There is a global need for sustainable, renewable and clean energy sources. Microbial production of hydrogen from renewable carbon sources, biorefinery compounds such as succinic acid or from food and drinks industry waste meets all these criteria. Although it has been studied for several decades, there is still no large scale bio-hydrogen production because the rate and yield of hydrogen production are not high enough to render the process economical. The dependency of biological hydrogen production of incipient light energy is also an important factor affecting economics. In order to improve the prospects of biohydrogen as a renewable and sustainable energy alternative, the genetic and process engineering approaches should be helped and targeted by metabolic engineering tools such as metabolic flux balance analysis. The overall aim of this research was the development of computational metabolic flux balance analysis for the study of growth and hydrogen production in Rhodobacter sphaeroides. The research reported in this thesis had two approaches; experimental and computational. Batch culture experiments for growth and hydrogen production by Rhodobacter sphaeroides were performed with either malate or succinate as carbon source and with glutamate as the nitrogen source. Other conditions investigated included; i) aerobic and anaerobic growth, ii) light and dark fermentation for growth, and iii) continuous light and cycled light/dark conditions for hydrogen production. The best growth was obtained with succinate under anaerobic photoheterotrophic conditions with the maximum specific growth rate of 0.0467 h– 1, which was accompanied with the maximum specific hydrogen production rate of 1.249 mmol(gDW.h)– 1. The range of the photon flux used was 5.457 - 0.080 mmol(gDW.h)– 1. The metabolic flux balance model involved 218 reactions and 176 metabolites. As expected the optimised specific rates of growth and hydrogen production were higher than those of the experimental values. The best prediction was for hydrogen production on succinate with computed specific hydrogen production rates in the range of 2.314 - 1.322 mmol(gDW.h)– 1. Sensitivity analyses indicated that the specific growth rate was affected by the nitrogen source uptake rate under aerobic dark condition whereas the flux of protein formation had the largest effect on the specific growth rate under anaerobic light condition.

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Concerns about climate change and our awareness on energy security have risen during the last decades leading the search for new forms of energy to reduce the world’s dependence on fossil fuels. Bioenergy has been proposed as one route to contribute significantly to meet global energy demand by using renewable sources of energy. The overall objective of this work was to study and optimise a hydrolysis treatment of lignocellulosic biomass but particularly of Miscanthus \(\chi\) giganteus under the biorefinery concept. A modified organosolv method using subcritical water, ethanol and carbon dioxide on a high-pressure batch reactor was proposed and tested for its efficacy on the hydrolysis and fractionation of Miscanthus into its lignocellulose main components, hemicellulose, cellulose and lignin. Temperature (80–200\(^0\)C), reaction time (5–60 min), ethanol concentration (0–70%), carbon dioxide initial pressure (10–55 bar) and load size (2.5–15 g) were the parameters studied and respective ranges. Optimisation models for solubilisation and delignification were obtained and validated using a central composite design based on a response surface methodology. According to both models temperature is the parameter that affects hydrolysis the most obtaining the highest hydrolysis solubilisation and delignification at 200\(^0\)C. On the other side CO2 initial pressure was not significant, what should be further investigated in the future at higher pressures. Reducing sugars quantification obtained a maximum concentration of 2g/10g Miscanthus by DNS assay with an optimal temperature to hydrolyse hemicellulose from 140 to 180\(^0\)C. FTIR analysis of each fraction confirmed a successful separation of the biomass main components with a reduction in the cellulose fibres crystallinity. Temperature was considered the most significant parameter to fractionate biomass with the highest temperature (200 \(^0\)C) being the one that produced a better quality fibres, supernatant and lignin in terms of contamination by the other fractions. However, results also showed that higher temperature tends to oxidise lignin. Fibres analysis by scanning electron microscopy showed that fibre structure was preserved but presented lignin-type globules on their surface indicating lignin reprecipitation.

