Effects of temperature and light intensity on photofermentative hydrogen production by Rhodobacter capsulatus DSM1710 by use of acetic and lactic acids as substrates were studied. Experiments were conducted at 20, 30 and 38oC incubator temperatures under light intensities in the 1500 &ndash / 7000 lux range. pH of the medium and quantity of hydrogen forming together with quantity of biomass, and concentrations of acetic, lactic, formic, butyric and propionic acids in the medium were determined periodically. Growth took place and hydrogen was produced under all experimental conditions. Growth was found to increase with increase in temperature but to decrease with increase in light intensity. Total hydrogen produced increased with light intensity up to 6000 lux at 20oC, 5000 lux at 30oC and 3000 lux at 38oC and decreased beyond these values. Medium temperature of about 30oC was found to be optimum for cumulative hydrogen. pH was found to increase slightly and almost all of lactic acid and most of acetic acid was consumed while formic, butyric and propionic acids were first formed and then consumed in the experiments. Growth data fitted well to the logistic model and hydrogen production data fitted well to the Modified Gompertz Model. Lactic acid was found to be almost completely consumed by first order kinetics in early times. Consumption of acetic acid was found to follow zero order kinetics in the early times when lactic acid existed in the system but the order shifted to one later when most of lactic acid was consumed.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016. / Grape producers and wine makers in South Africa are currently affected by various challenges, which include anti-alcohol lobbies, climate change, over-production in some vintages and the lack of transformation including empowerment in certain sectors of the industry. Climate change and global warming lead to poor quality wine grapes and as a result, poor quality wine. Therefore, there is a need to channel grapes away from normal wine production and provide an alternative source of income for the industry. The overall aim of this study was therefore to provide an alternative outlet for overproduced wine grapes by producing balsamic-styled vinegar (BSV) in South Africa. Balsamic vinegar is different from other vinegars because it is a direct product of grape must and not a downstream or by-product of wine production. Balsamic vinegar entails lower production costs when compared to the production of wine due to the low technological process requirements during production; therefore, this could be an opportunity for small business entrepreneurs with low capital start-up. In addition, balsamic vinegar can command a high price, which is a benefit for grape producers. The primary aim of this investigation was to biochemically analyse a BSV production process in which 5 non-Saccharomyces yeast and 15 acetic acid bacteria (AAB) were used for a multicultural alcoholic-acetous (EtOH-AcOH) fermentation process. To achieve this aim, a fermentation process was designed where the data generated was fitted into kinetic models and the proliferation including the population dynamics of the microbial consortia were studied.

Depuis quelques années les raffineries ont commencé à subir des déséquilibres forts en termes d’offre et de demande de produits pétroliers dus à l’exploitation de pétrole de plus en plus lourd et à la forte demande des fractions légères telles que l’essence et les distillats. Cette problématique a conduit à la recherche et le développement de nouveaux procédés en matière de raffinage qui permettent de valoriser les résidus pétroliers de faible valeur commerciale telle que les résidus atmosphériques et sous vide. Dans la gamme des procédés de raffinage des résidus pétroliers, le procédé d’hydroconversion de type slurry se présente comme une technologie attractive en raison de sa capacité de traiter les résidus pétroliers les plus lourdes. Cependant, la conversion profonde des résidus pétroliers ne peut être menée en mode passage unique. Le mode de fonctionnement recyclage offre une alternative pour atteindre la conversion profonde tout en offrant aussi une flexibilité opérationnelle aux unités d'hydroconversion en termes de sévérité et de consommation de catalyseur. L’objectif de cette thèse a été l’étude de l’impact du mode recyclage sur les performances du procédé d’hydroconversion en phase slurry d’un résidu sous vide. La première partie de cette thèse a été dédiée à la fiabilisation d’un micro-pilote continu et à la génération des données expérimentales à partir de cette unité. Pour les expériences d’hydroconversion, trois variables opératoire ont été variés : température, temps de séjour et taux de recycle. Les résultats expérimentaux obtenus ont permis d’évaluer l’impact du mode recyclage sur le procédé d’hydroconversion slurry. Afin de mieux comprendre l’impact du mode recyclage, la deuxième partie de la thèse a été dédiée au développement d’un modèle du micro-pilote en mode recyclage. Ce modèle a été développé prenant en compte la cinétique chimique déterminée précédemment dans un réacteur semi-batch et les modèles physique (hydrodynamique et transfert de matière) du micro-pilote. Le modèle a été validé en comparant ses prédictions avec les données expérimentales / In recent years, refineries have experienced strong imbalances in supply and demand of petroleum products due to the extraction of increasingly heavy petroleum and the high demand for light fractions such as naphtha and middle distillates. This problem has led to the research and development of new technologies for upgrading of heavy fractions with low commercial value such