CCS Mesh

The atomic structure of a single pore in a newly developed metal organic framework showing how carbon dioxide molecules (gray and red spheres) bind to the tetraamines (blue and white spheres), building a CO2 polymer that threads through the pore. Low-temperature steam can strip out the CO2 for sequestration, allowing the material to be reused to capture more carbon from power plant emissions.

Researchers from the University of California, Berkeley; Lawrence Berkeley National Laboratory; and Exxon Mobil Corp. have developed a new material able to more effectively and inexpensively capture carbon dioxide from natural gas power plants' flue emissions for eventual reuse or sequestration.

UC Berkeley announced the findings July 23 in advance of the paper's publication July 24 in the journal Science.

The material is a highly porous metal-organic framework, or MOF, which the researchers modified with nitrogen-containing amine molecules. These materials are extremely porous, which means that an amount of the material equivalent to the weight of a paper clip has an internal surface area equal to that of a football field that can be used for adsorbing gases. Specifically, the researchers replaced diamines with tetraamines. The resulting material immediately outperformed their diamine-appended MOF when tested.

After capturing carbon dioxide, low-temperature steam can be used to flush the captured CO2 from the material for reuse or sequestration. The researchers found the material has a six-times-greater capacity for removing CO2 from flue gas than current amine-based technology. They also found it captures more than 90 percent of the CO2 emitted, and said it could cut the cost of capture in half.

Because this particular carbon-capture material is able to use low-temperature steam to regenerate the material for multiple uses, less overall energy is required in the process.

"For CO2 capture, steam stripping—where you use direct contact with steam to take off the CO2—has been a sort of holy grail for the field. It is rightly seen as the cheapest way to do it," senior researcher Jeffrey Long, UC Berkeley professor of chemistry and chemical and biomolecular engineering and senior faculty scientist at Berkeley Lab, said in a news release. "These materials, at least from the experiments we have done so far, look very promising."

Capturing carbon emissions is one step in a process known as carbon capture and sequestration. Large amounts of CO2 are captured, compressed, transported and stored in geological formations in the process, although some solutions divert the captured material for reuse in industrial processes, such as making fuels or other chemical products (see CEM No. 1581).

The California Air Resources Board issued a study on carbon capture and sequestration, which was discussed at a Dec. 11 workshop. Natural gas-fired power generation plants and refineries were deemed ideal locations for such technologies. The challenge for these types of projects is that they have been unable to overcome high upfront costs. Constructing a new facility with a carbon-capture system—based on existing conventional technologies—could add between 25 and 90 percent to the price tag. Some facility operators currently using CCS technology are concerned that they will need to stop the process if reliable incentives are not available (see CEM No. 1569).

The researchers said that because there is not much of an existing market for captured CO2, power plants would likely either inject it back into the ground or sequester it. They also note there is a need for "the cost of scrubbing the emissions . . . to be facilitated by government policies, such as carbon trading or a carbon tax, to incentivize CO2 capture and sequestration, something many countries have already implemented."

Long's group at UC Berkeley's Center for Gas Separations, which is funded by the U.S. Department of Energy, discovered a chemically modified MOF six years ago.

The current work was funded by Exxon Mobil, which is working with both the Berkeley group and Long's startup, Mosaic Materials Inc., on the development, scaling and testing of carbon-capture processes.