The impact of manufacturing methods on the performance of pelletized, iron-based oxygen carriers for fixed bed chemical looping hydrogen in long term operation

Thermochemical Hydrogen Storage via the Reversible Reduction and Oxidation of Metal Oxides

“…Reduction kinetics are evaluated for different temperatures by Pineau et al, Teplov, and Bleeker . Steam–iron oxidation has been heavily researched in the field of chemical looping, with temperatures usually upward of 500 °C considered. ,, Only a limited number of studies have investigated steam–iron oxidation at temperatures in the range 100–500 °C, and are the focus of this work. ,− Iron can also be oxidized with liquid water instead of steam, commonly referred to as hydrothermal oxidation of iron. , Several methods of catalyzing this hydrothermal oxidation reaction have also been explored. ,− …”

“…Finally, many kinetic studies make use of powders. When such powders are pelletized, the total reaction time can be up to 15 times longer and conversion extents can be lower . A packed bed reactor would likely use pellets or granules to avoid large pressure drops across the reactor.…”

“…Prolonged cycling with good kinetics for CLH was obtained with alumina supported iron pellets of 2–3 mm diameter consisting of 95 wt % Fe 2 O 3 and 5 wt % Al 2 O 3 . Upon redox cycling at 800 °C, the conversion extent of the pellets started at approximately 79% of the theoretical maximum for the first cycle and decreased to 67% after 100 cycles . For chemical looping, higher cycling stability can be preferred and some materials are stable for thousands of redox cycles .…”

“…Furthermore, some materials proposed for CLH and thermochemical hydrogen production undergo partial reduction resulting in a low storage density and thus are not suitable for application in hydrogen storage. Examples of such materials are perovskites and cerium-based oxides. − Another major difference is the process temperatures, where all of the above applications operate at high temperatures above 600 °C, , which would not be practical for hydrogen storage. Lower temperatures would likely benefit the energy demand and increase the material’s cycling stability.…”

Thermochemical Hydrogen Storage via the Reversible Reduction and Oxidation of Metal Oxides

“…Because the process already includes the addition of additives [4], it should be possible to add for example alumina without additional processing cost. For their alumina-supported iron pellets for chemical looping, Zacharias et al used a preparation process similar to the one industrially used [8]. Still, some studies on iron oxidation prepare their samples using non-mechanical methods such as co-precipitation [9].…”