Browsing by Author "Key, David"
Now showing 1 - 12 of 12
Results Per Page
Sort Options
Item Catalytic cracking of naphtha: The effect of Fe and Cr impregnated ZSM-5 on olefin selectivity(Springer Nature, 2018) Mohiuddin, Ebrahim; Mdleleni, Masikana M.; Key, DavidThis study focuses on the modification of ZSM-5 in order to enhance the catalytic cracking of refinery naphtha to produce light olefins. ZSM-5 was metal modified using different loadings (0.5–5 wt%) of Fe and Cr via the impregnation method. The metal modified ZSM-5 samples are compared and the effect of metal loading on the physicochemical properties and catalytic performance is investigated. Fe and Cr modification had an effect on both the physicochemical properties of the catalysts as well as catalytic activity and selectivity. Metal loading caused a decrease in the specific surface area which decreased further with increased metal loading. Fe had a greater effect on the total acidity in particular strong acid sites when compared to Cr. The optimum Fe loading was established which promoted selectivity to olefins, in particular propylene. Fe also had a dominant effect on the P/E ratio of which a remarkable ratio of five was achieved as well as enhanced the stability of the catalyst. Cr was found to be a good promoter for selectivity to BTX products with a two-fold increase observed when compared to Fe-modified catalysts.Item Development of a gas chromatographic technique for the analysis of some groundwater contaminants from fuel leaks and its application in a site-specific study(University of the Western Cape, 2009) Philander, Ghouwaa; Key, David; White, Richard; Dept. of Chemistry; Faculty of ScienceThis study focuses on the development of a Direct Aqueous Injection Gas Chromatographic method with Flame Ionization Detection (DAI-GC/FID) for the analysis of MTBE and TBA. The analytical method was then applied in a site specific study where MTBE contamination was evident. The method achieved detection limits of 1 ppm for MTBE and 0.1 ppm for TBA. The method showed good precision, accuracy and selectivity. The method was selected primarily for its ability to simultaneously analyze MTBE and TBA. The result of the site specific study showed the persistence of high concentrations of MTBE and TBA at the source of contamination, whilst concentrations at the adjacent primary school dropped to below detection limits as a result of rapid natural attenuation. It was found that an overall decrease in MTBE concentrations was met with an increase in TBA concentrations; which is a direct indication of MTBE degradation. Despite the fact that problematic MTBE concentrations persist at the source of contamination, limited evidence of the persistence of MTBE contamination was identified at the adjacent primary school. As such, MTBE health risks from existing pathways were found to be irrelevant for receptors at the adjacent school.Item The development of appropriate brine electrolysers for disinfection of rural water supplies(University of the Western Cape, 2005) Siguba, Maxhobandile; Key, David; Dept. of Chemistry; Faculty of ScienceA comparative study of electrolysers using different anodic materials for the electrolysis of brine (sodium chloride) for the production of sodium hypochlorite as a source of available chlorine for disinfection of rural water supplies has been undertaken. The electrolyser design used was tubular in form, having two chambers i.e. anode inside and cathode outside, separated by a tubular inorganic ceramic membrane. The anode was made of titanium rod coated with a thin layer of platinum and a further coat of metal oxide. The cathode was made of stainless steel wire. An assessment of these electrolysers was undertaken by studying the effects of some variable parameters i.e.current, voltage and sodium chloride concentration. The cobalt electrolyser has been shown to be superior as compared to the ruthenium dioxide and manganese dioxide electrolysers in terms of hypochlorite generation. Analysis of hydroxyl radicals was undertaken since there were claims that these are produced during brine electrolysis. Hydroxyl radical analysis was not successful, since sodium hypochlorite and hypochlorous acid interfere using the analytical method described in this study.Item Effect of Fe-Mo promoters on HZSM-5 zeolitecatalyst for 1-hexene aromatization(Elsevier B.V., 2018-11-15) Key, David; Mdleleni, MasikanaThe promotional effect of Fe-Mo species introduced into HZSM-5 (Zeolyst Int.,SiO2/Al2O3 30) zeolite catalyst by the wetness impregnation method for the 1-hexene aromatiza-tion was investigated. The structure and catalytic performance for the aromatization of 1-hexeneover