁₄—MA—MCNR₂. The influence of the amount of polymer additive on the system fluidity was studied. The results showed that the solidification point first decreased to –34°C and then increased sharply to –17°C whereas the CFPP changed from –2 to –5°C and then remained steady as the amount of additive was increased. The crystallization behavior of the diesel fuel was studied using differential scanning calorimetry (DSC), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The system enthalpy at first decreased as CFI was added to the diesel fuel and then began to increase as the amount of additive was increased further, showing that the liquid—solid phase transition was delayed whereas the crystallization started at a lower temperature than that for the base diesel fuel. The XRD pattern of the CFI confirmed the presence of complex crystalline particles with long-range order. TEM showed that addition of CFIs to diesel fuels caused fine crystals to grow unevenly and bind to each other. The wax crystals had different sizes because of a shortage of crystallization centers and binding of the particles. The CFIs acted through a eutectic mechanism.