Pretreatment of willow using the alkaline-catalyzed sulfolane/water solution for high-purity and antioxidative lignin production.

In this study, an alkaline-catalyzed sulfolane/water solvent system was developed for isolating high-purity and antioxidative lignin from willow (Salix matsudana cv. Zhuliu). Optimization of the pretreatment conditions such as temperature, sulfolane/water ratio, and alkaline catalyst (NaOH) dosage were comprehensively investigated for effective lignin extraction from willow. The 44.4% of lignin was recovered from the biomass with 54% of delignification in 50/50 (w/w) sulfolane/water system at 170 °C. As the addition of the alkaline catalyst (NaOH) increased to 4%, the delignification yield was increased up to 94% with about 70% of lignin recovery yield. The recovered lignin was comparatively investigated with its control, milled wood lignin (MWL). The ß-O-4 linkages and phenolic hydroxyl were well preserved in the extracted lignin fractions with the sulfolane/water system. Furthermore, excellent radical scavenging ability was observed with the extracted lignins by sulfolane/water pretreatments owing to rich phenolic hydroxyl groups in the lignins. Hence, systematical investigation on the lignin properties and potential applications under sulfolane organosolv pretreatment would promote the utilization of lignin in biorefinery processes.

Structural elucidation of the lignins from stems and foliage of Arundo donax Linn.

As one of the potential energy crops, Arundo donax Linn. is a renewable source for the production of biofuels and bioproducts. In the present study, milled wood lignin (MWL) and alkaline lignin (AL) from stems and foliage of A. donax were isolated and characterized by FT-IR spectroscopy, UV spectroscopy, GPC, ³¹P NMR, 2D HSQC NMR, and DFRC. The results indicated that both stem and foliage lignins were HGS type lignins. The semiquantitative HSQC spectra analysis demonstrated a predominance of ß-O-4' aryl ether linkages (71-82%), followed by ß-ß', ß-5', ß-1', and α,ß-diaryl ethers linkages in the lignins. Compared to stem lignins, foliage lignins had less ß-O-4' alkyl-aryl ethers, lower weight-average molecular weight, less phenolic OH, more H units, and lower S/G ratio. Moreover, tricin was found to incorporate into the foliage lignins (higher content of condensed G units) in significant amounts and might be alkaline-stable.