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1
Quantrille, Thomas E. "Prolog and artificial intelligence in chemical engineering." Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-06062008-170029/.
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Hashemi, Fardad Ali 1976. "Design of a precision chemical mechanical planarization research system." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89285.
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Shaw, Rebecca Custis Riehl. "Combining combustion simulations with complex chemical kinetics." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648248.
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Rock, Reza M. "An Imaging Ammeter for High Throughput Electrochemical Research." Research Showcase @ CMU, 2013. http://repository.cmu.edu/dissertations/235.
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Rapid testing of electrocatalysts and corrosion resistant alloys accelerates discovery of promising new materials. Imaging amperometry, based on the deployment of colloidal particles as probes of the local current density, allows simultaneous electrochemical characterization of the entire composition space represented in a thin-film alloy "library" electrode. Previous work has shown that nanometer scale variations in particle-electrode distance for single particles in electric fields can be measured optically and translated into local current density, independent of electrical measurements. Implementation of this method to enable simultaneous measurements across non-uniform samples involves using a sparse, uniform layer of particles, which requires modification of previously existing theory and methods. Imaging individual particles for this application is infeasible at the low magnification levels needed to image an entire macroscopic (~1 square cm) sample. Mapping of electrochemical activity across the surface can be achieved nevertheless by imaging the entire electrode surface and gridding the resulting images into a mosaic of square “patch” areas 100 μm to a side, each containing 15-30 particles. The work presented in this dissertation shows that the integrated light intensity in each patch is the sum of the light scattering from all of the particles present in that patch, and that this total measured intensity can be used to infer the current density in the patch during electrochemical experiments.
In addition to scaling the imaging ammeter up to ensembles of particles, the theory for translating measured particle motion to current density has been substantially improved. These improvements involve proper modeling of the current distribution on the electrode below the particles, which has a profound impact on the forces acting on each particle. This work demonstrates that the use of realistic kinetic models for the imaging ammeter is both vital and a discovered opportunity to increase its sensitivity. Finite element analysis was used to explore the variable space of the parameters involved, to better understand the impact of factors such as the current density and solution conductivity on the motion of the particles. Going forward, this information will be leveraged to improve the accuracy of the macroscopic imaging ammeter.
To complete the groundwork for the imaging ammeter laid out in this thesis, proof of concept experiments using a nickel/iron composition spread alloy film were performed. In a 1×5 mm2 area containing alloy compositions from 20% iron to 100% iron, expected trends in electrochemical activity were observed during experiments, i.e. the current density as a function of voltage increased with increasing nickel content on the electrode surface. Future work will probe Fe/Ni alloy compositions with less iron, subsequently moving on to other binary and eventually ternary alloy systems.
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Man, Peter Lau Weilen. "Statistical methods for computing sensitivities and parameter estimates of population balance models." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608291.
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Jin, Xiaoxia. "Investigation of Intrinsic Cell Magnetophoresis for Label-Less Cell Separation and Analysis and the Optimization of the CTV Instrumentation for Such Studies." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1268002273.
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Xalabile, Philasande. "Development of bimetallic Pd-Zn catalysts for methanol steam reforming: hydrogen production for fuel cells." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24325.
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Proton exchange membrane fuel cell (PEMFC) has been reported as clean and efficient energy technology from conversion of H₂. However, one of the main challenges remains the storage and transport of hydrogen. The promising alternative is to produce H₂ on site by a reformer using a H₂-dense liquid as a fuel, a technology known as fuel processing. Methanol is an attractive source of H₂ compared to other fuels as it presents several advantages, i.e. it is obtained sulphur-free, has a high H to C ratio and therefore produces a H₂-rich reformate, can be reformed at low temperatures (200 - 300°C) and is a liquid at ambient conditions so that it can be easily handled. Typically, Cu-based catalysts are used for steam reforming of methanol due to their high activity (i.e. H₂ production) and high selectivity towards CO₂. As CO poisons anodic catalyst of PEMFC, high selectivity towards CO₂ is crucial so as to eliminate or at least minimize CO removal load downstream a fuel processor. However, Cubased catalysts are thermally unstable and suffer deactivation due to sintering at high temperatures (> 250°C). Moreover, Cu-based catalysts are pyrophoric and therefore difficult to handle. Recent studies show that PdZn catalysts are very promising as they exhibit comparable activity and selectivity to Cu-based ones. Furthermore, PdZn catalysts are thermally stable in the typically methanol steam reforming temperature range (200 - 300°C). Most literature attributes high CO₂ selectivity of PdZn catalysts to formation of PdZn alloy. It is generally agreed that PdZn alloy is formed when PdZn catalysts are reduced in H₂ at high temperatures (> 250°C). In this work, a Pd/ZnO catalyst aimed at 2.5 wt% Pd was successfully prepared via incipient wetness impregnation and the duplicate preparation of the catalyst was successful. Both impregnation catalysts were confirmed by ICP-OES to contain similar weight Pd loadings i.e. 2.8 and 2.7 wt%, respectively. The actual Pd loading (ICP-OES) was slightly higher than the target loading (2.5 wt%) due to Pd content of Pd salt underestimated during catalyst preparation. Furthermore, crystallite size distribution, i.e. PdO crystallites on ZnO support, was similar (i.e. 6.7 ± 2.4 nm and 6.3 ± 1.9 nm) for both impregnation catalysts.
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Khasu, Motlokoa. "In situ study of Co₃O₄ morphology in the CO-PROX reaction." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/24905.
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The preferential oxidation (PROX) reaction is an effective process for the removal of trace amounts of carbon monoxide from a reformate stream. Tricobalt tetraoxide (Co₃O₄) is the candidate for CO-PROX in a H₂ rich gas and could be an alternative to the rare and expensive PGMs. This study investigates the effect of different Co₃O₄ morphologies in the preferential oxidation of carbon monoxide in H₂ rich gas. Reports have shown morphology dependency in CO oxidation in the absence of hydrogen, no study has investigated the morphology dependency in H₂ rich atmospheres. Different morphologies of nanocubes, nanosheets and nanobelts were prepared using hydrothermal mn and precipitation. Conventional spherical nanoparticles from our group were included to compare the activity of conventional nanoparticles with nanoparticles of different morphology. The model catalysts were supported on silica spheres which were also prepared. The CO-PROX experiments were conducted in the in situ UCT-developed magnetometer and PXRD capillary cell instruments by induced reduction at temperatures between 50 and 450°C. Catalyst tests showed two distinct temperature regions with maximum activity. In the range of 150 – 175ᵒC, activity decreased from nanoparticles > amine nanosheets > nanobelts. However, the surface area specific rate of CO₂ formation displayed an inverse trend. In the region of 225 – 250ᵒC, nanocubes > NaOH nanosheet > HCl nanocubes showed maximum activity. The surface area specific rate was the same for amine nanocubes and NaOH nanosheets. None of the model catalysts retained their morphology after the temperature was ramped from 50ᵒC to 450ᵒC, and back to 50ᵒC. The catalysts were partially reduced to metallic Coo (other phase being CoO). Figure 1: In situ PXRD analysis and kinetics of CH4, CO and CO₂ showing the behaviour of Co₃O₄/SiO₂ (amine nanocubes) under CO-PROX conditions
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Jackson, Colleen. "SiC and B₄C as electrocatalyst support materials for low temperature fuel cells." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27313.
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Supported nano-catalyst technologies are key for increasing the catalyst utilisation and achieving economically feasible platinum metal loadings in hydrogen polymer electrolyte fuel cells (PEFCs). High surface area carbons are commonly utilised as support materials for platinum due to low cost, large surface areas and high conductivity. However, PEFCs using this technology undergo oxidation of carbon supports, significantly reducing the lifetime of the fuel cell. In this work, silicon carbide and boron carbide are investigated as alternative catalyst support materials to carbon, for the oxygen reduction reaction for low temperature fuel cells. Electrochemical testing, accelerated degradation studies as well as advanced characterisation techniques were used to clarify the structure-property relationships between catalyst morphology, metal-support interaction, ORR activity and surface adsorption onto the Pt nanoparticles. Extended X-ray Absorption Fine Structure (EXAFS) analysis gave insights into the shape of the clustered nanoparticles while X-ray Photoelectron Spectroscopy (XPS) and in-situ X-ray Absorption Near-Edge Spectroscopy (XANES) analysis provided information into how the metal-support interaction influences surface adsorption of intermediate species. Electronic metal-support interactions between platinum and the carbide supports were observed which influenced the electrochemical characteristics of the catalyst, in some cases increasing the oxygen reduction reaction activity, hydrogen oxidation reaction activity and Pt stability on the surface of the support.
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Chimonyo, Wonder. "An investigation into the relationship between electrochemical properties and flotation of sulphide minerals." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20730.
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There is a growing importance in the mineral processing industry to find ways which are economic and effective in improving the recovery of minerals in the flotation process. The focus of this study was on the recovery by flotation of minerals found in the Merensky reef, which is one of the major reefs in the Bushveld complex. In that reef, base metal sulphide (BMS) minerals are commonly associated with PGMs and this has an effect on the way in which these minerals are concentrated by flotation (Vermaak et al. 2004; Wiese et al. 2005b; Miller et al. 2005; Schouwstra et al. 2000).A major problem in this process has been reported to be losses of valuable minerals (PGMs) associated with the loss of BMS (Wiese et al. 2005b), during flotation. The present investigation has focused on studying the relationship between the flotation of sulphide minerals using xanthates as collectors and the electrochemical properties of the flotation system. It is well known that electrochemical mechanisms in flotation systems have a major influence on flotation since the reactions occurring at the mineral/solution interface are of critical importance in the process (Woods, 1971).The aim of this study was to investigate the extent to which there was a relationship between the electrochemical reactions occurring in this ore which could indicate the effectiveness of the flotation process. The electrochemical reactions were studied by determining the redox potential changes occurring when various changes were made. These were the length of the alkyl chain length of the xanthate collector, changing the pH or using various chemical reagents to change the potential of the system. It was found from the rest potential measurements, that collectors of different chain length have different extents of interaction with mineral surface. A greater interaction, which is indicated by a greater change in the mixed potential after addition of the collector, is considered to be indicative of a greater adsorption of the collector at the mineral surface. It was hypothesized that this stronger adsorption by collectors of longer alkyl chain length would result in improved flotation performance. However, this was not observed to be the case and that was consistent with previous results on the relationship between the recovery of sulphide minerals in the Merensky ore and xanthates of different chain lengths. Thus it was shown that there was no correlation between the interactions between collectors of different alkyl chain lengths as determined through electrochemical studies and the flotation performance of valuable minerals under the tests conditions used.
