The effect of alkali and alkaline earth metals oxides addition on oxygen uncoupling rate of copper-based oxygen carrier: A kinetic and experimental investigations

Abstract

Oxygen uncoupling is one of the most valued properties of oxygen carriers in chemical looping field. It allows to combust the fuel without gasification step and significantly enhances reactivity in all chemical looping fuel oxidation technologies (combustion, gasification, and reforming). Furthermore, it progressed recently to produce pure oxygen (Chemical looping air separation). However, few materials have this merit, among which CuO has the highest reactivity and oxygen transport (uncoupling) capacity. However, it needs a high temperature (about 950 °C) for a high effective reaction rate; in contrast, it suffers high attrition rate and sintering about this temperature. This work aimed to test the ability to enhance the uncoupling at lower temperatures by adding a small amount of common alkali and alkaline earth metals (AAEMs) oxides. CuO was prepared with 5%wt of Na2O, K2O, MgO, and CaO. An isothermal test was conducted in TGA at (850, 890, and 930 °C) to investigate the effect of additions. For deeper investigation, kinetic analysis has been conducted based on isothermal results. The model of reaction inferred was A2α of Avrami-Erofeev (gα=-ln1-α1/2) for pure CuO and with all additions, and then the activation energies and pre-exponential factors were calculated. Accordingly, CaO addition showed little increase in the reaction rates while the effect of MgO was significant. In contrast, Na2O and K2O addition declined the uncoupling rate.