CO2-negative fuel production using low-CO2 electricity: Syngas from a combination of methane pyrolysis and dry reforming with techno-economic analysis

Abstract

This work investigates the use of CO2 as a feedstock through a thermochemical approach using low-carbon electricity, in which the CO2 reforming and methane pyrolysis reactions are combined in a single electrically heated reactor (PY/DMR). The process is enabled by a molten metal catalyst which was recently reported. Kinetic data are experimentally determined for a molten Ni-In alloy and are then used to generate a process model and a techno-economic analysis. The activation energy for methane pyrolysis and dry reforming over molten Ni-In are 187 and 99 kJ/mol respectively. This results in a 236 m3 rate-limited bubble-column reactor producing 500 kta syngas. PY/DMR is compared with a dry-reforming-based technology that is combined with steam reforming (SMR/DMR), state-of-art autothermal reforming (ATR), and CO2 co-electrolysis using solid oxide electrochemical cells from both an economic and environmental standpoint. In our present-day base case, SMR/DMR is the most affordable if no decoking is required ($179.2/t), while the commercialized ATR ($193.7/t) is similar to PY/DMR ($222/t). CO2 co-electrolysis is the least affordable case ($393.2/t). A sensitivity analysis indicates that the cost of PY/DMR is the most economically competitive case when clean (carbon intensity ≤ 160 g/kWh) and affordable (≤¢2.9/kwh) electricity is used, the solid carbon is sold at over $377/t, or when abatement cost reaches $104/t-CO2eq. Both PY/DMR and co-electrolysis result in net-negative CO2 emission, after heating and fugitive emissions are accounted for. The overall carbon footprints are −0.329 kg and −1.06 kg of CO2eq/kg-syngas respectively. PY/DMR has the lowest levelized CO2 mitigation cost ($60/t).