Hydrogen is an emerging energy carrier for oil refining and fuel cell applications. The development of an efficient and stable catalyst to produce hydrogen gas is required for industrial applications. However critical issues in the catalyst that lead to the deactivation of reactions include active metal particle growth and carbon fouling. Industrial catalysts that are frequently overwhelmed by such issues are substituted or re-treated, which is not time and cost efficient. Therefore, developing durable catalysts that are resistant to sintering and carbon fouling remains an area of interest. A novel and anti-agglomeration Ni@yolk-ZrO2 catalyst is first reported in this thesis. A specific study of the ZrO2 hollow shell showed that the varied porosity of the hollow shell contributed to the catalyst’s ability to inhibit the agglomeration of active Ni particles. The steam reforming of methane was selected as the probe study for this catalyst in this research. Before a thorough analysis of the Ni@yolk-ZrO2 catalyst was performed, the systematic synthesis of Ni@SiO2 was studied. The analysis showed that the Ni particle size can be controlled by tuning the synthesis temperature. Water-to-surfactant ratio in the microemulsion was shown to influence the morphology of the Ni@SiO2 particle. The tetraethyl orthosilicate (TEOS) amount added with fractionated dispensing and the amount of NiCl2 were found to have affected the size and morphology of the Ni@SiO2. For the Ni@yolk-ZrO2 sample, the catalyst was characterised by Transmission Electron Microscopy (TEM) and X-Ray Diffraction. TEM was used for morphology analysis, while X-ray Diffraction was performed for phase analysis and crystallite size measurements. Nitrogen adsorption-desorption isotherm was done to measure specific surface area, total pore volume, and the t-plot micropore volume of the samples. Reducibility analysis of the Nickel species of the Ni@yolk-ZrO2 catalyst was carried out using Temperature Programmed Reduction. The anti-agglomeration property of the Ni@yolk-ZrO2 was established from the TEM and X-ray Photoelectron Spectroscopy analysis. Results showed that the active Ni particles were inside the yolk-shell structured framework, which deterred Ni particles from moving onto the surface of the catalyst. Ni particles were found to be stabilised by the abundant volume of pores in the ZrO2 hollow shell. This result indicates that the Ni particles were anchored by the pores and remained stable during the steam reforming of methane. The Ni@yolk-ZrO2 catalyst was tested by varying the volumes of feed (GHSV) and the steam-to-carbon ratio. This catalyst was also subjected to a recyclability test and proved to be better than conventional impregnated Ni/ZrO2 catalysts. The Temperature Programmed Hydrogenation analysis also proofed that the yolk-shell structure framework inhibited higher order of carbon deposits on the Ni@yolk-ZrO2 catalyst. Varying the porosity of the ZrO2 hollow shell was found to affect the performance of the steam reforming of methane. This varied porosity can be achieved by varying the amount of surfactant during the synthesis of Ni@SiO2@ZrO2. X-ray Photoelectron Spectroscopy analysis results showed that the porosity of the ZrO2 hollow shell contributed to the moderately strong hydrothermal stability of the catalyst for the steam reforming of methane. The hollow shell of the ZrO2 was influenced by the instability of the SiO2. TEM analysis of used BrNi-4.8 catalysts showed that the yolk-shell structure framework of the catalyst collapsed. This result suggests that the shell has weak integrity, and proves that the SiO2 was not able to maintain the yolk-shell framework. The results also suggest that the varied porosity of the ZrO2 hollow shell influences the catalysts’ efficiency even though they share the same yolk-shell structure framework. This is likely due to the differences in the pores of each catalyst configuration, which directly affects the Nickel species involved in the catalytic reaction. Finally, it was demonstrated that the Ni@yolk-ZrO2 catalyst exhibits excellent catalytic performance in comparison to conventional catalysts for the steam reforming of methane. Catalytic activity remained stable and achieved a methane conversion of more than 90 % for 150 hours under operating conditions of GHSV of 50400 mL gcat-1h-1 and S/C = 2.5 at 750 oC.

