A closed‐loop NaOH molten salt system for biomass pyrolysis hydrogen production and in situ CO 2 carbonation sequestration

BACKGROUND Biomass pyrolysis for hydrogen is usually held back by modest H 2 yields and by the CO 2 and CO formed alongside. This work reports a closed‐loop NaOH molten salt system, tested on Euonymus japonicus over 500–700 °C, in which the melt both upgrades the gas and mineralizes the carbon it captures. RESULTS The minimum NaOH‐to‐biomass ratio needed to suppress COx completely rose with temperature, from 0.9:1 at 500 °C to 1.6:1 at 700 °C. At the optimum (700 °C, 1.6:1), CO and CO 2 disappeared from the gas, H 2 exceeded 85 vol%, CH₄ was the only carbon‐bearing species (14–15 vol%), and the total gas yield reached 3.4 times that of salt‐free pyrolysis. The cold gas efficiency reached 82%, and the hydrogen conversion efficiency exceeded unity above 600 °C, peaking at 1.65 at 700 °C; NaOH acts as both a reforming catalyst and, through carbonation, an additional hydrogen donor. The melt fixed more than half of the biomass carbon as Na 2 CO 3 (net increment 2.03 g at 700 °C), and this carbon was mineralized permanently as CaCO 3 via Na 2 CO 3 + Ca(OH) 2 → 2NaOH + CaCO 3 , which regenerated NaOH at 85.4% on average (maximum 91%). CONCLUSION A thermochemical conversion–thermal energy storage–carbon capture and sequestration (TC‐TES‐CCS) module is proposed that couples pyrolysis hydrogen production, CaO/Ca(OH) 2 heat storage and CO 2 mineralization into a closed loop with net‐negative‐carbon potential.