as atmospheric and vacuum residues. In this context, slurry-phase hydroconversion appears as an attractive technology capable of treating the heaviest feeds. However, the deep conversion of petroleum residues can’t be carried out in once-through mode. The recycling mode offers an excellent alternative to achieve the deep conversion while also providing operational flexibility to the hydroconversion units in terms of severity and catalyst consummation.The aim of this work was to study the impact of recycling mode on the slurry-phase hydroconversion performances of a vacuum residue. The first part of this work was dedicated to the reliability of a continuous micro-scale pilot unit and the generation of experimental data from this unit. For the hydroconversion experiments, three operating variables were varied: temperature, residence time and recycling rate. The experimental results obtained allowed evaluating the impact of recycling mode. In order to better understand the impact of recycling mode, the second part of this work was dedicated to the development of a model of the micro-scale pilot in recycling mode. This model was developed taking into account the chemical kinetics determined previously in a semi-batch reactor and the physical characterization (hydrodynamics and mass transfer) of the micro-scale pilot. The model was validated by comparing its predictions with experimental data

La valorisation des résidus pétroliers est une nécessité compte tenu de l'amenuisementdes ressources en pétrole conventionnel et de la progression de la demande du marché en carburants. Le procédé d'hydroconversion en lit bouillonnant permet de convertir des résidus pétroliers en fractions plus légères dans des conditions très sévères de température (>400°C) et de pression d'hydrogène (>100bar), en présence d'un catalyseur bimétallique d'hydrogénation. Le craquage thermique est prépondérant dans ce type de procédé et met en oeuvre des réactions radicalaires. Toutefois, les mécanismes et la réactivité des charges ne sont pas clairement identifiés du fait de la complexité chimique des fractions lourdes du pétrole. L'objectif de la thèse consiste donc à étudier les mécanismes de conversion des résidus pétroliers dans ces conditions. Après une caractérisation analytique détaillée de différents résidus sous vide (Athabasca, Oural et Duri), une étude de réactivité systématique a été entreprise sur ces charges à l'aide d'un réacteur batch développé spécifiquement pour cette étude. Des essais ont également été réalisés sur différentes fractions du résidu sous vide Athabasca, de distributions SARA (Saturés, Aromatiques, Résines et Asphaltènes) différentes. Il a été montré que les mécanismes de conversion sont essentiellement thermiques et peuvent être inhibés par l'activité hydrogénante du catalyseur. Des réactivités différentes sont observées d'un résidu à l'autre et l'avancement de la conversion en fonction de la sévérité de craquage dépend de la naturedes charges traitées. Cependant, pour un même avancement en conversion, les rendements en produits sont similaires pour toutes les charges étudiées. Il semble ainsi que les différents résidus soient composés de "briques" élémentaires similaires, malgré des compositions globalement différentes. Il a également été démontré que la cinétique de conversion suit un ordre apparent de 2. Cependant, il n'est a priori pas possible d'expliquer les différences de réactivité des résidus simplement en fonction de leur composition SARA. Finalement, les conclusions de ce travail permettent d'envisager une réduction forte de l'expérimentation requise sur un résidu pour prédire les structures de rendement des procédés d'hydroconversion. / Nowadays, more and more petroleum residues have to be converted into lighter fractions due to a decline in conventional crude oil production and to an increasing demand for motor fuels. Ebullated bed hydroconversion process converts heavyfeed stocks at elevated temperature (>400°C) and high hydrogen partial pressure (>100bar), with a bimetallic hydrogenation catalyst. Thermal cracking is the driving component for conversion and involves radicals formation. Nevertheless, detailed reaction mechanisms and feedstock reactivity are still not well established due to the detailed composition complexity of feeds. The objective of this thesis is to study conversion mechanisms of petroleum residues in these conditions. A detailed analytical characterization of several vacuum residues (Athabasca, Oural and Duri)was conducted initially and the reactivity of these feeds was then tested in a batch reactor specifically developed for the purpose of the study. Reactivity tests were also conducted on Athabasca residue fractions, characterized by different SARA distributions (Saturates, Aromatics,Resins and Asphaltenes). It was demonstrated that hydroconversion mechanisms are mostly thermal and can be inhibited by hydrogenation activity of the catalyst. Differences of reactivitywere observed for the different feeds tested and conversion level in function of severity depends on the nature of the feeds. At a same conversion level, product yields are similar whatever the feed considered. This suggests that residues could be composed of similar elementary units. It was also demonstrated that residue hydroconversion reaction can be adequately represented by an apparent second order kinetics. However, residue reactivity differences cannot a priori be explained based on SARA composition differences. Finally, the conclusions of the present work enable to consider a significant reduction of the number of experiments required in order to predict yield structures resulting from hydroconversion of aresidue.

