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New compound provides a better cage for carbon dioxide

The views expressed are those of the author and are not necessarily those of Scientific American.


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mg-mof-74Capturing carbon dioxide is simple chemistry. In fact, you may have seen it in your high school chem lab. Remember that tightly sealed bottle of sodium hydroxide, aka lye? Simply popping the top off that strong base and exposing it to air resulted in a chemical reaction in which the ambient CO2 was absorbed and the lye became sodium carbonate.

So it would seem like carbon capture and storage might be relatively simple—thus neatly solving global climate change.

Unfortunately, it’s not quite that simple, largely because getting the CO2 back out of any of a number of different materials put forward over the years has proven energy-intensive. For example, getting CO2 out of carbonate requires heating to more than 900 degrees Celsius in an industrial kiln.

However, in the November 30 Proceedings of the National Academy of Sciences, chemists at the University of California, Los Angeles, (U.C.L.A.) report that a new compound—affectionately known as Mg-MOF-74—readily traps CO2 and then releases 87 percent of it back again at room temperature*. "If we continue to blow, we blow the CO2 back off again," says U.C.L.A. chemist David Britt, lead author on the paper presenting the results.

The molecular lattice can absorb roughly 9 percent of its weight in CO2, and heating to a relatively mild 80 degrees Celsius releases the rest for your preferred storage option. "Mg-MOF-74 strikes an excellent balance between strong adsorption and ease of regeneration that makes it highly promising as a carbon dioxide capture material," Britt says.

The U.C.L.A. chemists began exploring Mg-MOF-74—a metal-organic framework employing magnesium ions—because they knew it released relatively little heat when adsorbing CO2, suggesting that it might require relatively little heat to get the CO2 back out again. Plus, magnesium is a key component of the plant enzyme RuBisCO that allows photosynthesizers to begin the process of turning CO2 into food. Essentially, the new metal-organic framework works as a crystal cage, allowing mixed gas to flow through it and selectively trapping the CO2.

The latter trick is important since power plants and other sources of carbon dioxide, rarely deliver a pure stream of the greenhouse gas. In tests using a mix of 20 percent CO2 and 80 percent methane, the Mg-MOF-74 captured only the CO2 while allowing the methane to pass through (also of vital interest to the natural gas purification industry).

But the chemical filter will probably still need some tweaking, particularly if the compound will be exposed to CO2 and water vapor, according to Britt. "Given the nearly endless possibility of MOF structures, we expect that it will be possible to tailor the environment of the [magnesium] ion to address this issue," he says.

Plus, it’ll be relatively inexpensive. "Magnesium is a cheap and highly abundant metal and the organic linker in Mg-MOF-74 is commercially available," Britt says. If that proves to be the case, and engineering kinks can be worked out, then the compound could even be used in devices to capture CO2 directly from the air. Not only would that make its discoverers eligible for the $25-million Virgin Earth Challenge, it also just might help combat climate change.

Image: Courtesy of David Britt

* Correction (1-11-10): This sentence was changed to reflect the fact that the compound in question has been known since 2008. Thanks to chemist Antek Wong-Foy of the University of Michigan for pointing this out.





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  1. 1. scientific earthling 5:09 pm 11/30/2009

    The coal industry is packed chock a block full of idiots if they believe carbon capture and storage is economically viable. Nature generally finds the most effective way to do what it does and it uses photosynthesis to manage carbon dioxide.

    Just like the weather cycles, food cycles and other natural cycles there is a carbon cycle. The second law of thermodynamics must be considered when discussing the carbon cycle. Converting carbon dioxide to carbon requires a lot more energy than it releases when it is reconverted to carbon dioxide. It is because of this requirement that we have life on earth.

    Nature provided the planet with billions of trees and other vegetation, which soaked up solar energy to convert carbon dioxide into carbon, this action utilised solar energy and prevented it from heating our little planet. The vegetative mass on earth acted as an effective damper on climate change, in fact it creates the climate we are all addicted to.

    The only way to return our planet to stable weather that suites us is to re-vegetate the planet.

    Link to this
  2. 2. dwbd 7:25 pm 11/30/2009

    The beauty of this is to make automated Methanol production plants that only need water, atmospheric CO2 and surplus green electricity to store energy in fuel.

    Excellent to store summer surplus Hydro in the North for heating fuel in the Winter.

    And Nuclear plants could run full out 24/7, producing CO2 neutral Methanol when power demand is low.

    Link to this
  3. 3. JamesDavis 8:32 am 12/1/2009

    scientific earthling: You are more correct than these wantabe scientiests. Why are they more concerned about CO2 that feeds our plants and give us back oxygen. Shouldn’t they be more concerned with CO1 (carbonmonoxide)? Carbonmonoxide is the toxic gas burn off from fossil fuel that kills our plants and smothers and kills us. Stop using fossil fuel by mass producing electric cars, trains, and planes and that should take care of the deadly CO1 that we are putting tons of into the air, water, and ground. Why are they ignoring the most deadly of fossil fuel gasses?

    Link to this
  4. 4. rockjohny 11:19 pm 12/1/2009

    I agree, what if a western country ‘bought’ a chunk of the Sahara for the purpose of reclaiming viable land from the dessert with the goal of expanding it to a country-sized mass? That would be a more ‘noble’ form of colonizing, wouldn’t it.

    Link to this
  5. 5. TMock 10:57 am 12/26/2009

    Trees are the Answer…

    Southern Oregon Coast Mixing Nature, Tradition, and Economics for Sustainable Future – (http://www.nxtbook.com/nxtbooks/sldt/0509/#/24)

    "Located in the headwaters of the Port Orford Community Stewardship Area in Southern Oregon, Ocean Mountain Ranch overlooks the newly-designated Redfish Rocks Marine Reserve and the largest remaining old growth forest on the southern coast in Humbug Mountain State Park. OMR is planned to be developed pursuant to a forest stewardship management plan which has been approved by the Oregon Department of Forestry and Northwest Certified Forestry under the high standards of the Forest Stewardship Council (FSC)."

    Sustainable Land Development Goes Carbon Negative – (http://www.nxtbook.com/nxtbooks/sldt/0809/#/18 )

    "Ocean Mountain Ranch is also serving as a pilot program and is expected to achieve carbon negative status through the utilization of low impact development practices, energy efficient buildings, renewable/clean energy systems, distributed waste management systems, biochar production, and other practices – with certification as a SLDI-Certified Sustainable Project."

    Sustainable Land Development International
    http://www.SLDI.org

    Link to this

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