Directly synthesis of H-form ZSM-5 zeolites with n-butylamine in the presence of seed and ethanol

Abstract

In the research of directly synthesizing H-form ZSM-5, ammonium hydroxide is commonly used as an alkali source instead of NaOH to avoid multiple ion exchange steps. However, the volatile nature and the lack of structure-directing effect of ammonium hydroxide limit its application in practical. In this study, n-butylamine (NBA) was used as the main alkali source to directly prepare HZSM-5 zeolites with SiO2/Al2O3 ratios ranging from 40 to 300 under traditional hydrothermal conditions. The influence of the amount of NBA, ethanol, seed, and pre-crystallization on the synthesis products was investigated under the condition of SiO2/Al2O3 = 80. Theoretical simulation suggested that n-butylamine cations (NBA+) play the most potent directing role in the formation of the MFI structure but could lead to difficulties in removal during calcination. The addition of ethanol as the zeolite growth modifier (ZGM) could decrease the usage of NBA and reduce the difficulties in calcination, and the addition of seed provided the conditions for initiating crystallization in the system that could not spontaneously nucleate. HZSM-5 with different SiO2/Al2O3 ratios were prepared under the optimal crystallization conditions, and the as-synthesized samples exhibited superior textural and acid properties compared to commercial zeolite. Finally, the 1 L scale-up synthesis and MTP reaction were conducted to demonstrate the practicality of this economically and environmentally-friendly synthesis strategy.