Syngas production over reducible metal oxides

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2013
Çalışan, Atalay
The scope of this thesis was to study thermodynamics of lead oxide and cobalt oxide as the chemical looping agent for oxygen. Furthermore, the theoretical results were verified experimentally. Ellingham diagrams were constructed for the selected oxides. Then, detailed thermodynamic analysis was conducted for stability analysis at different temperatures and pressures. Equilibrium product compositions for various reactions involving these oxides were calculated via Gibbs free energy minimization analysis. Finally, it was shown that cobalt, lead and their oxide forms can be used for syngas production. In the experimental part PbOx, CoOx, Pt-doped CoOx and Pt-doped cobalt alumina, and mixed lead cobalt oxides were synthesized. In addition, technical grade cobalt oxide and lead rods were also used. XRD analysis indicated that Co3O4, Pb2O3 and α-PbO were the main crystal structures. Oxygen evolution from mixed oxides was monitored by TPD in a home built system. Re-oxidation of the reduced metals was successfully conducted using CO2 and H2O as oxidizing agents. Oxygen TPD studies indicated that oxygen evolution rates and amounts were higher and started at lower temperatures when two oxides were together. These observations were consistent with the predictions obtained from thermodynamics. In a series packed bed reactor, evolved oxygen from the mixed oxides were used to react with coal packed upstream of the oxides. It was found that coal oxidation can be achieved around 400oC and 600oC by using Pb/Co=3 (wt./wt.) looping media with almost no CO2 formation. It was also found that desired product selectivity (CO) can be increased by controlling reactive agent (O2) concentration in reaction environment.