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Little, Lucy. "The development and demonstration of a practical methodology for fine particle shape characterisation in minerals processing." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22741.
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Due to continually declining ore grades, increasing mineralogical complexity, and increasing metal demand, models for the design and optimisation of minerals processing operations are of critical importance. These models do not currently incorporate particle shape, which, although rarely quantified, is known to affect numerous unit operations. Automated Scanning Electron Microscopy (Auto-SEM-EDS) is a widely used tool for mineralogical analysis. It also provides an opportunity for simple, quantitative and mineral-specific shape characterisation. Existing mineralogical databases could therefore become useful resources to facilitate the incorporation of shape effects in minerals processing models. A robust Auto-SEM-EDS shape characterisation methodology is required to ensure that the particle shape information in these databases is interpreted appropriately. For this work, a novel methodology for Auto-SEM-EDS shape characterisation was developed that is suitable for the analysis of fine particles (<75 μm). This involved testing the response of various shape descriptors to image resolution, and measurement with different devices and image processing routines. The most widely used shape descriptor in minerals processing, circularity, was found to be highly dependent on both image resolution and image processing settings, making it a poor choice for shape characterisation of fine particles. Roundness and aspect ratio were found to be more robust descriptors. However, in the interest of being able to compare particulate shape measurements across different studies, the precise definition of aspect ratio is important as variation in 'length' and 'width' definitions can significantly impact aspect ratio measurements. The possibility that preferential orientation of particles would introduce bias to the 2-D cross-sectional measurements was also addressed through comparison of roundness distributions measured from orthogonal cross-sections of a particulate sample mounted within a block of resin. The excellent repeatability of these measurements indicated that the particles were randomly orientated, and thus it can be inferred that 2-D measurements of a sufficient number of particles will be directly related to the particulate sample's 3-D properties. Roundness and aspect ratio were then used in conjunction to produce surface frequency distributions that allow for distinction between non-rounded particles that were smooth and elongated and non-rounded particles that were neither elongated nor smooth. Three applications of the shape characterisation methodology developed were then demonstrated, which highlighted some of the potential contributions that this methodology can make towards minerals processing. The applications were all based on a case study of the Upper Group 2 (UG2) Chromitite, a platinum group mineral (PGM) ore of key economic significance to South Africa.
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Nyathi, Thulani Mvelo. "Preferential oxidation of carbon monoxide in hydrogen-rich gases over supported cobalt oxide catalysts." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20547.
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The preferential oxidation of CO (CO-PROX) has been identified as one route of further reducing the trace amounts of CO (approx. 0.5 - 1 vol%) in the H2-rich reformate gas after the high- and low-temperature water-gas shift reactions. CO-PROX makes use of air to preferentially oxidise CO to CO₂, reducing the CO content to below 10 ppm while minimising the loss of H₂ to H₂O. In this study, a Co₃O₄/γ-Al₂O₃ model catalyst was investigated as a cheaper alternative to the widely used noble metal-based ones. The CO oxidation reaction in the absence of hydrogen has been reported to be crystallite size-dependent when using Co₃O₄ as the catalyst. However, studies looking at the effect of crystallite size during the CO-PROX reaction are very few. Metal-support interactions also play a significant role on the catalyst's performance. Strong metal-support interactions (SMSI) in Co₃O₄/Al2o₃ catalysts give rise to irreducible cobalt aluminate-like species. Under CO oxidation and CO-PROX reaction conditions, such strong interactions in a similar catalyst can have a negative effect on the performance of Co₃O₄ but can keep its chemical phase intact i.e., help prevent the reduction of the Co₃O₄ phase. The catalysts used to investigate these two effects (i.e., crystallite size and metal-support interactions) were synthesised using the reverse micelle technique from which nanoparticles with a narrow size distribution were obtained. Certain properties of the microemulsions prepared were altered to obtain five catalysts with varying Co₃O₄ crystallite sizes averaging between 3.0 and 15.0 nm. Four other catalysts with different metal-support interactions were also synthesised by altering the method for contacting the support with the cobalt precursor. The crystallite size of Co₃O₄ in these four catalysts was kept in the 3.0 - 5.0 nm size range.
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Mhonde, Ngoni Pepukai. "Investigating collector and depressant performance in the flotation of selected iron ores." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22742.
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As the excessive extraction of high grade iron ore reserves has led to the rapid depletion of these ore bodies, there is a growing need to extract and upgrade low grade iron ores into more economically viable products with an iron content in excess of 50%. The beneficiation of low grade iron ores through the reverse cationic flotation procedure is gradually gaining popularity as a possible processing route of the future for South Africa's iron industry. Reverse cationic flotation employs a reagent suite consisting of an amine compound which functions as a quartz collector in addition to providing the frothing effect in the flotation system, and hydrolysed starch which serves to depress hematite during flotation. The aim of this project was to investigate the effect of using five amine collectors with different molecular structures on the flotation recovery of quartz and the entrainment of hematite in the flotation of a South African iron ore and a Brazilian iron ore. Laboratory batch flotation tests were conducted on both ore samples and the grade and recovery of hematite were recorded. The collectors were characterised through surface tension measurements and pKa value analysis. An attempt at using different polysaccharides as hematite depressants entailed the use of a CMC and a guar gum in batch flotation tests of the Brazilian iron ore.
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Jackson, Colleen. "Preparation and characterisation of Pt-Ru/C catalysts for direct methanol fuel cells." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/24322.
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The direct methanol fuel cell (DMFC) is identified as a promising fuel cell for portable and micro fuel cell applications. One of the major benefits is that methanol is an energy dense, inexpensively manufactured, easily stored and transported, liquid fuel (Hamann et al., 2007). However, the DMFC's current efficiency and power density is much lower than theoretically possible. This inefficiency is predominantly due to the crossover of methanol from the anode to the cathode, Ru dissolution and Ru crossover from the anode to the cathode. In addition, the DMFC has a high manufacturing cost due to expensive catalyst costs and other materials. Catalyst expenses are further increased by catalyst loading due to low activity at the anode of the DMFC (Zhang, 2008). Hence, with increasing activity and stability of the Pt-Ru/C catalyst, catalyst expenditure will decrease due to a decrease in catalyst loading. In addition, performance will increase due to a reduction in ruthenium dissolution and crossover. Therefore, increasing the activity and stability of the Pt-Ru/C catalyst is paramount to improving the current DMFC performance and viability as an alternative energy conversion device. Pt-Ru/C catalyst synthesis method, precursors, reduction time and temperature play a role in the activity for methanol electro-oxidation and stability since these conditions affect structure, morphology and dispersivity of the catalyst (Wang et al., 2005). Metal organic chemical deposition methods have shown promise in improving performance of electro-catalysts (Garcia & Goto, 2003). However, it is necessary to optimise deposition conditions such as deposition time and temperature for Pt(acac)₂ and Ru(acac)₃ precursors. This study focuses on a methodical approach to optimizing the chemical deposition synthesis method for Pt-Ru/C produced from Pt(acac)₂ and Ru(acac)₃ precursors. Organo-metallic chemical vapour deposition (OMCVD) involved the precursor's vapourisation before deposition and a newly developed method which involved the precursors melting before deposition. An investigation was conducted on the effects of precursor's phase before deposition. The second investigation was that of the furnace operating temperature, followed by an exploration of the furnace operating time influence on methanol electro-oxidation, CO tolerance and catalyst stability. Lastly, the exploration of the Pt:Ru metal ratio influence was completed. It was found that the catalyst produced via the liquid phase precursor displayed traits of a high oxide content. This led to an increased activity for methanol electro-oxidation, CO tolerance and catalyst stability despite the OMCVD catalyst producing smaller particles with a higher electrochemically active surface area (ECSA).
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Barkhuizen, David Andrew. "Preparation and water-gas shift performance of zinc oxide supported dispersed gold catalysts." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/22065.
