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Abstract
In this dissertation, investigations on a range of photocatalytic reactors based on waveguides (optical fibres and quartz tubes) are presented. A study on a coupled photocatalytic filtration system is also presented. The work started with the development of integrated computational fluid dynamics (CFD) models to simulate oxalic acid photodegradation in a TiO2-coated glass-bead photoreactor irradiated by end-emitting optical fibre (EEOF) or side-emitting optical fibre (SEOF) bundle. The reactor walls were found to be best modelled with specular reflectivity. The developed model then demonstrated that at high incident radiant power, a uniform light distribution of the SEOF bundle gave quicker oxalic acid photodegradation.
An optical fibre reactor with thirty hexagonal channels distributed within the optical fibre structure was then studied. The TiO2-coated channelled optical fibre reactor (COFR) was assessed for a photocatalytic degradation of gas-phase ethylene. The ethylene reaction rate was found to be independent of the incident photons and the incidental angle. This was attributed to the COFR design, where the propagating light was wholly confined within the reactor and, in turn, more effectively utilised by the TiO2. The COFR was studied further using the developed CFD model, which was also used to optimise the COFR channel configuration. The computational results demonstrated that the radiation distribution on the TiO2-coated channel walls was governed by the spatial distance between channels. Six alternate channel configurations were considered for optimising the COFR with an improvement of up to 33% in overall ethylene conversion being achieved.
The next part of the work involved a study on a bundled tube reactor (BTR). The BTR was found to have an optimised configuration with eight 6-mm TiO2-coated tubes, based on the tube light profile and the photocatalytic reaction rate of ethylene. Introducing an intermediate layer between the TiO2 and quartz tube allowed the light to propagate in a frustrated total internal reflection manner improving both the tube light profile and the photocatalytic reaction rate of ethylene.
The last part of the work concerns integrating photocatalytic and filtration technologies as a hybrid system. A fluidised bed aerosol generator (FBAG) was adapted to prepare TiO2-loaded ventilation filters for the photodegradation of ethanol in gas phase. Compared to a manually loaded filter, the FBAG coated filter demonstrated a more uniform particle distribution on the filter, which resulted in significantly improved photocatalytic performances. Substituting the blacklight blue lamps with a UV-light-emitting-diode (UV-LED) array led to further improvement as well as suppressed the electrical energy per order by a factor of six. This was attributed to its capability to convert electrical energy to photons more efficiently and provide more uniform light distribution on the filter surface.