A Comparative Study of Lignin Recovery Conditions Using GVL-Organosolv and Lignin Characterization

Delignification is a critical step of the wood fractionation process in a biorefinery. It directly influences the purity of lignin and aids in breaking bonds within lignin and lignin–carbohydrate complexes surrounding cellulose. The recalcitrant nature of lignocellulose poses challenges in fractionating the material, notably during delignification. Recent progress in understanding lignin’s physical and chemical properties has led to the development of numerous value-added products from lignin sources. This study discusses lignin recovery from Norway spruce using γ-valerolactone (GVL)-based organosolv. The lignin recovery was investigated by changing GVL concentration in deionized water (60/20 and 80/20 v/v), temperature (140, 160 and 180 °C), and addition of catalyst (sulfuric acid and phosphoric acid). The highest delignification and lignin recovery were achieved with 60% GVL at 180 °C in the presence of phosphoric acid (78% delignification and 66% lignin recovery) and 80% GVL at 140 °C in the presence of sulfuric acid (67% delignification and 50% lignin recovery). The lignin samples were analyzed by FTIR, GPC, Py-GC/MS, and 2D HSQC NMR. FTIR spectra of lignin showed that they have similar spectra with different intensities in the fingerprint zone. Additionally, 2D HSQC NMR results show that the lignin extracted from the 80% GVL at 140 °C in the presence of sulfuric acid experiment had an abundance of about 47% (per 100 Ar) β-O-4 linkage. The results showed that the GVL-organosolv is a promising method for lignin recovery, and the GVL-lignin is a good candidate for high-value applications.

γ-valerolactone, a green solvent, has been utilized to recover lignin under mild conditions, achieving high purity and yield.