Multiproduct biorefinery of Paulownia wood by synergy of hydrothermal and deep eutectic solvents (DES) pretreatments for polymers isolation and various cellulose applications

This study highlights the efficiency of using coupled pretreatments to fractionate Paulownia wood (PW) into separated streams of high-added value products, including hemicelluloses, lignin, phenolic compounds, bioethanol, succinic acid, and cellulose nanocrystals (CNCs), following a green biorefinery approach. The sequential process began with a hydrothermal treatment (at 203 °C under non-isothermal regime), enabling the solubilization of the hemicellulosic fraction and achieving a high recovery of xylooligosaccharides (66.5 %). Subsequently, deep eutectic solvents (DES) were applied, resulting in a cellulose-enriched solid (81 %) and high-purity lignin recovery (85 %) under optimized conditions (130 °C, 1 h, choline chloride:lactic acid, 1:9 molar ratio, 8 mL/g liquid-to-solid ratio). The DES treatment also yielded a lignin-free black liquor rich in residual carbohydrates and phenolic compounds (2.70 g/100 g initial PW). The autohydrolyzed and DES-delignified PW was then subjected to three different types of valorizations: (i) bioethanol production, reaching 41.79 g/L (80 % yield), (ii) succinic acid production, achieving 32.02 g/L (0.76 g of succinic acid per g of glucose), and (iii) CNCs with an average aspect ratio of 17.71 (length: 90-558 nm, width: 11-23 nm), demonstrating the potential of coupling hydrothermal and DES pretreatments to produce high-value products from lignocellulosic biomass.