Reaction rate data at 50oC was generated in a batch reactor over a wide range of initial concentrations in the reaction mixture. In each case the reaction was allowed to reach equilibrium. Equilibrium conversion data clearly indicated that it is important to consider the non-ideality of the system. The NRTL activity model proved to be the most suitable model to calculate the activity based equilibrium constant, as the percentage standard deviation of the equilibrium constant calculated in this manner was only 7.6% for all the different experiments as opposed to 17.8% when the equilibrium constant was based on concentration. The NRTL parameters used were obtained from Gmehling&Onken (1977) who determined the parameters from vapour liquid equilibrium. The Langmuir-Hinshelwood kinetics proposed by Song et al. (1998) and Pöpken et al. (2000) provided an excellent representation of the reaction rate over a wide concentration range with an AARE of 6% and 5% respectively. It was shown that when the NRTL activities were used in the rate expression that a power law model provided a similarly accurate prediction of the reaction rate (AARE = 4.1%). When the Eley-Rideal reaction expression (in terms of the adsorption of methanol and water) was used, a slight improvement was achieved (AARE = 2.4%). As both the Langmuir-Hinshelwood and Eley-Rideal models require separate experiments for the measurement of adsorption constants, it seems that the activity based power law model should be the kinetic expression of choice. It can be concluded that a two parameter activity based rate expression predicts the reaction rate with similar accuracy as the multi-parameter adsorption models. This indicates that it is not necessary to know the concentration on the resin surface (adsorption models) or in the resin gel (absorption models) when describing the reaction rate as long as the bulk liquid phase activities can be adequately described. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2007. / Chemical Engineering / unrestricted

Within the context of the imminent implementation of the Pb-free soldering in Europe in 2006, this thesis addresses the gap in understanding that has emerged in the fundamental materials issues between well-understood and mature lead-containing solders and a plethora of new, Pb-free solders for which there are neither long term reliability data nor understanding of the materials behaviour and how these might be influenced by manufacture and in-service conditions. In addition, this thesis also addresses the question as to whether the solder joint size and geometry could become a reliability issue and therefore affect the implementation of the Pb-free solders in ultrafine micro joints. Thermodynamic calculations using MTDATA (developed by the National Physical Laboratory, NPL, UK) together with a thermodynamic database for solders under either equilibrium or Scheil conditions, have shown their usefulness in Pb-free solder design and processing, generating a wealth of information in respect of the temperature dependence of phase formation and composition. The predictions from MTDATA on a number of selected systems is generally in good agreement with the results from experimental work, and has assisted in the understanding of the microstructure and mechanical properties of the Pb-free solders and the implications of their interactions with a tin-lead solder. However, further critical assessment and the addition of new elements into the solder database, such as Ni and P, are required to make MTDA TA a more effective computational tool to assist the optimization of processing parameters and cost-effective production in using Pb-free solders. Molten solder can interact with the under bump metallizations (UBM) and/or board level metallizations on either side of the solder bump to form intermetallic compounds (IMCs) during solder reflow. In the modelling of the kinetics of the dissolution process of UBM into the liquid solder, the commonly used NernstBrunner (N-B) equation is found to have poor validity for these calculations for micro joints at 100 μm in diameter or less. Three bumping techniques, i.e. solder dipping (SD), solder paste stencil printing followed by reflow (SPR) and electroplating of solders and subsequent reflow (EPR), are used to investigate the interfacial interactions of molten Sn/Sn-rich solders, i.e. pure Sn, Sn-3.5Ag, and Sn-3.8AgO.7Cu, on electroless nickel immersion gold (ENIG) and copper pads at 240°C. The resultant bulk and interfacial microstructures from a variety of pad sizes, ranging from 1 mm down to 25 μm, suggest that in general the small bumps contain smaller β-Sn dendrites and Ag₃Sn IMC particles, nevertheless the interfacial IMC is thicker in the smalI bumps than in the large bumps. In addition, one and two-dimensional combined thermodynamic and kinetic models have been developed to assist the understanding of the kinetics of interdiffusion and the formation of interfacial intermetallic compounds during reflow. Both the experimental results and theoretical predictions suggest that the solder bump size and geometry can influence the as-soldered microstructure, and therefore this factor should be taken into consideration for the design of future reliable ultrafine Ph-free solder joints.

