Turning emissions into fuel—method converts carbon dioxide into useful compounds

November 27, 2017 by Rob Matheson, Massachusetts Institute of Technology
Ball-and-stick model of carbon dioxide. Credit: Wikipedia

MIT researchers have developed a new system that could potentially be used for converting power plant emissions of carbon dioxide into useful fuels for cars, trucks, and planes, as well as into chemical feedstocks for a wide variety of products.

The new membrane-based system was developed by MIT postdoc Xiao-Yu Wu and Ahmed Ghoniem, the Ronald C. Crane Professor of Mechanical Engineering, and is described in a paper in the journal ChemSusChem. The membrane, made of a compound of lanthanum, calcium, and iron oxide, allows oxygen from a stream of carbon dioxide to migrate through to the other side, leaving behind. Other compounds, known as mixed ionic electronic conductors, are also under consideration in their lab for use in multiple applications including oxygen and hydrogen production.

Carbon monoxide produced during this process can be used as a by itself or combined with hydrogen and/or water to make many other liquid hydrocarbon fuels as well as chemicals including methanol (used as an automotive fuel), syngas, and so on. Ghoniem's lab is exploring some of these options. This process could become part of the suite of technologies known as carbon capture, utilization, and storage, or CCUS, which if applied to electicity production could reduce the impact of fossil fuel use on global warming.

The membrane, with a structure known as perovskite, is "100 percent selective for oxygen," allowing only those atoms to pass, Wu explains. The separation is driven by temperatures of up to 990 degrees Celsius, and the key to making the process work is to keep the oxygen that separates from carbon dioxide flowing through the membrane until it reaches the other side. This could be done by creating a vacuum on side of the membrane opposite the carbon dioxide stream, but that would require a lot of energy to maintain.

In place of a vacuum, the researchers use a stream of fuel such as hydrogen or methane. These materials are so readily oxidized that they will actually draw the oxygen atoms through the membrane without requiring a pressure difference. The membrane also prevents the oxygen from migrating back and recombining with the carbon monoxide, to form carbon dioxide all over again. Ultimately, and depending on the application, a combination of some vaccum and some fuel can be used to reduce the energy required to drive the process and produce a useful product.

The energy input needed to keep the process going, Wu says, is heat, which could be provided by solar energy or by waste heat, some of which could come from the power plant itself and some from other sources. Essentially, the process makes it possible to store that heat in chemical form, for use whenever it's needed. Chemical energy storage has very high energy density—the amount of energy stored for a given weight of material—as compared to many other storage forms.

At this point, Wu says, he and Ghoniem have demonstrated that the process works. Ongoing research is examining how to increase the oxygen flow rates across the membrane, perhaps by changing the material used to build the membrane, changing the geometry of the surfaces, or adding catalyst materials on the surfaces. The researchers are also working on integrating the membrane into working reactors and coupling the reactor with the fuel production system. They are examining how this method could be scaled up and how it compares to other approaches to capturing and converting , in terms of both costs and effects on overall power plant operations.

In a power plant that Ghoniem's group and others have worked on previously, Wu says the incoming natural gas could be split into two streams, one that would be burned to generate electricity while producing a pure stream of carbon dioxide, while the other stream would go to the fuel side of the new system, providing the oxygen-reacting fuel source. That stream would produce a second output from the plant, a mixture of hydrogen and monoxide known as syngas, which is a widely used industrial fuel and feedstock. The syngas can also be added to the existing natural gas distribution network.

The method may thus not only cut greenhouse emissions; it could also produce another potential revenue stream to help defray its costs.

The process can work with any level of concentration, Wu says—they have tested it all the way from 2 percent to 99 percent—but the higher the concentration, the more efficient the process is. So, it is well-suited to the concentrated output stream from conventional fossil-fuel-burning or those designed for such as oxy-combustion plants.

Explore further: Technique uses solar thermal energy to split H2O and CO2 for jet fuel

More information: Xiao-Yu Wu et al, H2-assisted CO2 thermochemical reduction on La0.9Ca0.1FeO3-δ membranes: a kinetics study, ChemSusChem (2017). DOI: 10.1002/cssc.201701372

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14 comments

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MR166
1 / 5 (2) Nov 27, 2017
Well I do not see a lot of value in a process that requires 990C "waste heat" to produce energy.

