Biohydrogen Breakthrough? Using Xytose to Produce Hydrogen

A team of Virginia Tech researchers has discovered a way to extract large quantities of hydrogen from any plant, a breakthrough that has the potential to bring a low-cost, environmentally friendly fuel source to the world.

“Our new process could help end our dependence on fossil fuels,” said Y.H. Percival Zhang, an associate professor of biological systems engineering in the College of Agriculture and Life Sciences and the College of Engineering “Hydrogen is one of the most important biofuels of the future.”

Zhang and his team have succeeded in using xylose, the most abundant simple plant sugar, to produce a large quantity of hydrogen that previously was attainable only in theory. Zhang’s method can be performed using any source of biomass.

The discovery is a featured editor’s choice in an online version of the chemistry journal Angewandte Chemie, International Edition.

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Obstacles to commercial production of hydrogen gas from biomass previously included the high cost of the processes used and the relatively low quantity of the end product.

But Zhang thinks he has found the answers to those problems.

For seven years, Zhang’s team has been focused on finding non-traditional ways to produce high-yield hydrogen at low cost, specifically researching enzyme combinations, discovering novel enzymes, and engineering enzymes with desirable properties.

The team liberates the high-purity hydrogen under mild reaction conditions at 122 degree Fahrenheit and normal atmospheric pressure. The biocatalysts used to release the hydrogen are a group of enzymes artificially isolated from different microorganisms that thrive at extreme temperatures, some of which could grow at around the boiling point of water.

The researchers chose to use xylose, which comprises as much as 30 percent of plant cell walls. Despite its abundance, the use of xylose for releasing hydrogen has been limited. The natural or engineered microorganisms that most scientists use in their experiments cannot produce hydrogen in high yield because these microorganisms grow and reproduce instead of splitting water molecules to yield pure hydrogen.

To liberate the hydrogen, Virginia Tech scientists separated a number of enzymes from their native microorganisms to create a customized enzyme cocktail that does not occur in nature. The enzymes, when combined with xylose and a polyphosphate, liberate the unprecedentedly high volume of hydrogen from xylose, resulting in the production of about three times as much hydrogen as other hydrogen-producing microorganisms.

The energy stored in xylose splits water molecules, yielding high-purity hydrogen that can be directly utilized by proton-exchange membrane fuel cells. Even more appealing, this reaction occurs at low temperatures, generating hydrogen energy that is greater than the chemical energy stored in xylose and the polyphosphate. This results in an energy efficiency of more than 100 percent — a net energy gain. That means that low-temperature waste heat can be used to produce high-quality chemical energy hydrogen for the first time. Other processes that convert sugar into biofuels such as ethanol and butanol always have energy efficiencies of less than 100 percent, resulting in an energy penalty.

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