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

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.