Other researchers are skeptical about how “green” the process actually is, since it extracts embedded energy from refined aluminum by, in effect, “burning” the valuable metal and rendering it effectively unrecoverable.
This development is one example of several so-called Green H2 production technologies that promise to be an alternative to conventional processes. Others include electrolysis of water and steam-methane reformation of natural gas.
Electrolysis is a relatively clean process, but scaling it to industry-scale has been challenging. It also has low conversion efficiencies, typically 60% to 75%, and that’s before the additional energy required to compress the gas to 2,500-3,500 pi for storage is factored in.
These issues are some of the reasons that steam reformation still produces roughly 95% of today’s H2 supply. It burns 25% to 35% of the fuel in the process, while leaving tons of undesired byproducts (CO and CO2) to be disposed of somehow.
MIT’s Low-Carbon Aluminum-Based “Green” Hydrogen
In contrast, MIT’s news release cites a recent study, published in Cell Reports Sustainability,1 that describes its technology as “a low-carbon, cost-effective process based on the aluminum-water reaction (AWR), which uses recycled aluminum, waste heat, and alloy recovery to produce hydrogen with just 1.45 kgCO2 (equivalent) per kg of hydrogen.”
In addition to being cost-competitive with other commercial green hydrogen technologies (around $9/kg), the study claims that the commercial value of the byproducts it produces (such as boehmite ) will make the process a commercial success.
These optimistic claims are being challenged by other researchers who point out that the process simply extracts the 13 to 16 kWh worth of electricity, which had originally been used to refine it from alumina ore in the first place—much of it is still produced by coal- and gas-fired powerplants. And this doesn’t even count the 400 kg worth of carbon anodes that the Hall-Héroult electrolytic process consumes per metric ton of aluminum it produces.
While it’s far better to use scrap aluminum to produce hydrogen fuel than consign it to a landfill, recycling it into virgin stock requires roughly 5% of the energy required to refine it from raw bauxite. It’s no wonder then that scrap aluminum’s market value hovers in the range of $800-$1,100 per ton.
Critics of aluminum-derived H2 point out that a whole-lifecycle analysis of the process brings into question many of the process’ claimed economic and environmental benefits.
Meanwhile, as this story goes to press, your intrepid editor has uncovered news from Peregrine Hydrogen Inc. about its novel hydrolysis technology that requires 50% less energy and produces valuable industrial byproducts. It may shift the H2 debate yet once again. Stay tuned for more details soon…
With the merits of AL-2-H2 still undecided, we invite you to read further and draw your own conclusions. Here are a few good places to start:
Reference
1. Aly Kombargi, et al., “Life-cycle assessment and cost analysis of hydrogen production via aluminum-seawater reactions,” Cell Reports Sustainability, 100407.
