Table 1 (Taken from the US National Biodiesel Board)
A study made by the Environmental Protection Agency announced that long-term exposure to diesel exhaust increases the risk of lung cancer. The exhaust from biodiesel can reduce cancer-causing impurities by up to 90%.
Biodiesel comes from renewable sources, and is very environmentally friendly. A quote from the US National Biodiesel Board describes biodiesel as "more biodegradable than sugar and less toxic than table salt". Using biodiesel does not reduce fuel economy, and the fact that it is more lubricating, means it can increase the life of an engine. Biodiesel can be mixed with conventional diesel in any proportion, and adding the smallest amount can increase lubricity by as much as 65% (Journey to Forever website).
How is Biodiesel produced?
Biodiesel comes from a variety of sources, which can be classed in to two types: fresh and secondary. Fresh sources are those made from the oil that has come straight from the plant, where as secondary sources include waste oil that has been used for other purposes, for cooking in deep fat fryers, for example. It is also possible to use animal fats as a source, though only the process using vegetable oils will be discussed here.
Manufacture from fresh oil
The vegetable oil can come from various plants, such as rapeseed and soya beans. The oil can be extracted from the seeds or beans through pressing. Pure rapeseed oil will burn badly in a diesel engine because it contains fatty acids, which do not burn easily. To make the combustion process more efficient, the acids need to be converted in to more combustible forms, methyl and ethyl esters. This conversion process is known as transesterification. The following diagram taken from the Biodiesel in Europe paper, demonstrates the reactions quite well.
Figure 1: Outline of reactions
The esters are formed by reacting the fatty acids with an alcohol, such as methanol or ethanol used. Methanol is cheaper than ethanol, and is therefore preferred. Currently, most of the methanol produced comes from fossil-fuel sources, although ethanol can be produced naturally by fermenting sugar with yeast. The reaction is catalysed by acids or alkalis, although anhydrous sodium hydroxide is most frequently used.
The exact ratio of sodium hydroxide to oil is fairly crucial, too much sodium hydroxide and the reaction may proceed too far, and a soap like substance will be formed. Too little, and some of the fatty acids will remain un-neutralised. With fresh oil, the amount of fatty acids present will be fairly constant from batch to batch.
The methanol is mixed with the sodium hydroxide in an exothermic reaction to form sodium methoxide. This is added to the oil, whilst the mixture is constantly stirred. The reaction proceeds fairly quickly, with most of the reactants being used up within the first half an hour. The reaction products will consist of a solid glycerine phase (by-product) and a liquid biodiesel phase. The products should be left to settle for at least several hours before the biodiesel can be siphoned off.
Manufacture from Waste Oil
Using waste oil to produce biodiesel is slightly more complicated. The waste oil may contain water, and an unknown amount of fatty acids may have been produced when the oil was cooked. The present of water will cause problems with the sodium hydroxide and increase the likelihood that a soap like substance is formed. The water can be removed by heating the oil above 100 ºC and letting the water boil off. This must be done under constant stirring to prevent the formation of water pockets that may explode under the surface of the oil.
The correct amount of sodium hydroxide to be used can be determined from a simple titration. A sample of the oil is taken, and is titrated with a solution of sodium hydroxide. The amount of sodium hydroxide to neutralise the sample is found, which means the amount required to neutralise the full batch of oil can be calculated.
Once the biodiesel is formed from the waste oil, it may need to be washed to remove any traces of soap, glycerine or other impurities. This can be done by adding water, and stirring it thoroughly. The water is then allowed to settle out, and the biodiesel siphoned off again. This can be repeated until the biodiesel reaches a pH of 7.
Alternative methods of manufacture do exist, such as using concentrated sulphuric acid as a catalyst instead of the sodium hydroxide. This will, however, introduce sulphur-based compounds in to the biodiesel, and mean that the resulting mixture is acidic. The acid can be neutralised by adding a small amount of sodium hydroxide. This route has a smaller risk of producing soap, as shown in the reactions in Figure 1.
Methods using enzymes as catalysts are being investigated.
Marketing
The US National Biodiesel Board suggests that biodiesel is widely available in America. Distributors can be found in all fifty states, and there are even some biodiesel pumps spread throughout the country. Biodiesel can be bought either as pure biodiesel (B100) or as a pre-mixed blend, such as B20. For those who do not live near a pump, biodiesel can be delivered by the drum. Some of the major distributors are in fact petrochemical companies.
