Kinetics and transport phenomena in the chemical decomposition of copper oxychloride in the thermochemical Cu-CI Cycle

Abstract

The thermochemical copper-chlorine (Cu-Cl) cycle for hydrogen production includes three chemical reactions of hydrolysis, decomposition and electrolysis. The decomposition of copper oxychloride establishes the high-temperature limit of the cycle. Between 430 and 530 oC, copper oxychloride (Cu2OCl2) decomposes to produce a molten salt of copper (I) chloride (CuCl) and oxygen gas. The conditions that yield equilibrium at high conversion rates are not well understood. Also, the impact of feed streams containing by-products of incomplete reactions in an integrated thermochemical cycle of hydrogen production are also not well understood. In an integrated cycle, the hydrolysis reaction where CuCl2 reacts with steam to produce solid copper oxychloride precedes the decomposition reaction. Undesirable chlorine may be released as a result of CuCl2 decomposition and mass imbalance of the overall cycle and additional energy requirements to separate chlorine gas from the oxygen gas stream. In this thesis, a new phase change predictive model is developed and compared to the reaction rate kinetics in order to better understand the nature of resistances. A Stefan boundary condition is used in a new particle model to track the position of the moving solid-liquid interface as the solid particle decomposes under the influence of heat transfer at the surface. Results of conversion of CuO*CuCl2 from both a thermogravimetric (TGA) microbalance and a laboratory scale batch reactor experiments are analyzed and the rate of endothermic reaction determined. A second particle model identifies parameters that impact the transient chemical decomposition of solid particles embedded in the bulk fluid consisting of molten and gaseous phases at high temperature and low Reynolds number. The mass, energy, momentum and chemical reaction equations are solved for a particle suddenly immersed in a viscous continuum. Numerical solutions are developed and the results are validated with experimental data of small samples of chemical decomposition of copper oxychloride (CuO*CuCl2). This thesis provides new experimental and theoretical reference for the scale-up of a CuO*CuCl2 decomposition reactor with consideration of the impact on the yield of the thermochemical copper-chlorine cycle for the generation of hydrogen.