Coupling Polyolefin Conversion and Methanol Reduction for C₉-C₁₀ Alkylaromatic Production

This work presents a strategy for integrating polyethylene (PE) aromatization and Friedel-Crafts-type alkylation reactions via methanol reduction for upgrading PE to 79.0 wt% liquid with 56.1 wt% aromatics at 280 °C, enabled by a bifunctional NiGa/ZSM-5-H catalyst. In the catalyst design, hierarchical ZSM-5-H promotes cracking of PE, while Ga serves not only as an active site for aromatization and alkylation but also suppresses Ni⁰ formation by withdrawing electron density from Ni, ensuring that Ni²⁺ remains as the active catalytic site for methanol reduction. Hydrogen species derived from PE aromatization participate in methanol reduction, while methanol functions mainly as a hydrogen sink and methyl donor yet also releases some hydrogen under reaction conditions, allowing the PE aromatization and methanol reduction steps to be coupled. In the presence of hydrogen, methanol reduction generates methyl species that promote Friedel-Crafts-type alkylation, incorporating methyl groups into the alkyl substituents of aromatics and boosting C₉-C₁₀ alkylaromatics yields by more than 600%. By introducing 0.99 g/g methanol equivalent into the PE-catalyst reaction system, aromatic and C₉-C₁₀ alkylaromatics yields are more than double those without methanol. The strategy is applicable to upgrading of polyolefins and offers a practical route for industrial processing of plastic waste.