A non-equilibrium heat and mass transfer model to describe the chemical absorption of ammonia, carbon dioxide and hydrogen sulfide in an aqueous solution containing sodium hydroxide and/or ammonia is introduced. The influence of chemical reactions on mass transfer in the electrolyte system is accounted for by enhancement factors. The pilot plant concept, as well as the applied experimental and analytical procedures to achieve experimental results for the validation of the model are presented. A comparison between the experimental data and the simulation results proves the predictivity of the presented mass transfer model. The discussion of the results leads to an optimum pH range for the operation of the given process. (C) 2003 Published by Elsevier B.V.