THERMODYNAMIC ANALYSIS OF THE THERMOCHEMICAL DECOMPOSITION OF H2S IN THE PRESENCE OF IRON SULFIDE

The decomposition of H2S by a two-step closed loop thermochemical decomposition process was investigated. In the first step, H2S decomposes by reacting with iron sulphide to produce hydrogen and a solid solution consisting of FeS and S2. In the second step, the solid solution is decomposed at high temperature to recover sulphur and the iron sulphide which is reused in the first step. The thermodynamics of the first reaction were studied in detail by taking into account 12 gas phase chemical reactions and the phase equilibrium that is established between the sulphur in the gas and in the solid solution. The non-linear system of 13 equations, which relate the fugacities of the components at equilibrium to the equilibrium constants, were numerically solved by the Newton-Raphson iteration technique. The calculation results showed that the gas phase at equilibrium contains predominantly H-2S, H-2, and H-2S-2. The equilibrium conversion was found to decrease with increasing temperature; however, when the sulphur content of the solid solution was small, high hydrogen yields were possible even at high temperatures.