Process Simulation and Comparative Performance Evaluation of SIFSIX-3- Cu and Mg-MOF-74 for Direct Air CO₂ Capture in Packed Bed Columns

Abstract This study systematically evaluates the performance of SIFSIX-3-Cu in the direct air capture (DAC) process, with a comparison to Mg-MOF-74. The adsorption and working capacities of both sorbents are assessed, revealing that SIFSIX-3-Cu achieves substantial CO₂ adsorption even at low concentrations (400 ppm). Simulations of packed bed columns demonstrate that SIFSIX-3-Cu effectively captures CO₂ from ambient air, exhibiting a breakthrough time of 500 minutes, in contrast to only 70 minutes for Mg-MOF-74 at the same operating conditions. Temporal assessments of CO₂ uptake along the column indicate that SIFSIX-3-Cu attains a CO₂ uptake of 1.4 mmol g⁻¹ under ambient conditions, while Mg-MOF-74 reaches only 0.12 mmol g⁻¹. The enhanced performance of SIFSIX-3-Cu is attributed to its superior affinity for CO₂ at the atmospheric concentration. In addition, the desorption behaviors of both materials are investigated. SIFSIX-3-Cu releases CO₂ gradually because of its smaller pore opening and stronger interactions with CO₂ whereas Mg-MOF-74 displays a two-step desorption mechanism. Furthermore, notable differences are observed in the temperature profiles during the adsorption and desorption stages. SIFSIX-3-Cu requires higher temperatures and lower pressures for efficient CO₂ desorption, while the larger pore dimensions of Mg-MOF-74 facilitate the CO₂ release. Overall, SIFSIX-3-Cu demonstrates significant promises for DAC applications, particularly due to its superior CO₂ adsorption capacity at low concentrations, highlighting its potential for effective CO₂ capture from ambient air.