Effect of Pour Point Depressants Combined with Dispersants on the Cold Flow Properties of Biodiesel-Diesel Blends

Poor cold flow property is a major issue that hinders the application of biodiesel-diesel blends. In this work, a series of methacrylate-benzyl methacrylate-N-vinyl-2-pyrrolidone terpolymers (RMC-MB-NVP, R= C12, C14, C16, C18) was synthesized and used as the pour point depressants (PPDs) for waste cooking oil biodiesel blends. To further improve their depressive effects, dispersants, including Tween (40, 60, and 80), Span (40, 60, and 80), phthalic acid esters (PAEs), and fatty alcohol polyoxyethylene ether (FAPE; FAPE 5, FAPE 7, and FAPE 9), were optimized and combined with the C14MC-MB-NVP terpolymers. The effects of C14MC-MB-NVP terpolymers and combined PPDs (PPDC) on the cloud point (CP), cold filter-plugging point (CFPP), and pour point (PP) of biodiesel blends were studied. Here, results showed that the presence of dispersants can efficiently enhance the solubility and dispersibility of polymeric PPDs in biodiesel blends; thus, the PPDC presents better depressive effects. Among of them, C16MC-MB-NVP (5:1:1) combined with FAPE 7 dispersant at 4:1 mass ratio (PPDC-FAPE 7) showed the best synergistic effect, and the CP, CFPP, and PP of B20 treated with 2000 ppm PPDC-FAPE 7 decreased by 4, 10 and 19 °C, respectively. Moreover, differential scanning calorimetry, polarizing optical microscope and rheological analyses were performed to rationalize the action mechanism of these PPDs and dispersants in biodiesel blends.