Advancements in methane pyrolysis: A comprehensive review of parameters and molten catalysts in bubble column reactors

Abstract

Methane pyrolysis using molten catalysts in bubble column reactors is a promising method for hydrogen production without carbon emissions. This review analyses the role of molten metal and salt catalysts, as well as key operating parameters, including reaction temperature, methane concentration, gas hourly space velocity, superficial gas velocity, and bubble size, alongside the impact of refractory coatings and reactor design on process efficiency. The findings reveal that molten tin and gallium catalysts achieve methane conversion rates exceeding 90 % at temperatures above 1000 °C, while molten salts help obtain carbon with high purity and provide operational stability. Methane concentration range from 90 to 100 % is shown to be optimal for maximizing hydrogen yield. A methane flow rate range of 100–300 ml/min, combined with adequate reactor volume and molten catalyst bed area, enhances gas-liquid interaction and methane conversion. Smaller bubble sizes, around 0.5 mm, are most effective for improving surface area and mass transfer, accelerating reaction kinetics and boosting conversion rates. The use of refractory coatings extends reactor lifespan by mitigating corrosion and thermal stress, while optimized reactor design, including increased column height and adjusted orifice size, improves gas dispersion and reactor performance. This review uniquely bridges the gap between molten metal catalysts and reactor dynamics in methane pyrolysis, offering actionable insights for process optimization and industrial scalability. By highlighting overlooked synergies and operational parameters, this study provides a novel and prospective roadmap for advancing hydrogen production technology.