This work concerns the modelling of scenarios for a residential hydrogen refuelling system. Such a system is under construction within the Engineering Safe and Compact Hydrogen Energy Reserves (ESCHER) project. Non-reacting and reacting simulations are compared against experimental data before being applied to a residential garage scenario. The non-reacting simulations utilise natural ventilation, which utilises the natural buoyancy of hydrogen and vent locations to disperse flammable mixtures. This is favoured over mechanical ventilation, which could fail. The non-reacting work focuses on investigating the most suitable venting configuration for a release of hydrogen from a refuelling system located within a residential garage. Different vent configurations are examined initially before proceeding to take into account atmospheric conditions, wind, and the presence of a vehicle for the two best venting configurations. This is to determine the venting configuration that would diminish the accumulation of a flammable mixture, as well as dissipating the mixture quickest after the release has stopped. The modelling strategy utilised for this work is validated against two different sets of experimental data, prior to the investigation into residential garages. The predicted and experimental results show good agreement for the modelling procedure suggested. The reacting investigations are for both premixed and non-premixed combustion. The non-premixed combustion investigates the temperature distributions and as such the possible harm to people for such a scenario, compared against experimental data. The results show some over predictions of the temperatures. The premixed combustion investigates the potential overpressures that may occur if a homogeneous mixture was to form and ignite, within a residential garage. This work is preceded by a validation of the combustion model with the predicted results compared to data from The University of Sydney. The validation results show that the modelling strategy matches the peak overpressures accurately. The non-reacting studies show that having a lower vent opposite the release and an higher vent near the release produces the smallest flammable mixture as well as dissipating the mixture to the external surroundings quickest. The non-premixed reacting work shows good agreement with experimental results. The premixed reacting work shows that the garage would destruct with major consequences to people and surroundings. This work would be applicable to any potential usage of indoor refuelling for hydrogen vehicles, helping to determine a suitable configuration for mitigating hydrogen releases. It should be noted that all such work is geometrically dependent and as such the strategy proposed would be useful for investigating individual scenarios.

Strong dependency on fossil fuels and the associated price and supply chain risk increase the need for more efficient utilisation of existing non-renewable energy sources. Carbon capture and hydrogen purification technologies are expected to play a key role in the future low-carbonised energy matrix. Integrated Gasification Combined Cycles (IGCCs) are one of the emerging clean coal technologies which pave the way for producing power from coal with a higher net power efficiency than conventional PC-fired boiler power plants. It is also advantageous that in an IGCC power plant a carbon capture unit can be applied to a stream having a very high CO2 partial pressure ahead of gas combustion that would not be available in case of a PC-fired boiler power plant, leading to less energy penalty involved in carbon capture. At the same time, the production of ultrapure hydrogen is both a sought target and an appropriate environmental solution because it is commonly utilised as feedstock in refineries’ hydrotreaters and hydrocrackers as well as energy carrier in fuel cells. A high purity of hydrogen has been commercially produced out of raw synthesis gas using a Hydrogen Pressure Swing Adsorption (H2 PSA) process. In this thesis, it was aimed to design and optimise a bespoke H2 PSA system tailored for a decarbonised syngas feed originating from a carbon capture unit. Therefore, a novel H2 PSA has been studied that is applied to an advanced IGCC plant for cogenerating power and ultrapure hydrogen (99.99+ mol%) with pre-combustion CO2 capture. In designing the H2 PSA, it is essential to increase the recovery of ultrapure hydrogen product to its maximum since the power consumption for compressing the H2 PSA tail gas up to the gas turbine operating pressure should be minimised to save the total auxiliary power consumption. Hydrogen recovery was raised by increasing the complexity of the PSA step configuration that allows a PSA cycle to have a lower feed flow to one column being used for adsorption and more pressure equalisation steps. An in-depth economic analysis was carried out and discussed in detail. The industrial advanced IGCC performances have also been improved by process integration between the H2 PSA unit and other units in the plant.

