Method for synthesizing molecular sieve by using fluorine-containing silicon powder

Abstract

The invention belongs to the technical field of solid hazardous waste resource recycling, and provides a method for synthesizing a molecular sieve by using fluorine-containing silicon powder, which comprises the following steps: fully mixing an aluminum source, an alkali source, a template agent, a fluorine complexing agent and fluorine-containing silicon powder in deionized water, and stirring to obtain synthetic gel; and transferring the mixture into a crystallization kettle with a stirring device, adding a molecular sieve seed crystal, sequentially carrying out at least two sections of dynamic crystallization processes, washing, separating and drying to obtain a fluorine-free molecular sieve product. According to the present invention, the organic amine and quaternary ammonium ion synergistic strategy is adopted, the fluorine-containing silicon powder is adopted to synthesize the high crystallinity and purity molecular sieve, the crystallization time range is wide, the control is easy, and the fluorine does not enter or is mixed into the molecular sieve product, such that the treatment problem of the dangerous solid waste can be effectively solved, and the molecular sieve synthesis cost can be substantially reduced; the resource utilization rate is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource recovery and utilization of solid hazardous waste, and relates to a method for synthesizing molecular sieve by using fluorine-containing silicon powder. Background Art

[0002] Fluorine-containing silicon powder is a by-product in the process of processing phosphate rock to produce fluorosilicon, and it is a hazardous solid waste, which is characterized by large output, high treatment difficulty and serious environmental pollution risk. The treatment of fluorine-containing silicon powder is a major challenge at present. Traditional landfill and stacking not only occupy a large amount of land resources, but also cause serious harm to the environment. The entry of fluorine into the air will exacerbate the potential risks to the ecosystem and human health. Developing diversified utilization ways to convert fluorine-containing silicon powder into high-value-added products is an efficient treatment method. Fluorine-containing silicon powder contains a large amount of silicon dioxide resources. If the SiO2 therein can be utilized and fluorine element can be effectively separated and recovered, the cost can be reduced, turning waste into treasure, and double economic and environmental benefits can be generated. Therefore, the efficient recovery and utilization of fluorine-containing silicon powder is not only beneficial to alleviating the environmental pressure brought by it, but also a key step in realizing resource recycling and promoting green development.

[0003] As an important microporous material, molecular sieves have shown extensive application potential in the fields of catalysis, adsorption separation, and environmental governance. Using fluorine-containing silicon slag as a raw material to produce molecular sieves is a technical direction that has received extensive attention. Chinese Patent CN118529744A discloses a method for preparing Beta molecular sieves using fluorine-containing silicon slag as a silicon source. This method synthesizes Beta molecular sieves by the dry gel method, without mother liquor discharge and with high raw material utilization rate. However, it is unable to separate and recover fluorine, and all the fluorine in the fluorine-containing silicon slag enters the Beta molecular sieve product. Chinese Patent CN112939003B discloses a method for preparing SBA-15 molecular sieves using fluorine-containing silicon slag, and realizes the recovery of fluorine resources in the fluorine-containing silicon slag by adding metals. However, there are still some fluoride ions retained in the small cages of the molecular sieve in this method. Chinese Patent CN117735569A discloses a method for preparing silicon-aluminum molecular sieves and cryolite from fluorine-containing silicon slag. The synthesized solid product is a molecular sieve, and aluminum source is added to the filtrate to adjust the pH to obtain cryolite, and the Si and F elements in the fluorine-containing silicon slag are recycled in the forms of silicon-aluminum molecular sieves (4A molecular sieves) and cryolite products respectively. Chinese Patent CN116947062A discloses a method for preparing titanium-silicon molecular sieve TS-1 using fluorine-containing silicon slag, as well as its modification and application. The prepared modified titanium-silicon molecular sieve TS-1 catalyst can be used in the catalytic ammoxidation of cyclohexanone to prepare cyclohexanone oxime reaction. In addition to producing molecular sieves, fluorine-containing silicon powder can also be used in the production of other chemicals. Chinese Patent CN115869950A discloses a method for preparing a Fenton-like catalyst from fluorine-containing silicon slag and by-producing a fluorine salt product. Chinese Patent CN113371720A discloses a method for removing impurities from fluorine-containing silicon slag by dry method with sulfuric acid to prepare white carbon black.

