liquid fuels produced from biomass using biological (as opposed to geological) processes. The two most common types of biofuels are ethanol and biodiesel. Ethanol is usually derived from sugarcane and corn starch, while biodiesel is processed from vegetable oils (primarily palm oil) or animal fat.
Materials, such as wood and its byproducts, as well as waste and agricultural residue can also serve as a source of biofuels. There is a lot of ongoing research focused on looking for new sources for biofuels and improving existing and developing new techniques for their production.
The production process of biofuels
The basic steps for the production of ethanol at a large scale are:
- Microbial fermentation of sugars;
- Distillation (to use ethanol in car engines, most of the water has to be removed);
- Dehydration (three techniques to remove the final small percentage of water from the mixture to make it suitable for engine use) .
The production process of biodiesel is different and is called transesterification, a chemical reaction of lipids (vegetable oil or animal fats) with alcohol producing fatty acid esters .
A wide spectrum of sources and a range of processing techniques reflect the complexity of what is collectively called “biofuels”. The final products, ethanol or biodiesel, work exactly as other liquid fuels: both are primarily used to fuel cars, although they also have use in aviation and trains.
Ethanol is very popular in the US and in Brazil. Biodiesel is more popular in Europe for cars, while in North America it is mostly used to power trucks.
The biggest issue with the use of biofuels is their low efficiency compared to fossil fuels. Therefore, ethanol and biodiesel are frequently used as mix-ins and additives.
How does biofuel energy work?
Ethanol is approximately 30 per cent less efficient per unit of volume than gasoline, which means more pure ethanol is required to fuel the same mileage than gasoline. Furthermore, use of pure ethanol in engines is restricted to automobiles, lights-duty trucks and motorcycles and only when engines were specifically adapted for the use.
In most cases, however, ethanol is used in mixtures with gasoline. At gas stations, such mixed fuels are marked with an “E” sign followed by the percentage of ethanol in the mixture.
E70 would mean a mixture with seventy per cent of ethanol and thirty per cent of gasoline. Adding ethanol increases an octane number of the fuel, which is better for higher performance of combustion engines.
Mixtures E5-E20 are also called gasohol and do not require any adaptation of the engine . The higher the percentage of ethanol in the mix, the more modifications are required. An E85 mixture is commonly used in the US and Europe for flexible fuel vehicles.
Output of biodiesel is also lower than that of gasoline; however, it highly depends on the blend and quality of the fuel. Biodiesel comes is blends commonly referred under “B” sign followed by the percentage of biodiesel in the fuel mix.
Same as in case of ethanol, the lower the number – the less need there is for modifications of the engine. Use of pure biodiesel (B100) may lead to maintenance and performance problems in the long-run – although, in Europe, there are provisions to use B100 in agricultural engines .
Biodiesel is generally more common in the European Union than in the US. In Germany, there is even the lowest percentage of biodiesel in transport diesel fuels is set by law at 7 per cent .
Interesting facts about uses of biofuels
- Global ethanol production is expected to increase from ca. 114 Bln L in 2014 to 134.5 Bln L by 2024, according to FAO.
- United States and Brazil are the main producers and consumers of ethanol.
- Global biodiesel production is projected to increase by 27 per cent by 2024 from 2014 and expected to reach 39 Bln L.
- European Union is by far the largest producer and consumer of biodiesel, followed by Indonesia, the USA, and Brazil.
Biofuels are as old as car engines; however, low price and wide availability of fossil fuels over the twentieth century made them less competitive and reduced their share of the market. Currently, biofuels are considered to be an alternative energy source.