ZSM-22 molecular sieve as well as preparation method and application thereof

Abstract

The invention provides a ZSM-22 molecular sieve preparation method, which comprises: mixing a silicon source, an aluminum source, an inorganic alkali source, a template agent, an etching agent and water to form a gel, and carrying out dynamic crystallization, separation, washing, drying and roasting to obtain a ZSM-22 molecular sieve, the etching agent is selected from at least one of isopropanol, 1, 6-hexanediol, lysine, tris (hydroxymethyl) nitromethane and 1, 2, 4-triazole. According to the method for preparing the ZSM-22 molecular sieve, the etching agent is added into the synthesized gel mother liquor, the etching effect is preposed to a molecular sieve precursor or crystal nucleus with the minimum size and is matched with growth, then the axial diameter ratio of the ZSM-22 molecular sieve is greatly reduced, meanwhile, crystallization of the molecular sieve is dynamically adjusted by utilizing the addition-bond breaking dynamic change process, and the yield of the ZSM-22 molecular sieve is improved. The internal structure of the crystal is optimized, and the catalytic performance of the ZSM-22 molecular sieve is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve synthesis technology, specifically to a ZSM-22 molecular sieve, its preparation method, and its applications. Background Technology

[0002] ZSM-22 molecular sieve is a catalytic material with a Tonoton-Orthogonal (TON) topological framework. Its main channel structure consists of one-dimensional linear ten-membered ring channels without intersecting channels. Due to its unique channel structure and suitable pore size, it exhibits excellent selectivity in the isomerization of long-chain alkanes. However, the high axis-to-diameter ratio (the ratio of the average circumference to the diameter of the crystal) of ZSM-22 molecular sieves prepared by conventional hydrothermal synthesis easily leads to secondary fracture of long-chain alkanes or the formation of multi-branched isomers, resulting in a significant loss of viscosity index. Molecular sieves with a low axis-to-diameter ratio are beneficial for improving the diffusion rate of reactants and products within the molecular sieve channels, reducing the occurrence of the above problems, and preventing carbon buildup and pore blockage. This improves the selectivity for single-branched isomers and reduces the significant decrease in viscosity index caused by cracking and excessive isomerization.

[0003] Currently, the methods for synthesizing low-axis-diameter-ratio ZSM-22 molecular sieves typically involve post-processing of high-axis-ratio molecular sieves, including desilication and dealuminization, ball milling, and secondary crystallization. This results in a long synthesis process and high cost, significantly limiting the industrial application of molecular sieves. For example, Chinese patent document CN113149030A discloses a method for preparing size-controllable silicon-aluminum ZSM-22 molecular sieves, including the following steps: uniformly mixing silicon source, aluminum source, alkali source, template agent, and deionized water to form a mixed gel; obtaining a primary crystallization mixture after high-pressure crystallization; and then, after cooling, adding different types of additives to a reaction vessel for secondary crystallization to obtain rod-shaped crystals. The diameter of these crystals remains constant, while the length can be adjusted between 80 nm and 1 μm. However, this technology requires secondary crystallization, making the preparation process complex and unsuitable for industrial application.

[0004] To address the aforementioned issues, Particuology 24 (2016) 138-141 disclosed the successful preparation of length-controllable ZSM-22 molecular sieves using a microwave-assisted solvothermal method, and investigated the effects of different co-solvents, including ethanol, ethylene glycol, 2-propanol, and glycerol, on the axial-to-diameter ratio of the molecular sieves. However, the addition of these co-solvents led to an increase in the length of the ZSM-22 molecular sieves, which was detrimental to reducing the axial-to-diameter ratio.

