Influence of Base-Catalyzed Organosolv Fractionation of Larch Wood Sawdust on Fraction Yields and Lignin Properties

• Published in: Catalysts 2019-12, Vol.9 (12), p.996-20
• Main Authors: Hochegger, Markus, Trimmel, Gregor, Cottyn-Boitte, Betty, Cézard, Laurent, Majira, Amel, Schober, Sigurd, Mittelbach, Martin
• Format: Article
• Language: English
• Subjects: Alcohol; Anthraquinones; Biomass; Carbohydrates; Catalysts; Cellulose; Chemical reactions; Design of experiments; Efficiency; Ethanol; Fractionation; Fractions; Glass transition temperature; Independent variables; Life Sciences; Lignin; Lignocellulose; Process variables; Sawdust; Sodium hydroxide; Solvents; Usability; Vegetal Biology
• ISSN: 2073-4344; 2073-4344
• DOI: 10.3390/catal9120996

Lignocellulose-based biorefineries are considered to play a crucial role in reducing fossil-fuel dependency. As of now, the fractionation is still the most difficult step of the whole process. The objective of this study is to investigate the potential of a base-catalyzed organosolv process as a fractionation technique for European larch sawdust. A solvent system comprising methanol, water, sodium hydroxide as catalyst, and anthraquinone as co-catalyst is tested. The influence of three independent process variables, temperature (443–446 K), catalyst loading (20–30% w/w), and alcohol-to-water ratio (30–70% v/v), is studied. The process conditions were determined using a fractional factorial experiment. One star point (443 K, 30% v/v MeOH, 30% w/w NaOH) resulted in the most promising results, with a cellulose recovery of 89%, delignification efficiency of 91%, pure lignin yield of 82%, residual carbohydrate content of 2.98% w/w, and an ash content of 1.24% w/w. The isolated lignin fractions show promising glass transition temperatures (≥424 K) with high thermal stabilities and preferential O/C and H/C ratios. This, together with high contents of phenolic hydroxyl (≥1.83 mmol/g) and carboxyl groups (≥0.52 mmol/g), indicates a high valorization potential. Additionally, Bjorkman lignin was isolated, and two reference Kraft cooks and a comparison to three acid-catalyzed organosolv fractionations were conducted.