| Bio-fuels for Road Transport |
| Wednesday, 26 April 2006 | |
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Robert Skelton reviews the use of fuels derived from plants With concerns over carbon emissions, there is considerable pressure to increase use of bio-fuels across the EU, and a recent directive states that by 2010 at least 5.75% of road transport fuel should be of bio origin. Though the technology does exist to achieve this target much will depend on the level of subsidies, which at the moment vary widely across the EU. So what exactly are bio-fuels, and how are they used?
Use of bio-ethanol requires some modification of engine timing, though about 10% can be added to petrol without making alterations.With growing interest in the EU and USA some manufacturers, including Ford and Saab, now produce dual fuel vehicles which can run on petrol or bio-ethanol. A drop in sugar beet subsidies and increasing grain surpluses have kindled interest in the UK, and British Sugar have received planning permission to build the UK’s first bioethanol plant at Wissington, close to Kings’ Lynn. An alternative to bio-ethanol is biodiesel. The term bio-diesel is generally applied to methyl esters of naturally occurring glycerides in the form of vegetable oils. The product is often referred to as Fatty Acid Methyl Ester (FAME). This technology is not as mature as bio-ethanol, though there are a number of large-scale plants in Europe. Manufacture involves reacting vegetable oil with methanol in the presence of a suitable catalyst, usually sodium or potassium hydroxide.The product is the ester, with glycerol as a by-product. The two are separated and the ester is subjected to several purification steps. Provided that the product meets tight European standards it can be used without engine modification, though there may be seal problems with older engines and the ester attacks all forms of rubber. It also has detergent properties and will dislodge deposits in the fuel system resulting in filter blockage. Hence the use of 100% biodiesel is recommended only for new vehicles. Like bio-ethanol, bio-diesel is mostly only sold as a 5–10% blend. The Department of Chemical Engineering have developed a novel process for production of bio-diesel which has now been sold to a venture capital company. It is hoped to have a commercial plant operational by the end of 2006. www.cheng.cam.ac.uk/research/groups/ polymer/OFM/biodiesel.html Robert Skelton is a retired Senior Lecturer in the Department of Chemical Engineering |
There are two forms of bio-fuel for road transport, bio-ethanol which is a
petrol substitute/extender, and bio-diesel fuel. Bio-ethanol is the best established
technology and Brazil, which has the largest sugar cane crop in the world, has
been fuelling a high percentage of its road vehicles with bio-ethanol since
the 1980s. The fuel is produced from sugar cane using fermentation and distillation.
The processes are not dissimilar from those used to produce spirits for drinking,
though it is necessary to remove almost all water from the fuel. | < Prev | Next > |
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