Abstract
ZSM-5 zeolites are highly silicate materials that have significant application in catalytic processes in petrochemistry, especially due to their high selectivity. Most reactions in the petrochemical industry are acid-catalyzed. The acidic properties of zeolite depend on the number of acid centers, i.e. the presence of hydrogen ions, and therefore, in this paper the possibility of reducing the sodium content in the pores of high silicate zeolite ZSM-5 with the modulus (SiO2 / Al2O3 = 1000) will be investigated, by applying ion exchange with hydrochloric acid. Chemical analysis of samples before and after ion exchange, and application of instrumental methods of X-Ray diffraction, FT-IR spectroscopy, and SEM analysis monitored the influence of the quantity of hydrogen ions on the chemical composition and the structure of ZSM-5 zeolite at different acid concentrations and at different exchange times. It has been shown that the application of ion exchange with hydrochloric acid can reduce the sodium content in zeolite. Even with the application of 5% HCl for 6 hours, the content of sodium in the zeolite is reduced by over 98%. A similar effect is achieved by applying more concentrated hydrochloric acid solutions for a shorter ion exchange time. By prolonging the ion exchange time, there are no significant changes in terms of the final ion exchange. On the other hand, the application of HCl solutions of higher concentrations leads to a slight decrease in the aluminum content in the zeolite, which may partially affect the structural stability of the zeolite. The results obtained by FT-IR and SEM analysis and X-Ray diffraction confirm the possibility of ion exchange with hydrochloric acid, without significant changes in the crystal structure of the zeolite.
Highlights
Zeolites are crystalline aluminosilicates composed of an ordered system of channels and cavities
It is noticed that the application of 10% HCl (Figure 10) with increasing ion exchange time shifts the peaks to the right, which indicates the dominance of the process of partial decomposition of the crystal lattice, and binding of hydrogen ions to aluminium, where aluminium ions are separated from the zeolite structure
By reviewing the literature and analyzing the obtained results, it can be concluded that the ion exchange of zeolite ZSM-5 (SiO2/Al2O3 = 1000) with hydrochloric acid can reduce the sodium content in the zeolite
Summary
Zeolites are crystalline aluminosilicates composed of an ordered system of channels and cavities. Since the silicon atom has four valence electrons, SiO4 tetrahedra are electroneutral, but when the Si4+ ion is replaced with Al3+ in the center of the tetrahedron, the crystal lattice becomes negatively charged. Because extraframework cations are bound by weak electrostatic forces to water molecules or structural atoms of silicon or aluminum, they are extremely mobile and can be exchanged in ion exchange processes without disturbing the crystal structure. This depends on the chemical composition and crystal structure of a particular zeolite [11,12,13,14]. The catalytic activity and selectivity of ZSM-5 zeolite depend on the chemical composition of the starting materials for synthesis, degree of crystallinity, temperature and crystallization time, type of template, and many other factors [9,16,17]
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