3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Assessment of BTEX concentrations on-board in-service public buses in Johannesburg, South Africa(2019-07) Mansoor, YusufExposures to BTEX compounds in indoor environments are of great concern as these compounds have been shown to negatively influence human health. For urban dwellers, a major part of the day is spent indoors within microenvironments such as offices, schools, homes and while commuting on-board vehicles. Of the different types of microenvironments, vehicle cabins have been shown to have the highest BTEX concentrations due to the vehicle being a source of emissions itself and due to its close proximity to other sources of emissions. This study specifically considers BTEX concentrations on-board public buses as these vehicles transport large numbers of people over various distances and that commuters frequently spend a considerable amounts of time commuting on-board these vehicles daily. The aim of this study was to determine the BTEX concentrations on-board in-service public buses travelling along major routes through Johannesburg during the off-peak and peak times and to determine the factors which might affect these concentrations. The factors which were specifically taken into consideration were on-board temperature and humidity, ventilation mode, passenger number and the characteristics of the travelled routes. Two sampling campaigns were conducted; one during the off-peak and another during the peak commute times. For each campaign, buses travelling along three different routes, representing major commuter routes, were sampled. A total of 21 and 42 samples were collected on-board the buses for the off-peak and peak campaign, respectively. An active sampling approach was taken using personal air sampling pumps attached to coconut charcoal sorbent tubes. iButtons were used to collect on-board temperature and humidity and a GPS was used to collect the route data. The charcoal tubes were prepared using solvent extraction and subsequently analysed using gas chromatography (time – of – flight) mass spectrometry. In addition, field blanks, lab and solvent blank samples were analysed as quality assurance measures during both campaigns. The mean BTEX concentrations measured during the off-peak and peak campaigns were Benzene - 24.39 μ/m3, Toluene - 85.88 μ/m3, Ethylbenzene - 4.80 μ/m3 and Xylene - 5.70 μ/m3 and Benzene- 28.19 μ/m3, Toluene - 9.85 μ/m3, Ethylbenzene - 2.94 μ/m3 and Xylene - 7.5 μ/m3, respectively. A significant difference (p > 0.05) was noted between the off-peak and peak toluene concentrations, while no significant differences were observed amongst the other BEX compounds between campaigns. The analysis of the BTEX concentrations along travelled routes returned a result indicating no significant differences (p < 0.05) between sampled routes for both campaigns; except for the ethylbenzene measured during the off-peak campaign which showed a significant difference (p < 0.05) between Routes A and C. With regards to the effects of ventilation mode, passenger number and on-board temperature and humidity, no discernible effects on BTEX concentrations could be observed from the data. Furthermore, the lab and field blank samples measured varied levels of BTEX concentration, which would suggest sample contamination, which introduced a level of uncertainty in deriving actual BTEX concentrations. In general, no definitive conclusions could be drawn from this study, regarding the BTEX concentrations on-board the buses during the off-peak and peak times, effects of travelled routes, passenger number and ventilation mode, potential sources of BTEX compounds and their interaction with the on-board temperature and humidity. However, given that a study of this nature has not been published in South Africa; the current study is of value in guiding future researchers as to the potential challenges and barriers that might be faced when conducting such a study. Furthermore, this study has the potential to stimulate interest in the field of in-vehicle emission testing with regards to not only buses and VOCs but other pollutants such as NOx, PM, and CO amongst a variety of vehicle types and across other microenvironments in general.Item Assessment of asphaltene stability at different temperatures using salicylic and iso-phthalic acids as inhibitors(2019) Agostinho, Luisa TuairaDuring crude oil production, processing, transportation and storage, the change in temperature, pressure and fluid composition can lead to the instability of asphaltene in the system. The posterior deposition of asphaltene can clog or completely close the production, processing, and transportation facilities, thus decreasing production and increasing maintenance costs. A cost-saving manner to prevent this problem is the use of processes such as addition of chemicals inhibitors, which prevent asphaltene precipitation. In this project, several experiments were performed to assess the stability of asphaltene in crude oil varying parameters as temperature, precipitant amount, inhibitors concentrations and time. The asphaltene behaviour and the reduction of the precipitated particles size in crude oil samples were controlled using an optical microscope. In order to propose a preventive method for the asphaltene deposition, different amount of Salicylic and Iso-Phthalic acids as asphaltene inhibitors and n-heptane as asphaltene precipitant agent were added at 35 ºC, 65 ºC, and 80 ºC. The results showed that the sizes of the asphaltene particles were reduced with increase in temperature. At almost room temperature such as 35 ºC, the inhibition of Salicylic acid was better for lower concentration (15%). While at higher temperature such as 65 ºC and 80 ºC, the best inhibition concentration for Salicylic acid was 25%. For Iso-Phathalic acid, at 35 ºC it was found that 25% was the best concentration, at 65 ºC, 20% was the best concentration, and at 80 ºC, small concentration of 2.5 % was sufficient to inhibite asphaltene in the crude oil. The precipitant agent n-heptane had an effect on the size of asphaltene aggregates. A minimum of 2 ml n-heptane was able to initiate the precipitation process at various temperatures (35 ºC, 65 ºC and 80 ºC). An increase in precipitant agent amount such as 3.5 ml increased the aggregates particle sizes. It was concluded that asphaltene is more stable at 80 ºC for Salicylic acid, showing the best inhibition capacity at this temperature, when compared to Iso-Phthalic acid which showed the best inhibition capacity at 65 ºC, for both inibitors asphaltene showed to be more instable at 35 ºC. The inhibition profile of Salicylic acid showed less variation