Heteroatomic ewt structure molecular sieve, preparation method thereof and method for synthesizing tetramethylbenzene by alkylating pseudocumene with methanol

Abstract

The present disclosure relates to a kind of heteroatom EWT structure molecular sieve and its preparation method and the method of synthesizing tetramethylbenzene by alkylating trimethylbenzene with methanol, the skeleton of the heteroatom EWT structure molecular sieve includes silicon element, aluminum element and heteroatom element, the molar ratio of silicon element in the heteroatom EWT structure molecular sieve with SiO2 and aluminum element with Al2O3 is 10 or more, the molar ratio of silicon element in the heteroatom EWT structure molecular sieve with SiO2 and heteroatom element with heteroatom oxide is 10 or more;Heteroatom element includes one or several of boron, iron, titanium, gallium and germanium.The heteroatom EWT structure molecular sieve shows advantage in improving acid center utilization rate, is used in trimethylbenzene and methanol alkylating reaction, and its activity, selectivity and stability are higher, catalytic performance has obviously improved, trimethylbenzene conversion rate and tetramethylbenzene selectivity are higher than ZSM-5 molecular sieve.

Description

Technical Field

[0001] This disclosure relates to the field of petrochemical technology, specifically to a heteroatom EWT structure molecular sieve and its preparation method, as well as a method for synthesizing tetramethylbenzene by alkylation of pseudotrimethylbenzene and methanol. Background Technology

[0002] 1,2,4,5-TEMB (1,2,4,5-TEMB) is a C-type polymethyl ether with extremely high utilization value. 10 + Heavy aromatics are mainly used to produce pyromellitic dianhydride (PMDA), which then reacts with 4,4-diaminodiphenyl ether to produce polyimide. Currently, the methods for preparing pyromellitic dianhydride both domestically and internationally rely on C1... 10 Heavy aromatic hydrocarbon separation. The raw materials for this method mainly come from reforming units in refineries and wide-fraction reforming units in chemical fiber plants, which limits production capacity and has resulted in a persistent shortage of mesitylene. Pseudotrimethylbenzene is a cheap and readily available chemical product, while methanol faces a supply surplus in China. Therefore, developing a technology for preparing mesitylene through the alkylation reaction of pseudotrimethylbenzene and methanol can address the demand for mesitylene production capacity. When using HZSM-5 molecular sieve to catalyze the alkylation reaction of pseudotrimethylbenzene and methanol, the conversion rate of pseudotrimethylbenzene is 10-30%, and the selectivity of mesitylene in the tetramethylbenzene mixture is >90%. However, the tetramethylbenzene yield of this molecular sieve is low, only 2-10%, with a relatively high amount of byproducts such as benzene, toluene, and xylene, leading to a low mesitylene yield. This is because the ten-membered ring channel size of the ZSM-5 molecular sieve is small, resulting in low utilization of acidic centers.

[0003] Based on the number of pore window rings, molecular sieves can be classified into microporous molecular sieves (8MR), mesoporous molecular sieves (10MR), macroporous molecular sieves (12MR), and ultramacroporous molecular sieves (>12MR). Ultramacroporous molecular sieves overcome the pore limitations of traditional molecular sieves, exhibiting advantages in improving the reactivity of macromolecules, extending sieve lifetime, and enhancing product selectivity. Of the 255 molecular sieve structures disclosed on the IZA website, only about 10 are ultramacroporous, including aluminum-phosphorus / gallium, silicon-germanium / gallium, and aluminum-silicon molecular sieves. However, ultramacroporous aluminum-silicon molecular sieves have a relatively small number of boron acid centers, requiring synthesis under high-silica or pure silicon conditions, making them difficult to apply in macromolecular acid catalysis. The addition of aluminum can regulate the acid centers of the molecular sieve; therefore, promoting aluminum incorporation into the ultramacroporous molecular sieve framework is a key issue. Inserting large aluminum-oxygen tetrahedra into a regular silica molecular sieve framework can cause irregular deformation of the framework, extending to the entire molecular sieve crystal, complicating the coordination of the molecular sieve framework atoms. This is evident from the molecular sieve's... 29 Si MAS NMR and 27Al MAS NMR spectra show (1. CAFyfe, H. Strobl, GT Kokotailo, CT Pastzto, GE Barlow, S. Bradley, Zeolites, 8 (1988); 2. J. Stelzer, M. Paulus, M. Hunger, J. Weitkamp, ​​Microporous Mesoporous Mater., 22 (1998) 1.; 3. J. A. Van Bokhoven, DC. Koningsberger, P. Kunkeler, P. van Bekkum and A. PM. Kentgens, J. Am. Chem. Soc., 122 (2000) 12842.). Besides aluminum, boron is one of the most common elements that can be inserted into the molecular sieve framework. Compared to aluminum, boron-oxygen tetrahedra are smaller and more easily inserted into the molecular sieve framework. Without distorting the silicon-oxygen tetrahedra, the coordination of silicon and boron in silicon-boron molecular sieves is relatively simple, which can be observed from the molecular sieve... 29 Si MAS NMR and 11 The B MAS NMR spectrum shows (4.C.Yang,Q.Xu,C.Hu,Mat.Chem.Phys.,63(2000)55;5.SIZones,SJ.Hwang,Microporous Mesoporous Mater.,58(2003)263.). However, due to the low stability of boron-containing molecular sieves, boron atoms are easily detached from the framework during the thermal / hydrothermal treatment of ion exchange. Summary of the Invention

[0004] The purpose of this disclosure is to provide a heteroatom EWT structured molecular sieve, its preparation method, and a method for synthesizing tetramethylbenzene by alkylation of pseudotrimethylbenzene and methanol. The heteroatom EWT structured molecular sieve exhibits advantages in improving the utilization rate of acid centers. When used in the alkylation reaction of pseudotrimethylbenzene and methanol, it has high activity, selectivity, and stability, and its catalytic performance is significantly improved. The conversion rate of pseudotrimethylbenzene, the selectivity of tetramethylbenzene, and the yield of tetramethylbenzene are all higher than those of ZSM-5 molecular sieve, and the byproducts such as benzene, toluene, and xylene are significantly reduced.

[0005] To achieve the above objectives, the first aspect of this disclosure provides a heteroatom EWT structured molecular sieve, wherein the framework of the heteroatom EWT structured molecular sieve comprises silicon, aluminum, and heteroatom elements, wherein the molar ratio of silicon (calculated as SiO2) to aluminum (calculated as Al2O3) in the heteroatom EWT structured molecular sieve is 10 or more, and the molar ratio of silicon (calculated as SiO2) to heteroatom elements (calculated as heteroatom oxides) in the heteroatom EWT structured molecular sieve is 10 or more; the heteroatom elements include one or more of boron, iron, titanium, gallium, and germanium.

