Synthesis and development of processes for the recovery of sulfur from acid gases. Part 1, Development of a high-temperature process for removal of H(sub 2)S from coal gas using limestone -- thermodynamic and kinetic considerations; Part 2, Development of

摘要

Limestone can be used more effectively as a sorbent for H(sub 2)S in high-temperature gas-cleaning applications if it is prevented from undergoing calcination. Sorption of H(sub 2)S by limestone is impeded by sintering of the product CaS layer. Sintering of CaS is catalyzed by CO(sub 2), but is not affected by N(sub 2) or H(sub 2). The kinetics of CaS sintering was determined for the temperature range 750--900(degrees)C. When hydrogen sulfide is heated above 600(degrees)C in the presence of carbon dioxide elemental sulfur is formed. The rate-limiting step of elemental sulfur formation is thermal decomposition of H(sub 2)S. Part of the hydrogen thereby produced reacts with CO(sub 2), forming CO via the water-gas-shift reaction. The equilibrium of H(sub 2)S decomposition is therefore shifted to favor the formation of elemental sulfur. The main byproduct is COS, formed by a reaction between CO(sub 2) and H(sub 2)S that is analogous to the water-gas-shift reaction. Smaller amounts of SO(sub 2) and CS(sub 2) also form. Molybdenum disulfide is a strong catalyst for H(sub 2)S decomposition in the presence of CO(sub 2). A process for recovery of sulfur from H(sub 2)S using this chemistry is as follows: Hydrogen sulfide is heated in a high-temperature reactor in the presence of CO(sub 2) and a suitable catalyst. The primary products of the overall reaction are S(sub 2), CO, H(sub 2) and H(sub 2)O. Rapid quenching of the reaction mixture to roughly 600(degrees)C prevents loss Of S(sub 2) during cooling. Carbonyl sulfide is removed from the product gas by hydrolysis back to CO(sub 2) and H(sub 2)S. Unreacted CO(sub 2) and H(sub 2)S are removed from the product gas and recycled to the reactor, leaving a gas consisting chiefly of H(sub 2) and CO, which recovers the hydrogen value from the H(sub 2)S. This process is economically favorable compared to the existing sulfur-recovery technology and allows emissions of sulfur-containing gases to be controlled to very low levels.