[0004] In the presence of fluorine in the molecular sieve synthesis system, fluorine usually enters the molecular sieve structure. Due to the strong electronegativity of F - , its lone pair electrons can form hydrogen bonds or ion pairs with N-H (with partial positive charge) in the organic amine template agent, enhancing the adsorption ability of F - in the amine solution. Furthermore, F may enter the molecular sieve together with the organic amine, resulting in the entry of fluorine into the molecular sieve structure and affecting its performance (Chinese Patent CN113979448B). The introduction of F element not only changes the original properties of the molecular sieve, but also introduces a new pollution source into the finished molecular sieve, causing new difficulties and obstacles to the recovery and reuse of the used molecular sieve. In addition, the F-containing substances released by the dissolution of fluorine-containing silicon powder will affect the pH value of the system, causing the synthesis system to deviate from the synthesis phase region of the molecular sieve. Therefore, it is usually necessary to add NaOH to further increase the alkalinity of the system, resulting in the formation of a large amount of NaF with low solubility, which is difficult to remove when mixed in the molecular sieve product.

[0005] Therefore, developing a technical solution for synthesizing molecular sieves using fluorosilica powder as a raw material requires solving two problems: First, how to effectively treat fluorine elements to prevent F from entering the molecular sieve structure; Second, avoid the formation of insoluble NaF microcrystals mixed in the molecular sieve product, forming new fluorine-containing hazardous waste.

[0006] In addition, in existing technical solutions, the processes for preparing molecular sieves using fluorosilicate slag involve fewer types of molecular sieves. If some molecular sieves that have been widely used in recent years, such as ZSM-35 and ZSM-22, can be synthesized using fluorosilicate slag, it will greatly expand the application scope of this technology. ZSM-35 molecular sieve has a unique two-dimensional pore structure, composed of perpendicular intersections of eight-membered rings and ten-membered rings. This special structure not only endows it with excellent thermal stability and hydrothermal stability but also enables it to exhibit excellent performance in various industrial processes. Its unique crystal structure and pore system make it an ideal choice for handling complex reaction systems, especially suitable for processes involving the conversion of long-chain alkanes. ZSM-22 molecular sieve belongs to the MWW topological structure type and has a three-dimensional cross-linked pore system. This structural feature endows it with good shape selectivity. In the petroleum refining industry, ZSM-22 is widely used in processes such as isomerization, cracking, and alkylation to improve the quality and yield of gasoline and enhance the anti-knock performance of fuels by improving the olefin and aromatic hydrocarbon content in gasoline. In addition, due to its good selectivity for specific-sized molecules, ZSM-22 is also used to separate specific organic compounds from mixed gases, demonstrating its application value in the field of gas separation. Summary of the Invention

[0007] Based on the above background, the present invention aims to propose a technical solution for synthesizing molecular sieves using fluorosilica powder to achieve the goal of solving the problem of storing hazardous solid waste.

[0008] The technology of the present invention adopts a synergistic strategy of organic amines and quaternary ammonium ions, introducing at least two basic organic substances in the synthesis of molecular sieves. One is an organic amine as a template agent, i.e., a structure-directing agent (SDA), and the other is a quaternary ammonium salt or quaternary ammonium base as a fluorine complexing agent, with TRA + representing the quaternary ammonium ion, where R is an alkyl or aryl group with a carbon number ≥ 4. Because the molecular sizes of these quaternary ammonium salts are relatively large, they cannot enter the molecular sieve pores as template agents. The template agent selects organic amines with relatively weak water solubility, such as cyclohexylamine, diethylamine, n-butylamine, and 1,6-hexanediamine, which direct the molecular sieve framework to arrange in a specific topological structure through intermolecular forces, forming regular pores and cage-like structures; The quaternary ammonium salt or quaternary ammonium base as a fluorine complexing agent has relatively strong water solubility, such as tetrabutylammonium hydroxide (TBAOH), tetrabutylammonium bromide (TBAB), or cetyltrimethylammonium bromide (CTAB), which dissociate in the aqueous phase to generate quaternary ammonium cations [R4N + , which can combine with F in the liquid phase -Quickly form a stable ion pair complex, effectively fix free fluorine, and release OH- simultaneously to adjust the pH of the system, which can partially replace the use of NaOH and avoid the formation of less soluble NaF precipitate. The synergistic effect of organic amine and quaternary ammonium ion not only ensures the precise construction of the molecular sieve pore structure but also significantly improves the dissolution stability of fluoride ions in the mother liquor, providing favorable conditions for the efficient recovery of subsequent fluorine resources.