[0006] Optionally, the molar ratio of silicon (calculated as SiO2) to aluminum (calculated as Al2O3) in the heteroatom EWT structure molecular sieve is 10–60, preferably 15–30; the molar ratio of silicon (calculated as SiO2) to heteroatom elements (calculated as heteroatom oxides) in the heteroatom EWT structure molecular sieve is 10–250, preferably 120–240.

[0007] Optionally, when the heteroatom element is boron, the molar ratio of silicon (calculated as SiO2) to boron (calculated as B2O3) in the heteroatom EWT structure molecular sieve is 120–180; when the heteroatom element is one or more of iron, titanium, gallium, and germanium, the molar ratio of silicon (calculated as SiO2) to heteroatom elements (calculated as heteroatom oxides) in the heteroatom EWT structure molecular sieve is 150–240.

[0008] Optionally, the total specific surface area of ​​the heteroatom EWT structured molecular sieve is 300–650 cm². 2 / g, preferably 450-580cm 2 / g; average pore size is 0.5–20 nm, preferably 1–5 nm, more preferably 2–5 nm; total pore volume is 0.25–0.60 cm³. 3 / g, preferably 0.25~0.45cm 3 / g; the volume of mesopores with a pore size of 2.0–20.0 nm is 0.05–0.35 cm³. 3 / g, preferably 0.10~0.25cm 3 / g; the percentage of mesopore volume with a pore size of 2.0–20.0 nm in the total pore volume is 30–50%, preferably 35–50%; the average particle size of the heteroatom EWT structure molecular sieve is 0.2–1.5 μm, preferably 0.3–1.0 μm; the relative crystallinity is 50–100%, preferably 75–95%; the ratio of Brønsted acid to Lewis acid content of the heteroatom EWT structure molecular sieve determined by pyridine adsorption infrared spectroscopy at 350 °C is 0.3–0.6; preferably, the heteroatom EWT structure molecular sieve is a hydrogen-type heteroatom EWT structure molecular sieve.

[0009] A second aspect of this disclosure provides a method for preparing the heteroatom EWT structured molecular sieve described in the first aspect of this disclosure, the method comprising:

[0010] (1) A silicon source, a heteroatom element source, a first alkali source, a first organic template agent and water are mixed, and the resulting first material to be crystallized is subjected to a first crystallization to obtain molecular sieve raw powder; the molecular sieve raw powder is calcined to obtain sodium-type molecular sieve;

[0011] (2) The sodium molecular sieve is subjected to ion exchange with an acid solution, the obtained molecular sieve intermediate is mixed with an aluminum source, a second alkali source and a second organic template agent, and the obtained second crystallization material is subjected to a second crystallization.

[0012] The heteroatom elements include one or more of boron, iron, titanium, gallium, and germanium; the first organic template agent and the second organic template agent are respectively a cyclic bis-quaternary ammonium base compound and / or a cyclic bis-quaternary ammonium salt compound; the temperature of the first crystallization is 60–180°C, preferably 100–170°C; the time is 96–168 h, preferably 96–144 h; the temperature of the second crystallization is 60–180°C, preferably 100–170°C; the time is 96–168 h, preferably 96–144 h.

[0013] Optionally, the silicon source is selected from one or more of silica sol, water glass, solid silica gel, tetraethyl orthosilicate, and fumed silica, preferably solid silica gel; the heteroatom element source is selected from one or more of boron oxide, boric acid, iron oxide, titanium oxide, gallium oxide, and germanium oxide, preferably boron oxide and / or boric acid; the first alkali source and the second alkali source are respectively selected from one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide, preferably both of the first alkali source and the second alkali source are sodium hydroxide; the aluminum source is selected from one or more of aluminum chloride, aluminum sulfate, hydrated alumina, sodium aluminate, and aluminum sol, preferably sodium aluminate; the first organic template agent and the second organic template agent are respectively selected from at least one having the structure shown in formula (1):

[0014]

[0015] R1, R2, R3, and R4 are each independently selected from alkyl groups having 1 to 4 carbon atoms. Preferably, R1, R2, R3, and R4 are each independently selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl, preferably methyl or ethyl; m is 2 or 3; n is any integer from 1 to 10; X - This includes hydroxide ions or halide anions.

[0016] Optionally, the silicon source is SiO2, and the heteroatom element source is heteroatom oxide. When the heteroatom element is boron, the molar ratio of SiO2 to B2O3 in the first material to be crystallized is 10 to 250, preferably 30 to 120. When the heteroatom element is one or more of iron, titanium, gallium, and germanium, the molar ratio of SiO2 to heteroatom oxide in the first material to be crystallized is 10 to 250, preferably 30 to 150.

[0017] Optionally, in step (1), the silicon source is SiO2, the heteroatom element source is heteroatom oxide, the first organic template agent is T1, and when the heteroatom element in the first material to be crystallized is boron, the molar ratio of SiO2 to B2O3 is 10-250, preferably 30-120; when the heteroatom element is one or more of iron, titanium, gallium and germanium, the molar ratio of SiO2 to heteroatom oxide is 10-250, preferably 30-150; and when the heteroatom element is OH... - The molar ratio of the first alkali source to SiO2 is 0.2–1.0, preferably 0.2–0.5; the molar ratio of T1 to SiO2 is 0.02–0.5, preferably 0.08–0.15; the molar ratio of H2O to SiO2 is 5–20, preferably 5–10; in step (2), the aluminum source is Al2O3, the second organic template agent is T2, and the molar ratio of SiO2 to Al2O3 in the second material to be crystallized is 10 or more, preferably 10–60, more preferably 15–30; the OH- - The molar ratio of the second alkali source to SiO2 is 0.2 to 1.0, preferably 0.2 to 0.5; the molar ratio of T2 to SiO2 is 0.02 to 0.5, preferably 0.08 to 0.15; and the molar ratio of H2O to SiO2 is 5 to 20, preferably 5 to 10.

[0018] Optionally, the calcination temperature is 400–650°C, and the time is 1–7 h; the weight ratio of the acid solution to the sodium molecular sieve is (1–100):1, the concentration of the acid solution is 0.01–0.10 mol / L, the ion exchange temperature is 60–90°C, and the time is 2–24 h; the acid solution is selected from one or more of hydrochloric acid solution, nitric acid solution, and sulfuric acid solution.

[0019] The third aspect of this disclosure provides a method for synthesizing tetramethylbenzene by alkylation of pseudotrimethylbenzene and methanol, the method comprising: contacting pseudotrimethylbenzene with methanol under alkylation reaction conditions and in the presence of a catalyst; wherein the catalyst is the heteroatom EWT structure molecular sieve described in the first aspect of this disclosure.

