A Comparative Study of Different Sorbents in the Context of Direct Air Capture (DAC): Evaluation of Key Performance Indicators and Comparisons

Abstract

Direct air capture can be based on an adsorption system, and the used sorbent (chemisorbents or physisorbents) influences process. In this work, two amine-functionalized sorbents, as chemisorbents, and three different metal organic frameworks, as physisorbents, are considered and compared in terms of some key performance indicators. This was carried out by developing a mathematical model describing the adsorption and desorption stages. An independent analysis was carried out in order to verify data reported in the literature. Results show that the equilibrium loading is a critical parameter for adsorption capacity, energy consumption, and cost. The considered metal organic frameworks are characterized by a lower equilibrium loading (10−4 mol/kg) compared to chemisorbents (10−1 mol/kg). For this reason, physisorbents have higher overall energy consumptions and costs, while capturing a lower amount of carbon dioxide. A reasonable agreement is found on the basis of the operating conditions of the Climeworks company, modelling the use of the same amine cellulose-based sorbent. The same order of magnitude is found for total costs (751 USD/tonneCO2 for our analysis, compared to the value of 600 USD/tonneCO2 proposed by this company).

Innovative Process Integrating Air Source Heat Pumps and Direct Air Capture Processes

“…For the refrigerant volume estimation, a cycle time of 0.1 h is assumed, as are 175 kg of CO 2 /ethane, 145 of CO 2 /R41, and 183 kg of CO 2 . The purchase costs for the adsorbent bed and fan are the same as those reported in Leonzio et al Locating the plant in Switzerland, the results show that the specific levelized CAPEX of the overall integrated process using CO 2 , CO 2 /R41, and CO 2 /ethane is 787, 709, and 781 $/tonCO 2 , respectively.…”

“…The outlet air here has a temperature of 15 °C (this value is suggested for the cooling fluid in the Climeworks plant) so that it can be used in the cooling stage of the adsorbent bed. Air for cooling is used by another DAC company, as Anteny, indicating that our proposed scheme is technically feasible and avoids the use of cooling water that Leonzio et al demonstrate to have a high impact on the operating costs. On the other hand, the hot water supplied from the ASHP at 100 °C is used for the regeneration of the bed, avoiding the use of an MWI as in the base case scenario.…”

“…Cooling water is used for the cooling step, while electricity for fans and heat for the regeneration step are provided by an MWI, as in the Climeworks plant. Table shows the main operating conditions, energy consumptions, data for the adsorbent bed and sorbent, and costs for the conventional DAC process …”

“…43 In our previous work, we develop a mathematical model for the DAC adsorption process using different sorbents (metal− organic frameworks and amine-functionalized sorbents) and we compare our results with those of the Climeworks company, who use the APDES-NFC-FD sorbent [3-aminopropylmethyldiethoxysilane (APDES) on nanofibrillated cellulose (NFC)], as in our work. 44 These adsorption systems require thermal energy at 100 °C for the regeneration stage, which is provided by a municipal waste incinerator (MWI), as in Climeworks. On the other hand, cooling for the cooling stage is provided by cooling water.…”

“…According to these considerations, we propose here a new process integrating an ASHP with a trans-critical cycle into a DAC adsorption process using the APDES-NFC-FD sorbent and investigated in our previous research. 44 We use a transcritical and not sub-critical cycle because the first one is the most investigated in the literature for an ASHP producing hot water at high temperatures. The heat pump provides cooling and heating for the DAC.…”