Formation and Regeneration of Shape-Selective ZSM-35 Catalysts for n-Butene Skeletal Isomerization to Isobutene

Skeletal isomerization of n-butene to isobutene was performed over formed ZSM-35 zeolites in a lab-scale, fixed-bed reactor. The formation conditions to produce isobutene with zeolites were varied to determine the most advantageous binding agent (pseudo-boehmite) amount and steam dealumination conditions. The optimal binding agent amount was 20 wt %. Steam dealumination stabilized the catalysts and enhanced the catalytic performance because of the stable Si/Al framework and suitable acidity. The optimized process conditions involved a reaction temperature of 410 degrees C, a weight hourly space velocity of 5 h(-1), and an n-butene concentration in feedstock of 50%. After being on-stream for 296 h, the catalysts were stable and were able to be regenerated with a comparable catalytic performance. An isobutene yield of 33-43 wt % was achieved, and the selectivity of isobutene was higher than 90% after the reaction was carried out for longer than 15 h. Carbon deposition modified the pore structure to enhance the selectivity of isobutene because of the selective shape effect. This study shows promising results for future industrialization of the skeletal isomerization of n-butene to isobutene in the presence of optimized ZSM-35 catalysts.