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Social, economic and political pressures have driven the development of renewable alternatives to fossil fuels. Biofuels, such as bioethanol, have proved to be successful alternatives. Mature technologies are crop-based, but this has brought criticism due to the conflicting use of land for fuel versus food production. Therefore, bioethanol production technologies have shifted to utilising the sugars that derive from the degradation of lignocellulosic biomass. The thermophilic, Gram-positive bacterium, Geobacillus thermoglucosidasius, can naturally utilise a large fraction of these sugars, and metabolic engineering has been used to create a strain that produces ethanol as the major product of fermentation. This strain, G. thermoglucosidasius TM242 (Δldh, Δpfl, pdhup), does however, produce small but significant quantities of acetate, an undesirable by-product of fermentation. Therefore, acetate metabolism in the G. thermoglucosidasius TM242 strain was the focus of this study. During fermentation, ethanol is generated from the central metabolite acetyl-CoA through the activities of a bifunctional enzyme: aldehyde dehydrogenase/alcohol dehydrogenase (ADHE). On the other hand, acetate is generated from acetyl-CoA through catalysis by phosphotransacetylase (PTA) and acetate kinase (AK). Acetate metabolism in G. thermoglucosidasius TM242 was studied in this project by investigating the enzyme activities governing flux from acetyl-CoA, and the feasibility of reduced acetate production was investigated by a pta-deletion strategy. This thesis reports the characterisation of PTA and AK, by studying activities from both native cell lysates and recombinantly expressed proteins. The results indicate that the activities of PTA and AK are greater than those of ADHE, suggesting that the potential metabolic flux is greater towards acetate production than to ethanol. However, the ethanol yield from G. thermoglucosidasius TM242 fermentations is greater than that of acetate, suggesting the existence of a regulatory mechanism controlling acetyl-CoA flux. Several possible regulatory mechanisms were studied in this project and are reported here. The viability of creating a strain that reduces acetate accumulation, and potentially increases ethanol yields, was investigated and reported in this thesis. The gene encoding PTA was deleted from G. thermoglucosidasius TM242, and the resulting strain was characterised. The Δpta strain had approximately 5% of the PTA activity measured in TM242, but acetate was still generated from pentose and hexose fermentations. Additional phosphotransacylase (PTAC) enzymes were discovered in G. thermoglucosidasius TM242 that could catalyse the conversion of acetyl-CoA and orthophosphate to acetyl-phosphate and CoA. A series of PTAC null strains were created and analysed, the results of which indicated that phosphotransbutyrylase (PTB) could be involved in acetate production in vivo. It was discovered that the cell lysates of G. thermoglucosidasius strains carrying deletions to both pta and ptb could no longer catalyse the conversion of acetyl-CoA and orthophosphate to acetyl-phosphate and CoA. However, these strains still accumulated acetate, suggesting the presence of alternative acetate-producing pathways in this organism. In addition, G. thermoglucosidasius strains carrying deletions to both pta and ptb could ferment glucose but not xylose, suggesting that the production of ATP by the PTA-AK pathway is crucial for micro-aerobic growth on pentose sugars.

The manufacturing process for solventless extruded double base propellants involves a number of rolling and reworking stages. Throughout these processes a decrease in weight average molecular weight was observed, this was attributed to denitration. Differential scanning calorimetery data indicated that the reworking stages of extruded double base propellant manufacture were crucial to the homogenisation of the propellant mixture. To determine the homogeneity of the final extruded product, a sample was analysed across its diameter. No variations in stabiliser concentration, molecular weight, or Vickers hardness were detected. An accelerated thermal ageing trial simulating up to 8 years of ageing at 25°C was carried out to evaluate the storage characteristics. Reductions in stabiliser concentration, number average molecular weight, weight average molecular weight and polydispersity compared with un-aged samples were observed. The glass transition temperature measured using differential scanning calorimetery decreased by ~3°C. The decrease was attributed to the initial denitration reducing the energy of bond rotation and shortening the polymer chains, both factors reducing the energy required for movement. Modulus values determined from dynamic mechanical analysis temperature scanning experiments, did not detect significant variation between un-aged and aged samples. Though it was considered that variations would be likely if a more extensive ageing program was completed. In order to evaluate propellant behaviour at very high and low frequencies, time temperature superposition (TTS) and creep testing were carried out. The TTS technique superpositioned data well, allowing future investigation of high frequency propellant properties. Creep testing was considered to be an appropriate approach, though the equipment available was not optimised for such testing. This thesis is concerned with understanding how propellants are manufactured from nitrocellulose, nitroglycerine and other constituents. It is also about how the propellants decompose during long periods of time in storage, and how these changes can be measured using thermal and mechanical methods. It is about how the physical, chemical and thermal properties of the propellant composition change throughout the manufacture. This is relevant as it could be used to develop more efficient manufacturing processes, allow operators to adjust processes to tailor product properties or be used to re-design manufacturing to compensate for a different starting material. The thesis also considers how and why the properties of the product change over the course of years of storage. A specific focus on whether changes in mechanical and thermal properties occur, and if so how they can be detected.

