Ferrosilicate MTW molecular sieves, their synthesis and uses

Abstract

This disclosure relates to ferrosilicate molecular sieves with the MTW framework topology, their synthesis, and uses. The MTW ferrosilicate may be directly prepared using 1,3-diisobutylimidazolium cation as a structure-directing agent. The MTW ferrosilicate may be used in organic compound conversion and sorption processes.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Application No. 18 / 165,387, filed February 7, 2023.

[0002] Field The present disclosure relates to ferrosilicate molecular sieves of MTW framework topology, their synthesis, and their use as adsorbents and catalysts for organic compound conversion reactions, particularly hydrocarbon conversion reactions. [Background technology]

[0003] Molecular sieve materials are classified by the Structure Commission of the International Zeolite Association (IZA) according to the rules of the IUPAC Commission on Zeolite Nomenclature, in which framework-type zeolites and other crystalline microporous materials with established structures are assigned three-letter codes and listed in the database of zeolite structures maintained by IZA (www.iza-structure.org / databases / ).

[0004] One known molecular sieve with an established structure is a material designated MTW, which is a molecular sieve with a unique one-dimensional system of 12-membered (12-MR) ring pores. Examples of MTW framework-type molecular sieves include CZH-5, NU-13, Theta-3, TPZ-12, and ZSM-12. The aluminosilicate ZSM-12 is an important commercial target due to its activity as a shape-selective acid catalyst in industrial hydrocarbon conversion processes such as the alkylation and disproportionation of aromatics, the hydroisomerization of linear alkanes, and hydrocarbon cracking.

[0005] While the one-dimensional pore system provides the aluminosilicate ZSM-12 with unique shape selectivity, it can also introduce significant diffusion limitations for reactants and products. For chemical reactions where diffusion is important, smaller crystallite size shortens the diffusion paths, thereby facilitating mass transfer and improving the desired reaction pathway, positively impacting the selectivity and conversion of such reactions.

[0006] In acid catalysis, the silica-to-alumina molar ratio is an important chemical characteristic of molecular sieves. Generally, high acidity is beneficial to overall catalytic activity, but the presence of Brønsted acidic sites (e.g., those formed at framework Al atoms) can catalyze secondary reactions detrimental to the desired chemical function. For example, hydroisomerization of linear alkanes using the aluminosilicate ZSM-12 can result in undesirable overcracking, which reduces the yield of isomerized alkanes. One strategy to overcome the acidity limitation is to reduce the acidity by isomorphously substituting framework aluminum atoms with metal atoms that have lower acidic strength than aluminum. Current methods for synthesizing aluminum-free ZSM-12 generally rely on post-synthetic modification of the aluminosilicate ZSM-12. These methods involve steam or acid treatment at high temperatures to partially remove aluminum from framework positions and create vacant silanol nests ([SiOH]4) that can be replaced with the desired metal atom. However, significant amounts of framework aluminum may remain and may be detrimental to many of the reactions involved, leading to significant reductions in yield and selectivity.

[0007] As a result, there is a continuing need for molecular sieve materials of the MTW framework topology with improved properties, particularly with respect to catalytic properties, for use in various applications, particularly for use in hydrocarbon conversion reactions such as the isomerization of linear alkanes.

[0008] In accordance with the present disclosure, it has been discovered that ferrosilicate molecular sieves of the MTW framework topology can be directly synthesized using 1,3-diisobutylimidazolium cations as structure directing agents, and in some cases, small crystalline forms of the molecular sieves can be produced. Summary of the Invention

[0009] In one embodiment, a ferrosilicate molecular sieve of MTW framework topology having a d50 crystal size of 0.5 microns or less is provided.

[0010] In another aspect, a method for making a ferrosilicate molecular sieve of MTW framework topology is provided, comprising: (1) forming a reaction mixture comprising: (a) an iron source; (b) a silicon source; (c) an alkali metal [M] source; (d) a structure directing agent [Q] comprising a 1,3-diisobutylimidazolium cation; (e) a hydroxide ion source; and (f) water; and (2) subjecting the reaction mixture to crystallization conditions sufficient to form crystals of the ferrosilicate molecular sieve.

