Is Cellulosic Ethanol the Next Big Thing in Renewable Fuels?

Ongoing efforts to commercialize this clean energy source may lead the US to a more independent energy future

For a long time it seemed like turning the inedible parts of plants into a commercially viable biofuel, known as cellulosic ethanol, was nothing more than a pipedream. The enzymes needed to release sugars from cellulose — the fiber that forms plant structure — to be fermented into ethanol were inefficient and expensive. And the cellulose found in virtually every plant, flower, tree, grass, and bush is by its very nature evolved to withstand decay.

 After the Harvest Photo by Dustin Oliver, on Flickr Corn stover, which includes a residue of stalk, leaf, husk, and cob left behind following a corn harvest, can be used as a feedstock for cellulosic ethanol.

Ethanol can be derived from sugar-based, corn-based, and cellulose-based materials. In Brazil, sugarcane is the feedstock of choice, while in the United States that designation goes to corn. The starch in corn kernels easily converts into simple sugars, with the enzyme catalyzing this process costing a mere .03-cents per gallon; the sugars are then fermented into alcohol (additives make it undrinkable). Because of the relatively low cost, corn-based ethanol has been meeting America’s demand for an alternative fuel source, especially as people drive less and fuel economy improves.

Why even bother with cellulosic ethanol?

For one, there’s the questionable carbon footprint of corn ethanol, which, depending on how it is produced, can be significantly better or significantly worse than that of petroleum. Greenhouse-gas emissions from cellulosic ethanol, on the other hand, are estimated to be roughly 86 percent less than petroleum sources. And using cellulosic materials doesn’t create a food-versus-fuel scenario.

Ramping up production of the biofuel could reduce the nation’s reliance on imported oil. In 2012, the US imported about 40 percent of the petroleum it consumed, nearly three-quarters of which fueled transportation around the country. The US government also spends millions of dollars on military support to keep oil shipping lanes open; money that could go toward domestic needs instead.

Cellulosic ethanol is renewable, clean, derived from the most abundant organic compound on Earth, and could lead the US closer to energy independence. These attributes have kept researchers at the National Renewable Energy Laboratory (NREL) in Golden, Colorado focused on developing this biofuel in spite of the challenges. “We stuck it out even when oil was $25 a barrel and even now when it’s under $80 a barrel,” says Richard Bolin, manager of the partnership development group for the National Bioenergy Center at NREL.

Cellulosic Ethanol Photo by Pat Corkery NREL has genetically engineered strains of Zymomonas mobilis, a bacterium that aids in the
fermentation of the multiple sugars found in biomass.

That stick-to-itiveness may be paying off. In 2014, the first three commercial-scale biorefineries producing cellulosic ethanol began operating in the United States. Next year, chemical giant DuPont will bring a refinery facility online in Nevada, Iowa. The plant will produce 30 million gallons of cellulosic ethanol annually and DuPont is billing it as the largest biorefinery in the world.

Collecting the Needed Material

Corn is the leading crop in the United States, but most of the roughly 90 million acres of corn planted each year nationwide is not the sweet corn we eat. It’s actually field corn used for fuel, livestock feed, high-fructose corn syrup, corn flour, plastics, batteries, adhesives, medicines, soaps, crayons, cosmetics, and much more. Currently, 40 percent of all US corn harvest goes to fuel.

While corn is considered critical to feeding the world’s increasing population — projected by the United Nations Population Division to be just shy of 10 billion by 2050 — there’s less incentive to grow the edible variety when farmers can make more money planting the nonedible kind on their land.

But a monocrop such as corn is inherently risky, and its vulnerability was made abundantly clear in 2012 when a severe drought ravaged crops across the Midwest. About 80 percent of the country’s agricultural land experienced water scarcity, making it the most extensive drought since the 1950s. Significant crop losses raised a challenging question: Is it wise to devote so much farmland to fuel instead of to feeding people?

Dr. Claudia Tebaldi, a climate statistician at the National Center for Atmospheric Research (NCAR) and co-author of the 2014 report “Climate Trends and Global Crop Yields,” says adverse temperatures and precipitation caused by climate change will reduce corn and wheat yields in the next 10 to 20 years. Historically, productions of these two staple crops have typically increased 10 percent each decade. But climate change will cut that expected increase in half — even as global demand for food and fuel grows.

“We find that anthropogenic climate change increases the chances of such slowdowns considerably, for both crops, but in particular for maize,” Tebaldi recently told a group of journalists visiting NCAR, citing her report.

So what about using a different feedstock for ethanol, one that doesn’t threaten food supply? Cellulosic ethanol is attracting attention because it is produced from inedible plant sources, including fallen branches and twigs in the forest, saw dust, woodchips, switchgrass, and municipal solid waste.

Corn stover, which includes a residue of stalk, leaf, husk, and cob left behind following a corn harvest, can also be used. Farmers usually till some of this corn stover to add carbon back into the soil and control erosion. Some harvest the stover for animal bedding and feed. But the majority is left on the ground to rot (releasing carbon dioxide into the atmosphere). As corn yields have increased over the years, so has stover.

