An H-1 NMR microimaging study of water vapor sorption by individual porouspellets

The H-1 NMR microimaging technique is applied to study water vapor sorption by the individual cylindrical silica gel and alumina pellets impregnated w ith hygroscopic salts. The two-dimensional images or the one-dimensional pr ofiles of the sorbed water distribution are detected sequentially to monito r the transport of water within the pellets in real time In the course of t he sorption process. The results identify the propagation of the sorbed wat er front through the dry regions of the pellets as the rate-limiting stage of the sorption process. This propagation can be facilitated by employing t he pellets with the eggshell distribution of the salt, but in such cases th e salt redistributes readily in the course of the sorption process, as reve aled by the relaxation weighted H-1 NMR microimaging experiments in which p aramagnetic salts are used. The diffusion equation with water content depen dent diffusivity is employed to model the one-dimensional radial profiles o f water distribution within the pellet with appropriate correction for the relaxation weighting effects.