Biodiesel is a renewable fuel processed by the transesterification of the fatty acid groups on the triglycerides found in vegetable oil, used cooking oil, or animal fats. Unlike ethanol-based fuels, which often can take the place of important food supplies, biodiesel precursors can come from waste products. Biodiesel can be used on its own, but is more commonly used as a blend with petroleum-based diesel in order to reduce fossil fuel consumption and greenhouse gas emissions. However, biodiesel is prone to eventual degradation to unsaturated aldehydes, short-chain carboxylic acids and networked polymers. In order to minimize these effects, antioxidants have been added to both prevent oxygen from interacting with the biodiesel and to inhibit the free-radical degradation of the ester tails. Most reports have indicated that the consumption kinetics of various antioxidants in biodiesel follows a first order reaction. We have found that in the case when there is an excess of a strong antioxidant added to a fairly oxidative-unstable biodiesel that zero-order (sometimes referred to as pseudo-zero order) kinetics is observed. We propose that in certain cases, a pseudo-zero order kinetics may be more reflective of actual antioxidant concentrations over time.
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