Researchers work to trap CO2 emissions

As researchers around the world race to develop more efficient ways to remove carbon dioxide emissions from the atmosphere, several recent breakthroughs hold promise for slowing the pace of global climate change.

The pressing need to combat the ongoing climate crisis and reduce CO2 emissions has driven researchers to explore carbon capture and utilization since the late 20th century. As the challenge of carbon capture looms, various attempts to store excess carbon dioxide underground are beginning to yield limited success.

"Carbon capture and storage is important and has been researched and trialed for decades now. It is important to sequester carbon dioxide so that it does not go back into the atmosphere. Carbon sequestration has yielded limited success, so far, including at the Gorgon Carbon Capture and Storage project," said Professor Akshat Tanksale, a lead researcher at Monash University in Melbourne, Australia.

The Gorgon project, one of the world's largest carbon storage endeavors by oil and gas giant Chevron, is located on Barrow Island in Western Australia. Traditional approaches to carbon capture and storage involve capturing CO2 at the emission sources and storing it in underground sites, with specific geological requirements.

Fighting climate change means keeping as much carbon out of the air as possible, whether that means generating energy from solar and wind sources or capturing the carbon that comes out of less clean sources.

To reduce the world's carbon footprint, however, experts say it will take more than just switching to electric vehicles or turning the lights off to conserve energy. It also will require massive installations that scrub carbon directly out of the air.

Among existing efforts, planting trees might be the most well-known, but this effort is problematic. Forest fires, for example, release the carbon stored in trees back into the atmosphere. Plus, some experts say the world has too little space to plant enough trees to significantly slow the pace of climate change.

Experts at the United Nations intergovernmental panel, IPCC, predict that we will need numerous effective negative emissions technologies by 2050 if we are going to deal with climate problems in the 21st century.

More strategies for capturing carbon emissions, meanwhile, are emerging, including liquefying it and storing it underground, as well as converting it into benign and useful substances.

Converting CO2 into acetic acid

Researchers at Monash tackled the atmospheric CO2 problem by asking, "Once the CO2 is captured, the question was could we do something useful with it?"

"As part of our research, we were exploring products or chemicals that can be made from that carbon dioxide, but with a process that does not emit CO2 back into the atmosphere," Tanksale explained. "The product would also need to be commercially useful, where sales from the products would also offset the cost of capturing the carbon dioxide."

Tanksale began researching the problem in 2019. A chemical engineer by trade, he studied sustainable chemicals and fuel production for several years, eventually settling on acetic acid as a focal point of the project.

Acetic acid is a vital chemical with various household and industrial applications and is an ingredient in vinegar, vinyl paints, and some glues. Global demand for acetic acid is currently estimated at 6.5 million metric tons per year, and significant carbon emissions are associated with its production from natural gas.

"If we could successfully use carbon dioxide to make acetic acid, which is then used to make polymers used in vinyl paints for instance, the polymers essentially lock away the CO2 for a long time," Tanksale explained.

Power of solid catalysts

While current research has explored the conversion of CO2 to acetic acid, the work relied on conventional commercial processes that use liquid-based catalysts.

"We wanted to come up with a new sustainable and cost-effective catalyst, and there was not a lot of literature where solid catalysts were used to make acetic acid," Tanksale said.

Determined to break away from expensive metals like rhodium or iridium, the team created a novel metal-organic framework, or MOF, a highly crystalline substance comprising repeating units of iron atoms linked with organic bridges.

Through controlled heating, these MOFs transform into iron nanoparticles embedded in a porous carbon layer, forming a unique and efficient solid catalyst. The solid iron catalyst represents a significant leap forward in acetic acid manufacturing, and it boasts several advantages, with Tanksale emphasizing its economic viability.

"We really wanted to move away from expensive metals because when you're attempting to solve one problem, you don't want to create a new one – in this case, the new problem would be extracting those metals. Iron, on the other hand, is found close to the surface of the earth and is available abundantly currently and would be easy to source," he said.

Moreover, the solid catalyst can be employed in a fixed-bed reactor, eliminating the need for a separate purification step, thus streamlining the production process, and reducing energy consumption.

This also presents an opportunity to significantly improve current manufacturing processes that pollute the environment, as well as a solution to slow down or potentially reverse climate change while providing economic benefits to the industry from the sales of acetic acid products.

Path to commercialization

After the research team discovered the catalyst and its properties, the next step was to understand how it worked. While Monash University had world-class facilities, they did not have all the necessary tools and needed further expertise from other stakeholders. Two of the team's key collaborators came from Hokkaido University in Japan and Pennsylvania State University in Pittsburgh, Penn.

"Assistant Prof Abhijit Shrotri from Hokkaido University, who was also my first Ph. D. graduate, supported us with materials testing to understand the properties of this catalyst," Tanksale said.

"At Penn State, I worked with Prof. Adri van Duin, who invented a computational program over 15 years ago that can predict the properties of materials in difficult circumstances. Some things happen at an atomic scale or molecular scale, and within a very short timeframe, hence making it impossible to observe experimentally."

"In such cases, we use computer simulations to observe minute changes in the properties of materials. Prof van Duin's software helped us simulate the behavior of our material, and how the material evolves with thermal treatment," he said.

The research project was supported by Monash University's Engineering Researcher Accelerator Award and will receive future support from the Industry Transformation Research Hub by the Australian Research Council.

The research team's vision also extends beyond academia, as they actively collaborate with industry partners with plans to send the development to market.

"Currently, the reaction takes a few hours to finish but can we reduce that to a few minutes? We are also attempting to work on the size of the reactor. If we can potentially increase the rate of reaction and have smaller reactors, this would mean lower capital cost and lower energy consumption," Tanksale said.

Speaking about his personal vision for the future, Tanksale told a reporter that he would like to explore what the project could further do to achieve true negative carbon emissions.

"We're trying to reduce carbon dioxide emissions in the first place from all the energy production and chemical industries. But reduction alone will not be enough, we need to actively remove carbon dioxide from the atmosphere so that we can reduce the effect of global warming faster," he said.

"By capturing carbon dioxide from the air and converting that carbon dioxide into materials that do not emit carbon dioxide back into the atmosphere, I'm hoping that one day we can achieve true net negative emissions," he added.