Simultaneous Sulfur Dioxide Absorption and Hydrogen Sulfide Generation in an Aqueous Solution of Sodium Sulfide

In flue gas desulfurization (FGD) processes, elemental sulfur is the desirable end product for SO 2 producers located in remote areas, since it is easier to handle and transport. To convert sulfur dioxide to elemental sulfur via the Claus reaction, hydrogen sulfide is needed as a reductant. In the present work, an attempt was made to generate H 2 S from aqueous sodium sulfide using SO 2 . The behavior of the Na 2 S (aq) −SO 2(g) −H 2 S (g) system was studied experimentally and by modeling. A three-stage pattern was observed in a semi flow batch reactor (SFBR) in regard to chemical properties of this system. It was concluded that aqueous Na 2 S solution can be used to absorb SO 2 in flue gas and to generate H 2 S under conditions of the second stage. The simultaneous SO 2 absorption and H 2 S generation in an aqueous Na 2 S solution were confirmed using a continuous flow tank reactor (CFTR). To simulate both the SFBR and the CFTR, two mathematical models were developed based on chemical equilibria of acid−base reactions and mass and charge balances. Results show that thermodynamic analysis of acid−base reactions can describe the behavior of the Na 2 S (aq) −SO 2(g) −H 2 S (g) system when redox reactions are suppressed.