Hollow fiber membrane supported metal organic framework-based packed bed for gas/vapor adsorption

Abstract

Crystalline metal–organic frameworks (MOFs) with high porosity have high sorption capacities for various gases. Their fragile and pulverulent characteristics have prompted significant efforts to prepare shaped bodies e.g., pellets, granules for use in adsorbers. A hollow fiber membrane-based strategy is adopted since hollow fiber membrane (HFM) modules are highly preferred for industrial separation processes due to very high surface area provided per unit device volume and their easy scalability. We report herein a solvothermal synthesis method whereby nanocrystals of the MOF, UiO-66-NH2, are synthesized directly inside submicron pores of hydrophilic hollow fiber membranes of Nylon 6 as well as in the bores of the HFMs. Nanocrystals of around 100 nm populate HFM pores. Cylindrical modules containing such HFMs and MOF nanocrystals and microcrystals in membrane pores, HFM bores and the extra capillary space were studied for adsorption of ammonia from a dilute gas stream. High values of ammonia breakthrough time were achieved. The corresponding behaviors of three MOF configurations namely, MOF in membrane pores, MOF in membrane pores and the HFM bores and MOF present in membrane pores, HFM bores and in extra capillary space were studied. The values of time/MOF weight achieved were very high. The MOFs synthesized were characterized by Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffractometer (PXRD), Brunauer-Emmett-Teller (BET) adsorption isotherms, surface area, and pore size distribution. High performance of HFM-supported MOF-based scalable devices for gas/vapor adsorption has been demonstrated with values of 20,000 min/g of MOF for trace ammonia breakthrough from humid ammonia feed gas stream employed. Other potential uses of such devices for adsorbing 2 to 3 gases and liquid phase adsorption have also been discussed.