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Title: Transport and diffusion in Faujasite and LTA zeolites
Author: Goncalves, J. A. S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1996
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A better characterisation and understanding of hydrocarbon transport and adsorption mechanisms within zeolite systems has been achieved using two types of microscopic techniques (deuterium and pulsed field gradient nuclear magnetic resonance) and one macroscopic method (zero length column): (i) Analysis of the lineshape of the spectra obtained from deuterated sorbates provides a qualitative understanding of molecular mobility within a zeolitic framework and its dependence on temperature. Relaxation times, T1 and T2, analysis and modelling (using the ALS model - Boddenberg and Beerwerth, 1989), bring additional qualitative and quantitative information in the form of characterisation, time constants and activation energies of the different types of molecular motion (translation, rotation and libration). (ii) Pulsed field gradient NMR experiments were used to measure self-diffusivities at different temperatures. This NMR method probes translational motion directly. Some restrictions, related to the applicability of this method, are found for systems with simultaneously short spin-spin relaxation time, T2, and long spin-lattice relaxation time, T1. (iii) Zero length column experiments have been developed from the method originally introduced by Ruthven and Eic (1988) to perform macroscopic measurements under well controlled external conditions, with negligible effects of heat transfer and external mass transport limitations. In addition to reproducible estimates of diffusivity and activation energy, ZLC measurements, when incorporated into an analytical model, also provide an estimate of the Henry constants and heats of adsorption. Although all the above experimental techniques have already been applied to study molecular adsorption and transport phenomena within zeolites, the combination of these methods to study adsorption and transport processes occurring within the same zeolite sample is novel.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available