Zeolites comprising an MTT framework and their preparation

Abstract

This invention provides zeolites comprising ZSM-23 and processes for the preparation of zeolites comprising ZSM-23. One of these zeolites is ZSM-23, and other zeolites are hybrid compositions comprising an MTT framework and an MFI framework, often a combination of ZSM-23 and ZSM-5. A process for preparing a zeolite composition comprising an MTT framework.

Description

C2-8128 ZEOLITES COMPRISING AN MTT FRAMEWORK AND THEIR PREPARATION CROSS REFERENCE TO RELATED APPLCIATION

[0001] The present application claims priority to U.S. Provisional Patent Application No. 63 / 613,169, filed December 21, 2023, which application is incorporated herein in its entirety. TECHNICAL FIELD

[0002] This invention relates to zeolites comprising MTT and MFI frameworks, and methods for making these zeolites. BACKGROUND

[0003] Zeolites have porous structures, and are known for their catalytic properties, and zeolites are often included as components of fluid cracking catalysts. MTT-type zeolites, especially ZSM- 23, have unique properties but are often challenging to prepare, especially on a commercial manufacturing scale. MTT-type zeolites are sometimes referred to as "one-dimensional" zeolites because they have parallel one-dimensional channels in their structures.

[0004] MTT zeolites, including ZSM-23, are often synthesized in the presence of organic templates, although the organic templates pose environmental and health risks. Seed-directed synthesis in the absence of organic templates has been reported for some zeolites, but do not always for zeolites having desired properties.

[0005] Improved methods for preparing MTT zeolites are continually sought. SUMMARY OF THE INVENTION

[0006] This invention provides zeolites comprising an MTT framework. One of these zeolites is ZSM-23, and other zeolites are hybrid compositions comprising an MTT framework and an MFI framework, often a combination of ZSM-23 and ZSM-5. The hybrid zeolite compositions are more stable than MTT frameworks alone. In the processes of this invention, an organic template is not necessary to form either an MTT framework or an MTT / MFI hybrid composition. The MTT / MFI hybrid compositions are comprised of in situ coproduced MTT and MFI frameworks, often a combination of ZSM-23 and ZSM-5.C2-8128

[0007] An embodiment of this invention is a hybrid composition comprised of an MTT framework and an MFI framework, the MTT and MFI frameworks being physically and / or chemically inseparable from each other without perturbation, wherein the zeolite composition has a silicon to aluminum molar ratio of about 55:1 or less.

[0008] Another embodiment of this invention is a process for producing a zeolite composition comprising an MTT framework, which process comprises: A) forming an alcohol-free aqueous zeolite precursor mixture comprising a silicon source, an aluminum source, a sodium source, water, and ZSM-23 seed crystals, wherein the sodium to silicon molar ratio is in the range of about 0.15:1 to about 0.5:1, and the ZSM-23 seed crystals are in an amount of about 1 wt% to about 50 wt%, relative to the total weight of the solids in the aqueous zeolite precursor mixture; B) optionally heating the aqueous zeolite precursor mixture at a temperature of about 25°C to about 300°C for about 1 minute to about 200 hours to form a heat-treated precursor; and C) crystallizing the aqueous zeolite precursor mixture or the heat-treated precursor by heating the aqueous zeolite precursor mixture or the heat-treated precursor at a temperature of about 60°C to about 300°C for about 1 minute to about 72 hours. The process usually produces either an MTT framework, often ZSM-23, or a hybrid composition comprised of an MTT framework and an MFI framework, often ZSM-23 and ZSM-5.

[0009] These and other embodiments and features of this invention will be still further apparent from the ensuing description and appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 has electron micrographs of a hybrid MTT / MFI zeolite composition of the invention from Example 1, obtained by scanning electron microscopy (SEM) at two different magnifications.

[0011] Fig. 2 is an X-ray powder diffraction (XRD) pattern for a calcined MTT / MFI hybrid composition of this invention from Example 1.

[0012] Fig. 3 shows argon adsorption isotherms for MTT / MFI hybrid compositions of this invention, produced according to a process of the invention, one composition produced using 5C2-8128 wt% ZSM-23 seeds in Example 1 (A), and the other composition produced using 30 wt% ZSM- 23 seeds in Example 4 (B).

[0013] Fig. 4 is an X-ray powder diffraction (XRD) pattern for a calcined MTT framework zeolite produced by a process of this invention in Example 9.

[0014] Fig. 5 is an argon adsorption isotherm for an MTT framework zeolite produced by a process of this invention in Example 9.

[0015] The Figures illustrate embodiments of specific aspects of the invention, and are not intended to impose limitations on the scope of the invention. FURTHER DETAILED DESCRIPTION OF THE INVENTION

[0016] Several types of zeolite compositions are provided by this invention. One type is composed of the fresh zeolite compositions which are the "as synthesized" zeolite compositions. Another type is composed of steamed zeolite compositions. Still another type is composed of calcined zeolite compositions.

[0017] As used throughout this document, the terms "co-crystal," "hybrid," and MTT / MFI (or ZSM-23 / ZSM-5) refer to zeolite compositions of this invention comprising MTT and MFI frameworks (or ZSM-23 and ZSM-5) which are physically and / or chemically inseparable from each other without perturbation.

[0018] The zeolite compositions of this invention have an MTT framework constituent (often ZSM-23, which has MTT topology), and an MFI framework constituent (often a pentasil zeolite, sometimes ZSM-5, which have MFI topology). These MTT / MFI hybrid zeolite compositions of the invention have a silicon to aluminum molar ratio of about 55:1 or less, typically about 10:1 to about 55:1, preferably about 20:1 to bout 45:1, more preferably about 25:1 to about 45:1, even more preferably about 25:1 to about 40:1. The performance of these hybrid or co-crystal zeolite compositions of this invention is increased as compared to physical blends of MTT framework zeolites and MFI framework zeolites, at least for olefin cracking.

[0019] So far as is presently known, there is no non-perturbative method for physically or chemically separating the MTT framework component from the MFI framework component of the hybrid MTT / MFI zeolite compositions of this invention. In other words, their respective topologies as combined in the hybrid compositions of this invention are believed to be physically or chemically inseparable without destroying their topologies. The zeolite compositions of thisC2-8128 invention cannot be formed by physically mixing a preformed MTT framework zeolite and a preformed MFI framework zeolite. Fig.1 has SEM images of an MTT / MFI hybrid composition of this invention showing the crystallinity of the composition at two different magnifications.

