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Methane pyrolysis experiments using a quartz glass-steel bubble column reactor filled with liquid tin and cylindrical quartz glass rings serving as a packed bed were conducted at various liquid metal temperature levels in the range of 930 °C to 1175 °C. Besides the liquid metal temperature, special attention was paid to the influence of the feed gas volume flow rate in the range of 50-200 mln/min and the inlet feed gas dilution with nitrogen. Increasing liquid metal temperatures resulted in increasing hydrogen yields, leading to a maximum hydrogen yield of 78 % at 1175 °C and 50 mln/min methane volume flow rate. Within all experimental runs, less than 1.5 mol-% intermediate products were detected in the product gas. The produced carbon appeared as a powder consisting of flake shaped agglomerations in the size range of 15 µm to 20 µm, wherein the particle size varied from 40 nm to 100 nm. During the experiments, the produced carbon was completely separated and accumulated at the top surface of the liquid metal. Only minor quantities were transported with the off gas stream. Within the liquid metal inventory, a thin carbon layer of about 10 µm, probably partly showing the formation of nanotubes, in the hot reaction zone, had been deposited on the quartz glass reactor wall.

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The development of a low-carbon technique to produce hydrogen from fossils would be of great importance during the transition to a long-term sustainable energy system. Methane decarbonisation, the well-known transformation of methane into hydrogen and solid carbon, is a potential candidate in this regard. At the Institute for Advanced Sustainability Studies (IASS), a new alternative technology for methane decarbonisation applying liquid metal technology was proposed and an ambitious programme was set up in collaboration with the Karlsruhe Institute of Technology (KIT). The comprehensive programme included the following: conceptual design of a liquid metal bubble column reactor and material testing, process engineering incorporating carbon separation and hydrogen purification, and a socioeconomic analysis. In the present paper, an overview of the programme along with some of the results, are presented. Results from the experimental campaigns show that the liquid metal reactor design works effectively in producing hydrogen and carbon separation. Other aspects of the technology such as socio-economics, environmental impact, and scalability also seem to be favourable making methane decarbonisation based on liquid metal technology a potential candidate for CO2-free hydrogen production.

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