Chemical enhancement factors for CO2 absorption into partially carbonated NH3 solutions in a stirred-cell absorber Here experimentally determined over a wide range of carbonation ratio in this work. The results reveal that the one-reaction promotion mechanism, which is traditionally used in the literature, has shortcomings in describing the effects of initial total ammonia concentration and carbonation ratio on absorption enhancement. A shuttle mechanism, by which NH3 and CO2 undergo an irreversible second-order reaction in the interface region while the chemical equilibrium of multiple reactions prevails in the bulk region to liberate free NH3. is then proposed for the absorption enhancement. The calculation of the bulk-liquid compositions is made hy using the rigorous thermodynamic package in ASPEN PLUS simulator, The chemical enhancement factors predicted by the present promotion mechanism are in good agreement with the experimental data available.