An innovative ‘sorption-egg-hanced’ reforming approach to producing highly pure green hydrogen from biomass-derived aqueous effluents

The hydrothermal treatment of biomass forms large quantities of chemical-rich aqueous effluents. In the context of a zero-waste biorefinery, the latter represents a valuable resource for recovery and/or further functionalisation. This work reports for the first time the production of H2 with in-situ CO2 capture from the aqueous fraction of hydrothermally-processed almond hulls using a Ni-based catalyst coupled with a calcium-based sorbent derived from calcined eggshells. The effect of the reforming temperature and relative amounts of catalyst and sorbent (CaO) have been evaluated using a continuous reforming unit. The reaction temperature and the relative amount of catalyst directed the overall product distribution, with high temperatures favoured gas formation, and the catalyst allowed for lower temperatures to be used. Additionally, the temperature and the relative amount of sorbent significantly impacted the gas composition, with H2 enrichment as the latter (calcined eggshells) increased. Process optimisation revealed that a gas with a highly high H2 content (>95 vol%) can be obtained at 500 °C with relative amounts of catalyst and sorbent of 9 g catalyst min/g organics and 70 g CaO min/g organics, respectively. Such conditions allowed for capturing up to 90 % of the CO2, which resulted in a very high H2 production (0.12 g H2/g organics, i.e., the stoichiometric value). This represents a step ahead for developing greener processes and opens the door to exploring novel avenues for process intensification, avoiding further downstream processes to ensure holistic, zero-waste biorefineries.