Improved biofuel quality in catalytic cracking of triglyceride-rich biomass over nanocrystalline and hierarchical ZSM-5 catalysts

Catalytic cracking of triglycerides over nanosized ZSM-5 (Nano-ZSM-5) and hierarchical ZSM-5 materials namely mesoporous ZSM-5 (Meso-ZSM-5) and nanosized ZSM-5/SBA-15 analog composite (Com-ZSM-5) was evaluated under fluid catalytic cracking conditions aiming to reduce the concentration of aromatics, especially benzene in the gasoline stream. The catalytic experiments were performed in a Single-Receiver Short-Contact-Time Microactivity Test unit (SR-SCT-MAT, Grace Davison) at 500 degrees C, catalyst-to-oil ratios of 0.3-1.0 (w/w) and contact time of 12 s. It was shown that the reduction of the ZSM-5 crystal size to nanometer (Nano-ZSM-5) or introduction of hierarchical porosity in ZSM-5 crystals (Meso-ZSM-5 and Com-ZSM-5) indeed improved the quality of gasoline by lowering the content of aromatics, particularly benzene. Compared to commercial ZSM-5, Meso-ZSM-5 and Nano-ZSM-5 produced more gasoline hydrocarbons while lowering the benzene content to ca. 2.0%, a relative decrease by ca. 50%. The advantage of Com-ZSM-5 over Meso-ZSM-5 and Nano-ZSM-5 was the lowest benzene level, i.e. ca. 0.8% which was below the permitted limit of less than 1% specified by the European regulation. The improved molecular transport along with the reduced density of strong Bronsted acid sites provided by the nanocrystalline and hierarchical ZSM-5 catalysts might be responsible for their superior catalytic performance.

Automated summary

The catalytic cracking of triglycerides over nanosized ZSM-5 and hierarchical ZSM-5 materials showed promising results in reducing the benzene content in gasoline, with Com-ZSM-5 exhibiting the lowest benzene level below the permitted limit specified by European regulation. This improvement in gasoline quality can be attributed to the modified molecular transport and reduced density of strong Bronsted acid sites provided by these catalysts.