Geração de porosidade secundária na zeólita ferrierita sintetizada por conversão do gel seco com adição de polímero catiônico seguido de tratamento alcalino

Abstract

Ferrierite is a medium-pore zeolite that has wide industrial application used in several reactions due to its excellent acid character, mainly in the isomerization of n-butene into isobutene, na input of great interest to the petrochemical and polymer industries. Despite this, the pore size of this material can often lead to a diffusional limitation, making it difficult for bulky molecules to access the interior of its structure. Over the years, several methods have been developed for mesopores generation in zeolitic structures. Therefore, the present work studied the creation of mesoporosity in zeolite ferrierite through direct synthesis with LUVIQUAT addition, a high molecular weight cationic polymer, as mesoporosity generator agent. Ferrierite synthesis was carried out by the vapor-phase transport dry gel conversion method using ethylenediamine as structure-directing agent. In order to improve the porosity gain, desilication was used as post-synthesis treatment. Samples were characterized by energy dispersive X-ray spectrometry, X-ray diffractometry, Fourier transform infrared spectroscopy, thermal analysis, nitrogen adsorption-desorption and scanning electron microscopy. Results obtained showed that polymer interacted well with microporous phase of ferrierite, not preventing its formation. Samples synthesized with 20, 40 and 60% LUVIQUAT showed that ferrierite had good crystallinity for 24 hours crystallization time. Zeolites presented a SiO2/Al2O3 ratio between 18 and 20, showing similarity in materials acidity. After desilication, there was a decrease in crystallinity and values of SiO2/Al2O3 ratios, due to structural silicon extraction. Thermogravimetric analyzes showed that mass loss events related to polymer organic compounds thermoxidation coincided with samples synthesized containing polymer and that the amount effectively incorporated into the materials after crystallization ranged from 3.9 to 5.1% of sample's mass. Materials synthesized with LUVIQUAT had little variation in micropores volume and increase in mesopores volume, in which sample with 40% Polymer doubled mesopores volume compared to standard sample, proving to be ideal sample among the others, forming a crystalline zeolite with physical properties superior to the properties of sample without polymer and generating higher mesopores volume. Desilication for standard sample and 20% polymer sample preserved micropores volume, and for those with 40 and 60% polymer this volume decreased. On the other hand, mesopores volume considerably increased with samples containing 40 and 60% of LUVIQUAT, reaching increases of 332.4 and 373%, respectively, compared to standard sample, showing that this post-treatment is able to increase mesopores formation for materials synthesized with polymers 3 to 6 times more than the standard material.