(144f) Characterization of Deep Eutectic Solvent Extracted Lignin Streams from Endocarp Biomass

Lignin is a promising direct source and contains upgradable building blocks of valuable aromatic chemicals and materials. Endocarp biomass represents a non-edible crop residue in an existing agricultural setting which cannot be used as animal feed nor soil amendment. With considerably higher lignin content and bulk energy density, endocarps have significant advantages to be converted into both biofuel and bioproducts as compared with other biomass resources. As a new pretreatment method, deep eutectic solvent (DES) pretreatment is shown to be highly effective in fractionating lignin from biomass with high yield and purity, in addition to merits of both environmental friendliness and low cost compared with several other pretreatment methods. However, the impact of DES pretreatment on the physical and chemical properties of extracted lignin is so far not clear. Therefore, this study aims to fractionate and characterize lignin streams from endocarps of peach and black walnut using DES in comparison with two conventional pretreatment methods, i.e., dilute acid and alkaline pretreatments. SEM and confocal microscopic analysis revealed distinct structural characteristics of peach and walnut endocarp biomass as compared to switchgrass and woody biomass. Chromatographic and nuclear magnetic resonance (NMR) spectroscopic techniques were employed to understand the lignin composition, structure and depolymerization during DES pretreatment. The resulting lignins were further characterized for purity, molecular weight distribution, and thermogravimetric properties. This study provides a foundation for developing novel conversion techniques for upgrading DES extracted endocarp lignin for value-added chemicals and materials.