Molecular sieve SSZ-91, method for preparing SSZ-91, and use of SSZ-91

Abstract

To provide a family of new crystalline molecular sieves designated as SSZ-91, a method for making SSZ-91 and use of SSZ-91.SOLUTION: A molecular sieve SSZ-91 is structurally similar to sieves belonging to molecular sieves of a ZSM-48 family, and is characterized as: (1) having a low degree of defects, (2) having a low aspect ratio that inhibits hydrocracking as compared to conventional ZSM-48 materials having an aspect ratio of greater than 8, and (3) being substantially pure phase.SELECTED DRAWING: None

Description

Technical Field

[0001] This application is related to U.S. Patent Application Nos. 14 / 837,071, 14 / 837,087, 14 / 837,108, and 14 / 837,094, all filed on August 27, 2015, the entireties of which are incorporated herein by reference.

[0002] Described herein are a new family of crystalline molecular sieves designated SSZ-91, methods for preparing SSZ-91, and uses of SSZ-91.

Background Art

[0003] Crystalline molecular sieves and molecular sieves are particularly useful in applications such as hydrocarbon conversion, gas drying and separation, etc. due to their unique sieving properties and their catalytic properties. Although numerous different crystalline molecular sieves have been disclosed, there is a continuing need for new molecular sieves having desirable properties for gas separation and drying, hydrocarbon and chemical conversion, and other applications. The new molecular sieves can contain novel internal pore structures and can provide improved selectivity in these processes.

[0004] Molecular sieves have individual crystal structures as indicated by their individual X-ray diffraction patterns. The crystal structures define cavities and pores characteristic of different species.

[0005] Molecular sieves are classified by the Structure Commission of the International Zeolite Association according to the rules of the IUPAC Commission on Zeolite Nomenclature. According to this classification, framework type zeolites and other crystalline microporous molecular sieves with established structures are assigned a three-letter code and are described in the "Atlas of Zeolite Framework Types", 6th revised edition, Elsevier (2007), and the molecular sieve structure database on the website of the International Zeolite Association (http: / / www.iza-online.org).

[0006] The structure of a molecular sieve can be ordered or disordered. A molecular sieve with an ordered structure has periodically ordered periodic building units (PerBUs) in all three dimensions. A structure that is structurally disordered shows periodic ordering in less than three dimensions (i.e., in two, one, or zero dimensions). Disorder occurs when the PerBUs are connected in different ways or when two or more PerBUs intergrow within the same crystal. The crystal structure created from PerBUs is called an end-member structure when periodic ordering is achieved in all three dimensions.

[0007] In a disordered material, planar stacking defects occur when the material contains two-dimensional ordering. Planar defects disrupt the channels formed by the pore system of the material. Planar defects located near the surface limit the diffusion pathways that would otherwise be necessary for feedstock components to access the catalytically active parts of the pore system. Thus, as the degree of defect increases, the catalytic activity of the material typically decreases.

[0008] In the case of a crystal with planar defects, the interpretation of X-ray diffraction patterns requires the ability to simulate the effects of stacking disorder. DIFFaX is a computer program based on a mathematical model for calculating the intensities from crystals containing planar defects. (See M.M.J. Treacy et al., Proceedings of the Royal Chemical Society, London, A (1991), Vol. 433, pp. 499 - 520). DIFFaX is a simulation program selected by and available from the International Zeolite Association for simulating the XRD powder patterns for the mutually growing phases of molecular sieves. (See M.M.J. Treacy and J.B. Higgins, "Collection of Simulated XRD Powder Patterns for Zeolites", 4th edition, issued for the Structure Commission of the International Zeolite Association, 2001). DIFFaX has also been used by K.P. Lillerud et al. to theoretically study the mutually growing phases of AEI, CHA and KFI molecular sieves, as reported in "Studies in Surface Science and Catarlsis" 1994, Vol. 84, pp. 543 - 550. DIFFaX is a well-known and established method for characterizing disordered crystalline materials with planar defects such as mutually growing molecular sieves.

[0009] The symbol ZSM-48 represents a family of disordered materials, each characterized as having a one-dimensional 10-membered ring tubular pore system. The pores are formed from rolled-up honeycomb-like sheets of condensed tetrahedral 6-membered ring structures, and the pore openings contain 10 tetrahedral atoms. Zeolites EU-2, ZSM-30 and EU-11 are classified as zeolites of the ZSM-48 family.

[0010] According to Lobo and Koningsveld, the molecular sieves of the ZSM-48 family consist of nine polytypes. (See J. Am. Chem. Soc. 2002, 124, 13222 - 13230). These materials have X-ray diffraction patterns that are very similar but not identical. The paper by Lobo and Koningsveld describes their analysis of three ZSM-48 samples provided by Dr. Alexander Kuperman of Chevron Corporation. Each of the three samples, labeled Sample A, B, and C respectively, was prepared using three different structure-directing agents. Comparative Examples 2 and 3 below in this specification correspond to Samples A and B described in the paper by Lobo and Koningsveld.

