Understanding the Role of Process Parameters on the Preparation of Silicalite-1 Zeolite Seed Crystals and Thin Films

Abstract

Silicalite-1 zeolite seed crystals were prepared by a hydrothermal technique under different experimental conditions. The thin films of silicalite-1 were developed on the porous ceramic substrate by (i) single-stage in situ, (ii) double-stage in situ, and (iii) ex situ (secondary) crystal growth processes. The prepared seed crystals and films were characterized by X-ray diffraction (XRD) and scanning electron microscopy. The XRD study showed that the crystallization of silicalite-1 seeds increased with the increasing temperature and processing time and with the decreasing water content of the precursor materials. The twin-free, pill-shaped silicalite-1 seed crystals were made in a shorter duration that is 5 h at 130°C. The thin film of silicalite-1 prepared on the porous ceramic substrate by single-stage and double-stage in situ processes showed a b-oriented crystal arrangement. However, ex situ (secondary) crystal growth process rendered a random orientation of crystals. The silicalite-1 films with double-stage in situ crystal growth process showed the permeances of 12 × 10−7 and 32 × 10−7 mol/m2/s/Pa for single gas N2 and O2, respectively, with their ideal selectively (O2/N2) of 2.66 at room temperature (30°C) and a transmembrane pressure of 1.5 bar.