A techno-economic assessment of pyrolysis processes for carbon capture, hydrogen and syngas production from variable methane sources: Comparison with steam reforming, water electrolysis, and coal gasification

Abstract

• Two pyrolysis processes – natural gas-to-hydrogen and biogas-to-syngas – were studied. • H 2 can be produced for less than 1 €/kg H 2 via thermal pyrolysis of natural gas. • Syngas can be produced with negative emissions of −1.28 kg CO 2 /kg syngas. • Local electricity and natural gas/biogas price govern economic appeal of pyrolysis. The economic and ecologic feasibility of thermal pyrolysis processes with the feedstocks natural gas (H 2 and carbon as products) or biogas (syngas and carbon as products) are studied for different locations – China, USA, Germany, Saudi Arabia, and Türkiye – and compared with state-of-the-art steam reforming and water electrolysis. At all considered locations, the current power generation still causes significant CO 2 emissions between 0.36 and 0.70 kg CO 2 e/kWh, leading to CO 2 emissions of H 2 production via water electrolysis of more than 18 kg CO 2 e/kg H 2 . In contrast, due to a lower energy demand, the thermal pyrolysis of natural gas allows for H 2 production with considerably less CO 2 emissions between 6 and 12 kg CO 2 e/kg H 2 . With a hypothetical power generation relying exclusively on renewable sources, thermal pyrolysis can produce H 2 with approx. 2 kg CO 2 e/kg H 2 (originating from natural gas production), which is ecologically more favorable than steam reforming with carbon capture and storage. Furthermore, the H 2 production costs from thermal pyrolysis of natural gas are lower than from electrolysis and steam reforming for locations with low natural gas and electricity costs. For instance, in the USA and Saudi Arabia, H 2 can be produced for less than 1 €/kg H 2 . Using biogas as feed for a thermal pyrolysis process even leads to negative CO 2 emissions of up to −1.28 kg CO 2 e/kg syngas if the electricity supply is provided from renewable sources, which transforms the process to an active CO 2 sink. However, a potential biogas-to-syngas process cannot compete with state-of-the-art steam reforming in terms of production costs, mainly due to high biogas prices and significantly lower production capacities. In summary, natural gas pyrolysis can be an economically and ecologically feasible alternative to large-scale steam reforming and water electrolysis, especially if prices for the produced carbon exceed 500–1000 €/t. Moreover, a decentralized framework of biogas pyrolysis plants can serve as a feasible CO 2 sink when valuable, sustainable syngas and carbon are produced.

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