Bioenergy technologies are the processes and mechanisms that convert plant and animal matter into energy sources.
The processing technologies for biofuels depend on the kind of feedstock and the type of biofuel derived from it. Given the several types of biofuels and the large array of potential feedstocks, there are many technological processes and pathways that are used for biofuels production. Furthermore, since biofuels technology is an area of active research, new technologies are continually being developed and novel processes are likely to emerge in the future.
This page gives a summary of some of the main types of technological processes to produce biofuels and bioenergy, organized by biofuel and feedstock type.
Fermentation is used to convert sugars into ethanol. Ethanol can be produced from grain and lignocellulosic biomass.
For grain-based feedstocks, wet milling or dry milling is the first stage, followed by the addition of enzymes to the slurry in order to ferment the sugars. Up to a third of the original dry weight of the feedstock is released as carbon dioxide. A 10-12% solution of ethanol (“beer”) is produced, which is then concentrated through distillation and dehydration.
For lignocellulosic biomass, cellulose-to-ethanol technology is first used to convert (break down) cellulose into sugars, a process also known as saccharification. Methods for this stage include hydrolysis. This technology is still in the early stages of commercialization. From the sugars so produced, ethanol can be produced by fermentation as described above.
Biodiesel can be produced from oilseed crops and waste grease. Oil can be extracted from oil seeds by mechanical press extraction or solvent extraction. Vegetable oils can be used as a diesel fuel without further processing, but the fuel quality can be improved through the chemical process known as transesterification, which transforms natural oils into biodiesel. More details here.
Methanol, also known as wood alcohol, is produced from wood or agricultural residues by thermochemical conversion. The first stage is gasification, which produces a synthesis gas (carbon monoxide and methane) that has to be scrubbed to remove tars and methane). The gas is then condensed into liquid methanol by adding a catalyst.