Material Compatibility in Biodiesel Production

Material Compatibility in Biodiesel Production


A common question in the biodiesel industry is whether a specific material is compatible with biodiesel or the ingredients that are used making it. Some metals, particularly copper and zinc or their alloys (such as brass or bronze), degrade over a period. Aluminum is compatible with pure biodiesel; however, the compatibility has a D (severe defect) rating with caustic substances such as sodium or potassium hydroxide catalyst used to make biodiesel. Stainless steel is the preferred metal to be used in biodiesel processing plants. Rubber is mainly used as gasket material or hoses. Fluorinated gasket materials in the class of FKM like Viton® are desirable for use in end use application of biodiesel fuel. In fuel production, however, FKM gaskets are not chemically compatible with the reagents and processing conditions to make fuel. At the University of Idaho in the short term, fuel production FKM gasket materials in methanol have swelled in excess of 5% volume resulting in seal failure. We tested four gasket materials used in methanol, three times, on 2-inch diameter gaskets. We found that PTFE swelled the least in 24 hours in this experiment and FKM swelled the most in this experiment. Buna-N, Nitrile, and chemically resistant fluoroelastomer have been used successfully for a few months in our biodiesel lab without developing a leak. They do tend to swell over time and are not recommended for long term use. There are also commercial gaskets available that use PTFE with barium sulfate. They would be an excellent choice if higher compressive forces needed to be applied to the gasket. Read the full TechNote online at www.biodieseleducation.org

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