Life cycle assessment of molten salt methane pyrolysis enhanced by chemical looping combustion for sustainable hydrogen and carbon production

Abstract

The melting method of methane pyrolysis technology has garnered widespread attention due to its ability to address the carbon deposition deactivation problem that typically occurs in traditional catalytic cracking catalysts as well as its advantage of not directly emitting CO₂ during the production process. It is viewed as a transitional bridge from fossil-based to renewable hydrogen production. However, while the pyrolysis reaction itself does not generate CO₂ emissions, the temperature and energy required to sustain the reaction indirectly result in greenhouse gas emissions. To address this, this study integrates the inherent carbon separation capability of chemical looping combustion technology into the methane pyrolysis process, achieving a zero carbon emission target for both the pyrolysis reaction and energy supply processes. Thermodynamically, the system achieves the tri-generation of hydrogen, electricity, and carbon with an energy utilization efficiency of up to 85.06 % and life cycle emissions (LCE) of approximately 83.28 kg CO₂ eq./kg MWh. Compared to traditional single-product systems, the LCE reduction rate can reach 87 %. Based on the allocation principle, the LCE of the poly-generation system is distributed, with the LCE associated with hydrogen production being only 0.44 to 0.58 kg CO₂ eq./kg H₂, which is significantly lower than that of other natural gas hydrogen production technologies. Furthermore, improving the raw material gas conversion rate, refining extraction technology, and utilizing clean electricity for natural gas and CO₂ pipeline transportation can effectively reduce the LCE. For instance, utilizing wind, hydro, solar, and nuclear power for energy supply can reduce LCE by more than 40 % compared to coal-fired power systems.