[0009] The inventors found through a large number of experiments that by adopting the technical solution of the present invention, during the dissolution process of fluorine-containing silica powder, the dissolution rates of silicon species and fluorine species are controllable. During the crystallization process, the segmented dynamic crystallization method is adopted, and the existence state of fluorine species in the system and the rate of silicon-aluminum species entering the framework are controlled by controlling the crystallization temperature and rotation speed. The first stage includes the dissolution of fluorine-containing silica powder and the formation of molecular sieve crystal nuclei, which requires being carried out at a lower temperature (20 - 100 °C) and a lower stirring speed (20 - 60 rpm) to promote the full dissolution of fluorine-containing silica powder and release all F elements; in the second stage, the crystal growth stage, the temperature range required for molecular sieve crystallization is 100 - 200 °C, and the rotation speed is increased to 250 - 500 rpm. During the crystallization process, a higher rotation speed can promote the diffusion of quaternary ammonium ions in the liquid phase, which is beneficial to competing with organic amines for F - , avoiding the co-entry of organic amines carrying F into the molecular sieve and affecting the composition and properties of the molecular sieve. After the synthesis is completed, the fluorine-free molecular sieve product can be separated, and precipitation method, resin adsorption method, etc. can be used to recover the fluorine in the mother liquor.

[0010] The process of this invention patent is simple, with high raw material utilization rate, which can significantly reduce production costs and is easy to realize industrial production. Taking the synthesis of ZSM-35 molecular sieve as an example: It is calculated that when synthesizing ZSM-35 molecular sieve with silica sol as the raw material by the conventional method, the utilization rate of the silicon source in the raw material is 60 - 73%. While adopting this technical solution and using fluorine-containing silica powder as the raw material to synthesize ZSM-35 molecular sieve, the utilization rate of the silicon source in the raw material is as high as 87 - 92%. In addition, when synthesizing ZSM-35 molecular sieve with silica sol as the raw material, a phase transformation phenomenon often occurs after 72 h of crystallization. Adopting this technical solution can effectively control the crystallization process, avoid the structural phase transformation of ZSM-35 molecular sieve into ZSM-5 molecular sieve, and has a relatively long crystallization stable period. Pure phase products of ZSM-35 molecular sieve can be obtained within 18 h - 150 h. In addition, the ZSM-35 molecular sieve synthesized with fluorine-containing silica powder has good crystallization, and the relative crystallinity is higher than that of the product synthesized by the conventional silicon source system.

[0011] The present invention can not only provide a method for synthesizing high-quality molecular sieves at low cost, but also realize the resource utilization of fluorine-containing silica powder, and solve the environmental pollution problem caused by the stacking and storage of hazardous solid waste. The product synthesized by this technical solution is a fluorine-free silica-aluminum molecular sieve, effectively avoiding the influence of the introduction of F on the performance of the molecular sieve and the secondary pollution caused by waste molecular sieves. Through reasonable technical scheme design and optimization, fluorine-containing silica powder can become an ideal substitute for the silicon source in the synthesis of molecular sieves, opening up a new way for the green synthesis and resource recycling of molecular sieves.

