New technique improves efficiency of biofuel production

Jun 30, 2010
Dr. Ratna Sharma-Shivappa and her colleagues at North Carolina State University have developed a more efficient technique for producing biofuels from woody plants that significantly reduces the waste that results from conventional biofuel production techniques. "Our eventual goal is to use this technique for any type of feedstock, to produce any biofuel or biochemical that can use these sugars," Sharma-Shivappa says. Credit: Roger W. Winstead, North Carolina State University

Researchers at North Carolina State University have developed a more efficient technique for producing biofuels from woody plants that significantly reduces the waste that results from conventional biofuel production techniques. The technique is a significant step toward creating a commercially viable new source of biofuels.

"This technique makes the process more efficient and less expensive," says Dr. Ratna Sharma-Shivappa, associate professor of biological and agricultural engineering at NC State and co-author of the research. "The technique could open the door to making lignin-rich plant matter a commercially viable for biofuels, curtailing biofuel's reliance on staple food crops."

Traditionally, to make ethanol, butanol or other biofuels, producers have used corn, beets or other plant matter that is high in starches or simple sugars. However, since those crops are also significant staple foods, biofuels are competing with people for those crops.

However, other forms of biomass - such as switchgrass or inedible corn stalks - can also be used to make biofuels. But these other crops pose their own problem: their energy potential is locked away inside the plant's lignin - the woody, protective material that provides each plant's structural support. Breaking down that lignin to reach the plant's component carbohydrates is an essential first step toward making biofuels.

At present, researchers exploring how to create biofuels from this so-called "woody" material treat the plant matter with harsh chemicals that break it down into a carbohydrate-rich substance and a liquid waste stream. These carbohydrates are then exposed to enzymes that turn the carbohydrates into sugars that can be fermented to make or .

This technique often results in a significant portion of the plant's carbohydrates being siphoned off with the liquid waste stream. Researchers must either incorporate additional processes to retrieve those carbohydrates, or lose them altogether.

But now researchers from NC State have developed a new way to free the carbohydrates from the lignin. By exposing the plant matter to gaseous ozone, with very little moisture, they are able to produce a carbohydrate-rich solid with no solid or liquid waste.

"This is more efficient because it degrades the lignin very effectively and there is little or no loss of the plant's carbohydrates," Sharma-Shivappa says. "The solid can then go directly to the enzymes to produce the sugars necessary for production."

Sharma notes that the process itself is more expensive than using a bath of harsh chemicals to free the carbohydrates, but is ultimately more cost-effective because it makes more efficient use of the plant matter.

The researchers have recently received a grant from the Center for Bioenergy Research and Development to fine-tune the process for use with switchgrass and miscanthus grass. "Our eventual goal is to use this technique for any type of feedstock, to produce any biofuel or biochemical that can use these sugars," Sharma-Shivappa says.

Explore further: Engineers devise technology for rapidly testing drug-delivery vehicles in zebrafish

More information: The research, "Effect of ozonolysis on bioconversion of miscanthus to bioethanol," was presented June 23 at the 2010 Annual International Meeting of the American Society for Agricultural and Biological Engineers in Pittsburgh, PA

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Parsec
3 / 5 (2) Jun 30, 2010
I wonder how much mechanical processing is required. I have read that just shredding the input biomass is a significant part of the energy cost, along with the water used to wash the biomass to insure that the shredder blades do not get exposed to small stones and whatnot.

The energy cost of ozone is really high. So the viability of this would depend on how many molecules of ozone are required to convert each carbon atom from lignin to a simpler enzyme digestible carbohydrate (of course the carbohydrates have more than one carbon, I am simplifying the ratios while preserving the idea).

I am presuming the above ratio would be something like .01 or so, but if its very high then the whole thing breaks down. I do not know the break even point.
Eikka
5 / 5 (1) Jun 30, 2010
Regardless of the process, gathering the required amount of biomass is a hard job.

Imagine a 500 MW powerplant running on wood chips. One dump truck can carry 25 tons of wood, which contains approximately 5 kWh/kg. The powerplant needs 1500 MW to run, which means it needs 300 tons of wood per hour, which means it needs to have a dump truck visiting every five minutes.

Or the wood may come in on a train, but still, somewhere out there someone must be logging a dumptruck full of woodchips every five minutes to satisfy the demand for one single powerplant.
Eikka
not rated yet Jun 30, 2010
Or, how much wood would you need to supply one car for one year?

Take an average consumption of 0.07 litres per kilometer, and about 10,000 km per year, which gives you 700 litres at 8.76 kWh/L, which is 6132 kWh, or 1.2 tons of wood per year. To account for the losses, you have to increase that figure to 2 tons of wood per year.

A city of a few million would easily decimate huge forests much more quickly than they can grow.
HaveYouConsidered
not rated yet Jul 01, 2010
I'm glad there are people like Eikka around to do some "back of the envelope" math on the reasonableness of ideas, as a lot of ideas sound great until this is done. But I will add that there is already a large paper-processing industry (using mainly renewable forestry) that produces a lot of bark trimmings--how much I don't know. Also, the article speaks about woody plants, not just wood.
jerryd
not rated yet Jul 01, 2010
A couple of details. Obviously Eikka is from Europe from his/her mileage which works out to about 45 mpg. Their gals are 10% or so larger.

20lbs of dry woody biomass equals a US gal for those in the US. US average is 26mpg US and we do about 10k miles, 35 % more.

If 20lbs/9kgs burned in a cogen 50% eff powerplant it would move my EV sportwagon and Harley size EV trike MC about 180 and 560miles.

While biomass has to be used close to it's source, that's no problem as just makes a lot of small businesses instead of 1 large one. It can easily provide 10% of our energy needs.