Biodiesel has the potential to be an environmentally sustainable alternative fuel source for diesel engines. It is made by the transesterification of triglycerides, which are the main components in fats and oils. Transesterification is a chemical reaction which, in the case of biodiesel, leads to the long fatty acid chain being removed from the glycerol backbone of a triglyceride (fat) molecule and being replaced by an alkyl group from a short chain alcohol, such as methanol, as shown in Figure 1. This has historically been done with the aid of a dissolved or liquid catalyst, either an acid or a base. Unfortunately, this leads to increased wastewater production, as the catalyst must be washed out of the fuel before being neutralised. Additionally, the faster basic catalysts are extremely sensitive to both water and free fatty acids (FFA), resulting in the formation of soap from the latter. If these catalysts can be replaced with a solid, water and FFA tolerant catalyst, the production of biodiesel can be made much cleaner and more economical.
My project is focused on developing a solid catalyst anchored on a support structure, which will allow the catalyst to be fixed inside a reactor while the oil and methanol are pumped through it. The main aims for the catalyst are that it:
- Does not dissolve (leach) into the reaction mixture
- Stays active for a prolonged period of time
- Is tolerant of FFA and water
Previous work at the University had focused on a zinc-amino acid complex, but this was ultimately shown to leach. Thus, focus has shifted to catalysts that can be physically incorporated into a coating layer, such as a sol-gel. Currently, strontium oxide is being examined as a candidate, as it is a very effective catalyst when used as a powder.
About the author
Ben Firth is in the first year of his PhD, studying "Biodiesel production in fixed bed catalytic reactors". He is supervised by Prof Stan Kolaczkowski in the Department of Chemical Engineering.
Further reading
KNOTHE, G., VAN GERPEN, J. & KRAHL, J. 2005. The biodiesel handbook, Urbana, Ill., AOCS Press.
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