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In this study the performance of pure, very fine iron (III) oxide powder was investigated as catalyst for the decomposition of sulphur trioxide into sulphur dioxide and oxygen. This highly endothermic reaction requires a catalyst to lower the reaction temperature. This reaction forms part of the HyS (Hybrid Sulphur) cycle, a proposed thermochemical process for the industrial scale production of hydrogen and oxygen from water. The study aimed at obtaining reaction kinetics for this reaction employing pure, unsupported iron (III) oxide as catalyst as a cheaper alternative compared to supported iron catalysts. It was found that the SO3 conversion was carried out in the absence of diffusion limitations and that the reverse reaction did not play a significant role. By assuming plug flow conditions in the reactor and 1st order kinetics, the kinetic parameters of the reaction were obtained. These parameters that form part of the Arrhenius law in describing the reaction rate constant, were determined to be 118(±23) kj / mol for the activation energy ( Ea ), and a value of 3(±0.5) x 108hr-1 was obtained for the Arrhenius frequency factor ( A ). Both values correspond to literature, although in general larger activation energies were published for iron (III) oxide derived supported catalysts. A comparison of the performance of the pure, unsupported iron (III) oxide catalyst with other iron (III) oxide derived supported catalysts (or pellets) has shown that the pure iron (III) oxide catalyst exhibit similar activities. Avoiding expensive catalyst preparation will be an initial step in the direction of developing a cost effective catalyst for the decomposition of sulphur trioxide. It is, however, recommended to investigate different particle sizes as well as purity levels of the unsupported iron (III) oxide to find an optimum cost to performance ratio, as the degree of fineness and the degree of purity will largely influence the final catalyst cost. A qualitative investigation with various reaction product species as well as water in the reactor feed was conducted to assess the influence of these species on the reaction rate. The addition of these species seems to have a larger influence on the reaction rate at low reaction temperatures around 700°C than at higher reaction temperatures (i.e. 750°C and 825°C). This can be attributed to adsorption rates of such species that reduce at higher temperatures. Observations at higher reaction temperatures also suggest that the reaction is of a first-order nature. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

South Africa has large coal reserves and produces approximately 74% of its primary energy from coal. Coal gasification using moving bed gasifiers is one of the most important coal utilisation technologies, consuming ± 17.5% of locally produced coal. This study was motivated by the need to investigate alternative coal gasification technologies for the utilisation of fine, high-ash and caking coals for future Integrated Gasification Combined Cycle (IGCC) and coal to liquids (CTL) plants. These coals are estimated to form a large percentage of the remaining coal reserves in South Africa and could be difficult to utilise efficiently in moving bed gasifiers. Fluidised bed gasification was identified as a technology that could potentially utilise these coals. Coals from the New Vaal and Grootegeluk collieries were selected as being suitable for this investigation. The coals were subjected to detailed characterisation, bench-scale and pilot-scale fluidised bed gasification tests. The results of the pilot-scale atmospheric bubbling fluidised bed gasification tests show that stable gasification is possible at temperatures between 880 °C and 980 °C. The maximum fixed carbon conversion achievable in the pilot plant is, however, limited to ± 88% due to the low reactivity of the coals tested and to thermal fragmentation and attrition of the coal in the gasifier. It was found that oxygen enrichment of the gasification air from 21% to 36% by means of oxygen addition produces a significant increase in the calorific value of the gas (3.0 MJ/Nm3 to 5.5 MJ/Nm3). This observation has not previously been reported at pilot-plant scale. A mathematical model for a bubbling fluidised bed coal gasifier was developed based on sub-models for fluidised bed hydrodynamics, coal devolatilisation, chemical reactions, transfer processes and fines generation. A coal devolatilisation sub-model to predict the products of coal devolatilisation in a fluidised bed gasifier was developed and incorporated into the model. Parameters associated with the rates of the gasification reactions and the devoltilisation process were obtained by means of bench-scale tests. The heat loss parameter (Q) in the model was estimated by means of a heat loss calculation. The results from the pilot-scale gasification tests were used to evaluate the predictive capability of the model. It was found that for temperature, fixed carbon conversion and calorific value of the gas the difference between measured and predicted values was less than 10%. Recommendations are made for further refinement of the model to improve its predictive capability and range of application. The model was used to study the effect of major operating variables on gasifier performance. It was found that increasing the reactant gas (air, oxygen and steam) temperature from 250 °C to 550 °C increases the calorific value of the gas by ± 9.3% and the gasification efficiency by ± 6.0%. Increasing the fluidised bed height has a positive effect on fixed carbon conversion; however, at higher bed heights the benefit of increasing the bed height is less due to the inhibiting effects of H2 and CO on the rates of char gasification. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

