Individual and simultaneous desorption of H 2S and CO 2 from synthetic green liquor

Abstract

Selective desorption of H 2S from green liquor has been investigated using a batch stirred tank reactor. It was found that the gas and liquid side resistances are dependent on the stirrer velocity. In this equipment for physical absorption and desorption of H 2S or CO 2 the resistance in the liquid side is dominant. Within the pH interval researched, the individual desorption rate of CO 2 as well as H 2S is mainly determined by the liquid side mass transfer rate and is not enhanced by any reaction in the film. For the desorption of H 2S from a Na 2S solution, an equilibrium model based on the film theory was evaluated. Another model also based on the film theory with finite reaction rate in the film as well as in the bulk was evaluated for the desorption of CO 2 from NaHCO 3 solution. Both models show values which are in good agreement with the experimental results. For the desorption of H 2S from synthetic green liquor a model was taken from the literature [M. Wallin, S. Olausson, Chem. Eng. Commun. 123 (1993) 43–59] and modified. The modified model takes into account that the desorption of H 2S from synthetic green liquor is enhanced by the chemical reaction from hydrogencarbonate to carbonate. The desorption of CO 2 from synthetic green liquor is well described by the model evaluated for the individual desorption of CO 2 from NaHCO 3 solution.