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Researchers Develop Method for Enzymatic Production of Hydrogen from Biomass at High Yields

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The synthetic metabolic pathway for conversion of polysaccharides and water to hydrogen and carbon dioxide. Click to enlarge.

Researchers at Virginia Tech, Oak Ridge National Laboratory (ORNL), and the University of Georgia have developed a novel method using multiple enzymes as a catalyst for the direct, low-cost production of hydrogen from biomass.

Applying the principles of synthetic biology, the researchers use a combination of 13 enzymes to form an unnatural enzymatic pathway to completely convert polysaccharides—e.g., starch and cellulose—and water into hydrogen at a yield higher than the theoretical yield of biological hydrogen fermentations. Their work is described in the 23 May issue of PLoS ONE, the online, open-access journal from the Public Library of Science.

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Hydrogen production from either 2 mM G-6-P or 2 mM starch (glucose equivalent) using the new method. Click to enlarge.

Starch is a high energy-density carrier, with 14.8 H2-based mass%. (The DOE long-term target for hydrogen storage is 12 mass%.) The enzymes, when added to the biomass solution, use the energy in the polysaccharides to break the water up into carbon dioxide and hydrogen.

A membrane bleeds off the carbon dioxide and the hydrogen is used by a fuel cell to create electricity. The water byproduct is recycled for the starch-water reactor. Laboratory tests confirm that it all takes place at low temperature—30° C—and atmospheric pressure. The researchers estimated the cost of hydrogen production using their method of approximately $2/kg.

The stoichiometric reaction is:

C6H10O5 (l) + 7 H2O (l) → 12 H2 (g)+6 CO2 (g)

The overall process is spontaneous and unidirectional because of a negative Gibbs free energy and separation of the gaseous products with the aqueous reactants.

The vision is for the ingredients to be mixed in the fuel tank of a car. A car with an approximately 12-gallon tank could hold 27 kg of starch, which is the equivalent of 4 kg of hydrogen. One kg of starch will produce the same energy output as 1.12 kg (0.38 gallons) of gasoline.

The research was based on earlier work by Y.H. Percival Zhang, assistant professor of biological systems engineering at Virginia Tech pertaining to cellulosic ethanol production (earlier post) and the ORNL and University of Georgia researchers' work with enzymatic hydrogen production.

One of the team, Michael W.W. Adams of the University of Georgia UGA, is co-author of the first enzymatic hydrogen paper in Nature Biotechnology in 1996. The researchers were certain they could combine the processes.

In nature, most hydrogen is produced from anaerobic fermentation. But hydrogen, along with acetic acid, is a co-product and the hydrogen yield is pretty low—only four molecules per molecule of glucose. In our process, hydrogen is the main product and hydrogen yields are three-times higher, and the likely production costs are low—about $1 per pound of hydrogen.

What is more important, the energy conversion efficiency from the sugar-hydrogen-fuel cell system is extremely high—greater than three times higher than a sugar-ethanol-internal combustion engine. It means that if about 30 percent of transportation fuel can be replaced by ethanol from biomass as the DOE proposed, the same amount of biomass will be sufficient to provide 100 percent of vehicle transportation fuel through this technology.

—Y.H. Percival Zhang

The next step for the team is to increase reaction rates and reduce enzyme costs.

Resources:

Comments

Henrik

Truly amazing! If this is true it will be very big. And I like the idea of filling the tank with cellulose flour shaken with water. Completely non-toxic and non-flammable. I would like to know more about the enzymes. Would you need a separate tank for that and how much would be needed a gallon?

Mark Allerton

Umm... so the process produces 11kg of CO2 for every 2kg of H2, right? As far as I can work out, that's at least factor of 2 better than a gas engine in terms of CO2 per unit of engine, but hardly carbon neutral.

Mark Allerton

Except that the carbon comes from plants. Doh! Sorry...

Stan Peterson

Fossil fuel CO2 comes from plants too, just older ones.

Energex42

Once we manage to produce CO2 in concentrated form, it becomes a resource as opposed to a waste. What products can we make from a purified CO2 source?

