Game-changing absorbents for increasing efficiency and lowering costs of direct air capture (DAC)
Project duration: July 2023–June 2026
Dr Graeme Puxty
Dr Nouman Mirza
Nouman Mirza, Graeme Puxty, Robert Bennett, Debra Fernandes.
Direct air capture (DAC) of CO2 is a promising negative emissions technology that’s considered vital in limiting global warming. The greatest hurdle to its large-scale adoption, however, is the technical challenge of extracting low concentrations of CO2 from large volumes of air.
To enhance capture, absorbents (primarily solids) are used. Current technology (water-based alkali or amine absorbents) tends to be inefficient due to its complexity, high water and energy requirements, and related costs. Liquid absorbents present an alternative, however almost no work has been done with their development, primarily due to potential evaporative losses in high gas flows, and the need for long-term stability in the face of high O2 content and thermal cycling. As a result, a significant knowledge gap exists in identifying suitable contenders for more efficient and effective liquid absorbents for DAC. This leaves huge potential for development of novel liquid absorbents, which could reshape the DAC industry and have a genuine impact on atmospheric CO2 concentrations.
Our aim is to find an absorption liquid with low water content and vapour pressure, high solubility and CO2 reactivity, and stability in a high O2 environment. Recent research has shown that one group of molecules, cyclic or polyamines, has not been studied for use in DAC applications. Some in this group have the structural features that address the challenges of liquid absorbents, which means they offer potential for increased efficiency, with low-cost and low energy inputs, and superior performance.
Our project looks at five novel ‘water-lean’ molecules, all of which are suitable for DAC applications. They’ve been selected for their high CO2 reactivity, low vapour pressure and water content, high solubility, and robust stability in high O2 environments. These characteristics will result in groundbreaking liquid absorbent technology with significant cost and energy savings compared to current DAC technologies. Finding a suitable water-lean absorbent would also position CSIRO as a leader in the emerging DAC sector. Moreover, CSIRO will own the IP, giving it significant leverage to engage with industry to commercialise the technology.
Industry hesitation in employing liquid absorbents is a direct result of the literature gap created by a lack of research into their use for DAC applications. If the challenges of liquid absorbents can be overcome to yield significant cost and energy savings, this would provide a commercial imperative for widespread take-up of the technology.
To date, CSIRO’s research on absorbents has been limited to its current benchmark, a liquid amino acid salt, which has a high water content and, therefore, high energy requirements. Water-lean liquid cyclic or polyamines offer the potential to provide greater efficiency and cost-effectiveness for industry, and enhance capability and commercial opportunities at CSIRO. At the very least, they provide an opportunity for comparison with CSIRO’s existing absorbent research. There is a small risk that none of the proposed molecules will work for CO2 capture but, given the experience of the project team and the selection of molecules for specific characteristics (one is similar enough to the current CSIRO benchmark to ensure it would work in a DAC application), this is a highly unlikely scenario.
Xu, Y., Wang, T., Yang, Q., Yu, H., Fang, M., & Puxty, G. (2021). CO2 absorption performance in advanced water-lean diamine solvents. Chemical Engineering Journal, 425, 131410.
Shell Internationale Research Maatschappij BV (2019). Process for the recovery of carbon dioxide from a gas stream. Australian patent. https://patents.google.com/patent/AU2007339756B2/en