[0011] In yet another aspect, there is provided a process for converting a feedstock comprising organic compounds to conversion products, comprising contacting the feedstock with a catalyst comprising a ferrosilicate molecular sieve of MTW framework topology having a d50 crystallite size of 0.5 microns or less under organic compound conversion conditions. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows a scanning electron microscope (SEM) image of the as-prepared ferrosilicate MTW product of Example 1.

[0013] [Figure 2] FIG. 2 shows powder X-ray diffraction (XRD) patterns of the as-prepared ferrosilicate MTW (top) and calcined ferrosilicate MTW (bottom) materials of Example 1.

[0014] [Figure 3] FIG. 3 is a plot of conversion as a function of temperature for n-decane conversion over the ferrosilicate MTW catalyst of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0015] definition The term "ferrosilicate" refers to a molecular sieve having a framework constructed from repeating FeO4 and SiO4 tetrahedral units.

[0016] The term "MTW" refers to an MTW-type topology or framework as recognized by the Structure Commission of the International Zeolite Association (IZA), and the term "MTW molecular sieve" refers to a crystalline microporous material whose primary crystalline phase is MTW.

[0017] The term "as-made" refers to the molecular sieve in its form after crystallization and before removal of the structure directing agent.

[0018] The term "extra-framework metal" refers to metal that is present on the surface and / or within the cages and / or pores of the molecular sieve and does not include atoms that make up the framework of the molecular sieve.

[0019] The term "Cn" hydrocarbon refers to a hydrocarbon compound having n number of carbon atoms per molecule. The term "Cn+" hydrocarbon refers to a hydrocarbon compound having n or more carbon atoms per molecule. The term "Cn-" hydrocarbon refers to a hydrocarbon compound having n or more carbon atoms per molecule.

[0020] Molecular sieve synthesis A ferrosilicate molecular sieve of MTW framework topology may be synthesized by: (1) forming a reaction mixture comprising: (a) an iron source; (b) a silicon source; (c) an alkali metal [M] source; (d) a structure directing agent [Q] comprising a 1,3-diisobutylimidazolium cation; (e) a hydroxide ion source; and (f) water; and (2) subjecting the reaction mixture to crystallization conditions sufficient to form crystals of the ferrosilicate molecular sieve.

[0021] The reaction mixture may have a composition, in molar ratios, within the ranges set forth in Table 1: [Table 1] In the formula, M is an alkali metal and Q represents a 1,3-diisobutylimidazolium cation.

[0022] Suitable iron sources include iron(III) salts. In some embodiments, organic iron(III) salts such as iron(III) acetate, iron(III) citrate, and iron(III) oxalate may be used. In some embodiments, inorganic iron(III) salts such as iron(III) halides, iron(III) nitrate, and iron(III) sulfate may be used. If desired, two or more different iron(III) salts may be used in combination. In certain embodiments, the iron(III) salt may be iron(III) nitrate and / or iron(III) sulfate.

[0023] Suitable sources of silicon include colloidal silica, precipitated silica, fumed silica, alkali metal silicates, tetraalkyl orthosilicates (eg, tetraethyl orthosilicate), and combinations thereof.

[0024] The alkali metal [M] can be lithium, sodium, potassium, rubidium, cesium, or any combination thereof. The alkali metal is preferably sodium or potassium, and is preferably sodium. Suitable alkali metal sources include alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide.

[0025] The structure directing agent (Q) comprises a 1,3-diisobutylimidazolium cation represented by the following structure (1): [ka]

[0026] Suitable sources of Q include hydroxides, chlorides, bromides, and / or other salts of quaternary ammonium compounds.

[0027] The reaction mixture may further include seed crystals of a crystalline molecular sieve material, such as a crystalline molecular sieve of MTW framework topology, from a previous synthesis. The amount of seed crystals is not particularly limited, but typically corresponds to 0.1 to 25 wt. % (e.g., 0.1 to 10 wt. %) based on the total weight of silica in the reaction mixture. Seeding can be advantageous in reducing the time required for complete crystallization to occur and / or minimizing the formation of other crystalline impurities.