The transition from a fossil fuel-dependent society to a cleaner, more sustainable society will not be possible without renewable energy sources. Hydrogen holds great potential as an energy carrier as an alternative to fossil fuels in such society. However, the compact and safe storage of hydrogen are still major challenges. Solid state hydrogen storage offers the possibility to store hydrogen in solids offering high volumetric and high gravimetric energy densities, while reducing the risks associated when handling hydrogen gas. However, no single system has fully achieved the required properties for on-board mobile applications. Various approaches can be adopted with the aims of improving the kinetics and thermodynamics of hydrogen sorption. The nanostructuring of materials is one of the more promising strategies to achieve these aims. Reduction of the particle size of hydrides by nanoconfinement in forms of porous matrix leads to an increased surface area of the active material, and shorter diffusion distances for hydrogen atoms or ions to travel in the solid state. Kinetic barriers can be overcome and thermodynamics manipulated. An enhanced dehydrogenation rate and a reduced dehydrogenation temperature can be achieved by impregnating metal hydrides into porous scaffolds. Two complex hydrides are selected for study in this work; LiAlH4 and LiNH2. LiAlH4, is the lightest of the alanates, with a theoretical hydrogen storage capacity of 10.5 wt.%, and 7.9 wt.% H2 evolved below 220 °C. LiNH2 mixed with LiH, as part of the Li-N-H system, can reversibly desorb/uptake 6.5 wt.% H2 at 300 °C. When LiNH2 is heated alone, it releases ammonia (which is decomposed to N2 and H2 at higher temperatures > 400 °C). In this work, LiAlH4 has been impregnated in different types of commercial and synthesised porous carbon scaffolds for the first time. Nanoconfinement of the active material was achieved using solution impregnation with diethyl ether as a solvent. Analogously, the confinement of LiNH2 in porous carbon was achieved “in-situ” using lithium-ammonia solutions. Both confined composites showed lower dehydrogenation temperatures in comparison with the respective bulk materials. The influence of the design of the carbon scaffold (as manifested for example, by the surface area and the pore volume and pore size distribution) on the dehydrogenation behaviour of the impregnated complex hydrides is demonstrated. By judicious selection of an appropriate porous host, we show how it is possible to induce faster H2 desorption and substantially reduce the desorption temperature. The onset of hydrogen release for confined LiAlH4 decreased significantly in temperature, being reduced by 51 °C (in both porous hosts used, AX-21 and FDU-15) in comparison with pristine LiAlH4. The temperature at which the hydrogen release was maximised was also lowered (by 16 °C in FDU-15 and by 26 °C in AX-21) in comparison with as-received LiAlH4. The confined LiNH2 showed a much earlier release of hydrogen compared with as-received LiNH2. Normally LiNH2 would thermally decompose to Li2NH with ammonia evolution, but ammonia release was eliminated for the confined sample. Reaction with carbon led to irreversible Li2CN2 formation and hydrogen evolution. A set of experiments to establish the formation of Li2CN2 with physically mixed samples were performed. The physically mixed samples showed hydrogen release between 400 - 450 °C, producing a mixture of Li2NH and Li2CN2, suggesting two decomposition pathways were followed. In contrast, confined LiNH2 released hydrogen ca. 220 °C lower than the physically mixed sample, with no detectable trace of ammonia release.

Global warming and the energy crisis are two of the greatest challenges on which mankind is currently focused. This has forced governments and other organisations to think how to protect the environment and how to reduce fuel costs. A variety of new and exciting technologies are being investigated to address the energy problem. Alternative energy sources such as solar power, fuel cells, wind power and tidal waves are active areas of commercial and scientific pursuit. A major area of current research is moving towards the hydrogen economy and hydrogen based energy systems. Hydrogen can be produced in many ways, most commonly by steam reforming of hydrocarbon (70% to 85% thermal efficiency) but the downside is that it releases carbon mono oxide (CO)), compared with commercial PEM electrolysers where performance has been reported to be 56 -73% at normal temperature pressure(NTP) with zero carbon emission. Electrochemical production of hydrogen has several advantages: (i) It gives pure hydrogen. (ii) It allows portability (e.g. Solar energy could be used to power the electrochemical cell). (iii) It can be produced on demand. The generation of Hydrogen via electrolysis has been the subject of many studies over the last two hundred years. However, there is still room for further work to improve both the efficiency of the process