Chemical looping combustion (CLC) process is an emerging alternative to traditional CO2 mitigation technology in many industrial applications since it could produce high pure CO2 gas stream with relatively low cost. The flow occurring in the CLC is intrinsically a gas-solid two-phase flow coupled with heterogeneous reactions whilst the performance of CLC is significantly affected by the efficiency of the combustion taking place in the fuel reactor. This PhD research project investigates the application of chemical looping combustion technology for CO2 sequestrations, focusing on the hydrodynamics and chemical kinetics of the flows of the CLC in the fuel reactor. As bypass fluidised bubbles in dense phase regions of the fuel reactor remarkably affect the efficiency of combustion in the CLC, the phenomena of bubble motion are experimentally and numerically investigated first. Chapter 2 proposes a new analytical approach coupled with the adoption of auto-correlated wavelet transform to experimentally study the correlations between the detected pressure fluctuation signals obtained from a model fuel reactor in which the chemical reaction has been redundant and the occurrence of bubbles. The sub-signals of pressure fluctuations obtained can be used as the indicator to identify the occurrence of bubbles, which has been validated by the snapshots of the fluidisation patterns. Experimental results clearly show that the formed bubbles in the dense phase regions behave two distinct types, small bubbles with the characteristics of high fluctuation frequency and large bubbles with lower fluctuation frequency. The characteristic frequencies of these detected bubbles can be also identified through the analysis of the pressure fluctuation signals. In parallel to the experimental study, the applications of Computational fluid dynamics (CFD) numerical modelling to study the flow dynamic behaviour of CLC in the fuel reactor were attempted. Eulerian-Eulerian two fluid model and Eulerian-Lagrangian approach, represented by Computational fluid dynamics/Discrete element method (CFD-DEM) in the present study, were employed, respectively, to study the hydrodynamics in the fuel reactor of CLC. Chapter 3 presents the work which CFD-DEM modelling was employed to investigate the bubble hydrodynamics in the dense region of fluidised bed fuel reactor under the different inlet conditions. Correlations between the local dynamic parameters such as the pressure fluctuation, local solid volume fraction fluctuation and instantaneous velocities are introduced to detect the occurrence of the bubbles, where the bubble has been defined in terms of the volumetrically averaged local void fraction. The simulations demonstrated that these bubbles are highly correlated with the local large eddies embedded in the flow. It was also revealed that small bubbles with high by-passing frequency mainly occur in the bottom region of the fuel reactor while large bubbles with relatively lower frequency are found in the region close to the free board surface. This finding affirms that the size of bubble is highly correlated with the local dynamic field. A modified Darton’s model that uses local Reynolds number and dimensionless height ratio was thus proposed for prediction of the equivalent diameters of the formed bubbles at the given height position. In Chapters 4 and 5, Eulerian-Eulerian two-fluid CFD modelling is employed to study the hydrodynamics of the CLC coupled with the heterogeneous reaction in the fuel reactors with different configurations. Based on the simulation results, the correlation parameters that correlate the local volume fractions with the local dynamic parameters such as the pressure, velocity and temperature fluctuations were proposed, aiming at indicating the bubble occurrence in the fuel reactor where the heterogeneous reaction takes place simultaneously. The frequency of bubble occurrence at the given height position is also identified quantitatively through monitoring the time-dependant pressure fluctuations obtained from the CFD modelling. As the CLC involves heterogeneous reaction among the reactants in the fuel reactor where the oxides are reduced to the metal particles before refeeding back to the air reactor, most of the previously documented studies using CFD modelling for prediction of hydrodynamics in the fuel reactor adopted shrinking core model proposed by Szekely’s et al. (1973) but the effects of the irregularity geometry of the oxygen carriers and product-layer diffusion on the simulation have been overlooked. Thus, an improved shrinking core model that takes effects of both the irregularity geometry of the oxygen carriers and product-layer diffusion into account was proposed. Compared with the predictions using the original shrinking core model, e.g. García-Labiano et al. (2004) and Zafar et al. (2007a), the simulation results obtained by using the improved model can significantly improve the accuracy for prediction of the conversion rates. The simulations also indicate that the effect of product-layer diffusion becomes more notable with an increase in the completeness of conversion. An empirical relation is thereby proposed to describe the variations of the effect of product-layer diffusion on the oxygen carrier conversion. In summary, this dissertation contributes to the knowledge and understanding of the CLC in several aspects, in particular hydrodynamics and chemical kinetics of the flow in the fuel reactor. Firstly, a new analytical method coupled the auto-correlated wavelet transform was proposed to study the bubble formation in the dense bed region by analysing the pressure fluctuation signals. Secondly, the correlation parameters that correlate the local volume fractions with those dynamic parameters such as the pressure and velocity were introduced to predict the occurrence of bubbles at the given height position of the fuel reactor. Thirdly, the conventional shrinking core model has been improved by taking the effects of irregularity of solid particle and the product-layer diffusion into account.

