March 20, 2008 issue


Cellulosic Ethanol—The Next Big Biofuel?

Story by Sam Calhoun

Is switchgrass the next cash crop for the United States? Cellulosic ethanol is a biofuel produced from the stalks and stems of plants such as switchgrass, rather than from sugars and starches as with corn ethanol, and it yields more than two times the amount of biofuel per acre compared to corn ethanol. †In his 2006 State of the Union Address, President George W. Bush touted switchgrass as an efficient and environmentally friendly biofuel that could reduce America’s dependence on oil. Switchgrass is a warm season grass and is one of the dominant species of the central North American tall grass prairie. Not long after the 2006 State of the Union, Bush set the goal of producing 35 billion gallons of renewable fuels per year by 2017 and proposed an expansion of the use of cellulosic ethanol.

Cellulosic ethanol is a fuel produced from the stalks and stems of plants, rather than from sugars and starches as with corn ethanol. According to BioCycle magazine, cellulosic ethanol can be produced from a wide variety of cellulosic biomass feedstocks, including agricultural plant wastes such as corn stover, cereal straws and sugarcane; plant wastes from industrial processes such as sawdust, wood chips and paper pulp; and energy crops grown specifically for fuel production, such as switchgrass.

According to the U.S. Department of Energy, one of the benefits of cellulosic ethanol is that it reduces greenhouse gas emissions by 85 percent compared to reformulated gasoline. By contrast, corn ethanol frequently uses natural gas to provide energy for the process and may not reduce greenhouse gas emissions at all depending on how the starch-based feedstock is produced, according to the U.S. Department of Energy.

A recent study by Nobel Prize winner Paul Crutzen found a net climate warming effect from corn ethanol compared to gasoline. However, ethanol, if made from cellulose, he found, emitted 80 percent less global warming pollution than gasoline.

What’s the Difference Between Cellulosic Ethanol and Corn Ethanol?

While chemically identical to ethanol produced from corn or soybeans, cellulosic ethanol exhibits a net energy content three times higher than corn ethanol and emits a low net level of greenhouse gases, according to BioCycle magazine.

TechnologyReview.com states that an acre of grasses or other crops grown specifically to make cellulosic ethanol could produce more than two times the number of gallons of ethanol as an acre of corn, in part because the whole plant can be used instead of just the grain.

Bill Moretz, owner of Moretz Mountain Orchard, said, for instance, an acre of switchgrass used to make cellulosic ethanol will produce 1,000 gallons of biofuel, whereas an acre of corn used to make corn ethanol will only produce 500 gallons of biofuel.

But Moretz is worried that farmers will start to switch their grass fields used for raising cattle to switchgrass fields, thereby raising the price of beef and other agricultural commodities.

“This is more of a future thing,” said Moretz. “But we thought corn-based ethanol was a few years down the road until gas prices shot up.”

Corn ethanol is becoming more popular in America. Many American carmakers are already selling cars that run on the biofuel, and corn ethanol is used widely in cars in Brazil, according to Wikipedia.org. The growth of the corn ethanol industry is taking its toll, though. Many farmers who used to plant wheat, hops and barley have switched to corn, causing barley, hops and wheat prices to skyrocket. Moretz is worried that this price increase in agricultural commodities is only going to spread in new directions when cellulosic ethanol takes off.

“[Cellulosic ethanol] is at least as likely as hydrogen to be an energy carrier of choice for a sustainable transportation sector,” wrote the National Resources Defense Council and the Union of Concerned Citizens in a joint statement released in 2006. “The global market for biofuels such as cellulosic ethanol will grow to exceed $10 billion by 2012.” 

Growing Pains

According to TechnologyReview.com, many experts estimate that corn ethanol producers will run out of land soon, in part because of the competing demand for corn-based food, limiting the total production to about 15 billion gallons of fuel per year—a far cry from Bush’s 35 billion gallon goal for 2017. Consequently, other sources of biofuel will be needed to reach that goal, but at what price?

Addressing Moretz’s concerns, Jeremy Ferrell with the ASU Energy Center said that the high cost of converting feedstocks into cellulosic ethanol will take away the opportunity to grow the cellulose feedstocks, such as switchgrass, from local farmers, and put the job in the hands of large production plants set up close to reliable feedstock sources.

