Crystallization of silica molecular sieves from piperazine — quaternary ammonium bromide — silica — water systems

Abstract

Crystallization from reaction mixtures containing piperazine, silica, water, and each of 11 quaternary ammonium salts at 120°, 150°, and 180°C has been investigated. In many cases, especially at 180°C, no crystalline material was obtained even though the corresponding quaternary-free reaction mixtures gave ZSM-39 or EU-19. Silicalite precursors were formed with tetrapropylammonium, tetrabutylammonium, tetrapentylammonium, tributylpentylammonium, and tributylheptylammonium bromide at 120° and 150°C. These precursors were characterized by X-ray powder diffraction, scanning electron microscopy, and thermal analysis.