[0020] Optionally, the alkylation reaction conditions include: in a fixed-bed reactor, contacting the catalyst with pseudotrimethylbenzene and methanol under gas-phase reaction conditions, wherein the gas-phase reaction temperature is 240–450°C, preferably 330–360°C; the time is 10–500 h, preferably 20–350 h; the pressure is 0.2–2.0 MPa, preferably 0.5–1.5 MPa; and the mass hourly space velocity (HSV) of pseudotrimethylbenzene is 0.5–3.5 h⁻¹. -1 Preferably 1-2 hours -1 The feed molar ratio of the pseudotrimethylbenzene to methanol is (0.2-4.0):1, preferably (0.5-1.5):1.

[0021] Through the above technical solution, the heteroatom EWT structure molecular sieve provided in this disclosure simultaneously contains aluminum atoms and heteroatoms in its framework. Aluminum atoms can adjust the acidity of the molecular sieve, while heteroatoms can adjust the position of aluminum atoms in the framework and the acid type. This disclosure employs a two-stage crystallization method of crystallization-decomposition-dissolution-recrystallization. First, an EWT structure molecular sieve containing silicon and heteroatoms is prepared. Then, some framework heteroatoms are removed to form silanol nests, providing vacancy sites to facilitate Al atoms entering the framework for isomorphous substitution, thereby preparing a molecular sieve with a lower silicon-to-aluminum ratio. Simultaneously, the acidity and pore structure of the molecular sieve are improved to meet the requirements of acidic catalytic reactions. Compared with EWT molecular sieves and ZSM-5 ten-membered ring molecular sieve catalysts, the heteroatom EWT molecular sieve provided in this disclosure, when used as a catalyst for the alkylation reaction of pseudotrimethylbenzene and methanol, exhibits advantages in improving the utilization rate of acid centers due to its 3D channel system composed of 21-membered and 10-membered rings. It has higher activity, selectivity and stability, and significantly improved catalytic performance. The conversion rate of pseudotrimethylbenzene, the selectivity of tetramethylbenzene and the yield of tetramethylbenzene are all higher than those of ZSM-5 molecular sieve, and the byproducts such as benzene, toluene and xylene are significantly reduced.

[0022] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is the XRD pattern of the heteroatom EWT structure molecular sieve 1 with boron atoms in its framework, prepared in Example 1 of this disclosure;

[0025] Figure 2 This is a SEM image of the boron-containing heteroatom EWT structure molecular sieve 1 prepared in Example 1 of this disclosure;

[0026] Figure 3This is a TEM image of the boron-containing heteroatom EWT structure molecular sieve 1 prepared in Example 1 of this disclosure;

[0027] Figure 4 This is the isotherm curve of the boron-containing heteroatom EWT structure molecular sieve 1 prepared in Example 1 of this disclosure;

[0028] Figure 5 This is the XRD pattern of the heteroatom EWT structure molecular sieve 2 with iron atoms in its framework, prepared in Example 2 of this disclosure;

[0029] Figure 6 This is the XRD pattern of the heteroatom EWT structure molecular sieve 3 with titanium atoms in its framework, prepared in Example 3 of this disclosure;

[0030] Figure 7 This is the XRD pattern of the gallium-containing heteroatom EWT structure molecular sieve 4 prepared in Example 4 of this disclosure;

[0031] Figure 8 This is the XRD pattern of the heteroatom EWT structure molecular sieve 5 with germanium atoms in its framework, prepared in Example 5 of this disclosure. Detailed Implementation

[0032] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0033] The first aspect of this disclosure provides a heteroatom EWT structured molecular sieve, wherein the framework of the heteroatom EWT structured molecular sieve comprises silicon, aluminum, and heteroatom elements, wherein the molar ratio of silicon (calculated as SiO2) to aluminum (calculated as Al2O3) in the heteroatom EWT structured molecular sieve is 10 or more, and the molar ratio of silicon (calculated as SiO2) to heteroatom elements (calculated as heteroatom oxides) in the heteroatom EWT structured molecular sieve is 10 or more; the heteroatom elements include one or more of boron, iron, titanium, gallium, and germanium.

[0034] The heteroatom EWT structured molecular sieve disclosed herein possesses a 3D channel system composed of 21-membered and 10-membered rings, which can significantly improve the utilization rate of acidic centers in the molecular sieve. Furthermore, the framework of the heteroatom EWT structured molecular sieve contains aluminum and heteroatom elements. Aluminum atoms can regulate the acidity of the molecular sieve, while heteroatom elements can regulate the position of aluminum in the framework and the acid distribution, thereby making its acidity more suitable and its intracrystalline mesopores more abundant. When used in the alkylation reaction of pseudotrimethylbenzene and methanol, this heteroatom EWT structured molecular sieve exhibits optimized catalytic performance, improving the conversion rate of pseudotrimethylbenzene and the selectivity of tetramethylbenzene.

[0035] In one embodiment of this disclosure, the molar ratio of silicon (calculated as SiO2) to aluminum (calculated as Al2O3) in the heteroatom EWT structured molecular sieve is 10–60, preferably 15–30; the molar ratio of silicon (calculated as SiO2) to heteroatom oxides in the heteroatom EWT structured molecular sieve is 10–250, preferably 120–240. In the above embodiments, by selecting preferred silicon-to-aluminum ratios and silicon-to-heteroatom ratios, the acid distribution and acid strength of the molecular sieve can be further adjusted, thereby improving the catalytic activity of the molecular sieve.

[0036] In one embodiment of this disclosure, when the heteroatom element is boron, the molar ratio of silicon (calculated as SiO2) to boron (calculated as B2O3) in the heteroatom EWT structure molecular sieve is 120–180; when the heteroatom element is one or more of iron, titanium, gallium, and germanium, the molar ratio of silicon (calculated as SiO2) to heteroatom elements (calculated as heteroatom oxides) in the heteroatom EWT structure molecular sieve is 150–240.

