Full Utilization of Lignocellulose with Ionic Liquid Polyoxometalates in a One-Pot Three-Step Conversion

The lignin-first concept is a new innovation for full utilization of lignocellulose into value-added chemicals. Ionic liquid (IL) polyoxometalates [MIMPS]₂ H₄ P₂ Mo₁₈ O₆₂ [MIMPS=1-(3-sulfonic group) propyl-3-methyl imidazolium] are reported to be active in the cleavage of β-O-4, α-O-4, and 4-O-5 bonds in three kinds of lignin models and also efficient for converting native lignocellulose. The three components in soft or hard lignocellulose were depolymerized in a one-pot three-step treatment. For soft lignocellulose (pine), lignin was first decomposed into guaiacol and phenol with yields of 15.3 and 12.9 % at 98.6 % delignification efficiency at 130 °C for 14 h. Meanwhile, hemicellulose and cellulose were intact during the delignifying process and were subsequently hydrolyzed to 3.5 % xylose at 100 % hemicellulose conversion efficiency at 150 °C for 14 h and 36.4 % glucose at 100 % cellulose conversion efficiency at 170 °C for 12 h, respectively. For hard lignocellulose (poplar), the yields of guaiacol and phenol were 10.1 and 8.7 % at 91.9 % delignification efficiency at 130 °C for 14 h, whereas 12.9 % xylose at 90.4 % hemicellulose conversion efficiency at 150 °C for 12 h and 32.9 % glucose at 100 % cellulose conversion efficiency at 170 °C for 12 h were obtained. [MIMPS]₂ H₄ P₂ Mo₁₈ O₆₂ achieved the full utilization of lignocellulose with total conversion in the lignin-first strategy and also showed the easy separation as a result of temperature-reversibility with ten recycling runs.