An ¹H NMR Microimaging Study of Water Vapor Sorption by Individual Porous Pellets

Abstract

The 1 H NMR microimaging technique is applied to study water vapor sorption by the individual cylindrical silica gel and alumina pellets impregnated with hygroscopic salts. The two-dimensional images or the onedimensional profiles of the sorbed water distribution are detected sequentially to monitor the transport of water within the pellets in real time in the course of the sorption process. The results identify the propagation of the sorbed water front through the dry regions of the pellets as the rate-limiting stage of the sorption process. This propagation can be facilitated by employing the pellets with the eggshell distribution of the salt, but in such cases the salt redistributes readily in the course of the sorption process, as revealed by the relaxation weighted 1 H NMR microimaging experiments in which paramagnetic salts are used. The diffusion equation with water content dependent diffusivity is employed to model the one-dimensional radial profiles of water distribution within the pellet with appropriate correction for the relaxation weighting effects.

Space-Resolved Profiling Relevant in Heterogeneous Catalysis

“…mass transfer limitations. Structural heterogeneity of catalyst supports such as alumina and silica as well as the mass transports in the pores have been studied by time-resolved imaging or pulsed gradient spin echo (PGSE) NMR to obtain diffusion constants [108][109][110][111][112][113][114]. MRI showed its practical importance in deriving design parameter for reactor performance optimization, e.g.…”

NMR imaging of mass transport processes and catalytic reactions

“…Some other possible applications that can be useful for catalysis and related disciplines are the drying of porous materials [29][30][31] (including contact drying, external mass transfer across the fluid/solid interface), adsorption [29,31,32] (including sorption of water vapor and adsorption of gases by various porous sorbents), and the in situ visualization of supported catalyst preparation [33].…”

In Situ MRI Study of 1-octene Isomerisation and Hydrogenation within a Trickle-bed Reactor

“…To a lesser extent measurements of molecular diffusion [4][5][6][7], liquid distribution during reaction [8] and coke distribution [9][10][11] within both single catalyst pellets and arrays of such pellets have been addressed. These studies have used both spatially unresolved and microimaging MR methods.…”