This study focuses on the utilization of solid carbonaceous wastes, the mitigation of CO2 and the development of CO2-based chemical production process which is divided into three main parts. The first part consists of the investigation of solid carbonaceous samples behaviours under pyrolysis and combustion processes. The second part covers experimental study of CO2 gasification aiming at the identification of interactions during co-gasification. Here, the presence of interactions will be further discussed, particularly in terms of increasing the gasification rate of low reactive carbonaceous sample and the effect of pyrolysis heating methods on gasification reactivity. The last part considers the thermodynamic assessment of conventional and CO2-enhanced biomass gasification. The objective is to identify the influence of CO2 as a gasifying agent in biomass gasification. Moreover, the comparisons study of bio-DME production based on conventional and CO2-enhanced gasification was also carried out in this thesis. (i) Pyrolysis of NMPCBS and combustion of solid carbonaceous materials This part consists of investigation of solid carbonaceous samples behaviours under pyrolysis and combustion processes. The objective is to explore the feasibility of the utilization of non-metallic part of waste printed circuit boards (NMPCB), including the thermal behaviours of NMPCB and its blends with two types of coals by using a thermogravimetric analyser (TGA). For individual sample, the results showed that the NMPCB had the fastest rate of pyrolysis and the highest maximum weight loss rate compared with coals, thus, the highest reactivity. These were attributed to the thermal degradation properties of the constituent elements in NMPCB. Meanwhile, based on kinetic study, it is evident that the lower heating rates favoured the pyrolysis process. For blends, it was revealed that there was 6%-7% deviation in terms of the yield of solid residue between experimental and calculated values, indicating a significant gap between the overall activation energy (Ea) of the blends and its average (Eave). Thus, it confirmed the existence of interactions in co-pyrolysis. Moreover, the combustion characteristics of an Australian coal, a suite of solid carbonaceous materials, and their blends were also investigated. A drop in both ignition temperature and burnout temperature was observed when carbonaceous wastes were blended with coal at different proportions (10 wt% and 30 wt%) which justified that there were strong interactions during the co-processing of coal with carbonaceous materials. The ignition index values of coal/polystyrene and coal/oat straw blends increased by 78% and 52%, respectively, when the blending ratio increased from 10 wt% to 30 wt%. Similarly, 2.6 times increase in combustion index was also observed in coal/oat straw blend. The presence of interactions in blends was further measured by using the root mean square interaction index (RMSII) which showed that coal/oat straw and coal/polystyrene blends had the highest RMSII values. This indicated the presence of strong interactions during co-combustion. (ii) CO2 gasification of solid carbonaceous materials The second part covers the feasibility evaluation of using CO2 as a gasifying agent, namely CO2 gasification, for various solid carbonaceous materials. The work includes the conversion of carbonaceous materials to syngas, gasification characteristics of coal, a set of waste carbonaceous materials, and their blends. The experiments were run by using a thermogravimetric analyser (TGA). The results showed that CO2 gasification of polystyrene completed at 470 °C, which was lower than those of other carbonaceous materials. This behaviour was attributed to the high volatile content coupled with its unique thermal degradation properties. Further results demonstrated that CO2 co-gasification process was enhanced as a direct consequence of interactions between coal and carbonaceous materials in the blends. The intensity and temperature of occurrence of these interactions were influenced by the chemical properties and composition of the carbonaceous materials in the blends. The strongest interactions were observed in coal/polystyrene blend at the devolatilisation stage, as indicated by the highest value of RMSII, whereas at char gasification stage, the highest interactions were found in coal/oat straw blend. The catalytic effect of alkali metals and other minerals in oat straw, such as CaO, K2O, and Fe2O3, contributed to these strong interactions, thus, the addition of polystyrene and oat straw enhanced the overall CO2 gasification of coal. On the other hand, interactions between petroleum coke and solid carbonaceous materials were also analysed with the aim of enhancing the gasification reactivity of highly unreactive petroleum coke. To achieve this, an Australian coal and gum wood were chosen for co-processing with petroleum coke. The addition of gum wood was found as the significant contributor of the enhanced gasification reactivity of petroleum coke. This is due to the combined influence of a number of unique features of bio-char, such as high surface area, more active sites, low crystalline index and the catalytic effect of alkali and alkaline earth metals (AAEM) compounds. These results confirmed that proper selection of solid carbonaceous materials for gasification of petroleum coke is an effective means to improve the conversion efficiency of petroleum coke, i.e., higher reactivity, and therefore expand its large scale utilization. In addition to coal and petroleum coke, the isothermal and non-isothermal CO2 gasification of an algal biomass (Chlorella) char were also carried out by using TGA under two different heating systems, i.e. conventional and microwave-assisted pyrolysis. Based on reactivity index, maximum peak temperature and maximum mass loss rate parameters, it was shown that microwave char had higher gasification reactivity than that of conventional char. Likewise, the activation energy value of microwave char also confirmed its higher reactivity which was found to be about 9.6% lower than that of conventional char. In addition, the physical properties of these chars, such as Brunauer-Emmett-Teller surface area, carbon crystalline structure and number of active sites, were systematically tested. Based on these properties, microwave char was found to be more reactive as demonstrated by its large BET surface area, low crystalline index and high active sites. Meanwhile, co-gasification experiments under isothermal condition revealed the existence of greater synergistic effects in coal char/microwave algae char blend than that present in coal char/conventional algae char blend. (iii) Process modelling and simulation The last part considers the process simulation of thermodynamic assessment for CO2-enhanced biomass gasification. The primary objective is to identify the influence of CO2 as a gasifying agent in biomass gasification. In this part, steam and CO2-enhanced gasification of rice straw was simulated using Aspen Plus simulator and compared in terms of energy, exergy and environmental impacts. It was found that the addition of CO2 had less impact on syngas yield than gasification temperature; the cold gas efficiency (CGE) increased with CO2/Biomass ratio. At lower ratios (below 0.25), gasification system efficiency (GSE) was below 22.1%, which is lower than that of conventional gasification. However, when CO2/Biomass ratio was increased, the GSE continued to increase and reached a peak of 58.8% at ratio of 0.87. In terms of syngas exergy, the value generally increases with CO2 addition mainly due to the increase in physical exergy. In this work, chemical exergy was found to be 2.05 to 4.85 times higher than physical exergy. The maximum exergy efficiency occurred within the temperature range of 800 oC to 900 oC, related to the peak of syngas exergy. For CO2-enhanced gasification, exergy efficiency was found to be more sensitive to temperature than CO2/Biomass ratios. In addition, the preliminary environmental analysis showed that CO2-enhanced gasification resulted in significant environmental benefits compared with stream gasification. However improved assessment methodologies are needed to better evaluate the advantages of CO2 utilization.

