Catalytic cracking of triglycerides over micro/mesoporous zeolitic composites prepared from ZSM-5 precursors with varying aluminum contents

A series of micro/mesoporous nano-ZSM-5/SBA-15 analog composites (ZSC) was prepared from ZSM-5 precursors with variable aluminum contents (Si/Al ratio = 10–50) and their catalytic performance was evaluated in the cracking of waste vegetable oil under the fluid catalytic cracking conditions using a Single-Receiver Short-Contact-Time Microactivity Test unit (SR-SCT-MAT, Grace Davison). It was found that the preparation of the ZSC catalyst by properly tuning the initial aluminum content enables to improve its catalytic performance in terms of selectivity toward light olefins and quality of gasoline. Compared to single materials, i.e. microporous H-ZSM-5 and mesoporous Al-SBA-15, the ZSC catalyst shows the enhanced concentration of C3 and C4 olefins in the gaseous hydrocarbon fraction (ca. 85%) while lowering that of aromatic hydrocarbons in the gasoline fraction (ca. 40%). Furthermore, the reduced aromatic hydrocarbons are offset by the more environment-friendly components for boosting the octane rating of gasoline, i.e. iso-paraffins and iso-olefins. The superior catalytic performance of the ZSC catalyst can be attributed to the bimodal pore system coupled to the medium acid amount, which effectively suppresses hydrogen transfer reactions of primary light olefins while facilitating the cracking and isomerization transformations of hydrocarbon intermediates, leading to the improved formation of C3 and C4 olefins and branched gasoline hydrocarbons.