[0020] The fresh hybrid MTT / MFI zeolite compositions of this invention have powder x-ray diffraction (XRD) patterns that can be interpreted as hybrids or co-crystals comprising an MTT framework and an MFI framework, often ZSM-23 and ZSM-5. In the XRD patterns of the hybrid MTT / MFI zeolite compositions, the ratio of intensity of the peak at about 7.8° to about 7.95° 2θ to the intensity of the peak at about 19.5° to about 19.8° 2θ is typically about 7.0 to about 7.8; this is visible in the XRD pattern shown in Fig. 2. From the XRD patterns, it appears that the MTT component of the hybrid compositions is typically about 25% to about 95%, often about 30% to about 85% of the hybrid composition, with the remainder being an MFI component. The hybrid compositions generally have surface areas of about 100 m2 / g or more, preferably about 120 m2 / g or more. The micropore volume in the hybrid compositions is often about 0.05 cm3 / g or more, preferably about 0.075 cm3 / g or more.

[0021] In some embodiments, the MTT / MFI hybrid compositions have about 25% to about 95% MTT, preferably about 30% to about 85% MTT, with the remainder being MFI, and surface areas of about 100 m2 / g or more, and / or micropore volumes of about 0.05 cm3 / g or more. In other embodiments, the MTT / MFI hybrid compositions have about 30% to about 85% MTT, with the remainder being MFI, and surface areas of about 120 m2 / g or more, and micropore volumes of about 0.05 cm3 / g or more, preferably about 0.075 cm3 / g or more. More preferably, the MTT component is ZSM-23, and the MFI component is a pentasil zeolite, preferably ZSM-5.

[0022] Another feature of the MTT / MFI hybrid compositions of the invention is shown in the argon adsorption isotherms in Fig. 3, in which A is an MTT / MFI hybrid composition produced using 5 wt% ZSM-23 seeds, and B is an MTT / MFI hybrid composition produced using 30 wt% ZSM-23 seeds. The argon adsorption isotherm curves for both MTT / MFI hybrid compositions show an absence of structural defects such as micropore blockage (sometimes referred to as closed behavior), although composition A in Fig.3 has an indication of structural irregularity at P / P0of about 0.4.

[0023] The MTT / MFI hybrid compositions of this invention can be made in the processes of this invention. The processes of this invention can also produce MTT framework zeolites, especially ZSM-23.C2-8128

[0024] In the processes of this invention, some of the steps may be considered to be carried out under hydrothermal conditions because the step or steps involve heating in the presence of water (sometimes in the form of steam).

[0025] The processes of this invention utilize an aqueous zeolite precursor mixture, which is comprised of water, a silicon source, an aluminum source, a sodium source, and ZSM-23 seeds. The aqueous zeolite precursor mixture usually has a pH in the range of about 9 to about 11. In some instances, the addition of an acid or a base may be needed to reach the desired pH value.

[0026] The amount of aluminum source and silicon source present in the aqueous zeolite precursor mixture depends on the silicon to aluminum molar ratio desired in the resulting zeolite composition to be produced. Typical silicon to aluminum molar ratios are about 10:1 to about 55:1, preferably about 20:1 to about 45:1, more preferably about 25:1 to about 45:1, and when forming an MTT / MFI hybrid composition, the silicon to aluminum molar ratio is even more preferably about 25:1 to about 40:1.

[0027] The molar ratio of sodium to silicon is generally in the range of about 0.15:1 to about 0.5:1, preferably about 0.15:1 to about 0.45:1, more preferably about 0.2:1 to about 0.4:1, even more preferably about 0.2:1 to about 0.35:1. For these molar ratios, all sources of sodium, including silicon and / or aluminum sources, sodium sources, and bases, are included when determining the molar ratio of sodium to silicon.

[0028] Suitable silicon sources include sodium silicate, sodium meta-silicate, stabilized silica sols, silica gels, polysilicic acid, tetraethyl orthosilicate (TEOS), fumed silicas, precipitated silicas, and combinations of any two or more of the foregoing.

[0029] Suitable aluminum sources include aluminum salts, such as Al2(SO4)3, AlCl3, AIPO4, Al2(HPO4)3, and Al(H2PO4)3, and water-insoluble aluminum compounds, e.g., alumina and aluminum trihydrate (Al(OH)3) such as gibbsite and bauxite ore concentrate, thermally treated aluminum trihydrate such as flash-calcined aluminum trihydrate, boehmite, pseudoboehmite, aluminum chlorohydrol, aluminum nitrohydrol, sodium aluminate, and combinations of any two or more of the foregoing. Preferred aluminum sources include aluminum sulfate.

[0030] The sodium source can be the silicon source or the aluminum source when the silicon source or aluminum source is a sodium compound, often a sodium salt. Suitable sodium sources, when the sodium source is not also the silicon source or the aluminum source, include sodium hydroxide, sodium oxide, sodium chloride, sodium bromide, sodium carbonate, sodiumC2-8128 bicarbonate, sodium amide, and combinations of any two or more of the foregoing. Combinations of one or more sodium-containing aluminum sources and / or one or more sodium-containing silicon sources with one or more sodium sources can be used. When a combination of sodium sources is used, the combination preferably includes a sodium-containing silicon source and a sodium source, for example sodium silicate and sodium hydroxide.

[0031] When an acid is used, the acid is preferably an inorganic acid. Suitable inorganic acids include sulfuric acid, phosphoric acid, nitric acid, boric acid, hydrochloric acid, and hydrobromic acid. Other acids, including organic acids, can be used if desired.

[0032] When a base is used, the base is preferably an inorganic base. Suitable inorganic bases include lithium hydroxide, sodium hydroxide, sodium oxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, aluminum hydroxide, gallium hydroxide, indium hydroxide, and combinations of any two or more of the foregoing. Other bases can be used.

[0033] Water is generally used in an amount to achieve the desired concentration and / or water- to-silicon molar ratio in the aqueous zeolite precursor mixture. The water in the molar ratios includes water introduced to the aqueous zeolite precursor mixture with other components, such as the silicon source. Molar ratios of water to silicon are typically in the 1:1 to about 50:1, preferably in the range of about 2:1 to about 35:1, more preferably in the range of about 5:1 to about 30:1, still more preferably about 7:1 to about 25:1.

