Elucidating the Zeolite Particle Size Effect on Butene/Isobutane Alkylation

In this study, X zeolites with average particle sizes of 0.9, 3.2, and 15.0 mu m (labeled as NaX-0.9 mu m, NaX-3.2 mu m, and NaX-15.0 mu m) were prepared. The latter two samples were single crystals, while NaX-0.9 mu m was an aggregate composed of nanosized crystals. After being transferred to their La forms, the alkylation performances of the zeolites were examined in a continuous-flow slurry reactor. Contrary to the general belief that reducing the particle size can effectively enhance catalyst stability, the results showed that LaX-3.2 mu m exhibited better stability than the other two samples. This phenomenon was explained by the balance between acidity and diffusion resistance. Although LaX-15.0 mu m possessed very similar acidities to LaX-3.2 mu m, its active sites cannot be fully utilized due to the diffusion limitations associated with the larger particle size. As for LaX-0.9 mu m, although it was theoretically favorable for product diffusion, it also suffered from more significant dealumination because of the high structural defect concentrations. As a result, LaX-0.9 mu m yielded lower Bronsted acidity, higher Lewis acidity, and weaker acid strength, all of which were disadvantageous for alkylation. Given the tradeoff effect between diffusion resistance and acidity, there is speculated to be an optimal particle size for LaX zeolites when used in a slurry reactor for alkylation. Furthermore, suggestions on catalyst design for isobutane alkylation were provided based on our results.

Automated summary

This study investigated the alkylation performance of X zeolites with different particle sizes in a continuous-flow slurry reactor. The results showed that larger particle size can enhance catalyst stability, while smaller particle size is favorable for product diffusion. However, significant dealumination and structural defects can occur in smaller particles, impacting their acidity and overall alkylation performance. Thus, an optimal particle size range is speculated for the use of X zeolites in a slurry reactor for alkylation.