(631d) Gas or Liquid Phase Separation By Adsorption in a Nanopacked Bed of Nanocrystals of Metal-Organic Frameworks Supported By Submicron Pores of a Membrane

Crystalline metal-organic frameworks (MOFs) with high porosity have high sorption capacities for gases/vapors as well as for solutes from a liquid phase. Their fragile/pulverulent characteristics have prompted significant efforts to prepare shaped bodies e.g., pellets, granules etc. for adsorption. Such structures lead to loss of surface area, collapse of crystal structure, reduced porosity etc., among others. We will illustrate an alternate strategy where such consolidation of loose powders is not required. We employ a porous flat membrane or a hollow fiber membrane having submicrometer pores. Direct solvothermal synthesis of the MOF is implemented in the submicron pores of the membrane. A hollow fiber membrane (HFM) based strategy was also implemented since HFM-based modules are highly preferred for industrial separations due to high surface area provided per unit volume and their easy scalability among others. The solvothermal synthesis was carried out at 120°C for 18 hr in a DMF-methanol solvent containing reactants NH₂-H₂BDC and ZrCl₄ in a Teflon-lined pressure vessel wherein flat porous Nylon membranes/ loose porous Nylon HFMs were inserted, wetted and submerged. After post-reaction cooling, washing and drying, HFMs were potted in a small cylindrical module; flat membranes were washed, dried and used as such. Nanocrystals of the MOF, UiO-66-NH₂, were synthesized directly inside the submicron pores of hydrophilic flat membranes and HFMs of Nylon 6; MOF microcrystals were synthesized in HFM bores as well. A 100 ppmv NH₃-containing N₂ stream (50% RH) was introduced into the shell side of the module for gas separation studies. Removal performance of ammonia from nitrogen will be described. Ammonia appears at module outlet at trace levels at times as high as 800 min. The time/weight values of MOF are as high as 20,000 min/g. The MOFs were regenerated a number of times without performance deterioration. For adsorption from liquids, flat membranes were used to remove methylene blue from an aqueous solution. Direct utilization of sorption capabilities of microcrystals and nanocrystals of UiO-66-NH₂ MOF in a high-surface-area adsorber was achieved in HFM based devices.