Dissertation (PhD)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Silver/Zinc batteries are extensively used for applications where a power source with a high energy density is needed. A reactor was developed to manufacture the zinc electrodes for these batteries. The parameters for the control of this reactor were identified. The interaction and relationships between the set of parameters were established and quantified. The novel design of the reactor includes features such as continuous replenishment of the constituting chemicals, parallel flow of the plating fluid, inert anodes and a serial electrical layout. The controlling parameters consist of both chemical and physical parameters. They are - zincate concentration, hydroxyl concentration, density, temperature, flow rate of the plating fluid, and current density. The unique solubility characteristics of zinc oxide in potassium hydroxide lend themselves to a novel approach for the determination of the zincate concentration in· the plating solution. A set of conditions for the manufacturing of electrodes, with the required characteristics, was identified. The requirements are densely packed zinc dendrite morphology with high porosity and mechanical stability. The designed reactor complies with the industries safety requirements. The batteries were successfully applied in their operational domain (torpedoes) after this extensive research project was completed. / AFRIKAANSE OPSOMMING: Silwer/Sink batterye word intensief aangewend in gebruike waar 'n kragbron met hoë energie digtheid benodig word. 'n Reaktor is ontwikkel wat die sink elektrodes van die tipes batterye vervaardig. Die veranderlikes vir die beheer van die reaktor is bepaal. Die interaksie en verwantskap tussen die stel veranderlikes is verkry en gekwantifiseer. Die unieke ontwerp van die reaktor het die volgende karakteristieke, nl. aaneenlopende vervanging van die chemikalië verbruik, parallelle vloei van die plateringsvloeistof, inerte anodes en elektriese uitleg in serie. Die chemiese en fisiese veranderlikes is beide beherende veranderlikes. Hierdie fisiese en chemiese veranderlikes wat die proses beheer is die sinkaat konsentrasie, hidroksiel konsentrasie, digtheid, temperatuur, vloeitempo van die plateringsvloeistof en die stroomdigtheid. Die unieke oplossingskarakteristieke van sinkoksied in kalsium· hidroksied leen hom tot die unieke proses om die sinkaat konsentrasie in die plateringsvloeistof te bepaal. 'n Steloperasionele kondisies vir die vervaardiging van die elektrodes met die spesifieke spesifikasies soos verlang, is geïdentifiseer. Hierdie kondisies is die diggepakte sinkdendriet morfologie met 'n hoë porositeit en meganiese stabiliteit. Die ontwerpte reaktor voldoen aan die industriële veiligheidsvereistes en die ergonomiese maatstawwe. Die batterye is suksesvol gebruik in hulle industriële aanwending as gevolg van die suksesvolle afhandeling van die stuk navorsing.

Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The photo-mineralization of organic compounds (in the combined presence of a Ti02 based semiconductor catalyst, UV radiation and molecular oxygen) represents an advanced oxidation technology with significant potential for environmental pollution abatement. This oxidation process (generally known as photocatalytic oxidation - PCO) is currently the subject of extensive global research, with the main objective being the oxidative removal of organic and inorganic pollutants from water, air and soil. Presently, many barriers still block the way to commercial implementation of this technology, hence a unique (and effective) configuration of catalyst, light source and reactor design needs to identified. In terms of the water treatment scenario (which is the emphasis of this work) the need exists to develop a practical and affordable PCO reactor for water treatment on a large scale. The two laboratory-scale PCO reactors investigated in this work were based on a "falling film" flow reactor design and were constructed with commercially available materials and components. Degussa P-25 Ti02 was used as semiconductor catalyst and two types of low-pressure mercury lamps as the UV light source. Three modes of operation were investigated in order to determine the practical feasibility of the reactors. These included the recirculation, single pass and sequential single pass modes. The reactors