In the present study, 24 data sets regarding CO2 absorption by the piperazine (PZ) activated aqueous methyldiethanolamine (MDEA) solution (30% wt) have been obtained from Khan et al.'s work and have been investigated using rate base model. Hence, mass transfer correlations such as Onda's, Bravo-Fair's, Billet-Schultes' correlations and liquid hold-up correlations of Billet-Schultes and Stichlmair have been studies in the current paper. In addition, important parameters like CO2 absorption (%), liquid temperature and rich solvent's loading have been compared in different mass transfer and liquid hold-up correlations. The results of using the rate-base model in the mass transfer and liquid hold-up correlations in 24 different experimental conditions indicate that the Bravo-Fair mass transfer correlations have higher accuracy compared to other mass transfer correlations. This comparison has been carried out based on CO2 absorption (%) and the rich solvent's loading. Moreover, studying mass transfer correlations give the following amounts for the average error of Onda's, Bravo-Fair's and Billet-Schultes' mass transfer correlations respectively for CO2 absorption (%) calculation in 16 different experimental conditions: 23.45, 14.63 and 38.59 (%). In the last part of the paper, rich solvent's loading is compared with real amounts in 12 different experimental conditions. The comparison shows that the average errors of Onda's, Bravo-Fair's and Billet-Schultes' mass transfer correlations are 14.80, 9.70 and 21.75 (%) respectively. Investigating liquid hold-up correlations indicates that Billet-Schultes' and Stichlmair's correlations give the same results regarding rich solvent's temperature, solvent's temperature profile along the absorption column, CO2 absorption (%) and rich solvent's loading. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.