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Sandia Applying Solar Thermochemical Hydrogen Technology to Recycling CO2 to Liquid Fuels

The CR5 thermochemical engine is the basis of the Sunshine to Petrol project. Click to enlarge.

Researchers at Sandia National Laboratories are extending work on the development of a device for the solar thermochemical production of hydrogen from the splitting of water to recycling CO2 into liquid hydrocarbon fuels.

The prototype device—the Counter Rotating Ring Receiver Reactor Recuperator (CR5)—will be applied to breaking the carbon-oxygen bond in carbon dioxide to produce carbon monoxide and oxygen. Combining the CO stream with the hydrogen resulting from the splitting of water by a CR5 device, an integrated “Sunshine to Petrol” (S2P) system could then synthesize a liquid combustible hydrocarbon fuel.

As originally developed for hydrogen production, the CR5 is a stack of rings made of a reactive ferrite material, consisting of iron oxide mixed with a metal oxide such as cobalt, magnesium, or nickel oxide. Every other ring rotates in opposite directions. Concentrated solar heat is reflected through a small hole onto one side of the stack of rings. The side of the rings in the sunlit area is hot, while the other side is relatively cold. As the rotating rings pass each other in between these regions, the hot rings heat up the cooler rings, and the colder rings cool down the hot rings. This arrangement results in a conservation of heat entering the system, limiting the energy input required from the sunlight.

Hydrogen production with these materials involves two chemical reactions: a high temperature (1,550°C) thermal reduction to produce oxygen followed by a lower temperature (1,100°C) water oxidation to produce hydrogen.

One of the keys to the device is the material used in the rings. For hydrogen production, the team found that suspending the ferrite material in zirconia, a refractory oxide that withstands high temperatures, delivered a high yield of hydrogen “quickly and repeatedly,” even after forming the mixture into complex solid shapes. Without using the zirconia, the ferrite material doesn’t hold together well; it essentially forms a slag and stops reacting.

The ferrite/zirconia structures are laid line-by-line using robocasting, a method developed and perfected by other team members that relies on robotics for computer-controlled deposition of materials through a syringe. The materials flow like toothpaste and are deposited in thin sequential layers onto a base to build up complex shapes.

Over the past year, the Sandia researchers have shown proof of concept of S2P and are completing a prototype device that will use concentrated solar energy to split carbon dioxide or water.

Rich Diver is the inventor of the CR5 device. Co-researchers on the project are Jim E. Miller and Nathan Siegel. Project champion is Ellen B. Stechel, manager of Sandia’s Fuels and Energy Transitions Department. Stechel says that researchers have known for a long time that theoretically it might be possible to recycle carbon dioxide, but many thought it could not be made practical, either technically or economically.

Funding for Sunshine to Petrol come from Sandia’s internal Laboratory Directed Research and Development (LDRD) program. The research has also attracted interest and some funding from DoD/DARPA (Defense Advanced Research Projects Agency).

Miller says that while the first step would be to capture the carbon dioxide from sources where it is concentrated, ultimate goal would be to snatch it out of the air. A S2P system that includes atmospheric carbon dioxide capture could produce carbon-neutral liquid fuels.

The research team has already proven that the chemistry works repeatedly through multiple cycles without losing performance and on a short enough cycle time for a practical device. The prototype should be completed by early next year. Initial tests will break down water into hydrogen and oxygen. That will be followed by tests that similarly break down carbon dioxide to carbon monoxide and oxygen.

A commercial S2P device is probably at least 15 to 20 years away, according to Stechel.



Harvey D

A machine to recycle CO2 into cleaner energy carriers (sources) would be very useful for all current and future coal fired power plants.

Can it be perfected in time or before we 2X CO2 emissions with a 1000 new worldwide coal fired and/NG power plants.

tom deplume

Optomisticly the first commercial unit won't be on-line until 2022. It won't make a significant impact on liquid fuel supply until 2032 and would take at least until 2050 before it could generate all our liquid fuel needs. This is the realistic time line for any new technology be cellulosic ethanol, Brussard's fusion device, fast reactors, whatever.


