Characterization Of Dissolved Precursors In Zeolite Synthesis By Nmr Spectroscopy

Author : Justin Provenzano
Publisher :
ISBN 13 :
Total Pages : 65 pages
Book Rating : 4.:/5 (812 download)

DOWNLOAD NOW!

Download or read book A Study on the Hydrothermal Synthesis of the Zeolite DDR written by Justin Provenzano and published by . This book was released on 2011 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gas separation is a critical operation in chemical and energy industries. Currently, energy intensive and costly processes such as distillation, cryogenic fractionation, absorption, and adsorption are widely used. With technological advances, membranes processes have the potential to be a viable alternative. Zeolite membranes are a relatively new class of membranes that have attracted interest due to their outstanding stability and separation selectivity. The DDR-type zeolite is a pure silica zeolite with an ultra-small pore aperture of 0.36 x 0.44nm. This structure is promising for membranes capable of separating small molecule gas mixtures which is important to future clean power generation systems. While the effectiveness and mechanisms of gas separation by DDR membranes are current research subjects, the synthesis of DDR zeolite crystals and polycrystalline membranes is still a challenge with limited reported success. Furthermore, some of the literature results on DDR synthesis were unable to be reproduced by other researchers creating unsettled scientific controversies. This MS thesis research focused primarily on developing a highly reproducible procedure for DDR zeolite synthesis. The effects of the precursor composition, precursor preparation, and the synthesis conditions were extensively studied. Advanced materials characterization techniques such as SEM, XRD, and BET microporosimetry were employed to characterize the materials. A new two-step synthesis method has been established for rapid production of DDR-type zeolite crystals. The first step is the preparation of Sigma-1 seed crystals under a three-day stirred synthesis using a precursor molar ratio of 3 Na2O: 20 1-Adamantanamine (ADA): 1 Al2O3: 60 SiO2: 2400 H2O originally reported in literature. The second step is a one-day static synthesis of DDR-type zeolite using a molar ratio of ADA: Silica: Ethylenediamine: Water = 12:100:100:11240 with the assistance of ball-milled Sigma-1 as seed. This new process uses a total of 4 days to produce pure DDR crystals which is drastically shorter than 25-30 days used in verified synthesis methods. The DDR zeolite was activated by firing at 600°C for 8 hours. The activated DDR zeolite had a BET microporous surface area of 294 m^2/g which is consistent with literature values. Based on the successful DDR zeolite particle synthesis, preliminary investigations were conducted on the fabrication of DDR membranes. A modified membrane synthesis procedure was developed in this research with a precursor containing NaOH. Membranes of DDR crystal phase were successfully obtained. However, a small amount of aluminum from the support was leached by the alkaline solution and incorporated into the zeolite structure. The membranes were further studied for their quality and gas permeation properties. A 10-micron thick membrane of DDR crystal phase was obtained by a three-day hydrothermal synthesis at 160°C and autogenous pressure. The membrane was free of large defects as evidenced by the very small N2 permeance of 1.57 x 10-10 mol/m2*Pa*s before template removal. However, the membrane exhibited post-firing permeance levels two orders of magnitude higher than reported literature which evidenced defect formation during the firing process. Further research is needed to investigate the structure evolution during the firing process to minimize defect formation.