Cheaper, safer industrial carbon capture

College of Science researchers at Oregon State University have demonstrated an improved carbon capture method using an inexpensive nanomaterial made from aluminum to scrub carbon dioxide from industrial emissions.

Recently, at the 2021 United Nations Climate Change Conference, 197 countries agreed to the new Glasgow Climate Pact, reaffirming the 2015 Paris Agreement and the need to reduce global CO2 emissions by 45% by 2030, relative to the 2010 levels, with 140 countries additionally seeking net-zero CO2 emissions by 2050.

While freestanding facilities that filter CO2 from the air are being constructed around the globe, running them consumes substantial energy. Overall, these facilities are less efficient than other technologies for mitigating CO2 at the source where it is formed during industrial processes.

One of those promising technologies involves nanomaterials known as metal organic frameworks, or MOFs, that intercept CO2 molecules through adsorption as gases make their way up smokestacks.

"The capture of carbon dioxide is critical for meeting net-zero emission targets," said Kyriakos Stylianou, an Oregon State assistant professor of chemistry leading the study. "MOFs have shown a lot of promise for carbon capture because of their porosity and their structural versatility, but synthesizing them often means using reagents that are costly both economically and environmentally, such as heavy metal salts and toxic solvents."

The water content of some gases also greatly complicates the process. Many MOF technologies lose effectiveness in humid conditions, and dehumidifying flue gases adds another significant expense to the CO2 removal process, enough to make it discouraging for many companies and nonviable for larger industrial applications.

"So, we sought to come up with a MOF to address the various limitations of the materials currently used in carbon capture: high cost, poor selectivity for carbon dioxide, low stability in humid conditions, and low CO2 uptake capacities," said Stylianou.

MOFs are hybrid materials comprised of positively charged metal ions surrounded by organic "linker" molecules known as ligands combined in a crystalline lattice that functions like a sponge. The metal ions make nodes that bind the linkers' arms to form a repeating structure with nanosized pores that adsorb gases.

MOFs are customizable with a variety of component properties; almost 100,000 MOFs have already been synthesized by chemistry researchers, and the properties of another half-million have been predicted.

"In this study we introduce a MOF composed of aluminum and a readily available ligand, benzene-1,2,4,5-tetracarboxylic acid," Stylianou said. "The synthesis of the MOF happens in water and only takes a couple of hours. And the MOF has pores with a size comparable to that of CO2 molecules, meaning there's a confined space for incarcerating the carbon dioxide."

The OSU team's new MOF is designed to function in damp conditions and has a propensity to adsorb carbon dioxide over nitrogen, differentiating between nitrogen oxides that can overwhelm poorly designed MOFs, wasting their capacity.

"This MOF is an outstanding candidate for wet post-combustion carbon capture applications," Stylianou said. "It's cost effective with exceptional separation performance and can be regenerated and reused at least three times with comparable uptake capacities."

The findings were published in Cell Reports Physical Science, with contributions from researchers at Columbia University, the Pacific Northwest National Laboratory and Chemspeed Technologies AG of Switzerland, and Oregon State chemists Ryan Loughran, Tara Hurley and Andrzej Gładysiak.