Preparation method of ammonium fluorosilicate modified molecular sieve

Abstract

This invention discloses a method for preparing ammonium fluorosilicate modified molecular sieves. The method includes the following steps: (1) contacting activated carbon with an aqueous solution of a fluorocarbon surfactant to modify it, thereby obtaining modified activated carbon; (2) mixing the modified activated carbon and molecular sieve obtained in step (1) with an ammonium fluorosilicate solution for reaction, and separating the reaction products to obtain waste activated carbon and modified molecular sieve precursors; (3) washing, drying, and calcining the modified molecular sieve precursors obtained in step (2) to obtain modified molecular sieves. The method has the advantages of simple operation, low cost, high fluoride removal efficiency, and high yield of modified molecular sieve products.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, and in particular to a method for preparing ammonium fluorosilicate modified molecular sieves. Background Technology

[0002] Molecular sieves, due to their strong acidity and unique three-dimensional pore structure, are widely used in important fields such as petrochemicals and fine chemicals, serving as catalysts, catalyst supports, ion exchangers, and adsorbents. When applied to catalytic and adsorption separation processes, most molecular sieves require modification to adjust their properties. For example, in heterogeneous catalysis, the catalytic activity of the molecular sieve needs to be improved by modifying the distribution and accessibility of active sites. Currently, commonly used molecular sieve modification methods include ion exchange, chemical treatment, steam treatment, and heteroatom isomorphic substitution. Among these, ammonium fluorosilicate isomorphic substitution-modified molecular sieves have advantages such as relatively mild reaction conditions, low non-framework aluminum content, and fewer crystal structure defects. This method is particularly advantageous in maintaining high crystallinity of the molecular sieve when the dealumination degree is high.

[0003] Patent CN111686787A discloses a hydrocracking catalyst support, its preparation method, and its application. This hydrocracking catalyst support is prepared from a Y-type zeolite / alumina composite material modified with ammonium fluorosilicate. The ammonium fluorosilicate-modified Y-type zeolite / alumina composite material is prepared by mixing activated alumina, a directing agent, a silicon source, and water, followed by hydrothermal crystallization and modification with ammonium fluorosilicate. This composite material possesses both the thermal stability, pore characteristics, and surface properties of activated alumina, and the improved acidity, open pore structure, high mesopore content, and abundant exposed acid centers characteristic of Y-type molecular sieves. When used as a support for hydrocracking catalysts, it exhibits superior properties in improving the conversion rate of macromolecules when processing heavy oil feedstocks.

[0004] Patent CN110372004A discloses a method and application for regulating the microscopic aluminum distribution of ZSM-5 molecular sieve. The method includes: loading cobalt ions onto the Na-type ZSM-5 molecular sieve using an ion exchange method to obtain a Co-type ZSM-5 molecular sieve; post-treating the Co-type ZSM-5 molecular sieve with ammonium hexafluorosilicate and ammonium acetate to obtain product B; washing, drying and calcining product B to obtain a ZSM-5 molecular sieve with regulated microscopic aluminum distribution. The prepared molecular sieve is suitable for C4 hydrocarbon catalytic cracking reaction.

[0005] Patent CN112237947A discloses a method for preparing a dewaxing catalyst support. The specific preparation method includes: (A) contacting a slurry containing HZSM-5 molecular sieve with ammonium fluorosilicate to carry out a dealuminization and silicon replenishment reaction to obtain a modified molecular sieve; wherein the Si / Al2 ratio of the HZSM-5 molecular sieve is greater than 120 and the average particle size is 5-50 μm; (B) mixing the modified molecular sieve with a binder, and then mixing it with an acid solution for sol-gelation, and then molding and calcining the mixture obtained by sol-gelation to obtain a support; the catalyst prepared with this support is used to dewax waxy feedstock oil, and the resulting lubricating oil base oil not only has a low pour point but also a high viscosity index, and can also improve the liquid yield of the lubricating oil base oil. Summary of the Invention

[0006] The inventors discovered through research that existing technologies for modifying molecular sieves with ammonium fluorosilicate suffer from the problem of "fluoride residue," which can damage the crystal structure of the molecular sieve under high-temperature conditions. However, existing technologies do not address this issue. Further investigation revealed that only one method in the existing technology can solve the "fluoride residue" problem: the washing and precipitation method. This method involves washing with large amounts of water and then utilizing the density difference between the fluoride and the molecular sieve material to remove the fluoride from the system. This process is repeated multiple times until the fluoride content meets the requirements. This method has low removal efficiency and inevitably causes loss of molecular sieve product during the modification process, resulting in a low yield of modified molecular sieve product.

