Hydrothermal conversion of lignin to substituted phenols and aromatic ethers

Hydrothermal liquefaction of lignin was performed using methanol and ethanol at various temperatures (200, 250 and 280 °C) and residence times of 15, 30 and 45 min. Maximum liquid product yield (85%) was observed at 200 °C and 15 min residence time using methanol. Increase in temperature was seen to decrease the liquid products yield. With increase in residence time, liquid yields first increased and then decreased. FTIR and 1H NMR showed the presence of substituted phenols and aromatic ethers in liquid products and breakage of β-O-4 or/and α-O-4 ether bonds present in lignin during hydrothermal liquefaction was confirmed through FTIR of bio-residue. In comparison to the existing literature information, higher lignin conversion to liquid products and maximum carbon conversion (72%) was achieved in this study.