The kinetic model for carboreduction of zinc oxide

Abstract

The carbothermal reduction of zinc oxide using highly concentrated solar radiation is a promising concept for the production of pure zinc and hydrogen. Solar energy is converted to chemical energy in the form of abundant fuel, easy to use and environmentally friendly. The present work is aimed to study kinetics of carboreduction of zinc oxide in laboratory reactor, developing the kinetic model and explore the possibility to accelerate the process (decrease in CO 2 concentration) by adding a catalyst to the solid ZnO and carbon mixture. A laboratory experimental set up for kinetic study of carbothermal reduction of zinc oxide is constructed and described in details. Experiments were carried out with mixtures of zinc oxide powder and 12-20 mesh activated carbon at temperatures of 1000-1300°C and C/ZnO wt, ratios =1:8. A kinetic model was proposed based on a mechanism of carboreduction that involves two chain gas-solid reactions with intermediate formation of CO and CO 2 . The rate constants and activation energy were determined from the experimental data. The validity of the model is discussed. The preliminary experiments were carried out on catalytic carboreduction of Zine Oxide. The sample for catalytic carboreduction was prepared by impregnation of the ZnO + C mixture with Nickel acetate solution. Two samples containing ZnO + C mixture and ZnO + C + 2%NiO were tested at 1000°C under the same conditions. It was found that adding Ni-catalyst to the mixture of Graphite and ZnO increases drastically the rate of carboreduction and conversion of Zinc Oxide.