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Includes bibliographical references (pages 99-107).Two deposition-precipitation style methods of preparing zinc oxide supported dispersed gold materials for use as water-gas shift catalysts were examined, with some of the better formulated materials being tested for catalytic activity, and compared to World Gold Council Au/TiO₂ reference material and a commercial copper-based WGS catalyst (Cu/ZnO/AlO₃ - C 18-7 from Sud-Chemie). Materials Synthesis: The classical deposition-precipitation synthesis from the group of Haruta (Tsubota et al., 1995) - where the support is added to a pH adjusted solution of HAuCl₄ and the system aged at constant pH and temperature - was examined, using ZnO as the support. Gold uptake by the support was confirmed to decrease with ageing pH, tending to zero as the IEPS of ZnO (~ 9) is approached. Such behaviour is both qualitatively and quantitatively consistent with theory, which proposes that the magnitude and polarity of the charge on the support surface will determine the effective carrying capacity of that surface for an (an)ionic solution phase gold species. Decreasing post-calcination (120°C) gold crystallite size with increasing ageing pH [as reported by Haruta (1997)] was also observed (figure 11.2) - but it is not clear whether this resulted from pH dependent crystallization dynamics, from crystallite size being simply determined by the amount of deposited gold (which clearly decreases with increasing pH), or from chloride induced sintering during heat treatment (with chloride uptake by the support decreasing with increasing pH [Kung et al., 2003)). Nevertheless, gold deposition at pH 8 produced highly dispersed gold crystallites around 3.5 nm in diameter. It emerged that an inherent trade-off exists with this, the classical depositionprecipitation method, in that acidic ageing pH promotes a high degree of gold uptake by the support, but produces large gold crystallites, and vice versa. To overcome this, a modified method - where HAuCI₄ and the base (ammonium carbonate) were simultaneously added dropwise to a slurry of the support, maintaining a constant pH of 8 (Fu et al., 2003b) - was investigated. This method was attractive because it is claimed to simultaneously achieve total gold uptake and post-calcination Au crystallite size in the range 5 - 6 nm. Since it was not clear from the published description whether a constant pH was maintained across the ageing period (practiced here as MDP1 ), or if the pH was rather allowed to drift (practiced here as MDP2), both alternatives were investigated. When a constant pH was maintained across the ageing period (MDP1 ), gold uptake by the support was found to reach a maximum (of ~ 60 %) when operating at a pH of ~ 8. The degree of gold uptake was found to be independent of both gold loading and support surface area. Furthermore, the degree of gold uptake achieved using this variation was increased to unity by allowing the pH to drift during the ageing period (after being initially held constant at 8 during HAuCI₄ addition) [= MDP2], instead of being maintained at a constant value via addition of nitric acid (as is done in MDP1). In terms of the size of the gold crystallites produced, after calcination in air at 400°C, a mean diameter of 3.8 ± 1.5 nm was observed for a sample 1.9 wt % in Au, increasing slightly with increasing gold loading [to 4.6 ± 1. 7 nm by 5.1 wt %Au].
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Moyo, Thandazile. "An electrochemical and leach study of the oxidative dissolution of chalcopyrite in ammoniacal solutions." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/23468.
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Chalcopyrite is not only the most abundant of the copper sulphides, but also the most stable, making it recalcitrant to hydrometallurgical treatment processes especially in atmospheric leaching. Hence, pyrometallurgical processes are traditionally used to treat chalcopyrite concentrates. However, ore grades are falling and concentration processes are becoming increasingly costly, prompting need to revisit hydrometallurgical treatment processes (especially heap leaching), which are otherwise regarded as relatively economic and environmentally friendly. Key hydrometallurgical processes for chalcopyrite treatment are ferric sulphate, chloride and ammoniacal systems. The ferric sulphate system does not work well under atmospheric conditions, except in combination with thermophilic microorganisms, whereas the chloride system has only recently been evaluated more seriously for heap leach processes. The ammonia system remains relatively unexplored and most studies date back more than 40 years, but the system has considerable potential for further development. Ammonia systems can be effectively used to leach copper from chalcopyrite in the presence of an oxidant. The ammoniacal leaching system is heavily reliant on a good surface mass transfer system, hence it being widely studied in high pressure systems where oxygen was accepted to be the oxidant. Leach reactors were designed to use agitation systems which promote the abrasion of an iron based deposit layer thought to passivate the mineral surface. Most research on the ammonia leaching systems has previously been carried out in controlled or bulk leaching studies and only a few used electrochemical studies. A disconnect exits between the two approaches, resulting in different proposed fundamental reaction mechanisms and kinetic understanding. A fundamental electrochemical and controlled leach study of the oxidative leaching of chalcopyrite in ammoniacal solutions has been undertaken. The study covered the following aspects: a description of the mixed potentials, chemistry and kinetics of the anodic reaction, the cathodic reduction of the oxidants, the formation and effect of surface deposits and lastly a look at how results from electrochemical studies compare to those from the leaching of a similar mineral sample under similar solution conditions. A detailed study of the mixed potentials on a more or less pure chalcopyrite electrode has shown the redox reactions on the surface of the mineral to be controlled by the oxidation of chalcopyrite and reduction of copper(II). The presence of oxygen has been found to have no significant effect on mixed potentials in ammoniacal solutions in the presence of initial copper(II). Constant potential and potentiodynamic studies on the anodic reaction have shown the rate of the anodic reaction to increase with an increase in potential in a standard 1M ammonia/ammonium sulphate solution (which buffers at pH 9.6) in exponential fashion supporting conventional Butler-Volmer behaviour with a anodic transfer coefficient of 0.42 and a rate constant k* CuFeS2 of 0.0431 cms⁻¹. Increasing total ammonia increased the rate of reaction only at low concentrations; at higher concentrations increasing total ammonia had no effect on the anodic reaction. An increase of pH at fixed total ammonia concentration showed an increase in reaction rate, but the effect cannot clearly be discerned from the concomitant shift in relative proportion of free NH₃ and NH₄⁺. Coulometric studies have shown the oxidation reaction to proceed via the formation of a thiosulphate intermediate and this to be a 7-8 electron transfer reaction. A surface deposit layer consisting of iron, oxygen and small quantities of sulphur was formed and the sulphur component of this product layer was seen to be gradually depleted during leaching. Anodic currents were found to gradually decrease with time and this was linked to the growth of the surface deposit layer. However, the surface deposit layer did not passivate the anodic reaction; instead, it was proposed that the surface deposit layer adsorbed copper ions and displayed "ohmic" behaviour. The formation of the surface deposit layer was found to apparently promote the cathodic reduction of copper(II). While reduction of copper(II) was shown to be the primary reduction reaction, the presence of oxygen was seen to promote this reduction reaction through the regeneration of copper(II) in experiments that ran for longer time periods. An apparent accumulation of copper(I) on the mineral surface was seen to adversely affect the rate of the cathodic reaction and thus the overall rate of dissolution. The nature and morphology of the surface layer was found to be significantly influenced by the choice of cation in solution, which was thought to influence primarily the complexation/precipitation of ferric species forming near the surface. The degree of agitation during leach studies influences the rate of leaching due to the fragmentation of surface deposits, which are seen to slow the anodic reaction. A kinetic model has been developed for the anodic and cathodic reactions. This thesis presents significant new findings regarding the role of the copper(I)/copper(II) redox couple on the oxidative leaching of chalcopyrite. It also highlights the potentially limiting role of the cathodic reactions which have frequently been overshadowed by the focus on chalcopyrite oxidation reactions. Furthermore, the growth of a surface inhibiting layer which cannot be removed in heap leach systems due to the lack of mechanical agitation can now potentially be addressed by looking into the complexation and precipitation characteristics of cations in solution for ammoniacal leach systems.
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De, Vries Christian. "Adding ammonia during Fischer-Tropsch Synthesis: Pathways to the formation of N-containing compounds." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25269.
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The Fischer-Tropsch synthesis (FTS) process, better known for its ability to produce synthetic fuel via the hydrogenation of CO, has shown potential to produce valuable chemicals when ammonia is added to the feed. In this work certain aspects of the pathway to the formation of N-containing compounds that form when NH₃ is added during FTS, using mostly iron based catalysts is investigated. In addition, the effect this has on the FTS reaction itself is evaluated. To achieve this goal, both theoretical and experimental techniques are used in this study. The CO adsorption and dissociation reactions are assumed to be important elementary reactions for many proposed FTS pathways. In the theoretical part of this thesis, spin-polarized periodic density functional theory (DFT) calculations are employed to study aspects of the initial stage of the pathway on a model Fe(100) surface. Considering the formation of N-containing hydro- carbons, one would assume that NH₃ initially adsorbs and dissociates on the catalyst surface, which could take place in the presence of CO. The surface chemistry of these adsorbates is well studied both experimentally and theoretically, but their co-existence has not yet been evaluated on model Fe surfaces. Initially a platform is generated by calculating the individual potential energy surfaces (PES) for the decomposition of CO and NH₃ on Fe(100) at a coverage of ϴ = 0.25 ML. These calculations provided the basis for comparing the adsorption and dissoci- ation profiles of CO and NH₃ on the Fe(100) surface via the use of the same computational methodology, and importantly making use of the same exchange correlation functional (RPBE) for both adsorbates. Furthermore, it was desired to evaluate the kinetics and thermodynamics of the NH₃ decomposition on the Fe(100) surface at relevant temperatures and pressures (by combining the DFT results with statistical thermodynamics) to better understand the role of NHₓ surface species involved in the pathway to the formation of the N-containing compounds on a model catalyst surface. The DFT results that are reported for the individual decomposi- tion PES for CO and NH₃ were generally found to be in close agreement with what has been reported in previous DFT studies and deduced experimentally for the relevant adsorption and decomposition pathways. The resulting Gibbs free energies for the PES suggests that NH₂ may be kinetically trapped on the Fe(100) surface at a coverage of ϴ = 0.25 ML and the reaction conditions (T = 523 K and p*NH₃ = 0.2 bar) where NH₃ is co-fed with synthesis gas during FTS. The individual adsorptions of CO and NHₓ (with x = 3, 2, 1, 0) were compared to their coadsorbed states, by calculating the heat of mixing (ΔEmix) and the activation barriers (Eₐ) for CO dissociation in the presence and absence of the NHₓ surface species on the Fe(100) sur- face. Similar to the individual adsorption of NH₃, the 0 K regime inherent to DFT calculations is bridged by calculating the Gibbs free energy of mixing for CO + NH₃ on Fe(100) at higher temperatures. Both repulsive and attractive interaction energies were calculated for the various coadsorbed states (CO + NHₓ on Fe(100)) and similarly some configurations resulted in an energetically favored or unfavored heat of mixing. The activation barrier for CO dissociation was lowered when coadsorbed with NH₃ and NH₂, and raised when coadsorbed with NH and N. With all the coadsorbed structures the CO dissociation reaction became more endothermic. Previous experimental studies have shown a concomitant reduction in oxygenate selectivity with an increase in the selectivity for N-containing compounds, when NH₃ is added during FTS. It is well-known that oxygenates undergo secondary reactions when using iron-based catalysts in FTS. In addition, the catalyst used in aforementioned studies (precipitated Fe/K) are active for the amination reactions of oxygenates. It is therefore hypothesized that some oxygenates pro- duced via the primary FTS pathway are converted to N-containing compounds via a secondary reaction. The experimental part of this thesis is therefore aimed at testing this hypothesis. A base case study included a comparison between a Fe-catalyzed slurry phase FTS reaction and a FTS reaction with all parameters remaining unchanged, except for the addition of 1 vol % NH₃ to the syngas (CO + H₂) feed. The activity (CO and H₂ conversion) data collected did not reveal any appreciable loss in the rate of the FTS reaction when 1 vol % NH₃ was added and steady state was reached (, that is after 48 hours time on stream (TOS)). A slower carburization period was however observed when comparing the CO conversion during the first 24 hours TOS, and further supported by the slow increase in CO₂ selectivity during the same period. The use of two-dimensional gas chromatography (GC × GC-TOF/FID) allowed for the discovery of a formation of a range of secondary and tertiary amines, not reported in previous studies. The expected loss in oxygenate selectivity was observed and further probed by co-feeding 1-octanol with the feed (CO + 2H₂ + 1 vol % NH₃) via a saturator. These results clearly indicated a significant loss in oxygenate formation as a result of secondary conversion to N-containing compounds. Questions regarding the stability of aliphatic nitriles prompted the co-feeding of nonanitrile under similar conditions. The results obtained after co-feeding nonanitrile, sug- gests that nonanitrile is readily converted to secondary and tertiary amines and that the ratios of aliphatic alcohols and nitriles are close to equilibrium. The use of CO₂ as carbon source, the investigation of the product spectrum at higher space velocities and the use of Rh-based catalysts, when NH₃ is added during FTS were included in shorter studies. The combination of these results, adds to the knowledge pool for the case where NH₃ is present in the FTS regime, as a poison or reactant. Additional information regarding the path to the formation of N-containing compounds was obtained via the detailed analysis of the product spectra with two-dimensional gas chromatography and the subsequent co-feeding reactions. The results ob- tained via co-feeding reactions, can be used to devise strategies to increase the selectivity of the desired N-containing compounds.