[0028] The reaction mixture components may be supplied by two or more sources. Likewise, two or more reaction mixture components may be provided by one source.

[0029] The reaction mixture can be prepared by any conceivable means, although mixing by agitation is preferred, preferably by stirring. The reaction mixture can be prepared in batch, continuous, or semi-continuous mode.

[0030] The reaction mixture may be in the form of a solution, a colloidal dispersion (colloidal sol), a gel, or a paste, with a gel being preferred.

[0031] Crystallization and post-synthesis treatment Crystallization of the molecular sieve from the reaction mixture can be carried out under static or stirred conditions in a suitable reaction vessel, such as a polypropylene jar or Teflon-lined or stainless steel autoclave, contained in a convection oven maintained at a temperature of 100° C. to 200° C. for a period sufficient for crystallization to occur (e.g., about 1 day to 21 days, or 1 day to 10 days). Preferably, crystallization is carried out under autogenous pressure, preferably in an autoclave.

[0032] Once the desired molecular sieve crystals are formed, the solid product can be separated from the reaction mixture by standard mechanical separation techniques such as centrifugation or filtration. The recovered crystals are washed with water and then dried for a few seconds to a few minutes (e.g., 5 seconds to 10 minutes for rapid drying) or for several hours (e.g., 4 hours to 24 hours for oven drying at 75°C to 150°C) to obtain the as-prepared molecular sieve crystals. The drying step can be performed under vacuum or at atmospheric pressure.

[0033] As a result of the crystallization process, the recovered crystalline molecular sieve product contains within its pores at least a portion of the structure directing agent used in its synthesis.

[0034] The as-prepared molecular sieve may be further subjected to heat treatment, ozone treatment, or other treatment to remove some or all of the structure directing agent used in its synthesis. Heat treatment (e.g., calcination) may be carried out by any method conventionally known in the art. For example, the as-prepared molecular sieve may be calcined at a temperature of 300°C to 800°C (e.g., 400°C to 650°C) for a period ranging from 1 hour to 10 hours (e.g., 3 hours to 6 hours). Additionally, calcination is generally carried out in an oxygen-containing atmosphere, such as air or an oxygen atmosphere.

[0035] The molecular sieves synthesized by the described methods may contain one or more extra-framework alkali metal cations (e.g., Na + ). It is usually desirable to remove extra-framework alkali metal cations from the molecular sieve by ion exchange or other known techniques and replace them with hydrogen, ammonium, or any desired metal ion. Particularly preferred cations are those that tailor the catalytic activity for specific hydrocarbon conversion reactions. These include hydrogen, rare earth metals, and metals from Groups 2 through 15 of the Periodic Table of the Elements. The amount of metal can range from 0.001 to 20 weight percent (e.g., 0.01 to 10 weight percent, or 0.1 to 5.0 weight percent) of the catalyst.

[0036] Molecular sieve characterization The ferrosilicate MTW molecular sieves synthesized by the methods described herein can have a SiO2 / Fe2O3 molar ratio of at least 50 (e.g., 50-500, or 50-250, or 50-125, or 75-500, or 75-250, or 75-125). The SiO2 / Fe2O3 molar ratio of the molecular sieve can be determined by conventional analysis.

[0037] The synthesis methods described herein can produce ferrosilicate MTW crystals with high purity, preferably phase pure. As used herein, the term "phase pure" means that the ferrosilicate MTW molecular sieve composition can contain at least 95 wt. % (e.g., at least 97 wt. % or at least 99 wt. %) molecular sieve having MTW topology, based on the total weight of the composition, as determined by powder XRD or NMR, or other known methods for such determination. The remainder of the composition is non-MTW material, which can include amorphous material, different crystalline phases, different framework types, or combinations thereof.

[0038] The crystals of the ferrosilicate MTW molecular sieve produced according to the methods described herein may be uniform, may have few or no twins and / or multiple twins, or may form aggregates.

