Chemical kinetics of copper oxide reduction with carbon monoxide

Abstract

In order to assess the potential for using copper oxide as the oxygen source in chemical looping combustion with coal, a study was undertaken to characterize the reaction rates of copper oxide with carbon monoxide, a major coal partial oxidation product. In the study, CO oxidation experiments were performed in a pressurized thermogravimetric analyzer (TGA) with copper II (CuO) and copper I oxide (Cu 2O). In these experiments, about 25 mg of CuO or Cu 2O particles having diameters less than 125 μm were placed on the balance pan of the TGA and mixtures of 1.6% CO in N 2 were admitted into the reaction chamber, which was maintained at selected temperatures between 473 and 773 K. The measured thermograms were used to develop a chemical reaction mechanism and associated kinetic parameters to described CO oxidation with copper oxide. The reaction mechanism takes into account CO adsorption at copper sites, CO surface migration, and CO 2 desorption. Calculations employing the mechanism indicate that the overall reaction rate becomes mass transport limited for copper oxide particles larger than 125 μm in diameter, exposed to 100% CO at temperatures above 873 K. The reaction mechanism reveals a reaction order of 0.7 with respect to the CO mole fraction and an overall activation energy of 20 kJ/mol and 25 kJ/mol, respectively, for the reduction of CuO and Cu 2O to Cu. Calculated results support an earlier hypothesis that under the conditions examined, there are two pathways for CuO reduction to Cu, one cascading (CuO → Cu 2O → Cu) and the other direct (CuO → Cu). Our results indicate that chemical looping combustion of coal employing CuO as the oxygen carrier will not be limited by chemical reaction rates.