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Hlabangana, Ntandoyenkosi. "Influence of particle size and morphology of Pt₃Co/C on the oxygen reduction reaction." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24324.
Full textAbstract:
Polymer electrolyte fuel cells have shown great potential in providing clean energy with no emissions. The kinetics of the cathode reaction, i.e. the oxygen reduction reaction (ORR) are sluggish necessitating high loadings of the catalyst metal, i.e. platinum. Platinum is a limited resource and expensive. Its price has been one of the major drawbacks in wide scale commercialisation of fuel cells. In an effort to improve the activity of the catalyst and therefore reduce Pt loadings on the catalyst, Pt can be alloyed with transition metal elements (e.g. Ni, Co and Fe) to form bimetallic catalysts. Alloying has been known to improve the activity and stability of a catalyst for the ORR. The enhanced activity of the alloys originates from the modified electronic structures of the Pt in these alloy catalysts which reduces the adsorption of spectator species therefore increasing the number of active sites for the ORR (Wang et al., 2012 (2)). The aim of this study was to gain a better understanding of the influence of Pt alloy particle size and active surface morphology on the ORR activity. The Pt alloy that was investigated was Pt₃Co/C. The surface morphology was modified by varying the Pt/Pt₃Co loading on a carbon support. The catalysts were prepared using thermally induced chemical deposition. The support used was Vulcan-XC-72R. The effects of varying the metal loadings on the ORR was investigated. The loadings that were investigated were 20, 40, 60 and 80 wt. % Pt and Pt₃Co. The alloy catalysts were subjected to annealing at 900 °C and acid leaching. The catalysts were analysed using electrochemical characterisation techniques such as cyclic voltammetry, CO stripping voltammetry, rotating disk electrode and rotating ring disk electrode. Physical characterisation of the catalysts was also implemented. The techniques used were x-ray diffraction, thermogravimetric analysis and transmission electron microscopy. The Pt particles on the carbon support were found not to agglomerate significantly despite the loading being increased. This trend was also observed for the Pt₃Co/C catalysts even after heat treatment and leaching. The lack of agglomeration was credited to a new reactor system developed in this work. The particle growth increased from low loadings to high loadings for both the Pt/C and Pt₃Co/C catalysts. Particle growth was more significant for the Pt₃Co/C catalysts at high loadings. At lower loadings (20 and 40 wt. %) the particle sizes between the Pt/C and Pt₃Co/C catalysts were comparable despite the Pt₃Co/C catalysts undergoing annealing and leaching. The mass specific activity of the Pt/C catalysts was not improved by alloying with the exception of the 20 wt. % catalyst which saw an enhancement factor of 1.66. The surface specific activity of the Pt/C catalysts was improved significantly with factors of 2.40 and 3.11 being recorded for the 20 and 80 wt. % Pt₃Co/C catalysts respectively. The enhancement factors of the intermediate loadings (40 and 60 wt. %) were lower and fairly similar at 1.30 and 1.35 respectively.
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Soldenhoff, Karin. "The solvent extraction of CU (II) from chloride solutions with certain non-chelating nitrogen donor ligands." Master's thesis, University of Cape Town, 1986. http://hdl.handle.net/11427/16408.
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Summary in English.Bibliography: pages 96-100.
The extraction of copper from chloride solutions with some aliphatic oximes as well as some pyridine carboxylates was studied and the complexes formed in the organic phase identified. The association of octanal oxime in toluene was taken into account in the extraction studies and formation constants for dimers and trimers obtained. Copper (II), Nickel (II) and Cobalt (II) are extracted by a solvating mechanism in which only the neutral MCl2 species is extractable. This reaction is largely independent of pH. Studies were also carried out on the use of the commercial reagent ACORGA CLX-20, for the selective extraction of copper from a synthetic solution simulating leach liquors obtained by ferric chloride leaching of complex sulphide ores. Results show that separation of copper from iron is dependent on the amount of acid and chloride present in the aqueous phase.
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Mohamed, Rhiyaad. "Electrocatalysis of oxide-based materials for the oxygen reduction and evolution reactions." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20983.
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Electrochemical devices, such as fuel cells and electrolysers, are said to be at the forefront of a renewable energy technology revolution centred on hydrogen as an energy carrier. These devices rely on the chemical reactions of oxygen, namely the oxidation of water to evolve oxygen (oxygen evolution reaction, OER) and hydrogen , carried out in electrolyser applications or the reverse reaction, the reduction of oxygen to water (oxygen reduction reaction, ORR) producing electricity in the case of fuel cells . Th e reactions of oxygen are however still hindered by extremely slow reaction kinetics. The resultant low efficiencies and associated high cost of electrocatalysts required hinder the widespread commercial success of these devices. In addition, current state - of - the - art electrocatalyst technologies suffer from severe corrosion during operation, presenting an additional barrier to commercialisation and ultimately delaying the successful implementation of a sustainable hydrogen economy. One primary goal of electrocatalysis research is thus the rational design of new materials with higher efficiencies. The fundamental understanding of the behaviour of the electrocatalyst materials towards these reactions will enable greater strides to be achieved in this area. To date much research has been conducted towards this end, however further progress is still required. This thesis details work towards the understanding of a new generation of electrocatalyst technologies for the OER and ORR. This study particularly explore s the use metal oxide based electrocatalyst materials for the oxygen evolution and reduction r eactions as employed in electrolyser and fuel cell applications respectively. The thesis is divided in two parts focusing individually on the OER and ORR respectively. New theoretical and experimental insight into the understanding of oxide electrocataly sts for the OER are discussed in Part I. Part II explores the ORR by studying metal oxides as both catalysts and catalyst support materials in alkaline and acidic environments respectively. Here the emphasis is placed on activity and durability of oxide ma terials under fuel cell operating conditions. The study confirms the promise of oxide based materials and highlights some of the challenges still present in their development for fuel cell applications. The final chapter presents a summary of the thesis. This study provides important insight and contributes towards the further understanding of the use of metal oxides for the OER and ORR. From this study several interesting and promising results were also obtained which warrant further intensive research and investigation. Directions for future research are discussed. [Please note: the full text of this thesis has been deferred until January 2018]
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Van, Niekerk Wesley. "Investigation into the behaviour of a wash-coated PGM-based catalyst layer onto micro-channel reactors for the steam reforming of methane." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25540.
Full textAbstract:
A wash-coating method which had originally been used for wash-coating a Rh/Al₂O₃ catalyst onto stainless steel micro-channels (MC) for the reforming of propane [24] was tested in the steam reforming of methane. The robustness of this method was unknown and was therefore tested for its possible application in methane steam reforming, which has far harsher reaction conditions. A 1 wt% Rh/Al₂O₃ catalyst was wash-coated onto heat treated MC reactor plates and tested at 700 °C with steam to carbon ratio of 3 at a number of catalyst mass specific space velocities (scc᛫(gcat᛫h)⁻¹). The MC tests yielded conflicting results with some tests having stable catalysts and the majority have unstable catalysts due to poor wash-coat adhesion. The unsuccessful cases were due to a loss of catalyst. The change in catalyst stability was postulated to be the result of the wash-coating suspension size being reduced too much. In the cases where catalyst instability due to poor adhesion and ultimately loss of the catalyst the suspension batch size was reduced such that the surface tension of the viscous suspension now exceeded the intermolecular forces in the liquid. This resulted bubble formation and due to the high viscosity of the suspension due to the presence of the polyvinyl alcohol (PVA) binder the bubbles remained during the wash-coating process which is thought to have adversely affected the wash-coats adhesion. Another possible cause which is thought to have amplified the poor adhesion of the unstable catalyst runs is the thermal expansion of the stainless-steel reactor plates. The results of this study could not give outright and straightforward conclusions as to why there were 2 stable runs and unstable runs due to a loss of catalyst. As a result, further work is required to confirm the postulations and trends seen in this study. Future work should concentrate on using a larger batch of suspension to mitigate bubble formation, adding an alumina primer layer before wash-coating the catalyst to aid adhesion through additional oxide bond formation and the use of a more thermally stable stainless steel reactor plate to mitigate thermal expansion.
