Pure hydrogen production by steam‐iron process: The synergic effect of MnO2 and Fe2O3. (24th October 2020)

• Record Type: Journal Article
• Authors: De Filippis, Paolo; D'Alvia, Livio; Damizia, Martina; de Caprariis, Benedetta; Del Prete, Zaccaria
• Is Part Of: International journal of energy research. Volume 45:Number 3(2021)
• Page Start: 4479
• Page End: 4494
• Publication Date: 2020-10-24
• Subjects: bioethanol -- chemical looping -- efficiency measurement -- hydrogen -- manganese oxides -- steam‐iron process; Power resources -- Periodicals; Power (Mechanics) -- Periodicals; Power resources -- Research -- Periodicals; 621.042
• DOI: 10.1002/er.6117
• Languages: English
• ISSNs: 0363-907X

Abstract

Summary: 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 deposition of coke is avoided by 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 (Fe2 O3 ) as raw iron oxide adopting several reduction times (7 minutes‐25 minutes), which correspond to different amount of ethanol fed (5 mmolC2H5OH /gFe2O3‐ 17, 95 mmolC2H5OH /gFe2O3 ). 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 Fe2 O3 ). 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 Fe2 O3, 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 Fe2 O3 and MnO2 in the reduction step was proposed in this article. Abstract : Steam iron process allows the production of pure H2 stream ideal for PEMFC. In this work, a sustainable pure H2 production is achieved using bioethanol to reduce FexOy bed. To avoid coke deposition during the reduction step, the amount of ethanol fed (mmolC2H5OH/gFe2O3) must be carefully monitored. MnO2 addition increases the amount of reducing agent leading to a better reduction of FexOy. The synergic effect of Fe2O3 and MnO2 improve the overall process efficiency.