We can suck CO2 from the air and store it in the ocean as baking soda

Carbon dioxide captured from the air could be turned into baking soda and stored in the world’s oceans, thanks to a newly identified material that researchers say could revolutionise the direct air capture (DAC) industry.

For years, carbon capture technology has focused on capturing CO2 from pollution sites before it enters the atmosphere – from the chimneys of coal and steel plants, for example.

Extracting carbon directly from the air represents a far greater challenge, as CO2 in the atmosphere is far more dilute and extracting it requires more energy and materials. It means current DAC plants are expensive to run, with a tonne of CO2 costing hundreds of US dollars to pull from the air.

Arup SenGupta at Lehigh University in Bethlehem, Pennsylvania, and his colleagues set out to develop a new absorbent material – called a sorbent – capable of pulling more CO2 from the air than current materials can.

By modifying existing amine solvents with a copper solution, the researchers say they have boosted the carbon capture potential of DAC by two to three times.

SenGupta says the new material could radically boost the potential of DAC as an effective, commercially viable technology for mitigating climate change – particularly as the materials needed to produce the sorbent are readily available at low cost.

“This material can be produced at very high capacity very rapidly,” says SenGupta. “That definitely should improve the cost-effectiveness of the process.”

Dawid Hanak at Cranfield University in the UK says the research has the potential to “substantially reduce the cost of DAC”.

The captured CO2 can be converted into sodium bicarbonate, or baking soda, with the addition of seawater. This can then be safely stored in the ocean, which represents an “infinite sink” for captured CO2, the team suggests.

Releasing baking soda into the ocean wouldn’t pose any ecological harm, says SenGupta. Sodium bicarbonate is an alkali, so it could offer some benefit by reversing the acidification of the ocean that occurs when CO2 is dissolved, he says. “Higher alkalinity also means more biological activity; that means more CO2 sequestration.”

Eventually, DAC plants using this sorbent could be installed offshore, says SenGupta, allowing countries without geological carbon storage potential to start removing carbon from the atmosphere.

The proposal is “elegant and clever chemistry”, says Stuart Haszeldine at the University of Edinburgh, UK. “[The] ability to store directly into seawater is also very powerful, because the very deep ocean has an immense capacity for accessible CO2 storage lasting hundreds to thousands of years.”

But further research is needed to understand how the material performs on an industrial scale after absorbing and releasing CO2 hundreds of times, he says. There may also be legal barriers to discharging the baking soda – which could be classed as industrial waste – into the ocean.

The use of carbon removal technologies must be rapidly scaled up in order to limit global warming to 1.5°C, moving from capturing almost 0.01 megatonnes of  CO2 per year today to almost 60Mt  per year by 2030, according to the International Energy Agency.

Myles Allen at the University of Oxford says that while the new sorbent may offer a technical breakthrough to improve DAC efficiency, what is really needed for the global market to expand at this rapid pace is for governments to force energy companies to invest.

“I’ve argued consistently that basically the only way this will ever happen at the scale it needs to happen is if it’s made a licensing condition of continuing to sell fossil fuels,” he says. “As soon as it is, it will happen on a scale that’s currently unimaginable.”