Polyurethane is one of the most diversified macropolymers with versatile properties for many applications including construction, transportation, personal wear, household appliance, etc. The research of this PhD study covers many aspects of polyurethane, including modelling on urethanisation and foaming mechanism, cell microstructure and packing polyhedrons, macroscopic properties and performance, and functional carbon materials developed from carbonisation of polyisocyanurate (PIR) foams. The work contains both theoretical modelling and experimental measurements. Urethanisation Kinetics The catalysed polyisocyanurate reaction kinetic model was developed based on generalized copolymerization scheme. PIR/PUR ratio was derived from mathematical manipulation on rate equations. The structural unit effects of isocyanurate, urethane and urea were evaluated based on Mayo-Lewise tercopolymerization scheme. Two reaction scenarios – bifunctional and macropolyol – were taken into consideration. Two ratios of isocyanate/polyol and urethane/urea rather than isocyanurate concentration were found to have impact on isocyanate conversion. Cell Growth and Foaming Process The cell microstructural configuration model was developed based on FOAMAT reactivity profiling (FOAMAT is a foam qualification system to measure the formation by curing and foaming parameters). The cell constructions were well understood by characterization of interstitial border area between cells. The cell anisotropic degree was calculated based on 2D cell shapes deformation comparison between free rising and stress stretching. The foaming process of continuous line panel production was further modelled based on cell anisotropic stretching. Plateau Borders The geometric Plateau border model for closed cell polyurethane foam was developed based on volume integrations of approximated 3D four-cusp hypocycloid structure. The tetrahedral structure of convex struts was orthogonally projected into 2D three-cusp deltoid with three central cylinders. The idealized single unit strut was modeled by superposition. The volume of each component was calculated by geometric analyses. The strut solid fraction f_s and foam porosity coefficient δ were calculated from developed strut model based on representative elementary volume (REV) of Kelvin and Weaire-Phelan structures. The specific surface area Sv derived from packing polyhedra model and deltoid approximation model respectively were put into contrast against strut dimensional ratio ε. The characteristic parameters modeled from this semi-empirical method were further employed to predict foam thermal conductivity. The correlation results show good agreement with actual measurement. The deviation gap can be caused by disorderedness and irregularity of actual cells. The periodical numerical method still has limit in predicting foam mechanics. Foam Defect Microstructure Streak and blister cell defects pose extensive surface problems for rigid polyurethane foams. In this study, these morphological anomalies were visually inspected using 2D optical techniques, and the cell microstructural coefficients including degree of anisotropy, cell circumdiameter, and the volumetric isoperimetric quotient were calculated from the observations. A geometric regular polyhedron approximation method was developed based on relative density equations, in order to characterize the packing structures of both normal and anomalous cells. The calculated cell volume constant, C_c, from polyhedron geometric voxels was compared with the empirical polyhedron cell volume value, C_h. The geometric relationship between actual cells and approximated polyhedrons was characterized by the defined volumetric isoperimetric quotient. Binary packing structures were derived from deviation comparisons between the two cell volume constants and the assumed partial relative density ratios of the two individual packing polyhedrons. The modelling results show that normal cells have a similar packing to the Weaire-Phelan model, while anomalous cells have a dodecahedron/icosidodecahedron binary packing. Insulation Performance Polyurethane (PU) is a commonly used insulation material for cold storage warehouses. The insulation performance of PU sandwich panels made from blended blowing agents were re-assessed by k-factor measurements and the insulation thickness was calculated based on cold warehouse design standard. The purposes of this study is test the impact of thermal conductivity value from experimental measurements on insulation barrier thickness calculation, and try to identity the gap between experimental data and empirical data in real practice and its impact on insulation design. The building design standard of cold warehouse can be a good benchmark to showcase this difference in aggressive cooling environment. The results have confirmed significant positive impact of blowing agents for energy saving. Post-curing Stability Problem The foam post-curing stability was evaluated by mathematic manipulation. The developed 3D paraboloid model based on gridding measurements has provided a scientific solution to foam panel shrinkage problem. Cell microstructure characterisation and post-growth angle coefficients calculation were further performed in this study. The results show the cell microstructure undergoes severe contraction during cooling and some cell destruction has happened on foam defects. Meanwhile, the cell anisotropic degree is getting more uniformed and this phenomenon is considerably prominent in central position. Thermal Degradation The thermal degradation of polyisocyanurate foam samples were studied by TG/DTA, FTIR, and SEM. All samples with different isocyanate index (NCO/OH = 100, 200, 300) were pre-treated by H2SO4, K2CO3, and NaOH before heating. The