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Biofuels are produced from plants, which have a high energy value. There are two families of biofuels:
Those that can replace diesel (diesel car engines). They come from oleaginous plants (rich in oil), mainly rapeseed and sunflower. These biofuels are produced in two different forms:
-
pure vegetable oil, which has the disadvantages of being highly viscous and difficult to ignite in vehicle engines; this latter is a major problem for a diesel engine!
- EMHV (methylic ester of
vegetable
oil), also called diester, which is produced from the reaction of
vegetable
oil with methanol. Diester can be mixed with diesel in various proportions. It can even be used alone in a modified diesel engine (this is the case in Germany, Austria and Sweden).
Those that can replace petrol. They result from plants that are rich in sugar (sugar beet, sugar cane) or in starch (wheat, maize, potato). These plants produce alcohols by fermentation. Again, there are two types of biofuels:
- Ethanol alcohol itself, which can be
used mixed with petrol or even pure, on its own (but in that case
a specially adapted engine is necessary);
- A combination of ethanol and isobutene, a petroleum product from refineries. This fuel is ETBE (ethyl tertiary butyl ether).
MTBE (methyl tertiary butyl ether) also exists, but is made from methanol produced from oil. ETBE and MTBE can be mixed with petrol in different proportions. |
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| Shot of a rapeseed field. Diesel can contain up to 5% of vegetable oil ester, a derivative of rapeseed or sunflower. |
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| To cultivate, harvest, transport and transform these energy-rich plants requires the expenditure of energy
(fertilisers, agricultural machinery, trucks, treatment and transformation units). It is essential therefore to ensure that at the end of the day more energy is recovered than is consumed, otherwise … it’s not worth the bother! That is what is called an energy balance. It is different according to the type of plant.
In the following table, the “net production ratio” represents the relationship between the energy provided by the biofuel and the energy expended to produce it. |
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| Plant |
Type of biofuel |
Net production ratio |
| Rapeseed |
Diester |
2.1 to 3 |
| Rapeseed |
Oil |
3 to 4.7 |
| Sugar beet |
Ethanol |
1.4 to 1.8 |
| Wheat |
Ethanol |
1.15 on average |
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| The table shows that the energy balance for ethanol from sugar beet and above all from wheat is not extraordinary. It is a lot better for products produced from rapeseed. |
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| To reduce greenhouse gas emissions and to diversify energy sources, biofuels are being developed, composed of petrol and bioethanol, coming from the fermentation of sugars originating in cereals and plants with significant sugar content, such as sugar beet. |
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