A zeolite is a crystalline hydrated aluminosilicate that can contain other metals in the framework of the zeolite crystal or that can be deposited, exchanged, or impregnated on the zeolite (i.e. on the surface or in the pores). A method for preparing a zeolite comprises: preparing an aqueous mixture of silicon oxide and sources of oxides of aluminum; and maintaining said aqueous mixture under crystallization conditions until crystals of zeolite form. In the crystalline structure, there are pores and channels that can be interconnected. The dimensions and configuration of these pores and channels allow access by molecules of certain sizes. Zeolites are used as catalysts for, among other things, isomerization, toluene disproportionation, transalkylation, hydrogenation, alkane oligomerization, and aromatization. Aromatization is a multi-step process that can comprise the steps of dehydrogenation of the hydrocarbon, cyclization of the dehydrogenated hydrocarbon, and aromatization of the cyclized hydrocarbon.
One such example of hydrocarbon aromatization is aromatization of naphtha. Naphtha is a mixture mainly of straight-chained, branched, and cyclic aliphatic hydrocarbons, light naphtha having from five to nine carbon atoms per molecule, and heavy naphtha having from seven to twelve carbon atoms per molecule. Typically, light naphtha contains naphthenes, such as cyclohexane and methylcyclopentane, and linear and branched paraffins, such as hexane and pentane. Light naphtha typically contains 60 to 99 weight percent (wt %) of paraffins and cycloparaffins. Light naphtha can be characterized as a petroleum distillate having a molecular weight range of 70 to 150 gram per mole (g/mol), a specific gravity range of 0.6 to 0.9 grams per cubic centimeter (g/cm3), a boiling point range of 50 to 320 degree Fahrenheit (° F.) (10 to 160 degree Celsius (° C.)), and a vapor pressure of 5 to 500 millimeter of mercury (mmHg) at room temperature. Light naphtha can be obtained from crude oil, natural gas condensate, or other hydrocarbons streams by a variety of processes, e.g., distillation.
A zeolite with one or both of improved selectivity and conversion for naphtha aromatization is desirable.
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