measurements of DTG and DTA presented corresponding variability for different acidic and alkaline treatments. The activation energy of thermal decomposition was calculated based on kinetic reaction evaluation. The pronounced polyol and isocyanate regenerations were observed over degradation. Further FTIR measurements at elevated temperatures suggested the possibility of acidic hydrogen bonding catalyzation and alkaline reversible amide regeneration during degradation by chemical treatments. The morphology study by SEM show localized corrosion is severe for high temperature carbonisation by acidic treatment (H2SO4) and microcrystallization occurs for alkalic treatments (K2CO3 and NaOH). The microcrystals vary by geometric shape. Carbonization The isocyanate index (NCO/OH) of diisocyanate and macropolyol can dictate the carbonisation of polyisocyanurate (PIR) foams. The carbon amorphousness was characterized by DSC which suggests the disorderedness can be aggravated by acidic pre-treatment. XRD investigation on crystallography suggests intercalation layered structure was created during carbonisation. Synchrotron-based X-ray photoelectron spectroscopy (XPS) analyses of all carbonaceous residues reveal that N-doping carbonisation has been realized by isocyanate dipolar cycloaddition. The N-doping structures with pyridinic (N-6) and pyrrolic (N-5) nitrogen atoms were found in carboncyclic rings, but no graphitic (N-Q) structure was identified. Higher isocyanate index (NCO/OH) can increase the opportunity for N-doping by creating more pyrrolic (N-5) nitrogen structure. The acidic treatment by H2SO4 can promote pyridinic (N-6) structure formation by cyanic acid trimerization. The derived carbons from higher isocyanate index (NCO/OH) were further found from electrochemical tests to possess improved capacitance but with negative resistivity which is attributed to more capacitive but amorphous N-doping carbon structure.

Many parts of the World have remained underdeveloped due to the lack of access to electricity. Developing and promoting alternative energy sources from renewable materials would assist to mitigate the energy crisis in many parts especially in the World. This research examined the possibility of using a 10KW power pallet as a sustainable energy generation system especially for energy poor areas. This was achieved through the gasification of woodchips at varying moisture content, varying gasification times and at varying electrical loads while investigating the numerous changes in the major factors affecting gasification such as temperature, fuel consumption rate, equivalence ratio (ER), quality of the producer gas, heating value, carbon conversion efficiency as well as the cold gasification efficiency of the gasifier. Experimental data was analysed and interpreted by one way Analysis of Variance (Anova) to establish a relationship on the effect of the major factors affecting gasification as investigated in this study. It was discovered that the gasifier is an autothermal system that maintains a steady state of thermodynamic equilibrium for longer hours as long as the gasifier is constantly supplied with a drier fuel. The gasifier stably and optimally operates with woodchips of moisture content less than 10% to produce an energy rich gas for gasification times longer than six hours to yield a gas rich in Hydrogen (H2), Carbon monoxide (CO) and methane (CH4) at a respective concentration of up to 18.1%, 25.3% and 2.2% with a corresponding Higher Heating Value (HHV), Cold Gas Efficiency (CGE) and gas production rate of 6.4MJ/m3, 75.8% and 2.34m3/kg respectively. The reactor takes longer time to attain thermodynamic equilibrium once operated with woodchips of moisture content above 15%. This subsequently affects the quality of producer gas yielding a gas of low calorific value that would even clog the engine. The moisture content of the wood chips was found to play a very significant role in determining the values of temperatures attained and subsequently determining the quality of producer gas. The gasifier was found to produce the required energy up to the design capacity of 10KW required for several industrial applications. Increasing the engine throttle valve increased the frequency of the engine and subsequently the voltage. The designed energy output of up to 10KW could only be produced if the engine frequency was 60HZ and could be lower if the engine operated at a lower frequency. A thermodynamic equilibrium model was further developed to predict the composition of producer gas going to the engine. The thermodynamic equilibrium model yielded a gas composition of 25.99%, 23.92%, and 0.42% for CO, H2 and CH4 respectively that was in good agreement with the experimental results at 850 ºC and ER of 0.27. Similarly, the modelled gasification temperature of 870.85ºC corresponds with a minor deviation of 2.5% with the experimental gasification temperature of 850ºC. The exhaust stream composition contained Carbondioxide (CO2) of upto 20% which is on the higher side because air was used as the gasifying agent and the gasifier was completely autothermal. Such CO2 concentration ought to be lowered if the gasifier is to be adopted as a sustainable renewable energy system. The gasifier was found to operate better with wood chips in the size range between 1.3cm - 4.0cm as very fine wood chips would block the flow of air hence compromising on the sustainability of the exothermic reactions and bigger wood chip particles would not be easily broken down by the auger hence resisting the flow of the woodchips into the reactor. Operating the gasifier at optimal conditions yields a gas of high calorific value good enough to make it a reliable standalone system that could be integrated into sustainable bioenergy systems.