[0011] The paper by Lobo and Koningsveld states that Sample A is polytype 6 and Sample B is defective polytype 6. The paper further states that the morphology of Sample A consists of needle-like crystals with a diameter of about 20 nm and a length of about 0.5 μm. The morphology of Sample B consisted of long, thin crystals with a width of about 0.5 μm and a length of 4 - 8 μm. As shown in Comparative Examples 2 and 3 below, scanning electron microscope images of Samples A and B are presented herein in Figures 3 and 4.

[0012] Kirschhock and co-workers have described the successful synthesis of pure phase polytype 6. (See Chem. Mater. 2009, 21, 371 - 380). In that paper, Kirschhock and co-workers describe that their pure phase polytype 6 material (which they call COK-8) has a morphology consisting of long needle-like crystals (width 15 - 80 nm; length 0.5 - 4 μm) with a very large length / width ratio that grow along the direction of interconnected pores.

[0013] As shown in Kirschhock's paper, the molecular sieve from the ZSM-48 family of molecular sieves consists of a 10-membered ring, one-dimensional pore structure, where the channels formed by interconnected pores extend perpendicular to the long axis of the acicular crystals. Thus, the channel openings are located at the short ends of the acicular crystals. As the length-to-diameter ratio of these acicular crystals (also known as the aspect ratio) increases, the diffusion path for the hydrocarbon feedstock also increases. As the diffusion path increases, the residence time of the feedstock in the channels also increases. A longer residence time results in an undesirable increase in the hydrocracking of the feedstock, accompanied by a simultaneous decrease in selectivity. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] Therefore, there is a current need for a ZSM-48 molecular sieve that exhibits a lower degree of hydrocracking than known ZSM-48 molecular sieves. Also, there is a continuing need for a ZSM-48 molecular sieve that is in pure phase or substantially pure phase and has a low degree of disorder (low degree of defects) within the structure. MEANS FOR SOLVING THE PROBLEMS

[0015] Described herein below is a family of crystalline molecular sieves with unique properties, referred to herein as "molecular sieve SSZ-91" or simply "SSZ-91". Molecular sieve SSZ-91 is structurally similar to the sieve belonging to the ZSM-48 family of zeolites and is characterized by (1) a low degree of defects, (2) a low aspect ratio that suppresses hydrocracking compared to conventional ZSM-48 materials having an aspect ratio greater than 8, and (3) being substantially in pure phase.

[0016] As shown in the following examples, ZSM-48 materials lacking any one of the unique combinations of the three properties of SSZ-91 (low aspect ratio, low EU-1 content, high polytype 6 composition) exhibit poor catalytic performance.

[0017] In one aspect, there is provided a molecular sieve having a molar ratio of silicon oxide to aluminum oxide of 40 to 200. In its as-made form, the X-ray diffraction pattern of Table 2 herein is indicative of SSZ-91.

[0018] As determined by DIFFaX simulation and as described by Lobo and Koningsveld in J. Am. Chem. Soc. 2012, 124, 13222 - 13230 (wherein disorder is tuned by three different defect probabilities), the SSZ-91 material is composed of at least 70% polytype 6 of the total ZSM-48 type material present in the product. It should be noted that the phrase "at least 70%" includes the case where no other ZSM-48 polytypes are present in the structure, i.e., the material is 100% pure phase polytype 6.

[0019] In another aspect, SSZ-91 is substantially a pure phase. SSZ-91 contains a further EUO type molecular sieve phase in an amount between 0 and 3.5 wt% (inclusive) of the total product.

[0020] Molecular sieve SSZ-91 is characterized by a morphology characterized as polycrystalline aggregates, each of the aggregates being composed of crystallites having an average aspect ratio collectively between 1 and 8 (inclusive). SSZ-91 exhibits a lower degree of hydrocracking than ZSM-48 materials having a higher aspect ratio. An aspect ratio of 1 is the ideal minimum value, in which case the length and width are the same.

[0021] In another aspect, there is provided a method for preparing a crystalline material by contacting, under crystallization conditions, (1) at least one source of silicon oxide; (2) at least one source of aluminum oxide; (3) at least one source of an element selected from Group 1 and Group 2 of the periodic table; (4) hydroxide ions; and (5) hexamethonium cations.

[0022] In yet another aspect, a method for preparing a crystalline material having the X-ray diffraction profile of Table 2 as-manufactured, comprising: (a) preparing a reaction mixture containing (1) at least one source of silicon oxide; (2) at least one source of aluminum oxide; (3) at least one source of an element selected from Group 1 and Group 2 of the periodic table; (4) hydroxide ions; (5) hexamethonium cations; and (6) water; (b) maintaining the reaction mixture under crystallization conditions sufficient to form crystals of the molecular sieve. The above method is provided thereby. BRIEF DESCRIPTION OF THE DRAWINGS

[0023]

Figure 1

[0024]

Figure 2

[0025]

Figure 3

[0026]

Figure 4

[0027]

Figure 5

[0028]

Figure 6

[0029]

Figure 7

[0030]

Figure 8

[0031]

Figure 9

[0032]

Figure 10

[0033]

Figure 11

[0034]

Figure 12

DETAILED DESCRIPTION OF THE INVENTION

[0035] Introduction The term "active source" means a reagent or precursor material that can supply at least one element in a form capable of reacting and can be incorporated into a molecular sieve structure. The terms "source" and "active source" can be used interchangeably herein.