[0012] The technical solution of the present invention is as follows:

[0013] A method for synthesizing molecular sieves using fluorine-containing silica powder, comprising the following steps:

[0014] (1) Preparation of synthesis gel: An aluminum source, an alkali source, fluorine-containing silica powder and deionized water are fully mixed to obtain a mixture A, and at least two basic organic compounds are added to the mixture A; one of them is a water-soluble weak organic amine as a template, i.e., a structure-directing agent SDA; the other is a water-soluble strong quaternary ammonium salt or quaternary ammonium base as a fluorine complexing agent, represented by TRA + indicating a quaternary ammonium ion, where R is an alkyl or aryl group with a carbon number ≥ 4; the above mixture is stirred evenly at a constant temperature to obtain a synthesis gel;

[0015] (2) Molecular sieve crystallization stage: The synthesis gel is transferred to a crystallization kettle with a stirring device, sealed after adding molecular sieve seeds, and undergoes at least two dynamic crystallization processes; the first crystallization is carried out at 20 - 100 °C, the stirring speed is 20 - 60 rpm, and the crystallization time is 1 - 24 h; the second crystallization is carried out at 100 - 200 °C and a stirring speed of 250 - 500 rpm for 10 - 200 h;

[0016] (3) Recovery of product: The product after crystallization is washed, separated by suction filtration, and dried to obtain a fluorine-free molecular sieve product.

[0017] In the step (1), the fluorine complexing agent is one or more of tetrabutylammonium hydroxide (TBAOH), tetrabutylammonium bromide (TBAB), and cetyltrimethylammonium bromide (CTAB).

[0018] In the step (1), the aluminum source is selected from one or more of sodium aluminate, aluminum sol, and pseudo-boehmite; the alkali source is selected from sodium hydroxide or potassium hydroxide.

[0019] The above method can be used for the synthesis of ZSM-35 or ZSM-22.

[0020] When synthesizing ZSM-35 molecular sieve, the molar ratio of each component of the synthesis gel is 2-4Na2O:1Al2O3:20-50SiO2:4-10SDA:12-16TRA + :500-1200H2O; The template agent is selected from one or more of cyclohexylamine, n-butylamine, and diethylamine. The crystallization temperature of the first stage is 40-80°C, the crystallization time is 2-12h, and the stirring speed is 35-60rpm; The crystallization temperature of the second stage is 150-180°C, the crystallization time is 18-150h, and the stirring speed is 300-360rpm.

[0021] When synthesizing ZSM-22 molecular sieve, the molar ratio of each component of the synthesis gel is 8-12Na2O:1Al2O3:60-90SiO2:15-22SDA:8-14TRA + :2500-3000H2O. The template agent is selected from one or two of diethylamine and 1,6-hexanediamine. The crystallization temperature of the first stage is 40-80°C, the crystallization time is 4-24h, and the stirring speed is 35-50rpm; The crystallization temperature of the second stage is 140-170°C, the crystallization time is 24-72h, and the stirring speed is 320-400rpm.

[0022] In all the above technical solutions, the seeding amount is 1-10% of the mass of SiO2 in the fluorine-containing silicon powder.

[0023] Compared with the existing molecular sieve synthesis methods, the present invention has the following technical effects:

[0024] (1) The present invention uses fluorine-containing silicon powder to synthesize molecular sieve, which can effectively separate silicon and fluorine therein. While reducing the production cost of molecular sieve synthesis and obtaining a fluorine-free molecular sieve product, it solves the environmental pollution problem caused by the accumulation and storage of hazardous solid waste, and can bring significant environmental and economic benefits.

[0025] (2) The present invention uses fluorine-containing silicon powder to synthesize molecular sieve, and adopts the synergistic strategy of organic amine and quaternary ammonium ion. Compared with the traditional synthesis process, quaternary ammonium salt or quaternary ammonium base is used to effectively keep F - in the liquid phase and prevent it from entering the molecular sieve product structure.

[0026] (3) The present invention uses fluorine-containing silicon powder to synthesize molecular sieve. By means of two-stage dynamic crystallization, the existence state of fluorine species in the system and the rate of silicon and aluminum species entering the framework are controlled by controlling the crystallization temperature and speed, which can inhibit the structural transformation of the molecular sieve into other crystal forms. The crystallization stable period is longer and it is easy to control. Brief Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0028] Figure 1 It is the X-ray diffraction pattern of the molecular sieves synthesized in the embodiments of the present invention and the comparative examples.

