Exploded view of the reactor with the tin filling system. (Image courtesy of Tobias Geißler/International Journal of Hydrogen Energy.)
“Our reactor operated without interruptions for two weeks, producing hydrogen with a 78 percent conversion rate at temperatures of 1200° Celsius,” said Thomas Wetzel, head of the Karlsruhe Liquid Metal Laboratory where the reactor was tested.
What is Methane Cracking?
Methane molecules (CH4) have been shown to “crack” at temperatures above 750° Celsius, yielding pure carbon and hydrogen.
The technical feasibility of methane cracking was proven decades ago, but past attempts at harnessing the effect in a reactor were hampered by issues like carbon clogging and low conversion rates. However, a novel reactor design has proven more successful.
The reactor is a 1.2-meter-high device made from a combination of quartz and stainless steel. Methane bubbles are injected at the bottom of a column filled with molten tin. The cracking reaction occurs when the bubbles rise to the surface of the liquid metal.
Carbon separates on the surface of the bubbles and is deposited as a powder at the top end of the reactor when they disintegrate. The reactor is resistant to corrosion and clogging because the microgranular carbon powder it produces separates from the molten tin easily.
Advantages of Methane Cracking
There is an inherent conflict between our reliance on fossil fuels and our efforts to mitigate climate change. Resolving this conflict is the primary motivation behind the methane reactor.
Most hydrogen production is based on conventional technologies like steam methane reforming (SMR) which releases significant amounts of carbon dioxide.
A life cycle assessment (LCA) of a hypothetical reactor based on a scaling-up of the prototype shows that methane cracking is comparable to water electrolysis and is more than 50 percent cleaner than SMR.
Preliminary calculations show that methane cracking could achieve costs of 1.9 to 3.3 euros per kilogram of hydrogen at current German natural gas prices.
This estimate assumes that some of the produced hydrogen would be used to generate the requisite process heat. It also does not account for the market value of the pure carbon derived from methane cracking, which enhances its economic viability.
Carbon and hydrogen are both vital resources for the coming decades. Whether our goal is building better transistors or exploring the solar system, methane cracking could be the key.
For more information, visit the Institute for Advanced Sustainability Studies website.