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Title: Crystallization of high silica molecular sieves
Author: Sinclair, Douglas Murray
ISNI:       0000 0001 3414 1694
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1987
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Tetraethyl silicate has been hydrolysed under controlled conditions to produce "clear" silicate sols. An investigation of these sols by both trimethylsilylation and reaction with molybdic acid solution did not reveal any major difference between these sols and those produced from fumed silica. However these sols remain clear when heated to temperatures normally used in the synthesis of high silica molecular sieves (353K to 473K) and do not separate into solution plus solid gel as is the case with sols normally used in molecular sieve synthesis. New methods to follow the growth of zeolite crystals have been developed. Since there is no solid gel phase the zeolite crystals can be recovered by filtration and then weighed. Thus crystallization can be followed directly by mass growth measurements. Crystallization from the "clear" sols can also be followed by silicate analysis of the solution phase. These methods are not appropriate for crystallization from gels. Reaction mixtures have been sealed inside glass capillary tubes and the crystals grown at different temperatures. The crystal growth of individual crystals can then be followed by optical microscopy. The effects of temperature and chemical composition on the crystallization of ZSM -5 type zeolites has been examined. Apparent activation energies of growth for the different crystal faces have been calculated from Arrhenius plots. Factors which influence the size and shape of the crystals have been determined. Conditions for the growth of relatively large crystals of ZSM -5 have been established. Similar conditions are found to produce larger crystals of some other high silica molecular sieves (e.g. EU -1, ZSM -39 and ZSM -48). The crystallization of silicalite -1 at 368K from reaction mixtures with the composition 1Na20 20SiO2 1960H2O 80Et0H 2TPABr has been studied in detail, using thermal gravimetric analysis, scanning electron microscopy, X -ray powder diffraction, pH measurements and crystal mass measurements. The rate of linear crystal growth has been determined by measurement of the largest crystals at various stages of the crystallization. Nucleation curves have been calculated from the final crystal size distribution and the crystal growth curve. The crystal mass growth curve has also been calculated from the crystal growth curve data and the final crystal size distribution. The calculated mass growth curve is found to be in close agreement with the actual mass growth curve obtained experimentally.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Zeolite crystal growth