The work presented in this thesis is focused on two specific areas of supercritical water oxidation (SCWO). Firstly, the design and testing of an innovative anticorrosive reactor design that can be used for the SCWO of hazardous organic waste. Secondly, exploiting the merits of counter current mixing reactor in combining two processes; Supercritical water oxidation (SCWO) and supercritical water hydrothermal synthesis (SCWHS) in one reactor. In Chapter 1, an introduction to supercritical fluid and supercritical water oxidation is given, followed by a brief account of the main problems associated with SCWO. This includes a review of the experience to date, with different reactor designs for corrosion control. This Chapter also provide an introduction to hydrothermal methodology and continuous flow reactor design for nanoparticle production, along with the aims and objective of this PhD. Chapter 2 details the components and construction of the experimental rigs used in this thesis. Additionally, this Chapter presents the principles behind the main analytical techniques used throughout this work, along with the definition of some important parameters. Chapter 3 reports the use of a physical modelling approach to assess mixingdynamics inside three different types of reactor where supercritical water is mixed with a second colder, waste containing, effluent flow. Physical or `pseudo'modelling was used to simulate the general flow patterns and mixing regimes in transparent pseudo reactors (to allow visualization). Towns water was used to simulate the supercritical water flow and 40% w/w aqueous sucrose solution to simulate the cold aqueous effluent flow. This visual technique allowed the quantification of mixing efficiency, as well as identification of issues such as flow recycling, stagnant zones, and other inconsistencies in the mixing dynamics. An upwards co-current protected wall reactor arrangement provided the `best' mixing i.e. with minimal wall contact during the downstream oxidation process. A combined process of SCWO and SCWHS in a continuous counter current reactor is the focus of Chapter 4. Acrylic acid was chosen as a model compound to represent an organic wastewater and the effects of the reaction temperature, residence time, oxidant ratio and acrylic acid concentration on chemical oxygen demand (COD) were all investigated. Two different experimental configurations for oxidant delivery were carried out in `pre-heated' and `non-preheated' oxidant configurations. With a stoichiometric excess of 100% oxygen, COD reduction levels of 80% (non-preheated) and 15% (preheated) were achieved with very short residence times. SCWHS was achieved through the addition of small amounts of various soluble metal salts in the cold up flow resulted in nanoparticles forming which increased the reaction rate and hydrothermal oxidation efficiency. The addition of small amounts of chromium nitrate (>5mM) results in nearly 100% COD reduction at 380C and residence times of 0.75 seconds. The potential economic benefits of combining the two processes together, in the different configurations, were also evaluated. In Chapter 5, The results of the catalytic oxidation in supercritical water of a non-biodegradable and highly toxic organic compound (phenol) are presented. The reactions were studied in a continuous counter current reactor through the in-situ formation of Fe2O3 catalyst. The preliminary results showed that catalytic non-preheated oxidant configuration resulted in increased COD removal when compared to other oxidant delivery methods. It was shown that temperatures below 400C could be used to decompose these compounds into final product and that complete conversion of COD could likely be expected within less than 1 second. It was demonstrated that SCWO combined with SCWHS is a feasible and cost-effective alternative for the destruction of contaminants in water. In Chapter 6, A laboratory-scale protected wall reactor rig was designed, constructed, tested, and operated to validate the pseudo modelling for application to SCWO. SEM, SEM/EDS, and XRD results showed that 1 meter long protected wall reactor was divided into two regions. 25% of the reactor length was protected by the flow of clean supercritical water. Near complete removal of the organic content of 2,4-DCP was obtained at mild operating conditions. To conclude, a summary of the work detailed in this thesis is delivered in Chapter 7. The most pertinent findings from this work are put forward, followed by a discussion of future work which could lead on from this thesis.

