The process models for an equilibrium CO2 absorber and a rate based CO2 absorber using potassium carbonate (K2CO3) solvents were developed in Aspen Custom Modeller (ACM) to remove CO2 from a flue gas. The process model utilised the Electrolyte Non-Random Two Liquid (ENRTL) thermodynamic model and various packing correlations. The results from the ACM equilibrium model shows good agreement with an inbuilt Aspen Plus (R) model when using the same input conditions. By further introducing a Murphree efficiency which is related to mass transfer and packing hydraulics, the equilibrium model can validate the experimental results from a pilot plant within a deviation of 10%. A more rigorous rate based model included mass and energy flux across the interface and the enhancement effect resulting from chemical reactions. The rate based model was validated using experimental data from pilot plants and was shown to predict the results to within 10%. A parametric sensitivity analysis showed that inlet flue gas flowrate and K2CO3 concentration in the lean solvent has significant impact on CO2 recovery. Although both models can provide reasonable predictions based on pilot plant results, the rate based model is more advanced as it can explain mass and heat transfer, transport phenomena and chemical reactions occurring inside the absorber without introducing an empirical Murphree efficiency. (C) 2018 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.