The solubility of CO2 in aqueous solutions of 1-methyl piperazine (1-MPZ) was measured at (313 and 353) K for (15 and 30) wt % and up to a pressure of 7815 kPa, reaching a gas loading of 0.67 molCO2/molalkalinity. The electrolyte–NRTL (nonrandom two-liquid) model was used to correlate the data. Five adjustable ionic pair interaction parameters and six molecular interaction parameters were regressed, which allowed for the correlation of the experimental solubility data within an average deviation of 2 % in pressure and temperature and 7 % in experimental loading. The model was used to predict the speciation, heat of absorption, and pH of the loaded solutions. The predicted properties were compared with PZ to show the advantages in using piperazine derivatives in CO2 capture.