[0039] The ferrosilicate MTW molecular sieves prepared as described herein may have small crystallite sizes. The ferrosilicate MTW molecular sieve crystals may have a d50 crystallite size of 0.5 microns or less (e.g., 0.2 microns or less, or 0.1 microns or less, or 0.05-0.5 microns, 0.05-0.1 microns, or 0.1-0.25 microns). More preferably, the ferrosilicate MTW molecular sieve crystals may have a d90 crystallite size of 0.5 microns or less (e.g., 0.2 microns or less, or 0.1 microns or less, or 0.05-0.5 microns, or 0.05-0.1 microns, or 0.1-0.25 microns). The ferrosilicate MTW crystals may have both d50 and d90 values ​​as described above.

[0040] Crystal size is based on individual crystals. Crystal size is the length of the longest diagonal of a three-dimensional crystal. Direct measurement of crystal size can be performed using microscopy techniques such as SEM and TEM. For example, SEM measurements involve examining the morphology of a material at high magnification (typically 1000x to 100,000x). SEM can be performed by distributing a representative portion of molecular sieve powder on a suitable mount so that individual particles are reasonably evenly spread across the entire field of view at 1000x to 100,000x magnification. From this population, a statistically significant sample of random individual crystals (e.g., 50-200) is examined, and the longest diagonal of each individual crystal is measured and recorded. (Particles that are clearly large polycrystalline aggregates should not be included in the measurement.) Based on these measurements, the d50 and d90 of the sample crystal size are calculated.

[0041] The ferrosilicate MTW molecular sieves synthesized as described herein are characterized by their powder XRD patterns. Powder XRD patterns representative of MTW molecular sieves can be found in "Collection of Simulated XRD Powder Patterns for Zeolites" by M.M.J. Treacy and J.B. Higgins (Elsevier, Fifth Revised Edition, 2007).

[0042] The powder X-ray diffraction data reported herein were collected by standard techniques using copper K-α radiation. Minor variations in the diffraction pattern may be due to variations in the molar ratio of framework species in a particular sample, resulting in changes in the lattice constants. Furthermore, sufficiently small crystals can affect peak shape and intensity, causing significant peak broadening. Subtle changes in the diffraction pattern can also result from changes in the organic compounds used in the preparation. Calcination can also cause slight shifts in the XRD pattern. Despite these small perturbations, the basic crystal lattice structure remains unchanged.

[0043] Uses of Ferrosilicate MTW Molecular Sieves Ferrosilicate MTW molecular sieves (with some or all of the structure directing agent removed) can be used as either adsorbents or catalysts to catalyze a wide variety of organic compound conversion processes. Examples of chemical conversion processes that can be effectively catalyzed by the ferrosilicate MTW molecular sieves described herein, alone or in combination with one or more other catalytically active materials (including other crystalline catalysts), include processes requiring catalysts with acid activity. Examples of organic conversion processes that can be catalyzed by the ferrosilicate MTW molecular sieves described herein include cracking, hydrocracking, disproportionation, alkylation, oligomerization, and isomerization.

[0044] Ferrosilicate MTW molecular sieves (with some or all of the structure directing agent removed) may be incorporated with another material that is resistant to the temperatures and other conditions used in organic conversion processes. Such resistant materials may be selected from active materials, inactive materials, synthetic zeolites, naturally occurring zeolites, inorganic materials, or mixtures thereof. Examples of such resistant materials may be selected from clays, silica, metal oxides such as alumina, or mixtures thereof. The inorganic materials may be naturally occurring or may be in the form of gelatinous precipitates or gels containing mixtures of silica and metal oxides. The use of resistant materials in combination with ferrosilicate MTW molecular sieves (i.e., combined with or present during the synthesis of as-prepared ferrosilicate MTW crystals where the crystals are active) tends to alter the conversion and / or selectivity of the catalyst in a particular organic conversion process. The inert resistant material preferably functions as a diluent to control the amount of conversion in a given process so that products can be obtained in an economical and orderly manner without employing other means to control the reaction rate. These materials can be incorporated into naturally occurring clays (e.g., bentonite and kaolin) to improve the crush strength of the catalyst under commercial operating conditions. The inert, resistant material (i.e., clay, oxide, etc.) acts as a binder for the catalyst. In commercial applications, it is desirable to prevent the catalyst from breaking down into powder-like materials, so a catalyst with good crush strength can be beneficial.

