Biological H{sub 2} from fuel gases and from H{sub 2}O
- National Renewable Energy Lab., Golden, CO (United States)
The two stand-alone objectives of the research are to economically produce H{sub 2} in the near term from biomass (thermally gasified to syngas) and in the mid term from H{sub 2}O using cyanobacteria or algae with an oxygen-tolerant bacterial hydrogenase. Photosynthetic bacteria have four different terminal enzymes that mediate their H{sub 2} metabolisms--nitrogenase, uptake hydrogenase, fermentative hydrogenase, and carbon monoxide-linked hydrogenase. Each has been microbiologically and biochemically examined for their potential to specifically generate H{sub 2} in large-scale processes. Based on measurements of maximal activities, stabilities, energy requirements, equilibria, and partial pressures of the H{sub 2} producing reactions, the Co-linked hydrogenase is easily the most suited for practical applications. The enzyme mediates H{sub 2} production from CO at rates up to 3 mmol/min {center_dot} g cell dry weight at near ambient temperature and pressure. At biological temperatures, equilibrium for the CO shift into H{sub 2} lies far towards H{sub 2} production. Less than 0.1 ppm of CO remains after a 20% CO gas phase is acted upon by bacteria. The necessary contact time between CO and bacteria is approximately ten seconds. Similar biological activities are observed with thermally generated fuel gases. The product gas can be directly used in fuel cells. New bacterial isolates from nature and mutant strains are being selected to further improve the novel technology. Oxygen-resistant enzymes identified in some bacterial strains could lead to a more general, second generation technology mediating the solar production of H{sub 2} from H{sub 2}O. Presently, mass transfer of gaseous CO limits the bacterial production of H{sub 2} from fuel gases. New bioreactor designs have significantly enhanced shift rates. Vapor-phase and bubble-train bioreactors employing immobilized or suspended bacteria are being scaled up. A User Facility has been established for the safe engineering scale up and validation of solar or dark technologies for the Hydrogen Program. The first system to be tested at the site will integrate fuel gas generators with biological shift reactors and a PEM fuel cell.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- OSTI ID:
- 305594
- Report Number(s):
- NREL/CP-570-25315-Vol.1; CONF-980440-Vol.1; ON: DE98007507; TRN: IM9906%%274
- Resource Relation:
- Conference: US DOE hydrogen program technical review meeting, Alexandria, VA (United States), 28-30 Apr 1998; Other Information: PBD: Aug 1998; Related Information: Is Part Of Proceedings of the 1998 U.S. DOE Hydrogen Program Review: Volume 1; PB: 425 p.
- Country of Publication:
- United States
- Language:
- English
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