(188c) A Closed-Loop Biorefinery for Woody Biomass Conversion Using Lignin-Derived Deep Eutectic Solvents

Lignocellulosic biomass is an attractive energy source; however, conversion of the biomass is still technically and economically challenging due to its rigid and compact structure and recalcitrant nature toward conversion caused by chemical and physical features of the biomass. Therefore, effective and innovative conversion technologies are eagerly needed for converting the biomass to fuels and industrial chemicals.

Deep eutectic solvents (DES) pretreatment is an effective method for biomass conversion and/or fractionation. DESs have been proposed as alternatives to ionic liquids (ILs). These solvents do not only share the typical properties of ILs such as low volatility, wide liquid range, non-toxicity, and biocompatibility, but they also have some advantages over the traditional ILs like easy synthesis and relatively inexpensive components, thus large scale application is feasible. Tuning properties of DESs by replacing the hydrogen bond donor (HBD) with phenolics sharing structural similarities with lignin can facilitate better solubility of lignin during the fractionation. Relatively mild pretreatment conditions minimize the unwanted lignin modification and keep relatively intact structures during the pretreatment; therefore, it promotes subsequent lignin valorization.

Herein, a biomass conversion and fractionation process employing novel deep eutectic solvents (DES) prepared from lignin-derived phenolic compounds is studied. With choline chloride as HBA, the proposed process utilized the fractionated lignin-derived compounds as an HBD to enhance the total biomass utilization. Different phenolic acids such as 4-hydroxybenzoic acid and caffeic acid were investigated for effective lignin fractionation and sugar release from woody biomass (poplar). To evaluate the impact of DES pretreatment on biomass conversion, enzymatic digestibility was conducted. Diverse analytical techniques including 2D HSQC NMR, ³¹P NMR, GPC, and wet chemistry using HPLC were performed to elucidate the structural changes during the reactions. Recyclability of DES was also studied to develop an economically feasible closed-loop system.