Considerable progress in understand and predicting turbulent bubbly flow in bubble column reactors has been advanced over the last two decades or so using a combination of model development, computational techniques and well-designed experiments. However, there remain many modelling uncertainties mainly associated with inadequate physical prescriptions rather than numerical schemes. The present project addresses some of these questions, in particular in relation to the interactions between the deformable rising bubbles and the turbulent eddies, with the later which from liquid shear flow or in the wakes of bubbles. Recent literature on existing models and experimental studies of bubble column reactors is reviewed in Chapter 1. It appears that the correlations and phenomenal models developed from early-stage experimental studies have been implemented into CFD modelling, and in return, accelerates the developments of theoretical understandings of the flow characteristics in the bubble columns. The research efforts made from both CFD modelling and experimental studies to understand the complicated mechanisms of gas-liquid interactions have been summarised in this chapter. In chapter 2, the inlet conditions, as one of the important issues in the CFD simulations of bubble columns, have been addressed. A kinetic inlet model is proposed, which considers the effects of number and size of holes on the gas spargers, the volume flow rate, and the gas-phase velocity profile. The proposed model achieves similar accuracy as modelling the real sparger holes while the computational costs have been significantly reduced. Chapter 3 applies a CFD-PBM method to investigate the influence of various shapes of bubbles on the bubble breakage rate and bubble size distribution. Bubbles are classified into spherical, ellipsoidal and spherical-capped shapes, and explicitly calculated in the breakage kernel. The correlation of aspect ratio of ellipsoidal bubbles is developed base on dimensionless numbers, summarising the effect of buoyancy, surface tension, and viscosity. The surface energy and pressure head have been adopted as two competing breakage mechanisms with the energy density constraint has been used as the breakage criterion. The simulation results demonstrate improvements in the estimations of gas holdup, liquid velocity, and bubble size distribution, as well as strong enhancements in mass transfer prediction. The effects of the turbulent kinetic energy spectrum for the turbulent bubbly flow on the bubble breakage are considered in Chapter 4. The κ-3 power law scaling behaviour of bubble induced turbulence is considered together with the Kolmogorov -5/3 law to characterise the turbulent eddies that interact with the subsequent bubbles. A characteristic length scale Λ is used to approximately separate the shear turbulence and bubble induced turbulence. The implementation of the modified breakage model into CFD modelling shows a great improvement in the prediction of bubble breakage rate, which believes to be competitive to the results obtained from Chen et al. (2004) that has artificially increase of breakage rate by 10 times. In Chapter 5, the approaching velocities of collision bubbles that are under the influence of shear turbulence and bubble induced turbulence are clearly distinguished. The turbulence dissipation rate that strongly affects the estimation of collision time has been calculated by taking into account the turbulence generation and dissipation in the wakes of bubbles, especially considering the anisotropic feature of bubble induced turbulence in the Reynolds stress turbulence model by using extra source terms. The modified coalescence model properly addresses the coalescence rate for different sizes of binary bubble coalescence. Chapter 6 presents the experimental study of the spatial velocity fluctuations and the turbulence energy spectrum in the wakes of bubbles by using PIV and highspeed imaging techniques. The experimental results clearly demonstrate the existence of the κ-3 power law scaling region due to bubble induced turbulence. The theoretical analysis successfully shows that the scaling exponent of -3 to be robust from three different aspect. In sum, some important issues of the gas-liquid interactions in turbulent bubbly flows have been addressed in this project. The implication is that the liquid phase turbulence is strongly affected by the size and shape of rising bubbles. Meanwhile, it can be found from the turbulence energy spectrum that the behaviours of turbulent eddies in the wakes of bubbles are very different from those in shear flow, thereby strongly influencing the kernels of bubble coalescence and breakage and hence the model predicted bubble size distributions.

Chapter 1 introduces the concept of wax crystal modification in middle distillate fuels and reviews the more common chemical additives used commercially, and by examination of the advantages and drawbacks of these additives discusses the possible benefits of polyolefin block copolymers. From this end functionalisation of polyethylene (PE) as a route to block copolymers is reviewed from different literature methods for their synthesis. Chapter 2 introduces the catalytic hydride insertion polymerisation mechanism as a route to end functional polyolefins and goes on to focus on the production of end functional ethylene/hexene copolymers. Using a range of comonomer concentrations and a number of catalysts, end-functional copolymers with a range of comonomer incorporation are produced. The thermal properties of these polymers are investigated and matrix assisted laser desorption/ionisation (MALDI) mass spectra were acquired. Finally, the chapter discusses the synthesis of short chain analogues of end functional PE. Chapter 3 describes the production of polyolefin-polar block copolymers via the free radical polymerisation of the functional polyolefins with a range of polar monomers. A reversible termination mechanism similar to nitroxide mediated polymerisation is proposed. The products are analysed by gel permeation chromatography (GPC) and by an in detail 2D NMR study to confirm block copolymer structure. Chapter 4 examines the physical properties of the synthesised block copolymers. The tendency of the copolymers to aggregate in solution into particles of varying size is investigated by VT NMR and dynamic light scattering (DLS), these findings were supported by transmission electron microscopy (TEM). The thermal properties of these copolymers were studied by differential scanning calorimetry (DSC). Following this the efficacy of these polymers as wax crystal modifiers (WCM) for fuels was investigated by cold flow plugging point (CFPP), optical microscopy and DSC of the treated fuels. Finally, the behaviour of the polymers in solid polyethylene wax was investigated by drop shape analysis (DSA) and x-ray photoelectron spectroscopy (XPS). Chapter 5 details the various experimental procedures used to carry out the work in this thesis. Appendix A gives an overview of polymerisations between ethylene and α- methylstyrene comonomers catalysed by hafnocene catalysts and goes on to detail the investigation of the materials acquired. Analysis was conducted using 2-D NMR, MALDI and diffusion-ordered spectroscopy (DOSY). Appendix B contains the DLS correlograms for samples analysed in chapter 4. Appendix C contains the schematic diagram for the gas burettes system used for metallocene polymerisations.