[0005] Chinese patent document CN105565339A discloses a method for preparing small-crystal ZSM-22 molecular sieves. This method involves uniformly mixing a silicon source, an aluminum source, an alkali source, a template agent, and deionized water to form an initial gel mixture. Then, one or more of activated carbon, graphite, graphene, carbon black, starch microspheres, chitosan, and polylactic acid microspheres are added and stirred until homogeneous. The mixture is then crystallized, and the solid product is filtered and separated, washed with deionized water until neutral, and dried and calcined to obtain the small-crystal ZSM-22 molecular sieve. However, this method introduces a large amount of carbon material to inhibit crystal growth, and the introduction of expensive carbon materials increases production costs, which is detrimental to industrial applications. Chinese patent document CN115959678A discloses a method for preparing ZSM-12 molecular sieves. A mixed clear solution of template agents Q1 and Q2 is added dropwise to a mixed solution of an aluminum source and an inorganic alkali. Then, a silicon source and water are added and mixed uniformly to obtain a gel. The resulting gel is crystallized, washed with distilled water, dried, and calcined to obtain the final product. However, the ZSM-12 molecular sieve synthesized by this method has a relatively long shaft diameter and a dendritic structure.

[0006] In summary, the preparation of ZSM-22 molecular sieves with low axis-to-diameter ratio using a method that is easy to apply industrially is of great significance for their use in the isomerization reaction of long-chain alkanes. Summary of the Invention

[0007] In view of this, the present invention provides a ZSM-22 molecular sieve, its preparation method and application. The method uses nucleophilic etching to regulate the anisotropic growth rate of the molecular sieve by utilizing the specific binding of the etching reagent with the surface of the molecular sieve crystal, thereby achieving the synthesis of ZSM-22 molecular sieve with low axis-to-diameter ratio.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] A method for preparing ZSM-22 molecular sieve includes the following steps:

[0010] A gel is formed by mixing silicon source, aluminum source, inorganic alkali source, template agent, etchant and water. After dynamic crystallization, separation, washing, drying and calcination, ZSM-22 molecular sieve is obtained.

[0011] The molar ratio of SiO2, Al2O3, inorganic alkali source, stencil agent, etching agent and water in the gel is 1:(0.01-0.05):(0.05-0.3):(0.1-0.5):(0.005-0.1):(40-60);

[0012] The etching agent is selected from at least one of isopropanol, 1,6-hexanediol, lysine, tris(hydroxymethyl)nitromethane, and 1,2,4-triazole.

[0013] In one optional embodiment, the molar ratio of SiO2 to the etchant in the gel is 1:(0.008 to 0.05).

[0014] In one optional embodiment, the molar ratio of SiO2 in the gel to the template agent is 1:(0.12 to 0.25).

[0015] In one optional embodiment, the dynamic crystallization temperature is 160–175°C and the time is 48–72 h.

[0016] In one alternative implementation, the dynamic crystallization is carried out in a crystallization reactor.

[0017] In one optional embodiment, the crystallization reactor rotates at a speed of 40 to 80 revolutions per minute.

[0018] In one alternative embodiment, the template agent is selected from at least one of isopropylamine, 1,6-hexanediamine, and 6-amino-1-hexanol.

[0019] In one optional embodiment, the silicon source is selected from at least one of silica sol, silica fume, water glass, and tetraethyl orthosilicate.

[0020] In one optional embodiment, the aluminum source is selected from at least one of aluminum sulfate, aluminum acetate, aluminum isopropoxide, and aluminum chloride.

[0021] In one alternative embodiment, the inorganic base source is selected from sodium hydroxide and / or potassium hydroxide.

[0022] In one optional embodiment, the calcination temperature is 500-600°C and the time is 8-10 hours.

[0023] In one optional embodiment, the drying temperature is 80-100°C and the time is 10-12 hours.

[0024] The present invention also provides a ZSM-22 molecular sieve prepared by the above-mentioned method, wherein the ZSM-22 molecular sieve has an axis-to-diameter ratio of 4.0-6.5.

[0025] In one optional embodiment, the specific surface area of ​​the ZSM-22 molecular sieve is 199-216 m². 2 / g, total pore volume is 0.27-0.35m³ 3 / g, with a relative crystallinity of 94%-104%.

[0026] The ZSM-22 molecular sieve prepared by the above-mentioned method of ZSM-22 molecular sieve provided by the present invention can be used to prepare catalysts.