[0037] In one embodiment of this disclosure, the total specific surface area of ​​the heteroatom EWT structured molecular sieve is 300–650 cm². 2 / g, preferably 450-580cm 2 / g; average pore size is 0.5–20 nm, preferably 1–5 nm, more preferably 2–5 nm; total pore volume is 0.25–0.60 cm³. 3 / g, preferably 0.25~0.45cm 3 / g; the volume of mesopores with a pore size of 2.0–20.0 nm is 0.05–0.35 cm³. 3 / g, preferably 0.10~0.25cm 3 / g; the percentage of mesopore volume with a pore size of 2.0–20.0 nm in the total pore volume is 30–50%, preferably 35–50%; the average particle size of the heteroatom EWT structure molecular sieve is 0.2–1.5 μm, preferably 0.3–1.0 μm; the relative crystallinity is 50–100%, preferably 75–95%; the ratio of Brønsted acid to Lewis acid content of the heteroatom EWT structure molecular sieve, determined by pyridine adsorption infrared spectroscopy at 350 °C, is 0.3–0.6. In a preferred embodiment, the heteroatom EWT structure molecular sieve is a hydrogen-type heteroatom EWT structure molecular sieve. In the above embodiments, the heteroatom EWT structure molecular sieve has abundant mesoporous structure, which is beneficial for catalyzing the alkylation reaction of pseudotrimethylbenzene and methanol, and improving the conversion rate of pseudotrimethylbenzene and the selectivity of tetramethylbenzene; by selecting a molecular sieve with preferred acid strength, it is beneficial to improve the catalytic activity and selectivity of the molecular sieve.

[0038] A second aspect of this disclosure provides a method for preparing the heteroatom EWT structured molecular sieve described in the first aspect of this disclosure, the method comprising:

[0039] (1) A silicon source, a heteroatom element source, a first alkali source, a first organic template agent and water are mixed, and the resulting first material to be crystallized is subjected to a first crystallization to obtain molecular sieve raw powder; the molecular sieve raw powder is calcined to obtain sodium-type molecular sieve;

[0040] (2) The sodium molecular sieve is subjected to ion exchange with an acid solution, the obtained molecular sieve intermediate is mixed with an aluminum source, a second alkali source and a second organic template agent, and the obtained second crystallization material is subjected to a second crystallization.

[0041] The heteroatom element includes one or more of boron, iron, titanium, gallium, and germanium. The first organic template agent and the second organic template agent are respectively a cyclic bis-quaternary ammonium base compound and / or a cyclic bis-quaternary ammonium salt compound. The temperature of the first crystallization is 60–180°C, preferably 100–170°C; the time is 96–168 h, preferably 96–144 h. The temperature of the second crystallization is 60–180°C, preferably 100–170°C; the time is 96–168 h, preferably 96–144 h. A cyclic bis-quaternary ammonium base compound refers to a cyclic compound containing two quaternary ammonium bases, and the nitrogen atoms of the two quaternary ammonium bases are not directly connected. A cyclic bis-quaternary ammonium salt compound refers to a cyclic compound containing two quaternary ammonium salts, and the nitrogen atoms of the two quaternary ammonium salts are not directly connected.

[0042] The preparation method disclosed herein is simple to operate. It employs a two-stage crystallization process of crystallization-decomposition-dissolution-recrystallization to first prepare an EWT-structured molecular sieve containing silicon and heteroatoms. Then, some framework heteroatoms are removed to form silanol nests, providing vacancy sites to facilitate the entry of Al atoms into the framework for isomorphous substitution, thereby preparing a molecular sieve with a lower silicon-to-aluminum ratio. This improves the acidity of the molecular sieve and meets the requirements of acidic catalytic reactions. The method disclosed herein not only synthesizes ultra-large porous molecular sieves with a 3D channel system composed of 21-membered and 10-membered rings, but also generates a large number of mesopores with larger pore sizes, effectively improving the pore structure of the molecular sieve. This allows for the introduction of larger aluminum atoms and heteroatoms into the molecular sieve framework, optimizing the acid distribution and acid strength of the molecular sieve, resulting in higher conversion rates of pseudotrimethylbenzene and tetramethylbenzene yields, while significantly reducing byproducts such as benzene, toluene, and xylene.

[0043] In one embodiment of this disclosure, the silicon source is selected from one or more of silica sol, water glass, solid silica gel, tetraethyl orthosilicate, and fumed silica, preferably solid silica gel; the heteroatom element source is selected from one or more of boron oxide, boric acid, iron oxide, titanium oxide, gallium oxide, and germanium oxide, preferably boron oxide and / or boric acid; the first alkali source and the second alkali source are respectively selected from one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide, preferably both of the first alkali source and the second alkali source are sodium hydroxide; the aluminum source is selected from one or more of aluminum chloride, aluminum sulfate, hydrated alumina, sodium aluminate, and aluminum sol, preferably sodium aluminate.

[0044] In one embodiment of this disclosure, the first organic template agent and the second organic template agent are each selected from at least one having a structure as shown in formula (1): Formula (1); wherein R1, R2, R3 and R4 are each independently selected from alkyl groups having 1 to 4 carbon atoms, preferably, R1, R2, R3 and R4 are each independently selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl, preferably methyl or ethyl; m is 2 or 3; n is any integer from 1 to 10; X - This includes hydroxide ions or halide anions.

[0045] In one embodiment of this disclosure, the silicon source is SiO2, and the heteroatom element source is heteroatom oxide. When the heteroatom element is boron, the molar ratio of SiO2 to B2O3 in the first material to be crystallized is 10 to 250, preferably 30 to 120. When the heteroatom element is one or more of iron, titanium, gallium, and germanium, the molar ratio of SiO2 to heteroatom oxide in the first material to be crystallized is 10 to 250, preferably 30 to 150.

[0046] In one embodiment of this disclosure, in step (1), the silicon source is SiO2, the heteroatom element source is heteroatom oxide, the first organic template agent is T1, and when the heteroatom element in the first material to be crystallized is boron, the molar ratio of SiO2 to B2O3 is 10-250, preferably 30-120; when the heteroatom element is one or more of iron, titanium, gallium, and germanium, the molar ratio of SiO2 to heteroatom oxide is 10-250, preferably 30-150; and when the heteroatom element is OH... -The molar ratio of the first alkali source to SiO2 is 0.2–1.0, preferably 0.2–0.5; the molar ratio of T1 to SiO2 is 0.02–0.5, preferably 0.08–0.15; the molar ratio of H2O to SiO2 is 5–20, preferably 5–10; in step (2), the aluminum source is Al2O3, the second organic template agent is T2, and the molar ratio of SiO2 to Al2O3 in the second material to be crystallized is 10 or more, preferably 10–60, more preferably 15–30; the OH- - The molar ratio of the second alkali source to SiO2 is 0.2 to 1.0, preferably 0.2 to 0.5; the molar ratio of T2 to SiO2 is 0.02 to 0.5, preferably 0.08 to 0.15; and the molar ratio of H2O to SiO2 is 5 to 20, preferably 5 to 10.

[0047] In one embodiment of this disclosure, the calcination temperature is 400–650°C, and the time is 1–7 h; the weight ratio of the acid solution to the sodium molecular sieve is (1–100):1, the concentration of the acid solution is 0.01–0.10 mol / L, the ion exchange temperature is 60–90°C, and the time is 2–24 h; the acid solution is selected from one or more of hydrochloric acid solution, nitric acid solution, and sulfuric acid solution.

