Study on plasma pretreatment of lignin to inhibiting pyrolysis intermediate polymerization and promoting Mo/ZSM-5 catalytic pyrolysis

Catalytic pyrolysis of lignin can produce renewable aromatics in one step, but the development of this process is severely constrained by problems such as high-temperature polymerization and catalyst coking. Here, we propose a method combining plasma rapid pretreatment with catalyst modification to efficiently convert lignin into aromatics through catalytic pyrolysis. Pyrolysis tests of lignin derivatives show that large amounts of oligomers form after pyrolysis of guaiacol and syringol, and intramolecular interactions between methoxy and hydroxyl groups are the main factors contributing to lignin intermediate polymerization during pyrolysis. Plasma pretreatment can rapidly break some connecting bonds and methoxy groups, significantly inhibiting secondary polymerization of intermediates and oligomer formation during pyrolysis, thus promoting the generation of lignin pyrolysis monomer phenols. Mo-modified ZSM-5 can enhance catalytic cracking and deoxygenation performance while reducing the formation of coke precursors such as naphthalene (drops from 1.45 to 1.03 wt%). Converting pretreated lignin to aromatics using Mo-modified ZSM-5 increases the yield to 6.0 wt%, while simultaneously suppressing intermediate polymerization and coking. Overall, this work demonstrates the inhibition mechanism of lignin pretreatment combined with Mo modification on polymerization and coking during lignin catalytic pyrolysis, providing a simple and environmentally friendly approach for the efficient pyrolysis of lignin. • The main factor of polymerization of pyrolysis intermediates have been identified. • Rapid plasma pretreatment for cracking partial linking bonds and methoxy groups. • Lignin pretreatment inhibits polymerization and increases monomer phenols yield. • Mo modified ZSM-5 can adjust acidity to improve MAHs yield and reduce heavy tar. • The MAHs yield of lignin pretreated by Mo/ZSM-5 catalytic pyrolysis is 6.0 wt%.