No description available.

The scope of work can be divided into; the measurement of the rheological properties of a new emulsified acid system that can be suitable for high temperature applications, a study of the performance of the new emulsified acid in stimulating both calcite and dolomite formations, measuring the reaction rate and diffusion coefficient when the new emulsified acid systems react with both calcite and dolomite, and testing the new emulsified acid using core samples obtained from carbonate reservoirs. The droplet size has a practical impact on the performance of emulsified acid. A good understanding and characterization of the emulsified acid by its size distribution will lead to better understanding of its stability, rheology and how it reacts with carbonate rocks. The influence of the concentration of the new emulsifier on the droplet size, droplet size distribution and upon the rheology of emulsified acids is studied in detail. The emulsified acid reaction kinetics with calcite rocks was studied before in few studies, and very little work was done with dolomite. One of the main objectives of the present work is to study in detail the reaction of the emulsified acid with both calcite and dolomite rocks using the rotating disk apparatus. Most of the previous studies on the emulsified acid were done using core samples that were saturated with brine or deionized water. One of the main objectives of the present work is to study in detail the effect of the presence of crude oil in the reservoir rock on the performance of emulsified acids. Lastly, an innovative technique of emulsifying the chelating agents is evaluated for high temperature applications. The rheology of the emulsified chelating agent is measured using an HPHT rheometer. Also, the reaction of the new emulsified chelating agent with calcite is studied using the rotating disk apparatus, and coreflood experiments were performed using chelating agents and calcite core samples.

Nuclear magnetic resonance (NMR) yields remarkably detailed structural information about virtually any molecule. However, its application to non-equilibrium systems is hampered by a lack of sensitivity. To increase the amount of signal that can be obtained from a NMR experiment, various hyperpolarization schemes have been previously introduced. One such technique is dynamic nuclear polarization (DNP), which can enhance NMR sensitivity by several orders of magnitude. The work detailed here focuses on the development of methods utilizing DNP to study non-equilibrium systems such as chemical and biochemical reactions in real-time. To work with hyperpolarized samples, we have designed and constructed a rapid injection and mixing system. This system allows samples to be transported between superconducting magnets used for polarization and for NMR spectroscopy in less than two seconds. Rapid transport is essential for successful use of samples with short spin-lattice relaxation times. For the study of reactions under non-equilibrium conditions, the system provides the additional capability for samples to be mixed with a second, unpolarized reagent. A chromogenic trypsin catalyzed ester hydrolysis reaction was used to validate the DNP-NMR technique as a tool for kinetic analysis. It is shown that the DNP-NMR method agrees with the conventional UV method within the uncertainty of the measurement. Hyperpolarization in this modality presents both challenges and opportunities, each of which motivate the development of new NMR techniques. In addition to the determination of kinetics, DNP-NMR is amenable to mechanistic analysis of a reaction. We have developed a technique based on selective inversion of spin-polarization, which allows for mapping of atoms between reactant and product of a reaction. This scheme was applied to a Grignard reaction, demonstrating applicability to organic reactions. Signal averaging, as it is applied for conventional multi-dimensional correlation spectroscopy cannot always be applied easily when using hyperpolarized sample. For the rapid measurement of heteronuclear correlation spectra, we have developed a technique utilizing the differential scaling of scalar coupling under off-resonance irradiation. Although DNP-NMR yields spectra of outstanding quality even with small quantities of sample, peak intensities are not quantitative. It is nevertheless possible to compare peak multiplets obtained from fractionally isotope labeled samples. Using biosynthetically labeled lipids from E. Coli cells, we showed that the resulting labeling patterns reflect their biosynthetic pathways. As a final case-study employing several of these newly developed methods, the uronate isomerase catalyzed isomerization of glucuronate into fructuronate was studied. The ability to follow the reaction in real-time while directly observing all anomeric forms of the reactant and product permits the independent determination of kinetics for each anomeric form of substrate and product. This study revealed the anomeric specificity of the enzyme.

