Acta Phys. -Chim. Sin. ›› 2009, Vol. 25 ›› Issue (09): 1921-1927.doi: 10.3866/PKU.WHXB20090919

• ARTICLE • Previous Articles     Next Articles

Crystallization Kinetics and Influencing Factors in the Syntheses of MFI/MFI Core-Shell Zeolites

KONG De-Jin, ZOU Wei, ZHENG Jun-Lin, QI Xiao-Lan, FANG Ding-Ye   

  1. College of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, P. R. China|Shanghai Research Institute of Petrochemical Technology, SINOPEC, Shanghai 201208, P. R. China
  • Received:2009-03-24 Revised:2009-06-19 Published:2009-09-03
  • Contact: KONG De-Jin E-mail:djkong@sript.com.cn

Abstract:

MFI/MFI core-shell zeolites with a low silica to alumina ratio core and a continuous shell of high silica to alumina ratio were successfully synthesized by a novel two-step procedure. This was done by a secondary growth of the ZSM-5 shell onto the modified ZSM-5 crystals and the pre-treatment step played an important role during the synthesis. Critical factors for the growth of the ZSM-5 shell including synthesis temperatures, periods, and core dosages were summarized. Results from cumene and 1,3,5-triisopropylbenzene (1,3,5-TIPB) cracking reactions showed that the core-shell zeolite and the core crystal had comparable activities for the cumene cracking reaction. Compared to the core crystal, the cracking activity of 1,3,5-TIPB of the core-shell zeolite was reduced by 68%, which coincided with the extent of aluminum reduction on the external surface. These results suggested that the acidity of the core crystals was largely preserved in the MFI/MFI core-shell structure. Crystallization kinetics curves were determined at different synthesis temperatures. The apparent energy of crystallization activation was found to be 26.5 kJ·mol-1 and the activation
energy of nucleation was 51.5 kJ·mol-1.

Key words: Crystallization kinetics, ZSM-5, MFI/MFI, Core-shell zeolite, Nucleation activation energy, Crystallization activation energy

MSC2000: 

  • O643