In this study the performance of pure, very fine iron (III) oxide powder was investigated as catalyst for the decomposition of sulphur trioxide into sulphur dioxide and oxygen. This highly endothermic reaction requires a catalyst to lower the reaction temperature. This reaction forms part of the HyS (Hybrid Sulphur) cycle, a proposed thermochemical process for the industrial scale production of hydrogen and oxygen from water. The study aimed at obtaining reaction kinetics for this reaction employing pure, unsupported iron (III) oxide as catalyst as a cheaper alternative compared to supported iron catalysts. It was found that the SO3 conversion was carried out in the absence of diffusion limitations and that the reverse reaction did not play a significant role. By assuming plug flow conditions in the reactor and 1st order kinetics, the kinetic parameters of the reaction were obtained. These parameters that form part of the Arrhenius law in describing the reaction rate constant, were determined to be 118(±23) kj / mol for the activation energy ( Ea ), and a value of 3(±0.5) x 108hr-1 was obtained for the Arrhenius frequency factor ( A ). Both values correspond to literature, although in general larger activation energies were published for iron (III) oxide derived supported catalysts. A comparison of the performance of the pure, unsupported iron (III) oxide catalyst with other iron (III) oxide derived supported catalysts (or pellets) has shown that the pure iron (III) oxide catalyst exhibit similar activities. Avoiding expensive catalyst preparation will be an initial step in the direction of developing a cost effective catalyst for the decomposition of sulphur trioxide. It is, however, recommended to investigate different particle sizes as well as purity levels of the unsupported iron (III) oxide to find an optimum cost to performance ratio, as the degree of fineness and the degree of purity will largely influence the final catalyst cost. A qualitative investigation with various reaction product species as well as water in the reactor feed was conducted to assess the influence of these species on the reaction rate. The addition of these species seems to have a larger influence on the reaction rate at low reaction temperatures around 700°C than at higher reaction temperatures (i.e. 750°C and 825°C). This can be attributed to adsorption rates of such species that reduce at higher temperatures. Observations at higher reaction temperatures also suggest that the reaction is of a first-order nature. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