This is almost certain to be some multiple of the cost of solar thermal electric power, but it neatly addresses the issue of long-term energy storage and special applications (like aviation).

Probably be 20 years before it's ready for prime time, though.  Solid-oxide fuel cells have been in the pipeline about that long, and they're not quite here yet.


Plants are a good collector of CO2 and hydrogen created from gasification would provide the CO2 necessary for this.


Joy, it's H2Car all over again.

(For some reason I read it as "ThermoNuclear" and wrote this)


It's not H2CAR.  It's a direct thermochemical method, which is far more efficient.  H2CAR is a dead end, this looks far better (though maybe not good enough).


*Shrug* Okay I guess you would know.

But it really does beg the question that if you were running a solar thermal electricity power plant using the same infrastructure, how much more transportation miles would you get.

The other question being, where will all this CO/CO2 come from?

Just in general, it's annoying when people try to act like these options will be the end all be all solution.

Rather than just a niche for things like cargoships, and aircraft.


Fermenting ethanol creates lots of CO2, you could use that as well.


This goes into the "neat scientific curiosity" department. Though we may see accelerated development if given enough R&D funding.


Would have been nice if they had found this 15-20 years ago. For now I agree with Cervus. Nice scientific curiosity, but nothing we could base any public policy on.


What we're not seeing here is the efficiency. I agree that solar thermal is probably loads cheaper, and *with good batteries* BEV is cleaner and easier.

As a CO2 recycling process, this had several challenges:
1) Is there enough acreage near large point sources for CO2 to crack the CO2 and solar-thermally create hydrocarbons?
2) Can you save the CO2 you produce at night?
3) What about in winter time?

Algae consumption of flue gasses has the same challenge, but probably is more vulnerable to invasive species and needs more trace nutrients and such. I've not idea which would ulitmately be cheaper, or preferable.

Still, it seems silly to say this is 15-20 years away. It doesn't sound like tokamak fusion where it needs some kind of unobtainium to make the process economical. It just sounds like it needs pilot projects to prove it at scale.


You find the 15-20 year figure in the original article. If you follow the link, they actually say:

“This invention, though probably a good 15 to 20 years away from being on the market, holds a real promise of being able to reduce carbon dioxide emissions while preserving options to keep using fuels we know and love,” she says. “Recycling carbon dioxide into fuels provides an attractive alternative to burying it.”


Perhaps this system could be used to regenerate Sodium Hydroxide in a system that scrubs CO2 from ambient air.


Perhaps the CR5 could be used to drive calcination (extracting the CO2 from the sodium carbonate) and then regenerate the Sodium Hydroxide farther down the pipeline....

Its late, I probably didn't phrase that properly. In any event, the .pdf link I posted describes a ambient air C02 scrubbing technology that has two chemical loops, both of which need energy (thermal..?) to regenerate.

The fact that the rings rotate apparently lowers the thermal requirements placed on the material much in the way intermittent exposure to fresh air allows the piston and cylinder walls to survive in an ICE.

With a process temperature low of 1,100C and an average of 1,325C, I can't imagine that material sciences guys are saying "that makes it way easier, now we can use plain 'ol iron"

But it really does beg the question that if you were running a solar thermal electricity power plant using the same infrastructure, how much more transportation miles would you get.
If you assume that the solar thermal and thermochemical processes have roughly the same efficiency (a guess), the ratio would be close to the efficiency of the combustion engine and drivetrain.  I dunno, between 3:1 and 6:1, advantage to thermal?
The other question being, where will all this CO/CO2 come from?
There's a lot of CO2 in products of fermentation, anaerobic digestion, and of course combustion.  If the process scales down well (and I don't see why not), it could be made farm-sized so that practically all the harvested carbon can become product rather than being lost as gas.

The beauty of this is that a CO+H2 syngas is a good fraction of the way to a huge number of fuel and chemical products.  Ethanol, methanol, methane, ethylene, F-T alkanes... all can be made from syngas, some with relatively cheap processes. 

