Researchers in the US have developed an approach to control methane emissions using a common, inexpensive clay called zeolite.
The MIT approach of the team, described in ACP environment Au, involves treating zeolite clay with a small amount of copper, making it effective at absorbing methane from the air, even at very low concentrations.
Co-author Desiree Plata, an associate professor of civil and environmental engineering, said that while many people associate atmospheric methane with drilling and fracking for oil and natural gas, these sources only account for about 18 percent of global methane emissions.
The majority come from sources such as slash-and-burn farming, dairy farming, coal and ore mining, wetlands and melting permafrost.
Zeolite is so cheap that it is currently used to make cat litter. In lab tests, tiny particles of the copper-reinforced zeolite material were reportedly packed into a reaction tube, which was heated from the outside as the gas stream — with methane levels ranging from just two parts per million to a concentration of up to two percent — passed through the tube.
This range includes everything that can exist in the atmosphere, the team said, down to flammable levels that can’t be burned or flared directly.
Plata said the process has several advantages over other approaches to removing methane from the air. Other methods typically use expensive catalysts such as platinum or palladium, require high temperatures of at least 600°C and complex cycling between methane-rich and oxygen-rich streams. This makes devices more complicated and risky, because methane and oxygen individually and in combination are highly flammable.
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According to researchers, the new process has maximum effectiveness at about 300°C. It can also work at methane concentrations lower than other methods can handle, even small fractions of one percent, and it does so in air rather than pure oxygen.
The method converts the methane into carbon dioxide, which many people would see negatively because of global efforts to reduce carbon emissions, Plata said. But she pointed out that carbon dioxide has much less of an impact in the atmosphere than methane, which is about 80 times stronger as a greenhouse gas in the first 20 years and about 25 times stronger in the first century.
This is because methane in the atmosphere turns into carbon dioxide over time. By speeding up the process, researchers said the method would “drasically reduce” climate impact in the near term, and that even converting half of the atmosphere’s methane to CO2 would lower the latter’s levels by less than one part per million. increase (about 0.2 percent of the current atmospheric CO2) and a saving of about 16 percent of the total radiant heating.
The ideal location for the systems, the team concluded, would be in places with a concentrated source of methane, such as dairy barns and coal mines. These usually already have air handling systems, as a build-up of methane can pose a safety risk.
Adapting the technology to specific locations should be relatively easy, Plata said, but large amounts of gas don’t readily flow through clay, so the team’s next steps will focus on ways to structure the clay material in a multi-scale, hierarchical configuration. which will help airflow.
Rob Jackson, a professor of earth science systems at Stanford University, said: “We need new technologies to oxidize methane at concentrations lower than those used in flares and thermal oxidizers.
“There is currently no cost-effective technology for oxidizing methane in concentrations below about 2,000 parts per million.
“Many questions remain for scaling up this and all similar work: how quickly will the catalyst foul up under field conditions? Can we get the required temperatures closer to ambient conditions? How scalable will such technologies be when handling large volumes of air? ?”
A potential advantage of the new system is that heat is released during the chemical process. By catalytically oxidizing the methane, the process is effectively 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 start the process and can be used to generate electricity.
The team’s calculations suggest that in coal mines, enough heat can generate electricity on “the scale of a power plant” for the device to “pay for itself.” The team has been awarded a $2 million grant from the U.S. Department of Energy, which will now use it to demonstrate a proof of concept and eventually create more devices that can be compatible with existing air handling systems.
