Pure hydrogen production by steam‐iron process: The synergic effect of MnO 2 and Fe 2 O 3 (original) (raw)
2020, International Journal of Energy Research
In the energy transition from fossil to clean fuels, hydrogen plays a key role. Proton-exchange membrane fuel cells (PEMFCs) represent the most promising hydrogen application, but they require a pure hydrogen stream (CO < 10 ppm). The steam iron process represents a technology for the production of pure H2, exploiting iron redox cycles. If renewable reducing agents are used, the process can be considered completely green. In this context, bio-ethanol can be an interesting solution that is still not thoroughly explored. In this work, the use of ethanol as a reducing agent in the steam iron process will be investigated. Ethanol at high temperature decomposes mainly in syngas but can also form coke, which can compromise the process effectiveness, reacting with water and producing CO together with H2. In this work, the coke deposition is avoided controlling the duration of the reduction step; in fact, the data demonstrated that coke deposition is significantly dependent on reduction time. Tests were carried out in a fixed bed reactor using hematite (Fe2O3) as raw iron oxide adopting several reduction time (7 min-25 min). The effect of the addition of MnO2 to increase the reduction degree of iron oxides was explored using different amount of MnO2 (10 wt% and 40 wt% with respect to Fe2O3). The hypothesis is that MnO2, due to its high oxygen mobility, promotes the decomposition of ethanol in syngas, enhancing the methane cracking by oxidizing the coke formed in this reaction. The tests were performed at fixed temperatures of 675 °C and atmospheric pressure. The optimization of the reduction time in the chosen operating condition performed only with Fe2O3 shows that feeding an amount of 5 mmolC2H5OH/gFe2O3 coke deposition is avoided and therefore a pure H2 stream in oxidation is obtained. The addition of MnO2 leads to increased H2 yield and process efficiency confirming its positive effect on the reduction degree of the solid bed. A reaction pathway to demonstrate the synergic effect of Fe2O3 and MnO2 in the reduction step was proposed in this article.
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