Making biofuels from food crops is controversial because it can raise the cost of corn and grain. But making the alternative fuel from the part of the food crop that doesn't get eaten, such as the stalks, or from waste wood is expensive, as well as chemical- and energy-intensive.
A start-up company called Renmatix says it has an answer: Use water to extract the sugars.
The process, which involves supercritical water, isn’t that exotic. In fact, it's already used to decaffeinate coffee and extract hops to make beer. Supercritical water is basically water heated beyond its boiling point under high pressure. At that point, the water becomes something between a liquid and a gas.
What Renmatix does is put wood chips in a chamber with the supercritical water. This breaks off some of the sugars, the ones with five carbon atoms. (Ordinary table sugar has 12 carbon atoms.) The wood is then sent to another chamber to release the remaining sugars (which have six carbon atoms).
What’s left is lignin, a component of wood, which can be burned to provide energy for the whole process. (A diagram of the system can be found here.)
Once the sugars are extracted they can be fermented into biofuels, which are largely ethanol. Ethanol can be mixed with gasoline to work in most current cars. It's widely used in Brazil, where it's made from sugarcane.
But that’s the problem: It's a lot easier to get sugars from food, such as corn. Producing biofuels without stressing food supplies or putting more land under cultivation (and irrigation) will be a tall order; the U.S. Environmental Protection Agency has proposed that the country produce 36 billion gallons of ethanol by 2022, 16 billion gallons of which has to be cellulosic biofuel. The Renewable Fuels Association says the current production is about 13 billion gallons. That’s why companies such as Renmatix are looking for ways to use the stuff that people don’t eat.
Other companies use different methods to pull the fuel from plant material. South San Francisco, Calif.-based Solazyme uses algae and says it can use several kinds of feedstock. Envergent Technologies, a division of Honeywell, uses a fast-heating process. KL Energy has a demonstration plant in Wyoming that uses a heat pretreatment process and the addition of enzymes to break down the feedstock.
Renmatix says the fact that it needs no additional chemical treatments or enzymes (which are commercially available but expensive) is its big advantage. The company has been operating a demonstration plant in Kennesaw, Ga., and is breaking ground on a research facility in King of Prussia, Pa. The big question will be whether Renmatix can make the process work on a scale large enough to operate profitably.