Spatially Resolved Characterization of the Gas Propagator in Monolithic Structured Catalysts Using NMR Diffusiometry

Abstract

Gas diffusivity measurements in opaque porous media were performed using nuclear magnetic resonance. An optimized pulsed-field gradient stimulated echo method with free volume selection was used to investigate the propagator of thermally polarized methane gas within commercial monolithic catalyst supports. Since signal losses due to T 2 relaxation were minimized by using a short echo time, diffusion processes could be characterized by the measured propagator functions and effective diffusion coefficients were determined for a broad range of observation times and in different spatial directions. The study of this noninvasive characterization of gas diffusion found a clear effect of the monolith type and its pore size and coating on the effective gas diffusion coefficient and the apparent tortuosity for a given observation time.

Diffusivities of Hydrocarbons in the Fresh and Aged Hydrotreating Catalysts Studied by Zero-Length Column Method

“…The internal diffusion effectiveness factor of the deactivated catalyst decreased by 10%, compared with the fresh one. 33,34 However, the diffusional results could not be related to the pore structural properties of the catalyst. 33 The detailed relationship between structure and diffusivity of the aged catalyst must be further clarified by a meaningful characterization method.…”

“…Recently, the diffusivity of asphaltene at comparatively high temperature and pressure has been monitored in terms of penetration depth. − It indicates asphaltenes are liable to be blocked at the periphery of the extrudate and macroporosity of the catalyst supports can diminish the diffusional effect on catalytic performances. , Furthermore, the diffusivities of probe molecules decreased as the coke content increased, as measured by pulsed-field gradient–nuclear magnetic resonance (PFG-NMR) technology. The internal diffusion effectiveness factor of the deactivated catalyst decreased by 10%, compared with the fresh one. , However, the diffusional results could not be related to the pore structural properties of the catalyst . The detailed relationship between structure and diffusivity of the aged catalyst must be further clarified by a meaningful characterization method.…”