Study on the low temperature fluidity of biodiesel blended oil by maleic anhydride polymers with different molecular structures

Abstract

ABSTRACT Adding pour point depressant (PPD) is one of the simple and high-efficiency methods to solve poor low-temperature flow performance of biodiesel-diesel blends, but the enhancing effect of polymeric PPDs is always influenced by the molecular structure. To explore the molecular structure-activity relationships, in this study, tetradecyl methacrylate-maleic anhydride (C14MC-MA), tetradecyl methacrylate-Itaconic anhydride (C14MC-IA) and tetradecyl methacrylate-citraconic anhydride (C14MC-CA) were synthesized and added into B20 (20 vol.% biodiesel +80 vol.% diesel). The enhancing effects of these different-structured copolymers on the low-temperature fluidity of B20 were compared. Results indicated that the enhancing effects of these copolymers were obviously affected by their molecular structure and polymerization ratios. The polar group imparted by acid anhydrides and the long side-chain alkyl group in methacrylic acid significantly enhanced the depressive effects, resulting in better fluidity at low temperatures for the synthesized polymers. Apart from the aldehyde group identical to that of MA, the methyl and methylene groups in CA and IA have considerable polarity and solubility, leading to an improvement of inhibition. Among that, C14MC-CA showed better enhancing effects on solid point (SP) and cold filter plugging point (CFPP) of B20 than that of C14MC-MA and C14MC-IA. When the dosage of C14MC-CA was 1000 ppm and the mole ratio was 9:1, the best depressive effect was achieved, and CFPP and SP were reduced by 12°C and 14°C, respectively. Also, the depressing mechanism of these copolymers on the eutectic reaction was studied by polarizing microscopy, differential scanning calorimetry and viscosity-temperature curves.