Investigating hydrothermal carbonization to convert urban pruning biomass into valuable furanic and phenolic...

This study aims to investigate the valorization of Liquidambar styraciflua L. urban pruning biomass through hydrothermal carbonization to promote liquid phase (liquor) production as a source of high-value chemicals. The objective is determining operating conditions that selectively maximize the yields of furanic and phenolic compounds. Methodologically, urban pruning biomass collected in Concepción, Chile, was processed in a laboratory Parr reactor. A sequential screening approach was applied to evaluate the effects of temperature (150-300 °C), final residence time (0-240 min), initial pH (2-13), particle size (<250-3150 μm), and biomass-to-water ratio (1:1 to 1:25), with the liquor composition analyzed via GC-MS and GC-FID. The results show that mild conditions (200 °C, pH 2) promoted furanic compounds, yielding a maximum 5-hydroxymethylfurfural content of 6.59 wt% (dry basis), while more severe conditions (>225 °C) and alkaline environments (pH > 11) promote phenolic compounds. In particular, 2,6-dimethoxyphenol reached 5.38 wt% at 300 °C under alkaline conditions. Further, smaller particle sizes (<1000 μm) and a low biomass-to-water ratio promoted phenolic recovery. To the best of the author's knowledge, this is the first study to demonstrate that hydrothermal valorization of urban pruning biomass can be selectively "switched" between furanic or phenolic production in the liquor by adjusting operational parameters. Thus, urban pruning becomes a tunable source of high-value chemicals, supporting a sustainable pathway for urban biorefineries.