Method for rapidly synthesizing ZSM-5 molecular sieve

Abstract

The invention discloses a method for rapidly synthesizing a ZSM-5 molecular sieve, which comprises the following steps: S1, mixing an aluminum source and deionized water to obtain a clear aluminum source solution, adding an alkali source, and stirring to obtain a clear solution A; s2, adding a silicon source, a seed crystal and crystallization accelerators R1 and R2 into the settled solution A, stirring at room temperature to form gel, and performing crystallization reaction on the gel at 160-220 DEG C for 4-8 hours; the accelerant R1 is one or more of sodium chloride, sodium sulfate, potassium chloride and potassium sulfate, and the accelerant R2 is sodium tripolyphosphate and / or sodium hexametaphosphate; and S3, filtering the crystallized product, washing to be neutral, and drying to obtain the ZSM-5 molecular sieve. In the synthesis process of the molecular sieve, an expensive organic template agent is not added, a crystal seed and a crystallization accelerant are used for promoting the nucleation process of the molecular sieve, and a structure guiding effect is provided for the growth of the molecular sieve.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and in particular relates to a method for rapidly synthesizing a ZSM-5 molecular sieve. Background Art

[0002] Molecular sieves are a type of crystalline material with an ordered pore structure. Since the 1940s, when molecular sieves were first artificially synthesized by studying the synthesis conditions of natural zeolites, a large number of researchers have devoted themselves to the field of artificial synthesis of molecular sieves. In the past few decades, a large number of new molecular sieves have been artificially synthesized. These molecular sieves have been widely used in catalytic cracking, alkylation, aromatization, methanol to olefins, tail gas denitrification, organic synthesis and adsorption separation due to their excellent properties (such as high structural stability, excellent ion exchange and mass transfer capacity, strong acidity, low production cost and screening ability brought by their own three-dimensional pore structure).

[0003] At present, the most commonly used method for synthesizing molecular sieves is the traditional hydrothermal method. The hydrothermal synthesis of zeolite mainly includes two processes: the formation of silicate hydrate gel and the crystallization of hydrate gel. The entire synthesis steps can be roughly summarized as follows: first, the initial raw materials such as silicon source, aluminum source, template agent, alkali source, etc. are mixed at a specific temperature and dynamically stirred. After a period of time, the resulting gel is transferred to a closed reactor and placed in a high temperature environment for crystallization. Then, the reactor is taken out and the product is separated from the liquid to obtain the zeolite molecular sieve. The current theory generally divides the crystallization process into four steps: (1) the repolymerization of silicates and aluminates in different polymer states; (2) the nucleation process of zeolite; (3) the growth process of the nucleus; (4) the growth of zeolite crystals and the secondary nucleation process that may be triggered. The advantages of the hydrothermal synthesis method are that the reactants in the system are uniformly dissolved, the reaction conditions are mild, and it is easy to use; the reactant cost is low. However, the disadvantage of this method is that the crystallization time required is relatively long. In order to further accelerate the crystallization process of the molecular sieve, many researchers have tried to add various crystallization promoters to the initial gel to accelerate the synthesis process.