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Abrahams, Robin Kyle. "A study on the effect of lateral interactions on methanation over Fe(100)." Doctoral thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/27859.
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In this thesis, the lateral interactions involved in conversion of synthesis gas, a mixture of H2 and CO, to methane over Fe(100) and the effect they have on the kinetics of the process is explored. Understanding the methanation of syngas allows for a better understanding of the initial stages of Fischer-Tropsch synthesis. Density functional theory was used to calculate the energies and properties of simple methanation adsorbates on an Fe(100) surface. All of the parameters were tested and optimized in order to find a balance between efficiency and accuracy. A number of configurations were calculated to investigate nearest neighbour and next nearest neighbour interactions. An energetic break down of the lateral interactions is postulated using the components of the Hamiltonian. The charges associated with the different atoms in each configuration were identified using the Mulliken population analysis and the Bader population analysis. These gave insights into configurations which displayed large electrostatic lateral interactions. Lateral interactions were investigated using larger unit cells than typically utilized in molecular modelling up to now (viz. p(4x4) and p(3x2) unit cells) to enable the estimation of nearest neighbour and next nearest neighbour interactions. When using larger p(4x4) unit cells for CO adsorption on Fe(100), the results showed that the heat of adsorption can differ by as much as 0.24 eV at 0.25 ML. It was concluded that lateral interactions are a function of local coverage (i.e. number of nearest and next nearest neighbours) and not necessarily global coverage. Nearest neighbour interactions are typically repulsive and much larger than next nearest neighbour interactions, which varied between repulsive and attractive interactions. While this is not a unique conclusion it did allow for the creation lateral interaction matrices that vary with temperature. The study has shown that lateral interactions can be broken down into kinetic and potential energy and an inverse relationship exists between these component energies. If this relationship is truly understood, then the total energy can be calculated knowing either kinetic or potential energy instead of both. This would then give additional value to well explored electrostatic interaction models. The lateral interactions were empirically related to nearest neighbour and next nearest neighbour interactions. Two kinetic studies were investigated in this thesis and in both cases, mean field approximations and quasi chemical approximation (QCA) were used and compared to incorporate lateral interactions into the kinetics. The mean field approximation over estimates the lateral interactions and considers global coverage while the QCA approximation considers probability of local combinations. The first kinetic study was a simulated CO TPD experiment on Fe(100). The mean field approximation was an improvement on systems which considered no lateral interactions but did not describe all the aspects observed in the experimental TPD. The prediction by the quasi-chemical approximation shows good agreement for the desorption of associatively bound CO. The deviation observed for the dissociatively adsorbed CO is attributed to the presence of alternative pathways for the adsorbed species (specifically the diffusion of oxygen into the lattice of the solid). A microkinetic model for the methanation of syngas over Fe(100) was also created. The results showed that different methods of lateral interaction incorporation resulted in significantly different coverage profiles and reaction energy profiles. Both methods showed a build-up of oxygen on the surface towards the end of the simulation. The build-up of oxygen on the surface of Fe(100) may indicate that iron-based catalysts need to undergo phase changes to complete the catalytic cycle.
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Brown, Darryl Edward. "Kinetic models for the Pt/CeO₂ catalysed water-gas shift reaction." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/27914.
Full textAbstract:
As the global population grows, so does the world's demand for energy. Consequently, there exists an increased interest in the development of fuel cells for power generation due to their low greenhouse gas emissions. For fuel cells to be a successful power source, a reliable hydrogen source is required. Ultimately, the goal is for hydrogen to be supplied from renewable energy technology however, this type of technology is currently not mature enough to meet the continuous demand of the world's energy systems. Producing hydrogen from fossil fuels can be seen as a temporary solution while further advances are made in developing renewable hydrogen infrastructure. A fuel processing train, therefore, remains an important alternative to producing hydrogen. A fuel processing train converts fossil fuels into hydrogen for use in fuel cells and eliminates the need for hydrogen storage as hydrogen is produced on demand. Currently, the water-gas shift (WGS) reactor is one of the largest components in a fuel processing train and thus opportunity exists to reduce the size of this reactor. To design future WGS catalysts and an optimised fuel processor, the reaction kinetics taking place must be understood and quantified. In this study, kinetic measurements were conducted at 2 bar(a) and across a temperature range of 270 - 300 °C using 16 parallel fixed bed reactors (high throughput experimentation) over a 0.5 wt% Pt/CeO₂ catalyst. The feed composition was varied over the ranges 2 - 12 mol% CO, 20 - 45 mol% H₂O, 4 - 15 mol% CO₂ and 25 - 55 mol% H₂. An online micro gas chromatograph (μGC) was used to analyse the dry gas composition. Fitting of experimental data to various kinetic models was accomplished with the gPROMS software package. An initial evaluation of several Langmuir-Hinshelwood (LH) type mechanisms to two data sets obtained from literature was undertaken to evaluate the strengths and weaknesses of different kinetic expressions. The results of the initial evaluation indicate that a dual-site mechanism with an intermediate species results in the best fit for reducible supports, while a single site mechanism offers a better fit for non-reducible supports. For both kinetic models, the formation of the intermediate species is most likely to be the rate determining step. A power-rate law empirical rate expression and a LH type rate expression were both found to predict the WGS outlet composition well within 10 % error at 2bar(a). The apparent activation energy of the reaction was determined to be 110 kJ/mol. This value was confirmed to be constant, throughout the range of conditions evaluated, by means of a classical Arrhenius analysis. Simulations of increasing total system pressure, using both the empirical and "best fitting" LH model, indicate a significant pressure effect for the LH type equation, whereas the power-rate law empirical equation predicts a small, negative effect on the reaction rate with increaseing pressure. Consequently, further experiments were conducted to determine the true effect of pressure. It was found that increasing system pressure increased the WGS reaction rate, which has also been reported by Twigg (1989:288). Only the LH type rate expression was able to predict this. It is therefore recommended that either the power-rate law empirical rate expression or the LH type rate expression be used to predict the WGS outlet composition when operating below 2 bar(a). Furthermore, when predicting reaction rates outside of the window in which the rate equations were derived, it is recommended that the LH model be used as it is expected to give a better prediction as it is based on fundamental steps.
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Matsutsu, Molefi. "DFT insight into the oxygen reduction reaction (ORR) on the Pt₃Co(111) surface." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/22066.
Full textAbstract:
Proton exchange membrane fuel cells (PEMFC) are identified as future energy conversion devices, for application in portable and transportation devices. The preferred catalyst for the PEMFC is a Pt-catalyst. However, due to the slow oxygen reduction reaction (ORR) kinetics, high Pt loadings have to be used. The high Pt loadings lead to high costs of the PEMFC. Pt-Co alloys have been identified as catalysts having higher ORR activity higher than of a Pt-catalyst. Therefore, in the present study, the Density Functional Theory (DFT) technique is used to gain fundamental insight into the ORR on the Pt₃Co(111) surface. The calculations have been performed using the plane wave based code, the Vienna ab-initio Simulation Package (VASP). DFT spin-polarized calculations, utilizing the GGA-PW91 functional, have been used to study the adsorption of the ORR intermediates, viz. O₂, O, OOH, OH, H₂O and HOOH on the Pt₃Co(111) surface. The results obtained on the Pt₃Co(111) surface are compared to the results obtained on the Pt(111) surface. The adsorption strength of the ORR intermediates has been shown to be affected by the presence of Co to varying extents on the Pt₃Co(111) surface relative to adsorption on the Pt(111) surface. The most strongly stabilised ORR intermediate on the Pt₃Co(111) surface relative to adsorption on the Pt(111) surface is O: on the Pt₃Co(111) surface O is 0.45 eV more strongly adsorbed than on the Pt(111) surface. The least affected ORR intermediate is H₂O: H₂O adsorption on the Pt₃Co(111) surface is 0.20 eV more stable than on the Pt(111) surface. The energetically favorable, i.e. most strongly bound adsorption configurations for all the ORR intermediates involves a configuration in which the ORR intermediate is bonded to a surface Co atom. Therefore, the surface Co atom stabilizes the adsorption of the ORR intermediates, relative to adsorption on the Pt(111) surface. Coadsorbed configurations have been used to study the formation and dissociation of the ORR intermediates. From the coadsorption studies, it is shown that there is an energy cost associated with moving the adsorbates from their lowest energy sites, while separately adsorbed, to the higher energy coadsorbed state, prior to reaction. Hence, adsorbate-adsorbate interactions are expected to destabilize the coadsorbed state at the coverages considered in the present study. The Climbing Image Nudged Elastic Band (CI-NEB) method has been used to locate the transition states and to calculate the activation energies of the different elementary reaction steps. The calculated dissociation reaction activation energies for the Pt₃Co(111) surface are found to be lower than the dissociation activation energies calculated on the Pt(111) surface. The most lowered dissociation activation energy is for the dissociation of O₂: on the Pt₃Co(111) surface the activation energy is 0.08 eV, whilst on the Pt(111) surface the activation energy is 0.59 eV. For the hydrogenation reaction steps, only the hydrogenation of O to form OH occurs with a lower activation energy of 0.86 eV on the Pt₃Co(111) surface, compared to 0.95 eV on the Pt(111) surface. For other hydrogenation reaction steps, the activation energies on the Pt₃Co(111) surface are higher than those on the Pt(111) surface. Based on the calculated activation energies of the elementary ORR reaction steps, the dissociative and the O-assisted H₂O dissociation mechanisms are identified as the mechanisms most likely to be dominant on the Pt₃Co(111) surface, due to having lower activation energies relative to the associative mechanisms. For both mechanisms, the reaction step with the highest activation energy is the step involving O, i.e. O hydrogenation to form OH for the dissociative mechanism, and the O* + H₂O* --> 2OH* reaction for the O-assisted H₂O dissociation mechanism. Thus, the reaction step involving the reaction of the strongly adsorbed O species, is identified as the potential rate limiting step of the ORR. Both the dissociative and the O-assisted H₂O dissociation mechanisms are expected to be in competition on the Pt₃Co(111) surface, since the potential rate limiting step for both mechanisms have similar activation energies. Hence, the preferred mechanism will depend on the relative abundances of the H species and H₂O on the Pt₃Co(111) surface. A microkinetic analysis would be need needed to fully account for concentration and entropic contributions to the rate of reaction for the different ORR elementary reaction steps.
