(631c) Next-Generation Hybrid Ferromagnetic Structured Adsorbent for Biogas Upgrading Via Magnetic Induction Swing Adsorption (MISA)

Structured adsorbents, including monoliths, laminates, and foams, have gained significant importance in the gas separations applications to replace traditional pellets or beads due to their ability to fine-tune mass and heat transfer properties and lower pressure drop across the bed. However, to further improve their performance, a focus on fast cyclic operations with quick regeneration is needed. Regeneration can be achieved through Pressure Swing Adsorption (PSA) and/or Temperature Swing Adsorption (TSA), with the trend shifting towards TSA and the use of renewable electrical energy instead of fossil fuels. This shift towards electrification aligns with the chemical industry's push towards sustainability.

The present study had two main focusses: the development of a next-generation hybrid/multifunctional ferromagnetic structured adsorbent and its performance in gas separation processes. The novel structured adsorbent was prepared using an additive-free binderless method, where a 3D hierarchical structure was coated with Ni-MOF-74 and iron oxide (Fe₃O₄). Ni-MOF-74 is a distinct reticular material which exhibits distinguished CO₂ adsorption capacity and selectivity due to the open metal sites in the hexagonal channels aligned along the c-axis¹ and Fe₃O₄ is a ferromagnetic susceptor, which is capable of dissipating heat instantaneously when placed in a high-frequency alternating electromagnetic field through magnetic dissipation (hysteresis losses) and via the Joule effect because of the generated Eddy currents. It is referred to as Magnetic Induction Swing Adsorption (MISA). MISA is a very fast, in-situ and non-contact method to heat conductive and/or ferromagnetic materials in a homogeneous manner. Taking advantage of these properties, the potential of rapid CO₂ capture and uniform thermal regeneration/desorption via magnetic induction swing adsorption (MISA) was investigated.

The first part of the study involved coating a low-cost commercially available melamine sponge alternatively with Ni-MOF-74 and Fe₃O₄ multiple times. The successful incorporation of both ingredients was confirmed by SEM and XRD analysis, while TGA indicated the thermal stability of the composite under working conditions (< 250 °C). Next, breakthrough experiments with mixtures of CO₂ and CH₄ were performed at different flow rates (50 – 150 Nml/min), 1 bar and 298 K. The results demonstrated that the selective property of Ni-MOF-74 towards CO₂ was retained, with the composite showing a capacity of 1.911 mmol CO₂/g and a selectivity of 14. Further, the compressible nature of the melamine sponge allowed for an improvement of 44 % in the volumetric capacity of the adsorbent bed. In regard to regeneration, within 1 min. of subjecting the structured composite to the alternating magnetic field, an efficient desorption of CO₂ was achieved. Overall, for the first time a next-generation hybrid ferromagnetic structured adsorbent, which demonstrates a coalesce of its constituent properties, is presented for fast cyclic gas-phase separation processes.