Methane is a far more potent greenhouse gas than carbon dioxide, and it has a pronounced
effect within first two decades of its presence in the atmosphere.
In the recent international climate negotiations in Glasgow, abatement of methane emissions
was identified as a major priority in attempts to curb global climate change quickly.
Now, a team of researchers at MIT has come up with a promising approach to controlling
methane emissions and removing it from the air, using an inexpensive and abundant type
of clay called zeolite.
The findings are described in the journal ACS Environment Au.
Although many people associate atmospheric methane with drilling and fracking for oil
and natural gas, those sources only account for about 18 percent of global methane emissions.
The vast majority of emitted methane comes from such sources as slash-and-burn agriculture,
dairy farming, coal and ore mining, wetlands, and melting permafrost.
A lot of the methane that comes into the atmosphere is from distributed and diffuse sources, so
the researchers started to think about how they could take that out of the atmosphere.
The answer the researchers found was something dirt cheap — in fact, a special kind of
“dirt,” or clay.
They used zeolite clays, 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, similar
to cat litter, 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.
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 new process seems to have 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.
That might sound like a bad thing, given the worldwide efforts to combat carbon dioxide
emissions.
But the researcher points out that carbon dioxide 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.
This effect arises from that fact that methane turns into carbon dioxide naturally over time
in the atmosphere.
By accelerating that process, this method would drastically reduce the near-term climate
impact.
And, even converting half of the atmosphere’s methane to carbon dioxide would increase levels
of the latter by less than 1 part per million while saving about 16 percent of total radiative
warming.
The ideal location for such systems would be in places where there is a relatively concentrated
source of methane, such as dairy barns and coal mines.
These sources already tend to have powerful air-handling systems in place, since a buildup
of methane can be a fire, health, and explosion hazard.
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.