Fast synthesis of ZSM-22 zeolite by the seed-assisted method of crystallization with methanol

摘要

This is a study of the fast synthesis of ZSM-22 zeolite using crystallization seeds and a cheap source of silica. The effect of crystallization time, addition of methanol as organic solvent, SiO2/Al2O3 ratio (SAR), alkalinity (OH-/SiO2 ratio), addition of potassium cation, and agitation were studied on the properties of the produced zeolite. Syntheses were performed at 170°C with a fixed seed:SiO2 mass ratio of 10%. The seeds were synthesized by the hydrothermal method at 160°C in the presence of 1,6-diaminohexane organic template. Products were characterized using X-ray diffraction, thermal analysis, nitrogen adsorption at 196°C, and scanning electron microscopy. Under static conditions the best result was reached after 6 h of crystallization, obtaining a ZSM-22 with 80% crystallinity, in the presence of methanol, low alkalinity, without addition of K+and SAR 100. The synthesis of ZSM-22 with SAR 50 using the same method resulted in a slightly lower crystallinity than with SAR 100. The increase in alkalinity or potassium concentration in the synthesis reaction medium decreased the crystallinity of the zeolite. Synthesis with the same composition under agitated condition increased the crystallinity and specific surface area of the zeolite and decreased reaction time from 6 to 4h. The fastest synthesis was obtained under agitation with low methanol content in the reaction medium, obtaining the ZSM-22 structure after 3?h of reaction with higher crystallinity and surface area. The importance of fast synthesis is to reduce the cost of the zeolite production.