[0048] The third aspect of this disclosure provides a method for synthesizing tetramethylbenzene by alkylation of pseudotrimethylbenzene and methanol, the method comprising: contacting pseudotrimethylbenzene with methanol under alkylation reaction conditions and in the presence of a catalyst; wherein the catalyst is the heteroatom EWT structure molecular sieve described in the first aspect of this disclosure.

[0049] This disclosure uses a heteroatom EWT molecular sieve with a large porous structure as a catalyst. When used in the alkylation reaction of pseudotrimethylbenzene and methanol, it exhibits optimized catalytic performance, which can improve the conversion rate of pseudotrimethylbenzene and the selectivity of tetramethylbenzene, thereby improving the yield of tetramethylbenzene.

[0050] In one embodiment of this disclosure, the alkylation reaction conditions include: in a fixed-bed reactor, contacting the catalyst with pseudotrimethylbenzene and methanol under gas-phase reaction conditions, wherein the gas-phase reaction temperature is 240–450°C, preferably 330–360°C; the time is 10–500 h, preferably 20–350 h; the pressure is 0.2–2.0 MPa, preferably 0.5–1.5 MPa; and the mass hourly space velocity (HSV) of pseudotrimethylbenzene is 0.5–3.5 h⁻¹. -1 Preferably 1-2 hours -1The feed molar ratio of pseudotrimethylbenzene to methanol is (0.2–4.0):1, preferably (0.5–1.5):1. In the above embodiments, by selecting preferred alkylation reaction conditions and feed ratios, it is beneficial for pseudotrimethylbenzene and methanol to react fully, thereby further improving the conversion rate of pseudotrimethylbenzene.

[0051] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0052] Example 1

[0053] (1) Add an aqueous solution containing 0.01425 mol of the first organic template agent (denoted as T1, with the structure as follows) to the polytetrafluoroethylene liner. Where m = 2, n = 3, R1, R2, R3, and R4 are all methyl groups, the molar mass of T1 is 248 g / mol, the mass fraction is 25.74%, and X... - For Br - Add 0.0032 mol of boric acid; then add 0.02 mol of sodium hydroxide (the first alkali source) and 0.051 mol of water, and finally add 0.095 mol of coarse solid silica gel. Stir well to obtain the first material to be crystallized. The molar ratio of SiO2 to B2O3 in the first material to be crystallized is 30, with OH... - The molar ratio of the first alkali source to SiO2 was 0.21, the molar ratio of T1 to SiO2 was 0.15, and the molar ratio of H2O to SiO2 was 6.5. The polytetrafluoroethylene-lined cap was sealed, and the mixture was placed in a stainless steel crystallization autoclave. The autoclave was then placed in a rotary oven, and the crystallization temperature program was set. The first crystallization was initiated at 160℃ for 144 hours. After the first crystallization, the autoclave was allowed to cool to room temperature. The autoclave was then opened, and the product was washed and filtered with deionized water. Finally, it was dried in an oven at 80℃ for 12 hours. The resulting molecular sieve powder was then calcined in a muffle furnace at 550℃ for 5 hours to remove the first organic template agent, yielding a boron-containing sodium-type molecular sieve.

[0054] (2) Ion exchange of sodium molecular sieve with hydrochloric acid solution is carried out. Specifically, hydrochloric acid solution and sodium molecular sieve are mixed at a weight ratio of 40:1, heated to 80°C under stirring and reflux conditions, and kept for 12 hours. After washing, filtering and drying, molecular sieve intermediate is obtained. The concentration of hydrochloric acid solution is 0.03 mol / L. Add the following to a polytetrafluoroethylene (PTFE) liner: an aqueous solution containing 0.01425 mol of a second organic template agent (denoted as T2, T2 having the same structure as T1, with a molar mass of 248 g / mol and a mass fraction of 25.74%), 3.41 mL of sodium aluminate (containing 101.5 g / L alumina, 194 g / L sodium hydroxide, 150.35 g / L sodium oxide, with a specific gravity of 1.227 g / mL and a mass fraction of 20.50%), 0.02 mol of sodium hydroxide (a second alkali source), and 0.198 mol of water. Then add a molecular sieve intermediate and stir the resulting second crystallization material evenly. The molar ratio of SiO2 to sodium aluminate (calculated as Al2O3) in the second crystallization material is 2:8. - The molar ratio of the second alkali source to SiO2 was 0.384, the molar ratio of T2 to SiO2 was 0.15, and the molar ratio of H2O to SiO2 was 10.0. Finally, the polytetrafluoroethylene liner was sealed and placed in a stainless steel crystallization kettle, which was then placed in a rotary oven for a second crystallization at 160℃ for 144h, resulting in a heteroatom EWT structure molecular sieve 1 with an aluminum and boron skeleton, i.e., catalyst 1, denoted as C1.

[0055] Example 2

[0056] Similar to Example 1, except that: iron oxide is used instead of boric acid; the molar ratio of SiO2 to Fe2O3 in the first material to be crystallized is 50; the temperature of the first crystallization is 160°C and the time is 96 h; the molar ratio of SiO2 to sodium aluminate (calculated as Al2O3) in the second material to be crystallized is 25; the temperature of the second crystallization is 165°C and the time is 120 h, resulting in a heteroatom EWT structure molecular sieve 2 with an aluminum and iron atom framework, i.e., catalyst 2, denoted as C2.

[0057] Example 3

[0058] Similar to Example 1, except that: titanium dioxide is used instead of boric acid; the molar ratio of SiO2 to TiO2 in the first material to be crystallized is 60; the temperature of the first crystallization is 140°C and the time is 144 h; the molar ratio of SiO2 to sodium aluminate (calculated as Al2O3) in the second material to be crystallized is 20; the temperature of the second crystallization is 175°C and the time is 96 h, resulting in a heteroatom EWT structure molecular sieve 3 with a framework containing aluminum and titanium atoms, i.e., catalyst 3, denoted as C3.

[0059] Example 4

[0060] Similar to Example 1, except that gallium oxide is used instead of boric acid, the molar ratio of SiO2 to Ga2O3 in the first material to be crystallized is 80, the first crystallization temperature is 140℃, and the time is 148h; the molar ratio of SiO2 to sodium aluminate (calculated as Al2O3) in the second material to be crystallized is 20, the second crystallization temperature is 165℃, and the time is 96h, resulting in a heteroatom EWT structure molecular sieve 4 with a framework containing aluminum and gallium atoms, i.e., catalyst 4, denoted as C4.

