Cellulosic Ethanol FAQs       

What is cellulose?

Cellulose is the main component of plant cell walls. It’s the most abundant organic compound on earth. Sources of cellulose include crop and forest residues, municipal garbage, food processing waste, energy crops such as native prairie grasses, and even algae.

What’s in biomass that can be converted to fuel?

Biomass, sometimes called lignocellulose, is composed primarily of lignin, cellulose and hemicellulose.
Sugars stored in cellulose and hemicellulose can be tapped for energy. The problem is, these sugars are locked up in long chains of molecules, making them hard — and expensive — to separate and ferment for alcohol.

That’s a contrast to corn starch — the main ethanol feedstock in the United States — which is easily converted to sugar and fermented. However, more effective biomass conversion technologies are being developed.

Lignin, a biomass byproduct, has nearly the same energy content as coal, but without the sulfur. This clean energy source can be recovered during cellulosic ethanol processing and burned to produce steam to run the ethanol plant, or to generate electricity for sale to the power grid.

How is cellulosic ethanol made?
The plant material is chopped into small pieces and treated with steam or acid baths to separate lignin from cellulose and hemicellulose, where the sugars are stored. The lignin is burned to produce process heat or electricity. The cellulose and hemicellulose are mixed with cellulase enzymes, which release the sugars. Genetically engineered organisms “digest” the sugars, producing ethanol, which is then distilled.

Are there other methods for converting biomass to ethanol?
Yes. Biomass can be gasified to produce synthesis gas, which can then be converted to ethanol and many other products. Like cellulosic ethanol processing, biomass gasification is still in the research and demonstration phase. (See Ag Innovation News, April 2006, “Having a Gas with Biomass.”)

What are the advantages of cellulosic ethanol?
Cellulose is an abundant feedstock, which could greatly expand the volume of ethanol produced in this country. The U.S. Department of Energy estimates that the nation could produce more than one billion tons of biomass a year, mainly from farm waste. That’s enough cellulose to make 60 billion gallons of
ethanol — the equivalent of about one-third of our current petroleum use.

Are there other benefits?
According to advocates, cellulose yields more net usable energy per acre than corn, though this claim has not yet been tested. Cellulosic ethanol could be made from low-value waste materials or from energy crops such as prairie grasses, which can be produced on marginal lands with few inputs. And
food-crop residues, such as straw or corn stover, would offer farmers another source of revenue.

In addition, advocates say that cellulosic ethanol, like other renewable biofuels, could reduce America’s dependence on foreign oil, curb greenhouse gases and strengthen the farm economy.

What’s the downside of cellulosic ethanol?
Although biomass is abundant, collection and handling is expensive, and removing crop residues from
farmland may harm soil fertility and increase erosion and runoff. In addition, cellulosic ethanol technology is not fully developed, and many believe it will require huge public expenditures to
reach the commercial stage.

What are some of the technical problems that must be solved?
Government laboratories have been working for decades to convert tough plant fibers into liquid fuel. The effort began after World War II, when scientists started investigating the famous “jungle rot” microbes that ate soldiers’ tents and uniforms in the South Pacific.

Today, public and private research is focusing on three main technical challenges:

• pretreatment of plant material
• enzyme biochemistry
• microbial fermentation.

Meanwhile, cheaper biomass harvesting, handling and storage methods need to be developed. And it will be necessary to improve ethanol handling, transportation and storage.

The ultimate research goal, say advocates, is to develop biomass refineries, similar to petroleum refineries. These refineries would produce diverse products, such as ethanol, chemicals, polymers, lubricants, fertilizers and electricity.

                                                                 
What factors are encouraging the development of cellulosic ethanol?
Development is being driven by high oil prices, surging energy demand, national security, renewable fuel goals, environmental concerns and government incentives.

When will cellulosic ethanol become commercially available?
Cellulosic ethanol is still too expensive to compete in the marketplace against corn-based ethanol and gasoline. Many renewable-energy experts say commercially-viable cellulosic ethanol is at least a decade away.

The U.S. Department of Energy expects to have several cellulosic ethanol demonstration plants operating by 2012. A handful of companies around the world are planning or operating pilot plants, including Iogen, a Canadian company with a test facility in Ottawa capable of making a million gallons of ethanol per year from wheat straw.

Could cellulosic ethanol one day replace petroleum transportation fuels?
Probably not. However, ethanol and other renewable domestic biofuels could become a much more important part of the country’s energy mix. Today, ethanol displaces less than three percent of U.S. gasoline. Federal renewable energy goals call for ethanol from corn and cellulose to make up 30 percent of the nation’s motor fuel consumption by 2030.

Sources: U.S. Department of Energy; National
Renewable Energy Laboratory; Renewable
Fuels Association; Doug Tiffany, University
of Minnesota; Todd Reubold, Initiative for
Renewable Energy and the Environment; Ed
Wene, AURI; Wikipedia; Wall Street Journal;
Choices Magazine.