Common clay could curb methane emissions

Image credit: MIT
Image credit: MIT

Researchers in the US have developed a remarkable approach to controlling methane emissions using a common, inexpensive type of clay called zeolite.

The MIT team’s approach, described in ACS Environment Au, involves treating zeolite clays with a small amount of copper, making it effective at absorbing methane from the air even at very low concentrations.

The paper’s co-author Desiree Plata, associate professor Civil and Environmental Engineering, said that while many people associate atmospheric methane with drilling and fracking for oil and natural gas, those sources only account for around 18 per cent of global methane emissions.

The majority comes from sources such as slash-and-burn agriculture, dairy farming, coal and ore mining, wetlands and melting permafrost.

Zeolite is so inexpensive that it is currently used to make cat litter. In lab tests, tiny particles of the copper-enhanced zeolite material were reportedly packed into a reaction tube, which was heated from the outside as the stream of gas — with methane levels ranging from just two parts per million to up to two per cent concentration — flowed through the tube.

This range covers everything that might exist in the atmosphere, the team said, down to sub-flammable levels that cannot be burned or flared directly.

Plata said the process has several advantages over other approaches to removing methane from 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, as methane and oxygen are highly combustible on their own and in combination.

According to researchers, the new process has peak effectiveness at about 300°C. It can also work at concentrations of methane lower than other methods can address, even small fractions of one per cent, and it does so in air rather than pure oxygen.

The method converts the methane into carbon dioxide, which many people would view negatively due to worldwide efforts to reduce CO2 emissions, Plata said. But she pointed 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.