Rapid depletion of fossil fuel stock with a simultaneous rise in greenhouse gas emissions has led to an increase in the need for alternative energy. Cellulose based biofuels, especially bioethanol is a form of alternative energy that has the potential to replace petrol. The first step in cellulosic bioethanol production is the release of fermentable sugars via pre-treatment. Conventionally, physico-chemical and biological pre-treatment methods are energy intensive, environmentally unfavourable and expensive. This study, however reports on the use of a less energy consuming, cheap and environmental friendly alternative; photocatalysis, to produce fermentable sugars from cellulose. To achieve this, a range of photocatalysts were first screened based on their OH radical production rates using coumarin as a probe. TiO2 P25 was the photocatalyst that was found to have the highest OH radical production rate of 35.6 μM/hr, followed by Pt-C3N4 (0.88 μM/hr) and WO3 (0.28 μM/hr). LaCr-SrTiO3, Cr-SrTiO3 and yellow TiO2 did not produce any OH radicals due to their unsuitable electronic structure. P25 was further used for photocatalytic fermentable sugar production from cellulose. Photocatalytic cellulose I breakdown produced 0.04 % fermentable sugars whereas, with cellulose II feedstock the yield increased to 0.2 %. To further improve the yield, membrane bags were deployed which improved the sugar yields to 0.43 % and 0.71 % respectively from cellulose and cellulose II feedstocks. Photonic efficiencies followed the same trends as the sugar yields. Engineering design was further opted to enhance the sugar yields and hence a stacked frame photocatalytic reactor (SFPR) was designed. Various mixer configurations were designed and their mixing regime was determined using COMSOL Multiphysics 5.1 simulations. Amongst the mixers simulated, an 8-blade Rushton impeller was found to be the best configuration due its superior radial mixing profile and higher fluid velocity. The SFPR was then fabricated and operated with the impeller or a plus shaped magnetic bar as the mixer and the sugar yields were determined. Highest sugar yield and photonic efficiency was obtained from the cellulose II-impeller setup and was calculated to be 2.61 % and 9.45 % respectively. Respective lowest yields were obtained with cellulose I-stirrer bar setup and calculated to be 1.71 % and 5.64 %. Furthermore, the effect of H2O2 on fermentable sugar production was also tested. The cellulose II-stirrer bar configuration yielded 3.15 % fermentable sugars with the addition of 0.01 wt% H2O2 to the reaction mixture. The yield improved significantly to 14.1 % when the concentration of H2O2 was increased to 0.1 wt%.

