Determination of intrinsic rate constants of the CaO–CO2 reaction

The rate constant of the CaO–CO2 reaction was studied for two sorbents using an atmospheric thermogravimetric analyzer (ATGA) and a pressurized thermogravimetric analyzer (PTGA). A grain model was used to determine the rate-controlling steps. The intrinsic rate was found to have a variable order with respect to CO2 partial pressure, with a first-order reaction changing to zero-order dependence when the CO2 partial pressure exceeded ∼10kPa. No further rate enhancement was observed under pressurized conditions, which was explained by a two-step Langmuir mechanism. The activation energies were 29±429±4 and 24±6kJ/mol for the limestone and dolomite tested.