Infrastructure: The Hidden Life of Great Cities

Direct Air Capture of Methane

Direct air capture of CO2 has gotten a lot of attention recently, including many questions and concerns about captured CO2 being used to recover more oil. We posted here on a Squamish-based DAC company, and here is a good recent piece on enhanced oil recovery.

A related but different concept is the direct air capture of methane (CH4) – a far more potent greenhouse gas than CO2. Methane levels before the industrial revolution are estimated to have been under 0.7 parts per million, and they are currently around 1.9 ppm and show no signs of leveling off.

Direct air capture of methane makes for an interesting comparison with CO2. Because methane has a global warming potential of 28 over a 100 year time horizon (i.e. 28x the global warming potential of CO2), removing a single molecule of methane from the atmosphere will have 28x the impact of extracting a single molecule of CO2. But methane is much less common in the atmosphere than CO2; compare methane at 1.9 ppm vs CO2 levels at 407 ppm.

On the other hand, one of the main challenges with direct air capture of CO2 is finding something to do with the CO2. With methane, the simplest solution is to convert it into CO2, and just release the CO2 back into the atmosphere. Yes, it is still a GHG, but much less potent than methane. If the CO2 can be beneficially used or stored, even better, but just converting methane to CO2 reduces its climate impact by 27/28ths or over 95%. In theory this could be paired with CO2 capture to achieve further reductions, but the big win is from converting atmospheric methane to CO2.

A paper earlier this year in Nature Sustainability laid out the concept and proposed that it might be done using zeolites, which are used in a range of industrial chemistry processes including oxidizing methane to methanol.

Direct air capture of CO2 attracted a lot of attention from industry, likely because of the opportunity to use captured CO2 for enhanced oil recovery. There isn’t a potential revenue source for direct air capture of methane that I am aware of and to my knowledge there isn’t a company developing this technology. Seems like a strong case for government to fund some basic research.

Will Cleveland

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