Nanofabrication is the process of making functional structures with arbitrary patterns having nanoscale dimensions. Nanofabrication has been widely implemented in industry for improving microelectronic devices and data storage technology, to increase the component density, to lower the cost and to increase the performance. Other areas of applications include optics, cell biology and biomedicine. One of the most critical challenges in the development of next generation nanoscale devices is the rapid, parallel, precise and robust fabrication of nanostructures. In this thesis work, we demonstrate the possibility to parallelize the thermochemical nanolithography (TCNL) by creating nanoscale patterns with a tip array, containing five identical thermal cantilevers. The versatility of our technique is demonstrated by creating nanopatterns simultaneously on multiple surfaces, including graphene oxide and conjugated polymers. This work also involves the study of the reduction process of graphene fluoride through TCNL and the study of the local anodic oxidation of epitaxial graphene, to create high quality graphene nanoribbons.

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The pyrolysis of methyl nitrite (1 torr) in the presence of nitrogen dioxide (1 torr) was studied at 458K over the pressure range 0-760 torr of carbon tetrafluoride. The only detectable products were methyl nitrate and formaldehyde. The decomposition can be described by the following simple mechanism: CH₃ONO + M → CH₃O + NO + M (1); CH₃O + NO₂ → CH₃ONO₂ (2); CH₃O + NO₂ → HCHO + HONO (3). Step (1) was found to be stongly pressure dependent with a P½ value of 760 torr. The rate constant for decomposition k₁ was found from RRKM modelling to be given by the following expression: log (k₁/s⁻¹) = 15.89 - 8879/T. The ratio k₃/k₂ was determined over the pressure range and was also found to be pressure dependent. This was attributed to the pressure dependence of step (2). Estimates were also made for the ratio of disproportionation to combination for the reaction between nitric oxide and the methoxy radical. This ratio was also found to be strongly pressure dependent. The pyrolysis of perfluoroazo-2-propane, PAP, (25 torr) was studied over the temperature range 450-514K. The products were nitrogen and perfluorohexane, PFH, which were produced in equal amounts. The production of nitrogen was found to be first order with respect to the azo compound. First order kinetics were observed even for extents of reaction exceeding 60%. No surface effects were observed. The reaction was pressure independent. i-C₃F₇N²i-C₃F₇ → i-C₃F₇N₂ + i-C₃F₇ (4). The rate constant for decomposition, k₄, was found to be given by the following expression: log(k₄) = 16.74 - 9856/T. The pyrolysis of formaldehyde (4-10 torr) was studied using a static system over the temperature range 705-773K and 150-760 torr of carbon dioxide. Methane (4-10 torr) was used as an inert marker. Preliminary experiments showed that methane did not decompose under these experimental conditions. The only measurable products were hydrogen and carbon monoxide. No pressure dependence was observed, even at the highest temperatures studied. The rate of formation of products was found to be 1.04 ± 0.05 with respect to formaldehyde. From this the reaction was taken to be first order. The addition of small concentrations of toluene was found to markedly reduce the rate of formation of products. There did not appear to be any surface effects, indicating that the reaction was homogeneous.

The thermochemical copper-chlorine (Cu-Cl) cycle for hydrogen production includes three chemical reactions of hydrolysis, decomposition and electrolysis. The decomposition of copper oxychloride establishes the high-temperature limit of the cycle. Between 430 and 530 oC, copper oxychloride (Cu2OCl2) decomposes to produce a molten salt of copper (I) chloride (CuCl) and oxygen gas. The conditions that yield equilibrium at high conversion rates are not well understood. Also, the impact of feed streams containing by-products of incomplete reactions in an integrated thermochemical cycle of hydrogen production are also not well understood. In an integrated cycle, the hydrolysis reaction where CuCl2 reacts with steam to produce solid copper oxychloride precedes the decomposition reaction. Undesirable chlorine may be released as a result of CuCl2 decomposition and mass imbalance of the overall cycle and additional energy requirements to separate chlorine gas from the oxygen gas stream. In this thesis, a new phase change predictive model is developed and compared to the reaction rate kinetics in order to better understand the nature of resistances. A Stefan boundary condition is used in a new particle model to track the position of the moving solid-liquid interface as the solid particle decomposes under the influence of heat transfer at the surface. Results of conversion of CuO*CuCl2 from both a thermogravimetric (TGA) microbalance and a laboratory scale batch reactor experiments are analyzed and the rate of endothermic reaction determined. A second particle model identifies parameters that impact the transient chemical decomposition of solid particles embedded in the bulk fluid consisting of molten and gaseous phases at high temperature and low Reynolds number. The mass, energy, momentum and chemical reaction equations are solved for a particle suddenly immersed in a viscous continuum. Numerical solutions are developed and the results are validated with experimental data of small samples of chemical decomposition of copper oxychloride (CuO*CuCl2). This thesis provides new experimental and theoretical reference for the scale-up of a CuO*CuCl2 decomposition reactor with consideration of the impact on the yield of the thermochemical copper-chlorine cycle for the generation of hydrogen. / UOIT