Population growth and increasing standards of living have resulted in a rapid demand for energy. Our primary energy production is still dominated by fossil fuels. This extensive usage of fossil fuels has led to global warming, environmental pollution, as well as the depletion of hydrocarbon resources. The prevailing difficult situation offers not only a challenge but also an opportunity to search for alternatives to fossil fuels. Hence, there is an urgent need to explore environmentally friendly and cost-effective renewable energy sources. Oxygenates (alcohols, ethers) and ammonia are among the potential renewable alternative fuels of the future. This thesis investigates the combustion characteristics of promising alternative fuels and their blends using a combination of experimental and modelling methodologies. The studied fuels include ethanol, diethyl ether, dimethyl ether, dimethoxy methane, γ-valerolactone, cyclopentanone, and ammonia. For the results presented in this thesis, the studies may be classified into three main categories: 1. Ignition delay time measurements of ethanol and its blends by using a rapid compression machine and a shock tube. The blends studied include binary mixtures of ethanol/diethyl ether and ternary mixtures of ethanol/diethyl ether/ethyl levulinate. A chemical kinetic model has been constructed and validated over a wide range of experimental conditions. The results showed that a high-reactivity fuel, diethyl ether, may be blended with a low-reactivity fuel, ethanol, in varying concentrations to achieve the desired combustion characteristics. A ternary blend of ethanol/diethyl ether/ethyl levulinate may be formulated from a single production stream, and this blend is shown to behave similarly to a conventional gasoline. 2. Ignition delay time and flame speed measurements of ammonia blended with combustion promoters by utilizing a rapid compression machine and a constant volume spherical reactor. The extremely low reactivity of ammonia makes it unsuitable for direct use in many combustion systems. One of the potential strategies to utilize ammonia is to blend it with a combustion promoter. In this work, dimethyl ether, diethyl ether, and dimethoxy methane are explored as potential promoters of ammonia combustion. Chemical kinetic models were developed and validated in the high temperature regime by using flame speed data and in the low-to-intermediate temperature regime by using ignition delay time data. The results showed that even a small addition (~ 5 – 10%) of combustion promoters can significantly alter ammonia combustion, and diethyl ether was found to have the highest propensity to enhance ammonia ignition and flame propagation. Blends of combustion promoters with ammonia can thus be utilized in modern downsized turbo-charged engines. 3. Octane boosting and emissions minimization effects of next generation oxygenated biofuels. These studies were carried out using a cooperative fuel research engine operating in a homogenous charge compression ignition (HCCI) mode. The oxygenated fuels considered here include γ-valerolactone and cyclopentanone. The results showed that γ-valerolactone and cyclopentanone can be effective additives for octane boosting and emission reduction of conventional fuels. Overall, the results and outcomes of this thesis will be highly useful in choosing and optimizing alternative fuels for future transportation systems.

An investigation was undertaken to compare the kinetics of combustion and gasification reactions of chars prepared from two South African coals in different reaction atmospheres: air, steam, and carbon dioxide. The two original coals were characterised as vitrinite-rich (Greenside) and inertinite-rich (Inyanda) coals with relatively low ash content (12.5-16.7 wt. %, adb). Chars were prepared from the parent coals under nitrogen atmosphere at 900 °C. Characterisation results show that the volatiles and moisture were almost completely driven off from the parent coals, indicating that the pyrolysis process was efficient. Physicalstructural properties such as porosity and surface area generally increased from the parent coals to the subsequent chars. The heterogeneous char-gas reactions were conducted isothermally in a TGA on ~1 mm size particles. To ensure that the reactions are under chemical reaction kinetic control regime, different temperatures zones were selected for the three different reaction atmospheres. Combustion reactivity experiments were carried out with air in the temperature range of 387 °C to 425 °C; gasification reactivity with pure steam were conducted at higher temperatures (775 °C - 850 °C) and within 825 °C to 900 °C with carbon dioxide. Experimental results show differences in the specific reaction rate with carbon conversion in different reaction atmospheres and char types. Reaction rates in all three reaction atmospheres were strongly dependent on temperature, and follow the Arrhenius type kinetics. All the investigated reactions (combustion with air and gasification with CO2 and steam) were found to be under chemical reaction control regime (Regime I) for both chars. The inertinite-rich coals exhibit longer burn-out time than chars produced from vitrinite-rich coals, as higher specific reaction rate were observed for the vitrinite-rich coals in the three different reaction atmospheres. The determined random pore model (RPM) structural parameters did not show any significant difference during steam gasification of Greenside and Inyanda chars, whereas higher structural parameter values were observed for Greenside chars during air combustion and CO2 gasification (ψ > 2). However a negative ψ value was determined during CO2 gasification and air combustion of Inyanda chars. The RPM predictions was validated with the experimental data and exhibited adequate fitting to the specific rate of reaction versus carbon conversion plots of the char samples at the different reaction conditions chosen for this study. The activation energy determined was minimal for air and maximum for CO2 for both coals; and ranged from 127-175 kJ·mol-1 for combustion, 214-228 kJ·mol-1 and 210-240 kJ·mol-1 for steam and CO2 gasification respectively. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

