Carbon Removal at Extreme Temperatures: Porous Material Can Capture 'hot' CO₂ From Industrial Exhaust

Industrial plants, such as those making cement or steel, emit significant amounts of carbon dioxide, a potent greenhouse gas, but the exhaust is too hot for state-of-the-art carbon removal technology. The high energy and water demands to cool exhaust streams have hindered the adoption of CO2 capture in these highly polluting industries.

Now, chemists at the University of California, Berkeley have discovered a porous material that can act like a sponge to capture CO2 at temperatures close to those of many industrial exhaust streams. This material, a type of metal-organic framework (MOF), is described in a paper published in the journal Science.

At center left is one of the crystalline building blocks of a thermally stable metal-organic framework (MOF), known as ZnH-MFU-4l, that is able to reversibly and selectively capture the greenhouse gas carbon dioxide from a mix of many industrially relevant gases. CO2 is highlighted at left, among nitrogen, oxygen, hydrogen, carbon monoxide and water molecules. The MOF can capture CO2 over many cycles at 300 C, which is a typical temperature of the exhaust streams from cement and steel plants. The zinc hydride groups in the MOF reversibly bind and release the carbon dioxide molecules (right). Light-blue, gray, blue, red, and white spheres represent Zn, C, N, O, and H atoms, respectively. Credit: Rachel Rohde, Kurtis Carsch and Jeffrey Long, UC Berkeley

>> In Other News: Securing the Future of U.S. Industries with Decarbonization

Addressing High-Temperature Emissions

The dominant method for capturing carbon from power or industrial plant emissions employs liquid amines, which only work efficiently at temperatures between 40°C and 60°C. In contrast, cement manufacturing and steelmaking plants produce exhaust that exceeds 200°C, and some emissions approach 500°C.

"A costly infrastructure is necessary to take these hot gas streams and cool them to the appropriate temperatures for existing carbon capture technologies to work," said Kurtis Carsch, UC Berkeley postdoctoral fellow, and co-first author of the paper. The new MOF technology could eliminate the need for this costly cooling process.

"Our discovery is poised to change how scientists think about carbon capture," said Carsch. "We've found that a MOF can capture carbon dioxide at unprecedentedly high temperatures—temperatures relevant for many CO2-emitting processes."

Advancing Carbon Capture Mechanisms

"Our work moves away from the prevalent study of amine-based carbon capture systems," said Rachel Rohde, UC Berkeley graduate student and co-first author of the paper. "This new mechanism enables high-temperature carbon capture in a MOF, opening up applications previously considered impossible."

MOFs are known for their porous, crystalline structures with internal areas equivalent to about six football fields per tablespoon. This unique structure allows for a high density of sites where CO2 can be captured and released under appropriate conditions.

Under simulated conditions, the researchers demonstrated that the new MOF can capture CO2 at concentrations relevant to cement and steel manufacturing emissions, which average 20% to 30% CO2. It can also handle lower-concentration emissions, such as those from natural gas power plants, which contain about 4% CO2.

Implications for Industrial Sustainability

Removing CO2 from industrial emissions and using it for fuel production or storage is a key strategy for reducing greenhouse gases. While renewable energy reduces fossil fuel dependency, industrial processes like steel and cement production remain hard to decarbonize.

"We need to address emissions from industries that are difficult to decarbonize," said Rohde. "Flue gas capture is essential for reducing emissions from these sectors, even as energy infrastructure shifts toward renewables."

Moving from Amines to Metal Hydrides

Rohde and Carsch’s research, conducted in the lab of Jeffrey Long, UC Berkeley professor of chemistry, highlights the transition from amine-based systems to MOFs featuring zinc hydride sites. These sites are highly stable and enable deep carbon capture at high temperatures.

"This material is highly stable and captures 90% or more of the CO2 it encounters," said Rohde. "This level of performance is critical for point-source capture."

Once filled with CO2, the MOF can release the gas by lowering its partial pressure, allowing for reuse in subsequent cycles. "This reversibility and efficiency make it a game-changer for industrial applications," said Long.

Exploring New Directions in MOF Research

Rohde, Long, and their colleagues are now investigating variants of this MOF to enhance CO2 adsorption and explore its use with other gases. The flexibility of MOF design could enable high-temperature applications for various industrial processes.

"With the right functionality, such as zinc hydride sites, rapid and reversible high-capacity CO2 capture can be achieved at temperatures as high as 300°C," said Long. This discovery opens up new possibilities for gas separation processes in industrial settings.

Collaborative Contributions

Other contributors to the study include Jeffrey Reimer, UC Berkeley professor of chemical and biomolecular engineering, who used NMR spectroscopy to verify the unique mechanism; Craig Brown of the National Institute of Standards and Technology, who provided structural data; and Martin Head-Gordon, UC Berkeley chemistry professor, whose lab offered computational insights into the CO2 capture process.

About the Researchers

Kurtis Carsch, who has taken a faculty position at the University of Texas at Austin, emphasized the broader impact of their discovery. "This research has opened up new directions in high-temperature separation science."

The research team continues to explore the potential of MOFs, offering promising solutions for sustainable industrial practices and addressing global climate challenges.