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College professors discover breakthrough in CO2 separation

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Image of Long and Smit's new metal-organic framework, Mg2(dobdc)
Long and Smit's new metal-organic framework, Mg2(dobdc).

April 4, 2011

College of Chemistry professors Jeff Long and Berend Smit, together with professor Krishna, visiting the college on a sabbatical from the University of Amsterdam, have made a breakthrough that has the potential to dramatically reduce carbon dioxide emissions from clean-burning coal power plants.

Long and Smit head a Department of Energy-funded research center that focuses on clean energy gas separation technology. Their DOE Energy Frontier Research Center, announced less than two years ago, has discovered that an existing metal organic framework (MOF) can selectively absorb high volumes of carbon dioxide from a gas stream while allowing hydrogen gas to pass through.

This discovery could play a critical role in clean-burning coal power plants that use a process known as integrated gasification and combined cycle (IGCC), in which the coal is first gasified using steam to produce a mix of CO2 and hydrogen gas. Then the two gases are separated, the H2 burned for energy and the CO2 condensed and sequestered underground.

In comparison, in a conventional coal-fired power plant, the coal is burned in air, producing a waste-gas stream that is mostly nitrogen with a diluted amount of CO2. Unfortunately, it is difficult and expensive to separate the diluted CO2 from N2 in the waste gas. Sequestering CO2 is a much less daunting task for clean-burning coal power plants.

The metal-organic framework being studied in the Long group, Mg2(dobdc), combines the metal magnesium with the organic linker dioxidobenzenedicarboxylate. Under the pressures typically used in coal gasification, the MOF adsorbs very high volumes of CO2, on the order of 10-15 moles CO2 per liter of MOF. Yet it adsorbs almost no H2. The CO2-laden MOF can then be taken to a lower-pressure environment, where the CO2 is released for sequestration. The MOF is then reused.

According to Long, the MOF, a white crystalline powder, does not use any rare or expensive feedstocks. The German chemical maker BASF already produces similar compounds on the ton scale. Says Long, “We are still in the experimental stage, and we need to do more experiments to see how the MOF handles impurities like methane. So far there are no deal-breakers.”

An article on the breakthrough was published in the online on March 23 in the Journal of the American Chemical Society.

More Information

Catalyst Magazine, SP/SU 2010 Vol. 5, No. 1, page 10: “Capturing carbon Berend Smit explores a new world of materials”