(611e) CO2 Capture Using 3D Printed PEI Adsorbents Supported By Carbon Nanostructures

Processes that utilizes solid adsorbents to capture CO₂ are promising alternatives to state-of-art technologies using water-based amine solutions as absorbents for capturing CO₂ from large point sources such as power plants. Although the energy needs of solid sorbent-based processes are low, the process footprint and consequently the capital cost connected to its implementation can be large due to the relatively long cycle times needed to get the required capture rate and purity of the CO₂ product. To overcome this challenge, processes having structured adsorbents like laminates, monoliths etc. are needed owing to their low pressure drop and better mass transfer characteristics¹. In recent times, 3D printing of structured adsorbents has been gaining significant attention due the versatility in shapes of the adsorbents and good control over the channel dimensions².

Even though there are several published studies in the context of structured adsorbents, they are mostly restricted to characterization of the adsorbents with respect to equilibrium and mass transfer. Very few published studies exist on a process level demonstrating an improvement in the process performance in comparison with pellets^3-4. It has been shown that, the true potential of any adsorbent only be obtained through rigorous optimization of a cyclic adsorption process. Secondly, most of the published studies in the context of adsorption-based carbon capture have neglected the presence of water in the flue gas. Supported amine sorbents are currently being studied as alternatives to zeolites due their moisture tolerating abilities but like 3D printed adsorbents, their performance in an actual adsorption process is not well understood⁵.

Therefore, the aim of this work is evaluating the performance of a 3D printed adsorbent in the context of a vacuum swing adsorption process for CO₂ capture from a wet flue gas. In this work a series of novel adsorbents were prepared combining polyethylene-imine (PEI) with various nanomaterials such as multi-walled carbon nanotubes (CNT) in different ratios (Figure 1).These adsorbents were then printed in the form of monoliths by the 3D printing technique called robocasting. Breakthrough experiments were then carried out with a dry mixture of CO₂ and N₂ and a humid mixture containing 5% H₂O. Pressure drop tests were also carried out estimate the pressure drop across the 3D printed structure. Further, the breakthrough experiments were also used to estimate the adsorption kinetics. The information from the adsorbent characterization was then used to simulate and optimize a vacuum swing adsorption process in order to identify the operating conditions corresponding to 95% CO₂ purity and 90% CO₂ capture rate targets to capture CO₂ from a coal fired power plant containing 15% CO₂, 5% H₂O in N₂.

Keywords: Structured adsorbents, 3D printing, Vacuum Swing adsorption

References

1. Rezaei et al., Eng. Chem. Res. 2010, 49, 4832–4841
2. Couck et al., Micropor Mesopor Mater 255 (2018) 185-191
3. Nina Mohammadi, PhD thesis, 2017
4. Sharma et al., Eng. Chem. Res. 2020, https://doi.org/10.1021/acs.iecr.9b05337
5. Gelles et al., Adsorption 2020, 26:5–50