A study of water transport in zeolite 4A powder beds and sodium silicate films using broadline magnetic resonance imaging.

Zeolites are hydrated microporous aluminosilicate crystals. They are of great interest to the scientific and engineering communities due to their ability to catalyse reactions, ion- exchange and be size selective in their admittance of molecules. The main experimental work described in this thesis measures the long range transport rate of water through macroscopic powder samples of zeolite 4A using recent developments in broad-line NMR imaging techniques. Samples consisting of contacting beds of packed zeolite 4A powder were prepared with a step function concentration profile of water between the two beds. The equilibration of the water between the beds was then monitored as a function of time using a 1H NMR broadline profiling technique. This long range transport process was investigated as a function of temperature, initial hydration and resident cation. Long range self diffusion experiments were also performed by preparing one bed with the tracer molecule deuterium oxide. This gives a constant concentration profile across the two beds. Experiments were performed as a function of temperature. A detailed diffusion model was then derived, describing the long range transport of water through beds of zeolite 4A as a function of temperature and hydration. The long range transport was found to be an interplay between liquid intracrystalline diffusion and faster interparticle vapour diffusion. The relative importance of the two processes with respect to the effective transport rate, depends on the overall concentration in the bed. A concentration and temperature dependence is given. A set of mobility weighted, stray field imaging (STRAFI) profiles were taken of thin films of sodium silicate solutions during drying, as a function of temperature. It was found that for moderate drying temperatures up to 70°C, the mobility of water molecules within sodium silicate is dependent on local hydration and is independent of drying history