Rate-based modelling of SO2 absorption into aqueous NaHCO3/Na2CO3 solutions accompanied by the desorption of CO2

A rate-based model of a counter-current reactive absorption/desorption process has been developed for the absorption of SO₂ into NaHCO₃/Na₂CO₃ in a packed column. The model adopts the film theory, includes diffusion and reaction processes, and assumes that thermodynamic equilibrium among the reacting species exists in the bulk liquid. Model predictions were compared to experimental data from literature. For the calculation of the absorption rate of SO₂ into NaHCO₃/Na₂CO₃ solutions and concomitant CO₂-desorption, it is important to take into account all reversible reactions simultaneously. It is clear that the approximate analytical based model cannot be expected to predict the absorption rates under practical conditions because of the complicated nature of the reactive absorption processes. The rigorous numerical approach described here only requires definition of the individual reactions in the system, and subsequent solution is independent of specific assumptions made, or operational variables like pH or compound concentrations. As an example of the flexibility of this approach, additional calculations were conducted for SO₂ absorption in a phosphate-based buffer system.