Livermore’s new molecule to capture carbon dioxide from the flues of coal-fired power plants is designed to be tethered to a gas-water interface in the same way that these mosquito larvae cling to a water surface. |
The
current method of removing the greenhouse gas carbon dioxide 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 carbon dioxide, one that
mimics a naturally occurring catalyst operating in our lungs. With this
success, Lawrence Livermore National Laboratory has become a leader in
designing catalysts that mimic the behavior of natural enzymes.
This
small-molecule catalyst, dubbed “Cyclen,” mimics carbonic anhydrase,
which separates, captures, and transports carbon dioxide 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% 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.”
The
company, a supplier of steam-generation and environmental equipment for the
electric utility market, will provide benchtop and full-scale testing and
process modeling to determine how to implement Cyclen in new processes. A
kilogram of the stuff is on its way to Babcock & Wilcox, which is plenty
for use in its array of tests. 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
carbon dioxide is able to pass through it without being captured. Aines is not
worried. “We have demonstrated that quantum molecular calculations can
translate into real-world results and that we can synthesize catalysts that do
the job.”
