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Biodiesel Degradation

Biodiesel Degradation

Biodiesel is a transportation fuel alternative that has several distinct advantages over standard diesel (petro-diesel). It is usually synthesized by combining certain lipids, such as animal fat, with an alcohol. Biodiesel is made for use in standard diesel engines and can be blended with petro-diesel. Biodiesel use is on the increase and it has become a viable alternative fuel in many applications, both personal and industrial. By-products from biodiesel combustion are fewer and less polluting than those obtained from petro-diesel combustion, and the raw ingredients required to manufacture it are comparatively widespread and available to most nations with arable land.

The manifest benefits of using biodiesel fuel are many, however its intrinsic characteristics make it susceptible to natural degradation. Petro-diesel is not immune to degradation, but it does degrade at a slower rate. As it is derived from organic matter such as animals fats and vegetable oils, biodiesel will undergo oxidation when exposed to air. This degradation markedly influences its usefulness as a fuel and can lead to sediments which in turn may clog or impact the efficiency of an engine. Precautions to prevent or arrest the degradation need to be taken when storing biodiesel. Studies indicate that degradation of biodiesel exposed to air occurs far slower at temperatures between 4 and 20 degrees Celsius, and it can degrade at rates up to 40% quicker at higher temperatures.
Equally, care must be taken to ensure the fuel is stored in a container that will not facilitate degradation. Contact with metals such as copper, zinc, lead, tin and bronze will increase the rate of degradation through metal catalysed oxidation. Materials used to store petro-diesel will suffice to safely store biodiesel.

Similarly, biodiesel must be kept away from agents that might accelerate degradation. For this reason, biodiesel must be isolated from water to prevent degradation by hydrolysis. Moisture from air contact can be sufficient to contaminate the fuel. The fuel will dissolve water to a certain limit but further moisture will become “free water” and will be available to contaminate further fuel to pass through the storage vessel, or may rust the vessel or its associate parts. Free water may also encourage microbial growth. Like petro-diesel, biodiesel can degrade due to biological infestation and growth. Microbes may be introduced to the biodiesel via air contact. If certain conditions are present, namely the existence of nitrogen and water, microbes will continue to grow in the biodiesel and eventually cause it to breakdown. Ensuring minimal air and water contact will reduce microbial degradation. Anti-microbial additives are available and treatment with the appropriate classification of biocide will prevent microbial build-up.

Finally, studies have also shown that prolonged exposure to light can degrade biodiesel. Biodiesel exposed to 6 hours of light daily will have degraded 50% more after four weeks than biodiesel not exposed to light. Since the impact of most of the causes of biodiesel degradation increase directly with time, it is very important to store this type of fuel correctly and follow ASTM guidelines for shelf life. Currently, industry recommendations are to use biodiesel within six months of manufacture.

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