Fig. 4

Py-GC/MS results of untreated poplar wood (control) and solid residues after flowthrough pretreatments. a Untreated poplar wood and solid residues pretreated at 240 °C, 0.05 % (w/w) H₂SO₄ for 10 min (pretreatment severity ~5.0); b untreated poplar wood and solid residues pretreated at 270 °C, water-only for 10 min (pretreatment severity ~6.0)