ETD Collection
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Item Synthesis, development and characterisation of dehydrated castor oil poly (glyceryl phthalate) alkyd resins(1994) Nzeru, Arnold.The dissertation studies the synthesis, formulation development, crosslinking and spectral characterisation of dehydrated castor oil poly(glyceryl phthalate) alkyd resins for use as air-dry surface coating vehicles. Synthesis of alkyd resins involves simultaneous dehydration, alcoholysis and polyesterification reactions. Dehydration of castor oil is achieved in situ under phthalic anhydride catalysis. Alcoholysis of dehydrated castor oil by glycerol is also achieved in situ to form predominantly the monoglyceride. Polyesterification of the resultant mono- and diglycerides is realised through interaction with phthalic anhydride. The reaction is carried out at 280°C for 3 hours and at 225°C for 2 hours under azeotropic distillation with xylene. The parent poly(glyceryl phthalate) alkyd resin is synthesized by reaction of castor oil, glycerol and phthalic anhydride to a predetermined acid value. Formulation development experiments were carried out to study the effect of variations in the dibasic acid to polyol/oil and polyol to oil ratios on alkyd resin properties. Model formulations exhibiting the best alkyd performance were developed. Predictive model formulation equations were derived from model formulation data and their limits of reliability and applicability established. The formulation of water soluble alkyd resins is modified to introduce pendant carboxylic acid groups along the polymer skeleton. Water solubility is achieved by neutralisation of the residual pendant carboxylic acid groups by 'fugitive' amines to yield water soluble alkyd soaps. The effect of variations in the nature and level of incorporation of amine is investigated. Alkyd resin solubilisation and resin acidity guide formulae were studied and developed. Cross-linking chemistry of alkyd resins, both in the reactor (gelation) and on application (film formation) is investigated. Gelation manifested itself in two different forms, thermoplastic and thermosetting. An important alkyd constant, K, was established as an indispensable tool in control of premature gelation and in the prediction of resin drying characteristics. Autooxidation and solvent evaporation are the two competing curing mechanisms encountered in film formation. The nature and influence of each curing mechanism on the rate of cure and film characteristics is highlighted. Catalysis experiments were conducted with metallic driers (Co2 Mn2 and Pb2} to bring the rate of drying of resin films to economically feasible limits and catalyst addition levels were established. New spectral characterisation techniques based on Fourier Transform Infrared spectroscopy were investigated. An extensive study was carried out on FT IR spectral data to establish qualitative and quantitative relationships between transmission peak ratios and alkyd resin composition. Series dependent and series independent correlation equations, useful in quantifying alkyd resin components were derived. A new FT IR spectroanalytic characterisation method for dibasic acids is proposed. The method, if adopted, affords both qualitative and quantitative characterisation of the dibasic acid component in the alkyd resin matrix and it is envisaged the technique will supersede conventional methods in terms of speed and simplicity.'Item Lipase-catalysed hydrolysis of morita-baylis-hillman adducts(2019) Mguni, Lindelo MthabisiBiocatalysis is the use of biological systems, such as enzymes, to perform chemical transformations on organic compounds. These enzymes catalyse reactions as whole cell systems or in isolated forms and have been found to exhibit high regio- and stereoselectivity towards chiral compounds. Lipases have been extensively used to catalyse kinetic resolutions of chiral compounds such as the Morita-Baylis-Hillman (MBH) adducts. The MBH adducts and their esters are important intermediates in organic synthesis and have been found to be valuable in the production of biologically active compounds. In this study, we expressed and partially purified the Pseudomonas fluorescens P26504 lipase in an active and soluble form to catalyse the kinetic resolution on MBH acetates to obtain enantiopure MBH adducts. The Pseudomonas fluorescens P26504 lipase was overexpressed in BL21 (DE3) pLysS cells at 25 °C for 16 hours, with 1mM IPTG concentration. Enzymatic assays were conducted after partial purification using p-nitrophenyl esters. The recombinant enzyme was highly active towards short chain esters and showed moderate activity towards medium chained esters. The Morita-Baylis-Hillman reaction was conducted, giving rise to racemic MBH adducts derived from benzaldehyde and hydro-cinnamaldehyde. The