# 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

## TL;DR

This paper introduces a new method using maleic acid and ozone to reduce lignin condensation during wheat straw refining, improving lignin separation and structure.

## Contribution

A novel MA/O3 system is proposed to effectively reduce lignin condensation during biomass refining.

## Key findings

- The MA/O3 system achieved 38.07% lignin removal with reduced condensation bonds.
- The DL obtained had a high carboxyl group content of 2.96 mmol/g.
- 2D-HSQC-NMR confirmed minimal β-β and β-5 condensation bonds in treated lignin.

## Abstract

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.