Molten Metal Methane Pyrolysis for Distributed Hydrogen Production: Reactor Design, Hydrodynamics, and Technoeconomic Insights

Methane pyrolysis offers a compelling pathway for low-carbon hydrogen production by avoiding CO2 emissions and enabling distributed deployment in locations with natural gas supply, thereby eliminating the need for costly hydrogen transport. While promising, the commercial deployment is constrained by the lack of detailed reactor modeling and technoeconomic assessment at small production scales. This study addresses these gaps by designing and modeling a small-scale (1–10 t-H2/day) bubble column reactor employing molten Ni–Bi alloy catalyst for methane pyrolysis. A coupled kinetic–hydrodynamic model was developed to simulate gas holdup, bubble behavior, and conversion under different operating conditions. The reactor design was integrated into an Aspen Plus simulation of the full process, including heat recovery and hydrogen purification. Optimization of pressure, temperature, and single-pass conversion revealed that operation at 1100 ◦C, 15 bar, and 70–75 % conversion minimized reactor volume and cost. The lowest levelized cost of hydrogen (LCOH) achieved was $3.06/kg-H2 without sale of carbon, significantly lower than green H2 produced from water electrolysis and competitive with blue H2 produced via centralized reforming when transportation costs are included. Sensitivity analysis reveals that carbon byproduct is a key economic lever; carbon sale at $250/t-C reduces LCOH by 25 %, while a price of $700/t-C would meet U.S. DOE $1/kg-H₂ target. These results demonstrate the technoeconomic viability of molten metal methane pyrolysis and highlight future opportunities.