second step of the reaction was acetylation, producing chiral MBH acetates. A lipase-catalysed kinetic resolution was set-up, using the partially purified recombinant P. fluorescens P26504 lipase and the MBH acetates. TLC plate analysis showed that the recombinant lipase was able to hydrolyse both MBH acetates. However, further studies can be done to determine the enantioselectivity of the recombinant P. fluorescens P26504 lipase using chiral HPLC, which is more definitive.Item Photocatalytic degradation of methyl violet in water using TiO2/Cellulose-N-MWCNTs(2018) Mathebula, XiluvaABSTRACT TiO2-carbon based composites are of great significance in a wide range of applications including photocatalytic degradation. This is attributed to the high photodecomposition efficiency of the composites as compared to independent TiO2. Carbon materials such as cellulose polymer and multiwalled carbon nanotubes (MWCNTs) are considered as good supports for TiO2 owing to their unique properties such as lightweight, large surface area and high aspect ratio. Lately, the study of cellulose-MWCNTs composite has been an area of academic interest due to its large mass fraction, and prowess to facilitate toughening mechanisms in fiber bridging. However, a cost-effective method that can improve the dispersion and interfacial adhesion of the MWCNTs in the polymer is still required. Thus different modification methods of MWCNTs have been explored to increase the binding sites of the material. In this study, it was hypothesized that the cellulose’s potential as a TiO2 support can be improved by hybridizing it with MWCNTs resulting in high TiO2-C photocatalytic activity through synergistic effect. A catalytic decomposition of Fe-Co/CaCO3 was used over C2H2 to fabricate the MWCNTs. Thereafter, the MWCNTs were functionalized by (1) acid-treatment (referred to as fMWCNTs), (2) nitrogen doping by in situ and ex situ methods (referred to as in situ N-MWCNTs and ex situ N-MWCNTs, respectively) and (3) both acid treatment and nitrogen doping (referred to as in situ fN-MWCNTs and ex situ fN-MWCNTs). Moreover, cellulose-N-MWCNTs (C@fN-MWCNTs) hybrid was prepared by electrospinning a solution of cellulose acetate/in situ fN-MWCNTs (11/0.115) in DMAc at 25 kv and 1 mL/h. The prepared MWCNTs and cellulosic materials were further used as support materials of TiO2 in the photodegradation of methyl violet (MV 6B). The supported TiO2 catalysts were prepared by a sol-gel method and then analyzed using various techniques, such as transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy. iii TGA results revealed that in situ N-MWCNTs contained high impurities inclusive of as Fe, Co, Ca, and amorphous carbon which were identified by XRD analysis. Nevertheless, TGA, BET and TEM, showed that acid treatment of MWCNTs improves their purity, surface area and anchoring sites for the TiO2, respectively. Furthermore, SEM results showed that C@fNMWCNTs hybrid interacts with TiO2 better than cellulose fibers. This was in accord with the PL results which showed a reduction in the electron/hole recombination. However, the surface area of C@fN-MWCNTs was very low compared to cellulose fibers which resulted in low dye adsorption capacity by C@fN-MWCNTs. The photocatalytic degradation activity commercial TiO2 was enhanced by 3.7% and 5.6% after being supported on cellulose and C@fN-MWCNTs, respectively. Thus, incorporating in situ fNMWCNTs with cellulose did improve the cellulose’s potential as a TiO2 support. However, the overall photocatalytic degradation performance of TiO2/C@fN-MWCNTs was less than that of in situ TiO2/fN-MWCNTs. This may be due to the reduction in the surface area, which resulted in reduced adsorption and thus lowers degradation efficiency.Item The deactivation of silico-aluminophosphate catalysts during methanol conversion reactions(1993) Cornel, Veronica MayThis dissertation focusses on the deactivation of SAP0-34 and modified SAPOs during methanol conversion under various conditions, in comparison to H-ZSM-5. SAPO-34 was found to deactivate rapidly during methanol conversdon. This was shown by the decrease in activity, surface area and pore volume of the catalyst. The deposited "coke" was analysed by in situ diffuse reflectance infra-red Fourier Transform spectroscopy,solid-state magic angle spinning nuclear magnetic resonance, gas chromatography mass spectroscopy (GCMS) of the HF- and dichloromethane-extracted to "coke"; and GCMS of the organic specfes released during regeneration of the catalyst and trapped in resin capillary inlet tubes.The "coke" consisted of alkylated aromatics and naphthalenes which probably formed on the surface or in the large cavities of SAPO-34. The amount of "coke" deposited during methanol conversion increased with reaction temperature, decreased with dilution of the methanol with