[0036] The terms "molecular sieve" and "zeolite" are synonymous and include (a) intermediate and (b) final or target molecular sieves and molecular sieves produced by (1) direct synthesis or (2) post-crystallization treatment (secondary modification). Secondary synthesis techniques enable the synthesis of the target material from intermediate materials by heteroatom lattice substitution or other techniques. For example, aluminosilicate can be synthesized from intermediate borosilicate by post-crystallization heteroatom lattice substitution from B to Al. Such techniques are known as described, for example, in U.S. Patent No. 6,790,433, issued September 14, 2004, to C.Y. Chen and Stacey Zones.

[0037] 「 * The terms "MRE type molecular sieve" and "EUO type molecular sieve" include all molecular sieves and their isotypes assigned to the framework of the International Zeolite Association as described in the "Atlas of Zeolite Framework Types", edited by Ch. Baerlocher, L.B. McCusker and D.H. Olson, Elsevier, 6th revised edition, 2007 and the zeolite structure database on the website of the International Zeolite Association (http: / / www.iza-online.org).

[0038] The term "periodic table" refers to the IUPAC version of the periodic table of the elements dated June 22, 2007, and the numbering scheme for the groups of the periodic table is as described in Chem. Eng. News, 63(5), 26 - 27 (1985).

[0039] For the purposes of this specification and the appended claims, unless otherwise indicated, all numerical values representing amounts, percentages or ratios, and other numerical values used in this specification and the claims are to be understood as being modified in all instances by the term "about." Accordingly, unless otherwise indicated, the numerical parameters set forth in the following specification and attached claims are approximations and may vary depending upon the desired properties sought to be obtained. As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless specifically and explicitly limited to one referent. As used herein, the term "include" and its grammatical variations are non-limiting, and thus listing of items in a list does not exclude other like items that may be substituted for or added to the listed items. As used herein, the term "comprising" means including the elements or steps specified following the term, but such elements or steps are not exhaustive and an embodiment may include other elements or steps.

[0040] Unless otherwise specified, a detailed description of a type of element, material, or other component, where individual components or mixtures of components can be selected, includes all possible sub-generic combinations of the listed components and their mixtures. Further, all numerical ranges presented herein include their upper and lower limit values.

[0041] The patentable scope is defined by the claims and can include other embodiments that would occur to one of ordinary skill in the art. Such other embodiments are within the scope of the claims if the other embodiments have structural elements that do not differ from the literal meaning of the claims, or if the other embodiments include equivalent structural elements that have only a slight difference from the literal meaning of the claims. All citations referred to herein are incorporated herein by reference unless inconsistent with this specification.

[0042] Reaction Mixture and Crystallization In the preparation of SSZ-91, at least one organic compound selected to synthesize molecular sieves from zeolites of the ZSM-48 family is used as a structure directing agent (''SDA''), also known as a crystallization template. The SDA useful for manufacturing SSZ-91 has the following structure (1) [Chemical formula] represented by

[0043] The SDA cation is typically accompanied by an anion which may be any anion that does not harm the formation of the molecular sieve. Representative examples of anions include hydroxide ions, acetate ions, sulfate ions, carboxylate ions, and halide ions, for example, fluoride ions, chloride ions, bromide ions and iodide ions. In one embodiment, the anion is bromide ion.

[0044] Generally, SSZ-91 is (a) (1) a source of at least one silicon oxide; (2) a source of at least one aluminum oxide; (3) a source of at least one element selected from Group 1 and Group 2 of the periodic table; (4) hydroxide ions; (5) hexamethonium cation; and (6) a step of formulating a reaction mixture containing water, and (b) a step of maintaining the reaction mixture under crystallization conditions sufficient to form crystals of the molecular sieve prepared by

[0045] The composition of the reaction mixture in which the molecular sieve is formed is specified in Table 1 below in terms of molar ratios. [Table 1] In the table (1) M is selected from the group consisting of elements from Group 1 and Group 2 of the periodic table (2) Q is a structure-directing agent represented by the above structure 1.

[0046] Useful sources in this specification for silicon include fumed silica, precipitated silica, silica hydrogel, silicic acid, colloidal silica, tetra-alkyl orthosilicates (e.g., tetraethyl orthosilicate), and silica hydroxide.

[0047] Useful sources in this specification for aluminum include aluminates, alumina, and aluminum compounds such as AlCl3, Al2(SO4)3, Al(OH)3, kaolin clay, and other zeolites. An example of a source of aluminum oxide is LZ-210 zeolite (a type of Y zeolite).

[0048] As described above herein, for each embodiment described herein, the reaction mixture can be formed to contain at least one source of an element selected from Group 1 and Group 2 of the periodic table (referred to herein as M). In one sub-embodiment, the reaction mixture is formed using a source of an element from Group 1 of the periodic table. In another sub-embodiment, the reaction mixture is formed using a source of sodium (Na). Any M-containing compound that does not harm the crystallization process is suitable. Sources for such Group 1 and Group 2 elements include their oxides, hydroxides, nitrates, sulfates, halides, oxalates, citrates, and acetates.

[0049] For each embodiment described herein, the molecular sieve reaction mixture may be supplied by two or more sources. Similarly, two or more reaction components may be supplied by one source.

