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.

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