Acid gas (CO2 and H2S) removal from industrial gas streams by amine scrubbing is usually employed in industry. Among different amines, n-MethylDiEthanolAmine (MDEA) is preferred because of its high equilibrium loading capacity and low heat of reaction with carbon dioxide, associated to low energy requirement in the regeneration section. Piperazine (PZ) can be used as promoter because of its rapid transformation to carbamates with carbon dioxide when mixed to MDEA (PZ rate constant value has been found to be one order of magnitude higher than the one of MEA). A correct representation of properties of the absorbent solution, such as density and viscosity, is essential for rate-based calculations. This paper gives an in-depth analysis and calculation of the properties involved in the modeling of mass transfer of absorbed species and on the development of general correlations for the description of density and viscosity of the MDEA + PZ solution to be applied for a wide range of concentrations and temperatures. In this work, in addition, the influence of carbon dioxide loading on the solvent properties has been taken into account too. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.