Development of Sustainable Processes via Novel Synthesis Methods and Environments

Dwindling global resources necessitate the investigation, and development of more sustainable, optimised, and effective processes beyond conventional practices. Therefore, the present work explores novel synthesis methods and environments. The areas investigated are: hydrothermal carbonisation, alcohol/water mixtures, and aerosol-assisted sol-gel synthesis. Hydrothermal carbonisation is an emerging thermochemical conversion process. Herein hydrothermal carbonisation processing is performed on two novel biomass waste feedstocks, bread waste and avocado seeds. Both of these feedstocks are unsuitable for animal feed or other thermochemical processes and therefore are generally sent to landfill. The valorisation of these waste streams would therefore produce value from a genuine waste product. Hydrothermal carbonisation of bread waste is investigated at a range of different processing temperatures (160-200 °C) and retention times (30-90 min), in addition to two different pressurising gases helium and carbon dioxide. Under carbon dioxide at 200 °C after 60 mins the hydrochar displayed exceptional energy density at 36 MJ Kg-1 and contained a large portion of volatile matter (58.8%). Thus, bread waste demonstrated high potential in producing a renewable solid fuel or activated carbon material. Hydrothermal carbonisation of avocado seeds examined the potential to perform a one-pot catalyst synthesis procedure. A mixture of magnetite and heamatite was supported on the hydrochar in situ to yield a magnetic carbon composite material. This catalyst showed full regioselectivity in an exemplary catalytic testing procedure as well as viable adsorption of indigo carmine (~49 mg g-1). Therefore, the efficient production of catalytic materials is exhibited with potential application to a wide range of different lignocellulosic wastes and catalytic metals. The molecular interactions within alcohol/water mixtures at both ambient and hydrothermal (sub-critical) conditions was analysed using Fourier-transform infrared spectroscopy. Mathematical analysis methods such as deconvolution, and perturbation induced 2D correlation analysis were performed to analyse the data. Using this methodology the molecular transition points discussed in literature for ambient alcohol/water mixtures were identified by trends in blueshifting and excess intensity of the crucial peaks O-H and C-O stretching. Following this, novel information about the molecular dynamics of alcohol/water mixtures under hydrothermal conditions was acquired. Further to this, the effect of ethanol/water mixtures on the hydrothermal carbonisation of bread waste and avocado seeds was ii investigated. Whilst the properties of hydrochar were affected by varying ethanol concentration at lower processing temperatures these effects were reduced at higher processing temperatures. Aerosol-assisted sol-gel synthesis mechanisms were investigated using optical trapping instrumentation at the Central Laser Facility. The initial stages of synthesis were imitated by trapping a single droplet of the precursor solutions using focussed light. This droplet was monitored using Raman spectroscopy and heated externally, therefore replacing the space domain in the aerosol flow tube with a time domain. From this investigation, evidence against the expected reactions based on bulk sol-gel synthesis was obtained. Furthermore, insight was gained into the effects of different compounds in the precursor solution on droplet stability and evaporation. Finally, an alternative reaction mechanism to that observed in bulk sol-gel synthesis was proposed based on the observed Raman spectroscopic data.