Written by Rickdatech

Someone asked about copper and biodiesel again over on the infopop forum. It's a question that has gotten a lot of different answers over the years and one of those subjects where, "It works for me" is used repeatedly even when people post pictures of green biodiesel.

One of the ASTM tests for biodiesel is ASTM D130, The Copper Strip Corrosion test. It has been called a worthless test for biodiesel because all biodiesel passes it. When used on diesel, the test is an indication of sulfer in the diesel. Biodiesel does not normally have sulfur in it.

Copper forms an oxygen tight light green patina. We've all seen it on the roofs of banks, churches, and government buildings, the green roof. We can use copper for roofing even though it oxidizes quickly due to the fact that the "rust" or copper oxide that forms when it oxidizes is a protective coating that slows down and eventually stops the oxidation, making it perfect for roofs.

Some of us have a collection of biodiesel in jars. In one of my jars is some copper tubing. Where the tubing is below the biodiesel it's nice and shinny copper. Above the biodiesel, it's starting to turn green. There is also a green powder in the bottom of my jar, not to mention the biodiesel is green. This tells us that the protective green patina does not form on copper covered in biodiesel.

In a thread on infopop asking about the compatibility of copper and biodiesel. Kumar posted a link to a discussion about one of his customers. They had a home heating oil fired furnace and was using biodiesel. After a summer of inactivity, the fuel in the system was all green and smelled weird. The heating system used one of those pumps that sent the excess back to the tank, just like many diesel engines have a return line. When the furnace is 'on' it circulates the biodiesel through the copper lines between the furnace and the tank, providing for long term exposure and making green biodiesel.

On the side of "It works for me" is a large group of home brewers in the UK making biodiesel in copper tanks. They don't have any issues with green biodiesel at all.

So we have two sides to the penny, one reacting with biodiesel, and the other side not. If we take a look at the differences some facts stand out. The copper in my jar has been there a really long time, over a year. The guys making biodiesel in their copper tanks only have it in the tank a few hours by comparison, So the big difference is how long the biodiesel has been exposed to copper. Short durations, no problems, long term storage, big problem.

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