[0004] CN201911169395.7 discloses a method for rapidly synthesizing a Beta molecular sieve with controllable particle size, wherein a raw material silicon source, an aluminum source, an inorganic base, a microporous template, deionized water and a crystal particle size regulator R (imidazole, 2-methylimidazole, 2-chloroimidazole or 2-aminoimidazole) are uniformly mixed, and high-temperature crystallization is directly performed after stirring to obtain a beta molecular sieve with a particle size of 50nm-3um. However, the added imidazole and imidazole compounds are toxic to the human body, and are harmful to the environment when dissolved in water, and are therefore not suitable for large-scale use. CN112897547B discloses a method for rapidly synthesizing an aluminum-free Sn-Beta molecular sieve, wherein a silicon source is mixed with an organic template agent tetraethylammonium hydroxide, and an alkali metal or alkaline earth metal salt (Li 2-nitrogen) is added to the mixture.+ 、Na + , K + Mg 2+ , Ca 2+ , Ba 2 + Chloride, sulfate, nitrate, acetate) and Sn source are added, stirred for a certain period of time, and then hydrofluoric acid or ammonium fluoride is added as a mineralizer, and then dealuminated Beta or pure Si-Beta is added as a seed crystal. After uniform mixing, the mixture is placed in a molecular sieve crystallization kettle to quickly crystallize and obtain the product molecular sieve. Although this method can significantly change the properties of the colloid in the gel formation process by adding only a small amount of alkali metal salt or alkaline earth metal salt, promote the polymerization of species such as silicate, and thus shorten the time required for crystallization, fluoride promoters and organic templates are also added during the synthesis process, which is not environmentally friendly, and the addition of organic templates increases the synthesis cost, which is not conducive to the large-scale promotion of this technology. CN109987613B discloses a method for rapidly synthesizing pure silicon MCM-41 molecular sieve, wherein hexadecyl trimethyl ammonium bromide CTMAB is used as a surfactant, and sodium hydroxide and water are used to form a solution, sodium thiosulfate Na2S2O3 (sodium thiosulfate is a crystallization promoter) is added and uniformly mixed, and then H2SO4 is slowly added dropwise to adjust the pH value of the solution to 8.5-10.0, and a silicon source is added to the above solution to form a reaction sol, and the above reaction sol is crystallized at a crystallization temperature of 80-110°C for 2-12 hours to obtain a crystallized pure silicon MCM-41 molecular sieve. However, the invention uses an organic surfactant, which will cause environmental pollution when it is subsequently removed. CN115611294A discloses a method for preparing a fast synthesis of ZSM-48 molecular sieves, S1, adding a mixed solution of template P, template Q and water to a mixture of aluminum source, alkali source and water, and then adding a crystallization inducing agent aqueous solution to form a mixed solution A; S2, adding a mixed solution of morphology modifier, silicon source and water to the mixed solution A and stirring; S3, loading the mixture of S2 into an acid-base resistant sealed reactor, heating from 20°C to 120-180°C within 3-8 hours, rotating at 30-80 rpm, hydrothermal crystallization for 10-120 hours, filtering, washing, drying and roasting to obtain ZSM-48 molecular sieves; wherein, the drying conditions are: heating to 120°C within 3 hours under air atmosphere, drying for 2-4 hours; the roasting conditions are: heating to 550°C-600°C within 8 hours and roasting for 8-40 hours. This patent also uses organic surfactants.

[0005] Through the analysis of the above patents and prior art, it can be known that the addition of crystallization promoters can promote the formation of molecular sieve crystal phase structure and accelerate the crystallization of molecular sieves to a certain extent. However, such substances are usually organic substances, which are generally expensive. After adding them, the crystallization cost of molecular sieves will increase, and they need to be removed in the subsequent process. This process will pollute the environment and is not suitable for subsequent industrial mass production. Summary of the invention

[0006] In view of the many problems existing in the prior art, the present invention aims to develop a method for rapidly synthesizing ZSM-5 molecular sieves, which is green, low-cost, easy to operate, scalable and can significantly shorten the crystallization time.

[0007] To achieve the above object, the present invention provides a method for rapidly synthesizing ZSM-5 molecular sieve, comprising the following steps:

[0008] S1, mixing an aluminum source and deionized water to obtain a clarified aluminum source solution, then adding an alkali source and stirring to obtain a clarified solution A;

[0009] S2, adding a silicon source and a seed crystal to the clarified solution A, and then adding crystallization accelerators R1 and R2, stirring to form a gel, the gel undergoes a crystallization reaction at 160-220° C., and the crystallization time is 4-8 hours, the crystallization accelerator R1 is one or more of sodium chloride, sodium sulfate, potassium chloride and potassium sulfate, and the crystallization accelerator R2 is sodium tripolyphosphate and / or sodium hexametaphosphate;

[0010] S3, filtering the crystallized product, washing it to neutrality and drying it to obtain a ZSM-5 molecular sieve.

