The Evolution of Hydrogen and Iodine by the Decomposition of Ammonium Iodide and Hydrogen lodidet

Abstract

As a fundamental study on thermochemical production of hydrogen from water, the evolution of hydrogen and iodine from ammonium iodide and hydrogen iodide was investigated. Hydrogen was evolved by the reaction of nikel with ammonium iodide or with hydrogen iodia'e, and the resulting nicke1( I1) iodide was decomposed thermally at 600-s700°C to form nickel. First, the iodination of powdered nickel with ammonium iodide was studied by heating their powder mixture. The maximum yield of hydrogen was obtained at a temperature near 430°C. The iodination of powdered nickel with gaseous ammonium iodide or with dry hydrogen iodide gas was also investigated. In this case, coating of nickel particles with a layer of resulting nickel(ff) iodide prevented further conversion of nickel and lowered the reaction rate. Such a retardation effect was appreciably lessened by use of carrier. When nickel was supported on such a carrier as "isolite", the nickel was converted into nickel ( I1) iodide easily. In a reaction temperature from 400 to 500°C, the rate of reaction between nickel and hydrogen iodide increased slightly with the elevation of the reaction temperature. In the case of ammonium iodide, the reaction rate was higher than that for hydrogen iodide and decreased apparently with the elevation of the reaction temperature, because ammonium iodide decomposed to ammonia and hydrogen iodide. Tests using a fixed bed reactor charged with 8-10 mesh "isolite"-nickel(30 wt%) were also carried out. The maximum yield of hydrogen was about 80% for ammonium iodide at 430°C of reaction temperature and 60% for hydrogen iodide at 500°C.