Enhanced Production of Aromatic Hydrocarbons by Rapeseed Oil Conversion over Ga and Zn Modified ZSM-5 Catalysts

Rapeseed oil conversion has been investigated over catalysts based on Ga- and Zn-modified nanocrystalline HZSM-5 zeolite aimed to the production of hydrocarbons that could be used as both raw chemicals and/or fuels. The reactions have been carried out in a fixed bed reactor operating under nitrogen at 550 degrees C and atmospheric pressure. The incorporation of the metallic species to the parent zeolite was carried out by wetness-impregnation, resulting in a good metal dispersion, which is facilitated by the relatively high external surface area available in the nanocrystalline zeolitic support. This metal addition causes significant changes in the textural and acidic properties of the ZSM-5 zeolite. In all cases, a high deoxygenation degree of the raw oil was achieved through the formation of CO, CO2, and H2O, whereas the main products obtained were light olefins (mainly ethylene and propylene) and, aromatic hydrocarbons (BTX). The incorporation of Ga and Zn in the parent zeolite increased the formation of gasoline range hydrocarbons, promoting the conversion of light olefins into aromatics by a sequence of oligomeritation/cyclization/aromatization reactions. This effect was especially noticeable over the Zn/HZSM-5 catalyst, showing a strong enhancement in the production of aromatic hydrocarbons, which was assigned to the generation of new acid sites by the incorporation of the Zn species. Moreover, the addition of Ga on the zeolite increases the coke deposition, which may explain the more pronounced decrease in the aromatization activity observed along the time on stream for the Ga/HZSM-5 catalysts compared to the Zn/HZSM-5 ones.