What is biodiesel?
Biodiesel consists of fatty acid methyl esters (FAME) created as the result of a reaction between an alcohol and oils/fats of vegetable or animal origin. Methanol (wood alcohol) is usually the alcohol of choice, but ethanol may also be used. The conversion process releases glycerine, a by-product of the biodiesel production process.
Biodiesel may be used both as a carbon neutral fuel in diesel engines, and as a biofuel oil. The European diesel standard, EN 590, generally permits adding up to 5% biodiesel, while a number of passenger cars, lorries and buses may run on 100% biodiesel with a few minor adjustments.
In principle, the structure of all oils/fats is the same, regardless of whether they are of vegetable or animal origin. They consist largely of triglycerides, and only the proportion of individual fatty acids differs. It is especially the content of unsaturated fatty acids in relation to the saturated fatty acids that is important for the product. As the following table shows, palm oil and animal fat contain almost the same level of unsaturated fatty acids, while the level is far higher in rapeseed oil and soy bean oil..
| Animal fat | Rapeseed oil | Palmoil | ||
| Palmitic acid (16:0) | 24 | 4 | 42 | |
| Palmitoleic acid (16:1) | 4 | 0 | 0 | |
| Stearic acid (18:0) | 16 | 2 | 40 | |
| Oleic acid (18:1) | 43 | 60 | 43 | |
| Linoleic acid (18:2) | 11 | 20 | 10 | |
| Lenolenic acid (18:3) | 1 | 10 | 0 | |
| Other | 1 | 4 | 1 |
A high level of unsaturated fatty acids lowers the congealing point, not just for the oil/fat, but also for the resulting FAME. This is particularly significant in connection with the use of pure biodiesel, while it is less important for admixtures.
Advantages of Biodiesel
Many studies also indicate that particle pollution is significantly reduced with the use of biodiesel, which is why it is used in urban buses in a number of large towns and cities, e.g. Graz in Austria. Biodiesel also provides cleaner combustion and good lubrication of the engine, where it can replace the standard additives.
In the event of environmental spills, biodiesel breaks down faster. Among other things, this reduces the risk of pollution from residential oil tanks. Biodiesel may, however, result in an increase in the emission of nitrogen oxides. The future use of biodiesel should therefore be considered in conjunction with various filter systems designed to reduce the amount of hazardous materials in car exhaust fumes.
In most countries, the use is driven by a mandatory requirement für admixture of biofuel to fossil fuel. The 2012 requirement is that 5.75% of biofuel must be added to fossil fuel (measured on the basis of energy content). As a result, companies now add 7% biodiesel and 5% ethanol to petrol (volume basis).
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