Revealing the hydrodynamic braking effect in novel counter-current gas-lift reactors: A framework for thermally self-sustained methane pyrolysis

The catalytic pyrolysis of methane in molten metals is a promising technology for producing turquoise hydrogen, yet its industrial-scale application is hindered by the high energy cost and scalability challenges of conventional electrical heating. This study addresses this bottleneck by quantitatively investigating the complex internal hydrodynamics of a novel dual gas-lift reactor operating with a counter-current downcomer flow. Through systematic cold-flow investigations, the riser gas velocity (U GR ) was established as the primary governing parameter for liquid circulation. To account for variations in reactor architecture, a mechanistic unified model was developed by incorporating geometric resistance factors. This framework characterizes the “hydrodynamic braking effect” induced by the counter-current downcomer flow as a function of both U GR and the downcomer gas velocity. To evaluate the operational feasibility of this logic, a lab-scale prototype was operated with molten tin at a baseline reactor temperature of 350 °C and preheated gas at 610 °C. The experimental results demonstrated the transitions between overheating, stable, and quenching regimes, indicating a qualitative alignment with the proposed engineering logic. While based on idealized assumptions, the resulting Process Operating Map provides a preliminary guide for identifying the stable windows required for the design and control of self-sufficient methane pyrolysis reactors. • A novel gas-lift reactor is demonstrated for auto-thermal methane pyrolysis. • Counter-current gas flow creates a ‘hydrodynamic braking effect’ limiting heat transfer. • A unified mechanistic model couples geometric resistance with riser gas velocity (U GR ) • Hydrodynamic braking restricts stable operation to a narrow, non-linear regime