Síntese da zeólita ZSM-5 com adição de sementes, empregando-se diferentes fontes de silício

Abstract

The ZSM-5 zeolite is used in various processes in the petroleum refining and petrochemical, this is possible due to properties such as acid catalyst and high hydrothermal stability. Whereas it is a material of great commercial interest, it is essential that synthesize zeolite in the absence of organic compounds (SDAs), a factor that increases the production cost of these materials. Thus it is necessary the development of new synthetic methodologies for obtaining this material more economically. In this context, the aim of the study was to synthesize ZSM-5 zeolite by hydrothermal method by varying several parameters, such as silica source, SAR, OH/SiO2 reason, utilization of seeds and crystallization time in order to achieve shorter times in the formation of crystalline material. In the synthesis of these materials were used: aluminum sulphate octadecahydrate as an aluminum source, silica gel, sodium silicate as silicon source, sodium hydroxide as sodium source and sulfuric acid. Samples of commercial ZSM-5 CBV 2314 were also employed in the synthesis gel as crystallization seeds. All samples synthesized were characterized by XRD. However, only the sample used as a reference standard was also characterized by FT-IR, TG / DTA and BET in order to understand its physicochemical properties. The XRD analyses indicated the formation of ZSM-5 zeolite for all sources of silica used, however, best results were obtained with sodium silicate as a precursor source of silicon, SiO2/Al2O3 ratio = 50. The samples with the SAR’s 25 and 100 obtained concurrent phases at times greater than 15 and 24 hours, respectively. The spectra in the infrared region confirmed absorption bands characteristic of ZSM-5 zeolite. The thermal analysis showed two stages of weight loss, the first related to the removal of physically adsorbed water and the second to the desorption of the molecule of ammonia, as ZSM-5 commercial in its ammonia form was used as a seed. The results of BET, in turn, showed type I isotherm and high value of specific area, typical characteristics of microporous solids. In microscopy, it could be observed crystallites in the prismatic form with different sizes in length, consistent with the literature. The results showed that synthetic methodologies were effective in formations of crystals of ZSM-5. In this sense, this study showed the sodium silicate as silicon source most appropriate with SiO2/Al2O3 ratio = 50, OH/SiO2 = 0.15 and 10% of seeds, which revealed 100% of crystalline material in 13 hours of synthesis to 170 °C. So, it was possible to propose a plausible rout of synthesis to the zeolite studied.