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Muketekelwa, Saliya L. "Investigating the potential of using hydrocyclone-fine screen hybrid systems to improve the performance of classification circuits." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27538.
Full textAbstract:
Classification is an integral part of comminution operations that controls the performance of the circuit. Hydrocyclones are normally used to perform the classification function. They offer numerous advantages that include, the ability to handle high throughputs, low floor space occupation and relatively low capital and running costs. Despite these advantages, hydrocyclones are inherently inefficient classifiers as they are predominantly dependent on hydrodynamics to effect separation. This effect is more prominent in operations handling complex ores such as a dual-density ore, where the heavy fine particles are misplaced to the underflow and the lighter middling particles report to the overflow. Several attempts have been made to improve the separation efficiency of cyclones either by modification of the cyclone or use of multi-stage cycloning. Most of the results obtained from experimental and simulation studies have shown considerable improvements. Even though some have not yet found wide application in the minerals industry due to practical limitations related to control and unstable operations. More recently, fine screening has gained recognition in the classification role. This development has allowed the use of fine screens in closed-circuit grinding operations resulting in significant metallurgical and economic benefits. Screens provide a sharper cut at the desired size and reduce the fraction of fines bypassing classification compared to hydrocyclones but have capacity limitations at smaller apertures. In an effort to mitigate the classification challenges of both the hydrocyclone and fine screen, this study investigated the potential of combining the high throughput performance of the hydrocyclone operation and the high precision classification characteristics of fine screening to result in a hybrid classification circuit Plant scale tests were conducted using five different classification circuit configurations at an operational Base Metal Concentrator treating a polymetallic ore. The classification circuit configurations considered included (i) a two-stage hydrocyclone with primary underflow reclassification (ii) an inclined hydrocyclone, (iii) a fine screen and (iv) selected permutations of hybrid circuit designs that included a hydrocyclone-fine screen (2 stage) and two hydrocyclones-fine screen (3 stage) variants of the hybridised configurations. The efficiency curves and their respective key performance indicators were used to assess the performance of the circuit configurations tested. The results showed that classification circuits that included fine screens exhibited higher sharpness of separation compared to circuit configurations comprised of hydrocyclones. The fine screen configuration showed the sharpest separation while the hydrocyclone-fine screen hybrid configurations gave relatively higher separation efficiencies than the configurations with hydrocyclones only. The overall sharpness of separation values obtained for the two stage and three-stage hybrid circuits were 3.0 and 2.4, respectively. The two-stage hydrocyclone and inclined hydrocyclone circuits had sharpness of separation values of 1.7 and 0.5, respectively. The inclined hydrocyclone circuit configuration performed the poorest. Furthermore, the two-stage hybrid circuit showed a higher degree of separation compared to the three-stage hybrid configuration. However, it was observed that a finer corrected cut size was realised for the three-stage hybrid circuit design. The fishhook effect was seen at particle sizes less than 38μm for the configurations incorporating a fine screen and an inclined hydrocyclone. Notably, the effect appeared to be more pronounced in configurations involving a fine screen stage. The results have shown that application of hybrid classification configurations can improve the performance of classification circuits. In addition, reclassification of hydrocyclone underflow on fine screens will results in a sharper classification while reclassifying the overflow stream on fine screens will provide a clean circuit final product. An evaluation of the capital and operating costs associated with fine screens should be done to determine the economic feasibility of incorporating the units in conventional milling circuits.
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Luchters, Niels. "High throughput experimentation: a validation study for use in catalyst development." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/21002.
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High throughput and combinatorial experimentation is becoming more and more used in catalysis research. The benefits of parallel experiments are not only limited to shorten the time - to - market, but also give opportunities to study the process in more depth by performing more experiments. The influence of a parameter, for example the amount of the active metal and/or promoter, to the process is better understood with a broader parameter space investigated. To study the parameter space, multiple experiments need to be performed. It is of paramount importance to understand the variability of the data between these experiments. This is not always defined, specifically when literature gives contradictory results, most often due to the time for duplicate experiments necessary. In this project the reproducibility and variance in high throughput catalyst preparation and testing was determined and the use of parallel experimentation was demonstrated within a catalyst development study. The high throughput equipment was used for catalyst development studies for fuel processing, the production of fuel cell - grade hydrogen from hydrocarbon fuels. Fuel processing consists of three catalytic reactions, namely reforming, water - gas shift and a CO clean - up through either selective methanation or preferential oxidation. Focus has been placed on the first two reactions, steam methane reforming (SMR) and medium temperature water - gas shift (WGS), using platinum group metals (PGM). All catalysts in this study (except for the commercial WGS catalyst) were prepared using automated synthesis robot (Chemspeed ISYNTH) and the activity testing was performed on the Avantium Flowrence. For both reactions two types of studies were performed, one - to - many and many - to - many; referring to one catalyst tested in many reactors or many prepared catalysts (same composition, different batches) tested in many reactors. For the WAGS one - to - many a commercial low temperature shift catalyst was selected and for SMR a single batch of Rh/Al 2 O 3 . The many - to - many experiments comprised of eight batches of prepared catalysts for both reactions. The WGS reaction was performed with 1 wt% Pt/Al 2 O 3 catalysts and for the reforming reaction batches of 0.5 wt% Rh/Al 2 O 3 was used. It was proven that in all these studies the experimental standard deviations in the data is 6%, from preparation to activity measurements. A study on the rhodium metal loading on alumina in the steam methane reforming catalyst was studied between 0.05 and 0.6 wt%. A 0.4 wt% Rh/Al 2 O 3 was found to have the highest activity per amount of rhodium. Lower Rh content would require decreased space velocity, whereas higher metal content does not increase the conversion due to larger crystals sizes. This study has been performed up to a metal loading of 0.6 wt% and it is recommended to follow - up with studying the range of 0.6 to ~2.5 wt% to investigate the optimal metal loading. It was shown that the use of automated experimentation (parallel preparation and evaluation under same condition) for catalyst development results in highly reproducible results with a relative standard deviation of ~6% activity. The high throughput equipment was demonstrate d to be a very powerful tool in catalyst research
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Schnobel, Michael. "Partial oxidation of α-olefins over iron antimony oxide catalysts." Doctoral thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/22449.
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Bibliography: p. 179-188.Iron antimony oxide has been known to be an active and selective catalyst for the partial oxidation of propene to acrolein and the oxidative dehydrogenation of 1-butene to 1,3- butadiene. It has become the preferred catalyst for the industrial acrolein formation from propene. The main purpose of this work was to investigate the influence of catalyst parameters such as calcination temperature, Sb:Fe ratio, type of pre-treatment, absence or presence of gaseous oxygen on the activity and selectivity in the partial oxidation of propene. Furthermore the influence of the reaction parameters temperature, space time, partial pressure, time on stream and the carbon chain length of the olefin have been studied in partial oxidation reactions using a fixed bed U-tube glass reactor. Various models have been tested for the rate of formation of products in the range of C₂ to C₆ α-olefins. Increasing the calcination temperature from 500°C to 900°C resulted in an increase of the crystallite diameter and a simultaneous decrease of the surface area which might be ascribed to high temperature sintering of the catalyst. The activity decreased proportional to the decrease of surface area. At the same time the selectivity to acrolein increased with increasing calcination temperature.
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Van, der Walt Franschua Johan. "Factors influencing the catalytic activity of Fe-ZSM-5 during the catalytic conversion of N₂O." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24323.
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Zeolites have found widespread applications as acid catalysts for decades. By introducing transition metal ions in the cation position, the zeolite is transformed into a redox catalyst. The nature of the trivalent heteroatom influences the properties of the zeolite. Contrary to Al-zeolites, Fe-containing zeolites show redox properties, since Fe can easily change its oxidation state (Fe²⁺, Fe³⁺, or Fe⁴⁺). Catalytic function of isolated redox sites within zeolite cavities (or channels) may result in a material with specific redox properties (Kiwi-Minsker et al., 2003). The properties of transition metal exchanged zeolites have been studied from the 1960's onwards and the conversion of N₂O over Fe-Y zeolites has been studied by Fu et al. (1981) in late 1970's. In this study, the preparation of iron ZSM-5 zeolite catalysts by mechanochemical means and thermally induced solid-state ion exchange was studied. After grinding the NH4-Zeolite and ferrous chloride, no x-ray reflections characteristic of ferrous chloride are detected. After heating the sample to 120 and 200 °C reflections characteristic of ferrous chloride are visible but disappear upon further heating to 300 °C. No porosity is observed after grinding and heating up to 200 °C as a result of pore mouth blocking. Moreover, upon heating up to 500 °C porosity starts to develop with pore volumes and pore sizes slightly lower than those of the parent zeolite. From the thermogravimetric analysis it is evident that the ion exchange takes place during calcination from 150 and 420 °C in agreement with the literature. In the second part of the study commercial Fe-ZSM-5 catalyst samples with different N₂O conversion activities (in the presence of H₂O and NO at 425 °C), ranging between 70 and 90 % (high, mid and low activity) are studied and characterised. The effect of temperature during calcination of the plant produced and laboratory calcined extrudate catalyst material was investigated. Panov et al. (1996) reported in the literature that the Fe²⁺ is oxidised to Fe³⁺ in the presence of N₂O forming what they called the α-oxygen, a form of active surface oxygen, with the evolution of molecular nitrogen. During the conversion, two surface α-oxygen atoms migrate, combine and desorbs as molecular oxygen from the surface. The α-oxygen forms between 200 and 350 °C and desorbs as molecular oxygen above 350 °C (Taboada et al., 2005). In this study, no correlation to N₂O conversion activity could be found for the α-oxygen content and correspondingly the concentrations of the respective iron oxides and iron hydroxides in the Fe-ZSM-5 samples.
