Headline: Hydrogen production via methane pyrolysis in a liquid metal bubble column reactor with a packed bed

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 930–1175 °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 15–20 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.