Targeted catalytic fast pyrolysis of water hyacinth using acid-leached slag from spent Al2O3-based catalysts

Lignocellulosic biomass possesses significant potential as a carbon-based renewable energy source. Fast pyrolysis can convert biomass into valuable derivatives, though achieving high selectivity for target compounds remains a challenge. In this study, acid-leached slag (ALS) derived from spent Al2O3-based catalysts was employed as a catalyst to investigate its effect on the pyrolysis products of water hyacinth (WH). Under optimal conditions of a WH/ALS ratio of 1:3 at 500 °C, the bio-oil yield reached 70.81 wt%, and furfural yield achieved 97.37 area% with a concentration of 83.96 mg/mL. This enhancement is attributed to the synergistic catalytic activity of Brønsted and Lewis acid sites on ALS, which substantially improves the directional selectivity toward furfural. Concurrently, biochar undergoes aromatization, forming aromatic ring structures that promote graphitization, while the proportion of combustible syngas rises to 99.84%. Additionally, N-containing heterocyclics from the bio-oil are redistributed into the biochar (as graphitic-N, pyrrolic-N, and pyridinic-N) and syngas. This study demonstrates an effective strategy for simultaneously valorizing WH and ALS, offering a novel approach for producing high-value chemicals through catalytic pyrolysis of lignocellulosic biomass.