Delignification\nof Olive Tree Pruning Using a Ternary\nEutectic Solvent for Enhanced Saccharification and Isolation of a\nUnique Lignin Fraction

This work aimed at exploring the potentialities of eutectic\nsolvents\n(ES) in the fractionation of olive tree pruning (OTP) biomass within\na biorefinery framework, targeting efficient separation of cellulose\nfibers and lignin and simultaneously producing high-quality fractions\nfor further processing and application. In this sense, delignification\nperformances of cholinium chloride:ethylene glycol, ChCl:EG (1:9)\nand cholinium chloride:<i>p</i>-toluenesulfonic acid:ethylene\nglycol, ChCl:pTSA:EG (1:1:9) as binary and ternary mixtures, respectively,\nwere first evaluated. ChCl:EG demonstrated low efficacy for biomass\ndelignification, while the highest lignin extraction (62.7%) was achieved\nwith ChCl:pTSA:EG at 80 °C and 4 h. At the same conditions, the\ncellulose content (62.5%) of the resulting solid fraction increased\nalmost three-fold compared to that of the raw OTP (22.3%), using ChCl:pTSA:EG.\nThis ternary ES enabled the OTP matrix breakdown, which, combined\nwith lignin extraction, enhanced the enzymatic hydrolysis of the cellulose-rich\nfraction to a maximum saccharification yield of 81.8%. The sample\nexhibited an impressive aliphatic OH group content of 5.2 mmol·g<sup>–1</sup> lignin, one of the highest values among the state-of-the-art.\nThe resulting phenomenon is explained by the ethylene glycol grafting\nonto the lignin structure (aliphatic region), as demonstrated by <sup>31</sup>P and HSQC NMR, giving chemical functionality to the isolated\nlignin fraction. Finally, up to 90% of the initial mass of ChCl:pTSA:EG\nwas recovered through the adsorption of impurities. NMR data validated\nthe high purity and the same molar ratio (1:1:9) of recovered ES,\ntwo important outcomes to ensure a sustainable reutilization of this\nsolvent.