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Making hydrogen (and carbon) by cracking methane in molten metal

| By Gerald Ondrey

A process that converts methane into hydrogen and carbon black has been developed by researchers at the Institute for Advanced Sustainability Studies (IASS; Potsdam; and the Karlsruhe Institute of Technology (KIT; Karlsruhe, both Germany; In a joint project initiated by Nobel Laureate and former IASS scientific director, professor Carlo Rubbia, the proof-of-concept has now been demonstrated.

Based on a novel reactor design proposed by Rubbia, CH4 cracking takes place in molten metal. CH4 is introduced into the bottom of a column full of molten tin at temperatures above 750°C. As the bubbles rise, CH4 is thermally cracked into H2, with carbon black depositing on the bubble surface. The bubbles disintegrate at the top, releasing H2 and leaving behind a powder film of carbon black, which can recovered and sold.

From 2012 to 2015, IASS and KIT have performed experimental campaigns in KIT’s Karlsruhe Liquid Metal Laboratory (KALLA) in a 1.2-m tall reactor made of quartz and stainless steel. In a recent campaign, the reactor operated continuously for two weeks, producing H2 with a 78% conversion rate at temperatures of 1,200°C.

A lifecycle assessment (LCA), performed by IASS and RWTH Aachen University, shows that CH4 cracking is comparable to water electrolysis, and 50% “cleaner” than steam-methane reforming, with respect to CO2 emissions per unit of H2 produced

Preliminary economics calculations show that the technology could achieve costs of €1.9–3.3/kg of H2 (using German natural gas prices, and without taking the market value of carbon into consideration).

IASS and KIT will next focus on optimizing some aspects of the reactor design, such as the carbon-removal process, and progressively scale it up to accommodate higher flowrates.