Doctor of Philosophy / Department of Chemical Engineering / Peter H. Pfromm / Since its inception, the Haber-Bosch (HB) process for ammonia (NH3) synthesis has allowed for a significant increase in global food production as well as a simultaneous decrease in global hunger and malnutrition. The HB process is estimated to be responsible for the subsistence of 40% of the world population as approximately 85% of the over 182 metric tons of NH3 produced in 2017 was used as fertilizer for crop production. The natural gas consumed (mostly to generate H2) represents approximately 2% of the global energy budget, while the CO2 produced is about 2.5% of all global fossil CO2 emissions. Approximately 40% of food consumed is essentially natural gas transformed by the HB process into agricultural products. However global food production will need to double due to expected increase in world population to 9.6 billion by 2050 and rising demand for protein among developing nations. A novel thermochemical reaction cycle for sustainable NH3 synthesis at atmospheric pressure is explored herein. Both thermochemical and kinetic rationales are discussed regarding choice of Mn as the cycled reactant. The energetic driving force for these reactions is conceptually derived from concentrated solar energy. Mn was reacted with N2 forming Mn-nitride, corrosion of Mn-nitride with steam at 500 °C formed MnO and NH3, and lastly MnO was reduced at 1150 °C in a 4 vol % CH4 – 96 vol % N2 stream to Mn-nitride closing the cycle. Optimum nitridation at 800 °C and 120 min produced a Mn6N2.58-rich Mn-nitride mixture containing 8.7 ± 0.9 wt. % nitrogen. NH3 yield was limited to 0.04 after 120 min during nitride corrosion but addition of a NaOH promotor improved NH3 yield to 0.54. Mn6N2.58 yield was 0.381 ± 0.083 after MnO reduction for 30 min with CO and H2 but no CO2 detected in the product. Mn-nitridation kinetics were investigated at temperatures between 600 and 900 °C for 10 and 44 μm reactant powder particle sizes. That equilibrium conversion decreased with increasing temperature was confirmed. Jander’s rate law, which assumes gaseous reactant diffusion through a solid product layer, described the experimental data reasonably well. The rate constants and initial rates were as much as an order of magnitude greater for the 10 μm Mn reactant particle size. Additionally the activation energy was found to be 44.1 kJ mol-1 less for the 10 μm reactant particle size. Reducing the particle size had a small but positive effect on Mn-nitridation kinetics. Further reducing particle size will likely have a greater impact. A review of relevant classical thermodynamics is discussed with special attention paid to open systems. Confidence issues regarding over-reliance on x-ray diffraction are considered with options suggested for mitigation. Opportunities for future work are assessed.

Because of the high demand for hydrogen in the oil industries, new technologies for hydrogen production are being investigated. The thermochemical splitting cycle is one of them. Among the cycles that have been investigated, sulfur-iodine (S-I) water splitting is the most studied. In the S-I cycle, there are three reactions: H2SO4 decomposition, Bunsen reaction and HI decomposition. A new thermochemical cycle has been developed based on the S-I cycle, which is a H2S splitting cycle. In the H2S cycle, there are also three reactions. The only difference between S-I and H2S cycle is that the H2SO4 decomposition reaction is replaced by a reaction between hydrogen sulfide and sulfuric acid which produces sulfur dioxide, elemental sulfur and water. Research on this reaction has been done for many years, studying thermodynamic, kinetics and mass transfer. This reaction produces sulfur, sulfur dioxide and water. The SO2 produced is the used in the second reaction in the H2S cycle; the Bunsen reaction.<p> The main objective of this research was to find an operating condition to increase the production of SO2 from the reaction between H2S and H2SO4. This study investigated different conditions such as temperature, stirring rate and sulfuric acid concentration to maximize the production of SO2. The temperature and stirring rate range used in the reaction were from 120 to 160°C and from 0 to 400 rpm, respectively. The sulfuric acid concentrations were between 90 and 96 wt%. The results showed that increasing the temperature and the acid concentration in the reaction between H2S and H2SO4, the SO2 produced from this reaction will increase. There is no need to apply stirring in the reaction, because the stirring will increase the surface area which allows the produced sulfur dioxide in the gas phase to be dissolved more in sulfuric acid solution, which favors the unwanted side-reaction between SO2 and H2S. A model that was developed to predict the partial pressure change of SO2 in closed reactor. This model was used to compare the data between experimental and simulation through Matlab software. The simulated data was compared to the experimental data and the results indicated that the model fits the data satisfactorily. Additionally, study on the separation between the remaining sulfuric acid and produced elemental sulfur from the reaction between H2S and H2SO4 were performed. The mixture was placed in an oven at140°C of temperature for two hours. It was found that all small droplets of sulfur produced during the reaction between hydrogen sulfide and sulfuric acid agglomerated and the sulfuric acid solution became clearer.

