Researchers invent ‘methane cleaner’ that could become a permanent fixture in cattle and pig barns

In a new study, researchers at the University of Copenhagen used light and chlorine to remove low-concentration methane from the air. The result brings us closer to being able to eliminate greenhouse gases from livestock buildings, biogas production plants and wastewater treatment plants, benefiting the climate. The work is published in the journal Environmental Research Letters.

The Intergovernmental Panel on Climate Change (IPCC) has determined that reducing methane emissions will immediately reduce rising global temperatures. This gas is a greenhouse gas up to 85 times more powerful than CO₂and more than half is emitted by human sources, with livestock and fossil fuel production accounting for the largest share.

A unique new method developed by a research team from the University of Copenhagen’s Department of Chemistry and spin-off company Ambient Carbon has successfully removed methane from the air.

“Much of our methane emissions come from millions of low-concentration point sources like barns and pigsties. In practice, methane from these sources is impossible to concentrate to higher levels or remove. But our new “The results prove that it is possible using the reaction chamber we built,” says Matthew Stanley Johnson, a professor of atmospheric chemistry at UCPH who led the study.

Earlier, Johnson presented the research results at COP 28 in Dubai via online connection and in Washington DC at the National Academy of Sciences, which advises the US government on science and technology.

A reactor cleans methane from the air

Methane can be burned from the air if its concentration exceeds 4%. But most human-caused emissions are less than 0.1% and therefore cannot be burned.

To remove methane from the air, the researchers built a reaction chamber, which, to the uninitiated, looks like an elongated metal box with piles of pipes and measuring instruments. Inside the box, a chain reaction of chemical compounds takes place, which eventually breaks down the methane and removes much of the gas from the air.

“In the scientific study, we proved that our reaction chamber can remove 58% of methane from the air. And, since submitting the study, we have improved our laboratory results, so that the reaction chamber reaction is now at 88%.” said Matthew Stanley Johnson.

Chlorine is the key to the discovery. Using chlorine and light energy, researchers can remove methane from the air much more efficiently than in the atmosphere, where the process typically takes 10 to 12 years.

“Methane decomposes at a snail’s pace because the gas is not particularly willing to react with other elements present in the atmosphere. However, we discovered that with the help of light and chlorine, we can trigger a reaction and break down methane about 100 million times faster than in nature,” says Johnson.

Next step: Livestock barns, sewage treatment plants and biogas plants

A 40-foot shipping container will soon arrive at the Department of Chemistry. When it does, it will become a larger prototype of the reaction chamber the researchers built in the lab. This will be a “methane cleaner” which, in principle, can be connected to the ventilation system of a livestock barn.

“Today’s livestock farms are high-tech facilities where ammonia is already removed from the air. As such, removing methane through existing air purification systems is an obvious solution,” explains Professor Johnson.

The same goes for biogas and wastewater treatment plants, which are among the largest sources of human-caused methane emissions in Denmark after cattle production.

As a preliminary investigation for this study, researchers traveled across the country to measure the amount of methane escaping from barns, sewage treatment plants and biogas plants. In several places, researchers have observed that a large quantity of methane escapes into the atmosphere from these power plants.

“Denmark, for example, is a pioneer in the production of biogas. But if only a few percent of the methane from this process escapes, this cancels out any climate gains,” concludes Johnson.

The research was carried out in collaboration between the University of Copenhagen, Aarhus University, Arla, Skov and UCPH spin-out company Ambient Carbon, now led by Professor Matthew Stanley Johnson. The company was established to develop MEPS (Methane Photochemical Eradication System) technology and make it available to society.

About the method

The researchers built a reaction chamber and developed a method that simulates and significantly accelerates the natural process of methane degradation.

They dubbed this method the methane eradication photochemical system (MEPS) and it degrades methane 100 million times faster than in nature.

The method works by introducing chlorine molecules into a reaction chamber with methane. The researchers then shine UV light on the chlorine molecules. The energy from the light causes the molecules to split and form two chlorine atoms.

The chlorine atoms then steal a hydrogen atom from the methane, which disintegrates and decomposes. The chlorinated product (hydrochloric acid) is captured then recycled in the chamber.

Methane turns into carbon dioxide (CO₂) and carbon monoxide (CO) and hydrogen (H₂) in the same way as the natural process in the atmosphere.

Learn more about methane (CH₄)

Methane can be burned to remove it from the air, but its concentration must be greater than 4%, or 40,000 parts per million (ppm), to be flammable. Since most human-caused emissions are less than 0.1%, they cannot be burned.

The Intergovernmental Panel on Climate Change (IPCC) has determined that reducing methane emissions will immediately reduce rising global temperatures.

Methane is a greenhouse gas emitted naturally, among other things, by wetlands and by artificial sources such as food production, natural gas and wastewater treatment plants.

Today, methane is responsible for a third of the greenhouse gases that affect the climate and cause global warming.

It takes 10 to 12 years for methane to naturally break down in the atmosphere, where it is converted to carbon dioxide.

Over 25 years, methane is 85 times worse for the climate than CO₂. Over 100 years, methane is 30 times worse for the climate than CO₂.

The concentration of methane in the atmosphere has increased by 150% since the mid-1700s.

Methane alone increased exposure to anthropogenic radiation by 1.19 W/m²responsible for an increase of 0.6°C in the average air temperature on the planet’s surface, according to the IPCC.