Nick

Stan--

True enough, but burning biomass can be carbon neutral.

Neil

Certainly sounds interesting. I'd love to know what the energy efficiency of the system works out to be. If you're going to make hydrogen in a car then you really should run it through a fuel cell rather than use (ugh) ICE. I wonder if this process could have a use as a small scale local electrical generating system for remote locations.

C Harget

CO2 in concentrated form gets you carbonated beverages, dry ice, and is useful to feed algae farms if they can ever get the costs down on the bioreactors. The better question is, Is the process described above suitable only for large scale hydrogen creation, or could it be useful for home production? How affordable is it likely to be compared to oil and coal?

Mike@HCVN

This is a very cool development. I wonder how many (if any) of the enzymes are catalysts instead of reactants, implying that they'd be reused instead of consumed.

Mike

Ben

I question its ability to digest cellulose, also the great thing about biomass is making it into industrial organic chemicals, hydrogen has no use other then fuel and fertilizer. Then again: remember "Back to the Future" were Doc shows Marty how the 2015 revamped DeLorean runs off garbage?, well this is exactly that: just chuck your compost into the car out comes hydrogen fuel!

SJC

You could use the H2 with some extra CO from biomass gasification and make more methane. CH4 is the main component in natural gas and when you gasify biomass, you end up with more CO than H2 when you make the CH4.

I like the idea of biomass gasifiers in the mid west taking in corn stalks and making methane (SNG) then providing it to the nation via present NG pipelines.
You could solar thermally heat homes and buildings and then use the NG saved to run cars.

Henrik

This guy rocks: Mr Y.-H. Percival Zhang. Here is a link for more info on his research. http://filebox.vt.edu/users/ypzhang/research.htm. There is still a long way to go many years before this research result in a sugar fuel cell electric car. As I now get it is that biomass will be converted at a central factory using enzymes same process that is needed for cellulose ethanol. Then you simply load sugar and water on the car plus some enzymes. A reactor uses this to generate hydrogen for a standard hydrogen full cell. The whole process from sugar conversion to hydrogen to electricity to torque has a record efficiency conversion rate of 55%! Beating all other known processes. Show stoppers are currently the speed of the sugar hydrogen generator. When you drive the car you need energy fast and the enzymatic process seems to take hours (from what I understand) when it should take minutes. Another show stopper is making cheap enzymes. If all this is indeed solved and others succeed in making a 70 kW hydrogen fuel cell for the target price of $4000 then fuel cell cars is a relay good alternative to BEVs because they have a far more energy dense system. In addition the processes that convert lignocellulose to sugars is useful also for creating cheap sugar for humans and animal feed out of wood and grass. Wow! Even if the speed of the process can’t be solved there would still be much to gain from having a cheap but slow way to make hydrogen. All the best wishes to this guy and his team. The world needs people like him to combat GW.

Jim

Isn't this process better?
http://www.sciencedaily.com/releases/2007/05/070518163146.htm

Andrey

Wow! Things getting more and more exiting with every day passing by.

Glucose is main energy source/carrier for every living creature. Human body gets glucose mainly from sugars and starches (carbohydrates), proteins, and fats, and burns glucose in all organs. BTW, efficiency of conversion of food stock into mechanical work by muscles is only about 10%.

I can imagine biorefinery which converts glucose to ethanol (exactly what it is done by yeast in liquor and corn ethanol plants), to methane (in bogs, cow’s guts, or sewage/manure anaerobic digesters), to butanol, to organic acids (vinegar fermentation), or now – into hydrogen, or flexible combination of all.

The main problem remains to get glucose not from food stuff, but from cellulose. Cellulose is, actually, polymer consisting from long chains of glucose blocks. Hydrolysis of cellulose by some bacteria or refined from bacteria cultures enzymes cuts these long polymers into small blocks, which could be consumed further by other microorganisms. This is exactly the process which is usually described as first, most troublesome step of cellulosic ethanol production. But now it could be also first step of cellulosic hydrogen production.

tom deplume

If you are going to use biomass as an energy source the why throw away the energy embeded in the carbon?

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