[0061] Example 5

[0062] Similar to Example 1, except that germanium oxide is used instead of boric acid, the molar ratio of SiO2 to GeO2 in the first crystallization material is 100, the first crystallization temperature is 140℃, and the time is 48h; the molar ratio of SiO2 to sodium aluminate (calculated as Al2O3) in the second crystallization material is 15, the second crystallization temperature is 175℃, and the time is 96h, resulting in a heteroatom EWT structure molecular sieve 5 with a framework containing aluminum and germanium atoms, i.e., catalyst 5, denoted as C5.

[0063] Example 6

[0064] The preparation method is the same as in Example 1, except that the molar ratio of SiO2 to B2O3 in the first material to be crystallized is 60, and the molar ratio of SiO2 to sodium aluminate (calculated as Al2O3) in the second material to be crystallized is 30, thus obtaining a heteroatom EWT structure molecular sieve 6 with aluminum and boron atoms in its framework, i.e., catalyst 6, denoted as C6.

[0065] Example 7

[0066] The preparation method was the same as in Example 1, except that the temperature of the first crystallization was 150°C and the time was 148 h. After the first crystallization, the crystallization vessel was cooled to room temperature, the vessel was opened, and the product was washed and filtered with deionized water. Finally, it was dried in an oven at 120°C for 24 h. The resulting molecular sieve powder was calcined in a muffle furnace at 580°C for 10 h to remove the template agent, thus obtaining a sodium-type molecular sieve. The temperature of the second crystallization was 170°C and the time was 96 h, resulting in a heteroatom EWT structure molecular sieve 7 with an aluminum and boron atom framework, i.e., catalyst 7, denoted as C7.

[0067] Comparative Example 1

[0068] (1) Sodium hydroxide (alkali source), sodium aluminate (aluminum source), and the structure as shown in formula (1) are added. m=2, n=4, R1, R2, R3, and R4 are all methyl groups, X - For Br -The organic template agent is dissolved in water and mixed evenly to form a solution; solid silica gel (silicon source) is added to the solution and mixed evenly to form a gel-like material to be crystallized. The molar ratio of each material in the material to be crystallized is: n(SiO2) / n(Al2O3)=120, n(T) / n(SiO2)=0.15, n(OH) - ) / n(SiO2)=0.38, n(H2O) / n(SiO2)=7.3, where T is an organic template agent;

[0069] (2) The gel-like material to be crystallized was subjected to a first-stage crystallization reaction under autogenous pressure at a temperature of 120°C for 24 hours. The temperature was then raised to 160°C, and a second-stage crystallization reaction was carried out under autogenous pressure for 120 hours. After the second-stage crystallization, the material was filtered, washed, and dried, and then subjected to ammonium exchange with an ammonium salt solution. After the exchanged material was filtered and dried, it was calcined at 550°C for 4 hours to obtain a hydrogen-form EWT structured molecular sieve, which is the comparative catalyst 1, denoted as D1.

[0070] Comparative Example 2

[0071] ZSM-5 molecular sieve with n(SiO2) / n(Al2O3) = 40 (commercially purchased from Sinopec Changling Catalyst Plant) was subjected to ammonium exchange with ammonium salt. After filtration and drying, the exchanged material was calcined at 550℃ for 4 hours to obtain hydrogen-form ZSM-5 molecular sieve, which is the comparative catalyst 2, denoted as D2.

[0072] Reaction Example 1

[0073] A continuous flow pressurized fixed-bed reactor was loaded with 2g of C1 as a catalyst, and pseudotrimethylbenzene and methanol were added as reactants. The reaction conditions were: temperature 360℃, pressure 0.8 MPa, and mass hourly space velocity (WHSV) of pseudotrimethylbenzene 1 h⁻¹. -1 The reaction time was 35 hours, and the feed molar ratio of pseudotrimethylbenzene to methanol was 1:2. The evaluation results are shown in Table 3.

[0074] Reactions 2-9

[0075] Same as Example 1, except that C2 to C7 and D1 to D2 are used instead of C1, and the evaluation results are shown in Table 3.

[0076] Reaction Example 10

[0077] A continuous flow pressurized fixed-bed reactor was loaded with 2g of C1 as a catalyst, and pseudotrimethylbenzene and methanol were added as reactants. The reaction conditions were: temperature 330℃, pressure 0.8 MPa, and mass hourly space velocity (WHSV) of pseudotrimethylbenzene 2 h⁻¹. -1 The reaction time was 35 hours, and the feed molar ratio of pseudotrimethylbenzene to methanol was 1:1. The evaluation results are shown in Table 3.

[0078] Test case

[0079] In the embodiments and comparative examples of this disclosure, a Quanta 200F scanning electron microscope (SEM) from FEI Corporation was used for microscopic morphology analysis, with the working voltage of the SEM being 20 kV; the average particle size of the catalyst was tested using a Japan Hitachi S-4800 type instrument.

[0080] The total specific surface area and total pore volume of the catalyst were measured using the nitrogen adsorption BET specific surface area method, employing an AS-3 or AS-6 static nitrogen adsorption instrument manufactured by Quantachrome Instruments. The specific method involved placing the sample in the sample processing system and evacuating it to a vacuum of 1.33 × 10⁻⁶ at 300°C. -2 The sample was purified by holding it at a pressure of 4 h under pressure and temperature. At a liquid nitrogen temperature of -196℃, the adsorption and desorption of nitrogen on the purified sample under different specific pressures P / P0 were tested to obtain the N2 adsorption-desorption isotherm curves. Then, the total specific surface area was calculated using the two-parameter BET formula, and the adsorption amount below specific pressure P / P0 = 0.98 was taken as the total pore volume of the sample.

[0081] Total acid content was measured using the NH3-TPD method with an Autochem II 2920 temperature-programmed desorption instrument from Micron Technology, USA. The specific method was as follows: 0.2 g of the sample to be tested was weighed and placed in a sample tube, which was then placed in a thermal conductivity cell furnace. He gas was used as the carrier gas (50 mL / min), and the temperature was increased to 600 °C at a rate of 20 °C / min. The sample was purged for 60 min to remove impurities adsorbed on the catalyst surface. The temperature was then reduced to 100 °C and held for 30 min. The sample was then switched to an NH3-He mixed gas (10.02% NH3 + 89.98% He) for adsorption for 30 min. The sample was then purged with He gas for another 90 min until the baseline stabilized, and the physically adsorbed ammonia was desorbed. The temperature was increased to 600 °C at a rate of 10 °C / min and held for 30 min. The desorption was then completed. The gas composition changes were detected using a TCD detector, and the total acid content was obtained by automatic integration of the results.

