Cellulosic Ethanol Path is Paved With Various Technologies

In the midst of rising oil prices, the economics of producing cellulosic ethanol are becoming increasingly favorable and several companies are steadfastly moving to commercialize various process technologies. It would be easy to view this development as a race pitting one technology against the other but is that really the case? Is one approach better than another?
By Jessica Ebert | June 02, 2008
The development of technologies for the production of ethanol from biomass feedstocks such as wood dates back to the years leading into the first two world wars. Germany, in particular, being a land poor in petroleum began developing internal sources of fuel. Much of the country's war machine, in fact, was powered by locally produced ethanol. The process technology of choice at this time was a biological approach consisting of concentrated or dilute acid hydrolysis to release simple sugars from wood followed by microbial fermentation of those sugars to ethanol. Although pioneered by the German war effort, the United States, Russia and others followed suit, establishing their own wood-to-ethanol plants.

But this was not the only approach to the self-sustaining production of renewable fuels being spearheaded by warring nations. Scientists in coal-rich Germany had been developing a thermochemical process for the conversion of coal into synthesis gas that was subsequently reformed into fuel using a catalyst. This approach, dubbed the Fischer-Tropsch process for its originators, researchers Franz Fischer and Hans Tropsch, was also used in South Africa to produce liquid fuels from coal and natural gas during the years of apartheid.

"A lot of people talk about when is cellulosic ethanol going to become a reality," says Brian Duff, director of technical studies and engineering for BBI International. "Technically, it's been a reality since the '30s." The main difference between the years of the world wars and now is the reality of the cost of producing cellulosic ethanol at commercial scale. "The programs in the '30s and '40s weren't based on economics," Duff says. "They weren't based on making money. They were based on the war footing and the need to create alternative fuels. Now that oil has tripled in cost, it's making [cellulosic ethanol] technology look more economical."

Technologies at a Glance
To jump-start the commercialization of technologies for the production of ethanol from lignocellulosics, the U.S. DOE announced in early 2007, a $385 million plan to fund the construction of six large-scale biorefineries. The conversion technology employed by half of these plants will be a biological fermentation process, essentially an extension of the grain ethanol industry's approach.

"It was a logical progression of technology to go from starch hydrolysis to cellulose hydrolysis," says Robert Brown, a mechanical engineer at Ames-based Iowa State University who studies gasification and fast pyrolysis of biomass. "The problem is that Mother Nature intended starch as a storage carbohydrate while cellulose is part of a tough composite material evolved to resist biological degradation."

There are basically three steps required to overcome this recalcitrance of cellulosic feedstocks. The first is a pretreatment step using dilute acid or steam explosion to separate the cellulose from lignin and hemicellulose. This is followed by a hydrolysis step, which breaks apart the cellulose into small sugar units, using concentrated acid, dilute acid or enzymes. The sugars are finally fermented to ethanol using microbes such as the common brewer's yeast.

The remaining DOE-funded biorefineries will use a thermochemical process to produce cellulosic ethanol or a hybrid of the biochemical and thermochemical approaches. The thermochemical conversion of biomass can be carried out through a couple of different processes. In pyrolysis, biomass is converted to a bio-oil using moderate temperatures in an oxygen-starved environment. In the thermochemical approach called gasification, biomass is converted to a gaseous mixture of carbon monoxide and hydrogen by heating it to relatively high temperatures with no oxygen or very limited amounts of oxygen. The synthesis gas is then cleaned and either exposed to a catalyst, which reforms the gas into a liquid fuel, or in the hybrid approach, the syngas is fed to microbes, which transform it into ethanol.

"Gasification was developed in the early 1800s and even catalytic conversion of syngas to fuels dates back to the 1920s," Brown explains. "Many people assumed that thermochemical technology was already mature and that if it was not economically feasible today it never would be. However, this assessment falls short."

The First to Break Ground
The six DOE-funded plants are expected to be on line by 2011. The first company to break ground on its plant was Range Fuels Inc., a privately held gas-to-liquids company based in Broomfield, Colo. The first phase of the biorefinery, which is located in Soperton, Ga., will produce 20 MMgy of ethanol from leftover wood residues from timber harvesting. Using heat, pressure and steam in a two-step thermochemical process developed by Robert "Bud" Klepper, the company's chief technical specialist and inventor, biomass is converted into syngas, which is then passed over the company's proprietary catalyst and transformed into mixed alcohols, predominantly ethanol.

