Effects of Process Parameters on CO₂/H₂ Separation Performance of 3D-Printed MOF-74 Monoliths

Structuring metal–organic frameworks (MOFs) into monolithic contactors by 3D printing has become an increasingly attractive area of research; however, the process performances of these materials have rarely been investigated. In this study, we evaluated the CO₂/H₂ separation performance of a 3D-printed MOF-74 (Ni) monolith at varied adsorption pressure, superficial velocity, feed composition, and adsorption time. This was accomplished using breakthrough and cyclic adsorption–desorption experiments, where the adsorption pressure was varied between 1 and 10 bar, the superficial velocity of 60% H₂/40% CO₂ was varied from 0.44 to 1.80 cm/s, and different CO/CO₂/H₂ feed compositions were introduced. The adsorption time was also varied from 45 to 120 s in the cyclic experiments. The breakthrough experiments indicated that higher pressures enhance the degree of CO₂/H₂ wavefront separation, whereas elevating the superficial velocity leads to broadened breakthrough profiles. Moreover, the multicomponent breakthrough experiments indicated that increasing the CO concentration leads to higher competitive adsorption with CO₂ and broader wavefronts. Therefore, the breakthrough experiments indicated that the wavefronts become increasingly broadened as the flow rate, pressure, and CO concentration increase. The cyclic adsorption–desorption experiments revealed that increasing the adsorption pressure enhances the CO₂/H₂ separation at the expense of H₂ productivity, whereas increasing the feed superficial velocity and lengthening the adsorption time give rise to lower H₂ purity but increased productivity. Optimizing these heuristics revealed that the monolith displayed its best performance with 1.80 cm/s superficial velocity, 10 bar pressure, and 60 s sorption time, where it achieved 98% H₂ purity and 18 mmol H₂/h·g_monolith productivity. Overall, this study provides a thorough assessment of the process parameters that impact the CO₂/H₂ separation performance of 3D-printed MOF-74 (Ni) monoliths which could be applied for future scale-up.