Phase-splitting absorbents represent a promising technology in relation to the low energy levels required during the CO2 capture process. 1-Methylimidazole was added to a diethylenetriamine (DETA) aqueous solution for high CO2 loading via phase splitting of absorbents during CO2 absorption. Phase splitting was observed during the absorption process when the CO2 loading reached a value suitable for the mixture of DETA, 1-methylimidazole, and water. The distribution of individual components in each phase was determined according to the total organic carbon and gas chromatography. DETA and CO2 were concentrated in the bottom phase, 1-methylimidazole mostly in the top phase. Phase splitting during CO2 absorption was mainly due to the solubility limitation of DETA carbamate into 1-methylimidazole.