[0029] Figure 2 It is the scanning electron microscope photograph of the molecular sieves synthesized in Example 1 and Example 4 of the present invention. Detailed implementation manners

[0030] I. Explanation of performance testing methods

[0031] X-ray measurement method: Use a D / max-2500 type X-ray diffractometer from Rigaku Corporation, Japan. Testing conditions: The diffraction source is Cu Kα (λ = 0.154 nm), the tube voltage is set at 40 KV, the tube current is set at 100 mA, and the scanning range 2θ is 5 - 40°.

[0032] SEM measurement method: Observe using a NOVA Nano SEM 450 type scanning electron microscope from FEI Company, USA.

[0033] X-ray fluorescence spectroscopy analysis: Determine the element content in the synthesized sample using an Axios advanced type X-ray fluorescence spectrometer from PANalytical Company, the Netherlands.

[0034] Calculation of relative crystallinity of molecular sieve: Calculate the relative crystallinity of the synthesized sample based on the sum of the intensities of 5 characteristic diffraction peaks of ZSM-35 molecular sieve at 2θ of 9.4°, 22.4°, 23.6°, 25.1° and 25.6° (taking the crystallinity of the sample synthesized with conventional silicon source as 100%); calculate the relative crystallinity of the synthesized sample based on the sum of the intensities of 5 characteristic diffraction peaks of ZSM-22 molecular sieve at 2θ of 8.2°, 20.4°, 24.2°, 24.6° and 25.7° (taking the crystallinity of the sample synthesized with conventional silicon source as 100%).

[0035] II. The raw materials involved in the specific implementation manners of the present invention are as follows:

[0036] (1) Fluorine-containing silicon powder: containing 38% SiO2 and 7% F by mass fraction, industrial product;

[0037] (2) Colloidal silica: containing 31.4% SiO2 by mass fraction, industrial product;

[0038] (3) Sodium metaaluminate: containing 42.17% Al2O3 by mass fraction, industrial product;

[0039] (4) Sodium hydroxide: Content 96%, mass fraction, commercially available product;

[0040] (5) Cyclohexylamine: Analytically pure, commercially available product;

[0041] (6) Diethylamine: Analytically pure, commercially available product;

[0042] (7) Tetrabutylammonium hydroxide: Content 25%, mass fraction, commercially available product;

[0043] (8) Molecular sieve seed: Industrial product.

[0044] III. Examples and Comparative Examples

[0045] Example 1

[0046] Weigh 50.49 g of deionized water and add 0.77 g of sodium aluminate, 0.40 g of sodium hydroxide, and 12.63 g of fluorine-containing silica powder to prepare mixture A; successively add 1.90 g of cyclohexylamine and 9.96 g of tetrabutylammonium hydroxide to mixture A, and fully mix the above mixture for 30 min under a stirring environment at 20°C with a stirring rate of 100 rpm to obtain a synthesis gel. Transfer the synthesis gel to a crystallization kettle with a stirring device, add 0.10 g of molecular sieve seed and seal it. The first-stage crystallization process is carried out at 60°C for 4 h with a stirring speed of 40 rpm; the second-stage crystallization process is carried out at 170°C for 24 h with a stirring speed of 350 rpm. Then the product is filtered by suction, washed until neutral, and dried in an environment at 120°C for 6 h to obtain ZSM-35 molecular sieve.

[0047] Example 2

[0048] Weigh 63.14 g of deionized water and add 0.81 g of sodium aluminate, 0.69 g of sodium hydroxide, and 15.79 g of fluorine-containing silica powder to prepare mixture A; successively add 2.98 g of cyclohexylamine and 12.11 g of tetrabutylammonium hydroxide to mixture A, and fully mix the above mixture for 30 min under a stirring environment at 20°C with a stirring rate of 100 rpm to obtain a synthesis gel. Transfer the synthesis gel to a crystallization kettle with a stirring device, add 0.15 g of molecular sieve seed and seal it. The first-stage crystallization process is carried out at 80°C for 8 h with a stirring speed of 60 rpm; the second-stage crystallization process is carried out at 170°C for 72 h with a stirring speed of 300 rpm. Then the product is filtered by suction, washed until neutral, and dried in an environment at 120°C for 6 h to obtain ZSM-35 molecular sieve.

