che_february-2025 - 5

Chementator
Edited by: Dorothy Lozowski
Carbon-neutral calcium carbonate process uses emissions
from steel-making plant
C
Carbon Free
onstruction is imminent for a carbon-capture
project aimed at reducing CO2 emissions from
steel production while producing carbon-neutral
calcium carbonate. At the U.S. Steel (Pittsburgh,
Pa.; www.ussteel.com) manufacturing facility in Gary, Ind.,
a carbon-capture system designed by CarbonFree (San
Antonio, Tex.; www.carbonfree.cc) will capture CO2 emissions
from the fluegas of the steel plant and convert it into
powdered calcium carbonate for a wide range of applications,
including as a component in paints, coatings and
adhesives, as well as food, plastics and others.
CarbonFree has developed a process, known as SkyCycle™,
to convert exhaust CO2 into high-purity CaCO3.
The process works by contacting the flue gas with a magnesium
hydroxide solution that captures the CO2 as magnesium
bicarbonate (diagram). The magnesium bicarbonate
is
with
reacted
CaCl2
derived
from calcium-containing
slag
lowing
the product
onsite,
CaCO3
to
precipitate
out
alof
solution. Slag is a byproduct of the blast-furnace steel
process that contains a mix of metal oxides. The process
also involves recovering MgCl2 from the reaction that produces
the CaCO3 product and heating it to decompose it
into MgOH and HCl, which are then used in another cycle
of the process. Treating the slag with HCl can produce the
required CaCl2.
" We use LeChatelier's principle of chemical equilibrium
to drive the reactions in the cycle, " explains Bill Bryant,
marketing director at CarbonFree. " Instead of talking
about the cost of carbon required for carbon capture,
this approach allows us to talk about lowering the carbon
footprint of our customers' products, while making a sustainable
and profitable business. "
The carbon-neutral CaCO3 product, known as endurocal®,
was launched in November 2024, and Bryant says
pilot-scale samples of the product are available for applications
testing from the company's demonstration plant
at Southwest Research Institute (SwRI; San Antonio, Tex.;
www.swri.org).
CarbonFree says endurocal has the same properties as
conventionally produced precipitated calcium carbonate
(PCC), in terms of particle shape, particle size distribution
and purity, but with a lower cost and zero carbon footprint.
New sustainable materials from recycled carbon nanotubes
R
ecycling materials, such as plastics and metals,
is an attractive, but challenging path toward sustainable
material manufacture. Now, researchers
have made a discovery that may have far-reaching
implications in material manufacture by positioning
carbon nanotube (CNT) fibers as a sustainable alternative
to metals, polymers and much larger carbon fibers.
Researchers at Rice University (Houston, Tex.; www.
rice.edu) have demonstrated that CNT fibers can be recycled
without structural or property losses, and more
readily than some more-difficult-to-recycle materials.
" Recycling has long been a challenge in the materials
industry - metals recycling is often inefficient and energy
intensive, polymers tend to lose their properties after reprocessing
and carbon fibers cannot be recycled at all,
only downcycled by chopping them up into short pieces, "
said Matteo Pasquali, director of Rice's Carbon Hub
(carbonhub.rice.edu) and the A.J. Hartsook Professor of
Chemical and Biomolecular Engineering, Materials Science
and NanoEngineering and Chemistry. " We expected
that recycling would be difficult and would lead to significant
loss of properties. Surprisingly, we found that carbon
nanotube fibers far exceed the recyclability potential of existing
engineered materials, offering a solution to a major
environmental issue. "
In this research, solution-spun CNT fibers were created
by dissolving fiber-grade commercial CNTs in chlorosulfonic
acid. To simulate recycling of a variety of materials,
fibers made from different types of CNTs produced by different
manufacturers were initially processed into separate
single-source virgin fibers, then recycled by combining
them and mixing in chlorosulfonic acid. Surprisingly,
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mixing the two fibers led
to complete redissolution
and no sign of separation
of the two source materials
into different liquid phases.
This redissolved material
was spun into a mixedsource
recycled fiber that
retained the same structure and alignment of the virgin
fiber. Some materials degrade in quality during recycling,
but the CNT fibers retained 100% of their original properties
after recycling.
" The ability to fully recycle CNT fibers has broad implications
for industries like aerospace, automotive and electronics, "
said Michelle Durán-Chaves, a graduate student
in chemistry. " We hope this could pave the way for fully
recyclable composites in aircraft, vehicles, civil infrastructures
and more, ultimately reducing environmental impacts
across a wide range of sectors. "
This research is part of the broader program of the Carbon
Hub, a Rice-led initiative developing a zero-emissions
future, where advanced carbon materials and clean hydrogen
are co-produced efficiently and sustainably from
hydrocarbons. The work was published in the journal Carbon,
and was supported by the Department of Energy's
Advanced Research Project Agency, the Air Force Office
of Scientific Research, the Robert A. Welch Foundation,
the National Science Foundation, the Novo Nordisk Foundation
CO2 Research Center, the Ken Kennedy Institute
Graduate Fellowship from Schlumberger and Rice and a
Riki Kobayashi Fellowship from Rice's chemical and biomolecular
engineering department.
Jeff Fitlow/Rice University
FEBRUARY 2025
5
http://www.ussteel.com http://www.carbonfree.cc http://www.swri.org http://www.rice.edu http://carbonhub.rice.edu http://WWW.CHEMENGONLINE.COM
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