Ilmenite oxidation kinetics for pressurized chemical looping combustion of natural gas

Pressurized Chemical Looping Combustion (PCLC) is a promising technology for mitigating CO2 emission from fossil fuel combustion. This work investigates the oxidation kinetics of a natural ilmenite ore to assess the PCLC of natural gas since process economics are largely dependent on the air reactor performance, and data at pressurized conditions are scarce. Thermogravimetric experiments were conducted varying the temperature from 800 to 1050 °C and the oxygen partial pressure from 0.2 to 1.7 bar at a total pressure of 8 bar. The total pressure was also varied from 1 to 16 bar at 900 °C with air. The total pressure was found to hinder the rate of the oxidation reaction when maintaining a constant O2 partial pressure and enhance the rate of the oxidation reaction when maintaining a constant O2 volume fraction, up to a threshold. The oxidation kinetics were modelled using a dual-step mechanism; random nucleation and growth followed by solid-state diffusion. The activation energy and reaction order with respect to oxygen were found to respectively be 16.6 kJ/mol and 0.34 for the nucleation and growth, and 48.7 kJ/mol and 1.26 for the solid-state diffusion regime. Finally, considering the design and economics of PCLC, it was shown that elevated O2 partial pressures negatively affect the ilmenite particle structural integrity subjecting it to fragmentation, whereas lower O2 partial pressures favour the migration of iron to the particle surface where inherent attrition loses would result in an enriched titanium ore as spent material.