When President Bush spoke during his State of the Union address about turning something called “switchgrass” into a future source of ethanol, thus reducing the United States’ dependence on oil, it certainly caught R. Michael Raab’s attention.
Raab is president and founder of Agrivida, a Cambridge, MA-based biotech startup that wants to add genes to plants to make it cheaper and easier to process them into ethanol. He hopes the technology his company is developing will make ethanol derived from plants, including switchgrass, a viable alternative to gasoline.
For now, the company is focusing its efforts on corn, already a source of ethanol. But standard ethanol production uses just the kernels. Ethanol manufacturers process the kernels using enzymes that break down the starch into simple sugars. The sugars are then fed into a fermentation tank, where yeast digests them and produces ethanol. But in this process the corn stalks and leaves – about half of the plant mass – are thrown away.
Using the whole plant would produce much more ethanol – but the sugars in the stalks and leaves are in the form of cellulose, which is a much more complex chain of sugar molecules. To break down cellulose into simple sugars for the yeast requires a preconditioning process that includes heat, high pressure, and acids. Today, that process is too expensive to be worthwhile – as it would also be for switchgrass, a woody grass native to North America that can grow to nine feet tall (and which now no one uses for ethanol).
Agrivida proposes to add genes to the corn plants that will produce enzymes for breaking down the cellulose. This makes it much easier to process the cellulose into sugar, reducing production costs to a point where it’s feasible to use the whole plant, Raab says. He predicts the process will be about 50 percent cheaper than current processes once it matures. And it could be adapted to switchgrass, he says.
However, enzymes that break down a corn’s structural elements could also result in weakened stalks. So Agrivida has redesigned the enzymes to remain inactive during the plant’s life. Only when they encounter the conditions of processing, such as increased temperature or pressure or a change in pH level, are the enzymes activated. (Raab won’t explain the process in detail because it’s part of a patent application.)
Clearly, there’s a great deal of potential energy to be tapped. A study at Argonne National Laboratory estimates that a gallon of ethanol produced from kernels of corn in today’s processes provides about 20,000 BTUs more energy than the energy that went into making it. The study projects that using cellulose from switchgrass would triple that net gain, to about 60,000 BTUs per gallon, mostly because little fossil fuel would be used in farming the grass. But costs need to come down to make this practical.