From: Andy Soos, ENN
Published May 24, 2012 08:26 AM
CO2 Removal Catalyst
There are several ways to remove CO2 from a stack gas. None have
reached a commercial basis yet due to the expense of the processing. The
current method of removing the greenhouse gas carbon dioxide (CO2) from
the flues of coal-fired power plants uses so much energy that no one
bothers to use it. So says Roger Aines, principal investigator for a
team that has developed an entirely new catalyst for separating out and
capturing CO2, one that mimics a naturally occurring catalyst operating
in our lungs. With this success, the Laboratory has become a world
leader in designing catalysts that mimic the behavior of natural
enzymes.
The most commonly studied process for CO2 capture and removal are
amines. In Norway for example, the CO2 Technology Center at Mongstad
began construction in 2009, and was scheduled for completion early in
2012. It was to include two capture technology plants (one advanced
amine and one chilled ammonia), both capturing flue gas from two
sources. In addition, it would have included a gas-fired power plant and
refinery cracker flue gas (similar to coal-fired power plant flue gas).
Total capacity was to be 100,000 tons of CO2 per year. The project was
delayed to 2014, 2018, and then indefinitely. At 80% completion, project
cost rose to USD 985 million.
This small-molecule catalyst, dubbed "Cyclen," mimics carbonic
anhydrase, which separates, captures, and transports CO2 out of our
blood and other tissues as part of the normal respiration process.
Carbonic anhydrase is the fastest operating natural enzyme known. For
years, researchers have considered adapting it to capture carbon emitted
in industrial operations. But carbonic anhydrase cannot take the heat in
the intense conditions of industrial processes. Hot, high-pH flue gas
quickly degrades it.
The Livermore team's best designer molecule behaves like carbonic
anhydrase but has so far indicated that it is one tough cookie. "In
fact," Aines said, "it has turned out to be thermodynamically stable. It
is far more rugged than we had expected."
A team performing quantum molecular calculations led by computational
biologist Felice Lightstone examined potential candidate molecules. They
determined optimal designs to protect the essential zinc ion in the
molecule that activates the catalyst. Synthetic chemist Carlos Valdez
took the next step. Only about 2 percent of the computationally derived
structures made it to the synthesis state. Newly synthesized molecules
were tested by chemist Sarah Baker and her team to determine their
kinetic behavior and stability. The team made nine catalysts in a year
and a half. The name for the finalist comes from the chemical term for
the ring around the zinc ion.
"Our tests effectively determined Cyclen's chemical kinetics," Aines
said. "Pilot tests at the Babcock & Wilcox Power Generation Group in
Ohio will push Cyclen to measure its industrial kinetics."
One challenge with Cyclen remains. The catalyst is designed to create a
monolayer that clings to a gas-water interface much as mosquito larvae
do. However, the Cyclen layer is too thin and some of the CO2 is able to
pass through it without being captured.
For further information see
Catalyst.
New Molecule image via Lawrence Livermore Lab.
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