Because of the high demand for hydrogen in the oil industries, new technologies for hydrogen production are being investigated. The thermochemical splitting cycle is one of them. Among the cycles that have been investigated, sulfur-iodine (S-I) water splitting is the most studied. In the S-I cycle, there are three reactions: H2SO4 decomposition, Bunsen reaction and HI decomposition. A new thermochemical cycle has been developed based on the S-I cycle, which is a H2S splitting cycle. In the H2S cycle, there are also three reactions. The only difference between S-I and H2S cycle is that the H2SO4 decomposition reaction is replaced by a reaction between hydrogen sulfide and sulfuric acid which produces sulfur dioxide, elemental sulfur and water. Research on this reaction has been done for many years, studying thermodynamic, kinetics and mass transfer. This reaction produces sulfur, sulfur dioxide and water. The SO2 produced is the used in the second reaction in the H2S cycle; the Bunsen reaction.<p> The main objective of this research was to find an operating condition to increase the production of SO2 from the reaction between H2S and H2SO4. This study investigated different conditions such as temperature, stirring rate and sulfuric acid concentration to maximize the production of SO2. The temperature and stirring rate range used in the reaction were from 120 to 160°C and from 0 to 400 rpm, respectively. The sulfuric acid concentrations were between 90 and 96 wt%. The results showed that increasing the temperature and the acid concentration in the reaction between H2S and H2SO4, the SO2 produced from this reaction will increase. There is no need to apply stirring in the reaction, because the stirring will increase the surface area which allows the produced sulfur dioxide in the gas phase to be dissolved more in sulfuric acid solution, which favors the unwanted side-reaction between SO2 and H2S. A model that was developed to predict the partial pressure change of SO2 in closed reactor. This model was used to compare the data between experimental and simulation through Matlab software. The simulated data was compared to the experimental data and the results indicated that the model fits the data satisfactorily. Additionally, study on the separation between the remaining sulfuric acid and produced elemental sulfur from the reaction between H2S and H2SO4 were performed. The mixture was placed in an oven at140°C of temperature for two hours. It was found that all small droplets of sulfur produced during the reaction between hydrogen sulfide and sulfuric acid agglomerated and the sulfuric acid solution became clearer.

Of the many thermochemical conversion pathways for utilizing biomass as a renewable energy source, fast pyrolysis is a promising method for converting and upgrading carbonaceous feedstocks into a range of liquid fuels for use in heat, electricity and transportation applications. Experimental trials have been carried out to assess the impact of operational parameters on process yields. However, dealing with larger-scale experimental systems comes at the expense of lengthy and resource-intensive experiments. Luckily, the advances in computing technology and numerical algorithm solvers have allowed reactor modelling to be an attractive opportunity for reactor design, optimization and experimental data interpretation in a cost-effective fashion. In this work, a fluidized bed reactor model for biomass fast pyrolysis was developed and applied to the Bell’s Corners Complex (BCC) fluidized bed fast pyrolysis unit located at NRCan CanmetENERGY (Ottawa, Canada) for testing and validation. The model was programmed using the Microsoft Visual Basic for Applications software with the motivation of facilitating use and accessibility as well as minimizing runtime and input requirements. The application of different biomass devolatilization schemes within the model was conducted, not only for biomass fast pyrolysis product quantity but also liquid product composition (quality), to examine the effect of variable reaction kinetic sub-models on product yields. The model predictions were in good agreement with the results generated from the experimental work and mechanism modifications were proposed which further increased the accuracy of model predictions. Successively, the formulation of the modelled fluid dynamic scheme was adapted to study the effect of variable hydrodynamic sub-models on product yields for which no significant effect was observed. The work also looked into effect of the dominant process variables such as feedstock composition, bed temperature, fluidizing velocity and feedstock size on measurable product outputs (bio-oil, gas and biochar) and compared the results to those generated from the experimental fast pyrolysis unit. The ideal parameters for maximizing bio-oil yield have been determined to be those which: minimize the content of lignin and inorganic minerals in the feedstock, maintain the dense-bed temperature in a temperature range of 450-520 ºC, maximize the fluidization velocity without leading to bed entrainment, and limit the feedstock particle size to a maximum of 2000 μm.

