Methane Pyrolysis in Molten Potassium Chloride: An Experimental and Economic Analysis

Although steam methane reforming (CH4 + 2H(2)O -> 4H(2) + CO2) is the most commercialized process for producing hydrogen from methane, more than 10 kg of carbon dioxide is emitted to produce 1 kg of hydrogen. Methane pyrolysis (CH4 -> 2H(2) + C) has attracted much attention as an alternative to steam methane reforming because the co-product of hydrogen is solid carbon. In this study, the simultaneous production of hydrogen and separable solid carbon from methane was experimentally achieved in a bubble column filled with molten potassium chloride. The melt acted as a carbon-separating agent and as a pyrolytic catalyst, and enabled 40 h of continuous running without catalytic deactivation with an apparent activation energy of 277 kJ/mole. The resultant solid was purified by water washing or acid washing, or heating at high temperature to remove salt residues from the carbon. Heating the solid product at 1200 degrees C produced the highest purity carbon (97.2 at%). The economic feasibility of methane pyrolysis was evaluated by varying key parameters, that is, melt loss, melt price, and carbon revenue. Given a potassium chloride loss of <0.1 kg of salt per kg of produced carbon, the carbon revenue was calculated to be USD > 0.45 per kg of produced carbon. In this case, methane pyrolysis using molten potassium chloride may be comparable to steam methane reforming with carbon capture storage.

Automated summary

This study successfully demonstrated the simultaneous production of hydrogen and separable solid carbon from methane by using molten potassium chloride as a carbon-separating agent and pyrolytic catalyst, showing economic feasibility compared to steam methane reforming with carbon capture storage. The experimental results provide a new direction for methane pyrolysis and highlight the potential of using molten potassium chloride in this process.