[0049] Example 3

[0050] Weigh 28.34 g of deionized water and add 0.58 g of sodium aluminate, 0.49 g of sodium hydroxide, and 18.95 g of fluorine-containing silica powder to prepare mixture A. Then, add 0.70 g of n-butylamine and 11.61 g of tetrabutylammonium bromide to mixture A successively. Under a stirring environment at 20 °C, fully mix the above mixture for 30 min with a stirring rate of 100 rpm to obtain a synthesis gel. Transfer the synthesis gel to a crystallization kettle with a stirring device, add 0.30 g of molecular sieve seeds, and seal it. The first-stage crystallization process is carried out at 60 °C for 12 h with a stirring speed of 60 rpm; the second-stage crystallization process is carried out at 180 °C for 48 h with a stirring speed of 360 rpm. Then, the product is filtered by suction, washed until neutral, and dried in an environment at 120 °C for 6 h to obtain ZSM-35 molecular sieve.

[0051] Example 4

[0052] Weigh 58.75 g of deionized water and add 0.30 g of sodium aluminate, 0.76 g of sodium hydroxide, and 15.79 g of fluorine-containing silica powder to prepare mixture A. Then, add 1.65 g of diethylamine and 3.24 g of tetrabutylammonium hydroxide to mixture A successively. Under a stirring environment at 20 °C, fully mix the above mixture for 30 min with a stirring rate of 100 rpm to obtain a synthesis gel. Transfer the synthesis gel to a crystallization kettle with a stirring device, add 0.14 g of molecular sieve seeds, and seal it. The first-stage crystallization process is carried out at 60 °C for 24 h with a stirring speed of 50 rpm; the second-stage crystallization process is carried out at 160 °C for 48 h with a stirring speed of 360 rpm. Then, the product is filtered by suction, washed until neutral, and dried in an environment at 120 °C for 6 h to obtain ZSM-22 molecular sieve.

[0053] Comparative Example 1

[0054] Weigh 48.66 g of deionized water and add 0.77 g of sodium aluminate, 0.40 g of sodium hydroxide, and 15.29 g of silica sol to prepare mixture A. Add 1.90 g of cyclohexylamine to mixture A. Under a stirring environment at 20 °C, fully mix the above mixture for 30 min with a stirring rate of 100 rpm to obtain a synthesis gel. Transfer the synthesis gel to a crystallization kettle with a stirring device, add 0.10 g of molecular sieve seeds, and seal it. Crystallize at 170 °C for 24 h with a stirring speed of 40 rpm. Then, the product is filtered by suction, washed until neutral, and dried in an environment at 120 °C for 6 h to obtain ZSM-35 molecular sieve.

[0055] Comparative Example 2

[0056] Weigh 60.94 g of deionized water and add 0.81 g of sodium aluminate, 0.69 g of sodium hydroxide, and 19.11 g of silica sol to prepare mixture A; add 2.98 g of cyclohexylamine to mixture A, and fully mix the above mixture for 30 min under a stirring environment at 20 °C with a stirring rate of 100 rpm to obtain a synthetic gel. Transfer the synthetic gel to a crystallization kettle equipped with a stirring device, add 0.15 g of molecular sieve seeds, seal it, and crystallize at 170 °C for 72 h with a stirring speed of 60 rpm. Then, the product is filtered by suction, washed until neutral, and dried in an environment at 120 °C for 6 h to obtain the final product.

