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

The economic and ecologic feasibility of thermal pyrolysis processes with the feedstocks natural gas (H2 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 CO2 emissions between 0.36 and 0.70 kg CO2e/kWh, leading to CO2 emissions of H2 production via water electrolysis of more than 18 kg CO2e/kg H2. In contrast, due to a lower energy demand, the thermal pyrolysis of natural gas allows for H2 production with considerably less CO2 emissions between 6 and 12 kg CO2e/kg H2. With a hypothetical power generation relying exclusively on renewable sources, thermal pyrolysis can produce H2 with approx. 2 kg CO2e/kg H2 (originating from natural gas production), which is ecologically more favorable than steam reforming with carbon capture and storage. Furthermore, the H2 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, H2 can be produced for less than 1 €/kg H2. Using biogas as feed for a thermal pyrolysis process even leads to negative CO2 emissions of up to −1.28 kg CO2e/kg syngas if the electricity supply is provided from renewable sources, which transforms the process to an active CO2 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 CO2 sink when valuable, sustainable syngas and carbon are produced.