From Wired.com:
On a blackboard, it looks so simple: Take a plant and extract the cellulose. Add some enzymes and convert the cellulose molecules into sugars. Ferment the sugar into alcohol. Then distill the alcohol into fuel. One, two, three, four — and we're powering our cars with lawn cuttings, wood chips, and prairie grasses instead of Middle East oil.
Unfortunately, passing chemistry class doesn't mean acing economics. Scientists have long known how to turn trees into ethanol, but doing it profitably is another matter. We can run our cars on lawn cuttings today; we just can't do it at a price people are willing to pay.
Enzymes
The problem is cellulose. Found in plant cell walls, it's the most abundant naturally occurring organic molecule on the planet, a potentially limitless source of energy. But it's a tough molecule to break down. Bacteria and other microorganisms use specialized enzymes to do the job, scouring lawns, fields, and forest floors, hunting out cellulose and dining on it. Evolution has given other animals elegant ways to do the same: Cows, goats, and deer maintain a special stomach full of bugs to digest the molecule; termites harbor hundreds of unique microorganisms in their guts that help them process it.
No walk in the park
For scientists, though, figuring out how to convert cellulose into a usable form on a budget driven by gas-pump prices has been neither elegant nor easy. To tap that potential energy, they're harnessing nature's tools, tweaking them in the lab to make them work much faster than nature intended.
Addicted
While researchers work to bring down the costs of alternative energy sources, in the past two years policymakers have finally reached consensus that it's time to move past oil. The reasoning varies — reducing our dependence on unstable oil-producing regions, cutting greenhouse gases, avoiding ever-increasing prices — but it's clear that the US needs to replace billions of gallons of gasoline with alternative fuels, and fast. Even oil industry veteran George W. Bush has declared that "America is addicted to oil" and set a target of replacing 20 percent of the nation's annual gasoline consumption — 35 billion gallons — with renewable fuels by 2017.
But how?
Hydrogen is too far-out, and it's no easy task to power our cars with wind- or solar-generated electricity. The answer, then, is ethanol. Unfortunately, the ethanol we can make today — from corn kernels — is a mediocre fuel source. Corn ethanol is easier to produce than the cellulosic kind (convert the sugar to alcohol and you're basically done), but it generates at best 30 percent more energy than is required to grow and process the corn — hardly worth the trouble. Plus, the crop's fertilizer- intensive cultivation pollutes waterways, and increased demand drives up food costs (corn prices doubled last year). And anyway, the corn ethanol industry is projected to produce, at most, the equivalent of only 15 billion gallons of fuel by 2017. "We can't make 35 billion gallons' worth of gasoline out of ethanol from corn," says Dartmouth engineering and biology professor Lee Lynd, "and we probably don't want to."
Eat or Drive?
Cellulosic ethanol, in theory, is a much better bet. Most of the plant species suitable for producing this kind of ethanol — like switchgrass, a fast- growing plant found throughout the Great Plains, and farmed poplar trees — aren't food crops. And according to a joint study by the US Departments of Agriculture and Energy, we can sustainably grow more than 1 billion tons of such biomass on available farmland, using minimal fertilizer. In fact, about two-thirds of what we throw into our landfills today contains cellulose and thus potential fuel. Better still: Cellulosic ethanol yields roughly 80 percent more energy than is required to grow and convert it.
For more visit Wired.com
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