The key controlling factor in the effective energy conversion of coal to combustible gases during the UCG process is the behaviour of the pyrolysed char in the reduction zone of the UCG cavity, which has not been published in available academic literature. This study investigates the impact of the operating parameters during the reduction zone of UCG using a bespoke high pressure high temperature rig which was developed as part of this research work. This rig, operating at temperatures of up to 900 oC and at pressures up to 5.0 MPa, simulates the UCG process including each UCG zone individually for a broad range of underground conditions to a depth of 500 m. Carbon dioxide and steam were used as the primary reductants with char derived from dry steam coal and anthracite sample. Carbon dioxide and steam were injected at a variety of pressures and temperatures, plus at a range of relative H2O/CO2 proportions. The composition of the resulting product gas of both coals was measured and subsequently used to calculate carbon conversion (X), carbon conversion of combustible gases ( ), cold gas efficiency (CGE) and low heating value (LHV) of the product gas. Optimal operating conditions were determined for the dry steam coal and anthracite that produced the best gas composition both at atmospheric and elevated pressure and are unique for each UCG system. A shrinking core model was employed to describe the behaviour of the pyrolised char to determine the activation energy and pre-exponential factor at atmospheric pressure for both coals. The evolution of the volatile matter of both coals and its contribution to the overall UCG performance was also determined. An optimum H2O/CO2 ratio was determined for both coals which enhanced the gasification rate of both coal chars up to the ratio of 2:1, above this ratio the effect saturated for both coals. It was shown that pressure increases the reduction-gasification process of the chars which suggests that there is an optimum operating pressure which produces a peak in carbon conversion, CGE and LHV for the product gas over the conditions tested that differs for each coal. Therefore UCG projects aiming at reaching higher pressures will not achieve an increase in the output, unless there are some new effects occurring above 4.0 MPa. Pressure enhances the gas solid reactions and almost doubles the max carbon conversion ( of combustible gases achieved at elevated pressure compared to that at atmospheric pressure. A shrinking core model was modified to take into account the effect of total pressure to the gasification rate of dry steam coal at 900 oC and pressures ranging from 0.7 to 1.65 MPa. Reaction constants for various pressures at 900 oC were determined for both coal chars. Analysis of data shown that typical UCG operations on low rank coals provides a combustible product gas that relies heavily on releasing the volatile matter from the coal and does not depend on the carbon conversion of char to gas which justifies the high CGE and LHV of the product gas found in the field trials. It was found that carbon conversion X is not significantly affected by the type of coal and that the carbon converted during UCG is between approximately 45% for high rank coals up to 55% for low rank coals. Experimental results were used to calculate the output, size and UCG model of a potential power plant which produced realistic solutions and proves that high rank coals can be suitable for UCG projects. Anthracite can produce almost the same amount of combustible gases as the dry steam coal operating under specific conditions but with a lower CGE and LHV which suggests that anthracite may be found to be more suitable for producing hydrocarbons with UCG than energy.

There is a huge global challenge to establish alternative forms of energy in order to cope with the increasing worldwide energy demand, currently based on finite fossil fuel reserves. In the transportation sector, renewable liquid fuels, such as bio-ethanol and biodiesel which are made from biomass and are substitutes for the petroleum-derived gasoline and diesel, have received increasing interest. In spite of their recent development, the biofuel industries cannot compete with conventional liquid fuels because of their higher costs. Decisive changes are required to improve their economic sustainability, such as the establishment of novel processes that utilize their by-products for the production of value-added chemicals. In this study, the bioconversion of glycerol, which is the main by-product of the biodiesel industry, to succinic acid by using the bacterium Actinobacillus succinogenes has been investigated both experimentally and computationally. Initially, the cells were adapted to accept a glycerol rich environment by performing a series of experiments. Cells from the best experiment from each run were used as inocula for the next experiment. Batch fermentations were then performed in small scale anaerobic reactors (SARs) and in lab-scale bench top reactors (B-TRs) by using the new ‘adapted’ strain. The maximum succinic acid yield, productivity and final concentration obtained from this bioprocess were found to be 1.29 g/g, 0.27 g/L/h and 29.3 g/L, respectively. Moreover, cells have also grown successfully in both synthetic and biodiesel-derived crude glycerol, indicating that it is not necessary to remove the impurities that biodiesel-derived glycerol contains. Subsequently, an unstructured model that accounts for substrate and product inhibition was developed in order to predict the behaviour of experiments starting from different initial conditions. Model predictions were found to be in good agreement with experimental data obtained for both systems (SARs and B-TRs). Batch and fed-batch systems were optimized using the developed model to obtain high succinic acid productivity. Optimization results showed that productivity increased by 31% for batch and 79% for fed-batch systems. The corresponding optimal values were computed to be equal to 0.356 g/L/h for batch and 0.488 g/L/h for fed-batch systems. A semi-mechanistic model for the fungal fermentation on solid state rapeseed meal (i.e. the other main by-product of the biodiesel industry) was also constructed for small scale tray bioreactors. This fermentation targets to increase the nutrient factor of the rapeseed meal by decomposing its macromolecules to simple compounds which can then be used as a generic medium. The developed model effectively predicts the fungal growth, the temperature fluctuations and the moisture content inside the bed and the produced extracellular enzymes that break the complex compounds of rapeseed meal (i.e. proteins) to free amino acids. The economic sustainability of biodiesel production was investigated by the construction of a plant model of an integrated biodiesel biorefinery for the production of fuels (biodiesel) and chemicals (succinic acid) in Aspen Plus®. For a biodiesel plant with capacity of 7.8 ktons per year, it was found that the plant’s profitability can be increased by 60% (considering a 20 years plant life and an interest rate of 7%) if a fermentation and recovery process for producing succinic acid is added. The integrated biorefinery scheme demonstrated the highest profits (€ 9.95 M.) when compared with other scenarios which either purified or disposed of the glycerol. These results illustrate the critical role of glycerol when it is utilized as a key renewable building block for the production of commodity chemicals. It is clear, based on this work, that future studies targeting the sustainable development of biodiesel biorefineries should focus their investigation on novel bio-processes, like the succinic acid fermentation, supplementing the production of fuels with the co-production of platform chemicals.