The production of biodiesel from a butter factory effluent was the main focus of the study. The alkali transesterification reaction was used to produce the biodiesel. The effect of the temperature, alcohol to oil molar ratio, catalyst concentration and the reaction time was investigated to determine the optimal reaction conditions. The reaction temperature varied from 45 °C to 65 °C with a 5 °C increment. The alcohol to oil molar ratio varied from 3:1 to 8:1 with an increment of 1:1. The experiments with varying catalyst load were carried out at 0.8 wt%, 1.0 wt% and 1.2wt%. The reaction time was kept constant at 120 minutes, but samples of the reaction mixture were taken at 10 minute intervals. The optimal reaction conditions according to the results were 50 °C, 6:1 alcohol to oil molar ratio, 1.0 to 1.2 wt% catalyst loads and a reaction time of 60 to 90 minutes. The optimal temperature was also the maximum temperature since a further increase in temperature lowered the ester content. Increasing the alcohol to oil molar ratio above 6:1 had no effect on the ester content. The increase in catalyst load decreased the time needed for the reaction to reach equilibrium. The purification process was also investigated. The biodiesel was washed with water, Magnesol® DSOLTM and Purolite® PD-206. The Magnesol® D-SOLTM was the best method for lowering the water content and the acid value of the fuel. A Magnesol® D-SOLTM content of 1.0 wt% was mixed with the biodiesel for 30 minutes in order to lower the water content and the acid value to below the maximum limit. A kinetic model for the biodiesel reaction was developed. The model was based on the second order reversible reaction. The temperature range for the model is from 45 °C to 55 °C. The forward reaction was found to be exothermic with an endothermic reverse reaction. The activation energy for the exothermic forward reaction varied between 9.478 and 26.937 kJ/mol while the activation energy for the endothermic reverse reaction varied between 74.161 and 136.433 kJ/mol for the reactions with a catalyst load of 1.2 wt%. The biodiesel was tested according to the SANS 1935:2011 standard. The biodiesel did not meet all the requirements of the standard. The flash point, sulphur content, carbon residue, oxidation stability, free glycerol, total glycerol and cold filter plugging point did not meet the specification of SANS 1935:2011. The biodiesel should be blended with mineral diesel if it is to be used commercially. The butter factory effluent can be used as a feedstock for the production of biodiesel. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

The production of biodiesel from a butter factory effluent was the main focus of the study. The alkali transesterification reaction was used to produce the biodiesel. The effect of the temperature, alcohol to oil molar ratio, catalyst concentration and the reaction time was investigated to determine the optimal reaction conditions. The reaction temperature varied from 45 °C to 65 °C with a 5 °C increment. The alcohol to oil molar ratio varied from 3:1 to 8:1 with an increment of 1:1. The experiments with varying catalyst load were carried out at 0.8 wt%, 1.0 wt% and 1.2wt%. The reaction time was kept constant at 120 minutes, but samples of the reaction mixture were taken at 10 minute intervals. The optimal reaction conditions according to the results were 50 °C, 6:1 alcohol to oil molar ratio, 1.0 to 1.2 wt% catalyst loads and a reaction time of 60 to 90 minutes. The optimal temperature was also the maximum temperature since a further increase in temperature lowered the ester content. Increasing the alcohol to oil molar ratio above 6:1 had no effect on the ester content. The increase in catalyst load decreased the time needed for the reaction to reach equilibrium. The purification process was also investigated. The biodiesel was washed with water, Magnesol® DSOLTM and Purolite® PD-206. The Magnesol® D-SOLTM was the best method for lowering the water content and the acid value of the fuel. A Magnesol® D-SOLTM content of 1.0 wt% was mixed with the biodiesel for 30 minutes in order to lower the water content and the acid value to below the maximum limit. A kinetic model for the biodiesel reaction was developed. The model was based on the second order reversible reaction. The temperature range for the model is from 45 °C to 55 °C. The forward reaction was found to be exothermic with an endothermic reverse reaction. The activation energy for the exothermic forward reaction varied between 9.478 and 26.937 kJ/mol while the activation energy for the endothermic reverse reaction varied between 74.161 and 136.433 kJ/mol for the reactions with a catalyst load of 1.2 wt%. The biodiesel was tested according to the SANS 1935:2011 standard. The biodiesel did not meet all the requirements of the standard. The flash point, sulphur content, carbon residue, oxidation stability, free glycerol, total glycerol and cold filter plugging point did not meet the specification of SANS 1935:2011. The biodiesel should be blended with mineral diesel if it is to be used commercially. The butter factory effluent can be used as a feedstock for the production of biodiesel. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.

