Lignin Recovery from Spruce Sawdust: Impact of Catalyst Selection on Delignification Efficiency and Lignin Properties

Aim of study: Forestry residues and wood processing wastes are promising resources for biorefineries due to their abundance and easy accessibility. However, lignin recovery remains challenging in lignocellulosic biorefineries. This study investigates the delignification of spruce sawdust using ethylene glycol organosolv pretreatment, focusing on how catalyst selection affects cellulosic pulp and lignin properties. Area of study: Spruce sawdust samples were sourced from a wood processing plant in Bursa.Material and method: Spruce sawdust was delignified using ethylene glycol with phosphoric acid, acetic acid, or sodium hydroxide catalysts at 130 °C under atmospheric pressure. Characterization was done through elemental analysis, FTIR, TGA, Py-GC/MS, and SEC. Main results: The ethylene glycol-phosphoric acid (EGPA) system showed the highest delignification (41.55%) and lignin recovery (42.87%). The sodium hydroxide system (EGNa) produced lignin with stronger lignin-specific FTIR bands, indicating higher purity. Py-GC/MS analysis showed esterification in both fractions, with EGPAL producing mainly esters, acids and phenols, and EGNaL producing phenols, esters and aldehydes. SEC indicated EGPAL had a lower molecular weight (Mw=2814 g/mol, Mn=828 g/mol) than EGNaL (Mw=4725 g/mol, Mn=1258 g/mol).Research highlights: Ethylene glycol-based organosolv pretreatment shows promise for biomass valorization, highlighting catalyst effects on delignification, lignin recovery, and characteristics.