"I think today, thermochemical is leading the way," says Mitch Mandich, chief executive officer of Range Fuels. "But it's not something that just happened overnight." He explains that Klepper has been working on the technology for the better part of a decade. "He's built three pilot plants over that period of time and he's experimented with the technology. When we founded the company in July of '06 we looked at the technology and decided that it was really a scale-up in that we could take Bud's patents and augment those patents and really begin to commercialize the process at a larger scale," Mandich says. "We're showing that we think we can bring a thermochemical approach to the market much faster and cheaper and with less risk."

These are the keys to attracting investors, who are showing increasing interest in these technologies. Range Fuels, for example, recently expanded its Series B financing to more than $100 million. However, investors are not abandoning companies that are moving forward with biological-based cellulosic ethanol technologies. Mascoma Corp., an advanced cellulosic ethanol company based in Cambridge Mass., recently announced that it raised $61 million in a third round of financing including a $10 million equity investment by Marathon Oil Corp. Mascoma develops proprietary microbes at its laboratories in Lebanon, N.H. These microbes are engineered to express the enzymes needed to degrade cellulose and to process the resulting sugars into ethanol in a single step, explains Jim Flatt, senior vice president of research and development.

"Anytime you can simplify a process you reduce the amount of capital equipment required and you can also increase yield, so your operating costs can also decrease," Flatt says.

The technology is called consolidated bioprocessing and Mascoma plans to use this process to produce ethanol later this year at a demonstration plant, which is currently under construction in Rome, N.Y. In addition, the company recently received a $26 million DOE grant for the construction of a 2 MMgy switchgrass-to-ethanol plant in the Niles Ferry Industrial Park, in Monroe County, Tenn. "This plant is the final stepping stone to a full-scale commercial biorefinery," he says.

Likewise, Lignol Energy Corp., a British Columbia, Canada-based company, is fine-tuning a biochemical process that features a unique biomass pretreatment step. This project has also received significant backing including $20 million in equity and a recent $30 million grant from the DOE, according to Ross MacLachlan, president and chief executive officer of Lignol. The technology was pioneered by Kendall Pye at the University of Pennsylvania, and developed by General Electric Corp. throughout the 1980s. The pretreatment step differs from other biological approaches by extracting lignin upfront. This leaves two streams for further processing: a high-purity lignin stream and a very clean pulp, which requires half the amount of enzymes typically needed to break the cellulose into fermentable sugars. "Because we spend more money and more time upfront in our process to make it easier for the enzymes to work, we use fewer enzymes," MacLachlan explains. "In addition, we're producing more than just ethanol. We're producing other biochemicals. By doing these two things we've discovered that you can build cellulosic ethanol plants on a smaller scale than competing technologies while still being profitable."

The company is currently expanding its pilot facility in British Columbia and expects to be producing more than 26,000 gallons of ethanol per year starting this summer. In addition, this pilot plant will be used to test new equipment, enzymes and biological agents in an industrial setting. The results from these evaluations will be used to inform the construction of a small-scale biorefinery in Colorado, which MacLachlan projects will be completed by 2011.

In the end, the race to commercialize cellulosic ethanol may not really be about which technology is better or more economical than another. Each approach comes with its advantages and disadvantages therefore investors continue to invest in all three platforms. "The new renewable fuels standard is so aggressive with respect to the production of cellulosic biofuels that there is growing awareness and we should not be betting the farm on one technology pathway," Brown says.

Similarly, MacLachlan, doesn't view the growth of the industry as something marked by a single dominant technology. "What you're going to find is that there will be a lot of technologies out there, any of which will be appropriate for different feedstocks and different parts of the world," he says. "I'm hoping that everyone does well because, the truth of it is, the industry needs to have several successful projects and successful companies seeing their technologies deployed." Flatt sees the industry evolving into something of a hybrid where up-front biological processes will be integrated with thermochemical processes for maximum efficiency and cost effectiveness. "It's based on the simple observation that lignocellulosic feedstocks are roughly two-thirds sugar and one-third lignin. Sugars are very efficiently converted to things like ethanol, and biochemical processes have an inherent advantage when it comes to converting sugars," he explains. "Thermochemical processes on the other hand do have some inherent advantages in converting the lignin component."

The race then, may just center on striving—as a nation—to become energy independent, pitting financial, environmental and security needs against time. "I think they should be viewed as complementary technologies that are gearing up toward the same goal," Duff says. "One may establish itself as superior in economic terms as we go down this road but I would absolutely not admit that it was a done deal yet," he adds. "The jury's still out."

Jessica Ebert is an Ethanol Producer Magazine staff writer. Reach her at jebertserp@yahoo.com.