[0027] The beneficial effects of this invention are as follows:

[0028] Beneficial Effect 1: The method for synthesizing ZSM-22 molecular sieves provided by this invention, by adding an etchant to the synthesis gel mother liquor, pre-emulates the etching process on the smallest molecular sieve precursor or crystal nucleus, and coordinates it with growth, thereby significantly reducing the axial diameter ratio of the ZSM-22 molecular sieve. Simultaneously, the addition-bond breaking dynamic process is used to dynamically regulate the crystallization of the molecular sieve, optimizing the internal crystal structure and greatly improving the catalytic performance of the ZSM-22 molecular sieve. This solves the problems of long process and high cost in the existing technology for synthesizing low axial diameter ratio ZSM-22 molecular sieves.

[0029] Beneficial effect 2: The ZSM-22 molecular sieve prepared by the method of the present invention has a low axis-to-diameter ratio, which can improve the selectivity of single-branched isomers in the tail oil isomerization process, reduce oil viscosity index loss, and improve base oil yield. Attached Figure Description

[0030] Figure 1 The XRD pattern of the ZSM-22 molecular sieve prepared in Example 1 of this invention;

[0031] Figure 2 The image shows the XRD pattern of the ZSM-22 molecular sieve prepared in Comparative Example 4 of this invention.

[0032] Figure 3 The image shows the XRD pattern of the ZSM-22 molecular sieve prepared in Comparative Example 5 of this invention.

[0033] Figure 4 This is a SEM image of the ZSM-22 molecular sieve prepared in Comparative Example 1 of this invention.

[0034] Figure 5 This is an SEM image of the ZSM-22 molecular sieve prepared in Comparative Example 2 of this invention.

[0035] Figure 6 This is a SEM image of the ZSM-22 molecular sieve prepared in Example 1 of the present invention;

[0036] Figure 7 This is an SEM image of the ZSM-22 molecular sieve prepared in Example 2 of the present invention;

[0037] Figure 8 This is an SEM image of the ZSM-22 molecular sieve prepared in Example 3 of the present invention;

[0038] Figure 9 This is an SEM image of the ZSM-22 molecular sieve prepared in Example 4 of the present invention;

[0039] Figure 10This is an SEM image of the ZSM-22 molecular sieve prepared in Example 5 of the present invention. Detailed Implementation

[0040] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the content of the present invention.

[0041] Where specific experimental steps or conditions are not specified in the examples, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0042] All the raw materials involved in this solution are commercially available. Among them, silicon sources such as silica sol, fumed silica, water glass, and tetraethyl orthosilicate can meet the requirements for implementation of this invention. For ease of comparison, silica sol will be used in the following description.

[0043] The present invention is further illustrated below by way of examples, but it is not intended to be limited thereto.

[0044] Example 1

[0045] At room temperature, 59.4 g of water, 1.01 g of KOH solution, 0.61 g of Al2(SO4)3, and 0.12 g of (CH3COO)3Al were mixed and stirred until clear. Then, 1.76 g of 6-amino-1-hexanol was added and stirred for 0.5 h. Next, 0.072 g of tris(hydroxymethyl)nitromethane and 0.057 g of 1,6-hexanediol were slowly added and stirred for another 0.5 h. Finally, 9 g of silica sol (SiO2 mass concentration 40%) was added and stirred for 3 h at room temperature. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor was dynamically crystallized at 170 °C for 48 h at a rotation speed of 60 rpm. After crystallization, the mixture was washed with deionized water, filtered, and the resulting solid was dried at 80 °C and calcined at 500 °C for 8 h to obtain ZSM-22 molecular sieve.

