Predictive Modelling and Optimization of Lignin Extraction Efficiency and Quality in Birch Wood Ethanosolv Fractionation in a Semi-Continuous Flow-Through Reactor.

Abstract

Lignin, a complex and abundant biopolymer found in plants, holds immense potential for sustainable materials and chemicals. However, conventional extraction methods often lead to structural deterioration of the native-like aryl ether structure by condensation and other chemical alterations, limiting lignin utility. High delignification in conjunction with preservation of the versatility and functionality of lignin structure for high-value applications can be achieved using advanced mild extraction techniques. In this study, an integrated modeling-experimental approach is used to attain a scalable framework for lignin-first biorefining. Temperature and flow rate were optimized in a flow-through mild ethanosolv system utilizing crude birch wood chips (without extractive removal) to balance solvent use, delignification, and structure preservation. Delignification and lignin yield were monitored separately, as was its quality in terms of preservation of its native aryl-ether structure as determined by 2D HSQC NMR and GPC. Extraction kinetics were monitored using UV-Vis spectroscopy to allow for maximizing efficient solvent utilization. Response surface methodology identified optimal conditions (145–151 °C, 8 g_solvent.min^-1 flow rate), revealing temperature as the primary driver for extraction, exhibiting synergistic effects with the flow rate. Notably, higher flow rates at elevated temperatures (≥140 °C) mitigated β-O-4 linkage degradation without compromising delignification efficiency. Experimental validation of the optimized model at 150 °C and 8 g_solvent.min^-1 achieved 82 wt% delignification and yielded lignin with high β-O-4 linkage content (59.4/100 ArU), aligning closely with model predictions (81–87 wt%, ≥52 β-O-4/100 ArU). Solvent consumption was optimized from the model (13.1 mL.g^-1, solvent : biomass) and realized a reduction of over 40% of solvent consumption when compared with solvent consumption from typical batch organosolv systems (22.9 mL.g^-1, solvent : biomass). Finally, the optimization reduced extraction time significantly from typically 2 hours to 30 mins when compared with previous standard extraction conditions (120 °C, 2 g_solvent.min^-1 flow rate), without compromising on extraction efficiency and lignin quality. This study shows the potential of mild organosolv extraction with alcohol with optimized conditions. Keywords: lignin extraction, flow-through organosolv extraction, computational optimization, response surface methodology, biomass valorization