and methods of storage of the gas. The cleanest method at present is to produce hydrogen by electrolysis, and the main focus of this research is to design and develop such a green energy fuel cell for on-demand application. The aim of the work presented in this thesis was to further investigate the electrolysis method for hydrogen production. An Electrochemical fuel cell contains a minimum of two electrodes: the positively charged electrode called the anode where oxygen bubble will form, and the second negatively charged electrode called the cathode, where hydrogen bubbles will form during a chemical reaction caused by applying electrical current between these electrode. The project was initiated with the objective of finding a low cost solution for on-demand hydrogen generation. To establish a starting point, the first cell (cell-1) design was based on the work of Stephen Barrie Chambers (see chapter 3) to check the performance levels. The fabrication of the cell-1 design resulted in a mixture of hydrogen and oxygen in the same chamber, which means the cell-1 design, has a possible fire and explosion hazard. The device also has the drawback of lower performance of hydrogen production; columbic efficiency is between 40% to 46% at 1 amp to 3 amp current in 30% KOH alkaline solution. However, the advantage of reproducing Stephen’s innovation is that it allowed a quick and deep understanding of hydrogen generation. This thesis presents recent work on the fabrication of low cost electrolysis cells containing continuous flow alkaline (KOH, up to 30%) electrolyte using low cost electrodes (stainless steel 316) and membranes based on ultrahigh molecular weight polyethylene (UHMW PE) to produce hydrogen without the hazard of fire and explosion. In this research an On-Demand Hydrogen Generation cell-3 achieved a 95% hydrogen generation coulombic efficiency, which is about 49% efficiency improvement as compared to the stainless steel electrode, and was 22% better than the nano structured electrode. The typical cell voltage is 2.5 V at current flow ranging from 30 to 120 mA cm-2 in 30% KOH electrolyte. The achievement here of such high efficiencies paves the way for more research in the areas of space management, electrode surface structure and flow control (based on the application requirement). This invention can be used for aeronautic, marine and automotive application as well as in many other areas.

Hydrogen storage is a developing technology that can be used as an energy vector for sustainable energy applications such as fuel cells for transport applications or for supplying power to the grid in moments of high demand. However, before hydrogen can be used as a practical energy vector, hydrogen storage issues, such as low gravimetric storage density, need to be addressed. One possible solution could be using nanoporous materials to physically adsorb hydrogen at low temperatures and moderate pressures. Hydrogen adsorption excess isotherms in solid-state porous materials can be obtained experimentally. However, the total amount stored in them, a quantity of more practical interest, cannot be measured by experimental techniques. Therefore, a model developed at the University of Bath is used to predict the total amount of hydrogen contained in nanoporous materials from their experimentally derived excess isotherm data. According to inelastic neutron scattering experiments (TOSCA, ISIS, RAL, Oxfordshire), solid-like hydrogen is likely to exist within the pores. The model is applied in this work in order to search for relationships between intrinsic properties of the materials (BET surface area, pore volume and pore size) and the predicted total hydrogen capacity of the materials. The model assumes adsorbed hydrogen at a constant density within the pore (defined as the absolute), also taking bulk hydrogen in the pore (amount that is not considered to be adsorbed by the adsorbent), into account. Several MOF datasets have been used to search for these relations, since they are the materials that have the highest hydrogen uptake in solid-state adsorption. Different MOFs and MOF families have been tested in order to widen the range of the correlations. Also, different strategies, such as fixing the pore volume when applying the fittings, relying on experimental data, or using high pressure hydrogen isotherm data to increase the robustness of the model have been researched. These MOFs have been either synthesized and characterized at the University of Bath or their datasets obtained from literature. Some of these MOFs with zeolitic structure exhibited unreported flexibility, being their structures further characterized. Changes on accessible pore size for hydrogen storage were also investigated using C60 in IRMOF-1. The final aim of this work is to find possible correlations between BET surface area, pore volume and pore size to find out what the values of these parameters have to be in a specific material to fulfil the DOE hydrogen storage requirements.

