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Delivering a Sweet-Fueled Vehicle

By Jerry W. Kram
Biomass is an abundant resource. The challenge is converting it into a form of energy that is useful and convenient. You can't fuel your car with sawdust or plug your computer into a field of switchgrass. However, if work being done by Y. Percival Zhang at Virginia Tech comes to fruition, something close to that level of instant conversion could be possible.

Zhang and his research team have created a process that uses enzymes to digest starch or sugars in order to release hydrogen and carbon dioxide. Hydrogen has been made from biomass in the past, but only through pyrolysis or steam reforming using high temperature and pressure. Zhang's process uses mostly off-the-shelf enzymes to digest the biomass between room temperature and 180 degrees Fahrenheit. "We think our technology is the best because of the selectivity," he says. "We only produce hydrogen and carbon dioxide, no other byproducts. The product quality is very pure."

The pathway Zhang designed isn't found in nature. The enzymes in the system come from rabbits, spinach, yeast and bacteria. The key benefit of the system is that it's favored by thermodynamics. In other words, it spontaneously proceeds from beginning to end with no additional input of chemical or heat energy. Combined with hydrogen's natural advantages as a fuel, Zhang's process can deliver much more energy per pound of biomass. "Hydrogen is much more efficient than ethanol," he says. "If you use ethanol, it has to go into an internal combustion engine. That engine is very inefficient. If we can go to hydrogen, we can increase the engine efficiency greatly, maybe even two or three fold, or higher. That means the biomass can do more work."

While the cocktail of 13 enzymes and a phosphorus-containing cofactor sounds complex, Zhang says it's much simpler than systems found in nature. Plus, the artificial pathway is more efficient than any found in nature. The enzymes and cofactor chemically combine water and glucose to create 12 hydrogen molecules for every sugar molecule. "In using biological systems to create hydrogen, the traditional belief was that you could only make four molecules of hydrogen from sugar," he says. "This is the first time anyone has been able to make 12 molecules. We can extract all the energy from the sugar for the first time."

Zhang foresees a day in the future when hydrogen fuel cells will be connected to a sugar-fueled reaction chamber small enough to fit into an ordinary car. Biomass has a higher energy density than hydrogen gas, making it cheaper to transport and store on-site. "Most people believe that storing hydrogen is the biggest challenge (for fuel cell technology), but our idea is to use sugar as a hydrogen carrier," he says. "If you need hydrogen, you can convert sugar into hydrogen immediately."

Before that day arrives, there are 16 innovations that need to be developed, and Zhang's team has conquered the first six. "Right now, our reaction rate is very bad," Zhang says. "We haven't done any optimization. We were just trying to do a proof of concept. Before this, no one believed you could make this much hydrogen from sugar." He doesn't see the remaining challenges as insurmountable, but it will take time before the sugar-powered car becomes a reality. The first demonstration-scale application is likely to be a stationary facility such as a hydrogen-fueling station. That would require improving the system's reaction rate 100-fold, something Zhang thinks could be accomplished in as little as six years. However, he admits the ultimate application of running a car directly off of a tank of sugar will take longer.
 

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