[0046] Example 2

[0047] At room temperature, 36.8 g of water, 1.0 g of KOH solution / 0.25 g of NaOH solution, and 0.21 g of Al2(SO4)3 were mixed and stirred until clear. Then, 0.72 g of 6-amino-1-hexanol and 0.35 g of isopropylamine were added and stirred for 0.5 h. Then, 0.26 g of 1,2,4-triazole was slowly added and stirring continued for 0.5 h. Finally, 9 g of silica sol (SiO2 mass concentration 40%) was added and stirred for 3 h at room temperature. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor was dynamically crystallized at 160 °C for 72 h at a rotation speed of 40 rpm. After crystallization, the mixture was washed with deionized water, filtered, and the resulting solid was dried at 100 °C and calcined at 600 °C for 9 h to obtain ZSM-22 molecular sieve.

[0048] Example 3

[0049] At room temperature, 37.8 g of water, 0.13 g of NaOH solution, and 0.80 g of Al2(SO4)3 were mixed and stirred until clear. Then, 0.89 g of 6-amino-1-hexanol and 0.85 g of 1,6-hexanediamine were added and stirred for 0.5 h. Then, 0.35 g of 1,6-hexanediol was slowly added and stirring continued for 0.5 h. Finally, 9 g of silica sol (SiO2 mass concentration 40%) was added and stirred for 3 h at room temperature. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor was dynamically crystallized at 175 °C for 60 h at a rotation speed of 80 rpm. After crystallization, the mixture was washed with deionized water, filtered, and the resulting solid was dried at 90 °C and calcined at 550 °C for 10 h to obtain ZSM-22 molecular sieve.

[0050] Example 4

[0051] At room temperature, 49.8 g of water, 0.97 g of KOH solution, and 0.69 g of Al2(SO4)3 were mixed and stirred until clear. Then, 1.7 g of 6-amino-1-hexanol was added and stirred for 0.5 h. Next, 0.098 g of 1,6-hexanediol was slowly added and stirred for another 0.5 h. Finally, 9 g of silica sol (SiO2 mass concentration 40%) was added and stirred for 3 h at room temperature. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor was dynamically crystallized at 160 °C for 48 h at a rotation speed of 50 rpm. After crystallization, the mixture was washed with deionized water, filtered, and the resulting solid was dried at 80 °C and calcined at 550 °C for 9 h to obtain ZSM-22 molecular sieve.

[0052] Example 5

[0053] At room temperature, 49.6 g of water, 0.62 g of KOH solution, and 0.68 g of Al2(SO4)3 were mixed and stirred until clear. Then, 1.59 g of 6-amino-1-hexanol was added and stirred for 0.5 h. Next, 0.075 g of L-lysine was slowly added and stirred for another 0.5 h. Finally, 9 g of silica sol (SiO2 mass concentration 40%) was added and stirred for 3 h at room temperature. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor was dynamically crystallized at 175 °C for 48 h at a rotation speed of 80 rpm. After crystallization, the mixture was washed with deionized water, filtered, and the resulting solid was dried at 80 °C and calcined at 600 °C for 10 h to obtain ZSM-22 molecular sieve.

[0054] Comparative Example 1

[0055] This comparative example is similar to Example 1, except that no etching agent was added in this comparative example.

[0056] Comparative Example 2

[0057] This comparative example is similar to Example 4, except that the etching agent used is different: 0.1g of ethanol was used in this comparative example.

[0058] Comparative Example 3

[0059] This comparative example is similar to Example 4, except that the etching agent added is different: 0.16g imidazole was used in this comparative example.

[0060] Comparative Example 4

[0061] This comparative example is similar to Example 4, except that the amount of etchant added is different: 1.35 g of 1,6-hexanediol was used in this comparative example.

[0062] Comparative Example 5

[0063] This comparative example is similar to Example 4, except that the crystallization method is different: static crystallization is used in this comparative example, and the rotation speed of the crystallization reactor is 0 during the crystallization process.