water or nitrogen. and decreased with increased pressure, Incorporation of Ni into the SAPO framework did not decrease the rate of deactivation, but the "coke" that Has deposited was less bulky than that deposited in SAPO-34. Modification of the SAPO-34 with trlmethyl silylchloride decreased the rate at deactivation of the catalyst.Item Synthesis of copper nanoparticles contained in mesoporous hollow carbon spheres as potential catalysts for growing helical carbon nanofibers(2017) Magubane, AliceThe aim of this study was to synthesize helical carbon nanofibers with controlled diameter by using copper nanoparticles contained inside hollow carbon sphere. In this work, different methods have been explored to synthesize copper nanoparticles contained inside mesoporous hollow carbon spheres in order to minimize the sintering effect of the copper nanoparticles. Mesoporous hollow carbon spheres were used not only as a support for the copper nanoparticles but to stabilize and disperse these nanoparticles to prevent the formation of aggregates. Mesoporous hollow carbon spheres were synthesized using a hard templating method, in which mesoporous silica spheres or polystyrene spheres were used as a sacrificial template. Carbon nanofibers with different morphologies, including straight and helical fibers were obtained by a chemical vapor deposition method where acetylene was decomposed over copper nanoparticles contained inside mesoporous hollow carbon spheres catalyst at 350 °C. The synthesized carbon nanofibers were grown on the surface of the mesoporous hollow carbon spheres as the methods used to synthesize the catalyst failed to incorporate copper nanoparticles inside the spheres. Differences in the diameter of the straight and helical carbon nanofibers were observed from both catalysts. This supports the important effect of particle size on influencing the shape of the synthesized carbon nanofibers.Item Catalytic evaluation of Ru(II) and Co(II) salicylaldimine complexes for transfer hydrogenation of acetophenone(2017) Ndou, Dakalo LorraineN-(aryl) salicylaldimine ligands were prepared by the condensation of salicylaldehyde and aniline, 2,6 – dimethylaniline, 2,6 – diisopropylaniline and N,N-diethyl-p-phenylenediamine to give the desired ligands in good yields (70 - 93 % yield). The synthesised ligands were characterised by NMR spectroscopy, FTIR spectroscopy, ESI mass spectrometry and elemental analysis. The purity of these ligands was determined by determining the meting points. Co(II) and Ru(II) complexes were prepared from Co(OAc)2.4H2O and [RuCl2(η6-p cymene)]2 to afford the N-(aryl) salicylaldiminato complexes Co1 – Co4 and Ru1 – Ru4 with yields in the range 60 – 66 % and 90 – 97 %, respectively. These complexes were characterised by NMR spectroscopy, FTIR, ESI mass spectrometry, elemental analysis and TGA. The purity of these complexes was also determined by determining the melting point. The transfer hydrogenation of acetophenone was studied using 2-propanol as the hydrogen source and KOH as the base with the Ru (II) and Co (II) complexes as catalyst precursors. The catalytic activity of these complexes was evaluated using 1H-NMR and GC - MS. Preliminary studies were performed for 6 h at 82 oC and the conversion was evaluated using 1H-NMR. Due to the low catalytic activity of these complexes, the reaction time was increased to 48 h. Increasing the reaction time resulted in improvements in the conversion of the complexes. The catalysis was also evaluated at various temperatures to study the effect it has on the activity of the complexes. Temperature was found to not have a significant effect on the conversion. The ruthenium complexes were found to be active towards the transfer hydrogenation of acetophenone but the cobalt complexes were observed to have no catalytic activity in the transfer hydrogenation of acetophenone. The ruthenium complexes were investigated in an ionic liquid – organic biphasic system with the aim of separating the metal complexes in order to reuse the catalysts. Toluene was the organic phase and [BMIM]BF4 was the ionic liquid which afforded a biphasic system. Three cycles were performed and the performance of Ru1 – Ru3 decreased with each cycle but Ru4 behaved differently as the performance increased with each cycle.Item Adsorption studies on supported gold catalysts using temperature programmed desorption (TPD)(Wits University, 2007-06) Linganiso, Linda, ZikhonaItem An invesigation of the physical and chemical changes occuring in a Fischer-Tropsch fixed bed catalyst during hydrocarbon synthesis(1990) Duvenhage, Dawid JakobusDeactivation studies; making use of fixed bed reactors, wet chemical analysis, surface area, pore volume determinations and X-ray diffraction—, scanning electron microscope— and secondary ion mass spectrometry techniques; were