[0034] The ZSM-23 seeds are generally used in an amount of about 1 to about 50 wt%, preferably about 2 wt% to about 45 wt%, more preferably about 4 wt% to about 40 wt%, even more preferably about 5 wt% to about 35 wt%, relative to the total weight of the solid components of the aqueous zeolite precursor mixture.

[0035] The MTT framework compositions and the hybrid zeolite compositions comprising an MTT framework and an MFI framework can be produced pursuant to this invention, by combining a silicon-containing ingredient, an aluminum-containing ingredient, a sodium-containing ingredient, water, and ZSM-23 seed crystals.

[0036] In some embodiments, the silicon to aluminum molar ratio is about 10:1 to about 250:1; the sodium to silicon ratio is about 0.15:1 to about 0.45:1; the water to silicon ratio is about 1:1 to about 50:1; and / or about 2 wt% to about 45 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.C2-8128

[0037] In a preferred embodiment, the silicon to aluminum molar ratio is about 10:1 to about 250:1; the sodium to silicon ratio is about 0.15:1 to about 0.45:1; the water to silicon ratio is about 1:1 to about 50:1; and about 2 wt% to about 45 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

[0038] In other embodiments, the silicon to aluminum molar ratio is about 25:1 to about 150:1; the sodium to silicon ratio is about 0.2:1 to about 0.4:1; the water to silicon ratio is about 2:1 to about 35:1; and / or about 4 wt% to about 40 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

[0039] In a preferred embodiment, the silicon to aluminum molar ratio is about 25:1 to about 150:1; the sodium to silicon ratio is about 0.2:1 to about 0.4:1; the water to silicon ratio is about 2:1 to about 35:1; and about 4 wt% to about 40 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

[0040] In still other embodiments, the silicon to aluminum molar ratio is about 20:1 to about 100:1; the sodium to silicon ratio is about 0.2:1 to about 0.35:1; the water to silicon ratio is about 5:1 to about 30:1; and / or about 5 wt% to about 35 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

[0041] In a preferred embodiment, the silicon to aluminum molar ratio is about 20:1 to about 100:1; the sodium to silicon ratio is about 0.2:1 to about 0.35:1; the water to silicon ratio is about 5:1 to about 30:1; and about 5 wt% to about 35 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

[0042] To form the aqueous zeolite precursor mixture, the silicon source, aluminum source, sodium source, water, and ZSM-23 seeds are combined. The combining can be accomplished by any of the methods known in the art for preparing aqueous zeolite precursor mixtures. The components can be combined in any order; preferably, the ZSM-23 seeds are the last ingredient combined. The aqueous zeolite precursor mixture typically contains about 25 wt% solids or less, relative to the total weight of the aqueous zeolite precursor mixture, but greater or lesser amounts of solids can be used as desired.C2-8128

[0043] In the processes of this invention, once the aqueous zeolite precursor mixture is formed, the crystallizing step may be carried out. In some embodiments, an optional heating step is performed before carrying out the crystallization step. Because the processes of this invention can be carried out with or without the optional heating step, the process steps include a) crystallizing the aqueous zeolite precursor mixture, or b) heating and then crystallizing.

[0044] The aqueous zeolite precursor mixture is alcohol-free in the sense that no alcohol is added to or part of the mixture, although adventitious amounts of alcohol (e.g., less than 1 wt%) may be present in the aqueous zeolite precursor mixture. When an optional heating step is carried out, no alcohol is introduced before or after the optional heating step, so that the processes of this invention are considered to be alcohol-free.

[0045] The crystallization process may be started immediately after forming the aqueous zeolite precursor mixture. In some embodiments, the aqueous zeolite precursor mixture is stirred for a period of time at ambient temperature (without heating) before the crystallization step, typically for a minute or longer, usually about one minute to about one or two hours, preferably about one minute to about thirty minutes. In other embodiments, it is preferred to subject the aqueous zeolite precursor mixture to an optional heating step before the crystallization step.

[0046] In an optional heating step, the aqueous zeolite precursor mixture is heated at one or more temperatures in the range of about 25°C to about 300°C, preferably about 40°C to about 230°C, more preferably about 50°C to about 175°C, still more preferably about 75°C to about 150°C. This optional heating step is generally conducted in a sealed vessel under autogenous pressure with or without agitation, preferably with agitation. The duration of the heating step is typically about 1 minute to about 200 hours, preferably about 15 minutes to about 48 hours, more preferably about one hour to about 36 hours. The heating step can be carried out in a vessel, process piping, a heat exchanger, or other process equipment.

[0047] As used throughout this document, the phrase "heat-treated precursor" refers to the substance obtained at the end of the optional heating step. In some instances, the heat-treated precursor appears to be a gel, and in other instances the heat-treated precursor appears to be a slurry, and in other instances appears to be a paste. When the amount of water in the heat-treated precursor is very low, the heat-treated precursor may have a powder-like appearance.

[0048] In the crystallizing step, the aqueous zeolite precursor mixture or heat-treated precursor is heated at one or more temperatures in the range of about 60°C to about 300°C, preferably aboutC2-8128 100°C to 250°C, more preferably about 150°C to about 200°C. The crystallizing step is carried out for a time of about 1 minute to about 72 hours, preferably about 15 minutes to about 36 hours, more preferably about 30 minutes to about 30 hours, even more preferably about one hour to about 24 hours. The crystallizing step is sometimes conducted in a sealed vessel under autogenous pressure. The crystallization can be conducted with or without agitation, and is preferably conducted with agitation. In some crystallization steps, the water removed is in vapor form, and preferably is vented, preferably periodically, from the reactor or reaction zone in which the crystallization is conducted.

[0049] As is known in the art, the products produced by zeolite preparation processes can vary from the desired product(s). In the processes of this invention, an amorphous phase is sometimes formed in the MTT / MFI co-crystal zeolite compositions. At a given set of process conditions, an amorphous phase is obtained in the product when crystallization time is too short and / or the crystallization temperature is too low. Within a given set of process parameters, the crystallization times and temperatures to avoid formation of an amorphous phase can be determined. Similarly, the processes of this invention sometimes form MFI frameworks, rather than an MTT / MFI co- crystal zeolite composition. At a given set of process conditions, an MFI framework zeolite is obtained as the product when crystallization time is too long. Within a given set of process parameters, the crystallization time to minimize or avoid formation of a product containing an MFI framework without an MTT framework component can be determined.

