Research provides octagonal window of opportunity for carbon capture

February 8, 2012 By Chad Boutin
The roughly octagonal pores in zeolite SSZ-13 are like stop signs for carbon dioxide, capturing molecules of the greenhouse gas while apparently letting other substances through. The material could prove to be an economical smokestack filter. Credit: NIST

( -- Filtering carbon dioxide, a greenhouse gas, from factory smokestacks is a necessary, but expensive part of many manufacturing processes. However, a collaborative research team from the National Institute of Standards and Technology and the University of Delaware has gathered new insight into the performance of a material called a zeolite that may stop carbon dioxide in its tracks far more efficiently than current scrubbers do.

Zeolites are highly porous rocks—think of a sponge made of stone—and while they occur in nature, they can be manufactured as well. Their toughness, high surface area (a gram of can have hundreds of square meters of surface in its myriad internal chambers) and ability to be reused hundreds of times makes them ideal candidates for filtering gas mixtures. If an unwanted molecule in the gas mixture is found to stick to a zeolite, passing the mixture through it can scrub the gas of many impurities, so zeolites are widely used in industrial chemistry as catalysts and filters.

The team explored a zeolite created decades ago in an industrial lab and known by its technical name, SSZ-13. This zeolite, which has octagonal “windows” between its interior pore spaces, is special because it seems highly capable of filtering out carbon dioxide (CO2) from a gas mixture. “That makes SSZ-13 a promising candidate for scrubbing this out of such things as factory smokestacks,” says Craig Brown, a researcher at the NIST Center for Neutron Research (NCNR). “So we explored, on an atomic level, how it does this so well.”

Using neutron diffraction, the team determined that SSZ-13’s eight-sided pore windows are particularly good at attracting the long, skinny carbon dioxide molecules and holding onto their “positively-charged” central carbon atoms, all the while allowing other molecules with different shapes and electronic properties to pass by unaffected. Like a stop sign, each pore halts one CO2 molecule—and each cubic centimeter of the zeolite has enough pores to stop 0.31 grams of CO2, a quantity that makes SSZ-13 highly competitive when compared to other adsorbent materials.

Brown says a zeolite like SSZ-13 probably will become a prime candidate for carbon scrubbing because it also could prove more economical than other scrubbers currently used in industry. SSZ-13’s ability to attract only CO2 could mean its use would reduce the energy demands of scrubbing, which can require up to 25 percent of the power generated in a coal or natural gas power plant.

“Many industrial zeolites attract water and , which are both present in flue exhaust—meaning both molecules are, in a sense, competing for space inside the zeolite,” Brown explains. “We suspect that this novel CO2 adsorption mechanism means that water is no longer competing for the same site. A zeolite that adsorbs CO2 and little else could create significant cost savings, and that’s what this one appears to do.”

Brown says his team is still collecting data to confirm this theory, and that their future efforts will concentrate on exploring whether SSZ-13 is equally good at separating CO2 from methane—the primary component of natural gas. CO2 is also released in significant quantities during extraction, and the team is hopeful SSZ-13 can address this problem as well.

Explore further: Expert discusses using small-pore zeolites to remove troublesome pollutant from exhaust

More information: M.R. Hudson, et al. Unconventional, highly selective CO2 adsorption in zeolite SSZ-13. Journal of the American Chemical Society Published on the Web Jan. 10, 2012. DOI: 10.1021/ja210580b

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1 / 5 (1) Feb 08, 2012
Zeolites are used as oral supplements in the health industry, to capture free radicals. It's an expensive pill, so I wonder how much a smokestack would use, although it's reusable. I wouldn't want the job of cleaning them when they're loaded, though.
1 / 5 (4) Feb 08, 2012
There is no doubt that this could be of some use somewhere. But there is nothing more useless that trying to limit man made CO2 emissions. Every day more and more evidence piles up which shows how the AGW data was fudged and how corrupt scientists are working with governments to steal your autonomy,freedom and wealth. Wake up, nations are going bankrupt and cannot afford to support counterproductive policies. Every dollar that is wasted on this sort or rubbish is a dollar or possibly more in food that cannot be paid for.
5 / 5 (1) Feb 08, 2012
There is a use for it - capturing CO2 at power plants. The oil and gas industry uses a lot of CO2 for pressurizing wells to force the hydrocarbons out. If they can capture that, in pure form, at power plants, they could then pipe it directly to the oil fields. That would need less energy than trying to condense it from the air, as well as helping offset the cost of running the power plant.

ANY industrial waste product is a waste of resources, because it's something the industry has already paid for, and is simply throwing away. The best example is sulfur. It used to be mined, while smelters and power plants discharged large quantities into the air. Now, the world's sulfur needs are met by reclaimed "pollution", at lower cost than mining it.
1 / 5 (1) Feb 09, 2012
Some zeolites are cheap and used in washing powder. But the reusability will have to be increased beyond 100s to make this viable. Hopefully it can bypass/separate sulfur dioxide and carbon monoxide, which could also be useful as the previous poster suggested.
not rated yet Feb 09, 2012
i wonder if you could take some smokestackgas wich is already warm and pressurise it so maybe the co2 becomes supercritical fluid and maybe opens up another avenue for seperating the gasses and particles of the smokestack by being in different phases and or being sissolved in the supercritical co2 or i've already searched for this and they do use pressurized smokestackstreams, but more like to help them push go through the zeolites, but i just would want to see if you up the pressure a notch or two...
not rated yet Feb 13, 2012
Husky: To do a separation as you suggest you will need two phases to appear, for example a liquid and a gas. supercritical will not have a phase boundary to separate it from the gas phase, so really you need sub critical. Increasing pressure will need extra energy so is to be avoided. However if you cool and depressurise your smokestack gas, perhaps you can get dry ice snow to condense to get it apart from nitrogen or other harmless gas.

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