Now farmers have an opportunity to sell the material to commercial-scale biorefineries. DuPont’s facility, for instance, will use 375,000 tons of corn stover annually. “This is a waste stream, but you’re adding value to it,” Bolin says. The company launched a corn stover harvest program, targeting farmers within a 30-mile radius. An estimated 500 farmers will supply the biomass for the refinery.

This helps American farmers, as many need additional sources of revenue to make ends meet. Of the nation’s 2.1 million farms, about 1.5 million earn less than a quarter of their household income from the farm, according to the 2012 Agriculture Census. Commercializing cellulosic ethanol will also add much-needed jobs in rural communities; DuPont says its Iowa plant will create 85 permanent positions.

Making the Hard Part Easier

The National Renewable Energy Laboratory is the US Department of Energy’s main national lab for research and development on renewable energy and energy efficiency. On its 327-acre campus, staff work on the whole spectrum of renewable energy development, from scientific discovery to accelerating market adoption. Basically, they remove the risk incurred by private companies in bringing technological advancements to the marketplace.

Bolin says NREL has been working on cellulosic ethanol since 1980. The tedious process of turning cellulose into biofuel involves breaking up the complex cellulose-hemicellulose-lignin structure before fermentation begins. A big part of the challenge for researchers has been finding enzymes to facilitate this process.

A decade ago, the enzymes to produce cellulosic ethanol cost $3 a gallon. Bolin says NREL has reduced the cost to 30 cents, and is figuring out how to cut that amount in half by bioengineering more effective enzymes that will accelerate the process. In comparison, the enzyme cost for corn ethanol is around .03 cents a gallon.

In 2012, NREL met a challenge by the Department of Energy’s Advanced Energy Initiative to demonstrate at a pilot scale that cellulosic ethanol could be cost-competitive with other transportation fuels. Over the past decade, NREL has brought down the cost of cellulosic ethanol from about $10 a gallon to $2.15 a gallon, primarily by bioengineering better enzymes, says Bolin. Recent data has corn ethanol costing $1.92 a gallon.

The Clean Air Act of 1970, which created initiatives to reduce pollution from mobile sources such as planes, trains, and automobiles, marked the beginning of efforts to develop alternative fuels. The Energy Policy Act of 2005 went further by including a Renewable Fuel Standard (RFS) that originally required 7.5 billion gallons of renewable fuel to be blended into gasoline sold in the United States. And the Energy Independence and Security Act of 2007 increased that amount to 36 billion gallons of renewables by 2022. The EPA is deciding whether to scale back on the blend amounts, which could stifle the biofuel industry.

The Energy Independence and Security Act also set separate volume requirements for different renewable fuels, including advanced biofuels, biomass-based diesel, and cellulosic biofuels. The EPA called for 17 million gallons of cellulosic ethanol in 2014, which was significantly lower than the original target of 1.75 billion in the RSF. For the first time, cellulosic ethanol producers met and exceeded the requirement, reaching 18.2 million gallons as of November.

All cars and trucks today can use a fuel blend called E10, which is 10 percent ethanol and 90 percent gasoline. There’s also E15, which is 15 percent ethanol, and can only be used in cars made after 2001. An E85 blend, up to 85 percent ethanol, can be used on flex-fuel vehicles.

NREL has worked with companies, universities, and other institutions over the years on developing cellulosic ethanol. “The private-public partnership is essential,” Bolin says. “We have part of the answers to the whole equation of making cellulosic ethanol, and private industry has the other part of the answers.”

The strategy seems to be working. According to Bolin, the federal government has poured millions of dollars into bridging the gap to commercialization. Department of Energy (DOE) money was used to support the three refinery projects in Kansas, Iowa, and Florida. While DuPont did not receive any DOE funds for its facility, the company has collaborated with Iowa State University to develop a corn stover supply chain without risking soil health.

DuPont has invested more than $200 million into its biorefinery. Spokeswoman Wendy Rosen says the project shows the company’s commitment to “providing bio-based solutions to meet the needs of a growing population, while protecting our environment.” The company is partnering with the government of Macedonia and Ethanol Europe to expand this technology, which is “just one example of the market’s readiness for cellulosic ethanol and the global interest,” Rosen says.

Cellulosic ethanol biorefineries are also making higher-value products, such as chemicals and plastic bottles, to lower their risk of entering the biofuels market. DuPont recently announced an agreement to funnel cellulosic ethanol produced at its Iowa biorefinery into Procter & Gamble laundry detergent.

It is still unclear whether cellulosic ethanol will achieve widespread commercial use. “We’re still going to have the supply and demand issues (with cellulosic ethanol),” Bolin says, “So I’m not sure how that’s going to shake out.”

Despite the uncertainty, cellulosic ethanol has made gains recently and perhaps one day will become the shining centerpiece of America’s homegrown renewable fuel sources.

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