## 4 Conclusions  
An independent analysis is developed in this research work to evaluate some KPIs (energy consumption, CO\({}_{2}\) productivity, and costs) of a DAC processes, based on adsorption using different sorbents. In particular, chemisorbents (two amine-functionalized sorbents, SI-AEATPMS and APDES-NFC-FD) and physisorbents (three MOFs: MIL-101, MOF-5, and MOF-177) are compared. For this purpose, a mathematical model describing adsorption and desorption stages is developed for each sorbent. Results show that MOFs are characterized by a very low equilibrium loading and hence a very low working capacity in comparison to chemisorbents. For MIL-101, MOF-177, and MOF-5 this last parameter is, respectively, 0.00035 mol/kg, 0.00039 mol/kg, and 0.00084 mol/kg. On the other hand, for SI-AEATPMS and APDES-NFC-FD working capacity is, respectively, 0.367 mol/kg and 0.771 mol/kg. The equilibrium loading is a critical parameter because it influences the adsorption capacity, energy consumption, and cost. Better results are found for the adsorption processes using amine-functionalized sorbents. For the cellulose-based sorbent, 152 kgCO\({}_{2}\)/day are captured, consuming 299 kWhel/tonneCO\({}_{2}\) of electrical energy and 1427 kWhh/tonneCO\({}_{2}\) of thermal energy at an overall total cost of 751 USD/tonneCO\({}_{2}\). For MOF-177, the amount of captured CO\({}_{2}\), electrical energy and thermal energy consumptions, and total costs are, respectively, 72 kgCO\({}_{2}\)/day, 1350 kWhel/tonCO\({}_{2}\), 1,300,000 kWhh/tonCO\({}_{2}\), and 39,400 USD/tonneCO\({}_{2}\). It is evident that the huge amount of thermal energy requirement makes the processes based on MOFs impracticable. This independent analysis shows that costs reported in the literature appear to be with the same order of magnitude of our analysis. A comparison with the Climeworks Company (using the APDES-NFC-FD sorbent) shows a good agreement with KPIs, and total cost. Higher costs are expected when humidity is in the air. It is important to note that we are assuming here the availability of industrial waste heat--should this not be available, costs will be somewhat higher (22%, when a traditional boiler is used for heating, considering a cost for heat of 0.165 USD/kWh [112]. Suggestions to reduce costs are provided. It was found that for systems using amine-functionalizedsorbents, the use of air for the cooling stage and cheaper materials for equipment could reduce OPEX and therefore overall costs. For processes using MOFs, more research should be focused to improve their loading allowing a lower cost for thermal energy. The use of air for cooling could reduce costs too. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12052618/s1](https://www.mdpi.com/article/10.3390/app12052618/s1)]([https://www.mdpi.com/article/10.3390/app12052618/s1](https://www.mdpi.com/article/10.3390/app12052618/s1)), Figure S1: Breakthrough curve (CO\({}_{2}\) concentration at the outlet/CO\({}_{2}\) concentration at the inlet) for the experi-mental apparatus used in Wurzbacher (2015); Figure S2: Breakdown of the main contributions (cut-off 5%) to CAPEX for all adsorbent beds; Figure S3: Breakdown of the main contributions (cut-off 5%) to OPEX for the adsorbent beds with APDES-NFC-FD; Figure S4: Breakdown of the main contributions (cut-off 5%) to OPEX for the adsorbent beds with SI-AEATPMS; Figure S5: Breakdown of the main contributions (cut-off 5%) to OPEX for the adsorbent beds with MIL-101; Figure S6: Breakdown of the main contributions (cut-off 5%) to OPEX for the adsorbent beds with MOF-177; Figure S7: Breakdown of the main contributions (cut-off 5%) to OPEX for the adsorbent beds with MOF-5. Table S1: Dimensionless number values of the mathematical model; Table S2: Inputs used in Matches calculator for cost analysis; Table S3: CAPEX of different adsorbent beds; Table S4: OPEX of different adsorbent beds. Conceptualization, P.S.F., G.L. and N.S. ; methodology, G.L. and N.S. ; formal analysis, G.L. ; investigation, G.L.