SIMULTANEOUS ABSORPTION OF H2S AND CO2 INTO A SOLUTION OF SODIUM CARBONATE

The simultaneous absorption of H₂S and CO₂ has been studied both experimentally and theoretically. A model has been developed which predicts the absorption rates of H₂S and CO₂ into a sodium carbonate solution. The absorption rates are calculated according to the two-film theory. In the liquid film, the finite rate of the CO₂ reaction was considered. Otherwise, in the liquid film as well as in the liquid bulk, equilibrium conditions for all reactions were assumed. Absorption experiments were performed on a packed column using a counter-flow strategy. In the experiments the influence of the initial carbonate concentration, the gas flow rate and the temperature on the removal efficiencies of H₂S and CO₂ and the selectivity of H₂S were investigated. It is desirable to absorb the H₂S but not the CO₂. The agreement between the absorption model and the experimental results from the absorber tower was satisfactory. The mass transfer coefficients were determined by fitting the experimental data to the model with respect to the H₂S and CO₂ content in the outgoing gas. The H₂S content was used to determine the gas side mass transfer coefficient and the CO₂ content was used to determine the liquid side mass transfer coefficient, The effective contact area of mass transfer was taken from published data. With a constant packing height, both the experiments and the model indicated that high carbonate concentration benefits the removal efficiency of H₂S. Higher gas flow rate also benefits the selectivity for H₂S. However, the removal efficiency will decrease. At higher temperatures the selectivity and the removal efficiency of H₂S decreased. Under the conditions investigated, the absorption of H₂S was essentially controlled by gas-side mass transfer and the absorption of CO₂ was controlled by liquid-side mass transfer