(439a) Membrane Encapsulation of Catalysts by Fluidized Bed Film Coating

This study describes the application of fluidized bed film coating as an efficient method to coat porous membranes onto catalytic particles. These composite materials described as membrane encapsulated catalysts have the potential to increase reaction yield and selectivity by controlling the diffusion of products and reactants to and from the catalytic core. Membrane coated catalysts were synthesized by spray coating spherical zeolite particles with an alumina suspension in hydroxylpropyl cellulose (HPC) using a conventional fluidized bed (Mini-Glatt). Coated particles were subsequently calcined in a furnace to remove the HPC leaving a porous alumina membrane. The fluidized bed coating process was evaluated by its ability to coat uniformly as well as to control the coating thickness of the membrane. Scanning electron microscopy (SEM), Near Infrared Spectroscopy (NIR), and surface area and pore size distribution analysis (BET) were used as methods to characterize the coated catalyst. Results show that membrane coatings were uniformly coated and free of voids upon optimization of fluidization parameters for the range of membrane thicknesses (6.2-22.1 micrometers) tested in this study. Furthermore, membrane coating thickness was shown to adhere very closely to a theoretical thickness equation of Dewettinck (1997). The coating thickness estimated from the experimental techniques was in fairly good agreement with the theoretically predicted thickness of 22.1 micrometers and deviated by only ±0.83 micrometers. Deviation was smaller for thinner membrane thicknesses. The alumina membrane was also shown to adhere well to the catalyst after removal of HPC and its thickness remained unchanged after calcining. BET data shows that zeolite pores remained unchanged after the coating process. NIR absorption spectra was shown to correlate coating thickness with absorbance at 1186nm (R2=.987) as a method to replace image analysis for fast non-destructive characterization.