There has been increased interest in the development of innovative carbon dioxide (CO2) capture and storage (CCS) applicable to the integrated coal gasification combined cycle (IGCC) equipped with a water-gas shift reaction, to reduce greenhouse gas emissions to almost zero (IGCC-CCS). We Studied the heats of reaction (Delta H-r) and vapor-liquid equilibria for N-methyldiethanolamine and novel absorbents [1,2-dimethylimidazole, 2-methylimidazole, 1-methylimidazole, imidazole, and 4-(2-hydroxyethyl)morphine] obtained by the pK(a)-based screening method in our previous work and found a proportional relationship between pK(a) and Delta H-r values. This allows estimation of Delta H-r values by measuring their pK(a). Measurements of vapor-liquid equilibria of novel absorbents provided important information on the CO2 capacity per absorption/recovery cycle. 1,2-Dimethylimidazole and 4-(2-hydroxyethyl)morpholine would be nominated as candidates suitable to absorb/recover CO2 with partial pressures at 1.6 MPa or higher without loss of a CO2 pressure level, resulting in saving CO2 compression energy in the CCS process.