(622d) High-Pressure Hydrogen Production from Bio-Ethanol Feedstock with Fixed-Bed Chemical Looping

High-pressure
hydrogen production from bio-ethanol feedstock with fixed-bed chemical looping

Decentralized
hydrogen production with chemical looping hydrogen offers the use of locally
available renewable energy sources and has the inherent possibility for carbon
dioxide separation. The technology makes it possible to produce high purity
hydrogen in one compact unit without a complex gas purification step [1]. The
oxidation cycle can be performed with elevated pressure via closing the system
outlet and compression of the water feed [2]. Thereby high-pressure hydrogen is
generated without an additional product gas compression. Partial reduction of
the oxygen carrier from Fe₂O₃ to Fe₃O₄
yields thermodynamically to a product gas only containing CO₂ and H₂O.
By the subsequent condensation of steam, pure CO₂ is sequestrated.
Recent experiments performed in our research group showed the ability to
combine pressurized hydrogen production with the sequestration of a pure carbon
dioxide stream after water condensation. The proof of concept for pure
pressurized hydrogen production in combination with the sequestration of a pure
carbon dioxide stream could be demonstrated. Thereby, the separation of a
carbon dioxide stream with a purity of >98% could be yielded [4].

In our current
research activities, a combined lab test rig is investigated in ongoing
experiments based on the investigations from previous publications [3, 4]. A
bioethanol feed is converted to a syngas reducing the oxygen carrier and
releasing a high-pressure hydrogen stream in oxidation phase. Commercially
available bioethanol is applied to investigate the effects of trace compounds
on the attainable hydrogen purity in a pressurized system. Beforehand,
extensive research was conducted to characterize catalysts for ethanol
reforming on their capability of deriving a suitable syngas with a high share
of reductive compounds in order to increase the feedstock utilization.

The in-house
synthesized and pelletized iron-based oxygen carriers are characterized in a
thermogravimetric analysis system as well as a fixed-bed unit for better
demonstration of the impact of the exothermic and endothermic reactions on the
material. Different synthesis methods – such as dry mixing, impregnation and
sol-gel method are compared on the effect on the resulting material concerning
cyclic stability, reactivity as well as the mechanical stability of the oxygen
carrier material to satisfy the requirements of fixed-bed reactor systems. The
results show a positive influence of thermal treatment at elevated temperatures
(>900 °C) in combination with wet-chemical synthesis methods on the mechanic
integrity for fixed-bed applications. New results of the high-pressure hydrogen
production from bioethanol feed and from material development will be presented
at the conference.

Figure 1: High
pressure hydrogen release up to 95 bar and hydrogen impurities (left); Comparison
of the cyclic stability of oxygen carriers gained from wet chemical synthesis,
mechanical mixing and unstablized Fe as oxygen carrier (right)

[1]     V. Hacker, “A novel process for stationary hydrogen
production: The reformer sponge iron cycle (RESC),” J. Power Sources, vol. 118,
no. 1–2, pp. 311–314, 2003.

[2]     G.
Voitic, S. Nestl, K. Malli, J. Wagner, B. Bitschnau, F. Mautner, and V. Hacker,
“High purity pressurised hydrogen production from
syngas by the steam-iron process,” RSC Adv.,
vol. 6, no. 58, pp. 53533–53541, 2016.

[3]     S. Bock, R. Zacharias, and V. Hacker, “High purity hydrogen
production with a 10kWth RESC prototype system,” Energy Convers. Manag., vol. 172, pp. 418–427, 2018.

[4]     R. Zacharias, S. Visentin, S. Bock, and V. Hacker,
“High-pressure hydrogen production with inherent sequestration of a pure carbon
dioxide stream via fixed bed chemical looping,” Int. J. Hydrog. Energy, vol.
44, no. 16, pp. 7943-7957, 2019