In the United Kingdom, biodiesel usage is effectively nil, until recently the tax was simply too high. The British Association for Bio Fuels and Oils (BABFO) have been rallying the government to get them to modify the tax on biodiesel so that it can appear competitive when sold at the pump. Before April 2002, one had to pay more tax on biodiesel than any other fuel, which would have been uneconomical. Biodiesel has only been affordable for a short period of time, meaning it has not yet established a market for itself. BABFO’s second objective is to get a plant built that can begin large-scale production of biodiesel for use in the UK.
Conversely, biodiesel production in the rest of Europe is looking quite optimistic. Countries including Italy, Germany and France are producing several hundred thousand tonnes a year. It appears that Britain is lagging behind the rest of Europe.
Economics and Future Potential
Until April 2002 the taxes on bio-diesel were about the same as for conventional diesel, which made the production and sale of biodiesel fairly uneconomical in the UK. According to the Ebony-Solutions website, diesel is probably the cheapest fuel being produced (before taxes), and therefore it will be difficult to get biodiesel to compete with it, especially since the cost of vegetable oil before processing can cost as much as conventional diesel. Some of the most recent developments in the UK have been the introduction of a few Biodiesel petrol stations. People can drop off waste cooking oil at these stations, in return for a discount on the price of biodiesel.
A further difficulty with the future mass-production of biodiesel arises from the quantities required. Biodiesel comes from plants, which require space and time to grow. A paper discussing the future of biodiesel in Europe has investigated the space available to grow rapeseed, one of the major sources for the oil used in production. The paper concluded that biodiesel production could account for 10-15% of today’s diesel consumption. Unfortunately the report does not say what area this covers, but one assumes it refers to diesel consumption in Europe. These figures would suggest that biodiesel production would never be able to fully replace conventional diesel, without alternative sources being found.
There may also be a degree of seasonality associated with the production of biodiesel. The plants producing the oil need time to grow, and will only be suitable for harvesting at a certain time of year. This could mean during parts of the year, plants producing biodiesel will not be operating. In some parts of the world, the yield obtained may be affected by bad weather or other such natural occurrences. Through modern farming techniques, such as the use of fertilisers and pesticides, the effects can be reduced.
Waste Disposal
As can be seen in Figure 1, the transesterification process has some undesired side reactions, and produces solid glycerine as a by-product. Glycerine has several uses in the production of commercial goods such as soap, foodstuffs and pharmaceuticals.
For countries that are producing biodiesel on a large scale, this injects several thousand tonnes of glycerine in to the market every year. This gives an excess amount of glycerine, meaning that there is nothing left to do but incinerate it. This, however, wastes what could be a useful substance. Germany is trying to avoid the excess production of glycerine by looking in to alternative methods of production of biodiesel.
Conclusion
The environmental benefits of using biodiesel certainly do make it appeal as an alternative fuel. Since there is very little difference between the performance of biodiesel compared to ordinary diesel, it may seem like the ideal replacement for fossil fuels has been found. Biodiesel is also much safer to handle, since its flash point is much higher than the petroleum based diesel. It is also non-toxic and biodegradable, meaning it has almost no impact on the environment.
The main problems arise with the economics of biodiesel production and the availability of resources. For it to be able to compete with conventional diesel, the costs of its manufacture must be significantly reduced, especially since petroleum diesel is one of the cheapest fuels available.
At the rate that diesel is currently being consumed, biodiesel will not be able to replace the ordinary diesel as a consumer fuel. There is simply not enough land available to grow the crops that are required to produce the oil needed to turn in to biodiesel. For this reason, another source for biodiesel has to be found. Alternatively, to make biodiesel the fuel of the future, a method of reducing its rate of consumption needs to be investigated.
References
European Union Website on a Vocational Training Programme,
US National Biodiesel Board Website,
Pacific Biodiesel Website,
Report on future of biodiesel in Europe,
Ebony solutions website,
UK home brewers website,
British Association of Bio-Fuels and Oils,
Canadian Renewable Fuels Association website,
Veggie Van website,
University of Idaho website,
University of Sheffield website,
Website connected to a pioneering expedition from Hong Kong to Cape Town,
