Biofuels are becoming more attractive worldwide because of the high energy demands and the fossil fuel resources that are being depleted. Biodiesel is one of the most attractive alternative energy sources to petroleum diesel fuel and it is renewable, non toxic, biodegradable, has low sulphur content and has a high flash point. Biodiesel can be generated from domestic natural resources such as coconuts, rapeseeds, soybeans, sunflower, and waste cooking oil through a commonly used method called transesterification. Transesterification is a reaction whereby oil (e.g. sunflower oil) or fats react with alcohol (e.g. methanol) with or without the presence of a catalyst (e.g. potassium hydroxide) to form fatty acid alkyl esters (biodiesel) and glycerol. The high-energy input for biodiesel production remains a concern for the competitive production of bio-based transportation fuels. However, microwave radiation is a method that can be used in the production of biodiesel to reduce the reaction time as well as to improve product yields. Sunflower oil is one of the biodiesel feedstocks that are used in South Africa and is widely used in cooking and for frying purposes. This study aims to use microwave irradiation to reduce the energy input for biodiesel production. The effect of various reaction variables, including reaction time (10 – 60 seconds), microwave power (300 – 900 watts), catalyst (potassium hydroxide) loading (0.5 – 1.5 wt%) and methanol to oil molar ratio (1:3 – 1:9) on the yield of fatty acid methyl ester (biodiesel) was investigated. The quality of biodiesel produced was analysed by Gas Chromatography (GC), Fourier Transform Infrared Spectroscopy (FTIR) and viscometry. The FTIR results confirmed the presence of functional groups of the FAME produced during transesterification. The results showed that transesterification can proceed much faster under microwave irradiation than when using traditional heating methods. The interaction between the alcohol and oil molecules is significantly improved, leading to shorter reaction times (seconds instead of hours) and improved diesel yields. The highest biodiesel yield obtained was 98% at 1:6 oil-to-methanol molar ratio for both 1 wt% and 1.5 wt% potassium hydroxide (KOH) at a reduced reaction time (30 seconds). The chemical composition of FAME (biodiesel) obtained from different conditions i contained palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1) and 70% linoleic acid (C18:2). The physical properties (cetane number, viscosity, density and FAME content) of biodiesel produced met the SANS 1935 specification. The energy consumption was reduced from 1.2 kWh with the traditional transesterification to 0.0067 kWh with the microwave transesterification. Microwave irradiation was shown to be effective in significantly lowering the energy consumption for production of biodiesel with good quality for small scale producers. / Thesis (MSc (Engineering Sciences in Chemical Engineering))--North-West University, Potchefstroom Campus, 2013

Biofuels are becoming more attractive worldwide because of the high energy demands and the fossil fuel resources that are being depleted. Biodiesel is one of the most attractive alternative energy sources to petroleum diesel fuel and it is renewable, non toxic, biodegradable, has low sulphur content and has a high flash point. Biodiesel can be generated from domestic natural resources such as coconuts, rapeseeds, soybeans, sunflower, and waste cooking oil through a commonly used method called transesterification. Transesterification is a reaction whereby oil (e.g. sunflower oil) or fats react with alcohol (e.g. methanol) with or without the presence of a catalyst (e.g. potassium hydroxide) to form fatty acid alkyl esters (biodiesel) and glycerol. The high-energy input for biodiesel production remains a concern for the competitive production of bio-based transportation fuels. However, microwave radiation is a method that can be used in the production of biodiesel to reduce the reaction time as well as to improve product yields. Sunflower oil is one of the biodiesel feedstocks that are used in South Africa and is widely used in cooking and for frying purposes. This study aims to use microwave irradiation to reduce the energy input for biodiesel production. The effect of various reaction variables, including reaction time (10 – 60 seconds), microwave power (300 – 900 watts), catalyst (potassium hydroxide) loading (0.5 – 1.5 wt%) and methanol to oil molar ratio (1:3 – 1:9) on the yield of fatty acid methyl ester (biodiesel) was investigated. The quality of biodiesel produced was analysed by Gas Chromatography (GC), Fourier Transform Infrared Spectroscopy (FTIR) and viscometry. The FTIR results confirmed the presence of functional groups of the FAME produced during transesterification. The results showed that transesterification can proceed much faster under microwave irradiation than when using traditional heating methods. The interaction between the alcohol and oil molecules is significantly improved, leading to shorter reaction times (seconds instead of hours) and improved diesel yields. The highest biodiesel yield obtained was 98% at 1:6 oil-to-methanol molar ratio for both 1 wt% and 1.5 wt% potassium hydroxide (KOH) at a reduced reaction time (30 seconds). The chemical composition of FAME (biodiesel) obtained from different conditions i contained palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1) and 70% linoleic acid (C18:2). The physical properties (cetane number, viscosity, density and FAME content) of biodiesel produced met the SANS 1935 specification. The energy consumption was reduced from 1.2 kWh with the traditional transesterification to 0.0067 kWh with the microwave transesterification. Microwave irradiation was shown to be effective in significantly lowering the energy consumption for production of biodiesel with good quality for small scale producers. / Thesis (MSc (Engineering Sciences in Chemical Engineering))--North-West University, Potchefstroom Campus, 2013

