Hydrogen production from cascade reforming of aqueous phase by-product of biomass hydrothermal liquefaction

A large quantity of wastewater will be produced during biomass hydrothermal liquefaction (HTL) to produce bio-oil, referred to as the aqueous phase (AP) by-product. The AP by-product contains high levels of total organic carbon (TOC), chemical oxygen demand (COD) and ammonium, posing potential environmental risks if discharged untreated. This work recycled AP by-product for H2 production via aqueous phase reforming (APR), while reducing its environmental pollution. A three cascade APR processes were employed, and the effects of various reaction conditions on H2 production were studied. Results showed that the optimal reaction conditions for the three cascade reactions were the same: reaction temperature 300 °C, residence time 2 h, Ni loading 10%, and a 10% Ni/CeO2 catalyst amount 1/40 g/L. The TOC removal ratio of AP by-product was increased from 14.59% to 31.10%, and the COD removal ratio rose from 4.43% to 13.42%. The H2 yield was increased from 21.15 mmol H2/g TOC to 69.21 mmol H2/g TOC. Seven types of organic matter in both the AP by-product and the liquid products were identified: alcohols, alkanes, aldehydes, ketones, esters, phenols, and alkenes. Ketones consistently represented the largest proportion, indicating that they were difficult to transform in the APR.