Cheap, common kitty litter clay captures methane from the air
Carbon dioxide may hog the headlines as a climate change villain, but methane is actually a far more potent greenhouse gas. An MIT team has now demonstrated a new way to remove methane from the air, even at very low concentrations, with a common type of clay used to make cat litter.
Methane is emitted in large quantities from agriculture, coal mining, melting permafrost, and as a by-product of natural gas processing and transport. Compared to carbon dioxide, methane is 81 times more potent at trapping heat in the atmosphere in its first 20 years up there, and 27 times more potent over a whole century. That means methane capture and removal should be a key part of our climate mitigation strategies.
And now, MIT researchers may have a promising new approach using zeolite clays – common, porous mineral structures that are often used as commercial adsorbents, such as cat litter. The team found that by treating the zeolite with copper the material became very effective at pulling methane out of the air around it.
To test the idea in the lab, the researchers placed particles of the copper-treated zeolite into a reaction tube and passed air containing different concentrations of methane through it. The methane levels ranged from two parts per million (ppm), right up to two percent concentration, which the team says covers the range of methane levels in ambient air. The reaction tube was also heated to different temperatures to help the process along.
And sure enough, the zeolite was able to capture and convert 100 percent of the methane in the tube when heated to 310 °C (590 °F). That’s far cooler than other methane capture methods require, and it works at much lower concentrations, both of which could help the new technique function practically in the real world.
But there is, of course, a catch – the method converts the methane into carbon dioxide. Turning one greenhouse gas into another is less than ideal, but the researchers say that there would still be a net benefit. Converting half of the atmospheric methane (already a tall order) would only add about 0.2 percent of today’s atmospheric CO2, but bring about a saving of 16 percent in terms of radiative warming.
Other types of zeolites have been used in past studies for methane capture, but with the benefits of operating at room temperature and converting the gas to useful methanol. However, they only really worked with natural gas – the main component of which is methane – rather than ambient air, so they're more useful for stopping methane leaks at the source rather than pulling the gas out of the atmosphere.
The team says that the most promising place to first use the new catalyst would be in coal mines and dairy barns, which often contain concentrated pockets of methane. The technological requirements for these locations would be relatively simple and could be integrated into existing air circulation systems. However, there are of course more hurdles to overcome before this technique may reach viability, including how to get the air to flow more efficiently through the clay material.
“Many questions remain for scaling this and all similar work," says Rob Jackson, an Earth systems professor who was not involved in the study. "How quickly will the catalyst foul under field conditions? Can we get the required temperatures closer to ambient conditions? How scaleable will such technologies be when processing large volumes of air?”
The researchers have been awarded a US$2-million grant from the US Department of Energy to develop the technology into equipment that can be tested in mines and farms.
The research was published in the journal ACS Environment Au.