Two-stage steam reforming of bio-oil for hydrogen production: Influence of catalyst and temperature in the pre-reforming stage

In this study, the impact of pre-reforming procedure on the intermediate products and the production of hydrogen in the two-stage steam reforming of bio-oil generated from pine sawdust was explored. The evolution of the intermediate products in the liquid and gas phase affected by the pre-reforming catalyst (red mud, dolomite, biochar) and pre-reforming temperature was investigated, as is impact of intermediate products on the hydrogen production. The findings indicate that dolomite was identified as the most effective pre-reforming catalyst due to its high CaO/MgO content, which promoted the Boudouard reaction more effectively than the Fe2O3 in in red mud. Low-temperature pre-reforming (≤450 °C) was more beneficial than high-temperature pre-reforming (≥550 °C) at which coke precursors, including aromatic hydrocarbons and phenols were easily produced, leading to rapid catalyst deactivation. Liquid-phase intermediates were primarily composed of furans, phenols, and ketones, with ketones accounting for up to 55.63 %, which may be related closely to the greatly promoted ketonization by the alkaline Ca(OH)2 produced via the combination dolomite and water at low temperature. Ketones were actually more favorable to the second-stage reforming over Ni-based catalysts, and the ultimate hydrogen yield reached 66.52 %. Due to the low inclusion of phenol and aromatic hydrocarbon intermediates less susceptible to carbon deposition, the catalyst could be more stable. The two-stage steam reforming of pyrolysis bio-oil can avoid catalyst deactivation and enhance the hydrogen production to a higher degree, accomplished by changing the intermediates components with varied pre-reforming catalysts and temperatures.