[0011] In the method for rapidly synthesizing ZSM-5 molecular sieve of the present invention, the molar ratio of aluminum source, silicon source, promoter R1, promoter R2, alkali source and water is 1:30-200:0.3-4.5:0.3-3:4-8:500-2000, wherein the aluminum source, silicon source and alkali source are calculated as oxides.

[0012] In the method for rapidly synthesizing ZSM-5 molecular sieves of the present invention, when adding a seed crystal promoter, promoter R1 is added first and then promoter R2 is added.

[0013] In the method for rapidly synthesizing ZSM-5 molecular sieves of the present invention, the amount of seed crystal added is 1 to 10% of the total SiO2 mass in the system.

[0014] In the method for rapidly synthesizing ZSM-5 molecular sieves of the present invention, the crystallization reaction in step S2 is carried out under oil bath conditions.

[0015] In the method for rapidly synthesizing ZSM-5 molecular sieves of the present invention, the aluminum source is one or more of aluminum sulfate, aluminum chloride, aluminum hydroxide, sodium aluminate and pseudo-boehmite.

[0016] In the method for rapidly synthesizing ZSM-5 molecular sieves of the present invention, the alkali source is sodium hydroxide and / or potassium hydroxide.

[0017] In the method for rapidly synthesizing ZSM-5 molecular sieves of the present invention, the silicon source is one or more of silica sol, water glass, silica gel, sodium silicate and ethyl orthosilicate.

[0018] In the method for rapidly synthesizing ZSM-5 molecular sieves of the present invention, the seed crystals are one or more of Silicalite-1, ZSM-5 and ZSM-11 molecular sieves.

[0019] Beneficial effects of the present invention:

[0020] In the process of molecular sieve synthesis, no expensive organic template is added. Instead, seed crystals and crystallization promoters are used to promote the nucleation process of molecular sieves and provide structural guidance for the growth of molecular sieves. The crystallization promoter uses inorganic alkali metal salt R1 and dispersant R2. R1 can promote the generation of five-membered ring secondary structural units in the gel solid phase, and promote nucleation and crystallization by promoting the condensation and rearrangement of these structural units during the crystallization process. By adding R1 first and then R2, the silica-alumina gel formed by R1 and other materials can be dispersed and homogenized through R2, reducing the agglomeration of silicate to promote the uniformity of subsequent gel nucleation, increasing the growth sites of molecular sieve crystals, and shortening the crystallization time. Since there are no expensive organic templates and surfactants in the system, the pollution caused by the calcined template to the environment is eliminated and the synthesis cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the XRD diagram of ZSM-5 molecular sieve synthesized in Example 1-9.

[0022] Figure 2 This is a SEM photograph of the ZSM-5 molecular sieve synthesized in Example 1.

[0023] Figure 3 It is a comparison diagram of XRD of ZSM-5 molecular sieve synthesized in Example 3 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0024] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0025] Source of raw materials:

[0026] 1) Sodium hydroxide, analytical grade, Shanghai Testing Group

[0027] 2) Potassium hydroxide, analytical grade, Shanghai Testing Group

[0028] 3) Pseudo-boehmite, industrial product, collected from the catalyst plant of Lanzhou Petrochemical Company

[0029] 4) Aluminum sulfate 18-hydrate, analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0030] 5) Aluminum hydroxide, analytical grade, Shanghai MacLean Biochemical Technology Co., Ltd.

[0031] 6) Sodium chloride, analytical grade, Shanghai Testing Group

[0032] 7) Anhydrous sodium sulfate, analytical grade, Shanghai Testing Group

[0033] 8) Potassium chloride, analytical grade, Shanghai Testing Group

[0034] 9) Potassium sulfate, analytical grade, Shanghai Testing Group

[0035] 10) Sodium tripolyphosphate, industrial grade, Qingzhou Yibai Chemical Co., Ltd.

[0036] 11) Sodium hexametaphosphate, industrial grade, Hebei MiGaoMei Chemical Technology Co., Ltd.

[0037] 12) Sodium hypophosphite, analytical grade, Changshu Xinte Chemical Co., Ltd.