[0057] Comparative Example 3

[0058] Weigh 28.34 g of deionized water and add 0.58 g of sodium aluminate, 0.49 g of sodium hydroxide, and 18.95 g of fluorine-containing silica powder to prepare mixture A; add 0.70 g of n-butylamine and 11.61 g of tetrabutylammonium bromide to mixture A in sequence, and fully mix the above mixture for 30 min under a stirring environment at 20 °C with a stirring rate of 100 rpm to obtain a synthetic gel. Transfer the synthetic gel to a crystallization kettle equipped with a stirring device, add 0.30 g of molecular sieve seeds, seal it, carry out the first-stage crystallization process at 60 °C for 12 h with a stirring speed of 60 rpm; carry out the second-stage crystallization process at 180 °C for 48 h with a stirring speed of 60 rpm. Then, the product is filtered by suction, washed until neutral, and dried in an environment at 120 °C for 6 h to obtain the final product.

[0059] Comparative Example 4

[0060] Weigh 58.75 g of deionized water and add 0.30 g of sodium aluminate, 0.76 g of sodium hydroxide, and 15.79 g of fluorine-containing silica powder to prepare mixture A; add 1.65 g of diethylamine and 3.24 g of tetrabutylammonium hydroxide to mixture A in sequence, and fully mix the above mixture for 30 min under a stirring environment at 20 °C with a stirring rate of 100 rpm to obtain a synthetic gel. Transfer the synthetic gel to a crystallization kettle equipped with a stirring device, add 0.14 g of molecular sieve seeds, seal it, and crystallize at 160 °C for 72 h with a stirring speed of 360 rpm. Then, the product is filtered by suction, washed until neutral, and dried in an environment at 120 °C for 6 h to obtain ZSM-22 molecular sieve.

[0061] Comparative Example 5

[0062] Weigh 50.49 g of deionized water and add 0.77 g of sodium aluminate, 1.94 g of sodium hydroxide, and 12.63 g of fluorine-containing silica powder to obtain mixture A; add 1.90 g of cyclohexylamine to mixture A, and fully mix the above mixture for 30 min under a stirring environment at 20 °C with a stirring rate of 100 rpm to obtain a synthetic gel. Transfer the synthetic gel to a crystallization kettle with a stirring device, seal it after adding 0.10 g of molecular sieve seeds. The first-stage crystallization process is carried out at 60 °C for 4 h with a stirring speed of 40 rpm; the second-stage crystallization process is carried out at 170 °C for 24 h with a stirring speed of 350 rpm. Then the product is filtered by suction, washed until neutral, and dried in an environment at 120 °C for 6 h to obtain ZSM-35 molecular sieve.

[0063] Description of examples and comparative examples:

[0064] Through Figure 1 And the characterization results of all the synthesized samples shown in Table 1, it can be seen that when comparing Example 1 with Comparative Example 1, the relative crystallinity (141%) of the molecular sieve synthesized with fluorine-containing silica powder as the silicon source is higher than that of the molecular sieve synthesized with a conventional silicon source (100%); when comparing Example 2 with Comparative Example 2, when the crystallization time is extended, the synthesis system with fluorine-containing silica powder as the silicon source effectively inhibits the conversion of ZSM-35 molecular sieve to ZSM-5 molecular sieve; when comparing Example 3 with Comparative Example 3, under the same synthesis conditions, ZSM-35 molecular sieve can be effectively crystallized only under specific rotation speed conditions; when comparing Example 4 with Comparative Example 4, under the same conditions, two-stage dynamic crystallization is a necessary step to synthesize high-crystallinity pure-phase ZSM-22 molecular sieve.

[0065] As can be seen from Table 2 (Example 1), the product molecular sieve synthesized with fluorine-containing silica powder does not contain F element, while Table 3 (Comparative Example 5) shows that F element exists in the product under the condition of using a conventional base source (NaOH) and not using a fluorine complexing agent. Figure 2 SEM photos of ZSM-35 and ZSM-22 molecular sieves synthesized in Example 1 and Example 4.