xFeyMo-ZSM-5 catalysts in comparison with unmodified HZSM-5 catalysts were studied.The xFeyMo-ZSM-5 catalysts contain fixed loading (5 wt%) and variable Fe/Mo ratio. The cata-lysts were characterized by BET, ICP-AES, HRSEM-EDS, HRTEM, XRD, FTIR, H2-TPR,NH3-TPD, and pyridine DRIFT spectroscopy. The characterization data confirmed the existenceof Fe and Mo species in the zeolite matrix. With Fe and Mo species implementation to HZSM-5zeolite, the amount of the acid sites decreased, but the selectivities to C9+aromatics increased.The catalyst evaluation was performed at 350°C for 6 h on-stream at atmospheric pressure usinga fixed-bed quartz tube reactor. The selectivity to products of different carbon number was affectedby the Fe/Mo ratio within the zeolite. It was found the product distribution of grouped fractions ofC1–C17+from the liquid product. The results indicate that the optimum ratio of Fe/Mo is 1–1.5.The highest selectivity for gasoline and distillate ranges was obtained for the 2.5wt%Fe2.5wt%Mo- and 3wt%Fe2wt%Mo-ZSM-5 samples, which was higher than that for parent HZSM-5 cata-lyst.Item The electrogeneration of hydroxyl radicals for water disinfection(University of the Western Cape, 2006) Mangombo, Zelo; Key, David; Dept. of Chemistry; Faculty of ScienceThis study has shown that OHË radicals can be generated in an Fe/O2 cell from the electrode products via Fenton’s reaction and used for water disinfection. The cell system in which the experiments were carried out was open and undivided and contained two electrodes with iron (Fe) as the anode and oxygen (O2) gas diffusion electrode. Typically, 100 ml of Na2SO4.10H2O (0.5M) solution was used as a background electrolyte. OHË radicals were produced in-situ in an acidic solution aqueous by oxidation of iron (II), formed by dissolving of the anode, with hydrogen peroxide (H2O2). The H2O2 was electrogenerated by reduction of oxygen using porous reticulated vitreous carbon (RVC) as a catalyst.Item Evaluation of the leachate chemistry and contaminants attenuation in acid mine drainage by fly ash and its derivatives(University of the Western Cape, 2006) Gitari, Wilson Mugera; Key, David; Dept. of Chemistry; Faculty of ScienceThe mining industry in South Africa has a huge potential to impact negatively on the environment. Negative impacts include generation of reactive tailings and acid mine drainage (AMD). AMD is highly acidic (pH 2-4), sulphate-rich and frequently carries a heavy metal burden. South Africa uses more than 100 million tonnes of low grade bituminous coal annually to produce cheap electricity. The associated mining operations result in millions of tonnes of polluted water and in turn coal burning power stations produce vast amounts of waste ash such as fly ash. The highly soluble CaO occurring as sub-micron fragments on the fly ash particles is highly reactive and can be utilized in the neutralization of acid mine drainage. Acid mine drainage (AMD) was reacted with two different South African fly ashes in a batch setup in an attempt to evaluate their neutralization and inorganic contaminants removal capacity. The concentrations of major constituents in the AMD were found to determine the final pH attained in the reaction mixture and the reaction time of breakthrough to circum-neutral and alkaline pH. Efficiency of elemental removal in the AMD by the FA was directly linked to the amount of FA in the reaction mixture and to the final pH attained. Most elements attained ≈ 100 % removal only when the pH of minimum solubility of their hydroxides was achieved. In the second part of the study, Acid mine drainage (AMD) was reacted with coal fly ash in a 24 hour equilibration time using 1:3 and 1:1.5 FA: AMD ratios by weight to produce neutral and alkaline process waters. The capacity of the fly ash to remove the major inorganic contaminants from AMD was examined with time. The geochemical computer software PHREEQC and WATEQ4 database were used for geochemical modeling of the process water chemistry at selected reaction times. The collected solid residues were analyzed by X-ray diffraction, scanning electron microscopy (SEM) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). At both ratios the reaction mixture was at saturation or oversaturated with alunite, basaluminite, jurbanite, boehmite, gibbsite, diaspore, gypsum, barite, K, Na-jarosites, ettringite, amorphous Fe (OH)3 and goethite at specific contact times. The precipitation of the many inorganic contaminants was established in terms of the mineral phases at saturation or over-saturation. Sequential extraction revealed the amorphous fraction to be the most important in retention of the major and minor inorganic