No description available.

Biomass is an alternative to fossil fuels that has a lower impact on the environment and is thus of great interest to replace fossil fuels for energy production. There are several technologies to convert the stored energy in biomass into useful energy and this thesis focuses on the process of gasification. The purpose of this thesis is to investigate how the prediction accuracy of gas composition in a kinetic model for fluidized bed gasifier is affected when hydrodynamic parameters are introduced into the model. Two fluidized bed gasifier models has therefore been set up in order to evaluate the affects: one model which only considers the kinetics of a gasifier and a second model which includes both the kinetics and the hydrodynamic parameters for a bubbling fluidized bed. The kinetic model is represented by an already existing kinetic model that is originally derived for a downdraft gasifier which has quite similar biomass gasification processes as fluidized bed gasifiers. Gas residence time differs between the two gasifier types and the model has thus been calibrated by introducing a time correction factor in order to use it for fluidized bed gasifiers and get optimum results. Two sets of experimental data were used for comparison between the two models. The models were compared by comparing the results of the predicted gas composition yield and the amount of unreacted carbon after the reactor at various equivalence ratios (ER). The result shows that the model that only considers reaction kinetics yields best agreement with the experimental data that have been used. One reasons as to why the kinetic model gives a better prediction of gas composition is due to the fact that there are higher reactant concentrations available for chemical reactions in the kinetic, in comparison to the combined model. Less reactant concentrations in the combined model is a result of the bed in the combined model consisting of two phases, according to the two-phase theory of fluidization that have been adapted. Both phases contain gases but the bubble phase is considered solid free, chemical reactions occur therefore only in the emulsion phase since the kinetic model is based on gas-solid reactions. The model that only contains reaction kinetics considers only one phase and all concentrations are available for chemical reactions. Higher char conversion is thus achieved in the model that only contains reaction kinetics and higher gas concentrations are produced.

Fundamental studies on the mechanisms and kinetics of reduction of dense synthetic nickel oxide have been carried out in H2-N2 and H2-H2O mixtures. The influences of temperature, hydrogen partial pressure, and hydrogen-steam ratio on the reduction process were systematically investigated. The kinetics of the reduction process were followed metallographically by measuring the advance of the nickel product layer. The microstructures of the reduction products and their changes during heating were characterized using a high resolution scanning electron microscopy. In H2-N2 mixtures and H2-H2O mixtures with low steam content, it was found that the initial reduction rates were first order with respect to hydrogen partial pressure. In both sets of mixtures, it was found that the progress of NiO reduction was not a monotonic function of temperature. A minimum rate of advancement of NiO reduction was observed in the temperature range 700oC – 800oC depending on the hydrogen partial pressures and reduction time. A number of distinctly different nickel product microstructures, originating at the Ni-NiO interface were observed under various reduction conditions, namely coarse fibrous nickel with fissures, fine porous nickel-planar interface, large porous nickel-irregular interface and dense nickel product layer. The microstructures of reduction product were found to change with temperature and time. It was found that heating the coarse fibrous nickel structure resulted in a re-crystallization, grain growth and densification of nickel product. When the heat treatments were carried out on the porous nickel structures, the number of pores decreases with increasing temperature and time, which was accompanied by the increase in the pore sizes. The microstructures and kinetics of the reduction of nickel oxide were found to be a function of temperature, gas composition and reaction time. The study provides strong evidence for a link between the reduction kinetics and the changes in the reduction product microstructures. Mechanisms and kinetics of the reduction of nickel oxide have been discussed by considering reduction conditions, information on the structures and elementary processes involving in the reduction process.

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