[0050] In some instances, the processes of this invention sometimes form an MTT framework zeolite and not an MTT / MFI co-crystal zeolite composition. At a given set of process conditions, one or more of the process parameters can be varied to determine whether an MTT framework zeolite or an MTT / MFI co-crystal zeolite composition is formed, and thus the parameters of the processes of this invention can be adjusted to form an MTT framework zeolite or an MTT / MFI co-crystal zeolite composition as desired.

[0051] In the XRD patterns of MTT framework zeolites formed by the processes of this invention, the ratio of intensity of the peak at about 7.8° to about 7.95° 2θ to the intensity of the peak at about 19.5° to about 19.8° 2θ is typically about 0.92 to about 1.1; this is visible in the XRD pattern shown in Fig.4.

[0052] Another feature of the MTT framework zeolites formed by the processes of this invention is shown in the argon adsorption isotherm in Fig.5. The argon adsorption isotherm curve for theC2-8128 MTT framework zeolite shows an absence of structural defects such as micropore blockage, although there is an indication of structural irregularity at P / P0slightly above about 0.4.

[0053] The zeolite compositions of the present invention may be used in catalysts for cracking, at one or more elevated temperatures, a hydrocarbon feed, such as a feed comprised of a gaseous olefine or a mixture of gaseous olefins.

[0054] Olefin cracking can be representative of more complex catalytic cracking processes such as fluidized catalytic cracking (FCC) in refining applications. FCC catalysts and FCC additives containing ZSM-5 materials are well-established for use in FCC units to convert gasoline range components, in particular gasoline range olefins, to lighter olefins, such as propylene and / or butene and / or ethylene. Similarly, the zeolite compositions of the present invention may demonstrate improved olefin cracking compared to a typical ZSM-5 material and thus can also be used as a component in a FCC catalyst and / or a FCC additive to improve the light olefin yields during fluidized catalytic cracking when used as a substitute or in addition to more conventional zeolites such as ZSM-5.

[0055] In a typical olefin cracking process, a gaseous olefin or mixture of gaseous olefins, optionally in combination with an inert gas, usually helium, nitrogen, and / or argon, is brought into contact with an MTT / MFI co-crystal zeolite composition of the invention at one or more elevated temperatures, typically about 200°C to about 650°C, preferably about 300°C to about 550°C. The olefins typically have four to about eight carbon atoms; olefins having six carbon atoms, especially 1-hexene, are preferred. Some of the MTT / MFI hybrid zeolite compositions produced in the practice of this invention, especially ZSM-23 / ZSM-5 hybrid zeolite compositions, exhibit improved olefin yields, especially propylene yields and / or yields of butene and ethylene. In the olefin cracking processes, the MTT / MFI co-crystal zeolite compositions of the invention have the same features and preferences described above.

[0056] In addition, the zeolite compositions of the instant invention may be used to improve the performance of adsorbents, alkylation catalysts, isomerization catalysts, oligomerization catalysts, catalysts used in the cracking of biogenic or waste plastic-containing feedstocks, catalysts used in the alcohol-to-jet fuel applications, including alcohol dehydration, and methanol-to-olefins, methanol-to-gasoline, and methanol-to-jet fuel processes and technologies.

[0057] The following examples are presented for purposes of illustration, and are not intended to impose limitations on the scope of this invention.C2-8128 EXAMPLES

[0058] For characterization of the zeolites in the Examples and accompanying Tables, one or more of the following characterization methods were employed.

[0059] The specific surface area, more particularly the Brunauer-Emmett-Teller specific surface area (BET) surface area, was determined by argon adsorption at 87 K.

[0060] The mesopore surface area (MeSA) was determined by a t-plot method from data generated by an argon adsorption at 87 K.

[0061] The micropore volume was determined by nonlocal density functional theory (NLDFT or DFT) calculations from measured argon adsorption isotherms following examples in the literature including Thommes, M., "Textural Characterization of Zeolites and Ordered Mesoporous Materials by Physical Adsorption," in Stud. Surf. Sci. Catal., vol.168, J. Cejka et al., Oxford, UK: Elsevier B.V., 2007, 495-524.

[0062] In the tables below, PV is an abbreviation for pore volume; MiPV and μPV are abbreviations for micropore volume.

[0063] Powder x-ray diffraction (XRD). The x-ray powder diffraction analyses were performed on a D8 ADVANCE powder diffractometer (Bruker Inc.) which used a CuKα anode as the x-ray source (λ=1.54060 Å).

[0064] Catalytic results were determined with an inline gas chromatograph (GC; Agilent 6890) equipped with an FID detector was used to obtain catalytic conversion and product yields on a wt% carbon basis. Conversion was calculated by subtracting the total GC area of remaining C6olefins (C6=isomerization products) in the product from the feed hexene and dividing by the feed hexene. conversion (%) = (C6=feed − C6=products) / (C6=feed) x 100 Relative product yields were calculated by dividing the specific product's GC area by the total area. Product selectivity was calculated by dividing the product yield by the conversion. The hydrogen transfer index (HTI) is the ratio of isobutane divided by the total C4hydrocarbons present (isobutane, n-butane, isobutene, n-butenes and butadienes). EXAMPLE 1

[0065] In a flask were combined water glass (sodium silicate, aq., 33.05 g, 37.64%), aluminum sulfate (aq., 3.34 g, 27.18%), H2SO4, (aq., 4.74 g, 30%), water (33.36 g), and ZSM-23 seeds (0.51 g) to form an aqueous zeolite precursor mixture. The combined ingredients (aqueous zeolite precursor mixture) were stirred at 25°C for 10 minutes to form a gel. The flask containing the gel was transferred to an oven, and heated and stirred at 170 °C for about 24 hours to obtain a crystalline material comprising ZSM-23 and ZSM-5. The crystalline material comprising ZSM- 23 and ZSM-5 was calcined at 500°C for one hour and subjected to several measurements. Some of the reagent molar ratios and properties of the obtained crystalline hybrid material containing ZSM-23 and ZSM-5 are summarized in Table 1A. Fig. 1 shows electron micrographs of the obtained crystalline hybrid material containing ZSM-23 and ZSM-5, and Fig.3A shows an argon adsorption isotherm for the obtained crystalline hybrid material containing ZSM-23 and ZSM-5. The XRD peaks for a calcined sample of the obtained crystalline hybrid material containing ZSM- 23 and ZSM-5 are summarized in Tables 1B and 1C; the XRD pattern corresponding to Table 1B is shown in Fig.2. TABLE 1A Si to Al molar ratio (SAR) 30:1 Na to Si molar ratio 0.3:1 water to Si molar ratio 20:1 ZSM-23 seeds*5 wt% BET surface area 262.7 m2 / g mesopore surface area 55.7 m2 / g (MeSA) DFT micropore vol.0.118 cm3 / g*Relative to the total weight of the solid ingredients. TABLE 1B ZSM-23 / ZSM-5 Peak Position d-spacing (Ǻ) Rel. intensity (I / I0) 7.94 11.12 100 Calcined 8.22 10.75 158.85 9.98 47 9.09 9.72 17 13.91 6.36 10 14.78 5.99 10 15.89 5.57 10 19.72 4.50 13 20.84 4.26 11 23.05 3.88 61 23.27 3.82 38 23.67 3.76 15 23.89 3.72 35 24.37 3.65 21