contaminants at pH > 6.32 which implies that the concentration of total Fe and Al in the AMD being treated has a direct effect on the clean-up efficiency of the process. In the third part of the study, a column leaching of the solid residues (SR) blended with varying amounts of fly ash (5 %, 25 %, 40 %) and 6 % Ordinary Portland Cement (OPC) was carried out to assess the contaminant attenuation with time. The columns were drained with synthetic acid mine drainage (SAMD) over a period of 165 days. In addition the solid residues were modified with 1-6% OPC and their strength development monitored over a period of 365 days. The column solid cores were observed to acidify in a stepwise fashion, exhibiting three buffer zones. The SR alone and SR blended with fly ash exhibited strong buffering capacity at pH (7.5-9) for an extended period of time (97-110 days). Encapsulation of solid residue particles by the calcium silicate hydrate gels (CSH) in OPC blended solid residues obscured the appearance of the sustained buffering at pH 7-9.5. The fly ash and OPC blend solid residues exhibited decontamination efficiencies of (82-99 %) for Al, Fe, Mn and SO4 2- over the study period. However the OPC blend SR exhibited high attenuation efficiency even as the pH dropped to below 4. SR + 6 % OPC core was observed to be the most efficient interms of retention of highly mobile elements such as B and Mo. pH was observed to be the main determining factor in contaminants attenuation. Geochemical modeling results revealed that pH and SO42- concentrations in the leachate had a significant impact on the mineral phases controlling Fe and Al concentration in the leachates. In the SR + 6 % OPC solid cores, EDX analysis revealed that CSH gels and calcium aluminate hydrate gels were being precipitated. These gels were either incorporating Fe, Mg, Mn in their matrix or encapsulating the solid residue particles that were rich in these elements. Sequential extractions of the leached solid cores revealed the amorphous fraction to be the most important in retention of the major contaminants and were most enhanced in the OPC blend solid residues. The OPC blend solid residue slurries developed unconfined compressive strength (UCS) (2-3 Mpa) comparable to paste formulated from sulphidic rich mine tailings confirming that the solid residues can be used for backfilling. Therefore the solid residues (SR) can successively be applied for a dual purpose in mined out areas namely, to remediate acid mine drainage waters and also provide support for the overburden. Keywords: Acid Mine Drainage; Fly Ash; Neutralization; Sulphates; Metal ions; Solid Residues (SR); Column Leaching; Geochemical Modeling; Sequential Extraction; Buffering.Item The hydrochemical characteristics of groundwater in the Incomati Estuary(University of the Western Cape, 2007) Adonis, Shaheeda; Key, David; Okujeni, Charles; Dept. of Chemistry; Faculty of ScienceThe focus of this work was to monitor and evaluate the hydrochemical characteristics of the groundwater in the Incomati Estuary for a period of one year. The aims of this work were to evaluate the groundwater chemistry data for any spatial and temporal variations and to evaluate the suitability of the groundwater for drinking and irrigation purposes.Item Oxidative fixation of dinitrogen by photocatalysis(University of Western Cape, 2000) Karriem, Fatiema; Key, DavidThe heterogeneous photocatalytic oxidation of dinitrogen to nitrate, NO3 and/or nitrite, no2 using peroxy species of titanium (IV) in aqueous suspensions has been investigated. The photocatalysts used were titanium peroxide and Degussa p25 TiO2 pretreated with H2O2. These photocatalysts were investigated by SEM and FTIR spectroscopy.Item A review of the processes associated with the removal of oil in water pollution(MPDI, 2021) Cerff, Bradley; Key, David; Bladergroen, BernardWater plays an essential role in production and refining processes. Many industries that use petrochemicals also require water, especially for cleaning purposes. The wastewaters released by these processes are often rich in petroleum pollutants, which requires significant treatment prior to disposal. The presence of petroleum contaminants in rivers and oceans is a significant threat to human health, as well as to many animal species. A current challenge for most industries and conventional effluent treatment plants is compliance with accepted disposal standards for oil-polluted wastewater. Of particular importance is the processing of dispersed oil in water, as well as oil in water emulsion. Conventional oil and water separation methods for processing oil in water contamination have several technology gaps in terms of