Upgrading Biorefinery Lignins Through Green and Cost-Efficient Reactive Extraction

AquaSolv Omni (AqSO) process showed a great potential as a parameter-controlled type of biorefinery, which allows for tuning the properties of the produced lignins and functional ligno-carbohydrate hybrids (LCHs). Herein, a reactive extraction (REx) streamline was introduced to AqSO integrated biorefinery. It allowed for a simultaneous lignin functionalization during its extraction in order to obtain lignins with different tunable properties and chemical structure. For this purpose, hydrothermal treated (HTT) wood solids were refluxed with EtOH:H2O mixtures (70-99 %) in the presence of catalytic amounts of H₂SO₄ (C = 0.15-1.2 M). Wet chemistry methods and comprehensive NMR studies showed that both alkylation (ethoxylation) of aliphatic -OH groups together with esterification occurred during REx. We were able to extract partially ethoxylated lignins in 27-52 % yield (per available lignin) and tune their degree of substitution (DoS) with ethoxy groups in the range 9.3-27.4/100 Ar. An increase in [EtOH], the time, and the catalyst concentration increased the DoS, while preserving some key linkages present in lignin (e.g., lignin carbohydrate complex).