Catalytic pyrolysis of wood polymer composites over hierarchical mesoporous zeolites

Abstract

Hierarchical zeolites have superior catalytic properties over purely microporous zeolites, leading to the enhanced diffusivity of molecules and strong acidity of the catalyst. In this study, hierarchical desilicated mesoporous ZSM-5 and Beta were prepared by the desilication of commercial microporous zeolites and applied to the catalytic pyrolysis of wood polymer composites. Hierarchical desilicated mesoporous ZSM-5 and Beta showed the typical X-ray diffraction patterns of microporous ZSM-5 and Beta with higher mesoporosity compared to the parent materials. The activity of the desilicated zeolites for the catalytic pyrolysis of wood polymer composites was evaluated using a thermogravimetric analysis and tandem micro reactor-gas chromatography/mass spectrometry. Among the catalysts tested, the lowest decomposition temperatures of wood polymer composites were observed using hierarchical desilicated mesoporous Beta followed by hierarchical desilicated mesoporous ZSM-5 and ZSM-5. This trend correlated well with the mesoporosity of the catalysts. The formation efficiency of hierarchical desilicated mesoporous ZSM-5 was highest followed by microporous ZSM-5, hierarchical desilicated mesoporous Beta, and Beta, indicating that in addition to mesoporosity, the shape selectivity induced by microporosity and strong acidity are important for the aromatization of pyrolysis vapors. In addition, the aromatic formation efficiency of the catalysts differed according to the properties of wood polymer composites. Compared to wood polymer composite 2, wood polymer composite 1 produced a larger quantity of aromatics during catalytic pyrolysis over all the catalysts at 500 °C owing to its higher polyethylene content. Both wood polymer composites exhibited a similar aromatic formation efficiency during catalytic pyrolysis at 600 °C because the diffusion hindering effect of polypropylene molecules to the catalyst pores was lower at the higher temperature.