How sustainable and profitable are large-scale hydrogen production plants from CH₄ and H₂S?

The large-scale production of hydrogen through mature technologies such as steam methane reforming (SMR) has set a benchmark for emerging hydrogen production processes to gauge their economic viability for the hydrogen economy. In this work, we use detailed process modeling to perform a techno-economic and environmental assessments on the potential of alternative emerging hydrogen production processes based on H2S utilization including H2S-methane reforming (H2SMR), and H2S pyrolysis (H(2)SPyrol) compared to steam methane reforming (SMR), SMR with CO2 capture, storage, and utilization (CCUS), and CH4 pyrolysis (CH(4)Pyrol). Technically, the energy intensity of these processes in terms of electrical and thermal energy consumption was ranked as CH(4)Pyrol < SMR < SMR + CCUS < H2SMR < H(2)SPyrol. However, lower CH4 feedstock and absence of direct CO2 emissions were seen for H2SMR for the same target hydrogen production. Economically, both H2S-based hydrogen production technologies were competitive with levelized cost of hydrogen (LCOH) of $-1.000 and $3.537 per kg for H2SMR and H(2)SPyrol, respectively, compared to LCOH of $2.400, $2.410, and $1.930 per kg for SMR, SMR + CCUS, and CH(4)Pyrol, respectively, with consideration for by-product sales, and sensitivity analysis to their market prices and effect of carbon taxes. Environmentally, H2SMR and H(2)SPyrol revealed their lower contribution to global warming, with the absence of direct CO2 emissions, qualifying as low carbon hydrogen production processes. Although direct CO2 emissions are missing from CH(4)Pyrol, its qualification as low carbon hydrogen producer hinges on the level of decarbonization for the electricity grid. Conversely, the water footprint of H2S-based hydrogen production process remains to be the largest due to the indirect consumption of cooling water required for product recovery, although not necessarily impacting water stress, due to the lower quality of water required for cooling. In summary, transitioning from SMR wo/w CCUS to H2SMR or CH(4)Pyrol seems to be potentially attractive for competing with current processes for H-2 production within the existing policies for decarbonization.