Dynamics of water vapor sorption in a CaCl2/silica gel/binder bed:: The effect of the bed pore structure

The dynamics of water vapor sorption in a compact, binder-containing bed of a CaCl2-in-silica-gelpores sorbent has been investigated by NMR microscopy. The procedure suggested for the preparation of this bed allows the porous structure of the bed to be modified in a wide range. The bed pore structure and water transfer in the bed have been studied in relation to the particle size of the initial silica gel, the size of mesopores in the sorbent particles, and the binder content. By varying these parameters, it is possible to optimize the ratio of the diffusion resistance of the interparticle macropores to that of the internal mesopores of the particles. If sorption is controlled by water diffusion in the macropores, a sorption front forms in the sample to move inside the bed. The distance traveled by the front is proportional to the sorption time to the power 1/2. The effective diffusion coefficient of water in the macropores is estimated from the front motion dynamics to be between 0.8 x 10(-9) and 3.0 x 10(-9) m(2)/s, depending on the porous structure of the bed.