Controllable synthesis of hierarchical ZSM-5 for hydroconversion of vegetable oil to aviation fuel-like hydrocarbons

Abstract

Hydroconversion of soybean oils to aviation fuel-like hydrocarbons was investigated over aggregated hierarchical ZSM-5 microspheres composed of small ZSM-5 nanoparticles, which were synthesized via a hydrothermal method by controlling the Si/Al ratio with carbon nanotubes (CNTs) as the template. The prepared ZSM-5 microspheres were investigated by X-ray diffraction (XRD), N₂ adsorption and desorption (N₂-BET) and scanning electron microscopy (SEM). A low Si/Al ratio resulted in small-sized seed crystals, which then grew into ZSM-5 microspheres through 3D island growth. A high Si/Al ratio resulted in the opposite growth behavior and was prone to forming well-formed individual “classic-boat” ZSM-5 by 2D layer growth. The CNTs acted not only as a mesopore template, but also as a cage to offer suitable space making the ZSM-5 grow into the nanoparticles and form microspheres. The obtained ZSM-5 microspheres had a uniform size (2–3 μm) with a hierarchical structure containing intracrystalline and intercrystalline mesopores. The spherical ZSM-5 zeolites supporting a NiMo catalyst showed high activity and selectivity toward hydroconversion of soybean oil to aviation-like biofuel (C₉–C₁₅ hydrocarbons).