# Assessment of Appropriate Geometry for Thermally Efficient CO\({}_{2}\) Adsorption Beds
## 3 Results and Discussion
### The General Behavior of Adsorption/Desorption Processes  
The overall picture of the adsorption/desorption processes for the three beds can be obtained from the temporal temperature and uptake CO\({}_{2}\) contours of the symmetry plane that shows the sorption behavior along the beds. The adsorption process is given 1100 s to ensure CO\({}_{2}\) saturation (the inlet and surrounding temperatures are 25 \({}^{\circ}\)C). After that, up to 1800 s is given for the desorption process under heating from the external surface (120 \({}^{\circ}\)C). Figure 3 shows the temperature contours for the circular, square, and triangular cross-sectional beds at some selective adsorption and desorption times. During the adsorption process, the hot spots exist in the middle of the bed and crawl as time passes due to the adsorption process. As the adsorption process is exothermic, the regions that continue adsorbing CO\({}_{2}\) are hot. The places at the bed center are hotter than those closer to external surfaces due to the good cooling process closer to the surfaces. For the desorption process, the hotter zones are closer to the external walls where the heating is applied.  
The difference between the three-bed geometries is that the triangular one has hot regions (during the adsorption process) closer to the bottom since the distance between the top region and external surfaces is shorter than that in the middle. Thus, the top region of the triangular bed quickly becomes colder during the adsorption process and hotter during the desorption process.  
The temperature distribution along the bed is obtained from the applied conditions and the sorption processes. Figure 4 shows the CO\({}_{2}\) uptake during the adsorption and desorption processes. The CO\({}_{2}\) uptake is higher for colder zones (closer to the surfaces) and increases along the bed; the red zones show the regions that are saturated with CO\({}_{2}\). At t = 900 s, all the beds reach the saturated uptake. Applying the heating process leads to a desorption process that expels the CO\({}_{2}\) out from the bed. As the heating process is applied from the external surfaces, the regions closer to these surfaces are first regenerated. Again, the circular and square beds have similar adsorption and desorption uptake distribution,  
Figure 2: Breakthrough concentration ratio of CO2 and N2 at the bed outlet during the adsorption process using Mg-MOF-74 to compare the 3D simulation with the experimental data (at bed porosity = 0.674, particle size = 0.2 mm, bed length = 7 cm, bed diameter = 0.4 cm) [23]. Mg-MOF-74 is synthesized and characterized in the previous study [22].  
unlike the triangular one, in which the symmetry plane shows more adsorption/desorption at the top zones closer to the external surfaces.  
Despite Figures 3 and 4 showing the sorption behavior along the beds, the difference between beds in terms of higher uptake and better temperature dissipation can not be concluded from such plots. Therefore, the 2D profiles are discussed in the following sections.  
Figure 4: CO\({}_{2}\) uptake contours for the investigated beds at selective adsorption and desorption times.  
Figure 3: Temperature contours for the investigated beds at selective adsorption and desorption times.