[0038] 13) Silica gel, industrial product, sourced from Lanzhou Petrochemical Company Catalyst Factory

[0039] 14) Silica sol, industrial products, Shandong Chengshun Chemical Technology Co., Ltd.

[0040] 15) Ethyl orthosilicate, analytical grade, Beijing Inokai Technology Co., Ltd.

[0041] 16) ZSM-5 molecular sieve, purchased from Nankai Catalyst Factory

[0042] 17) ZSM-11 molecular sieve, Tianjin Delta Technology Co., Ltd.

[0043] 18) Silicalite-1 molecular sieve, Nankai Catalyst Factory

[0044] Specific analysis method:

[0045] The crystallinity of the molecular sieve was tested on a D / max-3C X-ray powder diffractometer manufactured by Rigaku, Japan, using the X-ray diffraction method to determine the crystallinity of the sample. The pore distribution test of the sample was conducted using the Autosorb-3B specific surface measuring instrument of Quantachrome, USA, and the specific surface area, pore size distribution and pore volume of the sample were determined by the N2 low temperature (77.3K) adsorption-desorption experimental method. Specific embodiment:

[0047] Examples 1 to 9 are methods for synthesizing molecular sieves.

[0048] Example 1

[0049] 3.24 g of pseudo-boehmite was added to 200 g of deionized water and stirred dynamically for 5 minutes; after the pseudo-boehmite was completely dissolved, 6.84 g of sodium hydroxide was added and continued to be stirred, and after stirring for 5 minutes, 44 g of powdered silica gel and 0.4 g of ZSM-5 molecular sieve seeds were slowly added, and 0.39 g of sodium chloride was added and stirred for 5 minutes, and finally 2.54 g of sodium tripolyphosphate was added and the formed gel was stirred at room temperature for 1.5 hours; the gel was crystallized at 160°C for 8 hours, the crystallized liquid was filtered, washed to neutrality, and the filter cake was dried at 120°C overnight to obtain the ZSM-5 molecular sieve.

[0050] Example 2

[0051] 0.4 g of pseudo-boehmite was added to 100 g of deionized water and the mixture was stirred dynamically for 10 minutes. After the pseudo-boehmite was completely dissolved, 2.13 g of sodium hydroxide was added and the mixture was continued to be stirred. After stirring for 15 minutes, 34 g of powdered silica gel and 3.3 g of silicalite-1 molecular sieve seeds were slowly added, and 0.73 g of sodium chloride was added and stirred for 5 minutes. Finally, 2.95 g of sodium tripolyphosphate was added and the formed gel was stirred at room temperature for 2.5 hours. The gel was crystallized at 220°C for 4 hours, the crystallized liquid was filtered, washed to neutrality, and the filter cake was dried at 120°C overnight to obtain ZSM-5 molecular sieve.

[0052] Example 3

[0053] Add 2.4 g of aluminum sulfate 18hydrate to 110 g of deionized water and stir dynamically for 15 minutes; after the aluminum sulfate 18hydrate is completely dissolved, add 8 g of sodium hydroxide and continue stirring, stir for 5 minutes, slowly add 90 g of silica sol and 1.5 g of silicalite-1 molecular sieve seeds, and add 1 g of sodium chloride at the same time and stir for 5 minutes, finally add 2.1 g of sodium tripolyphosphate and stir the formed gel at room temperature for 2 hours; crystallize the gel at 180°C for 6 hours, filter the crystallization solution, wash it to neutrality, and dry the filter cake at 120°C overnight to obtain ZSM-5 molecular sieve.

[0054] Example 4

[0055] Add 1.6 g of aluminum sulfate 18hydrate to 40 g of deionized water and stir dynamically for 15 minutes; after the aluminum sulfate 18hydrate is completely dissolved, add 2.8 g of potassium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 50 g of silica sol and 0.5 g of ZSM-5 molecular sieve seeds, and at the same time add 0.4 g of potassium chloride and stir for 5 minutes, finally add 2.4 g of sodium hexametaphosphate and stir the formed gel at room temperature for 3 hours; crystallize the gel at 180°C for 6 hours, filter the crystallization solution, wash it to neutrality, and dry the filter cake at 120°C overnight to obtain ZSM-5 molecular sieve.