[0064] The ZSM-22 molecular sieves prepared in each embodiment and comparative example were subjected to relevant performance tests, and the specific test results are shown in Table 1 below. The axial diameter ratio was obtained by estimating the average crystal diameter and axial length using SEM images (e.g., ...). Figures 4 to 10 (As shown), specific surface area and pore volume were tested using a McTristar 3000 fully automated specific surface area analyzer according to GB / T19587. Relative crystallinity was calculated using Comparative Example 1 as a reference sample. Based on the peak areas above the back surface of the target sample and the reference sample, the relative crystallinity of each sample was calculated from the XRD data (see XRD data). Figures 1 to 3 As shown, by Figure 2 and Figure 3 It can be seen that the molecular sieves prepared in Comparative Examples 4 and 5 are amorphous. Qualitative analysis was performed by XRD testing. The XRD diffraction patterns of the samples were compared with the standard card of ZSM-22 to determine whether the prepared samples were pure-phase ZSM-22 molecular sieves.

[0065] Table 1

[0066] serial number Shaft diameter ratio <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Total pore volume (cm 3 / g)]]> Relative crystallinity Comparative Example 1 24.8 150.1 0.24 100％ Comparative Example 2 26.7 150.8 0.22 96％ Comparative Example 3 25.3 155.6 0.23 98％ Example 1 6.5 211.6 0.35 97.0％ Example 2 6.2 206.8 0.31 94.3％ Example 3 5.4 215.4 0.29 103.6％ Example 4 4.2 206.3 0.28 99.5％ Example 5 6.0 199.6 0.27 98.6％

[0067] Note: Since the molecular sieves prepared in Comparative Examples 4 and 5 were amorphous, there is no data on specific surface area, total pore volume, etc.

[0068] The molecular sieves obtained in Example 4 and Comparative Example 1 were used to prepare catalysts in the following manner:

[0069] (1) Preparation of the carrier: ZSM-22 molecular sieve and pseudoboehmite were mixed for 30 minutes, with ZSM-22 molecular sieve accounting for 75 wt% of the mixture. Then, 1 wt% nitric acid and deionized water were added to the mixture and mixed for 30 minutes. The mixture was then extruded and calcined at 550°C in air to prepare the carrier.

[0070] (2) Determination of the saturated water absorption rate of the carrier

[0071] The method for determining the saturated water absorption rate of the carrier is as follows: Weigh 3g of the calcined carrier and immerse it in a beaker containing deionized water, ensuring the deionized water completely covers the carrier. Bubbles will be generated during this process. Gently shake the beaker until no more bubbles are produced. Transfer the carrier to filter paper and blot the surface water with the filter paper. Weigh the carrier after water absorption and record it as M grams. M-3 is the saturated water absorption of 3g of carrier, and (M-3) / 3 is the saturated water absorption rate of the carrier (g / g).

[0072] (3) Catalyst preparation

[0073] H2PtCl6·6H2O was dissolved in deionized water to obtain a platinum salt impregnation solution; the support was impregnated in the platinum salt impregnation solution (using a vacuum equal volume impregnation method) for 4 hours to obtain a wet catalyst strip; the wet catalyst strip was calcined at 320℃ for 10 hours to obtain the catalyst.

[0074] The catalysts prepared by the above method were evaluated using n-dodecane as a model compound. Under the process conditions of 300℃, hydrogen partial pressure of 2 MPa, and hydrogen / alkane ratio of 600 (volume ratio), the product distribution is shown in Table 2. The overall isomer yield is calculated as: (selectivity of single-branched isomers + selectivity of multi-branched isomers) × conversion rate.

[0075] Table 2

[0076] project Example 4 Comparative Example 1 Conversion rate, % 93 82 Single-branched isomer selectivity, % 79.8 80.1 Multi-branched isomer selectivity, % 11.2 10.1 Total yield of isomers, % 84.6 74.0

[0077] As can be seen from the results in Table 2, compared with the conventional method for preparing ZSM-22 (Comparative Example 1), under the same process conditions, the catalyst prepared by the scheme of the present invention has higher alkane conversion, single-branched isomer selectivity and total isomer yield.

[0078] The catalysts prepared by the above method were used as feedstocks from Dalian cracked tailings oil. The feedstock properties are shown in Table 3. The hydrogen partial pressure was 15 MPa, the reaction temperature was 310 °C, and the volume hourly space velocity was 1.0 h⁻¹. -1 Hydrogenation isomerization was carried out under process conditions with a hydrogen-to-oil ratio of 500. The product properties and yields are shown in Table 4.

