Modeling the performance of a metal-organic framework (MIL-101) for the adsorption of toluene in an industrial fluidized bed adsorber and comparison to other adsorbent materials

Abstract

In the present study, the application of a metal–organic framework (MOF) is investigated for the adsorption of toluene in an industrial fluidized bed adsorber. A previously-validated steady-state model is used that takes into account interactions between bubble and emulsion phases. The change in overall removal efficiency and partial pressure profile along the bed is discussed for different design and operating parameters. The performance of MOF (MIL-101) is then compared to that of a beaded activated carbon (BAC), a porous styrene–divinylbenzene polymer (Dowex Optipore V503), and a zeolite (50:50 USY-ZSM-5). The results show an increasing trend for the removal efficiency with an increase in adsorbent feed rate, weir height, or the number of adsorber stages. Increasing gas flowrate or inlet toluene partial pressure decreases the removal efficiency. Examination of the corresponding partial pressure profiles reveals that the major contribution to toluene removal inside the bed shifts from the bottom stages (where the gas enters the bed) to the top stages (where the gas leaves the bed) with increased gas flowrate or inlet partial pressure, or with decreasing the adsorbent feed rate. Comparison of the removal efficiencies obtained with different adsorbent materials shows a general trend as MOF > BAC > polymer > zeolite, except when the adsorbent feed rate is very low or the inlet partial pressure is very high. In those cases, high apparent densities for BAC and zeolite (at constant adsorbent feed rate) create longer adsorbent retention times inside the bed and change the removal efficiency trend to BAC > MOF > zeolite > polymer. Improving the adsorbent retention time by increasing the weir height or the number of stages is suggested to remedy the removal efficiency for adsorbents with low apparent densities (e.g. MOF and polymer).