[0050] The reaction mixture can be prepared batchwise or continuously. The crystal size, morphology, and crystallization time of the molecular sieves described herein can vary depending on the nature of the reaction mixture and the crystallization conditions.

[0051] The reaction mixture is maintained at an elevated temperature until the formation of molecular sieve crystals. Generally, zeolite hydrothermal crystallization is usually carried out under pressure, and the reaction mixture is subjected to autogenous pressure and is usually carried out in an autoclave at a temperature between 125 °C and 200 °C for more than 1 to 18 hours so that the reaction mixture is stirred if necessary.

[0052] As described above herein, SSZ-91 is a substantially pure-phase material. As used herein, the term "substantially pure-phase material" means that the material does not completely contain a zeolite phase other than those belonging to the zeolite of the ZSM-48 family, or is present in an amount that has no measurable effect on the selectivity of the material or does not impart a defect to the material. Two common phases that co-crystallize with SSZ-91 are EUO-type molecular sieves such as EU-1, as well as magadiite and kenyaite. These additional phases may exist as separate phases or may intergrow with the phase of SSZ-91. As shown in the following examples, the presence of a large amount of EU-1 in the product is detrimental to the selectivity for hydroisomerization by SSZ-91.

[0053] In one embodiment, the SSZ-91 product contains an additional EUO-type molecular sieve phase in an amount between 0 and 3.5 wt%. In one sub-embodiment, SSZ-91 contains EU-1 between 0.1 and 2 wt%. In another sub-embodiment, SSZ-91 contains EU-1 between 0.1 and 1 wt%.

[0054] The ratio of the powder XRD peak intensities varies linearly as a function of the weight fraction for any two phases in the mixture: (Iα / Iβ)=(RIRα / RIRβ)*(xα / xβ), where the RIR (reference intensity ratio) parameter is known to be found in the powder diffraction file (PDF) database of the International Center for Diffraction Data (http: / / www.icdd.com / products / ) for the diffraction data. The weight percentage of the EUO phase is thus calculated by measuring the ratio between the peak intensity of the EUO phase and the peak intensity of the SSZ-91 phase.

[0055] The formation of the total amount of the EUO phase is suppressed by selecting an optimal hydrogel composition, temperature, and crystallization time that minimize the formation of the EUO phase while maximizing the yield of the SSZ-91 product. The following examples provide guidance on how changes in these process variables minimize the formation of EU-1. Those skilled in the art of zeolite production can readily select the process variables necessary to minimize the formation of EU-1, as these variables depend on the size of the production operation, the available equipment capacity, the desired target yield, and the acceptable level of EU-1 material in the product.

[0056] During the hydrothermal crystallization step, molecular sieve crystals can nucleate spontaneously from the reaction mixture. The use of molecular sieve crystals as seed material may be advantageous in reducing the time required for complete crystallization. Additionally, seed addition can result in a high purity of the resulting product by promoting the formation of the molecular sieve preferentially over nucleation and / or any undesired phases. However, when seed addition is used, it has been found that the seed must be SSZ-91 of a very pure phase to avoid the formation of a large amount of the EUO phase. When used as a seed, the seed crystals are added in an amount between 0.5% and 5% of the weight of the silicon source used in the reaction mixture.

[0057] The formation of magadiite and kenyaite is minimized by optimizing the hexamethonium bromide / SiO2 ratio, controlling the hydroxide concentration, and minimizing the sodium concentration since magadiite and kenyaite are layered sodium silicate compositions. The following examples provide guidance on how changes in the gel conditions minimize the formation of EU-1.

[0058] After the molecular sieve crystals are formed, the solid product is separated from the reaction mixture by standard mechanical separation techniques such as filtration. The crystals are washed with water and then dried to obtain as-synthesized molecular sieve crystals. The drying step can be carried out at atmospheric pressure or under vacuum.

[0059] Post-crystallization treatment Molecular sieves can be used as-synthesized, but are typically thermally treated (calcined). The term "as-synthesized" refers to the molecular sieve in that form after crystallization and before removal of the SDA cation. The SDA can be removed by heat treatment (e.g., calcination), preferably at a temperature readily determinable by one of ordinary skill in the art sufficient to remove the SDA from the molecular sieve in an oxidative atmosphere (e.g., air, a gas having an oxygen partial pressure in excess of 0 kPa). The SDA can also be removed by ozonation and photolysis techniques (e.g., exposing the SDA-containing molecular sieve product to light or electromagnetic radiation having a wavelength shorter than visible light under conditions sufficient to selectively remove the organic compound from the molecular sieve), as described in U.S. Patent No. 6,960,327.

[0060] Subsequently, the molecular sieve may be calcined in steam, air, or an inert gas at a temperature in the range of 200 °C to 800 °C for 1 to 48 hours, or for a longer period. Usually, it is desirable to remove extra-framework cations (e.g., Na + ) by ion exchange and replace them with hydrogen, ammonium, or any desired metal ion.

[0061] If the molecular sieve formed is an intermediate molecular sieve, the desired molecular sieve can be achieved using post-synthesis techniques such as heteroatom lattice substitution techniques. The desired molecular sieve (e.g., silicate SSZ-91) can also be achieved by removing heteroatoms from the lattice by known techniques such as acid leaching.