The use of alternative feedstock sources to enhance the energy production of anaerobic systems, and thus their economic value, is one of the current research areas in the field of bioenergy production. Marine biomass represents a unique source of organic matter for the optimisation of anaerobic digestion systems and can be regarded as a sustainable alternative to purposely grown energy crops requiring significant amounts of water, fertiliser and land for their cultivation. Seaweeds are of particular interest as they are characterised by high biomass yields and interesting conversion rates. In temperate seas, brown seaweed species generally dominate the flora and their relative abundance on the sublittoral zone of the British coastline make them a substrate of choice for anaerobic digestion. However, little information is available on commercial-scale anaerobic digestion of seaweed for biogas production and the potential factors that could impair its successful conversion. This work was proposed in order to establish the potential and optimise the use of seaweed as an additional source of organic matter for anaerobic digesters. The study also investigated the use of the Anaerobic Digestion Model No.1 (ADM1) as a platform for process simulation. The model original structure is inadequate to accurately represent the anaerobic co-digestion of seaweed and was therefore updated with the addition of specific processes. The study was carried out in three main experimental stages. In a first stage, the effect of seaweed salinity (represented by sodium ions) on anaerobic digestion was investigated using a mesophilic laboratory-scale anaerobic digester. It was found that a rapid increase in sodium ion levels can negatively impact on biogas production and result in the accumulation of volatile fatty acids. The ADM1 does not originally take into account the inhibitory effect of sodium and was therefore modified to include a function representing the effect of sodium ions on the rate of acetate uptake. The extended model was able to reproduce experimental observations and was used to predict the effect of sodium ions in the presence of other process inhibitors. Microbial adaptation to salinity was also investigated during batch assays. It was found that a suitable period of adaptation can significantly reduce the adverse effect of salinity on methanogens. The phenomenon was successfully implemented in the model through the addition of a specific inhibition function and the calibration of kinetic parameters. The second stage of this research focused on the effect and mode of action of phlorotannin (a phenolic compound found exclusively in brown seaweed) on mixed microbial cultures through the monitoring of intracellular material leakage and transmission electron microscopy observations. Results suggested that phlorotannin induces strong extra- and intra-cellular effects on cells exposed to the compound, thus adversely impacting on energy requirements and final methane yields. The effect of phlorotannin was found to be dependent on both the degree of polymerisation of the compound and the morphology of microorganisms. Furthermore, the effect of phlorotannin during the anaerobic co-digestion of brown seaweed (Laminaria digitata) and vegetable residues was also investigated. Experimental results were successfully modelled using an extensively modified version of the ADM1, which introduces an uncompetitive function to the rate of acetate uptake in order to represent the inhibition of methanogenesis by phlorotannin. The model was also updated with a combination module for the simulation of co-digestion processes. The third stage focused on establishing operational guidelines for the anaerobic co-digestion of brown seaweed and non-saline feedstocks. Results suggested that although seaweed can be an alternative organic substrate in anaerobic digestion systems, phlorotannin content might limit its use for commercial-scale application. Whilst this study identified salinity and phlorotannin as key barriers to the use of brown seaweed as a substrate for anaerobic systems, the adaptation of operating conditions to favour microbial adaptation could lead to its effective use in large-scale applications.

