Developing the Greenest and Most Efficient Car Powered by Sugars

1. VT Developing the Greenest and Most Efficient Car Powered by Sugars Y.-H. Percival Zhang 1*, and Jonathan R. Mielenz 2 1Department of Biological Systems Engineering, Virginia Tech, Blacksburg, VA 24061; 2 Life Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. *, corresponding author. Email: ypzhang@vt.edu Tel: 540-231-7414 (O), 540-231-0747 (L) Three Birds are killed by one stone !!! Challenges Unique Features Likely lowest hydrogen production costs ($2/kg) Hydrogen Production Mild reaction conditions (30-100oC, no pressure) Highest yields from sugars (12 H2/glucose) Hydrogen Storage 14.8 H2-mass %, 108 kg H2/m3 Hydrogen DistributionStore and distribute solid sugars . Abstract The hydrogen economy offers a compelling clean energy future but there are four main obstacles: hydrogen production, storage, and distribution, as well as high costs of fuel cells. We have invented a synthetic enzymatic pathway consisting of 13 enzymes for producing hydrogen from starch and water as C6H10O5 (l) + 7 H2O (l)  12 H2 (g) + 6 CO2 (g). The unique features, such as mild reaction conditions (30oC and atmospheric pressure), high hydrogen yields, likely low production costs ($~2/kg H2), and a high energy-density carrier starch (14.8 H2-based mass%), provides perfect opportunities for mobile applications. With technology improvements and integration with fuel cells, this technology also solves the challenges associated with hydrogen storage, distribution, and infrastructure in the hydrogen economy We envision that future mobile appliances will store solid starch, produce hydrogen from starch and water via this reaction, and then generate electricity by hydrogen fuel cells at the same compact place.The prototype zero-pollution car powered by sugars is under development. Conceptual Sugar Car The supposed sugar-fuel cell (Figure 2) would achieve the highest energy efficiency (50-55%) than any other technology (e.g., ICE-electrical hybrid, hydrogen-fuel cell) in the world (7). Rationale and Challenges The future hydrogen economy is a linked network of chemical processes that produces hydrogen, stores hydrogen chemically or physically, and converts the stored hydrogen to electrical energy at the point of use. It would solve the problem of finite fossil fuel reserves and minimize the negative environmental impacts of hydrocarbon fuel burning (1,2) because hydrogen fuel cells have much higher energy efficiency (~50-80%) than do internal combustion engines (~18-23%), and do not produce any pollutants (1,2). Four main technical challenges for mobile hydrogen-fuel cell applications were outlined by the Department of Energy (DOE): 1) decreasing hydrogen production costs via a number of means, 2) finding viable methods for high-density hydrogen storage, 3) establishing a safe and effective infrastructure for seamless delivery of hydrogen from production to storage to use, and 4) dramatically lowering the costs of fuel cells. So far, all hydrogen-producing methods based on less costly biomass have been plagued with low energy yields and/or severe reaction conditions and/or complex processing requirements; all solid hydrogen storage methods have low energy storage densities and are not suitable for mobile applications; a large scale hydrogen distribution infrastructure does not exist. Sugar Car A B Our Invention Our idea is to utilize energy stored in polysaccharides to break up water and release all energy in the form of hydrogen by a novel enzymatic technology (synthetic enzymatic pathway engineering): C6H10O5 (l) + 7 H2O (l)  12 H2 (g) + 6 CO2 (g) [1] We designed an artificial enzymatic pathway comprised of reversible enzymatic reactions and pathways: 1) a chain-shortening phosphorylation reaction catalyzed by a-glucan or b-glucan phosphorylases (Equation 2) (3,4), 2) a conversion from glucose-1-phosphate (G-1-P) to glucose-6-phosphate (G-6-P) catalyzed by phosphoglucomutase (Equation 3), 3) a pentose phosphate pathway (Equation 4), and 4) hydrogen generation from NADPH catalyzed by hydrogenase (Equation 5) (5): (C6H10O5)n + H2O + Pi (C6H10O5)n-1 + G-1-P [2] G-1-P  G-6-P [3] G-6-P + 12 NADP+ + 6 H2O  12 NADPH + 12 H+ + 6 CO2 + Pi [4] 12 NADPH + 12 H+  12 H2 +12 NADP+ [5] Figure 2. The conceptual design for the integrated on-board bio-converter and fuel cell (A) and sugar car (B). Figure 1. The synthetic metabolic pathway for complete conversion of glucan and water to hydrogen and carbon dioxide.PPP, pentose phosphate pathway. The enzymes are: #1 GNP, glucan phosphorylase; #2 PGM, phosphoglucomutase; #3 G6PDH, G-6-P dehydrogenase; #4 6PGDH, 6-phosphogluconate dehydrogenase, #5 Ru5PI phosphoribose isomerase; #6 R5PI. ribulose 5-phosphate epimerase; #7 TKL, transketolase; #8 TAL, transaldolase; #9 TPI, triose phosphate isomerase; #10 ALD, aldolase, #11 FBP, fructose-1, 6-bisphosphatase; #12 PGI, phosphoglucose isomerase; and #13 H2ase, hydrogenase. The metabolites are: G1P, glucose-1-phosphate; G6P, glucose-6-phosphate; 6PG, 6-phosphogluconate; Ru5P, ribulose-5-phosphate; X5P, xylulose-5-phosphate; R5P, ribose-5-phosphate; S7P, sedoheptulose-7-phosphate; G3P, glyceraldehyde-3-phosphate; E4P, erythrose-4-phosphate; DHAP, dihydroxacetone phosphate; FDP, fructose-1,6-diphosphate; F6P, fructose-6-phosphate; and Pi, inorganic phosphate We (Virginia Tech, Oak Ridge National Laboratory, University of Georgia) are working together to increase reaction rates, reduce enzyme costs, increase enzyme stability, and develop the sugar car concept. Any collaborations towards this ambitious project and funding are welcome. References • J. A. Turner, Science305, 972 (2004). • B. C. H. Steele, A. Heinzel, Nature414, 345 (2001) • Y.-H. P. Zhang, L. R. Lynd, Appl. Environ. Microbiol.70, 1563 (2004). • Y.-H. P. Zhang, L. R. Lynd, Proc. Natl. Acad. Sci. USA102, 7321 (2005). • J. Woodward, M. Orr, K. Cordray, E. Greenbaum, Nature405, 1014 (2000). • Y.-H. P. Zhang, B. R. Evans, J. R. Mielenz, R. Hopkins, M.M W. Adams. under review (2007). • M. I. Hoffert et al., Science298, 981 (2002). We have finished the proof-of-concept experiment (data not shown). The manuscript is under review (6).