were operated either as a Ti02 slurry-phase reactor (Reactor 1), or with Ti02 immobilized on stationary fiber glass and fibrous activated carbon sheet modules (Reactors 2A and 28 respectively). Extensive parametric evaluations were done using conventional one-factor variation and statistical methods according to optimal experimental design principles. The PCO treatment of two model organic pollutants (para-Chlorophenol and cyanobacterial microcystin YA, YR, LR and RR) were investigated. These pollutants were spiked into various water matrices to the desired concentration level. The combined photocatalyticcarbon adsorption treatment of these two pollutants was also investigated in Reactor 28. The experimental results obtained through this work showed that both model pollutants were successfully degraded in several water matrices by means of treatment in the respective PCO reactors. Moreover, this research was the first ever demonstration of the Ti02 photocatalytic degradation of microcystin toxins in the aqueous phase. The large number of parametric and optimization studies yielded the relative contributions of the various process parameters (in terms of the defined photocatalytic efficiency parameters as responses) very effectively. Furthermore, statistical evaluation of the experimental data provided valuable insight into the scientific phenomena associated with Ti02 mediated PCO processes. / AFRIKAANSE OPSOMMING: Die foto-mineralisasie van organiese verbindings (in die gekombineerde teenwoordigheid van 'n Ti02 gebaseerde halfgeleier katalisator, UV straling en molekulêre suurstof) verteenwoordig 'n gevorderde oksidasie-tegnologie met beduidende potensiaal vir bekamping van omgewingsbesoedeling. Hierdie oksidasie-proses (algemeen bekend as fotokatalitiese oksidasie - FKO) is tans wêreldwyd die onderwerp van ekstensiewe navorsing, met hoofdoel die oksidatiewe verwydering van organiese en anorganiese besoedelingstowwe uit water, lug en grond. Huidiglik bestaan daar nog vele struikelblokke wat die weg na kommersiële implementering van hierdie tegnologie blokkeer, gevolglik moet 'n unieke (en effektiewe) konfigurasie van katalisator, ligbron en reaktor-ontwerp nog identifiseer word. In terme van die waterbehandeling situasie (wat die klem van hierdie werk is) bestaan die nodigheid om 'n praktiese en bekostigbare FKO reaktor te ontwikkel vir watersuiwering op 'n groot skaal. Die twee laboratorium-skaal FKO reaktore in hierdie studie was gebaseer op 'n "vallende film" vloeireaktor ontwerp en is gekonstrueer met kommersieël beskikbare materiale en komponente. Degussa P-25 Ti02 is aangewend as halfgeleier katalisator en twee tipes lae-druk kwik lampe as die UV ligbron. Drie bedryfsmodes is ondersoek met die doel om die praktiese haalbaarheid van die reaktore te bepaal. Hierdie het ingesluit die resirkulasie, enkeldeurvloei en enkeldeurvloei-sekwensie modes. Die reaktore is bedryf as óf 'n Ti02 flodder-fase reaktor (Reaktor 1) óf met Ti02 ge-immobiliseer op 'n stasionêre veselglas en veselagtige ge-aktiveerde koolstof blad-modules (Reaktor 2A en 28 onderskeidelik). Omvattende parametriese evaluasies is gedoen deur gebruik te maak van konvensionele een-faktor variasie en statistiese metodes na aanleiding van optimale eksperimentele ontwerp beginsels. Die FKO behandeling van twee modelorganiese besoedelingstowwe (para-Chlorofenol en siano-bakteriese mikrosistien YA, YR, LR en RR) is ondersoek. Hierdie besoedelingstowwe is ge-ent in verskeie watermatrikse tot die verlangde konsentrasievlak. Die gekombineerde fotokatalitiese - aktiveerde koolstof behandeling van die twee besoedelingstowwe is ook ondersoek in Reaktor 28. Die eksperimentele resultate verkry deur hierdie werk het getoon dat beide die modelbesoedelingstowwe suksesvol gedegradeer is in verskeie watermatrikse deur behandeling in die onderskeie FKO reaktore. Trouens, hierdie navorsing was die eerste demonstrasie ooit van die Ti02 fotokatalitiese degradasie van mikrosistien toksiene in die waterige fase. Die groot aantal parametriese en optimiseringstudies het die bydraes van die verskeie proses-parameters (in terme van die gedefinieerde fotokatalitiese effektiwiteitsparameters as response) baie effektief verskaf. Verder, statistiese evaluasie van die eksperimentele data het waardevolle insig verskaf tot die wetenskaplike verskynsels te assosieer met Ti02 gemedieërde FKO prosesse.