[0062] Molecular sieves produced by the methods disclosed herein can be formed into a wide range of physical shapes. Generally, the molecular sieves can be in the form of powders, granules, or shaped articles such as extrudates having a particle size sufficient to pass through a 2 mesh (Tyler) screen and be retained on a 400 mesh (Tyler) screen. When the catalyst is shaped by extrusion or the like with an organic binder, the molecular sieves can be extruded before drying, or dried or partially dried and then extruded.

[0063] Molecular sieves can be compounded with other materials that are resistant to the temperatures and other conditions used in the organic conversion process. Such matrix materials include active and inert materials as well as molecular sieves of synthetic or natural origin, in addition to inorganic materials such as clays, silica, and metal oxides. Examples of such materials and methods by which they can be used are disclosed in U.S. Patent Nos. 4,910,006 and 5,316,753.

[0064] Next, one or more active metals selected from the group consisting of metals of Groups 8 to 10 of the Periodic Table may be further added to the extrudate or particles to enhance the hydrogenation function by using techniques such as impregnation or ion exchange. As disclosed in U.S. Patent No. 4,094,821, it is desirable to co-impregnate the modifying metal and one or more Group 8 to 10 metals simultaneously. In one embodiment, at least one active metal is selected from the group consisting of nickel, platinum, palladium, and combinations thereof. After the metal addition, the extrudate or particles with the added metal may be calcined at a temperature of 200°C to 500°C in air or an inert gas. In one embodiment, the extrudate with the added metal is calcined at a temperature of 390°C to 482°C in air or an inert gas.

[0065] SSZ-91 is useful for various hydrocarbon conversion reactions such as hydrocracking of aromatic compounds, dewaxing, olefin isomerization, alkylation, and isomerization. SSZ-91 is also useful as an adsorbent for general separation purposes.

[0066] Characterization of Molecular Sieves The molecular sieves produced by the methods disclosed herein have a SiO2 / Al2O3 molar ratio (SAR) of 40 to 200. The SAR is determined by inductively coupled plasma (ICP) elemental analysis. In one sub - embodiment, SSZ - 91 has an SAR between 70 and 160. In another sub - embodiment, SSZ - 91 has an SAR between 80 and 140.

[0067] The SSZ - 91 material is composed of at least 70% polytype 6 of the total ZSM - 48 type material present in the product, as determined by DIFFaX simulation and as described by Lobo and Koningsveld in J. Am. Chem. Soc. 2012, 124, 13222 - 13230 (where the disorder is adjusted by three different defect probabilities). It should be noted that the phrase "at least X%" includes the case where no other ZSM - 48 polytypes are present in the structure, i.e., the material is 100% polytype 6. The structure of polytype 6 is as described by Lobo and Koningsveld. (See J. Am. Chem. Soc. 2002, 124, 13222 - 13230). In one embodiment, the SSZ - 91 material is composed of at least 80% polytype 6 of the total ZSM - 48 type material present in the product. In another embodiment, the SSZ - 91 material is composed of at least 90% polytype 6 of the total ZSM - 48 type material present in the product. The structure of polytype 6 has the framework code * MRE assigned by the Structure Commission of the International Zeolite Association.

[0068] Molecular sieve SSZ-91 has a morphology characterized by polycrystalline aggregates having diameters between about 100 nm and 1.5 μm, and each of the aggregates contains a collection of crystallites having an average aspect ratio between 1 and 8. As used herein, the term diameter represents the shortest length on the short end of each crystallite under consideration. SSZ-91 exhibits a lower degree of hydrocracking than ZSM-48 materials having a higher aspect ratio. In one sub - embodiment, the average aspect ratio is between 1 and 5. In another sub - embodiment, the average aspect ratio is between 1 and 4. In yet another sub - embodiment, the average aspect ratio is between 1 and 3.

[0069] The molecular sieves synthesized by the methods disclosed herein can be characterized by their XRD patterns. The powder XRD profiles in Table 2 are representative examples of as - synthesized SSZ-91 produced according to the methods described herein. Slight variations in the diffraction pattern can result from variations in the molar ratio of the framework species of a particular sample due to changes in the lattice constant. Additionally, sufficiently small crystals can affect the peak shape and intensity, resulting in a significant peak broadening. Slight variations in the diffraction pattern can also result from variations in the organic compounds used in the preparation and variations in the Si / Al molar ratio from sample to sample. Calcination can also result in a slight shift in the XRD pattern. Despite these slight perturbations, the basic crystal lattice structure remains unchanged.

Table 2

[0070] The X - ray diffraction pattern profiles in Table 3 are representative examples of calcined SSZ-91 produced according to the methods described herein.

Table 3

[0071] The powder X - ray diffraction patterns presented herein were collected by standard techniques. The radiation was CuK αIt is radiation. The peak height and position (as a function of 2θ, where θ is the Bragg angle) are read from the relative intensity of the peak (adjusted with respect to the background), and d (the lattice plane spacing corresponding to the recorded line) can be calculated.

Example

[0072] The following exemplary examples are non-limiting.

