Sequential Pretreatment of Wheat Straw: Liquid Hot Water Followed by Organosolv for the Production of Hemicellulosic Sugars, Lignin, and a Cellulose-Enriched Pulp

Abstract The complete valorization of the lignocellulosic fractions plays a fundamental role in biorefineries’ sustainability. One of the major challenges is finding technological configurations that allow using cellulose, hemicellulose, and lignin simultaneously. Cellulose has been extensively studied, yet, hemicellulose and lignin remain as platforms to be valorized. Sequential pretreatments have shown an opportunity to valorize the latter two components into sugar-rich and lignin-rich fractions. After the sequential pretreatment, a solid fraction enriched in cellulose could still be used for paper production. This work consisted of pretreating wheat straw with a sequential Liquid-Hot-Water/Organosolv, characterizing the respective hemicellulosic sugar and lignin extracts, and evaluating the final cellulose-enriched pulp for papermaking. Different pretreated pulp/cellulose pulp formulations were used for paper production as a proof-of-concept. Tensile strength and bursting pressure of the papers were measured. After pretreatment, the calculated solid composition was 70%wt cellulose, 26%wt hemicellulose, and 4%wt lignin, with extraction yields of 5.1%, 51.3%, and 89.9%, respectively. The tested pulp formulations showed similar tensile index and bursting index values at 10/90 (77.1 Nm/g, 3189 kPa) and 20/80 (63 Nm/g, 2419 kPa) %wt pretreated pulp/pulp when compared to the pulp (77 Nm/g, 4534 kPa). This proof-of-concept of the papermaking showed the potential of the LHW-OS pretreated wheat straw as a replacement for pure cellulose pulp and encourages studying other substitutes such as unbleached pulp or further treating the LHW-OS pretreated wheat straw. In addition, the hemicellulosic sugars and lignin extract can be valorized, indicating an option for developing a biorefinery concept. Graphical Abstract