Síntese e caracterização da zeólita HZSM-5 nanocristalina com porosidade hierárquica aplicada no craqueamento de polímeros
Zeolites are widely used by the industry in catalysis processes, adsorption, separation and ion exchange. However, the presence of only micropores limits the diffusion of bulky molecules in their channels, favoring the occurrence of adverse reactions due to long residence time of the reactants an...
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| Formato: | doctoralThesis |
| Idioma: | por |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/20554 |
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| Resumo: | Zeolites are widely used by the industry in catalysis processes, adsorption,
separation and ion exchange. However, the presence of only micropores limits the
diffusion of bulky molecules in their channels, favoring the occurrence of adverse
reactions due to long residence time of the reactants and products are transported
through the micropores of the zeolite. In order to overcome this problem has been
studied in this work synthesis methods for obtaining hierarchical nanocrystalline
ZSM-5 zeolite synthesized in the absence of organic template. First it carried out a
synthesis of zeolite ZSM-5 by the seed-assisted method from an organic-templatefree
system, where the samples were synthesized utilizing three different types of
seeds: two of these based on aqueous clear solutions containing the ZSM-5
precursors (non-silanized and silanized) and the third seed based on a commercial
ZSM-5 zeolite in powder form, in order to direct the formation of the MFI structure.
The second method used was the silanization process, using as silanizante agent
phenylaminopropyltrimethoxysilane (PHAPTMS), in order to lessen or prevent the
growth of zeolitic crystals of ZSM-5, obtaining favoring smaller crystals. The
synthesis of ZSM-5 was also performed in the absence of organic template 180°C for
27 hours after addition of PHAPTMS. All synthesized samples were characterized by
several techniques, among them X Ray Diffraction (XRD), Fourier Transform Infrared
Spectroscopy (FTIR), Argon adsorption-desorption, Electronic Microscopy (SEM and
TEM), and Temperature Programmed Desorption of Ammonia (NH3-TPD). It was
noted that the use of seeds gives a higher BET surface area and causes an increase
in the external surface area outside due to the decreasing size of the crystals.
Similarly for sample functionalized with silanizante agent (MFI (PHAPTMS)), which is
the lowest a dual system of pores, the first associated with the microporosity of the
zeolite ZSM-5 (0.5 - 2 nm) and the other related to intercrystalline mesopores (2 - 6
nm), confirming the obtaining of HZSM-5 zeolite hierarchical. All samples were
synthesized globular agglomerates formed by small nanounits (30 - 90 nm) with
different size and morphology of crystals of zeolite HZSM-5 used as reference. The
catalytic tests using the cracking of low density polyethylene (LDPE) and pyrolysis of
poly(ethylene terephthalate) - PET proved that the improvement in the textural
properties of the synthesized zeolite is advantageous in such processes, with a
better performance when compared to the reference sample, generating products
which can be useful feedstocks in the petrochemical industry. |
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