Depressive Effect of the PPDCs on Biodiesel Blends
To further improve the depressive effects of B20, four dispersants, namely, Span, Tween, PAEs, and FAPE are preferred and combined with C16MC-MB-NVP terpolymers as PPDCs. The ΔCP, ΔCFPP, and ΔPP of B20 treated with 2000 ppm PPDCs are shown in Fig 2.
As shown in Fig 2, the reduction effect of PPDCs on the CFPP and PP of the biodiesel blends is much better than that of a single PPD or dispersant. This finding indicates that dispersants can promote PPD to improve the dispersibility of wax crystals and increase the low temperature flowability of biodiesel. Unfortunately, not all PPDCs could show positive cooperative effect. The ∆CFPP and ∆PP of B20 range between 2~6 °C and 7~12 °C when using Tween and Span as dispersants, and between 3~10 °C and 12~19 °C when using PAEs and FAPE. In summary, PAEs and FAPE show better effects on improving the low-temperature performance of B20 than Tween and Span. Conversely, these dispersants have small and irregular effect on reducing CP. These experiments can be explained that although dispersants assist PPDs in dispersing the wax crystals and delay their growth time, however, most dispersants have no evident impact on the onset time of wax crystals. In particular, the ΔCP, ΔCFPP, and ΔPP of B20 treated with PPDC-DMP (4:1) are 4, 8 and 16 °C, respectively, at a dosage of 2000 ppm. In addition, the depressive effects of PPDC-FAPE 7 (4:1) are 4, 10 and 19 °C at the identical dosage. It can be explained that PAEs and FAPE act as wax growth arresters, and C16MC-MB-NVP acts as a nucleating agent. Their combination enhances the dispersibility of PPD to wax crystals. Thus, the wax crystals are more uniform and finely dispersed in the biodiesel blends, thereby improving the low-temperature performance of the fuel.