[0045] Naturally occurring clays that can be complexed with the ferrosilicate MTW molecular sieves include the montmorillonite and kaolin families, including sub-bentonite and kaolin commonly known as Dixie, McNamee, Georgia, and Florida clays, or other clays whose primary mineral constituents are halloysite, kaolinite, dickite, nacrite, or anauxite. Such clays may be used as originally mined or after initial calcination, acid treatment, or chemical modification. Binders useful for complexing with the ferrosilicate MTW molecular sieves also include inorganic oxides selected from silica, zirconia, titania, magnesia, beryllia, alumina, or mixtures thereof.

[0046] The ferrosilicate MTW molecular sieves (with some or all of the structure directing agent removed) can be composited with porous matrix materials such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, and ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia, and silica-magnesia-zirconia.

[0047] The relative proportions of ferrosilicate MTW molecular sieve and inorganic oxide matrix can vary widely, with the ferrosilicate MTW content ranging from 1 to 90 wt % (e.g., 2 to 80 wt %) of the composite. [Example]

[0048] The following illustrative examples are intended to be non-limiting. Example 1 Synthesis of ferrosilicate MTW molecular sieves

[0049] 0.62 g of deionized water, 1.68 g of 1 M NaOH solution, and 7.26 g of 9 wt % 1,3-diisobutylimidazolium hydroxide solution were added to a Teflon liner and stirred until the solution was homogeneous. Then, 1.00 g of fumed silica was added, and the mixture was stirred until homogeneous. Finally, 0.14 g of iron(III) nitrate nonahydrate was added. The final molar ratio of the gel was 1 part SiO: 0.01 parts Fe:O: 0.1 parts NaOH: 0.2 parts 1,3-diisobutylimidazolium hydroxide: 30 parts HO. The liner was placed in a stainless steel autoclave and rotated in a 150 °C oven for 7 days. The solid product was filtered, washed with excess deionized water, and dried in a 95 °C oven.

[0050] An SEM image of the as-prepared product is shown in Figure 1.

[0051] The as-prepared material was calcined to 550° C. for 5 hours in flowing air using a standard calcination protocol to remove the organic structure directing agent [Q].

[0052] The powder XRD patterns of the as-prepared and calcined products are shown in Figure 2, confirming that the synthesized material was MTW.

[0053] The calcined material was then ion-exchanged to the NH form by heating in an ammonium nitrate solution (typically 1 g NHNO / 1 g molecular sieve in 10 mL deionized water at 95°C for at least 2 hours). The molecular sieve was then filtered. This was repeated twice for a total of three exchanges. Finally, the molecular sieve was washed with deionized water to a conductivity of less than 50 μS / cm and dried in air at 95°C. The resulting NH form molecular sieve was converted to the H form by calcination using a standard calcination protocol.

[0054] Analysis by n-propylamine temperature-programmed desorption revealed that the product had an acid site density of 258 μmol H + / g.

[0055] Analysis by inductively coupled plasma atomic emission spectroscopy (ICP-AES) showed that the SiO2 / Fe2O3 molar ratio of the product was 90.

[0056] Example 2 Restraint Coefficient Test The Confinement Index (CI) is a test that describes the relative tendency of a material to decompose straight-chain versus branched alkanes. The competitive decomposition of n-hexane versus 3-methylpentane was first described by V.J. Frillette et al. (J. Catal. 1981, 67, 218-222).

[0057] The calcined ferrosilicate MTW product (H form) described in Example 1 was pelletized at 5 kpsi, crushed, and granulated to 20-40 mesh. A 0.6 g sample of the granulated material was calcined in air at 540°C for 4 hours and cooled in a desiccator to ensure dryness. 0.47 g of the material was then packed into a 1 / 4-inch stainless steel tube with alundum on both sides of the molecular sieve bed. The reactor tube was heated using an oven (Applied Test Systems, Inc.). Nitrogen was introduced into the reactor tube at 9.4 mL / min and atmospheric pressure. The reactor was heated to approximately 900°F (482°C), and a 50 / 50 n-hexane and 3-methylpentane feed was introduced into the reactor at a rate of 8 μL / min. The feed was delivered by an ISCO pump. Direct sampling to the GC was initiated 15 minutes after feed introduction.

