BioFuels Journal

By Susan Reidy, BioFuels Journal Editor

Towering rows of poplar trees and not green rows of corn may be the answer to increasing ethanol production.

Researchers at Purdue University, West Lafayette, IN, are studying if they can genetically modify poplar trees so that the cellulose material within them can more easily be extracted and used for ethanol production.

The focus of the three-year, $1.4 million study will be the cell wall polymer called lignin, which hinders the extraction of cellulose.

“The lignin gets in the way of the enzymes needed to degrade the cellulose,” said Clint Chapple, professor of biochemistry and one of three researchers on the project.

“Our hypothesis is that we’ll be able to modify the lignin in such a way that the trees won’t be compromised but the lignin could be modified so it doesn’t impede our ability to remove the cellulose as it does now.”

Other researchers include Richard Meilan, associate professor, department of forestry and natural resources, and Michael Ladisch, distinguished professor of agricultural and biological engineering.

Once Chapple and Meilan are satisfied with their results in modifying the trees, they will supply wood samples to Ladisch.

Then, using pilot-scale fermentation studies, researchers will measure the yield of fermentable sugars of the wood from the modified trees.

Ladisch already is examining some of the manipulations Chapple and Meilan completed earlier.

Chapple anticipates within 18 months they will have additional samples for Ladisch to study.

Poplar Potential

Poplars present several benefits over traditional row crops such as corn. For one, poplars don’t require intensive inputs.

Leaves that fall and degrade allow the nutrients to recycle every year.

Unlike corn, poplars wouldn’t have to be harvested every year. If poplar prices were down, the grower could chose to leave the trees to grow for another year, while waiting for prices to improve.

Researchers anticipate a hybrid poplar in its present form could generate about 70 gallons of fuel per ton of wood. An acre of poplars would yield about five to seven tons of wood, Chapple said.

“Trees are largely unimproved; their genetic potential is completely untapped,” Chapple said.

“I think there is every reason to believe we can domesticate these trees and be able to provide yield increases well beyond where we are today.”

Several varieties of poplars are available that can grow in a range of climates, from the subtropics in Florida to sub-alpine areas in Alaska, northern Canada, and Europe.

Under ideal conditions in the western United States, poplars can grow up to 90 feet in just six years.

One benefit of poplars as a cellulose feedstock is that the infrastructure to handle the trees already is available.

“Poplar is grown in plantations out west; it’s not that we have to invent the machinery that’s required to do that,” Chapple said.

“It is very dense, so unlike some other lighter materials, it won’t have to go through densification so that transportation is more economical.”

As cellulose ethanol production develops, the key will be finding what crop gives the best productivity in specific regions, Chapple said.

“In some regions, that may be Miscanthus or switchgrass,” he said.

“In other places, it may make more sense to turn over agricultural land into poplar plantations.”

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