(618b) 3D Hierarchical Porous MOF Based Structured Adsorbent for Gas-Phase Dynamic Separations

Separation processes are considered as the backbone of the world’s manufacturing industry. These processes are used for essential chores such as removal of contaminants from raw materials and recovery and purification of primary products.¹However, when adsorbent materials are used in the form of beads, pellets or granules, efficient gas separation processes operating at high throughput are compromised. System performance reduces rapidly due to high pressure drop associated with gas flow through a packed bed and mass transfer limitations related to gas diffusion into or out of the beads².

Structured sorbents like monoliths, fibre sorbents, foam structures, lamellar structures, or 3D printed structures offer improvement over traditional bead/pellet based packed bed structures by minimizing pressure drops, allowing faster cycle times and lower energy consumption. With additional degrees of freedom in bed design, structuring of adsorbents can provide efficient management of heat, mass, and momentum transportation^1,3. In general, to obtain structural adsorbents, there exists several processing routes such as extrusion, slip and tape casting, foaming, gel casting, spray drying, dry pressing, honeycombs and additive manufacturing or 3D printing technology^3,13,14. However, these techniques require a proper selection of additives to obtain suitable rheological properties without significant reduction in the surface area^13-16.

As an alternative, an interest in composite consisting of nanoscale porous materials such as MOFs and macroporous 3D hierarchical skeleton sponges has been noticed. Several case studies such as NH₃ adsorption¹⁸, Malachite Green dye (a toxic pollutant) adsorption¹⁸, and oil-water separation^19,20 have been carried out with such materials.

In this work, we report a MOF based melamine sponge (MS) composite for dynamic gas separation. The combination of the microporosity offered by MOF crystals with the permeability offered by the macroporous spatial skeleton of sponge can be of great potential for applications such as biogas and flue gas separation. Thus, taking MOF-74 as case study, in this work via a green, economical, and straightforward method, Mg-MOF-74 coated melamine sponge (Mg-MOF-74/MS) composite was developed and studied for CO₂ capture. The resulted composite exhibited good structural and thermal stability (< 250 °C). SEM image revealed a firm self-assembly of nanocrystals over the threedimensional (3D) skeleton surface (Fig. 1a). The resulted porous MOF-74 composite was subjected to breakthrough separation experiments with CO₂/N₂ and CO₂/CH₄ gas mixtures. Owing to the
combination of the spatial structure of the commercial sponge and the excellent adsorption capacity of MOF-74, the results showed that MOF-74 composite possessed good permeability, high mass transfer and dynamic adsorption capacity (Fig 1c).

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