[0066] From Table 1B, the intensity ratio of the peak at 7.94° 2θ to the peak at 19.72 ° 2θ can be calculated, and is 7.54. TABLE 1C ZSM-23 / ZSM-5 Peak Position d-spacing (Ǻ) Rel. intensity (I / I0) 7.82 11.29 100 8.72 10.13 56 8.98 9.84 13 Steamed 14.65 6.04 13 20.77 4.27 12 22.93 3.88 47 23.18 3.83 21C2-8128 23.80 3.74 30 EXAMPLE 2

[0067] Several runs to make crystalline material comprising ZSM-23 and ZSM-5 were conducted in a manner similar to Example 1, varying the Na to Si molar ratio and the crystallization time. For all runs, the components were sodium silicate, aluminum sulfate, H2SO4(aq., 30%), water, and ZSM-23 seeds; the molar ratios in all of the runs were Si:Al = 30:1; H2O:Si = 20:1; and ZSM-23 seeds (10 wt% relative to the total weight of solids in the mixture). In all of the runs, the combined ingredients were stirred at 25°C for 10 minutes to form a gel, and the flask containing the gel was transferred to an oven, and heated and stirred at 170 °C, and crystalline materials containing ZSM-23 and ZSM-5 were obtained. Results are summarized in Table 2. TABLE 2 Run Product Na:SiCryst.Cryst. T time a* ZSM-23+ZSM-5+amorph. 0.1:1 170°C 24 hr. b ZSM-23 + ZSM-5 0.2:1 170°C 24 hr. c ZSM-23 + ZSM-5 0.3:1 170°C 24 hr. * Comparative run. EXAMPLE 3

[0068] Several runs to make crystalline material comprising ZSM-23 and ZSM-5 were conducted in a manner similar to Example 1, varying the H2O to Si molar ratio. For all runs, the components were sodium silicate, aluminum sulfate, H2SO4(aq., 30%), water, and ZSM-23 seeds; the molar ratios in all of the runs were Si:Al = 30:1; Na:Si = 0.3:1; and ZSM-23 seeds (10 wt% relative to the total weight of solids in the mixture). In all of the runs, the combined ingredients were stirred at 25°C for 10 minutes to form a gel, and the flask containing the gel was transferred to an oven, and heated and stirred at 170 °C for about 24 hours, and crystalline materials containing ZSM-23 and ZSM-5 were obtained. Results are summarized in Table 3.C2-8128 TABLE 3 RunProduct H2O:SiCryst.Cryst. T time 1 ZSM-23 + ZSM-5 13.3:1 170°C 24 hr. 2 ZSM-23 + ZSM-5 15.1:1 170°C 24 hr. 3 ZSM-23 + ZSM-5 17.5:1 170°C 24 hr. 4 ZSM-23 + ZSM-5 20:1 170°C 24 hr. EXAMPLE 4

[0069] Several runs to make crystalline material comprising ZSM-23 and ZSM-5 were conducted in a manner similar to Example 1, varying the amount of ZSM-23 seed crystals. For all runs, the components were sodium silicate, aluminum sulfate, H2SO4(aq., 30%), water, and ZSM- 23 seeds; the molar ratios in all of the runs were Si:Al = 30:1; Na:Si = 0.3:1; and H2O:Si = 20:1. In all of the runs, the combined ingredients were stirred at 25°C for 10 minutes to form a gel, and the flask containing the gel was transferred to an oven, and heated and stirred at 170 °C for about 24 hours, and crystalline materials containing ZSM-23 and ZSM-5 were obtained. Results are summarized in Table 4. Fig.3B shows an argon adsorption isotherm for the one of the crystalline materials containing ZSM-23 and ZSM-5. TABLE 4 Ar BET surface area, m2 / g Ar DFT3 b 2Synthesis μPV, cm / g MeSA, m / g seedsafresh steamed retained fresh steamed retained fresh steamed 5wt% seeds 262.7 249.5 95.0%0.118 0.11698.3%55.731.710 wt% seeds 212.9 128.9 60.5% 0.114 0.0704 61.8% 4.7 12.9 20 wt% seeds 122.7 52.7 43.0% 0.058 0.0238 41.0% 29.1 14.7 30 wt% seeds 149.8 53.2 35.5% 0.0600.01829.8% 51.128.4a Relative to the total weight of solids in the aqueous zeolite precursor mixture. b MeSA is an abbreviation for mesopore surface area. EXAMPLE 5C2-8128

[0070] Several runs to make crystalline material comprising ZSM-23 and ZSM-5 were conducted in a manner similar to Example 1, varying the crystallization time. For all runs, the components were sodium silicate, aluminum sulfate, H2SO4(aq., 30%), water, and ZSM-23 seeds; the molar ratios in all of the runs were Si:Al = 36.3:1; Na:Si = 0.166:1; H2O:Si = 25:1; and 10 wt% ZSM-23 seeds (relative to the total weight of solids in the mixture). In all of the runs, the combined ingredients were stirred at 25°C for 10 minutes to form a gel, and the flask containing the gel was transferred to an oven, and heated and stirred at 170 °C, and crystalline materials containing one or more zeolites were obtained. Results are summarized in Table 5. TABLE 5 RunProductCrystallizationCrystallization timeT A*ZSM-23 + amorph. 24 hr. 170 °C B ZSM-23 + ZSM-5 30 hr. 170 °C C ZSM-23 + ZSM-5 33 hr. 170 °C D*ZSM-5 48 hr. 170 °C * Comparative run. EXAMPLE 6

