Storage Stability of Biodiesel and Ultralow Sulfur Diesel Fuel Blends

A biodiesel storage stability study was conducted on ultralow sulfur diesel fuel (ULSDF) and three biodiesel basestocks (B100) and fuel blends (B2, B5, B10, and B20). The storage stability study consisted in measuring and monitoring the changes in acid number (AN, ASTM D664-04) and kinematic viscosity (ASTM D445) over 10 months with different samples stored at $5°C$⁠, $40°C$⁠, and cyclic thermal conditions. Among the three biodiesel base fuels (B100) studied, Bio1 (from tallow) and Bio2 (from yellow grease) showed the largest increase in AN throughout 6 months of storage at $40°C$ while Bio3 (from canola) showed the least increase in AN. Bio1, Bio2, and Bio3 samples stored at $5°C$ showed very little increases in acidity after 10 month, while samples stored under thermal cycling conditions were comparable to those stored at $40°C$⁠. The AN for ULSDF and all blends between B2 and B20 for Bio1, Bio2 and Bio3 remained in the range of $0.1–0.3mgKOHg−1$ for all temperatures and throughout the storage period well below the ASTM 6751 limit of $0.5mgKOHg−1$⁠. All blends showed a lower increase in AN than any of the base fuels. All fuels were submitted to accelerated oxidative testing, which also revealed a greater stability of the blends than for the biodiesel base fuels. Bio1 (from tallow) blends displayed a greater stability under accelerated oxidative testing while Bio2 (from yellow grease) displayed the least. The impact of storage conditions on the viscosities of all the base fuels and blends was negligible.