Synthesis of zeolites in the system Na2O-SiO2-Al2O3-H2O-glycerol

Abstract

The synthesis of zeolites from a mixture of a non-aqueous glycerol aluminosilicate gel and a controlled quantity of water has been studied. It was found that a minimum water content in the synthesis mixture is required to achieve a measurable crystallization rate. A further increase of the water content may facilitate the crystallization process of omega and then switch the crystal structure of the product from omega to analcime. At the Si/Al ratio of 6.95 in the synthesis mixture an increase of the NaOH content leads to a product sequence of amorphous → omega → analcime → analcime and sodalite. An increase of the Si/Al ratio in the synthesis mixture leads to a product sequence of sodalite → omega(+analcime) → ferrierite → magadiite. At the Si/Al ratio of 6.95 in the synthesis mixture a change of the alkali cations in a sequence of Li⁺ +Na⁺ → K⁺ + Na⁺→ Rb⁺ +Na⁺ → Cs⁺ + Na⁺ corresponds to a product sequence of omega (+ analcime) → offretite → offretite → analcime. With the new synthesis system, crystalline microporous materials including omega, offretite, analcime, and ferrierite can be readily obtained. The behaviors of the new synthesis system are discussed and compared with those of the normal hydrothermal synthesis system for zeolites.