Synthesis and evaluation of bifunctional polymeric agent for improving cold flow properties and oxidation stability of diesel-biodiesel blends

The widespread application of biodiesel-diesel blends is one of the main ways for renewable energy to substitute for fossil fuels. However, the application of biodiesel-diesel blends is limited by the poor cold flow properties and oxidation stability. Adding pour point depressants and antioxidants are cost-effective ways to solve the above problems, while these two additives have no synergistic effect. In this study, bifunctional copolymers were prepared for the first time to improve the cold flow properties and oxidation stability of biodiesel-diesel blends. The copolymers were synthesized from tetradecyl methacrylate, styrene and citric anhydride, and then the antioxidant 3,5-Di-Tert-Butyl-4-hydroxybenzyl alcohol was grafted onto the copolymers. Results indicated that the grafted copolymer exhibited better depressive effects on CP, CFPP and PP of blends, which were lower than that of the ungrafted copolymers by 1–2 °C, 2–6 °C and 3–6 °C respectively. At the same time, after adding the grafted copolymer, the induction period of B10, B20 and B30 was increased significantly by 13.1, 8.5 and 7.1 h respectively in the Rancimat assay, indicating that the oxidation stability has been greatly improved. Finally, a mechanism for crystallization behaviour of biodiesel-diesel blend was discussed.