applicability and efficiency. The removal and effective processing of dispersed oil and emulsions from oily wastewater is a costly and significant problem. The objective of this paper is to provide a review of the principles associated with oil in water emulsion separation, with the aim of providing a more definitive understanding of the terminology, processes, and methodologies, which will assist the development of a more efficient, innovative and environmentally friendly process for the separation of oily wastewater.Item Synthesis and characterizations of nanostructured MnO2 electrodes for supercapacitors applications(University of the Western Cape, 2010) Mothoa, Sello Simon; Ji, S.; Key, David; Mohamed, Rushanah; Dept. of Chemistry; Faculty of ScienceThe objective of this research was to develop highly efficient and yet effective MnO2 electrode materials for supercapacitors applications. Most attention had focussed on MnO2 as a candidate for pseudo-capacitor, due to the low cost of the raw material and the fact that manganese is more environmental friendly than any other transition metal oxide system. The surface area and pore distribution of MnO2 can be controlled by adjusting the reaction time. The MnO2 synthesised under optimum conditions display high capacitance, and exhibit good cycle profile. This work investigates the ways in which different morphological structures and pore sizes can affect the effective capacitance. Various -MnO2 were successfully synthesised under low temperature conditions of 70 oC and hydrothermal conditions at 120 oC. The reaction time was varied from 1 to 6 hours to optimise the conditions. KMnO4 was reduced by MnCl.H2O under low temperature, whereas MnSO4.4H2O, (NH4)2S2O8 and (NH4)2SO4 were co-precipitated under hydrothermal conditions in a taflon autoclave to synthesise various -MnO2 nano-structures.Item Synthesis and properties of nanoparticulate titanium dioxide compounds(University of the Western Cape, 2009) Buthelezi, Motlalepula Isaac; Key, David; Dept. of Chemistry; Faculty of ScienceAn electrolytic cell was designed and constructed for the preparation of TiO2 nanotubes. Conditions of anodic oxidation were established to reproducibly prepare TiO2 nanotubes of average length 35-50 μm vertically orientated relative to the plain of a pure titanium metal sheet. A non-aqueous solution of ethylene glycol containing small percentage of ammonium fluoride was used as the electrolyte with an applied voltage of 60 V. The morphology and dimensions of the nanotube arrays were studied by scanning (SEM) and transmission (TEM) electron microscopy. The effect of calcination under different conditions of temperature and atmosphere (nitrogen, argon and air) were assessed by both X-ray diffraction (XRD) and cyclic voltammetry (CV). Cyclic voltammetry studies were made possible by construction of a specially designed titanium electrode upon which the nanotubes were prepared. CV studies established a positive correlation between crystallinity and conductivity of the nanotubes. Doping of the nanotubes with nitrogen and carbon was established by elemental analysis, X-ray photoelectron spectroscopy (XPS) and Rutherford back scattering (RBS). The effect of nonmetal doping on the band gap of the TiO2 nanotubes was investigated by diffuse reflectance spectroscopy (DRS).Item Technological advances in winery wastewater treatment: A comprehensive review(Stellenbosch University, 2022) Vlotman, David; Key, David; Bladergroen, BernardThe commercial production of wine is directly linked to the use of large amounts of fresh water coupled with the generation of copious amounts of wastewater containing significant amounts of organic and inorganic substances. The impact of this waste stream on the environment has required the wine industry to implement certain protocols in wastewater management to comply with respective effluent discharge regulations as set out by local authorities. Reduced accessibility to good quality water resources in recent years has forced wineries to consider more efficient wastewater management strategies to improve water recovery and re-use, thereby promoting more sustainable wine production and minimizing the impact on stressed water resources. This review presents a comprehensive overview of established and emerging, physicochemical, biological, advanced oxidation and hybrid wastewater treatment technologies specifically applicable to the wine producing industry. Herein, winery wastewater composition and treatment techniques, environmental implications, knowledge gaps, technological operational challenges, alternative disposal and recycling options of treated winery wastewater are critically evaluated.