The modelling of the multicomponent absorption with chemical reaction is not a trivial problem due to superposition of many driving forces - multicomponent diffusion, chemical interactions, convective flows, multicomponent thermodynamic interaction etc. Therefore, adequate theoretical description of multicomponent reactive systems calls for the application of the Maxwell-Stefan equations and for the use of matrix coupled mass transfer equations together with the relevant reaction kinetics. On this basis, a countercurrent absorption tower for chemisorption of nitrogen oxides (NOx) to nitric acid is considered and a general non-equilibrium stage model is developed for its design and optimization.