Structural Changes of Alkali Lignin under Ozone Treatment and Effect of Ozone-Oxidized Alkali Lignin on Cellulose Digestibility

The Synergetic Reduction of the Condensation Degree of Dissolved Lignin (DL) during the Refining Process of Wheat Straw Biomass Based on the MA/O3 System

Lignin, a natural pol2ymer with a complex structure that is difficult to separate, is prone to C-C bond condensation during the separation process. To reduce the condensation of lignin, here, a novel method is proposed for separating the components by using a combination of maleic acid (MA)/ozone (O3) to co-treat wheat straw. The removal of lignin, glucan, and xylan was 38.07 ± 0.2%, 31.44 ± 0.1%, and 71.98 ± 0.1%, respectively, under the conditions of ball-milling of wheat straw for 6 h, reaction temperature of 60 °C, and O3 holding time of 9 min. Lignin-rich solutions were collected to extract the dissolved lignin (DL) after washing the treated samples. The DL obtained under MA/O3 conditions had a carboxyl group (-COOH) content of 2.96 mmol/g. The carboxyl group of MA underwent esterification with the hydroxyl group (-OH) at the γ position of lignin and O3 reacted on the positions of the lignin side chain or the phenolic ring, resulting in a break in the side chain and the opening of the phenolic ring to introduce the carboxyl group. The 2D-HSQC-NMR results revealed that the phenolic ring-opening reaction of lignin in the presence of O3 was essentially free of β-β and β-5 condensation bonds.

Extraction of homogeneous lignin oligomers by ozonation of Miscanthus giganteus and vine shoots in a pilot scale reactor

Lignin, a complex phenolic polymer crucial for plant structure, is mostly used as fuel but it can be harnessed for environmentally friendly applications. This article explores ozonation as a green method for lignin extraction from lignocellulosic biomass, aiming to uncover the benefits of the extracted lignin. A pilot-scale ozonation reactor was employed to extract lignin from Miscanthus giganteus (a grass variety) and vine shoots (a woody biomass). The study examined the lignin extraction and modification of the fractions and identified the generation of phenolic and organic acids. About 48 % of lignin was successfully extracted from both biomass types. Phenolic monomers were produced, vine shoots yielding fewer monomers than Miscanthus giganteus. Ozonation generated homogeneous lignin oligomers, although their molecular weight decreased during ozonation, with vine shoot oligomers exhibiting greater resistance to ozone. Extracted fractions were stable at 200 °C, despite the low molecular weight, outlining the potential of these phenolic fractions.

A Value-Added Utilization Method of Sugar Production By-Products from Rice Straw: Extraction of Lignin and Evaluation of Its Antioxidant Activity

To value-added utilization of the rice straw, two types of lignin were extracted from the by-products of sugar production. The ether-extracted lignin with a purity of 98.7% was extracted from the pretreatment filtrate with two times the concentrated filtrate volume of ether, where the lignin yield was 6.62 mg/g of the rice straw. The ball-milled lignin with a purity of 99.6% was extracted from the milled enzymatic hydrolysis residue with a 1,4-dioxane solution, where the revolution speed and grinding time were 300 rpm and 12 h, respectively. The yield of ball-milled lignin was 34.52 mg/g of the rice straw, which was 421.5% higher than that extracted from extract-free rice straw. In the process of rice straw pretreatment and lignin extraction, 76.43% by mass of phosphotungstic acid catalyst and approximately 98% by volume of 1,4-dioxane solution could be recycled and reused. Compared with the soda lignin extracted from papermaking black liquor, the scavenging rates of DPPH radical and ABTS+ radical of ether-extracted lignin increased by 36.26% and 41.18%, respectively, while the above scavenging rates of ball-milled lignin increased by 30.22% and 37.75%, respectively. Moreover, the reducing power of the two extracted lignins was also stronger than that of soda lignin. The ether-extracted lignin and ball-milled lignin have the potential to be developed as natural macromolecular antioxidants.