Results and Discussion
Fuel Properties of BWCO and Biodiesel Blends
Table S4 shows the percentage of FAME in BWCO. As a consequence, BWCO contained higher levels of saturated fatty acid methyl esters (38.42 wt.%) that resulted in its poor cold flow properties.
The fuel properties of biodiesel blends (B20, B40, B60, and B80) are listed in Table 2. As shown in Table 2, various indicators of biodiesel blends are better than BWCO. Among them, the kinematic viscosity, acid value, and flash point of the blends comply with ASTM D7467. However, when the proportion of biodiesel with high acid value in the blends increases (B60 and B80), the acid value of the biodiesel blends becomes outside the standard range. It is worth mentioning that B20 has the best low-temperature performance, and CP, CFPP, and PP are -2, -4 and -14 °C, respectively. With the increase in BWCO content, the cold flow properties of the blends gradually deteriorate probably because BWCO contains more high melting point unsaturated fatty acid esters. Since the n-alkanes in diesel have a lower melting point, when the proportion of diesel in blends increases, wax crystals are formed at a lower temperature. Therefore, B20 has better cold flow properties than other biodiesel blends.
Depressive Effect of RMC-MB-NVP Terpolymers on Biodiesel Blends
The CP, CFPP, and PP of B20 are -2, -4 and -14 °C, respectively. The reduction in CP (ΔCP), CFPP (ΔCFPP), and PP (ΔPP) of B20 treated with 1000, 2000, and 3000 ppm RMC-MB-NVP (R=12, 14, 16, 18) are shown in Fig 1, and that of B20 treated with 500, 1500, and 2500 ppm RMC-MB-NVP are presented in Fig S4. The decrease in CP is the smallest compared with ΔPP and ΔCFPP under the same conditions.
Fig 1 (e, f) shows that RMC-MB-NVP terpolymers exert higher ΔCFPP and ΔPP at the dosage of 2000 ppm. At this dosage, the n-alkyl chain length and monomer molar ratio of terpolymers have important effects on the low-temperature performance of biodiesel blends. When the terpolymers have different monomer proportions, with decreasing ratio of the NVP monomer, the depressing effect initially increases and then decreases. When the monomer molar ratio of the terpolymer is 5:1:1, ΔCFPP have the best reducing effect because the appropriate NVP ratio can increase the solubility of the terpolymer, thereby improving the low-temperature fluidity of biodiesel. When the terpolymers have different side carbon chain lengths, with increasing carbon number in the side chain alkane, the depression effect reveals a trend of initially increasing and then decreasing. C16MC-MB-NVP terpolymers have the best depressing effect, which can be attributed to the influence of the length of the n-alkyl side chain on CFPP and PP in PPDs. In these experiments, C16MC-MB-NVP (5:1:1) presented the greatest reduction on the CP, CFPP, and PP of B20 (2, 4 and 9 °C). Thus, 2000 ppm C16MC-MB-NVP (5:1:1) has the best depressing effect, and B20 has optimal performance compared with other biodiesel blends.