Thermochemical decomposition of hydrogen sulfide with nickel sulfide
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INTRODUCTION
H Y D R O G E N sulfide has hitherto been treated by the Claus method as in the petroleum refining process to recover only elemental sulfur. The quantity of elemental sulfur produced has reached 16 million tonnes per year in the free world. Annual production of elemental sulfur from Japanese oil refineries is about 1.2 million tonnes. These represent a potential annual source of 11.2 9 109 and 8.4 9 108m 3 of H2, respectively. The utilization of H2S as a new H 2 source is likely to be a matter of great importance from now on for the following reasons. Firstly, extensive research and studies have been made on the thermochemical splitting of water as a process for preparing H2 within the concept of a proposed hydrogen economy.~ In this case, the change in free energy below about 40 kJ per mole of H2 is regarded as a criterion for selecting the constituent reactions. H2S as well as HI are compounds readily decomposable into U2, and the change in free energy of decomposition of H2S is taken up as a reaction for producing H2 in the thermochemical splitting cycle of waterf1-5 Secondly, a leaching method of generating H2S exists in the hydrometallurgical treatment of sulfide ores, 6 and the gaseous reduction with pressurized H2, which is carded out in recovering metals from the leach solution, is well known. 7 In the pyrometallurgical treatments, H2S or CaS is formed as a by-product at the time of direct reduction with H2, and the hydrometallurgical treatments of the CaS with CO2 gas permit ready conversion of the sulfur content into HzS and regeneration of CaCO3. 4 Thus, the regeneration of H2 from HzS becomes important. Thirdly, the necessity _for utilizing high-sulfur crude oil is increasing with decreasing fossil fuel resources, and the HIROMICHI KIUCHI is Research Associate, KIMIO FUNAKI is Graduate Student, and TOKIAKI TANAKA is Professor in the Department of Metallurgical Engineering, Faculty of Engineering, Hokkaido University, 060 Sapporo, Japan. Manuscript submitted March 24, 1981. METALI.URGICALTRANSACTIONSB
amount of by-product H2S will probably increase still more as the gasification or liquefaction of coal expands in the future. Furthermore, the development of natural gas with a high H,S content has started, and as a result the recovery of H2 f r o m H2S will be an important subject hereafter. Because of the oversupply of sulfuric acid, gypsum, and sulfur in Japan, the Claus method which has long been used as the only industrial means of treating I I2S appears now to be a doubtful long term method for the future. To offset the decrease in the added value of S ~ it will be necessary to r e c o v e r H2. For the reasons described above, the attempt at the simultaneous recovery of H2 is important in the utilization of H2S not only as a sulfur source but also as a new energy source. However, very few studies have been made on the recovery at present. In this paper~ the two-step thermochemical cycle for decomposing H2S into H2 and S ~ by sulfurization of Ni3S2 with H2S and by thermal decomposit
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