Roger Pham

Why not just use the H2 (produced in the first step) directly in vehicles and in power plants for electricity generation? Then, develop methods and matrices for absorbing H2 at 14-17% by weight at relatively low pressure for long-distance transportation and storage of the H2. This will make the transportation of H2 over long distances nearly as efficient as long-distance petroleum transportation.

H2-FCV can be 3x more efficient than current gasoline cars, while it is theoretically possible to make H2-ICE-HEV with 50% thermal efficiency tank-to-wheel, thus making the H2-renewable-energy economy eventually to be even more affordable than current petroleum-dependent transportation system and fossil-fuel electrical generation system.


Basically anything that uses 1500 deg to 1200 deg thermal energies to create any re useable fuel has been claimed un efficiant since the car motor. Think more on a natural level of chemical and solar transverses that mimic more towards a natural aproach like the pem fuel cell or a tree.

richard schumacher

Living plants have an overall efficiency so low that they can't provide a large fraction of transport fuel needs. You'd have to put tens of millions of hectares under the plow for it, which would be an ecological disaster in itself. In contrast artificial systems like this one, taking CO2 directly from the air and powered by nuclear, Solar, or other renewable sources, would be a complete carbon-neutral solution.

Perhaps "15 to 20 years" is the authors' estimate of how long it would take this process to become economical under existing market assumptions. A $50 per tonne tax on fossil carbon would speed that up a lot.


trees are much more efficient at turning CO2 and sunlight into useful products. they are also good for moderating surface temperatures, increasing cloud cover, providing fresh water, decreasing erosion.

so, where is the reforestation research?

where are the desert-hardy hybrids of trees that will reclaim the Sahara while providing useful products to those who look after them?


Richard Schumacher wrote:
Living plants have an overall efficiency so low that they can't provide a large fraction of transport fuel needs.

That may be, but it remains to be seen whether we can get anywhere near those levels of efficiency. Green plants also include in that efficiency the costs of production (including the extraction and processing of raw material), development, maintenance, and deployment.

We should be doing things we can understand and if its old hat thats OK. I have seen nothing really useful in the "waiting for God dept. Pleased to see that a lot of research is going into algae, though not much on
this site recently, I will try to bring some of those links in.
As I understand it a lot of he commentators on site are techs, If they were
also climbers ie technical rope acess climbers or such then they'd be a bit keener on standard ground based wind power. Also any ordinary motor tech with a bit of curiosity to aero props,turbines, lamina flow,
electronics, power generation and a whole host of associated fun stuff.
which should include anyone with one eye open and a spare brain cell or
three must surely find some merit in this technology. I know I'm not alone out there.
Maybe my aesthetics are a bit out there, and that seems to be the critics only valid reason for not getting on with it Someone said "No
It'll spoil the view."
"Better to sit around waiting for god to come up with ?** + good looking to boot."
Trouble is IMHO they wouldn't know good looking if it were gold plated.


Why not just use the H2 (produced in the first step) directly in vehicles and in power plants for electricity generation?
Roger, you are missing the forest for the trees (again).

That's what's great about this invention: all the advantages of hydrogen, without the schlep of a dangerous and difficult-to-handle fuel.


Recycling CO2 from a coal power plant and then burning it still creates the same amount of CO2 from the coal, although it does offset some CO2 from oil.


==Photosynthesis is much more efficient at turning CO2 and sunlight into useful products.==

No it's not.


Toss this one in for good measure.


Which is why you don't use CO2 from a coal powerplant.  This thermochemical scheme appears to be well-suited to small installations, like the 25 kW/unit solar Stirling dishes.  You could use it to turn excess CO2 into syngas (and from there to fuel, like methanol or ethylene) anywhere you have CO2 and sunlight; the closer you do it to the source, the lower the cost of transporting the CO2.

You could build installations like this to sit on farms, at landfills, and all kinds of places where you have a stream of gas containing CO2.  Our biggest fuel demand is for transport; if you can supply short-range energy demand with solar thermal plus batteries, solar thermochemical fuel could handle the long-range applications.  The big issue is supplying enough carbon to run the system, and my previous calculations say that it's difficult but possible.

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