(615b) PSA Assessment of 3D-Printed Activated Carbon Monoliths for CO2/CH4 Separation

In recent years, adsorbents have been structured into monolithic contactors using 3D printing.^[1-3] This research area has attracted significant attention because 3D printing allows the monolith geometry to be tuned digitally which can be enhance mass transfer, reduce pressure drops, and lower energy costs. However, most advancements in 3D-printed adsorbents have emphasized material development and have not focused on process performance assessment. Even in the few works that have targeted this area, most studies have used single-breakthrough experiments and not cyclic adsorption/desorption processes. This aspect is crucial to scale-up, so this study assessed the pressure-swing adsorption (PSA) performance of 3D-printed activated carbon monoliths for CO₂/CH₄ separation to strengthen this area of research. To this end, this study varied the i) adsorption pressure (3-10 bar), ii) adsorbate superficial velocity (1.4-2.3 cm/s of 60% CH₄/40% CO₂), and iii) adsorption time (2.5-10 min) to understand their influence on CH₄ purity, recovery, and productivity over 3D-printed activated carbon monoliths. This study also varied the monolith cell density between 200, 400, and 600 cells per squared inch (cpsi) to compare the pressure drops of printed adsorbent monoliths with those of commercial 1.5 mm beads by probe gas experiments. The PSA experiments revealed that increasing either the adsorbate velocity or the adsorption time enhance CH₄ recovery and productivity but yield more CO₂ bypass into the effluent CH₄ stream, leading to lower purity. The purity was found to increase upon increasing the adsorption pressure, however, the elevated pressure also lengthened the total cycle times and increased the amount of CH₄ co-adsorption, which decreased the CH₄ recovery and productivity. Therefore, the best performance was achieved at 3 bar, 1.4 cm/s superficial velocity, and 5 min adsorption time where the monolith packed bed generated 100% CH₄ purity, 38% CH₄ recovery, and 2.3 mmol CH₄/h^.g_monolith productivity. This was comparable to the performance of other benchmark adsorbents, however, the probe gas experiments also revealed that using 200 cpsi printed monoliths can reduce pressure losses by ~60% from commercial beads. Hence, 3D-printed activated carbon monoliths can achieve comparable PSA separation performance of CO₂/CH₄ mixtures whilst also reducing process energy costs.

References

1. S. Lawson et al. ACS. Mater. Interfaces 22 (10), 19076 (2018).
2. S. Lawson et al. ACS. Energy Fuels 33 (3), 2399 (2019).
3. H. Thakkar et al. ACS. Mater. Interfaces9 (8), 7489 (2017).