[0056] Example 5

[0057] Add 2.1 g of aluminum hydroxide to 200 g of deionized water and stir dynamically for 15 minutes; after the aluminum hydroxide is completely dissolved, add 6 g of sodium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 149.76 g of ethyl orthosilicate and 2 g of ZSM-5 molecular sieve seeds, and at the same time add 1.2 g of sodium chloride and stir for 10 minutes, finally add 8 g of sodium hexametaphosphate and stir the formed gel at room temperature for 3 hours; crystallize the gel at 180°C for 7 hours, filter the crystallization solution, wash it to neutrality, and dry the filter cake at 120°C overnight to obtain ZSM-5 molecular sieve.

[0058] Example 6

[0059] Add 2.1 grams of aluminum hydroxide to 200 grams of deionized water and stir dynamically for 15 minutes; after the aluminum hydroxide is completely dissolved, add 6 grams of sodium hydroxide and continue stirring, stir for 5 minutes, slowly add 130 grams of ethyl orthosilicate and 2 grams of ZSM-5 molecular sieve seeds, and add 0.6 grams of sodium chloride at the same time and stir for 10 minutes, finally add 4 grams of sodium tripolyphosphate and stir the formed gel at room temperature for 1.5 hours; crystallize the gel at 180°C for 8 hours, filter the crystallization solution, wash it to neutrality, and dry the filter cake at 120°C overnight to obtain ZSM-5 molecular sieve.

[0060] Example 7

[0061] 1.2 g of aluminum sulfate 18hydrate was added to 55 g of deionized water and stirred dynamically for 10 minutes; after the aluminum sulfate 18hydrate was completely dissolved, 4 g of sodium hydroxide was added and continued to stir, and after stirring for 5 minutes, 45 g of silica sol and 0.75 g of silicalite-1 molecular sieve seeds were slowly added, and 0.61 g of anhydrous sodium sulfate was added and stirred for 5 minutes, and finally 1.05 g of sodium tripolyphosphate was added and the formed gel was stirred at room temperature for 2 hours; the gel was crystallized at 180°C for 6 hours, the crystallized liquid was filtered, washed to neutrality, and the filter cake was dried at 120°C overnight to obtain ZSM-5 molecular sieve.

[0062] Example 8

[0063] Add 3.2 g of aluminum sulfate 18hydrate to 80 g of deionized water and stir dynamically for 10 minutes; after the aluminum sulfate 18hydrate is completely dissolved, add 5.6 g of potassium hydroxide and continue stirring. After stirring for 5 minutes, slowly add 100 g of silica sol and 1 g of ZSM-5 molecular sieve seeds, and at the same time add 0.94 g of potassium chloride and stir for 5 minutes, finally add 4.8 g of sodium hexametaphosphate and stir the formed gel at room temperature for 3 hours; crystallize the gel at 180°C for 6 hours, filter the crystallization solution, wash it to neutrality, and dry the filter cake at 120°C overnight to obtain ZSM-5 molecular sieve.

[0064] Example 9

[0065] The difference from Example 3 is that sodium tripolyphosphate is added first and then sodium chloride.

[0066] Add 2.4 g of aluminum sulfate 18hydrate to 110 g of deionized water and stir dynamically for 15 minutes; after the aluminum sulfate 18hydrate is completely dissolved, add 8 g of sodium hydroxide and continue stirring, stir for 5 minutes, slowly add 90 g of silica sol and 1.5 g of silicalite-1 molecular sieve seeds, and add 2.1 g of sodium tripolyphosphate at the same time and stir for 5 minutes, finally add 1 g of sodium chloride and stir the formed gel at room temperature for 2 hours; crystallize the gel at 180°C for 6 hours, filter the crystallization solution, wash it to neutrality, and dry the filter cake at 120°C overnight to obtain ZSM-5 molecular sieve.

[0067] Comparative Example 1

[0068] The difference from Example 3 is that no sodium chloride is added during the crystallization process.

