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Direct air capture (DAC) technology is advancing rapidly, with new sorbent materials and novel capture processes being developed which could help DAC systems become more cost-effective and energy-efficient by only requiring low-quality waste heat as their main energy source.

Summary​

Recent advancements in direct air capture (DAC) focus on overcoming energy-intensive regeneration processes through new sorbent materials. Two promising developments include COF-999, a crystalline covalent organic framework requiring only 60°C regeneration temperature using waste heat, and moisture-swing absorption using amine resins that release CO₂ through humidity changes. While COF-999 shows fast capture times and durability, moisture-swing systems offer energy efficiency but require dry conditions. Both approaches aim to reduce DAC costs below the $100/tCO₂ threshold needed for viability, addressing current limitations of high energy demands and operational costs. Challenges remain in material costs and environmental adaptability, but these innovations represent significant progress toward making DAC practical for climate goals.

The adoption of DAC and carbon capture technology, in general, has resisted rapid adoption due to a number of factors. The high capital and operational costs are a factor, but the extremely high energy requirement in the desorption/regeneration phases has proved to be the main limiting issue. The high energy requirement of DAC has made the cost to capture CO₂ prohibitive, with the current average cost well above the $100/tCO₂, which is the generally agreed price of economic viability 1. In addition to the cost of energy, the source of energy supplied to DAC systems is an equally important consideration, with cheap energy sources such as fossil fuels minimizing the effectiveness of the system by producing its own CO₂ emissions. To address these issues, much research has been conducted into the development of new sorbent materials and cycles which require low regeneration temperatures or low energy requirements, as well as high levels of durability. There is a large field of research and development into all areas liquid and solid sorbent systems, but the focus here will be on two recent and promising developments in solid sorbent materials: crystalline covalent organic framework (COF), and amine-based anion-exchange resins.

Crystalline covalent organic framework (COF)​

In 2024, an international team based out of the University of California, Berkeley, synthesized a crystalline COF material which they named COF-999. COF-999 is a porous crystalline material with highly efficient capture properties at ambient temperatures and humidities. The true breakthrough with COF-999 is its extremely low regeneration temperature of just 60°C (140°F), which makes it possible to run cycles using low-quality waste heat 2. Another highly desirable feature of COF-999 is its high durability, showing minimal degradation after 100 tested cycles while maintaining retention capacity and performance. The absorption times are also very fast, with 50% capture capacity reached within 19 minutes and 80% capacity in just over an hour, which the authors claim to be the fastest reported for any ambient air CO₂ capture system 2. COF-999 is still only in its early stages of development and little information is available on the cost of the material, but the potential of the material is high and may introduce the next generation of DAC systems that can help achieve the world's climate goals.

Amine-based anion-exchange resins (moisture swing absorption)​

Amine-based anion-exchange resins are types of organic resins that are capable of adsorbing CO₂ from ambient air when they are dry through a process known as moisture swing absorption. Once captured, moisture is released into the system, a process known as moisture swing or humidity swing, which causes the CO₂ to desorb from the resin 3 4. After desorption, the resin undergoes its regeneration process by evaporating the water on the resin, which can be assisted by supplying heat. This process is extremely energy efficient as it requires very little external energy to regenerate the resin, instead relying on the latent heat of evaporation. The creators of the technique see it being utilized in scenarios where high concentrations of CO₂ are not required, such as in agriculture where greenhouses require a constant enriched stream of CO₂ to stimulate plant growth 4. The main challenge for the moisture swing absorption process is its requirement of dry atmospheric conditions, which may make it unsuitable for usage in most climates 3.

Conclusions​

As the realities of climate change become more apparent, advances in DAC technology are becoming more important. The two breakthroughs discussed here, COF-999 and moisture swing absorption, are both promising developments that could help DAC systems become more cost-effective and energy-efficient. While both technologies have their own challenges, they represent a significant step forward in the development of DAC systems.

Sources​

Footnotes​

  1. Ozkan, M., Nayak, S. P., Ruiz, A. D., & Jiang, W. (2022). Current status and pillars of direct air capture technologies. iScience, 25(4), Article 103990. https://doi.org/10.1016/j.isci.2022.103990 ↩

  2. Zhou, Z., Ma, T., Zhang, H., Chheda, S., Li, H., Wang, K., Ehrling, S., Giovine, R., Li, C., Alawadhi, A. H., Abduljawad, M. M., Alawad, M. O., Gagliardi, L., Sauer, J., & Yaghi, O. M. (2024). Carbon dioxide capture from open air using covalent organic frameworks. Nature, 635(8037), 96–101. https://doi.org/10.1038/s41586-024-08080-x ↩ ↩2

  3. Sodiq, A., Abdullatif, Y., Aissa, B., Ostovar, A., Nassar, N., El-Naas, M., & Amhamed, A. (2023). A review on progress made in direct air capture of CO₂. Environmental Technology & Innovation, 29, Article 102991. https://doi.org/10.1016/j.eti.2023.102991 ↩ ↩2

  4. Sanz-Pérez, E. S., Murdock, C. R., Didas, S. A., & Jones, C. W. (2016). Direct capture of CO2 from ambient air. Chemical Reviews, 116(19), 11840-11876. https://doi.org/10.1021/acs.chemrev.6b00173 ↩ ↩2