Traditionally the reactor is recognised as the `heart' of a chemical process system and hence the focus on this part of the system is usually quite detailed. Steam reforming, however, due to the `building block' nature of its reaction products is unusual and generally is perceived as a `utility' to other reaction processes and hence the focus is drawn " towards the 'main' reaction processes of the system. Additionally as a `mature' process, steam reforming is often treated as sufficiently defined for the requirements within the overall chemical process. For both primary and secondary steam reformers several models of varying complexity were developed which allowed assessment of issues raised about previous models and model improvements; drawing on the advancements in modelling that have not only allowed the possibility of increasing the scope of simulations but also increased confidence in the simulation results. Despite the complex nature of the steam reforming systems, a surprisingly simplistic model is demonstrated to perform well, however, to improve on existing designs and maximise the capability of current designs it is shown that more complex models are required. After model development the natural course is to optimisation. This is a powerful tool which must be used carefully as significant issues remain around its employment. Despite the remaining concerns, some simple optimisation cases showed the potential of the models developed in this work and although not exhaustive demonstrated the benefits of optimisation.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

No description available.

Este trabalho utiliza a Análise de Fluxos Metabólicos para estudar o aumento da eficiência da linhagem Burkholderia sacchari (LFM101) na produção de PHB. Foram avaliadas as eficiências de conversão de açúcares em PHA de LFM101. Esta também foi cultivada em batelada alimentada em reator, apresentando o máximo teórico durante um estado pseudo-estacionário sob oferta de glicose. Estes dados, submetidos ao software Metatool, resultaram em mapa metabólico contendo os fluxos das reações centrais ede PHA ocorrido no experimento. Através do cultivo de LFM101 e C. necator sob oferta de glicose marcada com 13C, determinou-se que estas utilizam as mesmas vias para produção de PHA, não justificando a baixa eficiência de LFM101. Em um projeto paralelo, estudou-se a eficiência da produção de PHB utilizando melaço de cana, glicerol cru e acetato, em produtores de hidrogênio e PHA, onde verificou-se não apenas o aumento de PHA em mutantes nifh- de R. capsulatus mas a interação dos parâmetros luz e nitrogênio a partir das metodologias DOE e RSM. / This work applies Metabolic Flux Analysis to discuss the eficiency of Burkholderia sacchari (LFM101) in PHA production from sugars . Conversion yields of LFM101 and Cupriavidus necator from carbohydrates to PHA were assessed. LFM101 was also grown in reactor fed-batch cultivations, and presented the theoretical maximum in a pseudo-steady stage while grown on glucose. These data were submitted to Metatool and resulted in a metabolic network containing the experimental fluxes of central and PHA metabolism. Cultivation of LFM101 and C. necator under 13C- labeled glucose showed that both species use the same metabolic pathways for the biodegradable polymer synthesis. On a parallel project, the efficiency of biopolymer production from molasses, raw glycerol and acetate in strains producing hydrogen and PHA was tested. Results showed that there was not only an increase in PHA production by R. capsulatus nifH- mutants but also the interaction of light and nitrogen effects were studied by DOE and RSM.