[0082] The acid content of Brønsted (B) and Lewis (L) acids was measured using the 2,6-di-tert-butylpyridine adsorption infrared spectroscopy method, employing a Vertex 70 instrument manufactured by Bruker Instruments. The specific method involved pressing the catalyst to a concentration of 10 mg / cm³. 2 Thin slices were placed in an infrared cell with a CaF2 window. The cell was first evacuated to 400°C, then cooled to 150°C to adsorb 2,6-di-tert-butylpyridine for 15 minutes. After evacuation for 1 hour, the cell was cooled to room temperature, and spectra were collected. The amounts of Brønsted acid and Lewis acid were calculated. See Applied Catalysis A: General, 294, 2005: 92.

[0083] The conversion of pseudotrimethylbenzene and the selectivity of tetramethylbenzene were calculated using the gas chromatography peak area normalization method. The specific test method was as follows: nitrogen as the carrier gas, FID detector, column temperature 80℃, injector temperature 260℃, and detector temperature 250℃. The programmed temperature was 0℃ initially, held for 0 min at a rate of 3℃ / min, and reached a final temperature of 50℃ with a holding time of 20 min. The injection volume was 0.2 μL.

[0084] In the various embodiments and comparative examples:

[0085]

[0086]

[0087] Tetramethylbenzene yield = Trimethylbenzene conversion × Tetramethylbenzene selectivity × 100%

[0088]

[0089] Table 1

[0090]

[0091] Table 2

[0092]

[0093]

[0094] Table 3

[0095]

[0096] As can be seen from the results in Tables 1 to 3 above, the heteroatom EWT structure molecular sieve provided in this disclosure contains aluminum atoms and heteroatom elements in its framework, giving the molecular sieve suitable acidity and acid strength. Furthermore, the 3D channel system composed of 21-membered and 10-membered rings in the heteroatom EWT structure molecular sieve can improve the utilization rate of acidic centers, enhance the activity and stability of the catalyst, and enable it to maintain a high conversion rate of pseudotrimethylbenzene and a high selectivity for tetramethylbenzene when used as a catalyst in the alkylation reaction of pseudotrimethylbenzene and methanol, and can operate continuously for 300 hours. In Comparative Example 1, using an EWT structure molecular sieve without heteroatoms in its framework as a catalyst, the conversion rate of pseudotrimethylbenzene in the alkylation reaction of pseudotrimethylbenzene and methanol was extremely low. In Comparative Example 2, using a 10-membered ring ZSM-5 molecular sieve as a catalyst, the selectivity for tetramethylbenzene was low, and there were more byproducts such as benzene, toluene, xylene, and ethylbenzene. Therefore, the heteroatom EWT structure molecular sieves provided in Examples 1 to 7 of this disclosure have superior performance compared to the molecular sieves provided in Comparative Examples 1 to 2.

[0097] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0098] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0099] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A heteroatom EWT structured molecular sieve for the alkylation of pseudotrimethylbenzene and methanol to synthesize tetramethylbenzene, characterized in that, The framework of the heteroatom EWT structured molecular sieve includes silicon, aluminum, and heteroatom elements. The molar ratio of silicon (based on SiO2) to aluminum (based on Al2O3) in the heteroatom EWT structured molecular sieve is 15-30, and the molar ratio of silicon (based on SiO2) to heteroatom elements (based on heteroatom oxides) in the heteroatom EWT structured molecular sieve is 120-240. The heteroatom elements include one or more of boron, iron, titanium, gallium, and germanium. The mesopore volume with a pore size of 2.0~20.0 nm accounts for 30~50% of the total pore volume, and the ratio of the amount of Brønsted acid to Lønsted acid in the heteroatom EWT structure molecular sieve determined by pyridine adsorption infrared spectroscopy at 350℃ is 0.3~0.

6. The preparation method of the heteroatom EWT structured molecular sieve includes: (1) A silicon source, a heteroatom element source, a first alkali source, a first organic template agent and water are mixed, and the resulting first material to be crystallized is crystallized for the first time to obtain molecular sieve powder; the molecular sieve powder is calcined to obtain sodium molecular sieve. (2) The sodium molecular sieve is subjected to ion exchange with an acid solution, the obtained molecular sieve intermediate is mixed with an aluminum source, a second alkali source and a second organic template agent, and the obtained second crystallization material is subjected to a second crystallization. The heteroatom elements include one or more of boron, iron, titanium, gallium, and germanium; the first organic template agent and the second organic template agent are respectively a cyclic bis-quaternary ammonium base compound and / or a cyclic bis-quaternary ammonium salt compound; the temperature of the first crystallization is 60~180℃ and the time is 96~168h; the temperature of the second crystallization is 100~170℃ and the time is 96~168h.

2. The heteroatom EWT structured molecular sieve according to claim 1, characterized in that, When the heteroatom element is boron, the molar ratio of silicon (calculated as SiO2) to boron (calculated as B2O3) in the heteroatom EWT structure molecular sieve is 120~180. When the heteroatom element is one or more of iron, titanium, gallium and germanium, the molar ratio of silicon (calculated as SiO2) to heteroatom elements (calculated as heteroatom oxides) in the heteroatom EWT structure molecular sieve is 150~240.

3. The heteroatom EWT structured molecular sieve according to claim 1, characterized in that, The total specific surface area of ​​the heteroatom EWT structured molecular sieve is 300~650 cm². 2 / g, with an average pore size of 0.5~20nm and a total pore volume of 0.25~0.60cm³. 3 / g, the volume of mesopores with pore sizes of 2.0~20.0 nm is 0.05~0.35 cm³. 3 / g, wherein the mesopore volume with a pore size of 2.0~20.0nm accounts for 35~50% of the total pore volume; the average particle size of the heteroatom EWT structure molecular sieve is 0.2~1.5μm, and the relative crystallinity is 50~100%.

4. The heteroatom EWT structured molecular sieve according to claim 3, characterized in that, The total specific surface area of ​​the heteroatom EWT structured molecular sieve is 450~580 cm². 2 / g, with an average pore size of 1~5nm and a total pore volume of 0.25~0.45cm³. 3 / g, the volume of mesopores with a pore size of 2.0~20.0nm is 0.10~0.25cm³. 3 / g, the average particle size of the heteroatom EWT structure molecular sieve is 0.3~1.0μm, and the relative crystallinity is 75~95%; The heteroatom EWT structured molecular sieve is a hydrogen-type heteroatom EWT structured molecular sieve.

5. The heteroatom EWT structured molecular sieve according to claim 4, characterized in that, The average pore size of the heteroatom EWT structure molecular sieve is 2~5 nm.

