Trading Carbs for Hydrogen
by Jeremy Elton Jacquot, Los Angeles on 05.24.07
Hydrogen energy enthusiasts, rejoice: the recent revelation of a promising (and tasty) new technology that would convert sugars into hydrogen should breathe some much-needed air into the hydrogen fuel cell movement and partially rebuke those who've dismissed the notion of a viable hydrogen economy. Virginia Tech, Oak Ridge National Laboratory (ORNL), researchers led by Y.-H Percival Zhang, assistant professor of biological systems engineering, announced the discovery of a novel synthetic enzymatic pathway that would use a combination of 13 enzymes not normally found in nature to convert polysaccharides and water into hydrogen.
In light of the U.S. Department of Energy's 2006 Advance Energy Initiative that called for the creation of hydrogen-powered fuel cell vehicles by 2020, this technology would solve one of hydrogen's most vexing problems, the cost-efficient storage and transportation of the gas, by allowing future consumers to easily carry around the fuel in the form of starch and water.
Adding enzymes to the mixture would cause them to "use the energy in the starch to break up water into only carbon dioxide and hydrogen," according to Zhang. He and his colleagues believe these ingredients could be mixed in the fuel tank of a car to provide a more potent alternative to gasoline. Assuming a car with a 12-gallon tank could hold 27 kg of starch (the equivalent of 4 kg of hydrogen), it could presumably run for more than 300 miles since Zhang estimates that one kg of starch produces approximately the same energy output as 1.12 kg of gasoline.
While several substances have been suggested as possible "hydrogen carriers" over the years, including methanol, ethanol and ammonia, they all shared the disadvantage of requiring special storage and distribution. This is in contrast to starch, which can easily be distributed in grocery stores.
"So it is environmentally friendly, energy efficient, requires no special infrastructure, and is extremely safe. We have killed three birds with one stone," he said. "We have hydrogen production with a mild reaction and low cost. We have hydrogen storage and transport in the form of starch or syrups. And no special infrastructure is needed. The next R&D step will be to increase reaction rates and reduce enzyme costs. We envision that in the future we will drive vehicles powered by carbohydrate, or energy stored in solid carbohydrate form, with hydrogen production from carbohydrate and water, and electricity production via hydrogen-fuel cells."
::Novel sugar-to-hydrogen technology promises transportation fuel independence, ::ScienceDaily: Novel Sugar-to-hydrogen Technology Promises Transportation Fuel Independence, ::PLoS ONE: High-Yield Hydrogen Production from Starch and Water by a Synthetic Enzymatic Pathway
See also: ::Sweet! The Chocolate-Powered Hydrogen Fuel Cell, ::Using Woody Biomass To Extract Hydrogen From Water & Carbon From The Atmosphere, ::Garbage to Hydrogen, Just Add Sun, ::Green Diesel: Plant Carbohydrate-Based Fuel
Do we know what the consequences are when this "combination of 13 enzymes not normally found in nature" finds its way into nature, including us? Let's not get too excited about synthetic biochemistry just yet.
Wow. Reading in to it they say "photosynthesis efficiency from solar energy to chemical energy is not so high as that of solar cells", but it sounds easier than pumping hydrogen around the country.
Didn't realise that starch could contain more energy than petrol!
But I agree with C.
Unfortunately, you are back to using a food source for a transportation fuel, and incurring the associated environmental costs of growing and processing.
I'm extremely worried about this solution; the whole idea of using Hydrogen or any other alternative to fossil fuels is to reduce our dependency on fossil (non renewable) fuels and to reduce our emission of carbon dioxide. The chemical reaction described seems to indicate that huge amounts of carbon dioxide would be released.
It would be interesting to see a comparison of carbon dioxide emissions between this solution and fossil fuels.
It's neat to think you could drive a syrup-powered vehicle around, but you would still be spewing CO2 out of the tailpipe (or chimney or whatever).
One of the main reasons to pursue hydrogen power for vehicles is that water vapor could be the only exhaust emission from the vehicle, if pure hydrogen and oxygen are used for fuel. This method definitely loses that advantage.
I guess that really proves that the hydrogen economy is as viable as petroleum.
"The chemical reaction described seems to indicate that huge amounts of carbon dioxide would be released."
Yes, but that reaction would be (mostly) carbon neutral since that crabon dioxide was alraedy in the atmospheric carbon cycle, unlike fossil fuels which come from the Earth's crust.
How much Carbon Dioxide are we talking about here as the "other" by-product of this process?
If 4kg of hydrogen is produced, is 4kg of carbon dioxide produced?
Have you any idea where to read about this in more detail? Has the team published a paper, for instance? I'm very curious about it!
"use the energy in the starch to break up water into only carbon dioxide and hydrogen"
Well, this is confusing. Will it only work for carbonated water, or what? Water contains no carbon. Where does the carbon come from to make that carbon dioxide? Is that from the starch? I suspect so. Not a big deal really, just a little misleading.
Still, it's a neat idea! I'm interested in how Zhang would estimate the energy in 1 kg of starch to be equivalent to the energy in 1.12 kg of gasoline. That is astounding! Of course, it probably takes more than 1.12 kg of gasoline to produce 1 kg cornstarch - meaning that this isn't an energy source, but just a nice way to transport energy - albeit, it seems a very convenient way to store this energy, since you can produce the hydrogen on demand instead of having to store it in very heavy and bulky tanks. I guess, if you had efficient (and oil-free!) ways to produce corn (and cornstarch), you might have a viable alternative to petroleum (yay!)
And, of course, this still produces the greenhouse gas CO2 (though it would be interesting to learn how much CO2 is produced when using this method to separate the hydrogen compared to the CO2 produced in a conventional gasoline engine).
Hey Jesse,
If you want some more insight on the team's work, I recommend you check out their paper at the following website: http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0000456
As you note, the carbon does indeed come from the polysaccharides/starch used with the water and enzymes.
Thanks for the questions, and please feel free to weigh in with more!
Jeremy
Potato juice!!!
Note to admins: I'm not seeing any of the 9 comments listed on the main page after clicking on the post.
My point here is simple: How much energy does it cost to do the conversion? How efficient is it? Where are you getting that energy in the first place? At first blush, I don't see an improvement here over generating hydrogen with a wind or solar plant and some water.
The big issue with hydrogen is that you have to put a lot of energy in - much more than you get back from the H2 - to make the stuff. When I see comments like "rebuke the people who've dismissed the hydrogen economy" without actually addressing the biggest problems those people have brought up, it seems like just another energy pipe dream.
Seriously - a combination of 13 enzymes not normally found in nature, and we're entertaining the idea that this is going to be somehow more energy-efficient than shipping ammonia (also available in grocery stores)?