Chemical Engineering Science, Vol.151, 116-129, 2016
Oxidation of copper at high temperature as an example for gas-solid reactions in a downer reactor experiments and model-based analysis
The kinetics of a gas-solid reaction at high temperatures were studied in a downer reactor of 2.8 m length. As an example, the oxidation of copper particles was carried out at different wall temperatures (1073 K-1323 K), oxygen concentrations (14 Vol.-%-67 Vol.-%), and particle diameters (51 mu m-156 mu m). Although the residence time of the particles was of the order of 1-4 s only, considerable copper conversions could be achieved. XRD, EDX and SEM analysis of the formed products revealed that single layer formation of cuprous oxide prevails up to oxygen concentrations of about 25 Vol.-%. At higher oxygen concentrations, double layer oxidation occurs with a second cupric oxide layer forming on top of cuprous oxide. The remaining core radius of unreacted copper was determined through a combination of density measurements, analysis of TPR spectra, and direct SEM observation. Although significant scattering of the individual measurements was observed, it could be shown by independent elemental analysis of the products that the average values from all measurements are reliable. For quantitative evaluation of the measurements we developed a one-dimensional downer reactor model which allowed to calculate the residence time and particle temperature as a function of reactor length. Using this information we derived solid state diffusion coefficients, the activation energies of which agreed well with literature data. Overall it could be shown that the progress of a gas-solid reaction in a downer reactor can be successfully described with a combination of experimental methods and subsequent model-based data analysis. (C) 2016 Elsevier Ltd. All rights reserved.