Synthesis of NaX zeolite: Influence of crystallization time, temperature and batch molar ratio SiO2/Al2O3 on the particulate properties of zeolite crystals

In this study, the effects of crystallization time, temperature and SiO2/Al2O3 molar ratio in the synthesis gel on the end products (NaX zeolite) were investigated. The results revealed that crystallization time and temperature determined whether or not NaX zeolite was formed. Furthermore, SiO2/Al2O3 molar ratio was found to play a significant role in the particulate properties of the crystalline end products. A single phase NaX zeolite was obtained only with the SiO2/Al2O3 molar ratio of 1.5–4.0; the NaA zeolite was developed at SiO2/Al2O3 = 1.0 in addition to the NaX zeolite. However, at SiO2/Al2O3 = 0.5, a single phase NaA zeolite was generated. The Si/Al molar ratios of NaX zeolites were tested to be 1.38, 1.33, 1.29, 1.24 and 1.18 for the SiO2/Al2O3 molar ratios of 4.0, 3.5, 2.9, 2.0 and 1.5. The corresponding samples had the mean particle sizes of 464, 548, 689, 836 and 980 nm, with the particle size distribution ranges of 120–810, 202–815, 445–975, 605–1096 and 770–1218 nm, respectively. N2 adsorption–desorption results showed that the BET surface areas and micropore volume of the end product increased with the decrease of SiO2/Al2O3 molar ratio in synthesis gel, but all the NaX zeolite particles have relatively high total pore volumes. In addition, the effect of molar ratio of SiO2/Al2O3 on the amount of NaX zeolite formed in the products was also considered.

XRD patterns of samples synthesized in the synthesis gel with different SiO2/Al2O3 molar ratios. X: (a) 4.3, (b) 4.0, (c) 3.5, (d) 2.9, (e) 2.0, (f) 1.5, (g) 1.0, and (h) 0.5. It clearly revealed that suitable SiO2/Al2O3 ratio for NaX zeolite synthesis was in the range of 1.5–3.5, higher molar ratio was suitable for the NaA zeolite generated.Figure optionsDownload as PowerPoint slideHighlights
► Crystallization temperature determined whether or not NaX zeolite was formed.
► Suitable SiO2/Al2O3 ratio for NaX zeolite synthesis was in the range of 1.5–3.5.
► Elemental Si/Al ratios of NaX zeolites were determined.
► Low SiO2/Al2O3 favored the formation of crystals with bigger mean particle sizes.