A study on the effect of SiO2/Al2O3 ratio on the structure and performance of nano-sized ZSM-5 in methanol to propylene conversion

Abstract

The effect of SiO2/Al2O3 ratio on high silica content nano-sized HZSM-5 stability and selectivity in conversion of methanol to propylene (MTP) has been investigated in a continuous flow isotherm fixed-bed reactor. Highly crystalline HZSM-5 zeolite samples with SiO2/Al2O3 ratios ranging 150–200 have been prepared and characterized using XRD, ICP-AES analytical techniques, NH3-TPD, BET surface area and SEM imaging for studying their physical and chemical behavior. The reaction was conducted at 480 °C and 1bar with WHSV = 1 h−1 and a solution with 1:1 wt% of methanol and water as feed. Over thoroughly monitoring the catalyst synthesis conditions, the nanocrystal ZSM-5 zeolite samples were fabricated with fairly close microstructural properties and crystal sizes in order to be able to study the effect of SiO2/Al2O3 ratio on the ZSM-5’s performance in MTP. Results show that although the crystal size does not considerably affect the elementary structure of the zeolite active sites, it seems to be an influential factor in bond strength of Si–O versus Al–O. The results have also showed that increase of SiO2/Al2O3 ratio leads to higher selectivity and stability of catalyst.