A Dft-Based Kinetic Model for a Copper-Aluminum Oxygen Carrier in Chemical Looping with Oxygen Uncoupling (Clou)

Abstract

Understanding the kinetics of oxygen coupling is essential for the design of Chemical Looping with Oxygen Uncoupling (CLOU) reactors, yet existing modeling approaches to study these uncoupling reactions have been superficial. Creating a theoretical model that connects the micro-scale insights from Density Functional Theory (DFT) with the macro-scale of reaction kinetics presents a significant challenge. In this research, a Cu-Al oxygen carrier was synthesized for use in the CLOU process. DFT calculations were performed to identify the pathways of oxygen coupling at the CuO interface, which were found to follow a two-step mechanism involving surface reactions and subsequent O2 desorption. The kinetic rate constants were determined using the Transition State Theory. A rate equation informed by DFT, encompassing energies and frequencies, was formulated. This equation was then incorporated into both the particle model and the reactor model through a series of transport equations. To validate the theoretical predictions, experiments were executed using a micro-fluidized bed mass spectrometer (MFB-MS) to collect kinetic data on the oxygen uncoupling of the Cu-Al material. The results confirmed that the model accurately forecasts the kinetics of oxygen uncoupling for the Cu-Al carrier under high temperatures (925-1000°C) and varying oxygen partial pressures (0-8 vol%). The developed theory serves as a potent instrument for the screening and optimization of oxygen carrier materials in CLOU.

Keywords: Chemical Looping, oxygen carrier, oxygen uncoupling, Kinetics, rate equation