“Cost-effective cellulosic ethanol is a trick,” Ferrell said. “Typically, either bacteria or enzymes are used to break down the tough cellulose fiber into starches and eventually sugars, which can easily be converted into alcohol. This is an energy-intense process, often requiring [intense] heat and strong chemical acids.

“Our mountain region stands to benefit from this technology as we have tremendous wood resources, but I don’t think planting large acreages of [switchgrass] here in the mountains would attract any capital investors,” Ferrell continued. “On scalability, the high-tech nature of cellulosic ethanol would tend to favor large-scale plants located near a reliable feedstock source. I don’t foresee small-scale decentralized cellulosic plants at this point in time.”

Currently, it costs more to create cellulosic ethanol than corn ethanol.

Cellulosic ethanol costs more to produce than corn ethanol because of the greater amount of time needed to process the raw materials. According to Wikipedia.org, cellulosic ethanol requires more processing to make the sugar monomers available to the microorganisms that are typically used to produce ethanol by fermentation. 

“But if they get the process worked out, it will only be a matter of time before the [market for creating cellulosic ethanol] opens up,” said Moretz.

 “To the best of my knowledge, the problem is economic not technical,” wrote Ferrell. “But when gas hits $5 per gallon, cellulosic ethanol will be cost competitive.”

The Future Is Now

According to TechnologyReview.com, cellulosic ethanol plants are already operational in Canada, Spain and China. In 2007, Celunol, based in Cambridge, Mass., broke ground on a cellulosic ethanol plant in Louisiana that will produce 1.4 million gallons of the biofuel each year starting in summer 2008.

But, according to TechnologyReview.com, experts from industry and environmental groups said that without loan guarantees and other incentives, the cellulosic ethanol industry will fail to emerge from the current demonstration phase to produce commercial-scale quantities of cellulosic ethanol. And without that investment, the article states, it may be impossible to meet Bush’s goal of producing 35 billion gallons of biofuels per year by 2017.

The government is helping, though.

Construction of pilot-scale cellulosic ethanol plants—like the one in Louisiana—requires considerable financial support through grants and subsidies. On February 28, 2007, the U.S. Department of Energy announced $385 million in grant funding to six cellulosic ethanol plants. This grant funding accounts for 40 percent of the investment costs, and the remaining 60 percent comes from the developers of those facilities. Hence, a total of $1 billion will be invested for an approximately 140 million gallon capacity, translating into a $7 per year per gallon capital investment cost for pilot plants, even though future capital costs are expected to be lower. Corn ethanol plants cost roughly $1 to $3 per year per gallon. 

Food for Thought

As of 2007, ethanol is produced mostly from sugars or starches obtained from fruits and grains. In contrast, cellulosic ethanol is obtained from cellulose, the main component of wood, straw and many plants. Because humans cannot digest cellulose, the production of cellulosic ethanol does not compete with the production of food. The price per ton of the raw material is therefore much cheaper than grains or fruits. Moreover, because cellulose is the main component of plants, the whole plant can be harvested and processed, resulting in much better yields per acre—up to 10 tons, instead of 4 or 5 tons for the best crops of grain.

According to Wikipedia.org, the raw material is plentiful. Cellulose is present in every plant in the form of straw, grass and wood. Most of these biomass products are currently discarded and estimates are that 323 million tons of cellulose containing raw materials that could be used to create cellulosic ethanol are thrown away each year. This amount includes 36.8 million dry tons of urban wood wastes, 90.5 million dry tons of primary mill residues, 45 million dry tons of forest residues and 150.7 million dry tons of corn stover and wheat straw. Transforming such waste into cellulosic ethanol using efficient and cost-effective enzymes or other processes might provide as much as 30 percent of the current fuel consumption in the United States—and probably similar figures in other oil-importing regions such as China and Europe, according to Wikipedia.org.

Moreover, even agriculturally marginal land could be planted with cellulose-producing crops such as switchgrass, resulting in enough production to substitute for all the current oil imports into the United States, according to Wikipedia.org.