Modelling, Imaging and Sensing of Chemical Processes
Modelling, imaging and sensing of chemical processes is an important research area in the department and current projects include the development of sensors and the modelling and imaging of chemical reactions, among others.
Projects include the development of physicochemical models for biogas and bio-syngas for clean energy utilisation from renewable gaseous fuels, the visualisation of local temperature and concentration inside chemical reactors using near-infrared tomography, developing models for the mechanisms and chemical kinetics of biomass conversion to liquid and gaseous fuels, development of 3D modelling of the hydrogen isotopic exchange process inside stripping columns, and the development of a micro-optical ring electrode for multiple actinide ions monitoring.
The Micro-Optical Ring Electrode: A Sensor for Multiple Actinide ions Monitoring
The Micro-Optical Ring Electrode (MORE) is an electrochemical sensor consisting of a fibre optic light guide, which allows the delivery of light to the test environment, triggering a series of photochemical reactions and a concentric gold ring microelectrode capable of reducing (or oxidizing) small amounts of products of those reactions.
One of the challenges faced by the nuclear industry is the safe characterisation, retrieval and treatment of materials both during processing and for the purposes of decommissioning. For example fuel processing would benefit from the fast and in situ monitoring of key actinide ions such as Uranium, Neptunium and Plutonium to help track progress of extraction stages. Likewise decommissioning of plants such as high hazard ponds present at a number of civil nuclear sites (e.g. Sellafield, Harwell, Winfrith) requires the full and accurate characterization of the supernatant with minimum involvement from human operators, because of the radiological conditions around those ponds. A device capable of in-situ analysis of those environments is therefore desirable.
The Micro-Optical Ring Electrode (MORE) is an electrochemical sensor consisting of a central fibre optic light guide, which allows for the delivery of light to the test environment, triggering a series of photochemical reactions and a concentric gold ring microelectrode capable of reducing (or oxidizing) the very small amounts of the products of those photochemical reactions and generate a photocurrent, measured by an external potentiostat. A mathematical model has been devised which allows to correlate the electrochemical signal received by the potentiostat to the concentration of the analyte present in the bulk solution. Previous studies with this device have shown that this electrochemical response is dependent on (i) the illumination wavelength which must correspond to an absorbance peak of the target analyte and (ii) the working potential of the device which must be able to drive the oxidation or reduction of the products of the photochemical process. The MORE therefore offers two modes of differentiation (photochemical and electrochemical) allowing for analytes with similar physico-chemical properties to be monitored using a single device.
Uranium, plutonium and neptunium are possessed of singular spectrophotometric signatures (λmax U(VI)=420nm, Pu(III)=565nm, Pu(IV)=475nm and Np(IV)=725nm), which makes the photoexcitation of a single analyte in the presence of a mixture possible, indicating that simultaneous analysis of these species using a single MORE is possible. The aims of this project are to confirm the feasibility of multiple analyte monitoring using a single MORE by tuning both the excitation wavelength and the detection potential of the electrode, to investigate the potential interference from extraneous species in the analyte solution, and adapt the established mathematical model for the MORE to systems consisting of several analytes and under the target conditions.
Visualization of local temperature and concentration inside packed bed reactors by near-infrared tomography
This project looks by diffuse near-infrared tomography at local concentration and temperature distributions inside packed bed reactors/adsorbers/difusers, where water vapour and its isotopers are used as tracer examples owing to their highly spectral absorptions in near-infrared.
Conventional development strategies in which the catalyst is developed independently of reactor design have shown their limitations in providing a detailed solution at various scale levels of the reactor design. There is a need to carry out catalyst and reactor development simultaneously and improve the integration of catalytic chemistry and reaction engineering. The aim of this project is to develop research strategies to investigate heterogeneous gas-solid catalytic reactors based on spatiotemporal information. Gas-solid heterogeneous systems use packed beds in chemical technology such as reactors, separators, dryers or filters and energy generation technology such as combustion, fuel cells or energy storage. The design of packed beds by a detailed knowledge of local data in terms of composition, temperature and fluid dynamics is of upmost importance as suggested by recent developments of computer fluid dynamics. Experimental validations, however, are still not sufficiently mature. This project looks by diffuse near-infrared tomography at local concentration and temperature distributions inside packed bed reactors/adsorbers/difusers, where water vapour and its isotopers are used as tracer examples owing to their highly spectral absorptions in near-infrared. Flow maldistribution and uneven maps of temperature and composition in the core packed bed have been clearly observed which allow fine-tuning of local heat uptake/resource and cross-mixing profiles that were partly anticipated by CFD simulations.