A Novel Cyclic Reaction System Involving CaS and CaSO4 for Converting Sulfur Dioxide to Elemental Sulfur without Generating Secondary Pollutants. 3. Kinetics of the Hydrogen Reduction of the Calcium Sulfate Powder to Calcium Sulfide

Abstract

The reduction of calcium sulfate to produce calcium sulfide is not only a part of the cyclic process for converting sulfur dioxide to elemental sulfur described in part 1 of this series but also of interest as a means of producing elemental sulfur from gypsum. This reaction was investigated using a thermogravimetric analysis technique in the absence and presence of an impregnated nickel catalyst at reaction temperatures between 973 and 1153 K and hydrogen partial pressures between 1.7 and 86.1 kPa. As an example of the reactivity of the nickel-catalyzed calcium sulfate powder, more than 95% of fresh nickel-catalyzed calcium sulfate powders was converted to calcium sulfide in 20 min at 1123 K under a hydrogen partial pressure of 86.1 kPa. Furthermore, the reactivity remained relatively intact after 10 cycles of reactions and regenerations, which is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants. The Erofeev nucleation and growth kinetics equation ...