Fixed bed reactors are used in many different chemical processes, and are a very important part of chemical industry. To model fixed beds we must have a good qualitative understanding of heat transfer in them. Fixed bed models have been developed for high tube-to-particle ratio (N) beds. Modeling of low tube-to-particle beds (3 ¡ÃƒÅ“ N ¡ÃƒÅ“ 8), that are used in extremely exo- and endothermic processes in tube-and-shell type reactors, is complicated, due to the presence of wall effects across the entire radius of the bed. Heat transfer is one of the most important aspects. To obtain accurate models of heat transfer we need to study the physical mechanisms involved especially in the wall vicinity using CFD as a non intrusive tool to collect numerical data. An extra heat transfer resistance is always present near the wall. This is caused by three mechanisms which happen in the wall vicinity. The change of porosity which leads to a change of bed conductivity, the damping of mixing due to the lateral displacement of fluid, the presence of a laminar (viscous) sublayer at the wall. Many authors have been working on how to model the extra resistance near the wall. The main previous approach was to introduce a lumped parameter hw (heat transfer coefficient) which idealizes these three contributions to the extra heat resistance to be at the wall. Our approach will be to keep the parameter hw which will now represent only the viscous boundary layer idealized at the wall, and we are going to incorporate velocity and porosity profiles in the energy equation. In this way we will able to get rid of artificial parameters using the true conductivity of the bed, and the real velocity profile. So we need to study separately each contribution of the different physical mechanisms to clearly understand what happens in the wall vicinity. For this CFD will be a very powerful tool. How CFD models flow near the wall must be understood before starting simulations. Two main approaches for wall bounded flows are available and will be studied: either solve all way down to the wall, or bridge numerical values from the core of the bed to the wall using semi-empirical formulas called wall functions. These methods will be studied and compared. Also with CFD it is possible to run simulations without conduction in the bed, and so, study radial fluid displacement only and obtain reduced velocity profiles. Using the meshing it is also possible to get a very accurate porosity profile. These profiles will be combined in a simplified fixed bed model which will be used to predict temperature profiles. These may then be compared to the full CFD energy solution and to experiment to test the model.

This dissertation presents a method for enhancement of the efficiency and scalability of photocatalytic water purification systems, along with an experimental validation of the concept. A 3-dimensional photocatalyst structure, made from a TiO2-SiO2 composite, has been designed and fabricated for use in a custom designed LED-source illumination chamber of rotational symmetry that corresponds with the symmetry of the photocatalyst material. The design of the photocatalyst material has two defining characteristics: geometrical form and material composition. The design of the material was developed through the creation of a theoretical model for consideration of the system's photonic efficiency. Fabrication of the material was accomplished using a Ti alkoxide solution to coat a novel 3D support structure. The coatings were then heat treated to form a semiconducting thin-film. The resulting films were evaluated by SEM, TEM, UV-vis spectroscopy and Raman spectroscopy. The surface of the material was then modified by implantation of TiO2 and SiO2 nanoparticles in order to increase catalytic surface area and improve the photoactivity of the material, resulting in increased degradation performance by more than 500%. Finally, the efficiency of the photocatalytic reactor was considered with respect to energy usage as defined by the Electrical Energy per Order (EEO) characterization model. The effects of catalyst surface modification and UV-illumination intensity on the EEO value were measured and analyzed. The result of the modifications was an 81.9% reduction in energy usage. The lowest EEO achieved was 54 kWh per cubic meter of water for each order of magnitude reduction in pollutant concentration -- an improvement in EEO over previously reported thin-film based photoreactors.

