Dry-gel process for zeolite synthesis: Some fundamental aspects

The present study provides a systematic study of the zeolite synthesis parameters using basic raw materials, such as sodium aluminate, silicon oxide and sodium hydroxide. Sodalite zeolites were produced by grinding, homogenizing and heating the reactants without the addition of solvent (water). The effects of the following parameters are evaluated: (i) Si/Al and Si/Na ratios, (ii) reaction time, and (iii) stirring in the reaction medium, which resulted in a set of 15 solids. The Si/Al and Si/Na ratios have a strong effect on the formation of the zeolite phase generated in the presence of higher amounts of sodium, with the ratios Si/Al = 1 and Si/Na = 2 being the minimum satisfactory conditions for crystallization. A low diffusion rate and a longer reaction time and stirring time give rise to samples with higher crystallinities. The resulting zeolites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, water contact angle, small-angle X-ray scattering and thermogravimetric analyses. All materials exhibit dense, spherical and uniform particles with slightly rough surfaces according to SAXS measurements. The solvent-free method is demonstrated to be effective in the synthesis of samples with good crystallinity. This synthesis method is shown to be efficient, fast, economical and environmentally friendly.