Browsing by Author "Cornelius, Mero-Lee Ursula"

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    The role of aluminium content in the control of the morphology of fly ash based hierarchical zeolite X
    (University of the Western Cape, 2015) Cornelius, Mero-Lee Ursula; Petrik, Leslie; Fatoba, Olanrewaju
    Coal is the main source of electricity in South Africa, the combustion of which produces a large amount of waste (coal fly ash) annually. The large-scale generation of coal fly ash places major strain on landfills and the material is toxic in nature. The high silicon and aluminium content in fly ash makes it a suitable starting material for zeolite synthesis. Utilisation of fly ash as a starting material for zeolite synthesis alleviates an environmental burden by converting a waste product to an industrially applicable material. In this study, hierarchical zeolite X was synthesised from coal fly ash via the fusion method. The clear fused fly ash (FFA) extract (with molar composition 0.12 Al·14.6 Na·1.00 Si·163 H₂O) served as the synthesis solution for hydrothermal treatment. The influence of synthesis parameters (such as Si/Al ratio, aluminium source, hydrothermal temperature and stirring) on hierarchical zeolite X formation was studied to determine the cause behind the formation of this material. Synthesised zeolites and starting materials (Arnot coal fly ash and fused fly ash) were characterised by various analytical techniques such as XRD and SEM-EDS to determine the phase purity, morphology and elemental composition (framework Si/Al ratio) of these materials. The synthesis of hierarchical zeolite X under hydrothermal conditions was found to be highly sensitive to the aluminium content of the synthesis solution. The hierarchical morphology of zeolite X was formed preferentially in relatively aluminium-deficient (i.e. high Si/Al ratio) synthesis environments under stirred hydrothermal conditions of 90 °C for 16 hours. In the case of sodium aluminate addition, octahedral shaped zeolite X crystals were formed in relatively low Si/Al ratio synthesis environments, which was attributed to the presence of excess sodium cation content in the synthesis solution. Selected hierarchical zeolites (D2 and E2) were characterised further to gain more insight into the properties of this material. HR-TEM and FTIR revealed that hierarchical zeolite D2 and E2 exhibited the typical structural features of zeolite X. Zeolite D2 and E2 contained both micropores and mesopores and had a high BET surface area of 338-362 m²/g. These zeolites also exhibited appreciable solid acidity (0.81-1.12 mmol H/g zeolite). These properties make hierarchical zeolite X a favourable material for application in catalysis or adsorption. Overall, the formation of zeolite X with hierarchical morphology was proposed to be linked to the presence of zeolite P1 structural units in the framework of the zeolite.
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    Synthesis and characterisation of high silica zeolites with MOR and MFI framework type from South African coal fly ash.
    (University of the Western Cape, 2019) Cornelius, Mero-Lee Ursula; Petrik, Leslie F.
    High-silica zeolites are porous, aluminosilicate materials known for high thermal stability; making these materials favourable for application in various industrial processes involving elevated temperatures. The synthesis of zeolites from alternative feedstock such as coal fly ash has been investigated previously. Coal fly ash is a waste by-product of the coal combustion process, which is main source utilised for energy generation in South Africa. Coal fly ash is an ideal alternative feedstock for zeolites due to the large annual production as well as the rich mineral content (high in silicon and aluminium). Coal fly ash also contains a range of other elements which is known to result in environmental problems such as excessive land-use as well as air, soil, surface water and ground water pollution; including inorganic cations that may influence the zeolite crystallisation process. However, coal fly ash has successfully been utilised for the synthesis of a range of low-silica zeolites. High-silica zeolite synthesis from alternative feedstock has usually focused on the synthesis of zeolite ZSM-5. Furthermore, these synthesis routes commonly utilised additional silicon sources and/or a purification step by reflux treatment with a chelating agent to enhance the feedstock Si/Al ratio prior to crystallisation. This adds complexity to the conversion of coal fly ash to zeolite process, in terms of cost, energy and time.