(688b) A Continuous Process for the Thermochemical Production of Green Hydrogen

Thermochemical production of hydrogen and oxygen from water using heat from a renewable energy source such as concentrated solar energy is a carbon-free route to green hydrogen. Thermochemical water splitting cycles have been investigated for many years; the cycles described fall into two major categories: (i) multistep processes that involve halides and other toxic chemicals with reaction temperatures below 1000 °C, and (ii) two step processes using metal oxide-based solids that require temperatures well above 1000 °C. Some of us have reported on a multistep cycle that utilizes manganese oxides and sodium carbonate that operates at around 850 °C. This cycle has been investigated by others throughout the world and it is claimed to be one of the most promising cycles for industrial implementation. HGenium, Inc. is developing a process framework for the implementation of this chemistry on a continuous basis.

We report a “first of its kind” continuous thermochemical water splitting process that is being developed at HGenium, Inc. We show that for some energy sources (including renewable ones) the costs of heat energy can be ca. 30% the costs of generated electricity from that heat. Additionally, heat storage for 24/7 operation is less costly, relies on less costly materials and is safer than electricity storage. Initial techno-economic analyses (based on a plant producing 80 kta H₂) show that the cost of hydrogen production via the HGenium, Inc. process is highly dependent on the costs of the renewable heat. However, because of the lower cost of renewable heat compared to electricity, the process can be cost compatible with desired projections, e.g., from McKinsey, for renewable hydrogen. Experimental data from laboratory reactors moving solids in the ca. 2 kilograms/day size provide supporting evidence for larger scale processing, and some of these supporting data will be presented.