Effects of various reaction parameters on solvolytical depolymerization of lignin in sub- and supercritical ethanol

As the main components in the oil fraction, oxygenated phenols, guaiacol, and syringol as well as their alkylated forms were detected. The yield of alkylated phenols showed a drastic increase at 350 °C in the presence of initial hydrogen gas due to prevailing hydrodeoxygenation and hydrogenation reactions of the vinyl/allyl/oxygenated phenols. These reactions were also demonstrated indirectly from the results of atomic H/C and O/C of the oils. The highest amount of monomeric phenols released from lignin (1.0 g) was measured as ca. 96.7 mg at 350 °C, 40 min, 100 mL g−1, and 3 MPa of H2. In addition, GPC analysis suggested a possibility of condensation between lignin-degraded fragments during the solvolysis reaction.