che_december-2024 - 6

Upcycling gypsum to sulfuric acid in a zero-liquid-discharge
demonstration plant
A
new demonstration plant is upcycling gypsum
(calcium sulfate) - a material that is typically
challenging to dispose of - at a metal-refining
site using a process that combines salt-splitting
electrolysis, caustic direct-air capture (DAC) and mineralization.
Travertine Technologies, Inc. (Boulder, Colo.;
www.travertinetech.com) will be deploying its namesake
process technology at a facility owned by Sabin Metal
Corp. (East Hampton, N.Y.; www.sabinmetal.com), located
near Rochester, N.Y. " The Travertine Process will
be processing a legacy stack of mined gypsum at the
site and carbon dioxide captured directly from the air
into sulfuric acid, green hydrogen and calcium carbonate.
The gypsum is from a historical gypsum mine that
operated at the site prior to Sabin acquiring the land.
Sabin will be using the sulfuric acid we produce for recycling
and refining precious metals, " explains Owen
Cadwalader, chief operating officer at Travertine. Besides
sulfuric acid, the process also produces
a stream of " green " hydrogen in the electrolysis
step, which will be evaluated as potential fuel for
the site. Finally, adds Cadwalader, the carbonate
product acts as a permanent carbon sink
that will be tested for use as a supplementary
cementitious material.
At the heart of the process is the electrolyzer
unit, which splits sulfate salt into sulfuric
acid and caustic (NaOH), and can be configured to also
produce green hydrogen. " In the DAC unit, the caustic
reacts with the CO2 in air to produce sodium carbonate
and CO2-depleted air. The carbonate solution flows
into our mineralization unit operation and reacts with the
waste gypsum, forming the sulfate salt, which is recycled
to the electrolyzer, as well as precipitated calcium carbonate,
which permanently sequesters CO2, " says Cadwalader,
also noting that the plant is designed for zeroliquid
discharge.
All equipment is similar to equipment that has been
used at the industrial scale for decades: the electrolyzer
unit operation is inspired by membrane chlor-alkali; the
DAC unit resembles a cross-flow cooling tower; and the
mineralization unit consists of hydrometallurgical equipment.
The project with Sabin Metals will be the largest
demonstration of the Travertine Process to date, with a
nameplate capacity of 125 ton/d of sulfuric acid.
Travertine Technologies
Catalyst developed for conversion of CH4 to methanol
S
cientists at the Brookhaven National Laboratory
(BNL; Upton, N.Y.; www.bnl.gov) and collaborating
institutions have engineered a highly
selective catalyst that can convert methane into
methanol in a one-step reaction. The system could help
make better use of " stranded " natural gas reserves in remote
areas by converting methane gas into a transportable
liquid.
The researchers developed a palladium-based catalyst
(photo) for the reaction based on years of basic
research on the three-phase reaction of methane gas,
hydrogen peroxide as an oxidant and solid-powder
catalysts. Using the catalyst, the direct process for
methane-to-methanol conversion runs at lower temperatures
than traditional multistep conversions and
produces methanol without additional byproducts, the
BNL team says.
In addition, this new work " translates the laboratoryscale
catalyst synthesis into a more practical process for
making kilogram-scale amounts of catalytic powder, " explains
BNL chemist Sanjaya Senanayake, co-author of
a recent paper describing the work in the Journal of the
American Chemical Society.
A key aspect of the catalyst seems to be a layer of
carbon between the palladium and cerium oxide. The
BNL synthesis method yields Pd-iC-CeO2, where iC refers
to interfacial carbon. BNL chemical engineer and
study lead author Juan Jimenez says " Carbon is often
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overlooked as a catalyst, but in this study, we did a host
of experiments and theoretical work that revealed that
a fine layer of carbon between palladium and cerium
oxide really drove the chemistry. "
Modulating the activity of highly active metal-oxide interfaces
by the incorporation of carbon interlayers balances
the activation of the oxidant in tandem with the
CH4 to achieve ideal product selectivity, the researchers
say. This results in a methanol selectivity of 100% at
75°C, they add.
BNL is exploring collaborations with entrepreneurial
partners to bring the technology to market.
DECEMBER 2024
http://www.travertinetech.com http://www.sabinmetal.com http://www.bnl.gov http://WWW.CHEMENGONLINE.COM
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