Exergetic analysis of natural gas pyrolysis as a decarbonization strategy for low-emission hydrogen production

This study presents an exergy analysis of a low emission hydrogen production process based on the thermal pyrolysis of natural gas. The system was modeled in Aspen Plus with a production capacity of 2.6 and 6.3 tonnes per day of hydrogen and carbon black, respectively. The energy required by the process is supplied through the combustion of 22% of the produced carbon black and the residual gases from pyrolysis after hydrogen separation. The results revealed that the overall exergetic efficiency reaches 89.4% when both hydrogen and carbon black are considered valuable products, but decreases to 52.5% when only hydrogen is considered. This highlights the importance of valorizing carbon black to improve both the exergetic efficiency and the economic viability of the system. Carbon black has established applications in the production of tires, electrical components, printing inks, high-performance coatings, and plastics. The largest exergy destruction occurred in the pyrolysis reactor and the combustor, where chemical reactions and heat transfer contribute significantly to process irreversibilities. The process generates approximately 3.15 kg CO₂/kg H₂, significantly lower than typically emitted by conventional steam methane reforming (SMR). These low emissions qualify the hydrogen produced as low carbon under U.S. and Canadian standards, enabling access to clean hydrogen incentives. These findings position thermal natural gas pyrolysis as a promising alternative for sustainable hydrogen production and as a potential carbon removal strategy when fueled with renewable natural gas.