(615a) Electrical Swing Adsorption on 3D-Printed Activated Carbon for CO2 Capture

Temperature swing adsorption is a widely used technique for gas drying and volatile organic compound (VOC) capture. However, it still presents some drawbacks in the duration of the cycle time which can take up to several hours ^1,2,3. This implies large investment costs to have sufficient adsorbent inventory. Moreover, it is not energy efficient and the heating cycles lead to thermal aging of the adsorbent ^4,5. To obtain a viable TSA process, the several steps of adsorption, regeneration and cooling must cycle rapidly.

To overcome the disadvantages of TSA, alternative heating methods are investigated. Electrical swing adsorption is one of the options. It also fits in the purpose of electrification of the industrial processes. This alternative way to increase the temperature is believed to be more rapid, more efficient and able to reach higher product concentration than conventional heating methods ^1,2,3. These changes could be important for the economic feasibility of CO₂ capture. However, to be suitable for ESA, new requirements in terms of adsorbent materials arise as the porous solid phase needs to conduct electricity on top of the demand for good and selective CO₂ adsorption.

In this work, 3D-printed honeycomb monoliths, consisting mainly of activated carbon, were produced using Three-Dimensional Fiber Deposition (3DFD). This method results in interwoven structures with easy control on channel size, fiber thickness and geometry of the channels ^6,7.

The monolithic structures were investigated in terms of isotherms, porosity, mass transfer limitations and electrical characteristics. Next, they were subjected to consecutive cycles to look at the impact on their adsorption capacity regarding the regeneration method. The regeneration method varied with different parameters: (1) The power supplied to the adsorbent, (2) The duration for which the power was supplied, (3) Flow and composition of the purge gas used, (4) Use of a vacuum step instead of a purge. The impact of the regeneration on purity, recovery and energy usage were investigated. This was performed for different monoliths with different electrical properties.

It was demonstrated that the 3D-printed activated carbon monolith could be heated above 100°C in less than 20 s. In the figure left, homogenous heating of a 3D-printed monolith is shown. Using a biogas composition as feed, the enhancement on the CO₂ concentration was important as can be seen in the figure right. Adsorption steps were performed before and after the regeneration and the impact on the capacity was minor, while the increase in concentration is important.

Captions for figures:

Figure left: Thermal images of Joule heating (5V) of a 3D-printed monolith (AC + phenolic binder). Electrodes used in this pictures was cupper sponge.

Figure right: Joule heating experiment performed at 4V with mass spectrometer (MS) and temperature signal. 0-105 s: Heating by the sides of 3D-printed monolith; no gas flow through adsorbent, which is open to MS. 105-135 s: Short purge step with N₂ (100 Nml/min, 30s). Note: Temperature was measured 1 cm behind the monolith and is therefore an underestimation of the real temperature of the adsorbent.

References:

1. Ribeiro, R. P. P. L., Grande, C. A., and Rodrigues, A. E. (2014). Electric swing adsorption for gas separation and purification: a review. Separation Science and Technology 49, 1985–2002.
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6. Couck, S., Cousin-Saint-Remi, J., van der Perre, S., Baron, G. v., Minas, C., Ruch, P., and Denayer, J. F. M. (2018). 3D-printed SAPO-34 monoliths for gas separation. Microporous and Mesoporous Materials 255, 185–191.
7. Couck, S., Lefevere, J., Mullens, S., Protasova, L., Meynen, V., Desmet, G., Baron, G., and Denayer, J. F. M. (2017). CO2, CH4 and N2 separation with a 3DFD-printed ZSM-5 monolith. Chemical Engineering Journal 308, 719–726.