[0069] Add 2.4 g of aluminum sulfate 18hydrate to 110 g of deionized water and stir dynamically for 15 minutes; after the aluminum sulfate 18hydrate is completely dissolved, add 8 g of sodium hydroxide and continue stirring, stir for 5 minutes, slowly add 90 g of silica sol and 1.5 g of silicalite-1 molecular sieve seed crystals and stir for 5 minutes, finally add 2.1 g of sodium tripolyphosphate and stir the formed gel at room temperature for 2 hours; crystallize the gel at 180°C for 6 hours, filter the crystallization solution, wash it to neutrality, and dry the filter cake at 120°C overnight to obtain ZSM-5 molecular sieve.

[0070] Comparative Example 2

[0071] The difference from Example 3 is that sodium tripolyphosphate is not added as a crystallization accelerator during the synthesis process, but sodium hypophosphite is used as a crystallization accelerator.

[0072] Add 2.4 g of aluminum sulfate 18hydrate to 110 g of deionized water and stir dynamically for 15 minutes; after the aluminum sulfate 18hydrate is completely dissolved, add 8 g of sodium hydroxide and continue stirring, stir for 5 minutes, slowly add 90 g of silica sol and 1.5 g of silicalite-1 molecular sieve seeds, and add 1 g of sodium chloride at the same time and stir for 5 minutes, finally add 3.02 g of sodium hypophosphite and stir the formed gel at room temperature for 2 hours; crystallize the gel at 180°C for 6 hours, filter the crystallization solution, wash it to neutrality, and dry the filter cake at 120°C overnight to obtain ZSM-5 molecular sieve.

[0073] Table 1 shows that the molecular sieve obtained by using the patent of the present invention has higher crystallinity, specific surface area and pore volume and shorter crystallization time, and shows that in order to achieve the crystallization effect of rapid synthesis, it is necessary to use the crystallization promoters R1 and R2 in a certain order of addition. Using R1 alone or replacing R2 with other promoters cannot achieve the effect described in the patent of the present invention.

[0074] Table 1 Specific surface area and pore volume of molecular sieves

[0075]

[0076]

[0077] The present invention may also have other various embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for rapidly synthesizing ZSM-5 molecular sieve, characterized in that: The following steps are involved: S1, mixing an aluminum source and deionized water to obtain a clarified aluminum source solution, then adding an alkali source and stirring to obtain a clarified solution A; S2, adding a silicon source and a seed crystal to the clarified solution A, and then adding crystallization accelerators R1 and R2, stirring to form a gel, the gel undergoes a crystallization reaction at 160-220° C., and the crystallization time is 4-8 hours, the crystallization accelerator R1 is one or more of sodium chloride, sodium sulfate, potassium chloride and potassium sulfate, and the crystallization accelerator R2 is sodium tripolyphosphate and / or sodium hexametaphosphate; S3, filtering the crystallized product, washing it to neutrality and drying it to obtain a ZSM-5 molecular sieve.

2. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that: The molar ratio of the aluminum source, silicon source, promoter R1, promoter R2, alkali source and water is 1:30-200:0.3-4.5:0.3-3:4-8:500-2000, wherein the aluminum source, silicon source and alkali source are calculated as oxides.

3. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that: When adding seed crystal promoter, add promoter R1 first and then add promoter R2.

4. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that: The amount of seed crystal added is 1 to 10% of the total SiO2 mass in the system.

5. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that: The crystallization reaction in step S2 is carried out under oil bath conditions.

6. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that: The aluminum source is one or more of aluminum sulfate, aluminum chloride, aluminum hydroxide, sodium aluminate and pseudo-boehmite.

7. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that: The alkali source is sodium hydroxide and / or potassium hydroxide.

8. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that: The silicon source is one or more of silica sol, water glass, silica gel, sodium silicate and ethyl orthosilicate.

9. The method for rapid synthesis of ZSM-5 molecular sieve according to claim 1, characterized in that: The seed crystal is one or more of Silicalite-1, ZSM-5 and ZSM-11 molecular sieves.

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