The damage clusters produced by low dose, 80 keV Ni⁺ and W⁺ heavy-ion bombardment of pure nickel; of two nichrome alloys (with 8% and 17%Cr); and of a ternary alloy and 321 stainless steel which have the same base composition (Fe/Ni10%/Cr17%) have been studied by means of transmission electron microscopy. In all cases where the defects could be identified with confidence they were found to be vacancy in nature. Most of the defects were identified as Frank loops, some of which had partially dissociated. The number of loops that were identified as dissociated and the average degree of dissociation were dependent on the stacking fault energy γ, being greater in the low-γ ternary alloy and the stainless steel than in the high-γ nickel and nichrome alloys. In the high-y materials a small proportion (< 5%) of perfect loops was also observed. Defect yield values were between a factor of 2 and 5 higher for W⁺ ion bombardment than for the corresponding Ni⁺ ion irradiations, but the effect on the mean defect size and cascade efficiency was much less pronounced. In the case of the Ni⁺ ion bombardment, the defect yields in the two nichrome alloys were lower than in pure Ni. No such effect was observed for the W⁺ ion irradiations, when defect yield and cascade efficiency values very similar to those of pure nickel were obtained. The defect yield in the W⁺ ion irradiated ternary alloy was considerbly smaller than in the nichrome alloys and there was a further major decrease in the stainless steel. These reductions in defect yields were not accompanied by a change in the mean defect size nor in the distribution of the defect sizes which were very similar in all the materials for irradiation by a given ion species. The defect yield in W⁺ ion irradiated Ni remained constant with increasing irradiation temperature up to ~450°C and then decreased sharply at higher irradiation temperatures. The defect yield in W⁺ ion irradiated Ni/Cr17% remained constant up to at least 500°C. Possible physical explanations for these results are discussed.

Mushrooms are one of the protein rich foods, however they have a short pro-harvest life (2 to 3 days) compared to most vegetables. The aim of this study was to evaluate whether applying an anti-browning solution using vacuum impregnation and then electron beam irradiation can be used to extend the shelf life of fresh-cut mushrooms (Agaricus bisporus). Solutions made with (a) 2% ascorbic acid + 1% calcium lactate, (b) 2% citric acid + 1% calcium lactate, (c) 1% chitosan + 1% calcium lactate, and (d) 1% calcium lactate were used to impregnate mushroom slices at different vacuum pressures, vacuum pressure times, and atmospheric restoration times. Mushrooms were also irradiated at a dose of 1 kGy using a 1.35 MeV e-beam accelerator and their quality was evaluated in terms of color, texture, and microbial growth during 15 days storage at 4 degrees C. The best vacuum impregnation treatment was the 2% ascorbic acid and 1% calcium lactate solution using a vacuum pressure of 50 mmHg for 5 minutes and an atmospheric restoration time of 5 minutes. The control (not treated) and impregnated samples lost their structure (softening) during storage. The irradiated samples lost their firmness by day 4 of storage. The addition of calcium lactate to the samples during the treatment helped to keep the product’s texture during the 15 days storage time. Color of the mushrooms changed during storage for all the control and impregnated samples and only the irradiated samples showed an acceptable color by the end of day 15. Aerobics and psychrotrophics counts were significantly reduced by irradiation; while yeast and molds population increased by day 9 and were not completely inactivated with a dose of 1 kGy. Sensory panelists preferred the treated samples over the controls. The best treatment was the combination of vacuum impregnation with irradiation according to the consumer studies.

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Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 247-269.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 106-124). Also available in electronic version. Access restricted to campus users.