[0058] The ferrosilicate MTW catalyst exhibited a CI value of 1.

[0059] Example 3 n-Decane Hydroconversion The calcined ferrosilicate MTW product (NH4- form) described in Example 1 was impregnated with palladium at a 0.5 wt% loading using the required amount of tetraamminepalladium(II) nitrate dissolved in deionized water. The impregnated sample was washed to a conductivity of less than 50 μS / cm, dried, and calcined in air at 482°C for 3 hours. The resulting powdered catalyst material was pelletized at 5 kpsi, crushed, and sieved to 20-40 mesh.

[0060] To preheat the feed, 0.5 g of catalyst was placed in the center of a 23-inch long by 1 / 4-inch outer diameter stainless steel reactor tube, with alundum supported upstream of the catalyst. The operating conditions were as follows: 1200 psig total pressure, 8.3 mL / min downflow hydrogen rate, and 0.66 cm downstream n-decane feed rate, measured at 1 atmosphere and 25°C. 3 / h. All materials were first reduced at approximately 315°C in flowing hydrogen for 1 hour. Products were analyzed by online capillary gas chromatography (GC) once every 30 minutes. Raw data from the GC was collected by an automated data acquisition / processing system, and hydrocarbon conversion was calculated from the raw data.

[0061] Conversion is defined as the amount of n-decane that reacted to form other products (including iso-C10). Yield is expressed as mol% of products other than n-decane and includes the iso-C10 isomer as a product.

[0062] The results for n-decane hydroconversion are shown in Figure 3. The results demonstrate the strong selectivity of the ferrosilicate MTW catalyst for the isomerization of linear alkanes.

Claims

1. Ferrosilicate molecular sieves of MTW framework topology with d50 crystallite size of 0.5 microns or less.

2. 50 to 500 SiO ２ / Fe ２ O ３ 2. The ferrosilicate molecular sieve of claim 1, having a molar ratio of:

3. 75 to 125 SiO ２ / Fe ２ O ３ 2. The ferrosilicate molecular sieve of claim 1, having a molar ratio of:

4. 10. The ferrosilicate molecular sieve of claim 1 having a d50 crystallite size of 0.05 to 0.25 microns and a d90 crystallite size of less than 0.5 microns.

5. 1. A method for making a ferrosilicate molecular sieve of MTW framework topology, comprising: (1) forming a reaction mixture, the reaction mixture comprising: (a) an iron source; (b) a silicon source; (c) a source of alkali metal [M]; (d) a structure directing agent [Q] comprising a 1,3-diisobutylimidazolium cation; (e) a hydroxide ion source; (f) water; (2) subjecting the reaction mixture to crystallization conditions sufficient to form crystals of the ferrosilicate molecular sieve.

6. 6. The method of claim 5, wherein the iron source comprises an iron (III) salt.

7. 6. The method of claim 5, wherein the iron (III) salt is selected from the group consisting of iron (III) nitrate, iron (III) sulfate, and any combination thereof.

8. 6. The method of claim 5, wherein the silicon source is selected from the group consisting of colloidal silica, precipitated silica, fumed silica, alkali metal silicates, tetraalkyl orthosilicates, and any combination thereof.

9. The method of claim 5 wherein the alkali metal comprises sodium.

10. 6. The method of claim 5, wherein the crystallization conditions comprise heating the reaction mixture at a temperature in the range of 100°C to 200°C under autogenous pressure.

11. 6. The method of claim 5, wherein the reaction mixture has the following composition, in terms of molar ratio: Table 1A The method comprising:

12. 6. The method of claim 5, wherein the reaction mixture has the following composition, in terms of molar ratio: Table 1B The method comprising:

13. 10. A process for converting a feedstock containing organic compounds to conversion products, the process comprising contacting the feedstock with a catalyst comprising the ferrosilicate molecular sieve of claim 1 under organic compound conversion conditions.

14. 14. The process of claim 13, wherein the conversion process is at least one of a cracking process, a hydrocracking process, a disproportionation process, an alkylation process, or an isomerization process.

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