Synthesis and Molecular Transport Studies in Zeolites and Nanoporous Membranes

Download or read book Synthesis and Molecular Transport Studies in Zeolites and Nanoporous Membranes written by Vivek Vattipalli and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The advent of nanoporous materials such as zeolites and nanoporous membranes has provided cost-effective solutions to some of the most pressing problems of the 20th century such as the conversion of crude oil into fuels and valuable chemicals. Hierarchical zeolites and mesoporous inorganic membranes are showing great promise in addressing new problems such as the conversion of biomass into value-added chemicals and development of energy-efficient separation processes. The synthesis and fundamental aspects of molecular transport in these new materials with hierarchical porosities need to be better understood in order to rationally develop them for these desired applications. Pore narrowing and pore blockage have been proposed to cause the significantly slower than expected diffusion in hierarchical zeolites and zeolite nanoparticles. In the first part of this work, the diffusion of cyclohexane and 1-methylnaphthalene is studied in MCM-41, SBA-15 and conventional as well as hierarchical silicalite-1 zeolite. The role of sorbate-sorbent interactions is investigated and surface diffusion-mediated pore re-entry into micropores is proposed to cause the slower overall diffusion in these materials. Previous molecular transport studies in zeolites have been limited to the MFI zeolite framework, mainly due to ease of synthesis of siliceous MFI in comparison to other siliceous zeolites. Additionally, the requirement of fluoride for the synthesis of siliceous zeolites makes practical applications of these materials difficult. The second part of this work addresses these problems by developing a general, fluoride-free method for the synthesis of siliceous zeolites. The dry gel conversion (DGC) method is used to synthesize 2 new siliceous zeolites for the first time without using fluoride. Mechanistic aspects of siliceous zeolite synthesis, the DGC method in particular, are studied and employed to further improve the synthesis method. Mesoporous inorganic membranes have ideally suited properties for separations such as low pressure drop and thermal as well mechanical stability. However, two challenges impede their applications - the large-scale synthesis of defect-free mesoporous membranes and the development of a fundamental understanding of molecular transport in them. In the third part of this thesis, a new, scalable synthesis method with superior coverage is demonstrated for the synthesis of hybrid mesoporous silica-anodized aluminium oxide (AAO) membranes. Steady state non-equilibrium capillary condensation is studied in detail using the permeation of butane through AAO membranes. New aspects of this phenomenon are reported and experimental evidence is found in support of a partial capillary condensed state of a mesopore stabilized by molecular transport.