Kinetics of CO and CO2 Evolution During the Temperature-Programmed Oxidation of Coke Deposited on Cracking Catalysts

Abstract

The reaction kinetics of evolved carbon monoxide and carbon dioxide during the temperature programmed oxidation (TPO) of an industrially spent fluid cracking catalyst have been investigated. Two pathways to CO and two to CO2evolution, all involving either undissociated or dissociated surface oxide complexes, were assumed. Rate coefficient parameters and O2reaction orders were then optimized to simulate the TPO profiles recorded over a range of conditions: heating rates of 2, 5 and 10°C and O2partial pressures of 0.939, 1.11, and 5.0% in an atmosphere of N2. Evolution rates of CO during TPO are independent of the O2partial pressure, whereas an order of 0.75 is indicated for CO2formation. Because of differences in assumed mechanisms and carbon substrates, calculated preexponential factors and activation energies can not be readily compared with literature values, although some comparisons are made. If the heating rate is high (≥5°C min-1) and the oxygen partial pressure is low (≤1%), the shape of TPO profiles for highly saturated hydrocarbon coke deposited on cracking catalyst are affected by changes in the rate-determining step with increasing temperature.