Freeze-drying is an energy demanding operation involving dehydration through sublimation of ice crystals. It has important application in the production of high quality dried food such as instant coffee. Correlating the operating conditions with product attributes is essential to design processes that are energy efficient whilst producing product of desired characteristics. In this study, microstructure development and evaluation for gum arabic and coffee solutions during freeze-drying have been considered. Freeze-drying processes were carried by varying the material’s concentration (20-60% w/w) and properties as well as freezing and primary drying conditions. Microstructural evaluation and reconstitution behaviour of freeze-dried solids were assessed using scanning electron microscopy, X-ray computed tomography and high resolution camera. Initially, water crystallization was studied under temperature oscillation, slow, fast and unidirectional freezing where large crystal dendrites developed on fluctuating temperature and different freezing rates produced comparable crystal network. At reduced water content, smaller crystals developed and distinct orientation of crystal growth was visible. Meanwhile, at increasing primary drying temperature and concentration, the freeze- dried systems showed extensive structure expansion. The potential of aeration to assist freeze-drying of high solid solutions is demonstrated by improved structure uniformity and porosity. Reconstitution of the freeze-dried solids was influenced by the microstructure generated and physical mechanisms involved during dissolution. High porosity and presence of large pores enable rapid dissolution of the dried solids. Different dissolution mechanisms between gum arabic and coffee had strong impact on the kinetics of dissolution. The concept of process-microstructure-property relationship is thus very clear in this study.

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.

Intermediate temperature (IT) proton exchange membrane fuel cells (PEMFCs) offer a future that does not rely on the burning of fossil fuels, but dictate durable and high performance component materials. At operating conditions of 120 °C and 50 % relative humidity (RH), composite proton exchange membranes (PEMs) offer increased performance due to enhanced water uptake and retention resulting from the hydrophilic filler material. This project aimed to relate measured data for composite PEMs with literature data on Nafion-graphene oxide (GO) PEMs. In order to achieve this, the membrane casting method was optimised and GO was synthesised in-house. A range of membranes were tested using a calibrated and optimised high temperature test stand. In-situ and ex-situ testing was carried out between 80°C and 120°C, and between 25 and 95 % RH. In contrast with some published data, this study found inconsistent trends between water uptake, ion exchange capacity, membrane resistance and single cell performance. Overall it was found that recast and composite membranes had higher in-plane resistance than Nafion 212, but that composite membranes with low filler loading had comparable in-situ performance to the commercial membrane. Further single cell optimisation is likely to result in further advances for composite PEMs.

Between 50% and 70% of the total energy used in the extraction process may be attributed to comminution. Microwave pre-treatment has been suggested as a means to decrease the energy requirements. A variety of mineral ores have been investigated and the effects of microwave radiation quantified in terms of the mineralogy, changes in the Bond Work Index, flotability and magnetic separation. It has been shown that microwave pre-treatment is most effective for coarse grained ores with consistent mineralogy consisting of good microwave absorbers in a transparent gangue (up to a 90% decrease in Bond work index for Palabora copper ore) whereas fine grained ores consisting predominantly of good absorbers are not affected as well (a reduction of only 25% in work index for Mambula ore). Although the mineralogy of minerals are affected by exposure to microwave radiation, flotability and magnetic separation characteristics have been shown not to be adversely affected, unless the microstructure is completely destroyed after prolonged microwave exposure. Computer simulations have shown that significant changes to comminution circuits are possible as a result of microwave induced work index reductions (three mills reduced to one). Purpose-built microwave units may hold the solution for more efficient mineral extraction in the near future.

In this thesis we construct a series of mathematical models from first principles to examine the advection, diffusion and reactions of species within a planar Solid Oxide Fuel Cell (SOFC). We reduce the complexity of an SOFC to flow and reaction across a flat, impermeable plate and begin by establishing a simplistic model for the incompressible, isothermal flow and reaction of hydrogen. Throughout the thesis we seek to extend this initial model by adding appropriate levels of complexity such as alternative fuels, compressibility and thermal effects. In establishing solutions to these models we use a series of analytical techniques. We adopt the concept of boundary-layer flow and self similarity to simplify the model equations into a form where we can obtain analytical and efficient numerical solutions. We also utilise asymptotics to examine and validate the model around regions of singularities within the flow. Within each model we have examined the electrical performance of the cell and in some cases we have validated these results with existing experimental data.

Air pollution from DEEEs is becoming an increased international concern, and whilst attention has been primarily focused on the automotive industry, concerns have also been raised about emissions from diesel rail vehicles. The research is designed to assess the hypothesis that diesel rolling stock severely impacts air quality at Birmingham New Street station due to the station’s enclosed nature. To assess this hypothesis, an extensive series of long term measurements were made at Birmingham New Street station. The monitoring campaign consisted of diffusion tube measurements, to measure NO2 at locations in and around the station, followed by measurements of NOx, PM, CO2 and BC at stationary and mobile sites at the platform level. The results illustrated that diesel trains serving the station elevated pollutant concentrations, particularly oxides of nitrogen. During the sampling campaign the average NO2 concentration in the centre of platform 10/11 was 407 μg/m3, approximately 10 times greater than the EU ambient air quality limit. NO exceed its WEL 35% of the time during the monitoring campaign for the same site. Furthermore, this research concludes that CO2 is not suitable as a surrogate for assessing DEEEs exposure. NO2 concentrations exceeded their relevant exposure limits, whilst CO2 did not exceed the ventilation system’s 50% speed threshold, as a result it is unlikely that harmful pollutants were being successfully exhausted from the station. The environmental analysis identified a potential trapped vortex in the West end of the station, which could have an impact on the ventilation system in place at Birmingham New Street station. It is clear that this research has been pivotal in driving a focus towards air quality with the railway industry and has prompted further research at other enclosed railway stations.

