Comparison of Lignin Fractions Isolated from Wheat Straw Using Alkaline and Acidic Deep Eutectic Solvents

Abstract

This study aims to examine the characteristics of two solid lignin fractions isolated from wheat straw using alkaline and acidic deep eutectic solvents (DESs). The chemical properties and morphological characteristics of the two lignin fractions were evaluated by measuring their purity, elemental composition, molecular weight and particle size distributions, and microstructure. Their chemical structure was evaluated using DRIFT spectroscopy, GPC, TGA, 13 C NMR, 31 P NMR, and HSQC NMR. Our findings showed that the lignin isolated using alkaline DES was less pure and had smaller particle size, higher molecular weight, and thermal stability compared to the lignin isolated using acidic DES. Their lignin structure was also determined to be different due to varying selective fractures on the linkages of lignin. These results suggest that the DES treatments could selectively extract lignin from wheat straw with different yields, composition, morphology, and structure, which could then provide a theoretical basis for the selection of DESs for specially appointed lignin extraction.

Combining acid-based deep eutectic solvents and microwave irradiation for improved chestnut shell waste valorization

“…As mentioned above, the ability of acidic DESs to depolymerize and fractionate the lignin component of lignocellulosic biomass, as well of hemicellulose, is well known. [67][68][69][70][71] Although a literature comparison of the quantity of extracted biomolecules is of limited value on account of the different biomass sources, extraction protocols, and pretreatment carried out on the waste (for instance brulage or boiling), the here reported MWDA process using DES ChCloxalic acid dihydrate represents an appealing extraction system. This holds true both in terms of yield and TPC as well as for its innovative use of an alternative energy source.…”

History repeats itself again: Will the mistakes of the past for ILs be repeated for DESs? From being considered ionic liquids to becoming their alternative: the unbalanced turn of deep eutectic solvents

“…The findings described in the literature reveal that basic DESs lead to a less pure and highly recondensed lignin with small particle size compared with the material recovered with acidic DESs. 194 Among the acidic HBDs, LA is certainly the most commonly used, and its effect on lignin structure was evaluated under different conditions and on different biomasses. The techno-economic benefits of this medium have already been described and highlighted.…”

High-purity lignin fractions and nanospheres rich in phenolic hydroxyl and carboxyl groups isolated with alkaline deep eutectic solvent from wheat straw

“…Moreover, the remaining DES liquid can be recycled by separating the EtOH with a rotary evaporator and adjusting the DES properties by K 2 CO 3 make-up. The properties of L O were described in detail in our previous study (Yue et al, 2020). The insoluble DES lignin fractions L O , L 6 , L 4 , and L 2 were washed several times with DIW to neutral pH and freeze-dried for further analysis.…”