## 3 Results and Discussion
### KPIs: Energy Consumption and Cost of DAC Systems  
As explained previously, energy consumption includes the electrical energy for fans blowing air inside the bed, and thermal energy for the regeneration. Table 11 shows the amount of energy required for each sorbent. It is possible to underline why physisorbents are characterized by higher values of energy consumption in terms of both electrical and thermal energy. The electrical energy demand is higher for MOFs due to higher pressure drop and lower amount of captured CO\({}_{2}\) per day, compared to systems using amine-functionalized adsorbents. The required electricity energy for MOFs and amine-functionalized adsorbents is comparable with the values reported by [PERSON] et al. [53] in their work. In our research, the electricity con \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sorbent** & **MIL-101** & **MOF-177** & **MOF-5** & **SI-AEATPMS** & **APDES-NFC-FD** \\ \hline Mass of the sorbent (kg) & \(2.22\times 10^{4}\) & \(1.54\times 10^{4}\) & \(2.23\times 10^{4}\) & \(3.36\times 10^{4}\) & \(1.77\times 10^{3}\) \\ Average single pass recovery & \(5.2\times 10^{-1}\) & \(5.9\times 10^{-1}\) & \(5.3\times 10^{-1}\) & \(8.6\times 10^{-1}\) & \(8.9\times 10^{-1}\) \\ Adsorption time (s) & \(3.2\times 10^{2}\) & \(2.14\times 10^{2}\) & \(7.49\times 10^{2}\) & \(3.06\times 10^{5}\) & \(3.26\times 10^{4}\) \\ Desorption time (s) & \(9.9\times 10^{1}\) & \(1.6\times 10^{2}\) & \(3.15\times 10^{2}\) & \(1.67\times 10^{4}\) & \(1.85\times 10^{3}\) \\ Full cycle time (h) & \(1.2\times 10^{-1}\) & \(9\times 10^{-2}\) & \(2.9\times 10^{-1}\) & \(8.92\times 10^{1}\) & 9.53 \\ Number of cycles/day & \(2.07\times 10^{2}\) & \(2.71\times 10^{2}\) & \(8.15\times 10^{1}\) & \(3\times 10^{-1}\) & 2.5 \\ Captured CO\({}_{2}\) (kg/h) & 3.96 & 4.5 & 4.00 & 6.43 & 6.66 \\ Captured CO\({}_{2}\) (kg/cycle) & \(3.5\times 10^{-1}\) & \(2.6\times 10^{-1}\) & \(8.3\times 10^{-1}\) & \(546\times 10^{2}\) & \(6.03\times 10^{1}\) \\ Captured CO\({}_{2}\) (kg/day) & \(7.3\times 10^{1}\) & \(7.2\times 10^{1}\) & \(6.8\times 10^{1}\) & \(1.47\times 10^{2}\) & \(1.52\times 10^{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Main results from adsorption and desorption stages. sumption for MIL-101, MOF-177, and MOF-5 are, respectively, 1540 kWhel/tonneCO2, 1350 kWhel/tonneCO2 and 1520 kWhel/tonneCO2. The amine-based sorbents exhibit lower values: 357 kWhel/tonneCO2 and 299 kWhel/tonneCO2, respectively, for SI-AEATPMS and APDES-NFC-FD. Particular consideration is required for the thermal energy to regenerate the sorbent. No data of this parameter are present for MOFs capturing CO2 from air in the literature. For amine-functionalized sorbents, values similar to those reported by [PERSON] et al. [53], [PERSON] et al. [106], and [PERSON] et al. [3] are obtained: 1884 kWhth/tonneCO2 for the silica gel-based sorbent and 1427 kWhth/tonneCO2 for the cellulose-based sorbent. However, higher values are obtained for physiospents, ranging from 494,000 kWhth/tonneCO2 for MOF-5 to 1,300,000 for MOF-177 (due to the sensible heating requirements for the sorbent). These greater values are due to a very low working capacity for MOFs, ranging from 0.00084 mol/kg for MOF-5 to 0.00035 mol/kg for MIL-101 under atmospheric concentration of CO2. Working capacity depends on the equilibrium loading, this is then a critical parameter for the design of adsorption processes. This is an important finding in the context of MOFs. Moreover, it is evident that DAC facilities using MOFs are impracticable due the huge amount of thermal energy requirement. This is true not only for an energetic point of view but also for an environmental aspect because additional CO2 would be emitted by the MWI to produce the heat energy needed to regenerate the adsorbent. For DAC processes based on amine-functionalized sorbents, a life cycle assessment analysis is suggested to account for the additional emissions of MWI.