Evaluation of pretreatment effect on lignin extraction from wheat straw by deep eutectic solvent

Area of Science:

• Biomass valorization
• Green chemistry
• Lignin extraction

Background:

• Wheat straw is a rich source of lignin, a valuable biopolymer.
• Efficient lignin extraction is crucial for biomass valorization.
• Current methods often face challenges in selectivity and yield.

Purpose of the Study:

• To investigate the impact of hemicellulose removal on lignin extraction using choline chloride and lactic acid (ChCl-LA) based deep eutectic solvents (DES).
• To compare the effectiveness of DES and hot water presoaking pretreatments for wheat straw.
• To optimize a DES-based process for high-yield and high-purity lignin production.

Main Methods:

• Wheat straw was pretreated using ChCl-LA DES and hot water to remove hemicellulose.
• Morphological changes and chemical modifications of the cell wall were analyzed.
• Lignin extraction efficiency was evaluated after different pretreatments.
• A two-stage DES treatment (room temperature presoaking followed by elevated temperature extraction) was tested.

Main Results:

• Both DES and hot water pretreatments significantly removed hemicellulose and altered cell wall morphology.
• DES presoaking cleaved ether bonds between lignin and hemicellulose, selectively removing lignin from specific cell wall regions (CML, CC).
• DES presoaking led to cell wall disruption and swelling, facilitating subsequent lignin extraction.
• Hot water pretreatment removed more hemicellulose but did not enhance lignin extraction.
• The two-stage DES treatment resulted in high yield and purity of extracted lignin.

Conclusions:

• Hemicellulose removal is critical for efficient lignin extraction.
• DES pretreatment offers a selective and effective method for lignin removal by targeting lignin-hemicellulose linkages and cell wall structures.
• A two-stage DES process is a viable and efficient strategy for producing high-quality lignin from wheat straw.