Zeolites are crystalline aluminosilicate compositions which are microporous and which are formed from corner sharing AlO2 and SiO2 tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared, are used in various industrial processes. Synthetic zeolites are prepared via hydrothermal synthesis employing suitable sources of Si, Al and structure directing agents such as alkali metals, alkaline earth metals, amines, or organoammonium cations. The structure directing agents reside in the pores of the zeolite and are largely responsible for the particular structure that is ultimately formed. These species balance the framework charge associated with aluminum and can also serve as space fillers. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure. Zeolites can be used as catalysts for hydrocarbon conversion reactions, which can take place on outside surfaces as well as on internal surfaces within the pore.
One particular zeolitic material, classified as ZSM-5, is disclosed in Beck, et al., U.S. Pat. No. 6,180,550, issued on Jan. 30, 2001. The zeolite comprises a synthetic porous crystalline material having a composition involving the molar relationship:X2O3:(n)YO2,wherein X is a trivalent element, such as aluminum, boron, iron and/or gallium, preferably aluminum; Y is a tetravalent element such as silicon and/or germanium, preferably silicon; and n is less than 25, and Wherein the slope of the nitrogen sorption isotherm of the material at a partial pressure of nitrogen of 0.4 to 0.7 and a temperature of 77° K is greater than 30.
While there are many types of zeolites, new zeolites provide for improved reaction conditions in the conversion of lower value hydrocarbon streams to higher value hydrocarbon products.