(366f) On the Exergy Efficiency and Life Cycle Assessment of Sorbents for Direct Air Capture: A Review.

Direct air capture (DAC) is seen as crucial technology to reach the net zero emissions target set by worldwide environmental agencies[1]. Most of the market is currently dominated by adsorption technologies both in the form of packed bed and structured sorbent. The most popular sorbents under development make use of amine-functionalised materials, metal organic frameworks, carbonates and zeolites. Generally, the DAC process is a combination of temperature and vacuum swing using direct steam injection or indirect heating, with only recent adoption of alternative heating methodologies or alternative desorption mechanisms, such as moisture swing or electro-swing adsorption.

Several works report techno-economic assessment (TEA) of different sorbent-process combinations. Literature generally focusses on either packed beds arrangements or current Climeworks’ structured bed[2]. However, there is still a lack for inclusion of sorbent degradation in the TEA, cost of structuring the sorbent and its effect on both TEA and life cycle assessment.

In this work, to provide a simple metrics for process screening, a novel correlation of exergy efficiency is proposed, that takes into account both energy inputs on the DAC process and sorbent degradation. Indeed, the sorbent degradation is considered as degraded chemical exergy[3].

Moreover, an analysis on common structuring techniques (costing of monoliths and laminates) is here reported, including both cost of the structuring and replacement of the spent sorbent.

The analysis focus on sorbent lifetime, sorbent cost and structuring cost on overall economics of the DAC process and its efficiency. The efficiency of the different types of sorbents is compared, with assessment of benefits and disadvantages of each. The work also reports recent advancements in the engineering of DAC processes to improve sorbent lifetime and reduce energy consumption.

[1] https://www.iea.org/energy-system/carbon-capture-utilisation-and-storag…

[2] F. Sabatino et al., (2021), Joule, 5 (8), 2047-2076.

[3] G. Song et al., (2012) Energy 40 164-173