This term describes fuels of agricultural origin, in other words fuels of plant origin. It is a liquid fuel resulting from the transformation of non-fossil plant or animal matter. Biofuels were discovered at the beginning of the automobile era. Thus, the Ford T (1903-1926) used to run on ethanol and certain machine-tool motors ran on groundnut oil. There are several types of biofuel:
Those obtained from oilseeds (rape, sunflower) such as pure oil (direct product of seed pressing) immediately usable in traditional diesel engines, and methyl vegetable oil ester obtained as a result of the esterification reaction of the oil with methanol which is used as an additive or co-fuel with the diesel (between 5 and 30%) to form diester or biodiesel.
Those obtained from sugar fermentation (sacchariferous plants: Beets, sugar cane; starch-based plants: Potatoes, corn, wheat) into alcohol (methanol, ethanol). Certain alcohols are used pure to supply vehicle engines in Brazil. Alcohol can also react when refined with isobutylene to form ethers (ETBE: ethyl-tertiobutyl-ether and MTBE: Methyl-tertiary butyl-ether) that are mixed with gasolines.
These products improve combustion and reduce the emission of certain greenhouse gases. The vegetable oil derivatives contribute to better lubrication.
In France, 430,000 tons of biofuel were produced in France in 2004, of which 80% was biodiesel. Rape, beet and sunflower crops are harvested by approximately 400 co-operatives throughout the country. To increase the quantity of biocarburants used, the government needs to reduce inland duties on petroleum products.
Biofuels versus fossil hydrocarbons: Impact on the greenhouse effect
At the planetary scale, CO2, produced by the combustion of vegetal biomass, is without consequence on the global level of the gas emissions for purpose of greenhouse. The combustion of wood, straw, biofuels, or all other products resulting from biomass, only restore a CO2 mass that was already in atmosphere before being collected by photosynthesis. There is no addition because at the end of the lifetime, this CO2 mass is, in all the case, restored in the atmosphere.
On the contrary, the CO2 emitted by fossil matters combustion corresponds entirely to a massive destocking of carbon fossilized and accumulated in the terrestrial basements since million of years. Consequently, it corresponds to a CO2 addition in the atmosphere. Oil (more than 80 million barrels per day!) is the most significant example.
This is why, the biofuels use contributes to the reduction of gas emission for purpose of greenhouse.
The use of the biomass as a renewable energy has the advantage of being neutral from the point of view of CO2, contrary to the use of fossil matters (coal, oil, natural gas, uranium). Here are some explanations.
1st generation biofuels
1st generation biofuels are the biofuels currently available on market. They are mainly produced from:
- plants known as sugar (sugar canes, sugar beets) or starch-based plants (maize, corn) for bioethanol.
- oleaginous seeds for vegetal oils and the biodiesels.
The main drawback of this process is linked to the raw materials supply which is generally originally from dedicated cultures. Actually, more and more bioethanol manufacturing plants leave ground, consequently, the agricultural raw material demand increases. Thus, an appreciable increase concerning the cereals course was already noted in certain countries. This is all the more significant that the countries "large producers" of cereals are generally not the biofuels manufacturer countries (except the USA and Brazil). Moreover, this phenomenon is accentuated by the fact that the fuels industrial buys cereals at a price much higher than agribusiness. Therefore we can suppose that:
- the world level of cereals will reach very high costs.
- agribusiness will miss raw materials.
All things considered, we risk, in the near future, to have to choose between "eating" or "driving"!, consequently, there is an great interest to develop 2nd generation biofuels manufacturing processes, no longer manufactured from dedicated cultures but from agricultural or forest wastes.
2nd generation biofuels
This kind of process allows to produce bioethanol from wastes previously transformed into oil. This oil is next introduced into a gazeificator to produce crude gas which, next, must be refined in order to give a synthesis gas. To finish, the synthesis gas is transformed into bioethanol thanks to a traditional Fischer-Tropsch system.
A second kind of process of 2nd generation biofuels production is currently under development.
This way, known as "solid", allows the direct passage from the vegetal waste (or a “poor” coal) to a vegetal coal (or not) with high percentage of carbon.
In a second step, "rich" coal is transformed into synthesis gas, in only one step, by gasification at high temperature with hydrogen addition, in order to, the synthesis gas obtained, becomes a hydro fuel. This gas is then transformed into bioethanol thanks to a Fischer-Tropsch system and this, with a rate higher than in the process previously described.