Fast hydrothermal liquefaction of barley straw: Reaction products and pathways

Hydrothermal liquefaction (HTL) is an efficient method for converting lignocellulosic biomass into biocrude oil (BO). This study investigated the effects of temperature, reaction time, catalyst (K2CO3 or Ru/C), heating rate on product yields, quality and chemical composition of BO. Meanwhile, a comprehensive comparison of fast HTL with conventional HTL was conducted to explore the difference in reaction pathways. Higher BO yield was obtained at lower temperature (from 260 to 320 ◦C) and short reaction time (less than 15 min) via fast HTL of barley straw. In particularly, the catalytic HTL with K2CO3 was favorable for BO production, and the highest BO yield of 36.73% was obtained at 300 ◦C. As regard to the deoxygenation, the lowest O/C of 0.16 and 0.18 were
observed at 380 ◦C with K2CO3 or Ru/C, respectively. GC/MS and NMR analysis showed that BO from fast HTL of barley straw was featured by phenols and phenolic derivatives, carboxylic acids, hydrocarbons and oxygenates. Higher temperature and fast heating rate were particularly beneficial for hydrocarbons, which accounted for 15.39% of total peak area under fast HTL condition with temperature increasing to 380 ◦C. Meanwhile, fast heating rate dramatically increased the phenols contents (33.15% and 29.96%) at low temperature below 300 ◦C, which has potential for the production of phenolic resins in BO application.