Sequential separation-driven solar methane reforming for H2 derivation under mild conditions

Abstract

Steam methane reforming (SMR) is by far the dominant approach of hydrogen production, but its feasibility for producing low-carbon-footprint H₂ has been constrained by high reaction temperatures (>800 °C), complexity of processes, and high energy penalties associated with H₂ and CO₂ separation. To address such key challenges, we propose a new principle of multi-product sequential separation and a new method of sequential separation-driven SMR for the first time. Target product species H₂ and CO₂ are sequentially separated, so that their partial pressures are maintained close to their maxima at thermodynamic equilibrium to effectively drive methane conversion to full completion theoretically. The new principle enables a remarkable decrease in the SMR temperature and a dramatic reduction in energy penalties of separation in theory and practice. The effectiveness of the new principle and method is demonstrated by a proof-of-concept reactor with a Pd–Ag membrane and alternating nickel catalyst/hydrotalcite sorbent combinations. High-purity H₂ and CO₂ are directly obtained with >99% conversion of methane and >99% yield and selectivity of H₂ and CO₂ under mild conditions of 400 °C and 1 bar. Fast and stable production of H₂ and CO₂ is demonstrated over 6000 cycles. The highly compact reactor and mild operating conditions further enable integration with a parabolic trough solar collector, by which mid-temperature solar thermochemical H₂ production and CO₂ capture are achieved. The solar-to-H₂ efficiency is 3.4% with direct solar illumination. The efficiency can be enhanced to 46.5% or above with solar thermal energy storage and advances in mid-/low-temperature SMR catalysts and CO₂ sorbents, and can be further enhanced to beyond 60% with low-energy-penalty separation technologies.