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Biodiesel is an ester (more generally methyl ester) usually produced from vegetable oil. The use of vegetable oil as a vehicle fuel is not new. Rudolf Diesel, indeed, originally developed its engine by means of peanut oil.
Production pathways
Vegetable oils are obtained classically by simple pressing of oilseeds, such as rapeseeds, sunflower, soybeans, etc. Animal fats as well as waste cooking oil can also be used for this purpose. All of these oils, however, offer too much viscosity and a cetane number (the ability to auto-ignition) too low, making their direct use in traditional diesel engine difficult.
Figure : Biodiesel production process
In order to obtain similar characteristics with respect to conventional fossil diesel fuel, such vegetable oils must undergo a reaction of transesterification with an alcohol (usually methanol, CH3OH) in the presence of a catalyst, usually potassium hydroxide (KOH) or sodium (NaOH). It should be noted that the use of ethanol is also considered, but very rarely used on a commercial scale. The transesterification reaction is carried out at moderate temperature (20-80 °C) and atmospheric pressure. The above figure shows the schematic process of biodiesel production (source: Cropland Biodiesel).
The main biodiesel production pathways are described in more detail below.
Figure : Production of biodiesel from rapeseeds
Figure : Production of biodiesel from waste oil
Figure : Production of biodiesel from jatropha
Figure : Production of biodiesel from palm fruit
Figure : Production of biodiesel from soybeans
Figure : Production of biodiesel from sunflower
The production of biodiesel is relatively simple from a technical standpoint, which also allows the construction of small decentralized production units without excessive extra costs. Such a situation represents a definite advantage, thus limiting the transport of raw materials and permitting, in a transition phase, to start with modest-sized installations. This is particularly true in Switzerland, where the capacity of production facilities does not exceed 5 million litres per year.
Specifications of biodiesel (European Norm)
Since 1st January 2004, biodiesel marketed in the EU must conform to the European Norm EN 14214. As it stands, this standard limits (in practice) the use of biodiesel to the rapeseed methyl ester (RME). It should be reviewed in the coming months in order to open up the market to other vegetable oil methyl esters (EMHV).
See also ...
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