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Kumar, Girish. "Cell Engineering: Regulating Cell Behaviors Using Micropatterned Biomaterials." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1225816129.
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Skjellum, Anthony Morari Manfred. "Concurrent dynamic simulation : multicomputer algorithms research applied to ordinary differential-algebraic process systems in chemical engineering /." Diss., Pasadena, Calif. : California Institute of Technology, 1990. http://resolver.caltech.edu/CaltechETD:etd-11132007-090727.
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Kambow, Sumit H. "Characterization of Elastin-like Polypeptide Micelles Using Capillary Viscometry." Cleveland State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=csu1337605892.
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Li, Hang. "Neural Stem/Progenitor Cell 3-D Differentiation for Repair of Central Nervous System Injuries." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1428248647.
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Pattinson, Thomas. "Optimal sysnthesis of storageless batch plants using the Process Intermediate Storage Operational policy." Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-08272008-125107/.
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Owusu, Gyebi Prince. "Investigating the rheological behavior of Witbank coal water mixtures." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20984.
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South Africa has large low-grade coal reserves. With the prospect of expanding its coal demands for exports and power generation, it is important that the beneficiation and transport of coal in the country are economical. The current mode of transporting coal has some drawbacks, which include inefficient rail infrastructure, long distances, and several environmental concerns related to air pollution, water pollution, and traffic risks. It is, therefore, important to investigate efficient means of coal transportation, which will also reduce environmental impacts. The transport of highly concentrated coal-water slurries through pipelines has attracted the attention of many researchers as an efficient and economical means of fine coal utilization. The primary objectives of this study are to investigate the importance of surface charge, solids concentration and particle size on the stability and rheological behaviour of Witbank coal. This work was carried out to arrive at a sounder discernment of the function of dispersion addition on coal-water mixtures rheology and stability.
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Taggart, Diane. "Evaluating the effect of alternative neutralising agent and seeding on the zinc recovery through the Zincor iron removal circuit." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20326.
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Zincor's average zinc recovery was 90.29 % (for the period of 1 January 2009 to 30 September 2011), which was well below the industry standard of 96 %. Due to limitations in Zincor's iron removal technology, the maximum achievable recovery was 94 %. The zinc loss through the iron residue was the second biggest contributor to the overall zinc losses, so that there was much room for improvement. The calcine used for neutralisation in the Iron Removal Stage contained a portion of insoluble zinc ferrite. The insoluble zinc loss through the iron residue was associated with the presence of the insoluble zinc ferrite, as well as the phenomenon of coating of unleached neutralising agent by iron precipitate. The soluble zinc loss was a function of the dewatering characteristics of the precipitate. The work included the evaluation of alternative neutralising agents to supplement or replace calcine, as well as the implementation of a seed recycle. A review of literature found that the use of an alternative neutralising agent that contained little or no zinc could potentially reduce the insoluble portion of the zinc loss. Secondly, the presence of seed could potentially reduce both the soluble and insoluble zinc losses by promoting agglomeration growth and providing additional surface area for precipitation to occur (thereby reducing coating of zinc-rich neutralising agents). The laboratory work evaluated a number of alternative neutralising agents, but focused on the use of DRC oxide and limestone for neutralisation. These were evaluated separately and in combination, with and without a seed recycle.
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Jung, Jangwook Philip. "Engineering Modular Self-Assembling Biomaterials for Multifunctionality." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1291150805.
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Sodunke, Oluyomi. "Polymeric Micellar Network Derived from the Polymerization of Bicontiuous Microemulsion for Oral Drug Delivery Application." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1429738431.
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Bedford, Jordan M. (Jordan Mark). "Optimization of chemical reagent storage and distribution at Novartis Institutes for BioMedical Research." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39557.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering; and, (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; in conjunction with the Leaders for Manufacturing Program at MIT, 2007.Includes bibliographical references (p. 81-82).
The Novartis Institutes for BioMedical Research is the drug discovery arm of Novartis Pharmaceuticals. Drug discovery is generally considered to be the primary driver for success in the pharmaceutical industry. Success in the early stages of drug discovery relies on dependable, innovative, disease related high-throughput screening of biological compounds and the creation of a screening deck of highly diverse, proprietary chemical compounds. In contrast with many of its peers, Novartis relies strongly on combinatorial chemistry to populate its screening deck. The Chemical Libraries (CLI) group is responsible for this approach at Novartis and delivers more than 100,000 compounds per year to the Novartis Compound Archive. Since the introduction of high-throughput screening and combinatorial chemistry techniques, the bottleneck in many drug discovery processes has shifted to the roles that support these high-volume techniques. The aim of this thesis is to provide a general collection of short and long-term suggestions for process improvement in the chemical supply process. This process includes compound search and ordering, order fulfillment, and compound delivery, was investigated.
(cont.) The chemical supply process is responsible for delivering compounds to chemists that would otherwise cost hundreds of dollars per compound with a delay of between one and four weeks, or would require a multiple day synthesis procedure. Stockroom automation, content and process scope, and physical layout were all evaluated. The following major conclusions were developed as a result of the research. First, the procedures for using the compound archives and libraries must be clearly presented to the end user so that s/he is fully able to utilize and contribute to the libraries. Second, compound libraries should be conglomerated into one large library that is also responsible for compound acquisition. Third, compound metering for intermediates does not appear to be an effective use of resources and should be severely restricted following the successful implementation of the SciQuest compound management system. Finally, compound libraries should use automated pick and place systems but metering and dispensing systems should remain manual.
by Jordan M. Bedford.
M.B.A.
S.M.
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Menicucci, Joseph Anthony Jr. "Algal biofilms, microbial fuel cells, and implementation of state-of-the-art research into chemical and biological engineering laboratories." Thesis, Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/menicucci/MenicucciJ0510.pdf.
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Alternative energy technologies become more attractive as the price of energy from fossil fuels becomes more expensive and the environmental concerns from their use mount. While a number of biological alternative energy technologies currently exist, a complete understanding of these technologies has yet to be developed. This dissertation characterizes an aspect of biological alternative energy technologies: the production of algal biofuels and energy conversion in microbial fuel cells. Specifically, this dissertation addresses the characterization of microalgae as a biofilm and the characterization of the power limitations of microbial fuel cells. The attachment and detachment of algae were observed using temporal microscopic imaging in a flow-cell with autofluorescence and staining techniques as part of a collaborative Montana State University and Idaho National Laboratory project. Colonies of algae exhibit many characteristics seen in bacterial biofilms: adherence; detachment and sloughing; difference in structure of an attached colony; varying strength of attachment on different surfaces; association of other organisms in an EPS matrix; and the heterogeneous nature of attached colonies. The characterization of a microbial fuel cell was completed in less than 30 minutes using an empirical procedure to predict the maximum sustainable power that can be generated by a microbial fuel cell over a short period of time. In this procedure, the external resistance was changed incrementally, in steps of 500 ohms every 60 seconds, and the anode potential, the cathode potential, and the cell current were measured. This procedure highlights the inherent limitations of energy conversion in a microbial fuel cell. A voltage/current characterization of the microbial fuel was also completed from the data collected. This dissertation also includes the evaluation of A Hands-On Introduction to Microbial Fuel Cells, a laboratory developed for an introductory chemical and biological engineering course. The experiment has been updated to include a voltage/current characterization of the microbial fuel cell. Learning objectives have been identified and pre- and post-laboratory activities have been developed for further implementation into a chemical and biological engineering curriculum.
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Smith, Meghan Elisabeth. "Biologically Functional Scaffolds for Tissue Engineering and Drug Delivery, Produced through Electrostatic Processing." Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1251224066.
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Thesis(Ph.D.)--Case Western Reserve University, 2010Title from PDF (viewed on 2009-12-30) Department of Chemical Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
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Sun, Xin. "Fundamental research of the solvent role in the ionothermal synthesis of microporous materials." Diss., Kansas State University, 2012. http://hdl.handle.net/2097/13641.
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Doctor of PhilosophyDepartment of Chemical Engineering
Jennifer L. Anthony
Zeolites and zeolite-like materials are a group of porous materials with many applications in industry including but not limited to detergent builders and catalyst in the oil refining and petrochemical industry, due to their unique properties such as uniform pore size, large surface area and ion-exchange capacity. Researchers are constantly seeking new methods to synthesize zeolites. Zeolites are commonly synthesized in water. Then in 2004, a new method called ionothermal synthesis was invented by Dr. Morris and his colleagues, using ionic liquids (ILs) and eutectic mixtures as the solvent. In contrast to water, ILs and eutectic mixtures have negligible vapor pressure, thus making the use of high-pressure vessel unnecessary. In addition, they have various structures which could render new structures to frameworks of zeolite. Furthermore, since the cations of some ILs have structures which are similar to common structure directing agents, they theoretically could be used both as solvent and structure directing agent in ionothermal synthesis, possibly simplifying the synthesis process. This project is aimed at investigating the behavior of precursors of zeolites in ionic liquids and the interaction between precursors and ionic liquids in ionothermal synthesis because these fundamental properties could be useful in the current and future synthesis of zeolites. First, solubilities of different precursors, including Syloid 63 silica particles, aluminium isopropoxide (Al(OiPr)3) and phosphoric acid (H3PO4) in ILs with different structures are reported. Parameters such as activity coefficient and Henry’s constant are calculated from the solubility result. Second, interaction between precursors and ILs are studied. It is found that the addition of ILs in Al(OiPr)3 could change the structure of Al(OiPr)3, especially with the presence of H3PO4. Both ILs’ structures and temperature are capable of influencing the structure change of Al(OiPr)3. Third, hydrochloric acid is used for the first time as the mineralizer to synthesize aluminophosphates in ILs and it could lead to both dense and porous materials. Regardless of the acid used, frameworks synthesized after several hours always undergo a dramatic change after further heating. A slightly longer alkyl chain of ILs could accelerate the formation of crystalline materials. Increasing concentration of precursors in the reaction gel could increase the yield, but the same framework is not retained. Researches have also been done on stability of ILs in the synthesis process and it is found that heat and the presence of H3PO4 could decompose ILs, but the decomposed amount is extremely small.
