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
Fig. 3. Zeolites may be
breakthrough solution for
carbon capture issues.
Zeolites are highly porous rocksthink of a sponge made
of stoneand 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-13s 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 moleculeand 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-13s 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 exhaustmeaning
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 thats 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
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