Lithium is considered a borderline strategically important metal for the UK due to the limited availability of primary deposits, of sufficient grade, for economic processing (Naden, 2012). The rising demand, of approximately 10% yearly, has promulgated investigations for the development of secondary sources of lithium in order to secure long term reserves for the UK and Europe (Jaskula, 2015). The British Geological Survey (1987) estimated that the St Austell granite contained up to 3.3 million tonnes of recoverable lithium. Imerys Ltd also identified lithium-bearing mineral in their kaolin waste material in Beauvoir, containing up to 0.89 wt.% Li2O. The lithium-bearing minerals identified were; lepidolite (K(Li,Al)3(Si,Al)4O10(F,OH)2) and zinnwaldite (KLiFeAl(AlSi3)O10(F,OH)2), which can contain between 3.0 to 7.7 wt.% Li2O and 2.0 to 5.0 wt.% Li2O, respectively (Garrett, 2004). Lithium flotation concentrates containing up to 5.0 wt.% Li2O were optimised for the Beauvoir waste material with up to 80% lithium recoveries, whereas a lower flotation grade of 0.5 wt.% Li2O was found for the St Austell material. The St Austell waste materials did not prove viable to process via conventional flotation routes hence a novel process route for the bio-recovery of lithium from lithium rich micas was developed. Extraction of lithium by bioleaching has demonstrated the ability of fungi, of Aspergillus niger group, to leach lithium from the lepidolite in significant quantity, achieving 125mg/L of lithium in solution after twelve weeks of bio-leaching, at a recovery of 45%. Following this research, Imerys are applying to build a pilot plant, securing funding through the Innovative UK grant.

The problems of transport technology were analysed; present vehicles are polluting, inefficient and run largely on unsustainable fossil fuels. The theory proposed here is that a hydrogen fuel cell battery hybrid system is the best for future vehicles; zero emission, twice as efficient and running on renewable hydrogen from biomass, wind or solar. Early testing compared a crude Micro-cab prototype (compressed hydrogen, Ballard fuel cell, lead acid batteries and an electric motor) with a hydrogen combustion dual fuel van to assess the technical demands of the proposed technology. Then a battery scooter was modified and tested to show that a plug-in hydrogen battery hybrid with hydride store could have benefits which were quantifiable. A computer model was developed to predict the performance of this system. Reducing dissipation by removing DC converters was shown to be beneficial. A prototype Micro-cab was analysed and tested to show how improved drivetrain components could increase the vehicle efficiency. The main part of the project was to use these ideas to build an urban car driven by a plug-in hydrogen fuel cell lithium ion battery hybrid with efficient motors, no DC/DC converters and belt/pulley drive. The results showed that with a 2kg pressurised hydrogen store at 350bar, such a vehicle had good urban performance and a range of 200miles. The conclusion was that the overall design concepts were correct and that costs and hydrogen infrastructure were the main future difficulties of future application.

Supercritical carbon dioxide (SC-CO\(_2\)) and Soxhlet extraction using hexane as solvent were used to extract 2-acetyl-1-pyrroline (2-AP) from Pandan leaves. The effect of different extraction pre-treatments, such as particle size and drying on the extraction yield and concentration of 2-AP were investigated. The identification and quantification of 2-AP were carried out by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector, respectively. This work aims to provide an understanding of the phenomena that occur during cooking and storage; typically on the changes of 2-AP absorption when cooking rice grains with Pandan leaves. The parameters investigated were cooking method of excess and optimal water conditions. Even though low in yield, and the 2-AP concentration was obtained from supercritical carbon dioxide extraction, the extracts were pure without any contamination. The grinding and freeze-drying method revealed the best pre-treatments for supercritical extraction. The absorption of 2-AP during the cooking of rice grains did not smoothly increase with time. This unexpected result indicated that the phenomena occurring during cooking are quite complex. This work also quantified the potential of Pandan leaves to enhance the flavour of cooked rice, particularly under excess water conditions. Storage for 15 min at 24.0 \(\pm\)1.0\( \circ\)C is considered as the optimum time for obtaining cooked rice with a high quality of flavour.

Studies were conducted to explore whether high pressure (up to 700 MPa) could be used in combination with elevated temperatures (up to 90°C initial temperature) to produce ambient stable green beans (Phaseolus vulgaris) with improved quality compared with conventionally heat processed samples. Colour changes, texture change and chlorophyll retention were explored at a range of pressures, temperatures and times using a surface response methodology. Texture changes were essentially related to temperature effects; higher temperatures resulted in a greater loss in texture. Significant improvements in texture retention were possible using High Pressure Sterilisation (HPS) but sample colour was negatively affected. Colour parameters were predicted primarily by time and pressure so deterioration in green vegetable quality for a commercially sterile products appears inevitable when using HPS. The use of ohmic heating as a pre-heating method greatly reduced cook values (T\(_{ref}\) = 100°C, z = 39C°) for colour degradation (down to 0.24, 0.12, 0.35 from 3.02, 2.50, 3.70 minutes for ohmically heating and water bath heated samples respectively) which yielded significant benefits in terms of colour retention of raw materials at the start of the HPS cycle; values of a* and b* for ohmically pre-heated samples were close to that of blanched beans.