The manufacture of nonionic surfactants generally involves ethoxylation via ethylene oxide condensation onto a hydrophobe substrate, mostly in the presence of an alkaline catalyst. Nonionic surfactants are used widely in industrial applications, such as detergents, health and personal care, coatings, and polymers. In Australia, approximately one-third of the annual consumption of nonionic surfactants is imported from offshore manufacturers; the market is highly competitive with the local manufacturer facing increasing competition from imports. Optimisation is a pressing need for the current manufacturing plant of the industrial partner for this research project, Huntsman Corporation Australia Pty Limited, the sole domestic manufacturer of nonionic surfactants in Australia. Therefore, the objectives of this research project were to gain a better understanding of the various chemical and physical processes occurring simultaneously in an ethoxylation process; to identify the process limitation in an existing production plant operated by Huntsman Corporation Australia, and to explore measures for enhancing the asset productivity of the production plant. An ethoxylation process working model, describing the chemical kinetics and the physical transport processes involved, was developed to aid the exploration of optimisation opportunities, which would otherwise be empirical. Accordingly, this research project was structured into a two-stage program. The first stage determined the ethoxylation kinetics experimentally. The second stage investigated the interactions of physical transport processes numerically using a computational fluid dynamics (CFD) technique. The manufacturing scheme discussed in this thesis gave particular emphasis to the ethoxylation process operated in semi-batch stirred reactors. In the first stage, a series of kinetic experiments was performed in a well-stirred laboratory autoclave under base-catalysed conditions. The experimental outcomes were developed into a comprehensive kinetic model which took into account the non-ideal features in the reactor operation. Time-dependent physical changes of the reaction system, such as liquid volume, ethylene oxide solubility and density were also included. The ethoxylation behaviour predicted by the model was shown to be in good agreement with the experimental measurements. This indicated that the kinetic model was sufficiently robust to reproduce the reaction behaviour of a commercially operated ethoxylation operation. In the second stage, numerical simulations of an existing ethoxylation reactor system were presented. In addition, two components were addressed: identification of the process limitation and increasing productivity of the industrial-scale ethoxylation plant. An important assumption was made for the ethylene oxide injection system used in this research project which subsequently simplified the ethoxylation system into a single liquid with miscible chemical species. In the identification of the process limitation, three possible rate-limiting factors were examined: mixing, heat removal and reactor pressure rating. Examination and analysis of the physical data available from plant batch reports found that the reactor pressure rating and the presence of nitrogen padding were the rate-limiting factors to the ethoxylation operations in the industrial reactors. It was recommended that the reactor pressure rating be increased to raise the asset productivity of the reactor. In the numerical simulations of the ethoxylation reactor, time-dependent CFD models were developed for two systems: the ethylene oxide injection pipe and the stirred ethoxylation reactors. The heat transfer of ethylene oxide liquid injection was calculated in a two-dimensional model of the dip-leg pipe used in an industrial-scale ethoxylation reactor. The computation gave the temperature of the injection outflow which was validated against the calculated value by empirical correlation. The effects of various surrounding reaction temperatures, injection rates and pipe sizes on the heat transfer rate were investigated. From these, a range of operating conditions yielding a liquid ethylene oxide outflow was selected. Furthermore, it was found that boiling of ethylene oxide was significantly reduced with increasing pipe diameters. It was recommended that the asset productivity of the reactor be improved by keeping more ethylene oxide injected as a liquid in the reaction mixture to raise the reaction rate and shorten the reaction time. Three-dimensional simulations of a baffled reactor agitated by a single- or a dual-Rushton impeller were presented for both non-reactive and reactive flows. Multiple frames of reference and sliding grid methods were used in sequence to describe the relative motion between the rotating impeller and the stationary baffles. The turbulence parameters were modelled with the standard k- � turbulence model. The simulations of non-reactive flow were compared with the literature velocity data obtained from both the experiments and simulations. Good agreement was achieved. The model was then extended to incorporate ethoxylation flow with integration of the kinetics established in the first stage. Both the laboratory autoclave and the industrial-scale reactors were simulated. The former took into account the ethoxylation exotherm and the latter was carried out isothermally. Both simulations were validated against reaction data obtained from physical experiments, either the kinetic experiments or the plant batch productions. The validated model allowed us to determine the optimum operating condition and explore a new reactor system with enhanced asset productivity. A 50% increase in productivity could be accomplished if the ethoxylation was operated closer to the current design pressure limit. Furthermore, the operating pressure of a new reactor system needed to be doubled if the asset productivity were to be increased to approximately three times the current performance.

No description available.