Effects and mechanisms of novel multifunctional additives on critical biodiesel properties

• A Novel Multifunctional Additive for Pour Point, Corrosion and Oxidation Control. • POL-BHA lowers the biodiesel CFPP to below 0 °C, with a reduction of 7.5 °C. • The additive inhibits biodiesel crystal growth via feathery condensation mechanisms. This study developed a multifunctional additive through the ternary copolymerization of stearyl methacrylate, oleic acid, and itaconic anhydride, grafted with antioxidant functional groups butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and 3,5-di- tert -butyl-4-hydroxyphenylpropionic acid (DTBHA). Experimental results demonstrated that the POL-BHA (3:1:1) additive at 500 ppm exhibited the optimal pour point depression effect, reducing the cold filter plugging point (CFPP) of waste cooking oil biodiesel by 7.5 °C. At 500 ppm, POL-BHA (1:1:1) provided corrosion protection comparable to the monomeric BHA additive (copper sheet corrosion rating of Class 1b). Simultaneously, the additive significantly enhanced oxidative stability. At 2500 ppm, POL-BHA (1:1:1) extended the biodiesel oxidation induction period to 12.55 h. Using techniques including polarized optical microscopy, differential scanning calorimetry, and molecular dynamics simulations, this study revealed the pour point depression mechanism of the additive. The results indicate that the mechanism of action of this additive may involve selective adsorption on specific crystal planes, which inhibits unidirectional growth and promotes the formation of feather-like dendritic structures. In terms of antioxidant mechanisms, additives may achieve enhanced oxidative stability by relying on metal ion chelation; while in corrosion inhibition mechanisms, It is speculated that the mechanism reduces corrosivity by forming a dense molecular film on the metal surface. This work provides a comprehensive strategy for designing integrated additives, offering significant advancements in biodiesel quality enhancement and practical application.