Further advances toward the development of a direct heating solar thermal chemical reactor for the thermal dissociation of ZnO(s)

We designed, built and experimentally tested a solar thermal chemical reactor for producing Zn from ZnO(s). We describe the salient features of the reactor concept, the design process itself, and initial experimental results from testing the reactor under solar conditions for both the thermal reduction of ZnO(s) and the carbothermal reduction of the oxide. The reactor operated reliably for more than 100 h. Reactor cavity temperatures reached 2000 K. For the carbothermal reduction of ZnO(s), the solid product was Zn with a purity exceeding 95 mol%. For this reaction, we report reactor and process efficiencies versus cavity temperature. Average values were as high as 14% and 12% respectively. There is an optimal operating temperature and feed condition for these efficiencies: the positive effect of high reaction rates at high temperatures must be balanced against high radiation losses from the reactor at high temperatures. At the operating conditions leading to the highest efficiencies, we produced 1.5 moles of Zn for each mole of consumed carbon. Although the reactor operated mechanically as expected for the thermal reduction of ZnO(s), we were not yet able to obtain high Zn yields.