The suitability of water hyacinth (Eichornia crassipes) as a viable feedstock for renewable energy production was investigated in this project. Water hyacinth used in this study was harvested from the Vaal River near Parys in the northwest region of the Free State province, South Africa (26°54′S 27°27′E). The wet plants were processed in the laboratory at the North-West University by separating the roots from the leaves and the stems, thus obtaining two separate water hyacinth feedstock. Characterisation of the feedstock showed that the stems and leaves are more suitable for bio-energy production than roots, due to the higher cellulose and hemicellulose content and very low lignin content of the stems and leaves. Water hyacinth was evaluated as feedstock for the production of bio-ethanol gel, bio-ethanol, bio-oil and bio-char. The recovery of water from the wet plants for use in bio-refining or for use as drip-irrigation in agriculture was also investigated. Cellulose was extracted from water hyacinth feedstock to be used as a gelling agent for the production of ethanol-gel fuel. A yield of 200 g cellulose/kg dry feedstock was obtained. The extracted cellulose was used to produce ethanol-gel with varying water content. The gel with properties closest to the SANS 448 standard contained 90 vol% ethanol and 10 vol% water, with 38 wt% cellulose. This gel was found to ignite readily and burn steadily, without flaring, sudden deflagrations, sparking, splitting, popping, dripping or exploding from ignition until it had burned to extinction, as required by SANS 448. The only specifications that could not be met were the viscosity (23,548 cP) and the high waste residue (32 wt%) left after burning. The other major concern is the extremely high costs involved with the manufacturing of ethanol-gel from water hyacinth cellulose. It can be concluded that ethanol-gel cannot be economically produced using water hyacinth as feedstock. Chemical and enzymatic extraction of water from the feedstock, which is stems and leaves or roots, showed that the highest yield of water was obtained using a combination of Celluclast 1.5 L, Pectinex Ultra SP-L and additional de-ionised water. A yield of 0.89 ± 0.01 gwater/gwater in biomass was realised. This is, however, only 0.86 wt% higher than the highest yield obtained (0.87 ± 0.01 gwater/gwater in biomass) using only Pectinex Ultra SP-L and de-ionised water. It is recommended to use only Pectinex Ultra SP-L and de-ionised water at a pH of 3.5 and a temperature of 40°C. Using one enzyme instead of two reduces operating costs and simplifies the chemical extraction process. The extracted water, both filtered and unfiltered, was not found to be suitable for domestic use without further purification to reduce the total dissolved solids (TDS), potassium and manganese levels. Both the unfiltered and filtered water were, however, found to be suitable for industrial and agricultural purposes, except for the high TDS levels. If the TDS and suspended particle level can be reduced, the extracted water would be suitable for domestic, industrial and agricultural use. The potential fermentation of the sugars derived from the water hyacinth, using ultrasonic pretreatment, was investigated. Indirect ultrasonic treatment (ultrasonic bath) proved to be a better pretreatment method than direct sonication (ultrasonic probe). The optimum sugar yield for the ultrasonic bath pretreatment with 5% NaOH was found to be 0.15 g sugar/g biomass (0.47 g sugar/g available sugar) using an indirect sonication energy input of 27 kJ/g biomass. The optimum sugar yield is lower than those reported in other studies using different pretreatment methods. Theoretically a maximum of 0.24 g ethanol can be obtained per g available sugar. This relates to an ethanol yield of 0.08 g ethanol/kg wet biomass. The low yield implies that ethanol production from water hyacinth is not economically feasible. The production of bio-oil and bio-char from water hyacinth through thermochemical liquefaction of wet hyacinth feedstock was investigated. An optimum bio-char yield of 0.55 g bio-char/g biomass was achieved using an inert atmosphere (nitrogen) at 260°C and the stems and leaves as feedstock. With the roots as feedstock a slightly lower optimum yield of 0.45 g bio-char/g biomass was found using a non-reducing atmosphere (carbon monoxide) at 280°C. The bio-oil yield was too low to accurately quantify. As water is required during thermochemical liquefaction, it was found unnecessary to dry the biomass to the same extent as was the case with the pretreatment and fermentation of the water hyacinth, making this a more feasible route for biofuel production. Bio-char produced through liquefaction of roots as the feedstock and leaves and stems as the other feedstock had a higher heating value (HHV) of 10.89 ± 0.45 MJ/kg and 23.31 ± 0.45 MJ/kg respectively. Liquefaction of water hyacinth biomass increased the HHV of the feedstock to a value comparable to that of low grade coal. This implies a possible use of water hyacinth for co-gasification. The most effective route for bio-energy production in the case of water hyacinth was found to be thermochemical liquefaction (12.8 MJ/kg wet biomass). Due to the high production costs involved, it is recommended to only use water hyacinth as a feedstock for biofuel production if no alternative feedstock are available. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014