To produce ethanol from plant material, researchers must follow three main steps, said Percival Zhang, associate professor of biological systems engineering in Virginia Tech’s College of Agriculture and Life Sciences.
Those steps involve pretreating to separate the components of plant cell walls; breaking down cellulose, the carbohydrate that is the major component of plant cell walls; and fermenting the resulting sugars. If a gentle enough process is used, researchers could find potentially valuable byproducts from cellulose breakdown, Zhang said.
As a scientist at Dartmouth, then at Virginia Tech, Zhang developed a gentle and cost-effective pretreatment process. He combined chemical and enzyme-based solvents to replace the traditional high-heat, high-pressure process. The solvent solution can even be recycled.
The weakened cellulose can be fractionated into four products: lignin, acetic acid, hemicellulose sugars, and amorphous cellulose. "While the sugars are the target for biofuels, the lignin and acetic acid co-products can also generate income, making a biorefinery more profitable," Zhang said. "For instance, lignin has many industrial uses, from glue to polymer substitutes and carbon fiber."
In 2008, Biomethodes, a French biotechnology company, licensed Zhang's technology for converting biomass to ethanol and other products from Virginia Tech Intellectual Properties Inc. In March 2011, Biomethodes announced plans to build a pilot plant in Virginia. Goals are to improve the efficiency of the breakdown of celluose, optimize production of enzymes, reduce enzyme cost, and then do industrial scale testing with a commercial process deployment.
“Our strategy is to enable next generation of biocatalysts and biofuels by co-developing pre-industrial processes, to be further integrated by industrial partners,” said Gilles Amsallem, Biomethodes chief executive officer.
Locating the plant in Virginia will enhance the collaboration with Zhang as the process is optimized, Amsallem said. A U.S. based-plant is also important because “in the United States, the time to market is shorter for ethanol,” said Amsallem.
In the meantime, Zhang has developed another energy product from biomass sugars – hydrogen to power a fuel cell. His aim is to have the conversion occur in your car's fuel tank or at a fuel cell site.
U.S. Secretary of Energy Stephen Chu told Technology Review in 2009, "Four miracles need to happen before hydrogen fuel cells can be practical. … We need better ways to produce, distribute, and store hydrogen, and we need better, cheaper fuel cells."
Zhang said he is undaunted. He has already come up with a way to produce the highest yield of hydrogen from biomass sugar. And he has an idea and successful results from proof-of-concept experiments for hydrogen storage and distribution.
In 2007, Zhang and colleagues Barbara R. Evans and Jonathan R. Mielenz of Oak Ridge National Laboratory and Robert C. Hopkins and Michael W.W. Adams of the University of Georgia succeeded in completely converting starch and water into hydrogen using a combination of 13 enzymes never found together in nature.
Starch is used by plants for energy storage and is very stable. The enzymes use the energy in the starch to break up water into carbon dioxide and hydrogen. The hydrogen is used by the fuel cell to create electricity. Water, a byproduct of that fuel cell process, goes back into the tank for the starch-fed enzymes to convert to hydrogen and so on.
Experiments conducted at Oak Ridge National Laboratory using off-the-shelf enzymes from bacteria, yeast, rabbit, archaea, and spinach confirmed that it all takes place at low temperature – about 86 degrees Fahrenheit.
The researchers used cellulosic materials isolated from wood chips, but crop waste or switchgrass could also be used. It is not necessary to use food, such as corn, Zhang said.
And now Zhang has invented inexpensive, cell-free enzymes to convert biomass to energy. The result is three times the hydrogen with no left over, irrelevant cell mass.
And all the enzymes are produced by the E. coli bacterium.
Hydrogen storage and distribution
Yes. Zhang is recommending putting E. coli and a form of sugar in your vehicle's tank.
Hydrogen gas is difficult to store and to transport. But not if it is stored in a carbohydrate, something like flour or powdered sugar, enriched with enzymes. You could buy a bag of it from a grocery store or dry goods outlet – an instant mix to fuel a fuel cell. An onboard battery provides immediate energy for starting the vehicle while the enzymes get to work on their sugary snack. The fuel cell will recharge the battery later from excess sugar energy.
Stationary energy sites, such as large fuel cell stacks, can also take delivery of carbohydrate powder from local or distant biorefineries and generate hydrogen by using an enzyme cocktail, Zhang said.
The use of renewable carbohydrates and enzymes addresses the challenges associated with storage, safety, distribution, and infrastructure.
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