(544a) Structural Characterization and Catalytic Valorization of Co-Solvent Enhanced Lignocellulosic Fractionation Pretreated Lignin

A novel pretreatment named Co-solvent Enhanced Lignocellulosic Fractionation (CELF) using THF with water and dilute acid to reduce biomass recalcitrance was recently developed. During CELF pretreatment, more than 90% of lignin could be extracted and dissolved into the liquid hydrolysate. The extracted lignin, known as CELF lignin, can be then isolated from the hydrolysate by rotatory evaporation. Physicochemical characteristics of CELF lignin including molecular weights, monolignol composition, and hydroxyl groups content were measured by various analytical techniques such as GPC, ¹³C-¹H HSQC NMR, ³¹P NMR. GPC results indicated a dramatic decrease in MW of lignin after CELF pretreatment of poplar. HSQC NMR revealed that lignin β-O-4 linkages were significantly decreased after CELF pretreatment, and in fact, almost all the interlinkages were disappeared for pretreatment done at 180 ^oC using FeCl₃ as the catalyst. ³¹P NMR showed that CELF pretreatment resulted in significant decrease of aliphatic OH group, possibly due to the oxidation of lignin side chains. On the other hand, the content of total phenolic hydroxyl groups was significantly increased, suggesting the drastic cleavage of interunit linkages in CELF lignin as confirmed by 2D NMR. A catalytic hydrodeoxygenation of CELF lignin into fuels was also achieved in supercritical methanol using Cu-doped porous metal oxide as the catalyst.