Hydrogen-Assisted Calcination of CaCO₃: Kinetics and Mechanistic Insights under Desorption-Enhanced Reverse Water Gas...

This study investigates the kinetics of CaCO₃ calcination in H₂ under conditions relevant to the desorption-enhanced reverse water-gas shift (DERWGS) process. Thermogravimetric experiments performed with natural limestone between 600 and 800 °C showed that H₂ markedly accelerates calcination, enabling decomposition at temperatures about 150 °C lower than in conventional calcination environments. As a consequence, the CaO obtained under DERWGS conditions exhibited significantly improved cyclic performance, with nearly double the residual CO₂ carrying capacity of sorbents calcined under standard Ca-looping conditions. For small particles, CaCO₃ conversion followed a homogeneous pattern and was well described by an Avrami-Erofeev kinetic expression with n = 2. The derived kinetic model, which accounts for temperature, H₂ partial pressure, and the thermodynamic driving force associated with the equilibrium CO₂ partial pressure, accurately reproduced conversion curves obtained at different temperatures, calcination cycles, and gas compositions. The apparent activation energy was 184 ± 4 kJ mol^-1, consistent with literature values for reductive calcination. CO₂ was the only gas-phase species found to directly inhibit calcination, whereas CO and H₂O had no measurable independent effect. These findings support a sequential calcination-RWGS mechanism and provide a kinetic basis for the design and scale-up of DERWGS systems for low-carbon lime production and CO₂ utilization.