with temperature than the inhibition of Iso-Phathalic acid.Item Assessing solvents effect for mitigation of asphaltene precipitation in South African Oilfields(2018) Saide, Alda Brigida JoaquimAsphaltenes molecules is one of the heaviest components in petroleum fractions that under reservoir conditions can be found either in colloidal form or dissolved in crude oil liquid phase. However, when variation in thermodynamic parameters such as temperature, pressure and fluid composition occur can lead to asphaltene precipitation phenomenon and posterior asphaltene deposition in oil wells, pipelines and processing facilities consequently, resulting in several damages along the petroleum chain as well as economical loss for oil and gas companies. Therefore, several studies have been developed to understand this phenomenon and eventually help to monitor and prevent its occurrence. In relation to the present work, an experimental study will be developed in the crude oil samples of one of the South African oilfields to evaluate the effectiveness of different concentrations of two solvents (Salicylic acid and Iso- phthalic acid) in the asphaltene precipitation onset time when variation in temperature and fluid composition occur. This procedure combined with laboratory experiments have helped to define a solvent with great inhibitor capability to prevent asphaltene precipitation in this field and also, estimate the solvent inhibitor concentration and quantity to be used. The results obtained in this study could thus allow the building of a clear picture about probable situations and/or stages to intervene for mitigation of asphaltene precipitation in South African oilfields.Item Investigation of the use of nanomaterial surfactants for oil emulsion drilling muds for deep-hole conditions(2018) Kgwete, Maele NomaThe challenges faced by recovery methods for the extraction of oil and gas from reservoirs are related to existing drilling operations. Consequently, the muds become susceptible to poor heat transfer, disintegration, gelation, pipe sticking, poor cleaning ability, and poor lubrication. The challenges in drilling operations at high temperature and high pressure (HTHP) conditions can be mitigated when rheological properties are controlled and monitored. This research focusses on the investigation of the use of nanomaterial surfactants for oil emulsion (OBM) drilling muds in order to address the challenges in HTHP conditions. Emulsion drilling fluids with and without nanoparticle were prepared. ZnO nanoparticle was selected for this research based on its unique thermal stability properties. The drilling fluid package comprised 100 g of distilled water, 1 wt% of NaCl, 1 wt.% of CaCl2, various amount of surfactant (Triton® X-100 or DTAB) and + 6 wt.% of bentonite. The surfactant concentration varied from 0.25 to 1.25 % with 0.25 intervals. To evaluate and compare the contributions of surfactants and nanomaterial, the prepared drilling fluids were subject to rheological and filtration test. The results showed that DTAB surfactants-based drilling mud with ZnO nanoparticle showed a more stability compared to Triton. The decrease in viscosity with DTAB did not have a significant impact of the filtration loss in the presence of ZnO nanoparticles. The drilling fluids showed a dilatant and shear thickening behavior. The filtration test showed that 1 % of surfactant loss minimal amount of fluid and ZnO nanoparticle reduced the fluid lost capacity. The emulsion contained DTAB as surfactant and ZnO nanoparticle performs better in terms of retaining water and/or liquid in the mud; therefore, making it suitable for drilling at HTHP conditions.Item Experimental assessment of heavy crude oil production using emulsion flooding(2017) Sehlake, Portia BoitumeloIn many crude oil exploitation oil cannot be produced using its own natural drive after many years due to pressure depletion. In order to maintain the reservoir pressure and optimize the oil production, secondary oil recovery methods are usually used i.e. water injection, gas lift and reinjection of natural gas. Although, secondary oil recovery methods increase hydrocarbon production by about 35 - 45 %, they do not provide a definitive solution due to continuous pressure decrease and the excessive amount of water required. An alternative recovery technique known as tertiary recovery or enhanced oil recovery is usually used at this stage and focuses on increasing the mobility of the oil. Chemicals such as surfactants, polymers and nanoparticles are injected to improve recovery. These chemicals help improve properties of the injected fluid and its interactions with the rocks. Surfactants are well known for reducing interfacial tension formed between oil and water and polymers for improving sweep efficiency. Moreover, addition of nanoparticle is said to further reduce interfacial tension between water and oil and help reduce the capillary pressure. This study looked at emulsion stability of crude oil with cationic surfactants and non-ionic surfactants. The objective was to analyse how stable the solution with surfactants only is and also how the stability is affected by temperatures, nanoparticles and stirring mechanism. It further investigates which surfactant type is best suitable to stabilise emulsions and whether or not the combination of surfactant and nanoparticle can provide a more stable emulsion than surfactants only In the study, experiments were conducted to test emulsion stability based on temperature variation, water to oil ratios differences and droplet size formation. Cationic dodecyl trimethyl ammonium bromide (DTAB) and non-ionic Triton®X-100 surfactants were used; nanoparticle zinc oxide (ZnO) was later added into the two types of surfactants aqueous solutions and emulsion stability tests conducted. Temperature was raised from 250C to 60C to look at the effect this will have on emulsion stability. Water/ Oil ratios were analyse the effect/impact the different ratios had on emulsion stability. Droplet size distribution was analysed using a microscope to see how tight the emulsions are. The experimental results suggest that cationic DTAB is not a good candidate for emulsion stability especially at 600C. The potential application of non-ionic surfactant Triton®X-100 alone gave better stability. Addition of nanoparticle ZnO to DTAB did not help stability and when ZnO is added to non-ionic surfactant Triton®X-100 the stability was good at all temperatures but did not last for a longer periods vs having non-ionic surfactant Triton®X-100 only , suggesting that Triton®X-100 is best suitable to keep emulsions formed stable and further microscopic work supported this finding.