6. The method for preparing heteroatom EWT structured molecular sieves according to any one of claims 1 to 5, characterized in that, The preparation method of the heteroatom EWT structured molecular sieve includes: (1) A silicon source, a heteroatom element source, a first alkali source, a first organic template agent and water are mixed, and the resulting first material to be crystallized is crystallized for the first time to obtain molecular sieve powder; the molecular sieve powder is calcined to obtain sodium molecular sieve. (2) The sodium molecular sieve is subjected to ion exchange with an acid solution, the obtained molecular sieve intermediate is mixed with an aluminum source, a second alkali source and a second organic template agent, and the obtained second crystallization material is subjected to a second crystallization. The heteroatom elements include one or more of boron, iron, titanium, gallium, and germanium; the first organic template agent and the second organic template agent are respectively a cyclic bis-quaternary ammonium base compound and / or a cyclic bis-quaternary ammonium salt compound; the temperature of the first crystallization is 60~180℃ and the time is 96~168h; the temperature of the second crystallization is 100~170℃ and the time is 96~168h.

7. The preparation method according to claim 6, characterized in that, The first crystallization is carried out at a temperature of 100~170℃ for 96~144h; the second crystallization is carried out for 96~144h.

8. The preparation method according to claim 6, characterized in that, The silicon source is selected from one or more of silica sol, water glass, solid silica gel, tetraethyl orthosilicate, and fumed silica; The heteroatom element source is selected from one or more of boron oxide, boric acid, iron oxide, titanium oxide, gallium oxide, and germanium oxide; The first alkali source and the second alkali source are respectively selected from one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide; The aluminum source is selected from one or more of aluminum chloride, aluminum sulfate, hydrated aluminum oxide, sodium aluminate, and aluminum sol. The first organic template agent and the second organic template agent are each selected from at least one having the structure shown in formula (1): Equation (1); R1, R2, R3, and R4 are each independently selected from alkyl groups having 1 to 4 carbon atoms, m is 2 or 3; n is any integer from 1 to 10; X - This includes hydroxide ions or halide anions.

9. The preparation method according to claim 8, characterized in that, The silicon source is solid silicone; The heteroatom element source is boron oxide and / or boric acid; Both the first and second alkali sources are sodium hydroxide; The aluminum source is sodium aluminate; R1, R2, R3 and R4 are each independently selected from one or more of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl.

10. The preparation method according to claim 9, characterized in that, R1, R2, R3 and R4 are each independently methyl or ethyl.

11. The preparation method according to claim 6, characterized in that, The silicon source is SiO2, the heteroatom element source is heteroatom oxide, and when the heteroatom element is boron, the molar ratio of SiO2 to B2O3 in the first material to be crystallized is 10~250. When the heteroatom element is one or more of iron, titanium, gallium and germanium, the molar ratio of SiO2 to heteroatom oxide in the first material to be crystallized is 10~250.

12. The preparation method according to claim 11, characterized in that, The silicon source is SiO2, the heteroatom element source is heteroatom oxide, and when the heteroatom element is boron, the molar ratio of SiO2 to B2O3 in the first material to be crystallized is 30~120. When the heteroatom element is one or more of iron, titanium, gallium and germanium, the molar ratio of SiO2 to heteroatom oxide in the first material to be crystallized is 30 to 150.

13. The preparation method according to claim 6, characterized in that, In step (1), the silicon source is SiO2, the heteroatom element source is heteroatom oxide, the first organic template agent is T1, and when the heteroatom element in the first material to be crystallized is boron, the molar ratio of SiO2 to B2O3 is 10~250; when the heteroatom element is one or more of iron, titanium, gallium and germanium, the molar ratio of SiO2 to heteroatom oxide is 10~250; OH - The molar ratio of the first alkali source to SiO2 is 0.2~1.0, the molar ratio of T1 to SiO2 is 0.02~0.5, and the molar ratio of H2O to SiO2 is 5~20. In step (2), the aluminum source is represented by Al2O3, the second organic template agent is represented by T2, the molar ratio of SiO2 to Al2O3 in the second material to be crystallized is greater than 10, and OH... - The molar ratio of the second alkali source to SiO2 is 0.2~1.0, the molar ratio of T2 to SiO2 is 0.02~0.5, and the molar ratio of H2O to SiO2 is 5~20.

14. The preparation method according to claim 13, characterized in that, In step (1), when the heteroatom element in the first material to be crystallized is boron, the molar ratio of SiO2 to B2O3 is 30~120; when the heteroatom element is one or more of iron, titanium, gallium and germanium, the molar ratio of SiO2 to heteroatom oxide is 30~150; with OH - The molar ratio of the first alkali source to SiO2 is 0.2~0.5, the molar ratio of T1 to SiO2 is 0.08~0.15, and the molar ratio of H2O to SiO2 is 5~10. In step (2), the molar ratio of SiO2 to Al2O3 in the second material to be crystallized is 10~60, with OH... - The molar ratio of the second alkali source to SiO2 is 0.2~0.5, the molar ratio of T2 to SiO2 is 0.08~0.15, and the molar ratio of H2O to SiO2 is 5~10.

15. The preparation method according to claim 14, characterized in that, In step (2), the molar ratio of SiO2 to Al2O3 in the second material to be crystallized is 15~30.

16. The preparation method according to claim 6, characterized in that, The calcination temperature is 400~650℃, and the time is 1~7h; The weight ratio of the acid solution to the sodium molecular sieve is (1~100):1, the concentration of the acid solution is 0.01~0.10 mol / L, the ion exchange temperature is 60~90℃, and the time is 2~24h; the acid solution is selected from one or more of hydrochloric acid solution, nitric acid solution, and sulfuric acid solution.

17. A method for synthesizing tetramethylbenzene by alkylation of pseudotrimethylbenzene and methanol, characterized in that, The method includes contacting pseudotrimethylbenzene with methanol under alkylation reaction conditions and in the presence of a catalyst; wherein the catalyst is a heteroatom EWT structure molecular sieve as described in any one of claims 1 to 5.

18. The method according to claim 17, characterized in that, The alkylation reaction conditions include: in a fixed-bed reactor, contacting the catalyst with pseudotrimethylbenzene and methanol under gas-phase reaction conditions, wherein the gas-phase reaction temperature is 240~450℃, the time is 10~500h, the pressure is 0.2~2.0MPa, and the mass hourly space velocity of pseudotrimethylbenzene is 0.5~3.5h. -1 ; The feed molar ratio of the pseudotrimethylbenzene to methanol is (0.2~4.0):

1.

19. The method according to claim 18, characterized in that, The gas-phase reaction is carried out at a temperature of 330–360 °C for 20–350 h, at a pressure of 0.5–1.5 MPa, and at a mass hourly space velocity (WHSV) of 1–2 h⁻¹. -1 ; The feed molar ratio of the pseudotrimethylbenzene to methanol is (0.5~1.5):1.

Images