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Biodiesel Corrosion

With global oil reserves depleting and the fear of global warming looming over us, much work has gone into developing alternative fuel sources. One such energy source is bio‐fuels. There are two main types of bio‐fuel for transportation; bio‐ethanol, derived from sugar cane, as used in USA and Brazil, or bio‐diesel derived from vegetable oil. In 2008, biofuels provided 1.8% of the world’s transport fuel, while investment into biofuels production capacity exceeded $4 billion worldwide in 2007 and is continuing to grow.

In accordance with the European Directive – 2003/30/EC, diesel in the UK had to comprise of a minimum of 5% biofuels, with this figure rising to 7% in July 2010 and 10% by 2020 in accordance with 2009/28/EC. Failure to incorporate bio fuels at this government set level will lead to a substantial fine plus the loss of a duty benefit, therefore it is of huge economic importance to not only incorporate the biodiesel, but also to develop systems that do not corrode excessively in such environments. It is widely accepted that a blend of up to a 20% biodiesel can be incorporated into normal petroleum derived diesel with no, or minor modifications needed to diesel equipment. With these targets being set by government, it is of vital importance that the corrosive effect of storing up to 100% biodiesel at refineries be investigated. R-TECH sponsored an EngD to carry out this investigation, working with Valero oil Refinery in Pembroke Dock and the former Murco oil refinery in Milford Haven.

The project investigated the changes in chemistry of biodiesel in order to chart biodiesel corrosion over time and to determine the presence of any species created. Electrochemical methods (potentiodynamic and Scanning Vibrating Electrode Technique [SVET]) were used in order to determine the corrosive behaviour of both as received biodiesel and oxidised biodiesel. Furthermore microbiological species were cultivated in order to investigate if biodiesel was susceptible to microbiologically induced corrosion species.

The project found that corrosion of common oil refinery materials due to biodiesel is of little practical concern and if anything biodiesel acted as an inhibitor to corrosion.

SVET surface plots showing the difference in corrosion behaviour  of steel immersed in 3.5%NaCl on left, emulsion of biodiesel and 3.5% NaCl centre and emulsion of 3.5% NaCl and oxidised biodiesel on right.