Screening and evaluation of phase change absorbents by molecular polarity index: Experimental and quantum chemical calculation studies

•MPI is used to predict phase separation behavior of amine aqueous systems.•Monohydroxy tertiary amines favor the formation of phase-change absorbents.•Excessive intermolecular hydrogen bonds are detrimental to phase separation.•MPI of the tertiary amine is negatively correlated with the phase separation time. Phase change absorbents have recently received increasing attention due to their potential to reduce the energy penalty of CO2 capture. However, its complex composition makes the prediction of phase separation performance difficult. Phase separation behavior and phase separation rate have been investigated for the amine-aqueous 5.0 M amine blends by experimental and quantum chemical calculations (including MPI, hydrogen bonds and Gibbs free energy). The different phase behaviors upon CO2 absorption were discussed and well explained by the polarity change of components and the reaction products. A defined MPI value of tertiary amines was recommended to predict the immiscible type (MPI > 10.55 Kcal/mol), phase separation type (9.00 Kcal/mol