The description of the process that utilizes the waste CO2 from a power plant appears to require more energy than it produces since there is no energy left to be had from a CO2 molecule. If this is not the case bravo to the first group to create perpetual motion.
MR166
1 / 5 (3) Nov 27, 2017
Here is just a word of advice. If anyone comes up to you and says they have a process that can turn CO2 into fuel and save the world check your pockets and make sure that your wallet is still there.
TheGhostofOtto1923
5 / 5 (1) Nov 27, 2017
Well I do not see a lot of value in a process that requires 990C "waste heat" to produce energy.

The description of the process that utilizes the waste CO2 from a power plant appears to require more energy than it produces since there is no energy left to be had from a CO2 molecule. If this is not the case bravo to the first group to create perpetual motion.
So you would prefer magic then?
TheGhostofOtto1923
5 / 5 (2) Nov 27, 2017
Here is just a word of advice. If anyone comes up to you and says they have a process that can turn CO2 into fuel and save the world check your pockets and make sure that your wallet is still there.
Sounds funny coming from an anonymous poster with a bad rep here. Especially when its directed at real scientists getting real results.

I do hate it when morons denigrate scientists.
Whydening Gyre
5 / 5 (1) Nov 27, 2017
I'm just getting repeatedly impressed how so many educated people who are denying existence of perpetuum mobile furiously are so willing to imply it by interpretation of their own research. The conversion of carbon dioxide emissions into an useful compounds indeed produces another emissions - there is no way around it...

Not to mention the USE of those useful compound's (as a fuel) emissions...
There is all too many of these "CO2 to fuel" articles on here, lately, and it's makes me wonder if they are just recycling the same studies and research...
MR166
1 / 5 (3) Nov 27, 2017
"
I do hate it when morons denigrate scientists."

I do hate it when scientists bamboozle the educated but still ignorant.
MR166
1 / 5 (2) Nov 27, 2017
Q. How does a scientist turn CO2 into 1 gallon of motor fuel.

A. He starts with 2 gallons of motor fuel and a special process.
MR166
1 / 5 (2) Nov 27, 2017
Otto in the article they propose to do the following. They are going to take nat gas and burn it to produce the heat needed to turn the power plants CO2 emissions and, I assume, the processes's CO2 into syngas by adding even more natural gas. Do you really think that this can be done and not lose a lot of energy in the process? How does that reduce CO2 emissions when the energy needed for the conversion came from the burning of nat gas?
warmonger
5 / 5 (2) Nov 28, 2017
MR166
Dude, please try to be humble when you don't know about something. The scientists are talking about using waste heat. You may have noticed that a car engine produces a lot of excess heat. Or a nuclear power plant. Or a coal power plant. You could improve efficiency by using that heat, which is already being produced for another process. This is basic science.
TheGhostofOtto1923
not rated yet Nov 28, 2017
Otto in the article they propose to do the following
So The anonymous poster with the bad rep thinks that further cracked logic based on ignorance and misunderstanding and posturing and pomposity is something I would engage with?

I respect science which is why I hate bullshit artists like yourself.
MR166
1 / 5 (1) Nov 28, 2017
"The syngas can also be added to the existing natural gas distribution network.
The method may thus not only cut greenhouse emissions; it could also produce another potential revenue stream to help defray its costs."

To further illuminate the stupidity of this hoax I would like to point out that they are proposing the sale of the resulting gas instead of using it to power the power plant that is housed in the same complex. I don't think that syngas sells for more than nat gas in the marketplace.
MR166
1 / 5 (1) Nov 28, 2017
The saddest part of the article is that it comes from MIT, one of the highest ranked universities in the US. I do not believe that the researchers are that stupid but I do believe that they are that dishonest. They most likely needed to create this falsehood in order to fulfill the obligations under a government grant promoting alternate energy and/or CO2 abatement. The government has corrupted science and has dragged it into it's swamp.
MR166
1 / 5 (1) Nov 28, 2017
If they said that the syngas was used to supplement the natural gas going into the plant and that for 1 unit of energy input they now generated x+1 KWH whereas they generated x KWH previously then I would applaud the new development as a way to utilize the waste heat of the plant thereby increasing efficiency and thus reducing CO2 emissions. But, this is not the case.
MR166
1 / 5 (1) Nov 28, 2017
Well guess what this hoax was not sponsored by the US government but by Shell Oil and the King Abdullah University of Science and Technology.

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