Out of thin air: direct carbon capture is on the horizon

An Australian company could be selling modules that suck carbon dioxide directly from the air as early as next year, but it will be up to the highest bidder to decide what happens to that CO₂ once it’s been captured.

Melbourne-based Southern Green Gas (SGG) has just announced a partnership with Swiss Re, a multinational reinsurance company, to deliver its modules to market.

SGG’s carbon-removal technology consists of small, solar-powered modules that capture one to two tonnes of carbon dioxide from the atmosphere per year.

“We envision capture farms, involving 100,000 to a million of our modules, all aggregated together,” says Rohan Gillespie, managing director of SGG.

The modules use a substance called a metal-organic framework, or MOF, to remove CO₂. These MOFs are made from lattices of metal atoms and organic molecules (organic in the chemical sense – composed mostly of carbon and hydrogen). They can act like giant molecular sponges, removing CO₂, water or other substances, depending on their design.

“There are many different types of MOFs,” says Gillespie.

“It’s a platform technology. It’s a crystalline nanomaterial, and its properties can be tailored to suit the application. The particular MOF we use has been finely tuned to absorb CO₂ from the atmosphere, in preference to nitrogen and oxygen. And once they absorb CO₂, then we use heat to get it out in pure form. So it’s an absorption-desorption process.”

Read more: A machine to scrub CO₂ from the air

Once the gaseous carbon dioxide has been removed from the MOF, a few different things can be done with it.

“One option is to compress it and sequester it underground, so permanent storage in geological formations – so-called carbon capture and storage,” says Gillespie. This is a technique that stretches back several decades, but it still operates at a small scale.

“Another way is to actually embed the CO₂ in a product such as a carbonate. There are people developing technology that adds CO₂ with mineral salts and creates a carbonate, which they sell as a product.”

The CO₂ can also be turned into methane (CH₄), also called natural gas, which can then be combusted again. Gillespie says this is commercially interesting, as methane is widely used as a fuel already.

“You can just use all the infrastructure, and potentially export it as green LNG (liquefied natural gas),” he says.

“Of course, when that methane is consumed, it releases CO₂. But that is matched by the CO₂ extracted. So it’s carbon neutral; it’s a closed loop.”

Gillespie says that while this specific application isn’t carbon negative, it’s preferable to burning mined methane. “Swiss Re say, do your best – this is an example of substituting fossil fuels with renewables.”

Read more: We need a carbon-removal industry – should polluting companies pay for it?

SGG is currently working on a demonstration project for its modules, and hopes to have a product to market by 2022. It’s currently working on ways to manufacture the modules at large scale, as well as tweaking aspects such as energy usage and cycle time.

“The technology is technically proven but not commercially proven,” says Gillespie.

“We’re not sure, at this stage, which of these markets are going to go – and how quickly, and how large. So now the focus is getting the cost of CO₂ capture down below $100 [per tonne]. We think lots of markets will open up at that price point.”