Scientists unveil reactor that degrades methane 100 million times faster

Disposing off methane

Methane is a flammable gas but can only be burnt if its concentration exceeds four percent in the air. Human-led activities, however, produce methane at concentrations less than 0.1 percent, making it difficult to simply burn the gas off before it reaches the atmosphere.

"Methane decomposes at a snail's pace because the gas isn't especially happy about reacting with other things in the atmosphere," said Matthew Stanley Johnson, an atmospheric chemistry professor at the university. "However, we've discovered that, with the help of light and chlorine, we can trigger a reaction and break down the methane roughly 100 million times faster than in nature."

In their setup called MEPS, the researchers built a reaction chamber that looks no different than an elongated metal box with lots of hoses. Inside the box, though, chlorine and light are used to cause a chain reaction that breaks down methane.

How does the reaction occur?

First, methane gas is collected in the reaction chamber and then chlorine molecules are introduced subsequently. UV light is then used to split the chlorine molecules into two highly reactive chlorine atoms.

The chlorine atoms then steal hydrogen atoms from methane to make hydrochloric acid (HCl), which can be captured and recycled. The methane atoms decompose into carbon dioxide (CO2), carbon monoxide (CO), and hydrogen (H2), the same way it is processed naturally but at a rate that's roughly 100 million times faster in the reaction chamber.

In scientific experiments, the researchers found that their approach could degrade 58 percent of the methane present in the air and decided to publish their findings. In the time taken to publication, the approach has been further improved to clean up 88 percent of the methane in the chamber, a press release said.

Next up, the team is scaling up its technology to fit a 40-foot shipping container, which can then be connected to a ventilation system in a livestock barn, where much of the methane is produced. "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," Johnson added.

The research findings were published in the journal Environmental Research Lettersthis week and spun off a company Ambient Carbon to take this technology to the masses.

Abstract

Despite the urgent need, very few methods are able to efficiently remove methane from waste air with low cost and energy per unit volume, especially at the low concentrations found in emissions from, e.g., wastewater treatment, livestock production, biogas production, and mine ventilation. We present the first results of a novel method based on using chlorine atoms in the gas phase, thereby achieving high efficiency. A laboratory prototype of the methane eradication photochemical system (MEPS) technology achieves 58% removal efficiency with a flow capacity of 30 l min−1; a reactor volume of 90 l; UV power input at 368 nm of 110 W; chlorine concentration of 99 ppm; and a methane concentration of 55 ppm; under these conditions the apparent quantum yield (AQY) ranged from 0.48% to 0.56% and the volumetric energy consumption ranged from 36 to 244 kJ m−3. The maximum achieved AQY with this system was 0.83%. A series of steps that can be taken to further improve performance are described. These metrics show that MEPS has the potential to be a viable method for eliminating low-concentration methane from waste air.