Direct Air Capture of Methane? Is it in Our Future? Scientists Reveal Chemical Method that Consumes Methane 100 Million Times Faster Than Nature

     Researchers at the University of Copenhagen in Denmark have created a device that chemically consumes methane by reacting it with UV light and chlorine gas. The chlorine gas steals hydrogen ions from the methane to make hydrochloric acid which is captured and recycled, and “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.” The method is promising where “waste air” near facilities such as wastewater treatment plants, livestock production, biogas production, and mine ventilation. I am guessing that some oil & gas facilities and operations could be included as well.

     Methane is commonly burned or flared to make it less potent as a greenhouse gas. The result of combustion is CO2 and water vapor. Flaring is common at landfills, upstream, midstream, and downstream oil & gas and petrochemical facilities, and at some coal mines. In order to be flared the methane concentration of the air needs to be about 4% or more. This system can dispose of those smaller concentrations of methane that cannot be flared. In nature, methane is mostly non-reactive. Thus, this method has the ability to make it reactive and consume it where flaring won’t work. The reaction chamber shown below in both model and actual forms is known as a Methane Eradication Photochemical System (MEPS).

Source: Scientists unveil methane munching monster, 100 million times faster than nature. Ameya Paleja. Interesting Engineering. December 19, 2023. Scientists unveil methane munching monster, 100 million times faster than nature (msn.com)

First methane gas collects in the reaction chamber. Then UV light is introduced to split the chlorine gas into individual chlorine atoms which are highly reactive. Those chlorine atoms then steal hydrogen atoms from the methane to yield hydrochloric acid. The methane atoms decompose into carbon monoxide (CO), CO2, and hydrogen.

Source: A high efficiency gas phase photoreactor for eradication of methane from low-concentration sources. Morten Krogsbøll, Hugo S. Russell, and Matthew S. Johnson. December 18, 2023. Environmental Research Letters, Volume 19, Number 1. A high efficiency gas phase photoreactor for eradication of methane from low-concentration sources - IOPscience

     When the research was published the researchers were able to dispose of 58% of the methane in the waste air but since then they have achieved 88% disposal. Thus far the technique has only been successful at laboratory scale. The next step is to scale up “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.” Since at many higher-tech livestock farms, ammonia is already removed from the air. It is thought that adding methane removal is achievable at such facilities.

     For larger methane accumulations in waste air such as oil & gas and industrial sites, there are better methods to remove methane such as regenerative thermal oxidation (RTO), and catalytic thermal oxidation (CTO). According to the paper in Environmental Research Letters: “They operate by oxidizing pollution with heat, or by running the air stream over a catalyst bed at elevated temperatures. Due to the capital and operating costs, the RTO method is suited to high levels of VOCs including methane (above 0.1%–0.2%) in large air flows such as might be found in industrial settings [14]. Low-concentration methane sources can be treated but at prohibitively high cost and energy input. RTO will also produce NOx gases due to the high temperatures needed for effective methane removal. For CTO methods, the main costs are due to the increase in temperature and the size required for large air flows to gain the needed residence time over the catalyst [15]. For agricultural and wastewater treatment conditions working with flows at scales of >1 m3 s−1, these approaches would require unreasonably large systems. The minimum concentration for methane removal demonstrated in a laboratory for CTO is 200 ppm as reported by Gélin and Primet [15]. Industrial thermal and catalytic oxidisers typically have a high thermal efficiency, ca. 95% [16]. At a typical operating temperature of 1000 ∘C this implies a heat loss corresponding to a change in temperature of the airstream of 50 K. Taking the specific heat capacity of air ∼1 J (g K)−1 and the density of air ∼1.2 kg m−3, this means the specific power requirement is ∼60 kJ m−3. Thermal and catalytic oxidisers may not be suitable for some applications due to the need for addition of natural gas to keep the combustion bed hot, their cost, and the fact that they work best for stable pollution loads whereas many industrial processes are intermittent.”

     Oxidation of low-level methane emissions is an ongoing research problem. Thus far, none of these methods have been proven at scale “with an acceptable volumetric (kJ m−3) or specific (kJ kg−1) energy input.” This project utilizing chlorine radicals has proven to be cheaper and more energy-efficient than using hydroxide radicals. There are other advantages as well. The resulting hydrochloric acid (HCl) is recycled back into chlorine to lower costs and needs for disposal. The MEPS system was demonstrated at an air concentration of 50 ppm methane with a flow rate of 30 l min−1. This work has led to patents being filed.

Source: A high efficiency gas phase photoreactor for eradication of methane from low-concentration sources. Morten Krogsbøll, Hugo S. Russell, and Matthew S. Johnson. December 18, 2023. Environmental Research Letters, Volume 19, Number 1. A high efficiency gas phase photoreactor for eradication of methane from low-concentration sources - IOPscience

     The conclusions from the paper:

“MEPS, as described in this article, has been shown to effectively oxidize low-concentration methane in laboratory-scale experiments. Moreover, the process is easily controlled as the chlorine concentration and UV lights can be rapidly adjusted to match changes in pollution load. This technology is still under development and power efficiency is continually being improved, as described above. The technology is scalable and could eventually be deployed in a number of real-world scenarios. Further improvement in the chloride recycling system is also envisaged.”

 

“In the near future, the photoreactor will undergo field-testing at scale and once optimized, MEPS could be the first viable technology for direct oxidation of low-concentration point-source methane at scale. Perhaps with further improvements, MEPS would eventually be able to treat ambient concentrations of methane when used in combination with a CO2 DAC system.” (my emphasis)

My take is that this is an interesting development in methane mitigation via methane oxidation of low-concentration atmospheric methane. It should be interesting to see how it develops, how fast it can be deployed, whether it can be deployed economically, and whether it can actually make a dent in greenhouse gas reduction over say the next decade.  

References:

Scientists unveil methane munching monster, 100 million times faster than nature. Ameya Paleja. Interesting Engineering. December 19, 2023. Scientists unveil methane munching monster, 100 million times faster than nature (msn.com)

A high efficiency gas phase photoreactor for eradication of methane from low-concentration sources. Morten Krogsbøll, Hugo S. Russell, and Matthew S. Johnson. December 18, 2023. Environmental Research Letters, Volume 19, Number 1. A high efficiency gas phase photoreactor for eradication of methane from low-concentration sources - IOPscience