Biodiesel (Fatty Acid Methyl Ester / FAME)
Biodiesel – also called fatty acid methyl ester (FAME) – is a biofuel produced by transesterification of vegetable oils. In principle, biodiesel is suitable for the operation of diesel engines.
Biodiesel is mainly produced in Europe by the transesterification of rapeseed oil with methanol, which is why biodiesel is also called rape oil methyl ester (RME). Fatty acid methyl ester, which is made from recycled fats or oils, is also sometimes abbreviated as AME. In principle, a wide variety of fats can be used for the preparation of FAME, but in practice the limiting values of some parameters such as low-temperature properties, oxidation stability and carbon residue restrict the possible range of raw materials.
Biodiesel has a much lower viscosity than untreated vegetable oil, which facilitates its use. The oil and fat molecules contained in vegetable oil are fatty acids. In transesterification, the vegetable oil reacts with about 10 vol.% methanol. In addition, a catalyst (e.g. sodium hydroxide or potassium hydroxide) is added at a temperature of 50°C to 80°C. About 0.5 vol.% to 1 vol.% of the quantity of oil used is needed.
The lubricity of biodiesel in engines is higher than that of fossil diesel fuel, so biogenic fuel can reduce wear and tear. The energy content per liter is low compared to fossil diesel fuel, which can lead to a volumetric increase in consumption of up to 5%.
The production of biodiesel involves a high technical and energetic input. Methanol is needed, which at least so far generally comes from fossil sources; however, in future methanol from biomass could also be used. The glycerin generated as a by-product creates a credit in the energy balance sheet, because if it is then put to material use, it does not have to be produced elsewhere.
The requirements for the fuel quality of biodiesel are set out in the European-wide EN 14214 standard, which determines numerous parameters such as density, viscosity, ignition quality and the maximum ash or water content. In Germany, DIN EN 14214 was anchored in law by including it in the 10th BImSchV (Federal Emissions Protection Act).
FAME has similar properties to fossil diesel fuel, which is why it is fundamentally suitable for admixture. But pure biodiesel can also be used in diesel vehicles. However, not all vehicles are able to use pure biodiesel because it can attack plastic and rubber components in the engine, such as gaskets and fuel lines, as well as non-ferrous metals such as copper and brass, and zinc in the fuel system. Therefore, before fuelling with pure biodiesel, motorists should always ensure that the vehicle manufacturer has given explicit approval for this. Details can be found in the user manual or obtained from the dealer or manufacturer.
As a pure fuel, biodiesel has been relegated to a shadowy existence in Germany: In 2014, only 4,800 tons of biodiesel were consumed as a pure fuel, while diesel consumption was at 36,000,000 tons. At the end of the last decade, this was a different story, as there was a significantly reduced oil tax rate for pure biodiesel – however, this was increasingly equalized. DIN EN 590 provides for an addition of biodiesel – in accordance with DIN EN 14214 – to diesel fuel up to a maximum content of 7 vol.% (B7). Various laws in other European countries continue to allow its consumption as a pure fuel (e.g. Austria), as some tax exemptions ensure its competitiveness.
Status: December 2015
All information subject to change. Errors and omissions excepted.