Could new techniques for producing ethanol make old-fashioned trees the biofuel of the future?
MANKIND has used trees as a source of fuel for thousands of years. But now the notion of exploiting trees for fuel is being updated with a high-tech twist. The idea is to make ethanol, a biofuel that usually comes from maize (corn) or sugar cane, from trees instead. Politicians and environmentalists are embracing ethanol for a number of reasons. Unlike oil, ethanol is renewable: to make more of it, you grow more crops. And blending ethanol into ordinary petrol, or burning it directly in special "flex-fuel" engines, reduces greenhouse-gas emissions.
Why use trees, rather than maize or sugar cane, as a feedstock for ethanol? Because "treethanol" has the potential to be much more energy efficient. The ratio of the energy yielded by a given amount of ethanol to the energy needed to produce it is called the "energy balance". The energy balance for ethanol made from maize is the subject of much controversy, but America's energy department puts it at 1.3; in other words, the ethanol yields 30% more energy than was needed to produce it. For ethanol made from sugar cane in Brazil, the energy balance is 8.3, according to the International Energy Agency.
But for ethanol made from trees, grasses and other types of biomass which contain a lot of cellulose, the energy balance can be as high as 16, at least in theory. In practice the problem is that producing such "cellulosic" ethanol is much more difficult and expensive than producing it from other crops. But the science, technology and economics of treethanol are changing fast. Researchers are racing to develop ways to chip, ferment, distil and refine wood quickly and cheaply.
http://www.economist.com/displaystory.cfm?story_id=8766061
MANKIND has used trees as a source of fuel for thousands of years. But now the notion of exploiting trees for fuel is being updated with a high-tech twist. The idea is to make ethanol, a biofuel that usually comes from maize (corn) or sugar cane, from trees instead. Politicians and environmentalists are embracing ethanol for a number of reasons. Unlike oil, ethanol is renewable: to make more of it, you grow more crops. And blending ethanol into ordinary petrol, or burning it directly in special "flex-fuel" engines, reduces greenhouse-gas emissions.
Why use trees, rather than maize or sugar cane, as a feedstock for ethanol? Because "treethanol" has the potential to be much more energy efficient. The ratio of the energy yielded by a given amount of ethanol to the energy needed to produce it is called the "energy balance". The energy balance for ethanol made from maize is the subject of much controversy, but America's energy department puts it at 1.3; in other words, the ethanol yields 30% more energy than was needed to produce it. For ethanol made from sugar cane in Brazil, the energy balance is 8.3, according to the International Energy Agency.
But for ethanol made from trees, grasses and other types of biomass which contain a lot of cellulose, the energy balance can be as high as 16, at least in theory. In practice the problem is that producing such "cellulosic" ethanol is much more difficult and expensive than producing it from other crops. But the science, technology and economics of treethanol are changing fast. Researchers are racing to develop ways to chip, ferment, distil and refine wood quickly and cheaply.
http://www.economist.com/displaystory.cfm?story_id=8766061