South Africa has large coal reserves and produces approximately 74% of its primary energy from coal. Coal gasification using moving bed gasifiers is one of the most important coal utilisation technologies, consuming ± 17.5% of locally produced coal. This study was motivated by the need to investigate alternative coal gasification technologies for the utilisation of fine, high-ash and caking coals for future Integrated Gasification Combined Cycle (IGCC) and coal to liquids (CTL) plants. These coals are estimated to form a large percentage of the remaining coal reserves in South Africa and could be difficult to utilise efficiently in moving bed gasifiers. Fluidised bed gasification was identified as a technology that could potentially utilise these coals. Coals from the New Vaal and Grootegeluk collieries were selected as being suitable for this investigation. The coals were subjected to detailed characterisation, bench-scale and pilot-scale fluidised bed gasification tests. The results of the pilot-scale atmospheric bubbling fluidised bed gasification tests show that stable gasification is possible at temperatures between 880 °C and 980 °C. The maximum fixed carbon conversion achievable in the pilot plant is, however, limited to ± 88% due to the low reactivity of the coals tested and to thermal fragmentation and attrition of the coal in the gasifier. It was found that oxygen enrichment of the gasification air from 21% to 36% by means of oxygen addition produces a significant increase in the calorific value of the gas (3.0 MJ/Nm3 to 5.5 MJ/Nm3). This observation has not previously been reported at pilot-plant scale. A mathematical model for a bubbling fluidised bed coal gasifier was developed based on sub-models for fluidised bed hydrodynamics, coal devolatilisation, chemical reactions, transfer processes and fines generation. A coal devolatilisation sub-model to predict the products of coal devolatilisation in a fluidised bed gasifier was developed and incorporated into the model. Parameters associated with the rates of the gasification reactions and the devoltilisation process were obtained by means of bench-scale tests. The heat loss parameter (Q) in the model was estimated by means of a heat loss calculation. The results from the pilot-scale gasification tests were used to evaluate the predictive capability of the model. It was found that for temperature, fixed carbon conversion and calorific value of the gas the difference between measured and predicted values was less than 10%. Recommendations are made for further refinement of the model to improve its predictive capability and range of application. The model was used to study the effect of major operating variables on gasifier performance. It was found that increasing the reactant gas (air, oxygen and steam) temperature from 250 °C to 550 °C increases the calorific value of the gas by ± 9.3% and the gasification efficiency by ± 6.0%. Increasing the fluidised bed height has a positive effect on fixed carbon conversion; however, at higher bed heights the benefit of increasing the bed height is less due to the inhibiting effects of H2 and CO on the rates of char gasification. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

The reaction kinetics of Iroko and Mahogany were studied using TGA. The pyrolysis process was achieved using six different heating rates of 2,5,8,12,15 and 20˚C. A 15˚C/min heating rate was used for gasification in steam at different temperatures while varying the concentrations of nitrogen and steam in the process. The kinetic parameters, activation energy and pre exponential factor, were obtained by implementing two chosen kinetic models. These models are: Friedman’s Iso-conversional Method, Flynn-Wall-Ozawa Method (FWO). There were substantial differences in the values of the kinetic triplets found from the experiments. Due to the substantial differences in the values, it was not the best way to perform this kind of analysis (which is the traditional way) but instead to use pure regression analysis; but using it for the whole data set (that means for all heating rates) and minimize the difference with experimental data.

The goal of this PhD thesis was to develop dense aluminium compound-cubic boron nitride composites with a high cBN content. To achieve this goal, two different strategies were used: infiltration of cBN preforms and hot pressing of cBN-Al mixtures. The particle size of the cBN and the amount of aluminium were systematically varied and the influence of these parameters on densification and selected properties was evaluated. A basic understanding of the product that was formed over certain temperatures and times provides information that can be used in optimizing the infiltration and hot pressing of cBN with Al. For this reason, the reaction kinetics between Al and cBN was initially investigated. The reaction kinetics of the chemical interactions between Al and cBN was investigated in detail using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The reaction was studied using samples containing 50 volume percent of Al and 50 volume percent of cBN (12 μm) hot pressed at 800 oC. The prepared samples were allowed to react isothermally at temperatures between 1 000 oC and 1 400 oC under nitrogen (N2) and argon (Ar) atmospheres. It was found that the degree and rate of the reactions increased with increasing temperature in both N2 and Ar atmospheres. The degree of aluminium nitride (AlN) formation was considerably higher under N2 than under Ar. The difference in the formation of AlN between the two atmospheres was attributed to the reaction of N2 gas with the sample due to the open porosity. The infiltration of partially hexagonalized cBN matrix with molten Al was studied. The samples were found to have a density higher than 97% of the theoretical density. It was found that the amount of soft hBN phase present in the sample (due to hexagonalization) increases at temperatures higher than 1 300 oC, resulting in a hardness of the final material of Hv10 = 6.5 ± 4.8 GPa. Because of thie poor hardness this route was abandoned. Cubic boron nitride powder (12 μm) without hexagonal boron nitride (hBN) was also infiltrated with aluminium. The infiltrated samples were found to exhibit a density higher than 96% of the theoretical density. The Al reacted with cBN and no hBN was observed at temperatures below 1 400 oC. The resulting product showed a Vickers hardness of Hv10 = 14.4 ± 1.6 GPa compared with Hv10 = 6.5 ± 4.8 GPa obtained with the partially hexagonalized cBN matrix. Infiltration of 3 μm cubic boron nitride increased the Vickers hardness to 22.0 ± 0.6 GPa. However, this infiltration was not very reproducible. Al-cBN cermets were hot pressed at temperatures between 800 oC and 1 750 oC and at a pressure of 50 MPa in vacuum. The effect of the particle size of the starting powders, as well as the effect of the starting compositions and temperature, was investigated. The materials could only densify up to 80 – 92% of the theoretical density. After hot pressing at 800 oC, only Al and cBN could be observed by XRD, whereas higher hot-pressing temperatures resulted in the formation of AlN and AlB2 which retard the densification. The microstructure of the hot-pressed materials was studied using SEM. It was observed that there are oxide layers at the interface between the Al and cBN phases. The presence of these oxide layers prevented the Al from spreading, thereby preventing full densification.

