Storage Stability of Biodiesel and Biodiesel Blends

Abstract

The objectives of this work were to identify a practical accelerated oxidative stability test method and to define a reasonable, data-based, stability minimum requirement. The biodiesel (B100) samples show a broad distribution of stability on accelerated tests, with EN14112 induction time results ranging from less than 1 h to as much as 12 h and ASTM D2274 total insolubles ranging from less than 1 mg/100 mL to nearly 18 mg/100 mL. The accelerated test data indicate that if the B100 stability is above roughly a 3 h induction time, blends prepared from that B100 appear to be stable on the induction time and D2274 tests. The D4625 long-term storage results for B100 indicate that most biodiesel samples, regardless of initial induction time, will begin to oxidize immediately during storage. If induction time is near or below the 3 h limit, the B100 will most likely go out of specification for either stability or acid value within 4 months (4 weeks on the D4625 test). Even B100 with induction times longer than 7 h will be out of specification for oxidation stability at only 4 months, although these samples may not have shown a significant increase in acidity or in deposit formation. The 3 h B100 induction time limit appears to be adequate to prevent oxidative degradation for B5 blends in storage for up to 12 months and B20 blends for up to 4 months. The results indicate that B100 stability is the main factor that affects the stability of B5 and B20 blends, independent of diesel fuel aromatic content, sulfur level, or stability. Synthetic antioxidants were highly effective at preventing acid and insoluble formation during storage.