Air Apparents

Research & Development
30th May 2024

Article by Amanda Jasi

Amanda Jasi speaks to the innovators developing direct air capture technologies hoping to be next in line to move us towards a net zero future

DIRECT AIR CAPTURE (DAC) has a major part to play in the carbon removals portfolio, allowing operators to take CO2 directly from the atmosphere to be stored or used.

Climeworks has made a name for itself in this space, recently opening the world’s largest DAC plant with nameplate capacity of 36,000 t/y (see p28). But with removals needed at the gigaton scale, many more large-scale plants are required to have meaningful impact.

Fluidised capture

London-based Airhive is one company looking to help fill that gap. It expects to have two 1,000 t/y pilots operating by the end of the year using its fluidisation-based DAC technology. Jasper Wong, Airhive’s co-founder and chief technology officer, explains that fluidisation is a “process when a mixture of a gas and solid particles behave like a fluid. The fast mixing between the two phases means that mass transfer limitations are minimised; there is rapid contact between the gas and solid that speeds up the overall rate of chemical reactions”. He adds that fluidised beds are used across many industries including minerals processing, food, and pharmaceuticals.

While fluidisation has previously been explored in DAC, Lewis Thorne, technology development lead at Airhive, says it was abandoned because the pressure drops and energy consumption were too high to be scalable. “We’ve solved this by using shallow bed heights, with a horizontal fluid bed arrangement, and using ambient air without pre-treatment like heating or compression,” he says.

Wong offers further detail on Airhive’s capture process.

“Air is drawn into a chamber by inlet fans. The air passes from below up through a gas distribution plate and meets sorbent particles, based on natural minerals, that like to bind with CO2. The air uplifts this particulate matter and creates what is almost like a sandstorm inside the machine – you see very quick mixing between the sorbent particles and the gas through bubbles and vortices in the flow mixture.”

The rapid mixing means Airhive can remove 99% of the CO2 from the air blown through its system in less than 0.1 s.

“After the solid material has been fully saturated in CO2, it passes to an electric calciner,” Wong continues. “We heat up the material electrically and the CO2 is removed in a pure form where you can use it for things like e-fuels, for food-grade CO2, or for storage.”

The regenerated sorbent is returned to the capture system, closing the two-stage loop.

Founded in 2022, Airhive has already made great strides in developing its technology.

Airhive

Render of Airhive's 1,000 t/y pilot system

“We’ve gone from nothing to, by the end of this year we’ll have two 1,000 t/y pilot systems,” says Thorne. “That speed of development and speed of deployment, that’s all to do with the types of materials that we’re using and the technology, the fact that fluidisation is well understood. These processes are well understood, it’s putting them together that’s the novelty.

“That’s a key advantage compared to a lot of other DAC technologies, is that we’re able to go to manufacturers, design the equipment with them, make it bespoke to our technology, but still deliver it within a very short timeframe.”

The 1,000 t/y facilities are due for delivery later this year and will come online in Q4. One pilot is for a collaboration with Coca-Cola Europacific Partners, which will use the captured CO2 to make fizzy drinks. The other will serve a partnership with Deep Sky, a company developing carbon removal projects in Canada.

In future, these 1,000 t/y systems could serve as units in larger facilities, as Airhive pursues a modular approach. Explaining the concept, Thorne says: “If you wanted a facility that would do, say 5,000 t, you could have five of these repeated units. So, it’s massively reducing the amount of engineering you have to do each time.”

He adds that the modular approach reduces the cost and times of project delivery and is a path to meeting the “aggressive” timeline needed to deliver climate-critical technology.

The company expects that by late 2025 its 1,000 t/y units will be ready to scale out into a 5,000 t/y commercial facility. But in parallel, Airhive will develop next-generation systems that will potentially be at a more optimal scale.

In the meantime, the company is already testing a 60 t/y system, set to begin operating in June, which will be the largest operating DAC system in the UK. Known as project TENET (TEesside Negative Emissions Technology) it is Airhive’s first full-cycle system and will help answer questions such as the sorbent’s capture capability in a continuous operation and around material conveyance, thereby demonstrating the feasibility of Airhive’s technology at scale.

Gigaton scale may seem a daunting goal, but with technologies like these showing promise in labs through to those ready to deploy, the target is not as far out of reach as it once was.

Capacity x3

In the US, Jeevan Climate Solutions is in the early days of developing DAC technology inspired by ion exchange, a process commonly used for water softening and demineralisation.

The work is being led by CEO and founder Arup SenGupta, who is internationally recognised for advancing ion exchange science and technology. The subject of a paper¹ published last year, his team modified a globally available anion exchange resin by adding copper, which impacted its affinity for CO2. “The parent material is already in use for CO2 removal, and we showed that can improve the capacity by three times,” he says.

The company is now testing the capture material, DeCarbonHIX, in prototype fluidised bed reactors.

SenGupta says: “Air is blown through the sorbent…and CO2 from the atmosphere is captured or sorbed onto HIX. Subsequently, HIX is brought in contact with hot water at 80–90°C and CO2 is desorbed.”

JCS has already tested the technology in 3- and 4-inch reactors, and a 12-inch reactor that will capture 1–2 t/y of CO2 is set to arrive in mid-June.

Simultaneously, the company is operating a prototype slurry contactor that uses HIX in a 10% slurry with water to capture around 0.25 t/y of CO2. The process is simpler and doesn’t require high-energy fans, reducing energy requirements and costs.

JCS is applying for US grants to fund its efforts to increase capture to 2–5 t/y.

Capture support

At the US’ Rice University, Soumyabrata Roy has led a study focused on providing structural support to solid capture sorbents. He says that solid sorbents need to be distributed across a porous matrix, enabling unhindered air/flue stream flow, improving gas contact with the sorbent, and enabling efficient mass transfer and heat management (during regeneration via temperature swing).

The research team investigated making a support matrix for CALF-20,2 a promising metal-organic framework (MOF) for carbon capture.

Targeting sustainability, the researchers used basswood to create the support. Roy says they used a top-down approach, delignifying the wood to leave behind a structure of cellulose and hemicellulose. “Once the lignin is removed from the structure of the wood, you get this long, ordered array of porous channels through which the gas molecules can flow easily.” They then fill those pores with the CALF-20, creating their composite capture material. Roy says the material importantly has three scales of porosity which are “crucial for having an efficient system and platform for CO2 capture”. The wood structure offers macro- and meso-scale porosity, and the micro-porosity, the active part for CO2 uptake, is provided by the MOF.

The composite material eliminates uptake, mass transfer, and heat management issues and improves CO2 uptake compared to CALF-20 alone.

While this is promising, further work is needed to develop the composite, including scaling up from the lab.

The team recently published work in which they created their wood structure in a bottom-up approach that may be more suited to scaleup.