[0073] Summary of the Example The following examples demonstrate that ZSM-48 materials lacking any one of the three specific combinations of properties of SSZ-91 (low aspect ratio, low EU-1 content, high polytype 6 composition) exhibit poor catalytic performance. Table 4 below summarizes the hydrotreating performance for various examples outlined below. Only Example 8 (SSZ-91) showed excellent performance, i.e., excellent selectivity and low gas production compared to the other three examples. The remaining materials of the other three examples tested showed poor performance because each lacked at least one of the specific combinations of the three properties that define SSZ-91.

Table 4

[0074] (Comparative Example 1) Synthesis of ZSM-48 The product in this example was prepared using available reagents according to the teachings of U.S. Patent No. 5,075,269 to Thomas F. Degnan and Ernest W. Valyocsik (Mobil Oil Corp.), issued December 24, 1991.

[0075] 76.51 g of NaOH (50%), 846 g of deionized water, 124.51 g of HI-SIL 233 silica (PPG Industries), and 63 g of hexamethonium bromide (“HMB”, Sigma Aldrich) were added to a 1-gallon autoclave liner. After all solids were dissolved, 396 g of an aluminum stock solution prepared by dissolving 4.35 g of Al2(SO4)3·18H2O and 63 g of concentrated H2SO4 in 733.52 g of deionized water was added. Finally, 0.45 g of SSZ-91 seed crystals from Example 7 was added. The mixture was stirred until homogeneous. The composition of the aluminosilicate gel produced had the following molar ratios.

Table 5

[0076] The liner was transferred to a 1-gallon autoclave and heated to 160 °C over 8 hours while stirring at 150 rpm at autogenous pressure. After 80 hours, the product was filtered, washed with deionized water, and dried. The solid obtained was determined by XRD to be a ZSM-48 material (Figure 1). XRD indicated the presence of an unquantifiable amount of EU-1 in the product (presumably less than 1% EU-1). SEM showed aggregated long needle-like crystals of ZSM-48 with an aspect ratio of 7-12 (Figure 2).

[0077] (Comparative Examples 2 and 3) As described above, the paper by Lobo and Koningsveld describes their analysis of three ZSM-48 samples provided by Dr. Alexander Kuperman of Chevron Corporation. Each of the three samples, Samples A, B, and C, was prepared using three different structure-directing agents, respectively. The paper by Lobo and Koningsveld describes Sample A as polytype 6 and Sample B as defective polytype 6. The paper further describes that the morphology of Sample A (Figure 3) consists of thin needle-like crystals having a diameter of about 20 nm and a length of about 0.5 μm. The morphology of Sample B (Figure 4) consisted of long, thin crystals having a diameter of about 30 nm and a length of 4 - 8 μm. Despite Dr. Kuperman's material being reported to have a high concentration of polytype 6, the sample was characterized as having an aspect ratio (length / diameter) of 25 for Sample A and in the range of 133 - 266 for Sample B.

[0078] (Examples 4 - 11) Synthesis of SSZ-91 with various EU-1 concentrations in the product Each of Examples 4 to 11 was prepared by adding NaOH (50%), deionized water, HI-SIL 233 silica (PPG Industries), and hexamethonium bromide (Sigma Aldrich) to an autoclave liner. After all solids were dissolved, an aluminum stock solution prepared by dissolving 4.18 g of Al2(SO4)3·18H2O and 45.58 g of concentrated H2SO4 in 540.6 g of deionized water was added. The mixture was stirred until homogeneous. The molar ratios to the aluminosilicate gel and the heating periods are listed in Table 6 below.

Table 6

[0079] The liner was transferred to an autoclave and heated to 160 °C over 8 hours while stirring at a rate of 150 rpm under self-generated pressure. After the crystallization period, the product was filtered, washed with deionized water, and dried. The resulting solid was analyzed by XRD to determine the product and the level of EU-1 in the product. The bulk SiO2 / Al2O3 molar ratio and EU-1 content are listed in Table 7 below.

Table 7

[0080] The products from Examples 1 and 4 - 11 were analyzed by XRD and SEM. The XRD pattern for Example 7 is shown in Figure 5, which is illustrative of the XRD patterns collected for the remaining Examples 4 - 11.

[0081] The SEM images for Examples 7 and 8 are shown in Figures 6 and 7 respectively, which are illustrative of the SEM images for the remaining Examples 4 - 11. Figures 6 and 7 show that the SSZ-91 material consists of polycrystalline aggregates, each of which is composed of crystallites, where each crystallite has a characteristic average aspect ratio of less than 8. In contrast, the ZSM-48 materials of Comparative Examples 1 - 3 (Figures 2 - 4) contain long needle-like crystals and fibrous morphologies, the presence of which consistently exhibited poor catalytic performance.

[0082] Firing and Ion Exchange of Molecular Sieves The as-synthesized products from Comparative Example 1 and Examples 4 to 11 were held in an atmosphere of dry air at 120 °C at a heating rate of 1 °C / min for 120 minutes, followed by a second temperature rise to 540 °C at 1 °C / min and held at this temperature for 180 minutes, and finally a third temperature rise to 595 °C at 1 °C / min and held at this temperature for 180 minutes, and converted to the sodium form. Finally, the samples were cooled to below 120 °C. Subsequently, each of these fired samples was exchanged to the ammonium form as follows. Ammonium nitrate in an amount equal to the mass of the sample to be exchanged was completely dissolved in deionized water in an amount 10 times the mass of the sample. Subsequently, the sample was added to the ammonium nitrate solution, the suspension was sealed in a flask, and heated overnight in an oven at 95 °C. The flask was taken out of the oven and the sample was immediately recovered by filtration. The ammonium exchange procedure was repeated with the recovered sample, washed with a large amount of deionized water to a conductivity of less than 50 μS / cm, and finally dried in an oven at 95 °C for 3 hours.

