Carbon capture system sequesters record amounts of CO2 for direct air capture

Isophorone diamine (IPDA) in a “liquid-solid phase separation” system was found to remove carbon dioxide at the low concentrations contained in the atmosphere with 99 per cent efficiency. The researchers said that the compound is reusable with minimal heating and at least twice as fast as existing systems.

While the world is currently trying to reduce its carbon emissions to net zero, scientists are also looking at ultimately removing CO2 that has already been released in order to bring levels down to those found in the pre-industrial era.

Currently, many hurdles remain before carbon capture technologies can be deployed at scale. The biggest challenges come from efficiency, particularly in processing atmospheric air directly in direct air capture (DAC) systems.

The concentrations of CO2 are such that chemical reactions with sorbents are very slow. It has also proven difficult to get the CO2 out again in more sustainable capture-and-desorption cycles, which can be very energy intensive in themselves.

Even leading efforts to build DAC plants, such as those using potassium hydroxide and calcium hydroxide, suffer serious efficiency issues and recovery costs.

The researchers have been studying a class of DAC technology known as liquid-solid phase separation systems. Many DAC systems involve bubbling air through a liquid, with a chemical reaction occurring between the liquid and the CO2.

As the reaction proceeds, more of the reaction product accumulates in the liquid which makes subsequent reactions slower and slower. But liquid-solid phase separation systems offer a solution to this problem as the reaction product is insoluble and comes out of solution as a solid. There is no accumulation of product in the liquid, and the reaction speed does not slow down as much.

The team focused their attention on liquid amine compounds, modifying their structure to optimise reaction speed and efficiency with a wide range of concentrations of carbon dioxide in air, from around 400ppm to up to 30 per cent.

They found that an aqueous solution of one of these compounds, isophorone diamine (IPDA), could convert 99 per cent of the carbon dioxide contained in the air to a solid carbamic acid precipitate.

It was then demonstrated that the solid dispersed in solution only required heating to 60°C to completely release the captured CO2, recovering the original liquid.

The rate at which carbon dioxide could be removed was at least twice as fast as that of the leading DAC lab systems, making it the fastest carbon dioxide capture system in the world at present for processing low concentration carbon dioxide in air (400ppm), the researchers said.