Enhanced lignin extraction process from steam exploded corn stalk

• Corn stalk after steam explosion (SE) showed enhanced lignin extraction behavior.
• Neutral solvent leaching indicated lignin reactions during SE caused enhanced extraction.
• Lignin characterization demonstrated substantial depolymerization occurred after SE.
• Depolymerized lignin was dissolved directly during alkali extraction after SE.
• Lignin alkali-extraction kinetics after SE was described by a second order model.

In this work, the alkaline extraction processes of lignin from untreated and steam-exploded corn stalk were compared and the enhanced extraction process was investigated by neutral solvent extraction and structural analysis of lignin. It was found that a first order model could readily simulate the lignin extraction from untreated stalk while it was helpless to describe the enhanced process after steam explosion due to the intense dissolution of lignin at the beginning stage of extraction. The lignin extracted by neutral solvent from ball-milled corn stalk and its structural characterization demonstrated that the poor description of extraction process by a first order model was mainly attributed to the considerable depolymerization during steam explosion. Due to the depolymerization of lignin, the alkaline extraction after steam explosion became the direct dissolution of depolymerized lignin and was successfully simulated by a second-order model. Finally, the activation energy of lignin alkali-extraction decreased 37.78% after steam explosion treatment with 1.8 MPa and 5 min, which indicated that milder extraction conditions were available to extract lignin from steam-exploded corn stalk. This study also provides a basic guidance for delignification approaches of lignocelluloses after steam explosion.

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