[0083] Hydrogenation treatment test Ion exchange of ammonium-exchanged samples from Examples 1 and 4 to 11 was carried out using tetraamminepalladium(II) nitrate (0.5 wt% Pd). After ion exchange, the samples were dried at 95 °C and then calcined in air at 482 °C for 3 hours to convert tetraamminepalladium(II) nitrate to palladium oxide.

[0084] 0.5 g of each of the palladium-exchanged samples from Example 11 was loaded into the center of a 23-inch long and 0.25-inch outer diameter stainless steel reactor tube randomly packed upstream of the catalyst for preheating of the feedstock (total pressure 1200 psig; downflow hydrogen velocity 160 mL / min (measured at 1 atm and 25 °C); downflow liquid feed rate 1 mL / hour). All materials were first reduced in a hydrogen stream at about 315 °C for 1 hour. The products were analyzed online by capillary gas chromatography (GC) every 30 minutes. The raw data from the GC was collected by an automatic data collection / processing system, and the hydrocarbon conversion rate was calculated from the raw data.

[0085] The catalyst was first tested at about 260°C to determine the temperature range for the next set of measurements. The entire temperature range resulted in a wide range of hexadecane conversions, with a maximum conversion just below and exceeding 96%. At least five on-line GC injections were collected at each temperature. Conversions were compared with other products (iso-nC 16 The yield was defined as the amount of hexadecane reacted to produce nC 16 Yield expressed as weight percent of products other than iso-C 16 The results are included in Table 8. [Table 8]

[0086] For the preferred materials of this invention, the desired isomerization selectivity at 96% conversion is at least 85%. A good balance between isomerization selectivity and temperature at 96% conversion is critical to this invention. The desired temperature at 96% conversion is less than 605°F. The lower the temperature at 96% conversion, while still maintaining an isomerization selectivity of at least 85%, the more desirable the catalyst. The best catalyst performance is determined by the synergy between isomerization selectivity and temperature at 96% conversion. Large amounts of impurities can result in high levels of C4 - Cracking results in undesirable catalytic cracking with its attendant high gas production, as reflected in Table 8. Desirable C4 - Cracking is below 2.0%. Note that the selectivity begins to decrease at 6.82% EU-1 as increasing concentrations of EU-1 promote catalytic cracking.

[0087] Polytype distribution Using DIFFaX, simulated XRD patterns were created for ZSM-48 materials having between 70 - 100% polytype 6 and compared with the XRD patterns collected for the molecular sieve products from Examples 8 and 11. The simulated and product XRD patterns are shown in Figures 8 and 9 of this specification respectively. Comparing the product XRD pattern with the simulated pattern indicates that the products synthesized in Examples 8 and 11 contain more than 90% polytype 6.

[0088] Using DIFFaX, simulated XRD patterns were created for ZSM-48 materials having between 70 - 100% polytype 6 and compared with the XRD patterns collected for the molecular sieve products from Comparative Example 1. The simulated and product XRD patterns are shown in Figure 10 of this specification. Comparing the product XRD pattern with the simulated pattern indicates that the product synthesized in Comparative Example 1 contains 80% polytype 6.

[0089] The material synthesized in Comparative Example 1 was subjected to the hexadecane hydrotreating test outlined in Examples 4 - 11 above. The material from Comparative Example 1 showed an isomerization selectivity of 78% at a conversion of 96% at a temperature of 614°F. As shown in Table 9 below, C4 - decomposition was 2.8%. The isomerization selectivity at 96% conversion for the material of Comparative Example 1, which has only 80% polytype 6 content, was inferior to those described in Examples 4 to 10 shown in Table 7 above, even though the material of Comparative Example 1 contained a non-detectable (<1%) amount of EU-1. This indicates that the materials of Comparative Example 1 and Example 11 exhibited two of the three properties of SSZ-91 (low aspect ratio, low EU-1 content, high polytype 6 content), and the lack of the third property contributed to the poor catalytic performance of the material.

Table 9

[0090] (Examples 12 - 13) Synthesis of SSZ-91 with an alternative silica source The materials of Example 12 were prepared by adding NaOH (50%), deionized water, CAB-O-SIL M-5 silica (Cabot Corporation), and hexamethonium bromide (HMB) to an autoclave liner. After all solids were dissolved, anhydrous sodium aluminate from Riedel de Haen was added. Finally, an SSZ-91 slurry similar to the slurry from Example 4 was added. The mixture was stirred until homogeneous. The resulting aluminosilicate gel composition had the following molar ratios. [Table 10]

[0091] The liner was transferred to an autoclave, which was heated to 160 °C over 8 hours and stirred at 150 rpm at self-generated pressure. After 48 hours, the product was filtered, washed with deionized water, and dried. The resulting solid was determined by XRD to be SSZ-91 and to contain 0.30 wt% EUO. The bulk SiO2 / Al2O3 molar ratio was found to be approximately 102.

