Rapid-quench flow-through process for lignin recovery and co-production of xylose/nanocellulose via three-stage p-TsOH fractionation

A three-stage p -toluenesulfonic acid ( p -TsOH) fractionation protocol integrated with flow-through (F-T) quenching was developed for the efficient valorization of wheat straw ( Triticum aestivum L.), enabling simultaneous recovery of β -O-4-rich lignin, xylose, and lignin-containing cellulose nanocrystals (LCNC). In the first stage, response surface methodology (RSM)-optimized dilute p -TsOH treatment (5.6 wt%, 73.5 °C, 121.7 min) yielded 64.9% of the theoretical xylose as a solid powder. The second stage employed concentrated p -TsOH treatment (70 wt%, 80 °C, 3 mL/min) with F-T quenching for 10 min, achieving 77.6% delignification. Notably, 56.4% of the original lignin was recovered with 46.4% β -O-4 linkage retention and low degree of condensation. The third stage utilized recycled p -TsOH to hydrolyze the cellulose-rich residue (70 wt%, 80 °C, 60 min), thereby affording 31.7% LCNC with UV-blocking properties. This integrated process combines single-solvent recycling with reduced residence time and enables efficient fractionation and valorization of all major lignocellulosic components, offering a scalable biorefinery route with significant industrial potential.