Friday, August 17, 2018
2:00 P.M. – LGRT 201
"SYNTHESIS AND MOLECULAR TRANSPORT STUDIES IN ZEOLITES AND NANOPOROUS MEMBRANES"
Hierarchical zeolites and mesoporous materials have attracted significant interest over the past several years in the areas of oil refining, biomass conversion and next generation separation processes. The hierarchical porosity of these materials provides efficient mass transport with reduced diffusion limitations for zeolite catalysts and improved flux for membranes. However, previous studies on diffusion in hierarchical zeolites and mesoporous membranes have shown that the enhancement in mass transport is far lower than expected from their structure. It is imperative that the fundamental aspects of molecular transport in these new types of materials be better understood in order to rationally develop them for desired applications.
This thesis presents studies of molecular transport in hierarchical zeolites as well as mesoporous inorganic membranes. Challenges in the synthesis of these materials that are a hindrance to such molecular transport studies are also addressed by developing new synthesis techniques for siliceous zeolites as well as mesoporous silica hybrid membranes.
It was observed that the rate-limiting diffusional mechanism in hierarchical zeolites is governed by the strongest possible sorbate-sorbent interaction. Surface diffusion-mediated pore re-entry into micropores leading to additional configurational diffusion was found to cause the slower than expected overall diffusion in these materials. In order to better examine these observations, a general, fluoride-free technique was developed for the synthesis of siliceous zeolites. This technique opens up a wide range of possibilities for the synthesis of zeolites with controlled structure, composition and mass transport properties. In addition, the mass transport mechanism responsible for improved flux in mesoporous inorganic membranes was also elucidated and compared with hierarchical zeolites.