[0071] Several runs to make crystalline material comprising ZSM-23 and ZSM-5 were conducted in a manner similar to Example 1, varying the crystallization temperature. For all runs, the components were sodium silicate, aluminum sulfate, H2SO4(aq., 30%), water, and ZSM-23 seeds; the molar ratios in all of the runs were Si:Al = 30:1; Na:Si = 0.3:1; H2O:Si = 20:1; and 10 wt% ZSM-23 seeds (relative to the total weight of solids in the mixture). In all of the runs, the combined ingredients were stirred at 25°C for 10 minutes to form a gel, and the flask containing the gel was transferred to an oven, and heated and stirred at the crystallization temperature for about 24 hours, and crystalline materials containing ZSM-23 and ZSM-5 were obtained. Results are summarized in Table 6. TABLE 6C2-8128 Sample Run ProductCryst. T Cryst. time10003-16-23 i ZSM-23 + ZSM-5 165°C 24 hr. 10003-16-24 ii ZSM-23 + ZSM-5 175°C 24 hr. EXAMPLE 7

[0072] Olefin cracking tests were performed in a pulsed fixed bed reactor system. Each zeolite sample (10 mg) was placed in a quartz reactor tube and heated to and maintained at 480°C in a continuous 50 mL / min He flow. 1-Hexene (1 µL injection volume) was injected into the He flow at a rate corresponding to a zeolite to olefin ratio of 10:1 (wt / wt). Results are summarized in Tables 7A and 7B below; the reported values are an average of at least two runs. C6isomers were considered to be unreacted feed. TABLE 7A C6= catalytic cracking – fresh zeolites ZSM-23 / ZSM-51std. ZSM-52Conversion 98.0% 98.6% Ethylene 7.9 wt% 8.5 wt% Propane 9.3 wt% 10.4 wt% Propylene 19.6 wt% 19.0 wt% C4=15.4 wt% 13.1 wt% Total C426.4 wt% 25.5 wt% HTI32.1 1.8 C4= / C4paraffin1.4 1.1 C4= / C3=0.78 0.69 1 Prepared at molar ratios of Si:Al = 30:1; Na:Si = 0.3:1; H2O:Si = 20:1; 5 wt% ZSM-23 seeds (relative to the total weight of solids in the mixture); 24 hr. crystallization time; 170°C crystallization temperature. 2 Comparative run; standard ZSM-5 was prepared by techniques known in the art, and is equivalent to commercially-available ZSM-5.C2-8128 3 Hydrogen transfer index. TABLE 7B C6=catalytic cracking – steamed zeolites Zeolite ZSM-23 / ZSM-51std. ZSM-52Sample size32.5 mg 5 mg 10 mg 15 mg 5 mg 10 mg 15 mg 20 mg Conversion 28.6 % 44.3% 62.9% 74.0% 15.9% 39.66 55.2% 68.7% Ethylene, wt% 1.2 1.8 2.7 3.3 0.7 1.64 2.3 2.9 Propane, wt% 0.06 0.12 0.22 0.33 0.03 0.09 0.18 0.28 Propylene, wt% 13.0 18.6 25.6 29.0 8.3 18.4 23.9 28.0 C4=, wt% 7.9 13.1 19.4 23.7 3.7 10.6 15.8 20.8 BTEX4, wt% 0..13 0.03 0.04 0.22 0.08 0.02 0.02 0.08 HTI50.0 0.0 0.0 0.0 0.0 0.0 0.0 0.01Prepared at molar ratios of Si:Al = 301; Na:Si = 0.3:1; H2O:Si = 20:1; 5 wt% ZSM-23 seeds (relative to the total weight of solids in the mixture); 24 hour crystallization time; 170°C crystallization temperature.2Comparative run; standard ZSM-5 was prepared by techniques known in the art, and is equivalent to commercially-available ZSM-5.3Amount of zeolite used in the catalytic run.4Benzene, toluene, ethylbenzene, and xylenes.5Hydrogen transfer index. EXAMPLE 8

[0073] Olefin cracking tests were performed in a pulsed fixed bed reactor system. All zeolite samples were steamed at 788°C for 5 hours, 100%, before the catalytic run. Each zeolite sample (10 mg) was placed in a quartz reactor tube and heated to and maintained at 480°C in a continuous 50 mL / min He flow. 1-Hexene (1 µL injection volume) was injected into the He flow at a rate corresponding to a zeolite to olefin ratio of 10:1 (wt / wt). Results are summarized in Table 8 below; the reported values are an average of at least two runs. C6isomers were considered to be unreacted feed.C2-8128 TABLE 8 Zeolite Conversion C3=yield C4=yield Steamed ZSM-23 / ZSM-5162.9% 25.6% 19.4% Physical blend: 34.8% 16.4% 9.1% 25% steamed ZSM-23 + 75% steamed ZSM-52Physical blend: 50% steamed ZSM-23 + 50% steamed ZSM-52 22.9% 11.8% 5.4%Physical blend: 75% steamed ZSM-23 + 25% steamed ZSM-52 13.3% 7.4% 2.9%ZSM-23, std.21.5% 1.1% 0.1% 1 Results reported above in Table 7B; prepared at molar ratios of Si:Al = 301; Na:Si = 0.3:1; H2O:Si = 20:1; 5 wt% ZSM-23 seeds (relative to the total weight of solids in the mixture); 24 hour crystallization time; 170°C crystallization temperature. 2 Comparative run; the ZSM-23 and the ZSM-5 were prepared by techniques known in the art, and are equivalent to commercially-available ZSM-23 and ZSM-5. EXAMPLE 9 In a flask were combined water glass (sodium silicate, aq., 31.50 g, 37.64%), aluminum sulfate (aq., 2.03 g, 27.18% g), H2SO4, (aq., 4.98 g, 30%), water (35.45 g), and ZSM-23 seeds (1.03 g) to form an aqueous zeolite precursor mixture; the molar ratios were Si:Al = 45:1; Na:Si = 0.3:1; H2O:Si = 34:1; and 10 wt% ZSM-23 seeds (relative to the total weight of solids in the mixture). The combined ingredients were stirred at 25°C for 10 minutes to form a gel. The flask containing the gel was transferred to an oven and heated at 170°C for about 24 hours to obtain a crystalline material. Some of the properties of the obtained crystalline material, comprising mostly or completely ZSM-23, are summarized in Table 9A. Fig.5 shows an argon adsorption isotherm for the obtained crystalline material comprising mostly or completely ZSM-23. The XRD peaks for a calcined (500°C, 1 hour) sample of the obtained crystalline material comprising mostly or completely ZSM-23 are summarized in Tables 9B and 9C; the XRD pattern corresponding to Table 9B is shown in Fig.4. TABLE 9A Fresh ZSM-23 Steamed ZSM-23RetentionC2-8128 Ar BET surface area (m2 / g) 141.1 29.5 20.9% Mesopore surface area (m2 / g) 37.0 16.9 45.5% DFT MiPV*(cm3 / g) 0.066 0.010 15.1% TABLE 9B ZSM-23 Peak Position d-spacing (Ǻ) Rel. intensity (I / I0) 7.80 11.32 98 8.07 10.95 100 8.78 10.07 42 11.27 7.85 53 19.59 4.53 100 Calcined 19.97 4.44 16 20.83 4.26 74 22.79 3.90 98 23.14 3.84 8 23.75 3.74 45 23.97 3.71 86 25.91 3.44 52

