Síntese e avaliação catalítica da zeólita mordenita com sistema hierárquico de poros na presença de glutamato monossódico

Abstract

Mordenite is a zeolite with a relatively high Si/Al ratio, with values between 5 and 20, which has potential in the field of catalysis in different industrial processes, such as hydrocracking, hydroisomerization and alkylation reactions, due to its high acidity and thermal stability. However, mordenite is generally considered a one-dimensional pore system, which causes diffusional limitations to the active sites. To overcome this issue, introducing mesopores is a appropriate approach. The present work promoted the study of a new approach to the synthesis of the mordenite zeolite using monosodium glutamate via hydrothermal method at 170 ºC in an oven with agitation of 60 rpm at different crystallization times (2 to 48 h). Zeolites were characterized by X-ray diffraction, X-ray energy dispersion spectroscopy, scanning electron microscopy, thermogravimetric analysis, adsorption/desorption of nitrogen and temperatureprogrammed desorption of ammonia. The selected samples were evaluated in the n-hexane and ultra-high molecular weight polyethylene cracking reactions. The materials were obtained with high crystallinity, with the increment in the Si/Al ratio and decrease in the density of acid sites with the increase in the monosodium glutamate content. Thermal analysis revealed complete removal of the amino acid salt from the zeolite structure after washing. The micrographs showed crystal clusters of <10 μm with variable geometry and partial disaggregation of the crystals with the use of glutamate. Nitrogen adsorption/desorption measurements simultaneously indicated an improvement in micro and mesoporosity for the materials synthesized with monosodium glutamate/alumina ratio of 2 and 4, with an increase of 8% and up to 33% in the volume of micropores and mesopores, respectively. The catalytic tests of nhexane cracking resulted in a higher tendency for the formation of olefins. Lower values for the apparent activation energy were obtained in the thermocatalytic degradation of ultra-high molecular weight polyethylene in the presence of zeolites, with a percentage reduction ranging from 19 to 36% compared to pure polymer. This work provided new perspectives for the synthesis of micro-mesoporous mordenite zeolite through the use of low cost and high availability compounds such as amino acids and their derived salts.