Experimentelle Untersuchung der Methanpyrolyse zur Wasserstoffproduktion in einem Flüssigmetall-Blasensäulenreaktor

Hydrogen represents an energy vector with substantial potential for enabling the transition from today’s predominantly fossil-based energy supply system to a sustainable and CO₂-neutral alternative. Achieving this ambitious objective requires not only the substitution of conventional, carbon-intensive fuels and reducing agents, but also the climate-friendly and economically viable production of their respective alternatives. In this context, methane pyrolysis offers a promising route for hydrogen generation, particularly as an alternative to conventional methane steam reforming, since no carbon dioxide is produced in the fundamental reaction. During this process, methane is thermally decomposed in an oxygen-free atmosphere, yielding gaseous hydrogen and solid carbon as products. A variety of reactor concepts for technical implementation exist, whose performance is strongly dependent on the respective operating conditions.
This dissertation investigates methane pyrolysis in liquid metal bubble column reactors using molten tin as the continuous phase. The primary function of the liquid metal lies in its role as a highly efficient heat-transfer medium, rapidly heating the injected methane to the temperature required for decomposition. Within the scope of this work, a novel reactor concept is developed, thoroughly described, and comprehensively validated through experimental studies. This concept combines inductive heating with gas injection via purge lances. The focus is placed on the systematic investigation of a broad range of relevant process parameters particularly bath temperature, methane flow rate, and bath depth within a single reactor system. This approach enables the reproduction of literature-reported trends under standardized conditions, facilitates direct comparison, and extends the existing knowledge base with new and robust insights.
The results confirm several characteristic dependencies that can be inferred from studies conducted over the past two decades. Owing to the unprecedented combination of a wide temperature range from 300 to 1350 °C, methane flow rates between 0.005 and 3.00 Nl/min, and the implementation of Fourier-transform infrared spectroscopy for gas analysis, both a variety of temperature-dependent by-products and flow regimes governed by the methane throughput can be clearly identified. Furthermore, methane-hydrogen mixtures are examined as feed gases over a broad composition range for the first time, providing valuable insights for the design and operation of multistage process configurations.
In addition to the quantity of solid carbon produced, its purity is significantly influenced by the prevailing process conditions. The findings obtained within this dissertation therefore provide a solid foundation for the efficient design of industrial liquid metal bubble column reactors and highlight the potential of this reactor concept for the economic production of market-ready hydrogen and carbon.