[0074] From Table 9B, the intensity ratio of the peak at 7.87° 2θ to the peak at 19.65° 2θ can be calculated, and is 0.98. TABLE 9C ZSM-23 Peak Position d-spacing (Ǻ) Rel. intensity (I / I0) Steamed 7.87 11.23 100 8.14 10.86 82C2-8128 8.82 10.02 34 11.33 7.81 39 19.65 4.52 49 20.90 4.25 39 22.87 3.88 39 23.87 3.73 20

[0075] Further embodiments of the invention include, without limitation:

[0076] A) A zeolite composition comprised of an MTT framework and an MFI framework, the MTT and MFI frameworks being physically and / or chemically inseparable from each other without perturbation.

[0077] B) The zeolite composition as in A), wherein the zeolite composition has a silicon to aluminum molar ratio of about 55:1 or less.

[0078] C) The zeolite composition as in A) or B) wherein the MTT framework comprises about 25% to about 95% of the zeolite composition.

[0079] D) The zeolite composition as in any one of A)-C) wherein the composition has a surface area of about 100 m2 / g or more, and optionally a micropore volume of about 0.05 cm3 / g or more.

[0080] E) The zeolite composition as in any one of A)-D) wherein the surface area is about 120 m2 / g or more.

[0081] F) The zeolite composition as in any one of A)-E) wherein the MTT framework is ZSM- 23 and / or wherein the MFI framework is a pentasil zeolite.

[0082] G) The zeolite composition as in F) wherein the pentasil zeolite is ZSM-5.

[0083] H) A process for preparing a zeolite composition comprising an MTT framework, which process comprises: a) forming an alcohol-free aqueous zeolite precursor mixture comprising a silicon source, an aluminum source, a sodium source, water, and ZSM-23 seed crystals, wherein the sodium to silicon molar ratio is in the range of about 0.15:1 to about 0.5:1, and the ZSM-23 seedC2-8128 crystals are in an amount of about 1 wt% to about 50 wt%, relative to the total weight of the solids in the aqueous zeolite precursor mixture; b) optionally heating the aqueous zeolite precursor mixture at a temperature of about 25°C to about 300°C for about 1 minute to about 200 hours to form a heat-treated precursor; and c) crystallizing the aqueous zeolite precursor mixture or the heat-treated precursor by heating the aqueous zeolite precursor mixture or the heat-treated precursor at a temperature of about 60°C to about 300°C for about 1 minute to about 72 hours.

[0084] I) The process of H) wherein the silicon source is selected from sodium silicate, sodium meta-silicate, stabilized silica sols, silica gels, polysilicic acid, tetraethyl orthosilicate, fumed silicas, precipitated silicas, and combinations of any two or more of the foregoing; and / or the aluminum source is selected from Al2(SO4)3, AlCl3, AIPO4, Al2(HPO4)3, Al(H2PO4)3, alumina, aluminum trihydrate, aluminum chlorohydrol, aluminum nitrohydrol, and sodium aluminate, and combinations of any two or more of the foregoing.

[0085] J) The process of any one of H)-I) wherein the crystallizing step is conducted at one or more temperatures in the range of about 100°C to about 250°C.

[0086] K) The process of any one of H)-J) wherein the crystallizing step is conducted for about 15 minutes to about 36 hours.

[0087] L) The process of any one of Claims H)-K) wherein the silicon to aluminum molar ratio is about 10:1 to about 250:1; the sodium to silicon ratio is about 0.15:1 to about 0.45:1; the water to silicon ratio is about 1:1 to about 50:1; and / or about 2 wt% to about 45 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

[0088] M) The process of any one of Claims H)-K) wherein the silicon to aluminum molar ratio is about 10:1 to about 55:1; the sodium to silicon ratio is about 0.2:1 to about 0.4:1; the water to silicon ratio is about 2:1 to about 35:1; and / or about 4 wt% to about 40 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

[0089] N) The process of any one of H)-M) wherein the optional heating step is conducted at one or more temperatures in the range of about 40°C to about 230°C.

[0090] O) The process of any one of H)-N) wherein the optional heating step is conducted for about 15 minutes to about 48 hours.C2-8128

[0091] P) The process of any one of H)-O) wherein the MTT framework is ZSM-23.

[0092] Q) A process for olefin cracking at one or more elevated temperatures, which process comprises bringing a gaseous olefin or mixture of gaseous olefins into contact with a zeolite composition comprised of an MTT framework and an MFI framework, the MTT and MFI frameworks being physically and / or chemically inseparable from each other without perturbation, wherein the zeolite composition has a silicon to aluminum molar ratio of about 55:1 or less.

[0093] R) The process as in Q) wherein the elevated temperature is in the range of about 200°C to about 600°C and / or wherein the gaseous olefin has four to about eight carbon atoms.

[0094] S) The process as in Q) or R) wherein the zeolite composition has a silicon to aluminum molar ratio of about 10:1 to about 55:1, and / or wherein the MTT framework comprises about 25% to about 95% of the zeolite composition

[0095] T) The process as in any one of Q)-S) wherein the MTT framework is ZSM-23 and / or wherein the MFI framework is a pentasil zeolite.

