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Now showing 1 - 5 of 19

Recent Submissions

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    Outcomes, challenges and prospects of emicizumab prophylaxis in Sub-Saharan Africa - Insights from the Tanzanian experience
    (WILEY-BLACKWELL) Rebbecca Wughanga Mwakichako; Rajabu Hussein Mnkugwe; Clara Chamba; Peter Kunambi; Johnny Mahlangu; E et al
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    Molecular Epidemiology of Invasive Group B Streptococcus in South Africa 20192020
    Buhle Ntozini; Sibongile Walaza; B Metcalf; Scott Hazelhurst; L de Gouveia; S Meiring; D Mogale; S Mtshali; A Ismail; Kedibone Ndlangisa; Mignonette Du Plessis; V Quan; S Chochua; L McGee; Anne Von Gottberg; Nicole Wolter
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    Burden of SARSCoV2 infection and severe illness in South Africa March 2020August 2022 a synthesis of epidemiological data
    Larrise Bolton; Stefano Tempia; Sibongile Walaza; Wassila Jassat; Kaiyuan Sun; D Bradshaw; Rob Dorrington; Jacoba Kleynhans; Neil Martinson; Anne Von Gottberg; Nicole Wolter; Pulliam Juliet R C; Cheryl Cohen
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    Catalytic Conversion of Low Alcohols to Olefins and their Oligomers
    (University of the Witwatersrand, Johannesburg, 2023-09) Anekwe, Ifeanyi Michael Smarte; Oboirien, Bilainu Obozokhai; Isa, Yusuf Makarfi
    The global energy sector relies heavily on fossil fuels, resulting in significant greenhouse gas emissions. However, increasing concern about the environmental impact of these conventional energy sources has led to the search for alternative energy sources, such as low alcohols. Despite their potential, low alcohols, including bioethanol, face limitations as a fuel due to their inability to be used in their pure form (E100) in modern automobiles. The catalytic conversion of low alcohols (over acid zeolite catalyst) to hydrocarbons is required to overcome this limitation. While the micropores of ZSM-5 zeolite catalysts are advantageous for the mass transfer of small molecules, they are disadvantageous for the mass transfer of large molecules, as evidenced by diffusion limitations for reagents, intermediates, and products. Therefore, the novelty of this study was to synthesise a newly developed tunable ZSM-5 zeolite catalyst with mesopores to reduce the diffusion limitations of these large hydrocarbon molecules for enhanced conversion of low alcohols to olefins and their oligomers. The objectives of this study include the synthesis and promotion of a novel ZSM-5 zeolite catalyst using selected transition metals and the characterisation of as-synthesised catalysts using various techniques, the investigation of the effect of transition metal incorporation on ZSM-5 properties and catalytic performance, evaluating the effect of operating conditions and catalyst modification on product distribution and coke deposition, investigating the performance of metal-doped HZSM-5 catalyst in the conversion of low alcohols (methanol, ethanol and propanol) to fuel-range hydrocarbon, studying catalyst stability, deactivation and regeneration in bioethanol conversion, and conducting a techno-economic and environmental analysis (TEA) of the catalytic conversion process. The ZSM-5 catalyst was hydrothermally synthesised and promoted through dry impregnation with different concentrations (0.5 - 10 wt%) of transition metals (Co, Fe and Ni). The catalytic conversion process was carried out at 350-400 ᵒC and a weight hourly space velocity (WHSV) of 5-12 h⁻¹. The physical properties of the synthesised catalyst were investigated using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray fluorescence (XRF), particle size distribution (PSD), Brunauer-Emmett-Teller (BET), Particle size distribution (PSD) and ammonia temperature programmed desorption (NH3-TPD) analysis. Gas chromatography was used to analyse the hydrocarbon products, while thermogravimetric–differential thermal analysis (TG-DTA) was used to study the thermal stability of the material and coke deposition on the spent catalyst. The results showed that a mesoporous ZSM-5 zeolite catalysts was successfully synthesised and modification of ZSM-5 with transition metals affected the catalyst's surface area, morphology, particle size and acidity. The as-synthesised catalysts exhibited a prismatic crystal and remarkable textural properties including a surface area of 397.5 m²/g, a pore diameter of 2.22 nm, and a total pore size of 0.706 cm³/g (0.678 and 0.029 meso- and macropores, respectively). The catalytic evaluation revealed that the catalyst's performance was enhanced through metal modification during the conversion of low alcohols (methanol, ethanol, and propanol) into hydrocarbons. The effectiveness of the modification, low alcohol conversion, product selectivity and distribution were influenced by the operating conditions. The study also showed that the unmodified catalyst exhibited considerable stability compared to the metal-doped catalyst, attributed to high coke deposition on the metal-doped catalyst leading to deactivation. However, the metal-doped catalysts exhibited a broader product distribution (including gasoline and diesel fuel-range hydrocarbons) than the unmodified catalysts. The investigation of the regenerated catalysts demonstrated that the applied regeneration technique effectively maintained the catalyst's textural and morphological properties while enhancing its catalytic performance. The economic evaluation demonstrates that catalyst synthesis at baseline scale production (BSP) resulted in a net catalyst cost of $31.4/kg. Additionally, the operating and annualized capital costs associated with converting wet ethanol into fuel blendstocks are estimated to be $0.05/L presently, with a projected decrease to $0.03/L in the future. The predicted minimum selling prices for fuel blendstocks produced through CADO are comparable to those of traditional gasoline fuel when oil is priced at $100/bbl. The life cycle analysis revealed that CADO-derived fuel blendstocks achieve a reduction of >25% in greenhouse gas emissions compared to conventional gasoline derived from petroleum. The techno-economic and environmental analysis (TEA) demonstrated the economic and environmental viability of the catalytic process, making it a feasible and sustainable solution for upgrading low alcohols into fuel-range hydrocarbons. Conclusively, understanding the behaviour of coke deposition in ZSM-5 zeolite catalysts is pivotal for optimising the catalytic process and developing strategies to mitigate coke formation and deactivation for improved catalytic performance. These results indicate that the as-synthesised catalyst is promising for industrial applications where the stability and longevity of the catalyst play a crucial role. The catalyst thus offers a potential solution to the challenges associated with the conversion of low alcohols, providing a stable and efficient catalyst option for commercial and future use.
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    Guiding the development of the tuberculosis screening target product profile using singlescreen and multiscreen approaches a modelling study
    (ELSEVIER SCI LTD) Alexandra de Nooy; Cecily Miller; Tom Ockhuisen; Dennis Falzon; Nazir Ismail; Brooke Nichols; E et al