Microalgae are a promising feedstock for the production of sustainable, 3rd generation biofuels; however, current lipid-based processes are too expensive to effectively compete with existing transportation fuels. A potential solution is to convert the entire algae via hydrothermal liquefaction (HTL) instead, therefore allowing the use of faster-growing, and cheaper microalgae.This project sought to address some of the main challenges with this technology, currently restricting its use for large-scale fuel production. Fuels are low value products and unlikely to pay for the entire fuel production process on their own. Consequently, the possibility of producing additional by-products from the conversion of polymer- containing algae, or combining HTL with a more conventional lipid- extraction process, was explored. In addition, the project studied the conversion of microalgae produced during the bioremediation of domestic wastewater, in order to help to offset the overall biomass production costs.The majority of research into algal HTL has been confined to batch systems, which are not fully representative of the continuous flow processes used for large-scale fuel production. Consequently, an inexpensive laboratory-scale system was designed to study the continuous HTL of algae under a range of operating conditions. Using this system, it was found that, compared to a batch reactor, significantly enhanced oil yields could be obtained from the system, as a result of increased heating rates, together with prolonged reaction times.Finally, the poor quality of the bio-oils produced by the HTL of microalgae is a major challenge. Particularly their high nitrogen content restricts their conversion within conventional petrochemical refineries. Therefore, significant upgrading is required before the oil can be fractionated into fuels. In order to achieve this, a range of zeolite-supported nickel phosphide catalysts were synthesised in this project, and tested for the denitrogenation of the model compound quinoline, before they were applied to the upgrading of bio-oil obtained from the continuous liquefaction of the wastewater-derived algae. Although the synthesised catalysts showed only low activity towards the denitrogenation of the bio- oil, they were more active for the hydrogenation of quinoline, compared to two conventional sulphided transition metal catalysts, and following further optimization, could therefore represent a viable class of oil upgrading catalysts.
|Date of Award||16 Jan 2017|
|Supervisor||Chris Chuck (Supervisor), Valeska Ting (Supervisor), Asel Sartbaeva (Supervisor) & Mark Weller (Supervisor)|