[0096] U) The process as in T) wherein the pentasil zeolite is ZSM-5.

[0097] Components referred to by chemical name or formula anywhere in the specification or claims hereof, whether referred to in the singular or plural, are identified as they exist prior to coming into contact with another substance referred to by chemical name or chemical type (e.g., another component, a solvent, or etc.). It matters not what chemical changes, transformations and / or reactions, if any, take place in the resulting mixture or solution as such changes, transformations, and / or reactions are the natural result of bringing the specified components together under the conditions called for pursuant to this disclosure. Thus, the components are identified as ingredients to be brought together in connection with performing a desired operation or in forming a desired composition. Also, even though the claims hereinafter may refer to substances, components and / or ingredients in the present tense ("comprises", "is", etc.), the reference is to the substance, component or ingredient as it existed at the time just before it was first contacted, blended or mixed with one or more other substances, components and / or ingredients in accordance with the present disclosure. The fact that a substance, component or ingredient may have lost its original identity through a chemical reaction or transformation during the course of contacting, blending or mixing operations, if conducted in accordance with this disclosure and with ordinary skill of a chemist, is thus of no practical concern.C2-8128

[0098] The invention may comprise, consist, or consist essentially of the materials and / or procedures recited herein.

[0099] As used herein, the term "about" modifying the quantity of an ingredient in the compositions of the invention or employed in the methods of the invention refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods; and the like. The term about also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not modified by the term "about", the claims include equivalents to the quantities.

[0100] Except as may be expressly otherwise indicated, the article "a" or "an" if and as used herein is not intended to limit, and should not be construed as limiting, the description or a claim to a single element to which the article refers. Rather, the article "a" or "an" if and as used herein is intended to cover one or more such elements, unless the text expressly indicates otherwise.

[0101] This invention is susceptible to considerable variation in its practice. Therefore the foregoing description is not intended to limit, and should not be construed as limiting, the invention to the particular exemplifications presented hereinabove.

Claims

C2-8128 THAT WHICH IS CLAIMED IS:

1. A zeolite composition comprised of an MTT framework and an MFI framework, the MTT and MFI frameworks being physically and / or chemically inseparable from each other without perturbation.

2. The zeolite composition as in Claim 1 wherein the silicon to aluminum molar ratio about 55:1 or less.

3. The zeolite composition as in Claim 1 wherein the MTT framework comprises about 25% to about 95% of the zeolite composition.

4. The zeolite composition as in Claim 1 wherein the composition has a surface area of about 100 m2 / g or more, and optionally a micropore volume of about 0.05 cm3 / g or more.

5. The zeolite composition as in Claim 1 wherein the surface area is about 120 m2 / g or more.

6. The zeolite composition as in Claim 1 wherein the MTT framework is ZSM-23 and / or wherein the MFI framework is a pentasil zeolite.

7. The zeolite composition as in Claim 6 wherein the pentasil zeolite is ZSM-5.

8. A process for preparing a zeolite composition comprising an MTT framework, which process comprises: A) forming an alcohol-free aqueous zeolite precursor mixture comprising a silicon source, an aluminum source, a sodium source, water, and ZSM-23 seed crystals, wherein the sodium to silicon molar ratio is in the range of about 0.15:1 to about 0.5:1, and the ZSM-23 seed crystals are in an amount of about 1 wt% to about 50 wt%, relative to the total weight of the solids in the aqueous zeolite precursor mixture; B) optionally heating the aqueous zeolite precursor mixture at a temperature of about 25°C to about 300°C for about 1 minute to about 200 hours to form a heat-treated precursor; and C) crystallizing the aqueous zeolite precursor mixture or the heat-treated precursor by heating the aqueous zeolite precursor mixture or the heat-treated precursor at a temperature of about 60°C to about 300°C for about 1 minute to about 72 hours.C2-8128 9. The process of Claim 8 wherein the silicon source is selected from sodium silicate, sodium meta-silicate, stabilized silica sols, silica gels, polysilicic acid, tetraethyl orthosilicate, fumed silicas, precipitated silicas, and combinations of any two or more of the foregoing; and / or the aluminum source is selected from Al2(SO4)3, AlCl3, AIPO4, Al2(HPO4)3, Al(H2PO4)3, alumina, aluminum trihydrate, aluminum chlorohydrol, aluminum nitrohydrol, and sodium aluminate, and combinations of any two or more of the foregoing.

10. The process of Claim 8 wherein the crystallizing step is conducted at one or more temperatures in the range of about 100°C to about 250°C.

11. The process of Claim 8 wherein the crystallizing step is conducted for about 15 minutes to about 36 hours.

12. The process of Claim 8 wherein the silicon to aluminum molar ratio is about 10:1 to about 250:1; the sodium to silicon ratio is about 0.15:1 to about 0.45:1; the water to silicon ratio is about 1:1 to about 50:1; and / or about 2 wt% to about 45 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

13. The process of Claim 8 wherein the silicon to aluminum molar ratio is about 10:1 to about 55:1; the sodium to silicon ratio is about 0.2:1 to about 0.4:1; the water to silicon ratio is about 2:1 to about 35:1; and / or about 4 wt% to about 40 wt% ZSM-23 seeds are present in the aqueous zeolite precursor mixture, relative to the total weight of the solids in the aqueous zeolite precursor mixture.

14. The process of Claim 8 wherein the optional heating step is conducted at one or more temperatures in the range of about 40°C to about 230°C.

15. The process of Claim 8 wherein the optional heating step is conducted for about 15 minutes to about 48 hours.

16. The process of Claim 8 wherein the MTT framework is ZSM-23.C2-8128 17. A process for catalytic cracking at one or more elevated temperatures, which process comprises bringing a hydrocarbon feed into contact with a zeolite composition comprised of an MTT framework and an MFI framework, the MTT and MFI frameworks being physically and / or chemically inseparable from each other without perturbation.

18. The process as in Claim 17 wherein the hydrocarbon stream is a gaseous olefin or a mixture of gaseous olefins and wherein the elevated temperature is in the range of about 200°C to about 650°C.

19. The process as in Claim 17 wherein the zeolite composition has a silicon to aluminum molar ratio of about 10:1 to about 55:1, and / or wherein the MTT framework comprises about 25% to about 95% of the zeolite composition.

20. The process as in Claim 17 wherein the MTT framework is ZSM-23 and / or wherein the MFI framework is a pentasil zeolite.