Development of HZSM-5/AlMCM-41 hybrid micro–mesoporous material and application for pyrolysis of vacuum gasoil

The pyrolysis of vacuum gasoil (VGO) was studied alone and in presence of HZSM-5/AlMCM-41 hybrid catalyst. This micro–mesoporous material was synthesized by the hydrothermal method using dual templates of tetrapropilamonium and cetyltrimethylammonium ions at different crystallization times. The obtained materials were washed and calcined for remotion of the organic templates. The characterization by X-ray diffraction, nitrogen surface area by the BET method, scanning and transmission electron microscopies, evidenced that typical MFI structure was embedded into the bulk of the MCM-41 matrix, in order to obtain the hybrid micro–mesoporous phase. The protonic form of the material was obtained by ion exchange with ammonium chloride solution and subsequent thermal treatment. The total acidity, as determined by n-butylamine adsorption, was equivalent to 0.75 mmol g−1, in the temperature range of 300–500 °C, corresponding to strong acid sites. For catalytic reaction, a physical mixture of 10% of catalyst/VGO was decomposed in a thermobalance at heating rates of 5; 10 and 20 °C min−1, from 100 to 550 °C. From TG/DTG data, applying the model-free kinetics, it was observed that the activation energy for the pyrolysis of VGO alone was ca. 125 kJ mol−1. For VGO physically mixed to both AlMCM-41 and HZSM-5, the value decreased to ca. 80–90 kJ mol−1, whereas for the hybrid, the value was the lowest, ca. 65 kJ mol−1, evidencing the efficiency of the combined effect of the acid sites, crystalline phase and microporosity of ZSM-5 zeolite with the accessibility of the mesoporous of the AlMCM-41 ordered material. For determination of the catalytic properties, the samples of VGO and catalyst/VGO were submitted to pyrolysis-GC–MS system at 500 °C using helium as gas carrier. The VGO alone suffers decomposition to a wide range of hydrocarbons, typically C17–C41, while in the presence of catalyst, light fraction of hydrocarbons, in the range of liquefied petroleum gas (C3–C5), gasoline (C6–C10) and diesel (C11–C16) were obtained, evidencing that the HZSM-5/AlMCM-41 hybrid material is an effective catalyst for pyrolysis of VGO.

TEM images for sample ZSM-5/AlMCM-41, showing the hexagonal arrangement of the mesoporous (A), and the longitudinal system of the mesopores (B).Figure optionsDownload as PowerPoint slideHighlights
► The hydrothermal synthesis of the HZSM-5/AlMCM-41 using dual template mechanism.
► Crystalline phase of zeolite embedded on the mesoporous structure was obtained.
► Thermal analysis was applied for study of pyrolysis of vacuum gasoil.
► The HZSM-5/MCM-41 was an active catalyst for pyrolysis of vacuum gasoil.