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Storing Biodiesel Fuel

Many of our customers ask us, “How long can biodiesel be stored?’ As much as we would love to blurt out a simple number and be done with the question, truthfully, the answer may vary from days to years depending on storage conditions.

The truth is that all fuels will degrade over time. In fact, the EPA reports that ULSD diesel has a shelf life of between 3-6 months. Biodiesel, too, has a shelf life that can vary significantly, but with the proper fuel management, biodiesel's shelf life can be extended dramatically.

The biggest factors that affect biodiesel storage life include:

  1. Microbial contamination
  2. Chemical contamination
  3. Exposure to light
  4. Temperature
  5. Exposure to air
  6. The type of feedstock
  7. And the additives

If a sample of biodiesel (or petroleum diesel for that matter) is contaminated with a fast growing microbe, under favorable conditions, the rapid growth and multiplication of the organisms can render the fuel unusable within a matter of hours. To prevent this, always store biodiesel in clean airtight containers. The oxidative stabilizer sold on the Springboard Biodiesel website contains a biocide that will prevent the growth of known filter clogging microbes http://www.springboardbiodiesel.com/springboard-biodiesel-oxidative-stabilizer. If your fuel has already been attacked by a microbial outbreak, we recommend that you use a stronger biocide such as KILLEM.

Other than microbial attack, the other primary way that biodiesel fuel would “go bad” is through oxidative damage. Over time, oxygen can attack the chemical structure of the molecules of biodiesel. This typically occurs at the point in the carbon chain where there is a double bond between two of the carbon atoms. This oxidative attack results in acidic compounds being formed which makes the fuel acidic and can give it a rancid smell. As the oxidation progresses, the fuel becomes more viscous, more corrosive to components in the vehicles fuel system, and may even form sediments. There are many factors that can determine how long it takes for this process to occur to the point where the fuel becomes unusable. These factors include:

  1. Free oxygen content of the fuel: Many commercial biodiesel companies, store their biodiesel under pure nitrogen in order to prevent oxygen from being able to reach the fuel. The typical small scale producer can help to extend their fuel’s life by keeping in a sealed container with as little headspace as possible.
  2. Exposure to light: Sunlight is a powerful force that facilitates oxidation. Try taking a small sample of soy oil and putting it in direct sunlight and open air for a couple of days. You will find that it had turned into a rubbery plastic. This is due to polymers forming as the fuel is oxidized.
  3. Feedstock source: Try the same experiment with beef tallow (which has very few double bonds in comparison to soy oil) and you will see that it is much more stable.
  4. Temperature: The cooler the better. The seasoning process of cast iron cookware utilizes the tendency of oils to form polymers at high temperatures. You don’t want this to happen in your storage vessels.
  5. Chemical Contamination: The oxidation of the oils can be strongly catalyzed by the presence of trace metals, most notably, copper, iron, and zinc. Biodiesel is actually quite corrosive to copper and its alloys. Therefore it is important that plumbing, valves, and storage containers be free of copper, bronze, and brass.

There are several “stabilizers” on the market that effectively help slow the oxidation of the fuel. While there is no solution that can make the storage time indefinite, the oxidative stabilizer sold by Springboard Biodiesel is one of the most cost effective and efficient oxidative stabilizers on the market. For further information regarding the effect of the oxidative stabilizer on the storage life of biodiesel please refer to http://www.springboardbiodiesel.com/files/pdf/oxstabgraphs.pdf

As the previous points illustrate, there are many factors that can dramatically affect the storage life of biodiesel. If it is stored under optimum conditions in all of the above areas, the shelf life of biodiesel may reach a period of years. How well the fuel lasts in comparison to this optimum length largely depends on the care taken by the user and how well they are able to eliminate or mitigate the risk factors outlined above.