An investigation was undertaken to compare the kinetics of combustion and gasification reactions of chars prepared from two South African coals in different reaction atmospheres: air, steam, and carbon dioxide. The two original coals were characterised as vitrinite-rich (Greenside) and inertinite-rich (Inyanda) coals with relatively low ash content (12.5-16.7 wt. %, adb). Chars were prepared from the parent coals under nitrogen atmosphere at 900 °C. Characterisation results show that the volatiles and moisture were almost completely driven off from the parent coals, indicating that the pyrolysis process was efficient. Physicalstructural properties such as porosity and surface area generally increased from the parent coals to the subsequent chars. The heterogeneous char-gas reactions were conducted isothermally in a TGA on ~1 mm size particles. To ensure that the reactions are under chemical reaction kinetic control regime, different temperatures zones were selected for the three different reaction atmospheres. Combustion reactivity experiments were carried out with air in the temperature range of 387 °C to 425 °C; gasification reactivity with pure steam were conducted at higher temperatures (775 °C - 850 °C) and within 825 °C to 900 °C with carbon dioxide. Experimental results show differences in the specific reaction rate with carbon conversion in different reaction atmospheres and char types. Reaction rates in all three reaction atmospheres were strongly dependent on temperature, and follow the Arrhenius type kinetics. All the investigated reactions (combustion with air and gasification with CO2 and steam) were found to be under chemical reaction control regime (Regime I) for both chars. The inertinite-rich coals exhibit longer burn-out time than chars produced from vitrinite-rich coals, as higher specific reaction rate were observed for the vitrinite-rich coals in the three different reaction atmospheres. The determined random pore model (RPM) structural parameters did not show any significant difference during steam gasification of Greenside and Inyanda chars, whereas higher structural parameter values were observed for Greenside chars during air combustion and CO2 gasification (ψ > 2). However a negative ψ value was determined during CO2 gasification and air combustion of Inyanda chars. The RPM predictions was validated with the experimental data and exhibited adequate fitting to the specific rate of reaction versus carbon conversion plots of the char samples at the different reaction conditions chosen for this study. The activation energy determined was minimal for air and maximum for CO2 for both coals; and ranged from 127-175 kJ·mol-1 for combustion, 214-228 kJ·mol-1 and 210-240 kJ·mol-1 for steam and CO2 gasification respectively. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

To reduce the greenhouse effect, the use of renewable fuel has to be increased. As renewable fuel has different characteristics compared to fossil fuel regarding content of trace metals, alkali, chlorine and sulphur, the corrosion characteristics in high temperature energy processes have to be evaluated. This thesis concerns high temperature corrosion in the superheater region of a boiler and the syngas cooler area of a gasifier. For the superheater region, laboratory exposures were performed. The methods included a salt dip exposure, where samples were dipped in an equimolar solution of ZnCl2 and KCl, and two salt bed exposures with different chlorine concentrations, 10 and 20 wt%. Ranking of the materials showed that a Ni content above 10 wt% and Cr above 20 wt% reduced corrosion rates in the salt dip and in the 10% Cl salt bed exposure. For exposure in the 20% Cl bed, even higher alloying was needed. An alumina forming austenitic steel showed future potential in sulphidising-chlorinating environments. For the gasifier region, the effect of HCl in a simulated gasifier atmosphere was studied and also samples exposed in the syngas section of a biomass gasifier were investigated. Metal loss was low for all exposures and it was observed that chlorine had minor influence. For the plant exposed samples, a difference compared to that reported for coal gasifiers was the absence of FeS for the lowest alloyed steel. Instead, a deposit with pronounced content of Zn, Ca, S and O was present on the surface. Zinc was suggested to mitigate corrosion. Thermodynamic modelling was used to explain phases present and to predict the nitridation behaviour of an alumina forming austenitic steel. Equilibrium and kinetic modelling of the nitridation showed good coherence with the observed microstructures. However, the kinetic modelling resulted in larger nitridation depths than observed experimentally which was attributed to the presence of a thin oxide layer on the surface of the samples. / <p>QC 20160510</p>