Carbon dioxide (CO2) sequestration in the sub-surface is a potential mitigation technique for global climate change caused by greenhouse gas emissions. In order to evaluate the feasibility of this technique, understanding the behaviour of CO2 stored in geological rock formations over a range of length- and time-scales is crucial. The work presented in this dissertation contributes to the knowledge in this field by investigating the two-phase flow and entrapment processes of CO2, as well as other relevant fluids, in porous media at the pore- and centimetre-scales using a combination of lab-based nuclear magnetic resonance (NMR) experimental techniques and lattice Boltzmann (LB) numerical simulation techniques. Pulsed field gradient (PFG) NMR techniques were used to acquire displacement distributions (propagators) of brine flow through a model porous medium (100 µm glass bead packing) before and after the capillary (residual) trapping of gas-phase CO2 in the pore space. The acquired propagators were compared quantitatively with the corresponding LB simulations. In addition, magnetic resonance imaging (MRI) techniques were used to characterise the extent of CO2 trapping in the bead pack. The acquired NMR propagators were compared to LB simulations applied to various CO2 entrapment scenarios in order to investigate the pore morphology in which CO2 becomes entrapped. Subsequently, MRI drop shape analysis techniques were used to identify a pair of analogue fluids which matched certain key physical properties (specifically interfacial tension) of the supercritical CO2/water system in order to extend the work to conditions more relevant to CO2 sequestration in the sub-surface, where CO2 is likely to be present in the supercritical phase. As before, NMR propagator measurements and MRI techniques, along with LB simulations, were used to characterise the capillary trapping of the CO2 analogue phase in glass bead packs, as well as two different types of rock core plugs – relatively homogeneous Bentheimer sandstone, and heterogeneous Portland carbonate. In addition to capillary trapping, the effect of vertical permeability heterogeneity, such as is often present in underground rock formations, was investigated for the flow of miscible (water/brine) gravity currents in model porous media (glass bead packs), using MRI techniques such as 2D spin-echo imaging and phase-shift velocity imaging. Finally, a preliminary investigation was made into the effect of particle- and pore-size distributions on the gas/liquid (air/water) interface for porous media consisting of glass bead and sand packs of different average particle size using quantitative MRI techniques.

The work presented in this thesis was undertaken as part of the safety work package of the NATURALHY project which was an integrated project funded by the European Commission (EC) within the sixth framework programme. The purpose of the NATURALHY project was to investigate the feasibility of using existing natural gas infrastructure to assist a transition to a hydrogen based economy by transporting hydrogen from its place of production to its place of use as a mixture of natural gas and hydrogen. The hydrogen can then be extracted from the mixture for use in fuel cells or the mixture used directly in conventional combustion devices. The research presented in this thesis focused on predicting the consequences of explosions and fires involving natural gas and hydrogen mixtures, using engineering type mathematical models typical of those used by the gas industry for risk assessment purposes. The first part of the thesis concentrated on modifying existing models that had been developed to predict confined vented and unconfined vapour cloud explosions involving natural gas. Three geometries were studied: a confined vented enclosure, an unconfined cubical region of congestion and an unconfined high aspect ratio region of congestion. The modifications made to the models were aimed at accounting for the different characteristics of a natural gas/hydrogen mixture compared to natural gas. Experimental data for the laminar burning velocity of methane/hydrogen mixtures was obtained within the safety work package. For practical reasons, this experimental work was carried at an elevated temperature. Predictions from kinetic modelling were employed to convert this information for use in models predicting explosions at ambient temperature. For confined vented explosions a model developed by Shell (SCOPE) was used and modified by adding new laminar burning velocity and Markstein number data relevant to the gas compositions studied. For vapour cloud explosions in a cubical region of congestion, two models were used. The first model was developed by Shell (CAM2), and was applied using the new laminar burning velocity and other composition specific properties. The second model was based on a model provided by GL Services and was modified by generalising the flame speed model so that any natural gas/hydrogen mixture could be simulated. For vapour cloud explosions in an unconfined high aspect ratio region of congestion, a model from GL Services was used. Modifications were made to the modelling of flame speed so that it could be applied to different fuel compositions, equivalence ratios and the initial flame speed entering the congested region. Predictions from the modified explosion models were compared with large scale experimental data obtained within the safety work package. Generally, (apart from where continuously accelerating flames were produced), satisfactory agreement was achieved. This demonstrated that the modified models could be used, in many cases, for risk assessment purposes for explosions involving natural gas/hydrogen mixtures. The second part of thesis concentrated on predicting the incident thermal radiation from high pressure jet fires and pipelines fires involving natural gas/hydrogen mixtures. The approach taken was to modify existing models, developed for natural gas. For jet fires three models were used. Fuel specific input parameters were derived and the predictions of flame length and incident radiation compared with large scale experimental data. For pipeline fires a model was developed using a multi-point source approach for the radiation emitted by the fire and a correlation for flame length. Again predictions were compared with large scale experimental data. For both types of fire, satisfactory predictions of the flame length and incident radiation were obtained for natural gas and mixtures of natural gas and hydrogen containing approximately 25% hydrogen.