Several factors affecting the stability of biodiesel in standard accelerated tests

This study examined factors impacting the stability of biodiesel (B100) samples collected as part of a 2004 nationwide fuel quality survey in the United States. Biodiesel is significantly less stable than petroleum diesel, so an understanding of the chemical and environmental factors affecting its degradation is required. The survey included samples produced from soy, waste oils, and tallow. The 27 samples were assessed for stability using the ASTM D2274 test for insoluble formation and the OSI method (via Rancimat apparatus) for induction time. Additionally, the samples were characterized for fatty acid make up, relative antioxidant content, metals content, and total glycerin content (free glycerin plus glycerin bound as mono-, di-, and triglycerides). For the samples examined here the polyunsaturated content (or oxidizability) has the largest impact on both increasing insoluble formation and reducing induction time. However, the formation of insolubles is also measurably decreased by increasing relative antioxidant content and increased by increasing total glycerin content. The OSI or Rancimat induction time is also increased by increasing relative antioxidant content, as expected.