[0079] Table 3

[0080] Dalian adds tail oil <![CDATA[Density, g / cm 3 > 0.8326 Sulfur, μg / g ＜5 Nitrogen, μg / g ＜5 Pour point 31 Distillation range, °C 298-531

[0081] Table 4

[0082] Comparative Example 1 Example 4 Pressure P / MPa 15 15 Reaction temperature T / ℃ 310 310 <![CDATA[Space velocity LHSV / h -1 > 1.0 1.0 <![CDATA[Hydrogen-oil ratio H2 / iol]]> 500 500 Base oil yield / % 70.4 91.2 Pour point -10 -32

[0083] As shown in Table 4, compared with the conventional method for preparing ZSM-22 (Comparative Example 1), under the same process conditions, the catalyst prepared using the scheme of this invention yields a base oil with better low-temperature fluidity and a higher base oil yield. These results indicate that reducing the shaft diameter ratio can improve the selectivity for single-branched isomers during the tail oil isomerization process, reduce oil viscosity index loss, and increase base oil yield.

[0084] In summary, compared to the conventional method for preparing ZSM-22 (Comparative Example 1), the addition of etchant in Examples 1 to 5 of this case does not stimulate the growth of other impurity phases, and the resulting samples are pure-phase ZSM-22 molecular sieves. Under the action of the etchant, the axial diameter ratio of the ZSM-22 molecular sieve can be significantly shortened.

[0085] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing ZSM-22 molecular sieve, characterized in that, Includes the following steps: A gel is formed by mixing silicon source, aluminum source, inorganic alkali source, template agent, etchant and water. After dynamic crystallization, separation, washing, drying and calcination, ZSM-22 molecular sieve is obtained. The molar ratio of SiO2, Al2O3, inorganic alkali source, stencil agent, etching agent and water in the gel is 1:(0.01-0.05):(0.05-0.3):(0.1-0.5):(0.005-0.1):(40-60); The etching agent is selected from at least one of isopropanol, 1,6-hexanediol, lysine, tris(hydroxymethyl)nitromethane, and 1,2,4-triazole.

2. The preparation method according to claim 1, characterized in that, The molar ratio of SiO2 to the etching agent in the gel is 1:(0.008~0.05).

3. The preparation method according to claim 1 or 2, characterized in that, The molar ratio of SiO2 to the template agent in the gel is 1:(0.10~0.25).

4. The preparation method according to claim 1, characterized in that, The dynamic crystallization temperature is 160–175°C, and the time is 48–72 h.

5. The preparation method according to claim 4, characterized in that, The dynamic crystallization is carried out in a crystallization reactor; preferably, the rotation speed of the crystallization reactor is 40 to 80 rpm.

6. The preparation method according to claim 1, characterized in that, The template agent is selected from at least one of isopropylamine, 1,6-hexanediamine, and 6-amino-1-hexanol.

7. The preparation method according to claim 1, characterized in that, The silicon source is selected from at least one of silica sol, silica, water glass, and tetraethyl orthosilicate; The aluminum source is selected from at least one of aluminum sulfate, aluminum acetate, aluminum isopropoxide, and aluminum chloride; The inorganic base source is selected from sodium hydroxide and / or potassium hydroxide.

8. The preparation method according to claim 1, characterized in that, The roasting temperature is 500-600℃ and the time is 8-10h.

9. A ZSM-22 molecular sieve prepared by the method according to any one of claims 1-8, characterized in that, The ZSM-22 molecular sieve has an axis-to-diameter ratio of 4.0-6.5, and preferably, the specific surface area of ​​the ZSM-22 molecular sieve is 199-216 m². 2 / g, total pore volume is 0.27-0.35m³ 3 / g, with a relative crystallinity of 94%-104%.

10. The application of the ZSM-22 molecular sieve prepared by the method of any one of claims 1-8 in the preparation of catalysts.

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