New mechanism converts natural gas to energy faster, captures CO2

May 7, 2013 by Matt Shipman

( —North Carolina State University researchers have identified a new mechanism to convert natural gas into energy up to 70 times faster, while effectively capturing the greenhouse gas carbon dioxide (CO2).

"This could make power generation from natural gas both cleaner and more efficient," says Fanxing Li, co-author of a paper on the research and an assistant professor of chemical and biomolecular engineering at NC State.

At issue is a process called chemical looping, in which a solid, oxygen-laden material – called an "oxygen carrier" – is put in contact with natural gas. The oxygen atoms in the oxygen carrier interact with the natural gas, causing combustion that produces energy.

Previous state-of-the-art oxygen carriers were made from a composite of inert and . But Li's team has developed a new type of oxygen carrier that include a "mixed ionic-electronic conductor," which effectively shuttles into the natural gas very efficiently – making the chemical looping combustion process as much as 70 times faster. This mixed conductor material is held in a nanoscale matrix with an – otherwise known as rust. The rust serves as a source of oxygen for the mixed conductor to shuttle out into the natural gas.

NC State University researchers have developed a new type of oxygen carrier that include a "mixed ionic-electronic conductor," which effectively shuttles oxygen atoms into natural gas very efficiently -- making the chemical looping combustion process as much as 70 times faster. Credit: Fanxing Li, North Carolina State University

In addition to energy, the combustion process produces and CO2. By condensing out the water vapor, researchers are able to create a stream of concentrated CO2 to be capture for sequestration.

Because the new oxygen carrier combusts natural gas so much more quickly than previous chemical looping technologies, it makes smaller chemical looping reactors more economically feasible – since they would allow users to create the same amount of energy with a smaller system.

"Improving this process hopefully moves us closer to commercial applications that use chemical looping, which would help us limit ," Li says.

Explore further: A milestone for new carbon-dioxide capture/clean coal technology

More information: The paper, "Iron Oxide with Facilitated O2 – Transport for Facile Fuel Oxidation and CO2 Capture in a Chemical Looping Scheme," was chosen as part of the cover page story in the March issue of ACS Sustainable Chemistry & Engineering.

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1 / 5 (7) May 07, 2013
Alternately they could use steam rather than air in the oxide reforming stage and get hydrogen as a valuable fuel bi-product. Instead of hot rusting as a secondary combustion stage.
1 / 5 (4) May 07, 2013
get hydrogen as a valuable fuel bi-product

Steam reforming would consume all the energy released in the burning to free the hydrogen. It's already widely in use in the industry, e.g. in producing ammonia for synthetic fertilizers.
1 / 5 (1) May 07, 2013
Does this also make the process more efficient?
1 / 5 (7) May 07, 2013
Normal steam reforming of hydrocarbons to generate hydrogen (and carbon monoxide)requires energy as you said.
However I believe elemental iron can reduce water to hydrogen, by oxidising itself without any external energy: Iron being more electropositive than hydrogen. (Though its been a long while since I did any serious chemistry.)
So both parts of my suggested modified looping process would be exothermic. Though my second stage is not as strongly exothermic as their original 'burning' of the iron in air to recover the iron oxide.
1 / 5 (5) May 07, 2013
I'd like to know how much energy is required to produce the "oxygen carrier"...
1 / 5 (6) May 08, 2013
Are they comparing this to ambient air or other oxygen carriers? The up to 70 times faster is ambiguous. If you use air composed of 100% oxygen to begin with you will have a significant increase in efficiency.

IMO. This article is should have focused more on the CO2 capture and sequestration. What kind of gains are we looking at here and how does it compare to the other sequestration methods?
1 / 5 (4) May 08, 2013
EyeNStein: if you look at the thermodynamics of it, you'll find that turning CH4 into CO2 and H2 carries most of the energy away in the H2 molecules. It doesn't matter what intermediate steps you take.

1 / 5 (3) May 11, 2013
So where do would we put this CO2 so that it stayed safely out of our atmosphere for a thousand years or so?
1 / 5 (5) May 12, 2013
This is a better solution than current solutions but it still has to be sequestered which is shown to leak in the case of fracking. I am not sure whether or not fracking doesn't pump down as deep or in the same places so my evaluation might not be sound. In the case of fracking it has been known to have leaks. I would think it would be the same for CO2. Secondly, it is only an interim solution since we can only pump so much in the ground because if it did release suddenly as it is likely to do so in case of a ground fault, it would be disastrous. This would however buy us 50 years. Of course getting the natural gas and leakage environmental impacts still apply. Sequestering is also expensive. Using biomass to produce energy via hydrogen is a much better solution and can be done with nearly 100% efficiency (without counting the loss in the plants themselves and the NET CO2 is zero). This will take us from a 6 % biomass utilization to a 12% utilization, mainly with efficiency increase.
1 / 5 (6) May 13, 2013
Maybe I'm a little ignorant to the subject, but why is an increase in combustion speed significant. As far as I know we have no problems burning natural gas fast enough by purely conventional methods. I didn't see anything mentioned about this method having an increase in efficiency, so how would this be useful? And as far as the CO2 sequestration, we still need to figure out a storage solution. Until we figure that out, capturing it isn't going to get you far.
And on the topic of biomass utilization for energy production, does anyone know if someone has looked into using charcoal as a carbon sequestration material? It seems to me it would lend itself well to the task. It's non-toxic, stable and easily produced from all sorts of woody organic material. And as a byproduct of charcoal production you get a substantial amount of flammable gas that volatilizes out of the input materials. That could be used for power generation.

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