Storage risks from acidity of biofuels

With increased focus throughout the industry on alternatives to conventional fuels, Precision Polymer Engineering (PPE) makes this claim following a year long research project involving immersion of elastomer sealing materials commonly used in fuel handling in bioethanol and biodiesel fuel blends which resulted in swelling of the seals.

Biofuels are commonly classified into two main categories: bioethanol and biodiesel. Biodiesel blends are conventionally 5% biodiesel with 95% conventional oil based diesel. However, ASTM (American Society for Testing and Materials) specifications are now in place for a range of blends up to 20% biodiesel.

The results of 12 month immersion tests of a range of elastomer polymers showed that the seals are prone to significant swelling leading to seal failure in valves and other equipment. PPE says that the swelling is caused by increasing acidity of the biodiesel due to oxidation. Moreover, the presence of water contamination of the biodiesel was found to accelerate the rate of elastomer swelling.

The chemical nature of Biodiesel blends is said to be significantly different from that of 100%oil based fuel. The originating chemical structure generated from the biomass is that of a methyl ester. Over time and the inevitable exposure to atmospheric oxygen, biodiesel undergoes oxidation to produce carboxylic acids and lower the fuel’s pH.

The 12 month immersion tests by PPE showed that:

· Conventional elastomers suffer from significant swelling with biodiesel;

· Bisphenol-cured FKM elastomers which are prone to a reversal of the rubber curing process, should be replaced with peroxide-cured FKM for biofuel and biodiesel applications;

· The rate of swelling varies depending on the immersion conditions, for example aged fatty acid methyl ester is more aggressive than fresh fatty acid methyl ester.