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Octagonal opportunity for carbon capture

03.01.2012  |  Thinnes, Billy,  Hydrocarbon Processing Staff, Houston, TX

Keywords: [carbon capture] [zeolites] [carbon management] [climate change] [environment] [CO2] [filtering]

Filtering CO2 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 (NIST) and the University of Delaware has gathered new insight into the performance of a material called zeolite that may stop carbon dioxide in its tracks far more efficiently than current scrubbers do.

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 (Fig. 3). The material could prove to be an economical smokestack filter.


  Fig. 3. Zeolites may be a
  breakthrough solution for
  carbon capture issues. 

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 zeolite can have hundreds of square meters of surface in its myriad internal chambers) and ability to be reused hundreds of times make 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 CO2 from a gas mixture.

“That makes SSZ-13 a promising candidate for scrubbing this greenhouse gas out of such things as factory smokestacks,” said 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 the research team says makes SSZ-13 highly competitive when compared to other adsorbent materials.

Mr. Brown said 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% of the power generated in a coal or natural gas power plant.

“Many industrial zeolites attract water and carbon dioxide, which are both present in flue exhaust—meaning both molecules are, in a sense, competing for space inside the zeolite,” Mr. Brown said. “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.”

Mr. Brown said that 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 gas extraction, and the team is hopeful that SSZ-13 can also address this problem. HP

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Removing CO2 is possible by many mechanism and this is just one, and the extracted CO2 could be injected in salt domes or used in EOR, good way of relieving the atmosphere, but the total cost vs scrubbers it is the challenge

Hugo Garcia

A great development!! is there any comment on how the Zeolite will be reactivated and how the traped CO2 can be comercialized?

Allen Botha

So what happens when the zeolite becomes saturated- the CO2 is not converted and should be a greater source (concentration) of CO2 release to the atmosphere. To the best of my knowledge there is not market for CO2 as the present users can filter sufficient pure CO2 using Activated Carbon or other absobing material – it is hard to understand the excitement about removing it from the atmosphere.

Stanley Che, Ph.D; P.E.

What is the dressure drop for SSZ-13 during the capture of CO2? How is SSZ-13 regenerated, by pressure swing or by vacuum? In either case, additional hardware cost will be required. Has there any study been done?


I feel that the process is an excellent option vs amine absorption to purify CO2 for its use. but to remove it from the atmosphere to reduce climate change is a bigger problem.

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