Lignin depolymerization with alkaline ionic liquids and ethylene glycol in a continuous flow reactor

A novel alkaline ionic liquids N-allylpyridinium hydroxide ([APy]OH) was successfully designed and developed as a catalyst and co-solvent with ethylene glycol in the continuous depolymerization of lignin. Various reaction conditions, like lignin concentration, water content, and reaction temperature, were investigated under atmo-spheric pressure. Ethylene glycol was used as main solvent and repolymerization inhibitor of the aldehydes produced. The combination of [APy]OH and alkali metal salts exhibited a good synergistic effect for lignin depolymerization. Then, the depolymerization of three different lignins, including dealkaline lignin (DA-lignin), alkaline lignin (A-lignin), and sodium lignosulfonate (S-lignin), were also studied. S-lignin exhibited the highest yields of total liquid products (21.3 %) and aromatics (10.7 %). The change in lignin structure after depoly-merization was observed by means of FT-IR and DTG-DTA techniques. Lastly, a hypothetical pathway for lignin depolymerization was proposed based on the catalytic results of lignin model compounds (LMCs) with different linkages.

Automated summary

A novel alkaline ionic liquid ([APy]OH) was developed as a catalyst and co-solvent for the depolymerization of lignin. Different reaction conditions were investigated, and the combination of [APy]OH and alkali metal salts showed synergistic effects. The depolymerization of three different lignins was studied, with sodium lignosulfonate exhibiting the highest yields of liquid products and aromatics. Changes in lignin structure were observed and a hypothetical pathway for lignin depolymerization was proposed.