Catalyst-free liquefaction of lignin for monophenols in hydrogen donor solvents

Liquefaction of alkaline lignin in three hydrogen donor solvents (HDSs) was studied at temperatures of 300–440 °C in a high-throughput micro-reactor system capable for 20 parallel micro-reactors. The reactors can be heated to a designated temperature in less than 1 min without overshooting. The HDS 9,10-dihydroanthracene (DHA) was found to be better than 9,10-dihydrophenanthrene (DHP) and 1,2,3,4-tetrahydrocarbazole (THCA) in terms of monophenols yield (Yphenols). The effects of DHA loading, reaction time and temperature on the yields of liquid product (Yliquid) and monophenols were evaluated. Distribution of monophenols, DHA conversion and the quantity of hydrogen donated by DHA (QH) were elaborated to understand the reaction matrix. Results indicate that the HDSs significantly promote the lignin liquefaction and monophenols formation, and the liquid products and the phenols are formed via two routes. The optimal reaction conditions are 400 °C for 1–2 min or 350 °C for 8–10 min with the Yphenols of 10.3–10.7%. The maximum theoretical monophenols yield is about 12.7% for the lignin under the conditions studied.