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Plans for cellulosic ethanol on track
The path toward second-generation ethanol – made from cellulosic sources such as crop residues, wood chips, and municipal waste – has not been smooth, but it is still on track, say experts in the topic.
Claus Fuglsang, head of the bioenergy division of Novozymes (novozymes.com), says if crude oil prices surpass $75 per barrel, a system for turning biomass products such as cornstalks or sawdust can be competitive economically. Novozymes is the largest producer of the enzymes that, when mixed with corn or cellulose, convert starch to sugar. The sugar is then fermented into alcohol.
“It's harder for the enzymes to attack and break apart cellulose,” Fuglsang says. “The starch in corn grain is relatively easy to break down, but that's not true of cellulose.”
For example, enzyme cost is 3¢ to 4¢ per gallon of ethanol produced from corn. But it may take 50¢ of enzymes to convert cellulose to ethanol. Those enzymes are more specialized, it takes more of them, and it takes longer.
Also, corn grain is about 85% starch, while cellulose can be as low as 30%, further diminishing the efficiency of cellulosic ethanol. The ethanol feedstocks are bulky and harder to transport, generally limited to a 50-mile radius from a plant.
Still, Fuglsang is optimistic about cellulosic ethanol. Novozymes has developed a new product called a cellulosic enhancer, GH61, that will break down the cellulose before the enzymes are added, gaining efficiency in the process. When added to new proprietary enzymes developed by Novozymes, efficiency can be improved by a factor of 1.5, he says, and reduce production costs by as much as 10%.
“I think we can get the total production cost for cellulosic ethanol down to $2 per gallon,” he says. These costs are similar to current ones for corn grain-based ethanol.
Heather Youngs, who is a bioenergy analysis expert in California at the Energy Biosciences Institute of UC-Berkeley (energybiosciencesinstitute.org), thinks federal targets of 350 million gallons of cellulosic ethanol (out of about 15 billion gallons of total ethanol) can be hit by 2015. About a dozen cellulosic plants are in place or being planned now.
Youngs notes the economics of corn-based ethanol are good, and there is corn in surplus now. But long term, the day will come when the U.S. will need all of its corn for food, she says, and hopefully there will be a different model in place by then for bioenergy. One part of that will include converting waste cellulosic-based products to fuel.
In California, her group has found that there are 87.7 billion tons of biomass waste produced every year. Only 12% is agricultural crop residue. One half is municipal waste, which she sees as a prime opportunity for turning into biofuel.
“Up to now, the discussion about bioenergy has been about land-use priorities,” says Youngs. “I predict that is going to change to things like water use and resource inputs. The first plants for cellulosic ethanol are not the most efficient, but they'll get better as we move forward.”
One problem with cellulosic ethanol is that the co-products are not as readily usable as distillers' grains from corn ethanol. After cellulose is processed, what's left is lignin, a plastic-like product that resists digestion. Perhaps its best use is to burn it for fuel to power the ethanol plant, she says.