The Hydrolysis of Iron(II) Bromide

Abstract

As a fundamental study on thermochemical production of hydrogen from water, the hydro-lysis of iron (II) bromide
3 FeBr₂+4 H₂O →Fe₃O₄ + 6 HBr+ H₂ (1)
FeBr₂ + H₂O → FeO + 2 HBr (2)
has been investigated. First, solid FeBr₂ was hydrolyzed at ca. 490°C according to the equation (1), and the maximum amount of hydrogen in the highest yield was obtained at 620°C. The hydrolysis reaction was carried out by using a fixed bed reactor (25 mmΦ) charged with 120 g of FeBr₂ at 620°C. The maximum conversion rate of water was 10% at 30 g/hr of feed rate of H₂O, and the rate increased gradually with decreasing feed rate of H₂O, i. e., 11% at 20 g/hr and 13% at 10 g/hr. These higher values than that predicted by thermodynamic calculation, i. e., 9. 2%, suggested that sublimed FeBr₂ was also hydrolyzed.
Second, the hydrolysis of molten FeBr₂ was carried out by bubbling vaporized water through the molten salt at 700°C. At the initial stage of the reaction, FeBr₂ was hydrolyzed according to the equation (2) resulting FeO, and the conversion rates of water were higher than those in solid-gas reaction mentioned above. But continuous run of the reaction was difficult because resulting iron oxide closed the water feed pipe.
Third, the hydrolysis of vaporized FeBr₂ was also carried out in a flow system at 800∼900°C. In this case, FeBr₂ was hydrolyzed in terms of the both equation, (1) and (2). The fractions of FeBr₂ hydrolyzed according to these competitive reactions depended on a H₂O to FeBr₂ ratio.