CO2 absorption processes have a good potential for large scale capture of CO2 but a large amount of absorbing solution has to be regenerated, undesirably increasing the consumption of energy such as sensible heat and latent heat of vaporization. In this study, a cooling crystallization process which would separate the CO2-rich potassium bicarbonate crystals from CO2-lean water was developed to reduce the energy penalty. Sterically hindered alkanolamine additives were used to enhance the CO2 removal efficiency and their antisolvent effect on the crystallization was found in a continuous cooling crystallizer. The production yields of crystals were increased in the sequence of 2-amino-2-methyl-1-propanol (AMP) < 2-amino-2-methyl-1,3-propanediol (AMPD) < 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD), which are related to the number of hydroxyl groups in the additive molecules. Using 13carbon nuclear magnetic resonance, the additives favored the formation of bicarbonate ions by steric hindrance effect and increased the supersaturation of KHCO3. It is shown that the additives increase the mean size of crystals and crystal growth rate by increasing supersaturation. The additives are promising for enhancing the CO2 removal efficiency and reducing the regeneration energy cost of CO2 absorbing solution by promoting KHCO3 crystallization.