Application of electrolyte-nrtl model for prediction of the viscosity of carbon dioxide loaded aqueous amine solutions

A method based on the absolute-rate theory has been used and tested for estimation of the dynamic viscosity of CO₂ loaded aqueous solutions of a representative amine: monoethanolamine (MEA). In this approach the electrolyte-NRTL model is applied to estimate the activation free energy of the solution and consequently enable prediction of the dynamic viscosity of the strong electrolyte CO₂:MEA:H₂O system. Three different concentrations of the aqueous MEA solutions with 20, 30, and 43 wt %, in the temperature range from 40 to 70 C, and CO₂ loadings from 0.1 to 0.5 mol of CO₂/mol of amine were selected for the model investigation. The model displays a reasonable prediction ability from experimental viscosity data in the whole range of system variables. It is shown that the activation free energy for the flow process can be closely estimated through the Gibbs free energy of mixing with a correction on the sign of the energy term in the model equation from positive to negative. The result reveals that, having a reliable thermodynamic model for a selected solution, the absolute-rate-theory approach is applicable for estimation of the viscosities of strong electrolyte systems such as CO₂ loaded alkanolamine solutions at different solution concentrations, temperatures, CO₂ loadings, and operating pressures for various amines and amine blends.