Cyclen – CO2-removing catalyst which mimics natural enzymes

Current method of removing the greenhouse gas carbon dioxide (CO2) from the flues of coal-fired power plants usually requires complicated systems which require a lot of energy and maintenance. A group of researchers from the Lawrence Livermore National Laboratory came up with Cyclen – a small-molecule catalyst that mimics the behavior of natural enzymes which handle CO2.

Carbonic anhydrase is a naturally occurring catalyst which operates in our lungs, where it separates, captures, and transports CO2 out of our blood and other tissues as part of the normal respiration process. For years, researchers have considered adapting it to capture carbon emitted in industrial operations, however, the influence of heat and high-pH of flue gas degrade carbonic anhydrase in conditions of industrial processes.

Led by Roger Aines, Livermore team developed an entirely new catalyst for separating out and capturing CO2. Although it mimics carbonic anhydrase, it proved out to be thermodynamically stable.

A team led by computational biologist Felice Lightstone examined potential candidate molecules by performing quantum molecular calculations in which they found optimal designs able to protect the essential zinc ion in the molecule that activates the catalyst. Only about 2 percent of the computationally derived structures made it to the synthesis – a part of the process which was led by synthetic chemist Carlos Valdez.

In a year and a half, the team made nine catalysts whose kinetic behavior and stability were tested by chemist Sarah Baker and her team. The results revealed a finalist whose name Cyclen comes from the chemical term for the ring around the zinc ion. Although Cyclen is designed to create a monolayer that clings to a gas-water interface much as mosquito larvae do, the layer is too thin and it allows some of the CO2 is able to pass through it without being captured.

Livermore researchers are confident that problem will be solved, and a kilogram (2.2 pounds) of the synthesized Cyclen is on its way to Ohio’s Babcock & Wilcox Power Generation Group, a supplier of steam-generation and environmental equipment for the electric utility market, where it will go under benchtop and full-scale testing, as well as process modeling to determine the best way to use it in industrial applications.