[0066] Table 1 Phase analysis of synthesized samples in examples and comparative examples

[0067]

[0068]

[0069] Table 2 Elemental composition of ZSM-35 molecular sieve synthesized in Example 1

[0070]

[0071] Table 3 Elemental composition of ZSM-35 molecular sieve synthesized in Comparative Example 5

[0072]

[0073] The above are only the preferred embodiments of the present invention, which are only applicable to help understand the principle of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have corresponding changes and variations in the specific implementation manners and application scopes. Therefore, the embodiments in the present invention should be regarded as exemplary and non-limiting. All changes falling within the meaning and scope of the equivalent elements of the claims are encompassed in the patent of the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved. Any modifications, equivalent replacements, improvements, etc., made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for synthesizing molecular sieve using fluorosilica powder, characterized in that: It includes the following steps: (1) Preparation of synthetic gel: An aluminum source, an alkali source, fluorine-containing silicon powder, and deionized water are fully mixed to obtain mixture A, and at least two basic organic compounds are added to mixture A; one of them is an organic amine with relatively weak water solubility as a template agent, i.e., a structure-directing agent SDA; the other is a quaternary ammonium salt or quaternary ammonium base with relatively strong water solubility as a fluorine complexing agent, and TRA + represents a quaternary ammonium ion, where R is an alkyl or aryl group with a carbon number ≥ 4; the above mixture is stirred evenly at a constant temperature to obtain a synthetic gel; (2) Molecular sieve crystallization stage: Transfer the synthesis gel to a crystallization kettle with a stirring device, add molecular sieve seeds and seal it, and undergo at least two dynamic crystallization processes; Among them, the first crystallization is carried out at 20 - 100 °C, the stirring speed is 20 - 60 rpm, and the crystallization time is 1 - 24 h; the second crystallization is carried out at 100 - 200 °C and the stirring speed is 250 - 500 rpm for 10 - 200 h; (3) Recover the product: The product after crystallization is washed, separated by suction filtration, and dried to obtain a fluorine-free molecular sieve product.

2. The method according to claim 1, characterized in that: The fluorine complexing agent is one or more of tetrabutylammonium hydroxide TBAOH, tetrabutylammonium bromide TBAB, and cetyltrimethylammonium bromide CTAB.

3. The method according to claim 1, characterized in that: The aluminum source is selected from one or more of sodium aluminate, aluminum sol, and pseudo-boehmite; the base source is selected from sodium hydroxide or potassium hydroxide.

4. The method according to any one of claims 1 to 3, characterized in that: The molecular sieve includes ZSM-35 or ZSM-22.

5. The method according to any one of claims 1 - 3, characterized in that: When synthesizing ZSM-35 molecular sieve, the molar ratio of each component in the synthesis gel is 2-4Na2O:1Al2O3:20-50SiO2:4-10SDA:12-16TRA + :500-1200H2O; When synthesizing ZSM-22 molecular sieve, the molar ratio of each component in the synthesis gel is 8-12Na2O:1Al2O3:60-90SiO2:15-22SDA:8-14TRA + :2500-3000H2O.

6. The method according to any one of claims 1-3, characterized in that: The template agent for synthesizing ZSM-35 molecular sieve is selected from one or more of cyclohexylamine, n-butylamine, and diethylamine, and the template agent for synthesizing ZSM-22 molecular sieve is selected from one or two of diethylamine and 1,6-hexanediamine.

7. The method according to claim 1, wherein: The addition amount of the seed crystal is 1 - 10% of the mass of SiO2 in the fluorine-containing silica powder.

8. The method according to claim 5, characterized in that: When synthesizing ZSM-35 molecular sieve, the first crystallization temperature is 40 - 80 °C, the crystallization time is 2 - 12 h, and the stirring speed is 35 - 60 rpm; the second crystallization temperature is 150 - 180 °C, the crystallization time is 18 - 150 h, and the stirring speed is 300 - 360 rpm; When synthesizing ZSM-22 molecular sieve, the first crystallization temperature is 40 - 80 °C, the crystallization time is 4 - 24 h, and the stirring speed is 35 - 50 rpm; the second crystallization temperature is 140 - 170 °C, the crystallization time is 24 - 72 h, and the stirring speed is 320 - 400 rpm.

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