The production of biofuels and in particular bioethanol has increased rapidly since the early 1990’s. The advantages of biofuels include reduced CO2 production, a decrease in fuel importation for many nations (notably the US and Brazil), and comparatively simple blending with fossil fuels. The production of basic fuel ethanol (1st generation) involves the use of an energy crop feedstock (corn in US and sugar cane in Brazil). The feedstock is processed via simple mechanical methods to release the simple carbohydrates, mixed with water and fermented anaerobically via S. cerevisiae yeast into ethanol and CO2. Due to the low market value of fuel ethanol, profit margins are restrictive, and as a result sterilisation and aseptic techniques are not economically viable, and contamination by environmental organisms is commonplace. The current system of biocontrol involves the addition of antibiotics, primarily penicillin and virginiamycin, to the fermentation. While these antibiotics are broad spectrum and highly effective in reducing the impact of contamination, the negative environmental impacts of antibiotic usage are well known. In order to reduce the impact of contamination and reduce reliance on antibiotics an alternative system of biocontrol is required. In this thesis various biocontrol agents are assessed, including bacteriophage, hop acids, chitosan, onion oil extract, copper and silver ions. The effect of these agents on the growth of various contaminant bacteria and a strain of S. cerevisiae is assessed and fermentations are carried out under sterile and controlled contaminated conditions to generate data on the effect of the contaminant and the various methods of biocontrol. Other possibilities investigated include the insertion of plasmids containing heat shock proteins into S. cerevisiae to enhance thermo-tolerance.

When a gas undergoes an exothermic reaction in a closed vessel, spatial temperature gradients can develop. If these gradients become sufficiently large, the resulting buoyancy forces will move the gas, i.e. there is natural convection. The nature of the resulting flow is determined by the Rayleigh number, Ra = (β g ΔT L^3) / (κ ν). The evolution of such a system will depend on the interactions of natural convection, diffusion of both heat and chemical species, and chemical reaction. This study is concerned with a gas-phase system undergoing Sal'nikov's reaction: P → A → B, in the presence of natural convection. This kinetic scheme is used as a simplified representation of a cool flame, which is a feature of the low temperature combustion of a hydrocarbon vapour. Sal'nikov's reaction is one of the simplest to display thermokinetic oscillations, such as those seen in cool flames. The behaviour of Sal'nikov's reaction in the presence of natural convection was investigated using a combination of analytical and numerical techniques. First, a numerical model was developed to compute the temperature, velocity and concentrations when a simple exothermic reaction occurs in a spherical batch reactor, the results of which could be compared with previous experimental measurements. Subsequently, a scaling analysis of Sal'nikov's reaction proceeding in a spherical reactor was performed. This yielded significant insight into the general behaviour of this and similar systems. The forms of the analytical scales were confirmed through comparison with the results from numerical simulations. These scales were used to predict how the system responds to changes in certain key process variables, such as the pressure and the size of the reactor. It was shown that the behaviour of this system is governed by the ratios of the characteristic timescales for diffusion, reaction and natural convection. These ratios were used to define a regime diagram describing the system. The behaviour in different parts of this regime diagram was characterised and regions in which oscillations occur were identified.

This thesis covers the simulation and modelling of the transesterification of triglyceride oils to make biodiesel, using heterogeneous catalysts. Initially, data fitting was performed to fit overall kinetic rate equations to experimental data, ignoring diffusional behaviour. Additionally, experiments were undertaken to investigate the influence of feed ratio on the reaction kinetics. A single site mechanism with surface reaction as the rate limiting step was found to most closely match the experimental conversion profiles for the operating conditions studied. To incorporate diffusional behaviour into the modelling a multicomponent diffusion methodology was adapted for use within this system. To verify transport properties of the system and the suitability of this theoretical diffusion calculation, measurement of density and viscosity for a range of mixtures was undertaken, along with molecular dynamics simulation to produce diffusion coefficients. Finally, a novel algorithm was developed to simulate coupled diffusion and reaction within the pores of the catalyst and the subsequent bulk concentration changes this produced.