Virginia Tech team develops process for high-yield production of hydrogen from xylose under mild conditions
|Flow of the new process; enzymes are in red. Credit: Martín del Campo et al. Click to enlarge.|
A team of Virginia Tech researchers, led by Dr. Y.H. Percival Zhang, has developed a process to convert xylose—the second-most abundant sugar in plants—into hydrogen with approaching 100% of the theoretical yield. The findings of their study, published in the journal Angewandte Chemie, International Edition, suggest that cell-free biosystems could produce hydrogen from biomass xylose at low cost.
In the process, hydrogen is produced from xylose and water in one reactor containing 13 enzymes, including a novel polyphosphate xylulokinase (XK). The method can be performed using any source of biomass.
Zhang’s team has been focused for the last 7 years 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 (e.g., earlier post).
The new process uses mild reaction conditions of 50 ° C (122 °F) 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 constitutes as much as 30% 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.
Even more appealing, this reaction occurs at low temperatures; 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%, resulting in an energy penalty.
In his previous research, Zhang used enzymes to produce hydrogen from starch, but the reaction required a food source that made the process too costly for mass production.
Jonathan R. Mielenz, group leader of the bioscience and technology biosciences division at the Oak Ridge National Laboratory, who is familiar with Zhang’s work but not affiliated with this project, said this discovery has the potential to have a major impact on alternative energy production.
Mielenz said Zhang’s process could find its way to the marketplace as quickly as three years if the technology is available. Zhang said when it does become commercially available, it has the possibility of making an enormous impact.
Support for the current research comes from the Department of Biological Systems Engineering at Virginia Tech. Additional resources were contributed by the Shell GameChanger Program, the Virginia Tech College of Agriculture and Life Sciences’ Biodesign and Bioprocessing Research Center, and the U.S. Department of Energy BioEnergy Science Center, along with the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences of the Department of Energy. The lead author of the article, Julia S. Martín Del Campo, who works in Zhang’s lab, received her Ph.D. grant from the Mexican Council of Science and Technology.
Julia S. Martín del Campo, Joseph Rollin, Suwan Myung, You Chun, Sanjeev Chandrayan, Rodrigo Patiño, Michael WW Adams, Y.-H. Percival Zhang (2013) High-Yield Production of Dihydrogen from Xylose by Using a Synthetic Enzyme Cascade in a Cell-Free System. Angewandte Chemie International Edition doi: 10.1002/anie.201300766