Chemical and biological engineering: One for the road

From The Economist print edition

A new biofuel made from fruit sugars promises more oomph than traditional ethanol

REPLACING carbon-rich fossil fuels with more environmentally friendly alternatives should slow global warming. As part of that drive, both America and Europe have embraced biofuels—liquids derived from plants that can be used to power cars and other vehicles. By their very nature, biofuels cannot be carbon-free because carbon is essential to life on Earth. Burning biofuels does indeed release carbon dioxide, a greenhouse gas. The attraction is that the volume of gas released exactly matches that taken up by the plant when it was growing. So overall (and with the huge proviso that you do not count the fossil fuel used to farm the stuff) biofuels are carbon-neutral.

In America the Department of Energy has set a target for 30% of the 2004 gasoline demand for vehicles to be met by biofuels by 2030. The European Union wants 25% of transport fuels to be derived from biofuels by the same date. At present, the most widely used substance is ethanol, which can be made from sugar cane, sugar beet and maize (or corn, as it is called in America). But ethanol does not pack a particularly powerful punch. It is also susceptible to absorbing water, further diluting its oomph. It takes days to ferment the stuff. A biofuel that did not suffer from these limitations would be welcome.

That is what a team led by James Dumesic of the University of Wisconsin-Madison claims to have developed. The researchers think they have devised a biofuel that has a 40% higher energy density than ethanol, that repels water and that can be made relatively speedily.

One of the most frustrating aspects of biofuels is the stark contrast between what exists in nature and what you can put in the tank. Plants are rich in carbohydrates, a group of organic compounds based on carbon and water, itself a combination of hydrogen and oxygen. These carbohydrates take the form of chains of thousands of sugar units; each unit contains six carbon atoms and a similar number of oxygen atoms. An ideal fuel, on the other hand, should lack oxygen. Its molecules should also be small, that is, they should contain few carbon atoms. Creating an efficient fuel from plants thus presents a headache. More...