In this work, the hydrothermal synthesis of ZSM-5 and its coating with controllable crystal size and Si/Al ratio has been performed. The obtained catalysts have been studied in the methanol to hydrocarbon (MTH) reaction. This reaction is the last step in an integrated fuel processor for the conversion of bio resources to liquid fuels. The development of ZSM-5 coatings has been supported by advanced characterization and testing of catalysts for the determination of property/performance relationships. An optimal synthesis time of 72 h was found to provide the highest crystallinity of ZSM-5 coatings. The larger crystal size of ZSM-5 coatings leads to a higher selectivity towards gasoline (C8-11) hydrocarbons. The selectivity towards the gasoline fraction over ZSM-5 coatings with a thickness of 14 μm was similar to that of an industrial ZSM-5 catalyst, however the yield of the undesirable aromatics by-products was reduced by half due to shorter diffusion pathways in thin catalyst layers. In an attempt to improve the yield of the C8-11 hydrocarbons, two post-synthesis modifications have been performed: Ca ion-exchange and desilication by alkaline treatment. The maximum gasoline selectivity over Ca-H-ZSM-5 was observed at a Ca/H ratio of 0.1 while the longest lifetime in the reaction was observed at the ratio of 0.2. Mesoporosity has been introduced into microporous ZSM-5 catalysts. The obtained meso-microporous ZSM-5 coating show 3 times lifetime and 2.7 times selectivity towards C8-11 hydrocarbon fraction than microporous coating in the MTH reaction. Lumped kinetics of MTH reaction over H-ZSM-5 were used to design a microstructured reactor/heat-exchanger (MRHE) with reaction channels coated with the ZSM-5 catalyst. 2D and 3D convection and conduction heat transfer models coupled with the MTH reaction kinetics were employed to investigate temperature distribution in the MRHE. The effect of the dimension of the microreactor/heat-exchanger and flow condition on the temperature field has been studied. The 2D model under-predicts the magnitude of temperature gradient. The optimised reactor configuration shows a temperature gradient of 21 K in the reaction channels.

Recent advances in DNA computing have greatly facilitated the design of biomolecular circuitry based on toehold-mediated DNA strand displacement (DSD) reactions. The synthesis of biomolecular circuits for controlling molecular-scale processes is an important goal of synthetic biology with a wide range of in vitro and in vivo applications. In this thesis, new results are presented on how chemical reaction networks (CRNs) can be used as a programming language to implement commonly used linear and nonlinear system theoretic operators that can be further utilised in combination to form complex biomolecular circuits. Within the same framework, the design of an important class of nonlinear feedback controller, i.e. a quasi sliding mode (QSM) feedback controller, is proposed. The closed loop response of the nonlinear QSM controller is shown to outperform a traditional linear proportional+integrator (PI) controller by facilitating much faster tracking response dynamics without introducing overshoots in the transient response. The resulting controller is highly modular and is less affected by retroactivity effects than standard linear designs. An important issue to consider in this design process for synthetic circuits is the effect of biological and experimental uncertainties on the functionality and reliability of the overall circuit. In the case of biomolecular feedback control circuits, such uncertainties could lead to a range of adverse effects, including achieving wrong concentration levels, sluggish performance and even instability. In this thesis, the robustness properties of two biomolecular feedback controllers; PI and QSM, subject to uncertainties in the experimentally implemented rates of their underlying chemical reactions, and to variations in accumulative time delays in the process to be controlled, are analysed. The simulation results show that the proposed QSM controller is significantly more robust against investigated uncertainties, highlighting its potential as a practically implementable biomolecular feedback controller for future synthetic biology applications. Finally, the thesis presents new results on the design of biomolecular feedback controllers using the set of chemical reactions underlying covalent modification cycles.