[0092] The materials of Example 13 were prepared by adding NaOH (50%), deionized water, commercially available NALCO 2327 colloidal silica (40.3% SiO2), and hexamethonium bromide to an autoclave liner. After all solids were dissolved, Al2(SO4)3·18H2O pre-dissolved in some water was added. The mixture was stirred until homogeneous. The resulting aluminosilicate gel composition had the following molar ratios. [Table 11]

[0093] The liner was transferred to an autoclave and heated to 160 °C over 8 hours while stirring at 150 rpm at autogenous pressure. After 35 hours, the product was filtered, washed with deionized water, and dried. The resulting solid was determined by XRD to be SSZ-91 and contain 3.16 wt% of EU-1. The bulk SiO2 / Al2O3 molar ratio was found to be approximately 155. The material of Example 13 was analyzed by scanning electron microscope, and the SEM image from the analysis is shown in Figure 11.

[0094] Hydrogenation treatment test For the SSZ-91 materials synthesized in Examples 12 and 13, the palladium addition test and the catalyst test were carried out as described for the above examples. The results of the catalyst test are shown in Table 12 below. These two examples prepared by changing the raw materials used demonstrate the versatility of the preparation of SSZ-91. Example 12 showed another favorable example with a desirable isomerization selectivity of 88% at 96% at a considerably low temperature. Example 13 showed the results of crystals with poor catalyst performance and a bad aspect ratio of the crystals in a pure phase.

Table 12

[0095] Using DIFFaX, simulated XRD patterns were created for ZSM-48 materials having polytype 6 between 70 and 100% and compared to the XRD patterns collected for the molecular sieve products from Example 13. The simulated and product XRD patterns are shown in Figure 12 of this specification. The SEM images from this analysis are shown in Figure 11. Comparing the XRD pattern of the product to the simulated pattern indicates that the product synthesized in Comparative Example 1 contains more than 90% polytype 6. This shows that while the material of Example 13 has an essential low EU-1 content and a desired polytype distribution, the high aspect ratio contributed to the poor catalytic performance of the material. Example 13 reaffirms that the lack of any one of the three properties of SSZ-91 (low aspect ratio, low EU-1 content, high polytype 6 content) contributes to the poor catalytic performance of the material.

Claims

1. A molecular sieve belonging to the ZSM-48 family of zeolites, having a molar ratio of silicon oxide to aluminum oxide of 40 to 200, at least 70% of the polytype 6 of the total ZSM-48 type material present in the product, and a further EUO type molecular sieve phase in an amount between 0 and 3.5% by weight of the total product comprising, characterized by a morphology comprising polycrystalline aggregates containing crystallites having an average aspect ratio collectively between 1 and 8 said molecular sieve.

2. In its as-synthesized form, having substantially the X-ray diffraction pattern shown in the following table 【Table 1】 The molecular sieve according to claim 1.

3. The molecular sieve according to claim 1 or 2, having a molar ratio of silicon oxide to aluminum oxide of 70 to 160.

4. The molecular sieve according to any one of claims 1 to 3, having a molar ratio of silicon oxide to aluminum oxide of 80 to 140.

5. The molecular sieve according to any one of claims 1 to 4, comprising at least 80% of polytype 6 of the total ZSM-48 type material present in the product.

6. The molecular sieve according to any one of claims 1 to 5, comprising EU-1 between 0.1 and 2% by weight.

7. The molecular sieve according to any one of claims 1 to 6, wherein the crystallites collectively have an average aspect ratio between 1 and 5.

8. The molecular sieve according to any one of claims 1 to 7, comprising at least 90% of polytype 6 of the total ZSM-48 type material present in the product.

9. The molecular sieve according to any one of claims 1 to 8, wherein the crystallites collectively have an average aspect ratio between 1 and 3.

10. A method for preparing the molecular sieve according to any one of claims 1 to 9, comprising the steps of preparing a reaction mixture containing at least one silicon source, at least one aluminum source, at least one source of an element selected from Group 1 and Group 2 of the periodic table, hydroxide ions, hexamethonium cations, and water; and subjecting said reaction mixture to crystallization conditions sufficient to form crystals of the molecular sieve.

11. The molecular sieve has, with respect to the molar ratio, the following: 【Table 2】 [In the table, M is selected from the group consisting of elements from Groups 1 and 2 of the periodic table; Q is a hexamethonium cation] The method according to claim 10, prepared from a reaction mixture comprising

12. The molecular sieve is as follows with respect to the molar ratio: 【Table 3】 [In the table, M is selected from the group consisting of elements from Groups 1 and 2 of the periodic table; Q is a hexamethonium cation] The method according to claim 10, prepared from a reaction mixture comprising

13. A method for converting hydrocarbons, comprising contacting a hydrocarbon feedstock with a catalyst comprising the molecular sieve according to any one of claims 1 to 9 under hydrocarbon conversion conditions.

14. Use of the molecular sieve according to any one of claims 1 to 9 for converting hydrocarbons under hydrocarbon conversion conditions.

Images