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Nath, Pulak. "MEMS (Micro-Electro-Mechanical-Systems) Based Microfluidic Platforms for Magnetic Cell Separation." Cleveland State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1210043552.
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Celik, Hakan. "Time and Temperature Dependent Surface Tension Measurements of Responsive Protein-based Polymer Surfactant Solutions." Cleveland State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=csu1440182119.
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Sarsfield, Marissa. "Design of Experiment Approach to the Optimization of Gold Nanoparticle Synthesis on a Microfluidic Mixer Platform." Cleveland State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=csu152826984785663.
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Roham, Masoud. "Wireless Multichannel Microsystems for Time-Share Chemical and Electrical Neural Recording." Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1258145434.
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Thesis(Ph.D.)--Case Western Reserve University, 2010Title from PDF (viewed on 2009-12-30) Department of Electrical Engineering and Computer Science Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
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Akbarzadeh, Rosa. "Developing Hierarchical Polymeric Scaffolds for Bone Tissue Engineering." Miami University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=miami1376962498.
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Guzman, Nicole Denise. "Characterization and miRNA analysis of cancer cell-secreted microvesicles." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338156013.
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Patil, Pritam Suhas Patil. "FLUORINATED METHACRYLAMIDE CHITOSAN FOR OXYGEN DELIVERY INWOUND HEALING AND TISSUE ENGINEERING." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1532775888013965.
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Vidal-Gavilán, Georgina. "Induced biodenitrification of nitrate‐polluted groundwater: engineering strategies and assessment of chemical, microbial and isotope effects." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/284997.
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Nitrate pollution is a widespread problem that affects water bodies in many regions of the world, undermining water quality and therefore its safe use. Despite the application of improved management practices, nitrate pollution seems to increase, particularly in groundwater. The Nitrate Vulnerable Zone (NVZ) designation in Europe, for instance, has increased from 35.5% of the EU-15 territory at the end of 1999 to 44% at the end of 2003, and the Commission’s report for the period 2004-2007 revealed that 15% of groundwater monitoring stations in the EU-27 territory showed nitrate levels above the limit of 50 mg of nitrates per liter. Some trends towards nitrate attenuation are observed, but at least 33% of water bodies will clearly fail in achieving the 2015 goals set by the Water Framework Directive.
Several efforts have been addressed to either reduce nitrogen inputs or to decrease its already accumulated levels, particularly by designing nitrate-removal technologies aimed at recovering drinking-water standards. This PhD thesis, hence, focuses on the optimization of an already existing technology for nitrateremoval: enhanced in situ biodenitrification (EISB), which is now regaining attention due to its economic and environmental benefits and its potential for scale-up and design of casespecific solutions. EISB is an engineered application of microbial heterotrophic denitrification aimed at in situ nitrate removal from groundwater. Aimed at stimulating facultative denitrifiers, EISB is based on the injection of a C source into the aquifer. Microbial denitrification is then enhanced in a designated area of the aquifer, creating a biologically active zone (often referred as biowall) which removes nitrate from the naturally-flowing groundwater.
Among the different factors that affect the technical feasibility of EISB, the type and quantity of the injected C source is a key issue, particularly due to its influence upon the microbial processes that determine the treatment performance. The understanding of the subsurface geology and hydrogeology is also an issue of concern, particularly if highly heterogeneous media, such as fractured aquifers, are meant to be remediated.
Aimed at achieving our research goal, several EISB experiments were developed at different scales -batch, flow-through column and pilot scale-and involving different geological media -granular and fractured-. Combined chemical, microbial and isotope monitoring tools where applied to gain a better insight on the denitrification process and thus improve technology design and optimization.
The first set of batch-scale experiments focused on testing the viability of in situ heterotrophic denitrification and determining the most suitable biostimulants for a casespecific scenario in the Osona region, a Catalan NVZ showing historic nitrate pollution up to 200 mg/L. Native microbiota was stimulated and nitrate reduction was effectively achieved by addition of a carbon source (ethanol or glucose) as well as a phosphorous source (disodium hydrogen phosphate). Transient nitrite accumulation was observed, especially when using glucose as the C source. The N and O isotope fractionation was determined to be -13.0‰ and -17.1‰ for eN and -8.9‰ and -15.1‰ for eO in ethanol and glucose-amended experiments respectively, resulting in eN/eO values of 1.46 (ethanol-amended experiment), and 1.13 (glucose-amended).
Organic carbon (OC) consumption in batchscale experiments, expressed as .C/.NO3 -, varied slightly depending on the type of C source used: 1.6 mmolOC/mmolNO3 -for ethanol and 2.2 for the glucose, similarly to stoichiometric values associated with nitrate respiration (0.83 and 1.25 mmolOC/mmolNO3 respectively). When deriving stoichiometric reactions that accounted not only for the amount of electron donor used for nitrate respiration but also for cell synthesis, the following values were determined: 1.9 and 2.0 mmolOC/mmolNO3 -for ethanol and glucoseinduced biodenitrification respectively. These values were used for the numerical modeling of batch-scale experiments, aimed at quantifying microbial kinetics by applying the modified Monod expression. The (geochemical) numerical model also indicated a different effect of mineral precipitation on ethanol or glucose-induced denitrification, an effect that is linked to a different alkalinity production. Such effect could be taken into account when designing and/or optimizing EISB systems, particularly as a way to control geochemical clogging.
A pilot-scale application was then performed at the site, aimed at assessing the viability of EISB in a fractured aquifer. Ethanol was now used as the main C source, and based on labscale results, P was also added. Again, transient nitrite accumulation was detected, and evidences for incomplete denitrification and coexistence of other respiration processes (such as iron or sulfate reduction) and autotrophic denitrification were observed. Sulfate isotope characterization proved that autotrophic denitrification linked to sulfide oxidation could be occurring along with heterotrophic denitrification, while sulfatereduction couldn’t be verified.
Overall, results suggested that stimulated heterotrophic denitrification could be applied as a remedial alternative in a fractured media and despite the complexity of the formation. However, a deep understanding of the system is required and efforts must be addressed to control microbial population and stability as a key issue to avoid the decrease of groundwater quality due to incomplete denitrification or secondary respiratory processes. Different engineering approaches such as feeding or pumping strategies could help improving the system performance.
Aimed at testing the impact of such engineering approaches upon resulting water quality, a second study-case was studied, now in an alluvial media. . A flow-through experiment was built to simulate an EISB system and assess the influence of different C addition strategies upon the denitrification process. Heterotrophic denitrification was stimulated by the periodic addition of a C source (ethanol), and 4 different addition strategies were evaluated, being the first-one a weekly injection, and the others a daily injection with decreasing amounts of C.
Enhanced denitrification was stimulated following the first C addition, easily achieving drinking water standards for both nitrate and nitrite. Water quality in terms of remaining C, denitrification intermediates and other anaerobic respiration products varied during the experimental time. Ethanol, for instance, showed a cyclic behavior during the weekly feeding strategy while it was completely depleted when injected daily. A quasi steadystate nitrate outflow, similar to ethanol’s, was obtained in daily injection scenarios, with nitrate levels ranging from non-detected values and up to 10 mg/L, and nitrite’s remaining undetected. No dissimilatory nitrate reduction to ammonium was ever detected and some secondary microbial respiration processes, mainly manganese reduction, were suspected to occur temporarily.
Overall, results showed that biodenitrification could be successfully achieved by a daily addition of a C source slightly higher than the stoichiometric value, diminishing the accumulation of non-desired products and the biofilm growth and still obtaining the required denitrification results. Reducing the C/N ratio enables us to reduce treatment costs while achieving a better water quality in terms of remaining C and residual microflora, and potentially reducing the biofouling effect due to the increase of endogenous respiration. Endogenous activity –that provides internal C for denitrification-may become important when low C/N values are used, keep denitrification temporarily ongoing and reducing the biofilm growth, but may affect the biodenitrification performance at longer operation times. Such aspects should be further evaluated using modeling and/or experimental tools. Furthermore, results suggested that not only the feeding strategy but also the biofilm life-time have a direct effect on microbial population structure and hence on the biodenitrification performance, reducing the accumulation of nitrite over time.
The obtained eN/eO fractionation values for the flow-through experiment (1.01) fell within the low-end of previously reported data (varying from 0.9 to 2.3), an effect that may be linked to faster microbial kinetics in enhanced vs. natural biodenitrification. Similar low values were observed in our previous batch-scale experiments as well as in other work conducted in our lab. Concerning ethanol’s fractionation, on the other side, a two-trend behavior was observed, probably indicating a change in the dominating Cconsuming population. Interestingly, the second trend suggests an inverse fractionation of the C source that got depleted while being consumed.Esta tesis se destina a la evaluación de la viabilidad técnica de la biodesnitrificación in situ de aguas subterráneas contaminadas por nitratos, con el objetivo de optimizar las estrategias de bioestimulación y mejorar los resultados del proceso microbiano. El proyecto evalúa la aplicación de la tecnología en dos entornos geológicos distintos: un medio fracturado de baja porosidad y un aluvial arenoso. Se desarrollan ensayos a tres escalas distintas: batch, columna de laboratorio de flujo continuo y piloto. El seguimiento y estudio del proceso se desarrolla mediante la combinación de herramientas de análisis químico y microbiológico y la aplicación de isótopos estables del nitrato, el sulfato y el C.
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Janyasupab, Metini. "New Designs of Electrochemical H2O2 Based Biosensors For Advanced Medical Diagnosis." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1364561528.
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