The broad objective of the study was to gain further knowledge of the reaction rates and mechanisms by which carbohydrates, particularly 3(l-4) glucans, are transformed and degraded in aqueous alkaline solutions. While the isomerization, epimerization, and degradation of carbohydrates has been extensively studied and reviewed, there are practically no kinetic data available on these important reactions due apparently to a lack of reasonable procedures for assay of the reaction systems. Because of the important theoretical, physiological, and industrial implications of these reactions, it appeared useful to have kinetic data on them and concomitantly thus to develop a method for obtaining such data. The specific problem selected for study from this broad area was the measurement of reaction rates prevailing in the homogeneous system: cellobiose-l molar sodium hydroxide-water at 22°C. and to derive-the related rate constants from the reaction rate expressions and then to assess current understanding of these reactions in light of the kinetic data obtained.

Reactive chemicals are presented widely in the chemical and petrochemical process industry. Their chemical reactivity hazards have posed a significant challenge to the industries of manufacturing, storage and transportation. The accidents due to reactive chemicals have caused tremendous loss of properties and lives, and damages to the environment. In this research, three classes of reactive chemicals (unsaturated hydrocarbons, self-reacting chemicals, energetic materials) were evaluated through theoretical and experimental methods. Methylcyclopentadiene (MCP) and Hydroxylamine (HA) are selected as representatives of unsaturated hydrocarbons and self-reacting chemicals, respectively. Chemical reactivity of MCP, including isomerization, dimerization, and oxidation, is investigated by computational chemistry methods and empirical thermodynamic–energy correlation. Density functional and ab initio methods are used to search the initial thermal decomposition steps of HA, including unimolecular and bimolecular pathways. In addition, solvent effects are also examined using water cluster methods and Polarizable Continuum Models (PCM) for aqueous solution of HA. The thermal stability of a basic energetic material, Nitroethane, is investigated through both theoretical and experimental methods. Density functional methods are employed to explore the initial decomposition pathways, followed by developing detailed reaction networks. Experiments with a batch reactor and in situ GC are designed to analyze the distribution of reaction products and verify reaction mechanisms. Overall kinetic model is also built from calorimetric experiments using an Automated Pressure Tracking Adiabatic Calorimeter (APTAC). Finally, a general evaluation approach is developed for a wide range of reactive chemicals. An index of thermal risk is proposed as a preliminary risk assessment to screen reactive chemicals. Correlations are also developed between reactivity parameters, such as onset temperature, activation energy, and adiabatic time to maximum rate based on a limited number, 37 sets, of Differential Scanning Calorimeter (DSC) data. The research shows broad applications in developing reaction mechanisms at the molecular level. The methodology of reaction modeling in combination with molecular modeling can also be used to study other reactive chemical systems.