performed on a low temperature iron Fischer—Tropsch catalyst. It was revealed that this catalyst is mainly deactivated by sulphur poisoning, oxidation of the catalytic reactive phases, sintering of the iron crystallites and to a lesser extent deactivation through fouling of the catalytic surface by carbonaceous deposits. It was found that the top entry section of the catalyst bed deactivated relatively fast, the bottom exit section also deactivated, but not as fast as the top section The central portion of the catalyst bed was least affected. Sulphur contaminants in the feed gas, even though present in only minute quantities, results in a loss of catalyst performance of the top section of the catalyst bed, while water, produced as a product from the Fischer—Tropsch reaction, oxidized and sintered the catalyst over the bottom section of the catalyst bed.Item Manganese oxide- based gold catalysts for low temperature CO conversion(2015) Padayachee, DiandreeInitial investigations at Mintek, into the addition of gold to commercial hopcalite (CuxMnyOz), showed that it improved the activity of hopcalite. So this study was initially focused on investigating Aulhopcalite catalysts further. Also, since according to literature, MnxOy has catalytic potential, the study of AulMnxOy catalysts was included. Au/hopcalite and Aul/nxOy catalysts were made by means of deposition-precipitation, colloidal gold deposition and co-precipitation. Only one catalyst-type was highly active at room temperature - the co-precipitated Au/MnxOy catalysts. The optimised co-precipitated Au/MnxOy catalysts were more active than all the other catalysts by at least an order of magnitude. So the study focus changed, to make the optimisation of AulMnxOy catalysts a priority. Cerium is a well-known promoter on MnxOy catalysts, and so was also added to the co-precipitated Au/MnxOy catalysts. However, even small amounts of cerium had an adverse effect on the catalysts' activities. The compaction and crushing of a co-precipitated Au/MnxOy catalyst to obtain granules of larger particle size than the powders, was also carried out. The activities and surface areas of the catalysts were found to be comparable. This augers well for industrial purposes, since the use of powdered catalysts in industry is not viable.Item The effect of microwave heating on manganese promoted iron based Fischer-Tropsch catalysts(2012-01-18) Mohiuddin, EbrahimA study was performed in order to investigate the effect of preparation method and the effect of microwave heating on a manganese promoted iron based Fischer-Tropsch catalyst. The effects of preparation method and microwave heating on the structure and morphology of the catalyst, its surface area and reduction behavior were investigated using various techniques such as Transmission electron microscopy (TEM), Powder x-ray diffraction (PXRD), surface area measurements (BET) and temperature programmed reduction (TPR). The FTS performance of the catalysts were also studied using a fixed bed reactor with Fischer-Tropsch Synthesis conditions (270 C, flow rate of 30 ml/min, H2/CO ratio = 2, pressure of 10 bar). Characterization of the catalysts calcined at 350 C revealed that manganese enriched the surface of impregnated Mn/Fe catalysts and suppressed the reduction of the iron catalyst. However, the Mn acted as a structural promoter in the co-precipitated catalysts and also promoted the reduction of Fe2O3 as the manganese content increased. The co-precipitated catalyst calcined at 650 C suppressed the reduction of iron. The impregnated catalysts showed similar conversion (~ 70%) for catalysts with Mn loadings 5%, 10% and 20%. This suggests Mn promotes the activity of the iron catalyst since less iron is present in the catalyst as the manganese loading is increased. The co-precipitated catalysts showed a 10 wt% Mn loading to be the optimum amount for increased activity and selectivity to C2 – C4 hydrocarbons, lower molecular weight olefins and a lower selectivity to heavier molecular weight hydrocarbons relative to Mn loadings of 5, 20 and 50 wt%. Mn loadings in excess of 10 wt% showed a slight increase in selectivity to heavier weight hydrocarbons. The impregnated catalysts showed very little difference in activity and selectivity but the co-precipitated catalyst showed a decrease in activity after the catalyst was microwave heated. A slight increase in selectivity to lower weight olefins and heavier molecular weight hydrocarbons was noted after microwave heating. The TPSR (Temperature programmed surface reaction) results revealed that this may be due to the stronger adsorption of CO on the surface of the catalyst after microwave heating. A similar trend was observed for catalysts promoted with 0.1 wt% potassium i.e. a slight increase in selectivity to heavier weight hydrocarbons after microwave heating.