Calcium oxide can be an effective sorbent for separating CO 2 at high temperatures. The carbonation reaction is the basis for several proposed high temperature CO 2 capture systems when coupled with a calcination step to produce a pure CO 2 stream. Fresh calcined lime is known to be able to carbonate very readily at appropriate temperatures, but the average sorbent particle in a capture system using CaO as regenerable sorbent has to undergo many carbonation/calcination cycles. This work investigates the carbonation reaction rates in highly cycled sorbent particles of CaO (20–100s of carbonation/calcination cycles). A basic reaction model (homogeneous model) has been proved to be sufficient for interpreting the reactivity data obtained under different conditions: partial pressure of CO 2 , particle sizes and other relevant operation variables for the carbonation/calcination loop. The intrinsic rate parameter was found to be between 3.2 and 8.9×10 −10 m 4 /mols in agreement with other values found in the literature.