Mass-transfer dynamics of MOF-801 under forced-flow temperature-swing cycling
Metal-organic frameworks (MOFs) are nanoporous materials with strong potential for sorption-based atmospheric water harvesting, owing to their exceptionally high surface areas (~5,000 m²/g) and easy regeneration at low temperatures (~70 °C). However, their practical implementation is limited by slow heat and mass transport, poor sorbent utilization, and the difficulty of integrating MOF nanopowders into scalable macroscopic thermofluid systems.
This work studies the mass-transfer dynamics of MOF-801 during forced-flow temperature-swing cycling. A custom apparatus drives conditioned humid air through a MOF-801 powder bed confined between electrically heated meshes. Adsorption proceeds under forced flow, while desorption is triggered by Joule heating at reduced flow rates to rapidly humidify the outlet stream. Time-resolved temperature and absolute-humidity measurements quantify water-vapor uptake and release through a transient mass-balance formulation, accounting for sensor reliability, cycle-resolved water-transfer metrics, and sorption-kinetic fitting.
The experiments show repeatable periodic cycling over successive runs. Desorption occurs on the order of minutes, whereas adsorption requires longer times, revealing a clear sorption-kinetic asymmetry. Avrami fits show first-order adsorption uptake, while desorption is a nonlinear process governed by coupled thermal and vapor transport. Under favorable conditions, the water-vapor exchange corresponds to a harvesting potential exceeding 10 L day⁻¹ kg_MOF⁻¹. During regeneration, the outlet stream reaches dew points above ambient temperature, confirming that the MOF bed can generate condensation-favorable vapor streams. Overall, this work provides a transport-aware framework for evaluating binder-free MOF-801 beds and designing faster, scalable atmospheric water-harvesting systems.
This work is towards an M.Sc. degree under the supervision of Assoc. Prof. Alexandros Terzis, The Stephen B. Klein Faculty of Aerospace Engineering, Technion.
