The effect of Y-zeolite acidity on m-xylene transformation reactions

Abstract

m-Xylene transformation has been studied on as-prepared H-Y and a series of dealuminated Y zeolite catalysts. The conversion of m-xylene was found to increase initially with acidity, however, decreases subsequently. It has been proposed that the high concentration of acid sites in the H-Y catalyst increases paring reaction, in addition to the well-known isomerization and disproportionation pathways. A significant decrease was observed with respect to disproportionation/paring (D/Pa) ratio versus reaction temperature. This indicates that higher activation energy is required for paring as compared to disproportionation reaction. The p-xylene/o-xylene (P/O) was established to be independent of zeolite acidity. A higher coke deposition was found for the transformation of m-xylene over the parent H-Y as compared to the highly dealuminated USY zeolite. The formation of benzene and C 2 -C 4 gases were found to be proportional to zeolite acid concentration.Keywords: m-Xylene transformation, Y zeolite, isomerization, disproportionation, paring reaction. * Corresponding author. Tel.: +966-3-860-1429; Fax: +966-3-860-4234 E-mail address: skhattaf@kfupm.edu.sa 2 IntroductionXylenes are important starting materials for some industrial processes like the production of synthetic fibers, plasticizers and resins. The major sources of these aromatic hydrocarbons are the reforming and pyrolysis gasoline, which have a higher ratio of low-valued m-xylene. A convenient way to upgrade the low-valued m-xylene consists of its transformation to o-and p-xylene. In this context, the transformation of m-xylene has been studied over different types of zeolite catalysts [1][2][3][4][5][6][7][8].There is interest in ultrastable Y-type zeolites for m-xylene transformation, partly because of their increased chemical and thermal stability, with respect to other zeolites. Y-zeolite is made ultrastable by the removal of aluminum from the framework. The dealumination can be accomplished through the use of steam [9], acid leaching [10], or by chemical treatment with hexaflourosilicate or silicon tetrachloride [11][12][13]. However, the most common procedure is hydrothermal treatment at elevated temperatures under controlled atmosphere (steaming). The resulting material, USY (ultrastable Y) zeolites, being modified in the framework Si/Al ratio, structure and acidity, usually exhibits improved reactivity, selectivity and coking behavior for a catalytic reaction, which is of great interest to the petroleum industry. Several studies have been conducted on the effect of Y-zeolite acid properties on isomerization and disproportionation of m-xylene reactions [1,5,7]. However, studies correlating the intrinsic properties of Y-zeolite to other reaction pathways, apart from isomerization and disproportionation are somewhat limited. With this in mind, the present work reports the effect of acid properties of Y-zeolite on products selectivity and various reaction pathways during m-xylene transformation in a fluidizedbed reactor. As prepared H-Y zeolite ...

Control of acidity on the external surface of zeolite Y for m-xylene isomerization using a mechanochemical neutralization method

“…3 shows the changes in the conversion of m-xylene and the selectivity to o-and p-xylene as a function of the reaction temperature for a reaction time of 1 h on the catalysts neutralized with different alkali metal oxides. Here, propane, benzene, toluene and trimethylbenzene were also found as byproducts, as reported by Inui et al [7]; however, their selectivities were disregarded as there were no target compounds in this study. The neutralized catalysts exhibited higher m-xylene conversions than the un-neutralized, as shown in A).…”

“…Therefore, an alternative route is required for the syntheses of high value o-and p-xylenes from m-xylene [1][2][3][4][5][6]. Studies on the syntheses of o-and p-xylenes using Y-type zeolites, which have the homologous structure of FAU (fauzasite), have been reported by several research groups [7,8], partly due to their increased chemical and thermal stability. Zeolite-Y is made ultra stable by the removal of aluminum from its framework.…”

“…Zeolite-Y is made ultra stable by the removal of aluminum from its framework. However, FAU has large cavities inside its crystal channel structure, which can lead to the risk of rapid coke formation [7] when the intrinsic strength and concentration of the acid sites inside the cavity are too great. Coke formation particularly occurred at the external surface of the crystals, as there is little to restrict the growth of fused-ring aromatics, i.e., the precursors of aromatic coke.…”

Kinetics of toluene methylation over USY-zeolite catalyst in a riser simulator

“…The major sources of xylene are catalytic naphtha reforming and pyrolysis of gasoline [1]. However, xylene isomers from these sources generally do not match demand proportions as chemical intermediates, and further comprise of ethyl benzene, which is difficult to separate or convert [2].…”

Inhibition of Xylene Isomerization in the Production of Renewable Aromatic Chemicals from Biomass-Derived Furans

“…27 The bimolecular pathway, associated with disproportionation on adjacent acid sites, is favored in zeolites as the Si/Al ratio decreases (greater Brønsted acid site density) and the pore size of the zeolite increases. [24][25][26]28 Considerations of reaction temperature and the greater acid site density in zeolites indicate that the bimolecular mechanism, which produces toluene and trimethylbenzene, should occur when producing p-xylene from DMF using H-Y and H-BEA zeolite. 29 The role of strong acid sites within H-Y and H-BEA for catalyzing the dehydration of Diels−Alder cycloadducts of furans, while not promoting isomerization, is of primary interest.…”