dc.contributor.author Hu, Wenting dc.date.accessioned 2016-09-20T10:49:00Z dc.date.available 2016-09-20T10:49:00Z dc.date.issued 2016-02-02 dc.identifier.other PhD.39411 dc.identifier.uri https://www.repository.cam.ac.uk/handle/1810/260245 dc.description.abstract In chemical-looping, a fuel is oxidised by a solid metal oxide, MeO, in one reactor: (2$n+m$)MeO+C$_{n}$H$_{2m}\rightarrow$(2$n+m$)Me+$m$H$_{2}$O+$n$CO$_{2}$. The exit gas yields pure CO$_{2}$ after the steam has been condensed. The reduced metal oxide, Me, is transferred to an oxidation reactor and regenerated: Me+air$\rightarrow$MeO. Adding these reactions, the fuel has been combusted, but the CO$_{2}$ has been separated from the nitrogen in air. In fact, it is in a suitable form for sequestration in the Earth where prevention of greenhouse gas emissions to the atmosphere is desired. Generally, Me is a transition metal and, to withstand many such redox cycles, it has to be supported on a suitable refractory oxide, with particles of the resulting construct being termed the "oxygen carrier". This Dissertation is concerned with the release and uptake of gaseous oxygen when Me is copper. In particular, the interest is in the following reaction at temperatures exceeding ~900°C undertaken in a fluidised bed reactor:$\\$ en 4CuO$_{(s)}\Leftrightarrow$2Cu$_{2}$O$_{(s)}$+O$_{2(g)}$. (1)$\\$ The value of this reaction is that the oxygen released as part of a chemical looping scheme is important in combusting unreactive solid fuels, e.g. coal chars, whilst the Cu$_{2}$O could, in principle, be further reduced to Cu by the more reactive components of the fuel. This Dissertation investigates the development and characterisation of suitable, Cu-based oxygen carriers, which must (i) be inexpensive and easy to produce at a large scale and (ii) remain stable in prolonged operation in terms of mechanical integrity and chemical reactivity when fluidised. Here, a suitable oxygen carrier was developed, satisfying the above criteria, using a wet-mixing method and containing nominally 60 wt% CuO, 23 wt% Al$_{2}$O$_{3}$ and 17 wt% CaO. In particular, it was found that this oxygen carrier could operate between CuO and Cu$_{2}$O without problem in a circulating fluidised bed but agglomeration and de-fluidisation was observed when the carrier was re-oxidised from the Cu form. For design, it is important to understand the thermodynamics and kinetics of the release of gaseous O$_{2}$ from the oxygen carrier, because the combustion of the solid fuel depends critically on this reaction. A novel method was developed to measure experimentally the thermodynamics of reaction (1) for the supported copper oxide. It was found that the thermodynamic equilibrium deviated slightly from that of the pure CuO/Cu$_{2}$O system reported in the literature and that the enthalpy of reaction was lower by ~ 15%; the reasons for this are discussed. The rate of release of O$_{2}$ from the oxygen carrier was investigated using a thermogravimetric analyser and the activation energy for the forward reaction of (1) was found to be 59.7$\pm$5.6 kJ/mol, obtained after appropriate modelling of the external mass transfer resistances present in the experimental apparatus. A critical analysis of the seemingly disparate activation energies reported in the literature revealed that the activation energy of the forward step in reaction (1) was, in fact, similar for many CuO-based oxygen carriers supported on different materials. The associated pre-exponential factor for the forward rate constant was also determined in the present research, and the kinetic parameters were used in a numerical model to predict the behaviour of the oxygen carriers in a fluidised bed reactor. Excellent agreement between theory and experiment was found, confirming that the kinetic parameters obtained in this work reflect the intrinsic chemical kinetics of the oxygen carrier, rather than being totally dominated by transport effects. dc.language.iso en en dc.rights All Rights Reserved en dc.rights.uri https://www.rioxx.net/licenses/all-rights-reserved/ en dc.subject Research Subject Categories::TECHNOLOGY::Chemical engineering en dc.subject chemical-looping with oxygen uncoupling en dc.subject chemical-looping en dc.subject oxygen carriers en dc.subject CLOU en dc.title Development and characterisation of a copper-based oxygen carrier for chemical-looping with oxygen uncoupling (CLOU) en dc.type Thesis en dc.type.qualificationlevel Doctoral dc.type.qualificationname Doctor of Philosophy (PhD) dc.publisher.institution University of Cambridge en dc.publisher.department Department of Chemical Engineering and Biotechnology en dc.publisher.department Selwyn College en dc.identifier.doi 10.17863/CAM.4184 dc.contributor.orcid Hu, Wenting [0000-0001-7368-7163] en cam.supervisor Dennis, John cam.supervisor Scott, Stuart cam.supervisor.orcid Scott, Stuart [0000-0002-4597-9094] en
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