Methane emissions curbed by zeolite clays

“[This] is potentially a route to change the rate of climate change within 10–20 years by drawing methane out of the atmosphere or keeping it from getting there in the first place”Desiree Plata

Researchers at MIT has demonstrated a way to control methane emissions in the air using clay minerals called zeolites. This inexpensive and abundant type of clay, commonly used in cat litter, could lead to reduced methane emissions and help in the fight against climate change.

Most emitted methane comes from diffuse sources, such as slash-and-burn agriculture, dairy farming, coal mining, and melting permafrost, as well as the drilling and fracking for oil and natural gas. With methane being a much more problematic greenhouse gas than carbon dioxide, moves to reduce air emissions are welcome.

In this new study, reported in ACS Environmental AU [Brenneis et al. ACS Environ. Au (2022) DOI: 10.1021/acsenvironau.1c00034], zeolite was treated with small amounts of copper to make it effective at absorbing methane from the air, even at extremely low concentrations. Other methods of removing methane from air usually involve expensive catalysts and temperatures of at least 600⁰C, as well as complex cycling between methane-rich and oxygen-rich streams, making them more complicated and also riskier since methane and oxygen are highly combustible.

Here, small particles of copper-enhanced zeolite were placed in a reaction tube that was heated while the gas flowed through the tube. The process appears to reach peak effectiveness at around 300⁰C, much less than in other methane capture processes, and can be effective at lower methane concentrations. The zeolite undergoes a structural change that constrains the larger pore space, producing a geometrically constrained reaction center that promotes the addition of oxygen to the methane molecule.

These systems could ideally be located where there is a concentrated source of methane, such as coal mines, which already have air-handling systems to avoid hazardous build-up of methane. As researcher Desiree Plata told Materials Today, with the research “there is potentially a route to change the rate of climate change within 10–20 years by drawing methane out of the atmosphere or keeping it from getting there in the first place”.

Although the use of transition-metal doped zeolites to drive oxidation reactions in hydrocarbons is proven, how it was deployed here shows this will work in air, at low temperatures, and at low cost. This is managed by driving the reaction in air rather than pure oxygen, running it continuously instead of in a cycle between methane and oxygen, and operating at lower temperatures.

The technology can operate on any sub-flammable methane stream, but for the most benefit the team are looking to apply it in higher-methane dilute streams. As pushing large volumes of gas through a powdered material is not easy, they will now look at ways of structuring the material in a multiscale, hierarchical way to aid air flow, as well as showing it can work under more challenging conditions than in the lab.