Revolutionary Advances in Capturing ‘Hot’ CO2 Emissions from Industrial Factories

Researchers from the University of California, Berkeley, have recently found that a synthetic porous material can effectively absorb CO₂ at temperatures that are close to those found in industrial exhaust. This material, a type of MOF, will be detailed in a paper published on November 15 in the journal Science.

Current methodologies for capturing carbon from emissions at power or industrial facilities utilize liquid amines; however, these reactions function best at temperatures of 40 to 60°C (100 to 140°F). Cement and steel plants emit exhaust that typically exceeds 200°C (400°F), with some reaching nearly 500°C (930°F). Many new materials being tested, including certain MOFs enhanced with amines, deteriorate at temperatures above 150°C (300°F) or operate inefficiently at these levels.

“A costly infrastructure is necessary to cool these hot gas streams to the optimal temperatures required for traditional carbon capture technologies to be effective,” explained Kurtis Carsch, a postdoctoral fellow at UC Berkeley and co-first author of the paper. “Our finding is set to shift how scientists approach carbon capture. We discovered that a MOF can capture carbon dioxide at extraordinarily high temperatures—temperatures relevant to many CO₂-emitting processes, which was previously thought impossible for a porous material.”

“Our research shifts focus from the widely studied amine-based carbon capture systems and introduces a new carbon capture mechanism within a MOF that enables operation at high temperatures,” said Rachel Rohde, a graduate student at UC Berkeley and co-first author of the study.

This MOF, like all such frameworks, has a highly porous crystalline structure composed of metal ions and organic linkers, offering a staggering surface area equivalent to about six football fields per tablespoon, providing ample space for gas adsorption.

“Due to their unique structures, MOFs possess a high density of sites suitable for capturing and releasing CO₂ under specific conditions,” Carsch added.

In simulated conditions, the team demonstrated that this new MOF could effectively capture hot CO₂ at concentrations typical of cement and steel manufacturing exhaust, which ranges from 20% to 30% CO₂, as well as lower concentrations from natural gas plants, around 4% CO₂.

Removing CO₂ from emissions produced by industries and power stations, where it can be either stored underground or transformed into fuels and other beneficial chemicals, is crucial in efforts to reduce greenhouse gases that contribute to climate change. While the shift to renewable energy sources is diminishing the need for fossil fuel-burning power plants, industries that heavily rely on fossil fuels pose a greater challenge for sustainability, making flue gas capture vital.

“Attention must be directed toward CO₂ emissions from difficult-to-decarbonize industries, such as steel and cement manufacturing, as these sectors are likely to continue emitting CO₂, even as we work towards a more renewable energy infrastructure,” Rohde noted.

Transitioning from Amines to Metal Hydrides

Rohde and Carsch work in Jeffrey Long’s laboratory at UC Berkeley, where Long has been researching CO₂-absorbing MOFs for over ten years. His laboratory was responsible for a promising material developed in 2015, which has since been advanced by his startup, Mosaic Materials, acquired in 2022 by the energy technology company Baker Hughes. This previous material incorporates amines to capture CO₂, with new variants being trialed as alternatives to liquid amines in pilot-scale plants and for direct CO₂ capture from ambient air.

Nevertheless, like other porous adsorbents, these MOFs are inefficient at the high temperatures found in many flue gases, Carsch pointed out.

Research into amine-based adsorbents, such as those created by Long, has been prominent in carbon capture studies for decades. In contrast, the MOF investigated by Rohde, Carsch, Long, and their team features pores lined with zinc hydride sites that also attach to CO₂. Surprisingly, these sites exhibited remarkable stability, according to Rohde.

“Molecular metal hydrides can be reactive and exhibit low stability,” Rohde explained. “However, this material maintains high stability and employs a process known as deep carbon capture, allowing it to trap over 90% of the CO₂ it encounters, which is essential for point-source capture. Moreover, its CO₂ capacities are similar to those of amine-modified MOFs but function at significantly higher temperatures.”

Once the MOF is saturated with CO₂, the gas can be extracted, or desorbed, by reducing the partial pressure of CO₂, either by introducing another gas or creating a vacuum. The MOF can then be reused for subsequent adsorption cycles.

“Due to entropy favoring the presence of gas-phase molecules like CO₂ as temperatures rise, capturing such molecules with a porous solid at temperatures above 200°C was generally considered unfeasible,” Long remarked. “This study demonstrates that with the appropriate functional elements—in this case, zinc hydride sites—quick, reversible, and high-capacity CO₂ capture can be achieved at elevated temperatures, such as 300°C.”

Rohde, Long, and their colleagues are investigating variations of this metal hydride MOF to explore what other gases can be absorbed and to see if modifications might allow even greater CO₂ absorption.

“We are fortunate to have stumbled upon this discovery, which has unveiled new paths in separation science oriented towards designing functional adsorbents suitable for high-temperature applications,” said Carsch, who has secured a faculty position in the Chemistry Department at The University of Texas at Austin. “There are an immense number of ways to adjust the metal ion and linker in MOFs, potentially allowing for the systematic design of such adsorbents for various high-temperature gas separation processes relevant to industry and sustainability.”

Additional authors of the paper include Jeffrey Reimer, a UC Berkeley professor of chemical and biomolecular engineering, whose lab provided NMR spectroscopy evidence to affirm the MOF’s unique CO₂ capture mechanism; Craig Brown of the National Institute of Standards and Technology in Gaithersburg, Maryland, who contributed critical structural data to support the proposed mechanism; and Martin Head-Gordon, a UC Berkeley chemistry professor, who offered computational insights into the high-temperature CO₂ capture characteristics. Other contributors from UC Berkeley comprise Andrew Minor, a professor of materials science and engineering, and numerous other researchers.

Rohde’s graduate studies received support from a fellowship provided by NASA, while Carsch benefited from a postdoctoral fellowship from the Arnold O. Beckman Foundation.