After Gutenberg

This blog previously noted a way of capturing CO₂ developed at the University of Calgary. Now the Biopact team relays news from the University of California – Los Angeles (UCLA) about a major advancement in the development of CO2 capturing materials.

Illustration Credit: Yaghi Lab
“The technical challenge of selectively removing carbon dioxide has been overcome. Now we have structures that can be tailored precisely to capture carbon dioxide and store it like a reservoir, as we have demonstrated. No carbon dioxide escapes. Nothing escapes — unless you want it to do so. We believe this to be a turning point in capturing carbon dioxide before it reaches the atmosphere.”

As reported in the Feb. 15 issue of the journal Science, UCLA chemists have demonstrated successful capture carbon dioxide with a class of new materials known as ZIFs (Zeolitic Imidazolate Frameworks).

Their findings could lead to power plants efficiently capturing the greenhouse gas without using toxic materials, after which it can be stored in geological formations. The new materials make carbon capture less energy demanding, and can store up to five times as much CO2 than porous carbon materials being designed for the same task.

Efficient and affordable CO2 capturing technologies are needed. Dr. James Hansen recently cautioned the Massachusetts legislature to consider the phasing out of coal fired electric power generation until and unless the carbon dioxide emissions are captured and stored.

Continuing to build coal-fired power plants without carbon capture will lock in future climate disasters for our children and grandchildren… Changing the course dictated by fossil-fuel interests will not be easy. It requires leadership to define a path with increased support for energy efficiency and clean-energy sources.

Dr. James Hansen continues to repeat his proposal for a moratorium on the building of more coal-fired power plants in the United States.

While the concept of using zeolites for carbon capture is a new topic, this blog previously has noted the application of, and further potential for use of, zelolitic materials in the fine grain improvement of chemical processes. Nonetheless, the announcement from UCLA is being heralded as a breakthrough.

The carbon dioxide is captured using a new class of materials designed by Yaghi and his group called zeolitic imidazolate frameworks, or ZIFs. These are porous and chemically robust structures, with large surface areas, that can be heated to high temperatures without decomposition and boiled in water or organic solvents for a week and still remain stable.

Rahul Banerjee, a UCLA postdoctoral research scholar in chemistry and Anh Phan, a UCLA graduate student in chemistry, both of whom work in Yaghi’s laboratory, synthesized 25 ZIF crystal structures and demonstrated that three of them have high selectivity for capturing carbon dioxide (ZIF-68, ZIF-69, ZIF-70).

The selectivity of ZIFs to carbon dioxide is unparalleled by any other material, said Yaghi, who directs of UCLA’s Center for Reticular Chemistry and is a member of the California NanoSystems Institute at UCLA. Rahul and Anh were so successful at making new ZIFs that, for the purposes of reporting the results, Yaghi had to ask them to stop.

The inside of a ZIF can store gas molecules. Flaps that behave like the chemical equivalent of a revolving door allow certain molecules — in this case, carbon dioxide — to pass through and enter the reservoir while blocking larger molecules or molecules of different shapes:

Illustration Credit: Yaghi Lab

“We can screen and select the one type of molecule we want to capture. The beauty of the chemistry is that we have the freedom to choose what kind of door we want and to control what goes through the door.

In ZIFs 68, 69 and 70, Banerjee and Phan emptied the pores, creating an open framework. They then subjected the material to streams of gases – carbon dioxide and carbon monoxide, for example, and another stream of carbon dioxide and nitrogen — and were able to capture only the carbon dioxide.

…

Currently, the process of capturing carbon dioxide emissions from power plants involves the use of toxic materials and requires 20 to 30 percent of the plant’s energy output, Yaghi said. By contrast, ZIFs can pluck carbon dioxide from other gases that are emitted and can store five times more carbon dioxide than the porous carbon materials that represent the current state-of-art. For each liter of ZIF, you can hold 83 liters of carbon dioxide.

On a fundamental level, the invention of ZIFs has addressed two major challenges in zeolite science. Zeolites are stable, porous minerals made of aluminum, silicon and oxygen that are employed in petroleum refining and are used in detergents and other products. Yaghi’s group has succeeded in replacing what would have been aluminum or silicon with metal ions like zinc and cobalt, and the bridging oxygen with imidazolate to yield ZIF materials, whose structures can now be designed in functionality and metrics.

Banerjee and Anh automated the process of synthesis. Instead of mixing the chemicals one reaction at a time and achieving perhaps several reactions per day, they were able to perform 200 reactions in less than an hour. The pair ran 9,600 microreactions and from those reactions uncovered 25 new structures. The scientists say they keep producing new crystals of ZIFs every day.

References from the Yaghi Laboratory

Rahul Banerjee, et. al., High-Throughput Synthesis of Zeolitic Imidazolate Frameworks and Application to CO₂ Capture. Science 15 February 2008: Vol. 319. no. 5865, pp. 939 – 943 DOI: 10.1126/science.1152516

Hideki Hayashi, Adrien P. Côté, Hiroyasu Furukawa, Michael O’Keeffe & Omar M. Yaghi, “Zeolite A imidazolate frameworks” [*.pdf - at Yaghi Lab], Nature Materials 6, 501 – 506 (2007), Published online: 27 May 2007 | doi:10.1038/nmat1927

Omar M. Yaghi, et. al. “Exceptional chemical and thermal stability of zeolitic imidazolate frameworks” [*.pdf - at Yaghi Lab], PNAS, July 5, 2006, vol. 103, no. 27, 10186-10191, DOI: 10.1073/pnas.0602439103