A Novel Cyclic Reaction System Involving CaS and CaSO4 for Converting Sulfur Dioxide to Elemental Sulfur without Generating Secondary Pollutants. 2. Kinetics of the Reduction of Sulfur Dioxide by Calcium Sulfide Powder

Abstract

The process feasibility for converting sulfur dioxide to elemental sulfur by the cyclic reaction involving calcium sulfide and calcium sulfate was established in part 1 of this series. In this part, detailed experimental results are presented on the kinetics of the reaction between calcium sulfide and sulfur dioxide, which produces elemental sulfur and calcium sulfate. The experiments were carried out in the temperature range of 973−1153 K under sulfur dioxide partial pressures between 9 and 60 kPa by the use of a thermogravimetric analysis technique. As an example, about 60% of the calcium sulfide powder from the hydrogen reduction of fresh calcium sulfate was converted in 10 min at 1153 K under a sulfur dioxide partial pressure of 25.8 kPa. The reactivity decreased somewhat during the first five cycles of reaction and regeneration but remained largely intact thereafter up to the tenth cycle. A pore-blocking model was found to fit the reaction rate. The reaction is first order with respect to sulfur dioxide partial pressure and has an activation energy of 24−32 kcal/mol (101−134 kJ/mol) at different reaction cycles.