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Common clay materials may help curb methane emissions

Author : MIT

13 January 2022

With special treatment, minerals that are commonly found in cat litter could be an efficient way of removing methane from the air, researchers have said. A team at MIT has come up with an approach to controlling methane emissions using an inexpensive and abundant type of clay called zeolite.

Image: MIT
Image: MIT

The findings are described in the journal ACS Environment Au, in a paper by doctoral student Rebecca Brenneis, Associate Professor Desiree Plata, and two others. Reducing methane emission levels is seen as a major priority in attempts to curb global climate change quickly. While looking into ways of achieving this, the MIT researchers discovered that zeolite clays were effective in absorbing methane, a material so inexpensive that it is currently used to make cat litter. Treating the zeolite with a small amount of copper makes the material very effective at absorbing methane from the air, even at extremely low concentrations.

The system is simple in concept, though much work remains on the engineering details. In their lab tests, tiny particles of the copper-enhanced zeolite material were packed into a reaction tube, which was then heated from the outside as the stream of gas, with methane levels ranging from just 2 parts per million up to 2 percent concentration, flowed through the tube. That range covers everything that might exist in the atmosphere, down to subflammable levels that cannot be burned or flared directly.

The process has several advantages over other approaches to removing methane from air, Associate Professor Desiree Plata says. Other methods tend to use expensive catalysts such as platinum or palladium, require high temperatures of at least 600 degrees Celsius, and tend to require complex cycling between methane-rich and oxygen-rich streams, making the devices both more complicated and more risky, as methane and oxygen are highly combustible on their own and in combination.

“The 600 degrees where they run these reactors makes it almost dangerous to be around the methane,” as well as the pure oxygen, doctoral student Rebecca Brenneis says. “They’re solving the problem by just creating a situation where there’s going to be an explosion.” Other engineering complications also arise from the high operating temperatures.

The MIT researchers’ new process has its peak effectiveness at about 300 degrees Celsius, which requires far less energy for heating than other methane capture processes. It also can work at concentrations of methane lower than other methods can address, even small fractions of 1 percent, which most methods cannot remove, and does so in air rather than pure oxygen, a major advantage for real-world deployment.

The method converts the methane into carbon dioxide which is much less impactful in the atmosphere than methane, which is about 80 times stronger as a greenhouse gas over the first 20 years, and about 25 times stronger for the first century. The ideal location for such systems, the team concluded, would be in places where there is a relatively concentrated source of methane, such as dairy barns and coal mines.

One potential major advantage of the new system is that the chemical process involved releases heat. By catalytically oxidizing the methane, in effect the process is a flame-free form of combustion. If the methane concentration is above 0.5 percent, the heat released is greater than the heat used to get the process started, and this heat could be used to generate electricity. The team’s calculations show that “at coal mines, you could potentially generate enough heat to generate electricity at the power plant scale, which is remarkable because it means that the device could pay for itself,” Plata says. “Most air-capture solutions cost a lot of money and would never be profitable. Our technology may one day be a counterexample.”

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