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing ammonium fluorosilicate modified molecular sieves. This method introduces surface-modified activated carbon during the molecular sieve modification process, utilizing the adsorption and enrichment effects of the modified activated carbon on fluorides to achieve efficient fluoride removal. This method offers advantages such as simple operation, low cost, high fluoride removal efficiency, and high yield of modified molecular sieve products.

[0008] The first aspect of this invention provides a method for preparing ammonium fluorosilicate modified molecular sieves, the method comprising the following steps:

[0009] (1) Modified activated carbon is obtained by contacting it with an aqueous solution of fluorocarbon surfactant.

[0010] (2) The modified activated carbon and molecular sieve obtained in step (1) are mixed with ammonium fluorosilicate solution and reacted. The reaction products are separated to obtain waste activated carbon and modified molecular sieve precursors.

[0011] (3) The modified molecular sieve precursor obtained in step (2) is washed, dried and calcined to obtain the modified molecular sieve.

[0012] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the activated carbon in step (1) has a particle size of 10-50 mesh, preferably 20-30 mesh; and a specific surface area of ​​500 m². 2 / g-1800m 2 / g, preferably 800m 2 / g-1500m 2 / g; pore volume is 0.5cm 3 / g-1.5cm 3 / g, preferably 0.8cm 3 / g-1.0cm 3 / g, wherein the mesoporous pore volume accounts for 40%-80% of the total pore volume, preferably 50%-70%; the average pore size is 5nm-25nm, preferably 10nm-15nm.

[0013] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the fluorocarbon surfactant in step (1) is one or more of lithium 3-[2-(perfluoroalkyl)ethylthio]propionate, perfluorobutyl sulfonyl fluoride and sodium perfluorononenoxybenzenesulfonate, preferably lithium 3-[2-(perfluoroalkyl)ethylthio]propionate.

[0014] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the concentration of the aqueous solution of the fluorocarbon surfactant in step (1) is 0.01wt.%-0.10wt.%, preferably 0.03wt%-0.05wt.

[0015] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, in step (1), the ratio of activated carbon to aqueous solution of fluorocarbon surfactant is 1:(20-100), preferably 1:(40-60), based on g / mL.

[0016] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the modification process in step (1) is as follows: activated carbon is reacted with an aqueous solution of fluorocarbon surfactant at 30-60℃ for 1-3 hours, and then filtered and dried to obtain modified activated carbon.

[0017] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the molecular sieve in step (2) is a microporous molecular sieve, including any one of Y molecular sieve, ZSM-5 molecular sieve, and Beta molecular sieve; the particle size of the molecular sieve is 0.5μm-10μm, preferably 1μm-2μm; the silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of the molecular sieve is 3-80, preferably 5-30; and the specific surface area is 380m². 2 / g-900m 2 / g, pore volume 0.15cm 3 / g-0.38cm 3 / g.

[0018] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the concentration of the ammonium fluorosilicate solution in step (2) is 0.02mol / L-0.15mol / L, preferably 0.05mol / L-0.1mol / L.

[0019] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieve, in step (2), the ratio of the molecular sieve to the ammonium fluorosilicate solution is 1:(20-50) in g / mL.

[0020] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieve, the mass ratio of modified activated carbon to molecular sieve in step (2) is 1:(10-50), preferably 1:(10-30).

[0021] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the reaction conditions in step (2) are as follows: the reaction temperature is 60-100℃, preferably 80℃-90℃; the reaction time is 3h-6h, preferably 4h-5h.

[0022] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the separation equipment used in step (2) includes two layers of filter media, which are arranged in sequence according to the contact order with the material, including a first filter media and a second filter media. Preferably, the first filter media and the second filter media are arranged in an overlapping manner. The size of the first filter media is 80-300 mesh, preferably 100-200 mesh. Specifically, in this invention, the first filter media uses a 200-mesh stainless steel screen. The size of the second filter media is 100nm-5μm, preferably 500nm-3μm. Specifically, in this invention, the second filter media uses slow-speed filter paper with a pore size of 1μm-3μm.

[0023] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the separation process in step (2) is as follows: the reaction product enters the separation equipment and is separated by the first filter medium to obtain waste activated carbon and filtered material; the filtered material is separated by the second filter medium to obtain the modified molecular sieve precursor.

[0024] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the waste activated carbon in step (2) is regenerated. The specific operation process is as follows: the waste activated carbon is mixed with an acidic solution and reacted. After filtration, washing and drying, regenerated activated carbon is obtained. The acidic solution is sulfuric acid, and the concentration of the sulfuric acid is 60wt.%-80wt.%.

[0025] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the regenerated activated carbon in step (2) repeats the process of step (1).

[0026] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, in step (2), the solid-liquid ratio of waste activated carbon to acidic solution is 1:(6-15), preferably 1:(8-10, in g / mL.

[0027] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the operating conditions for the reaction of waste activated carbon and acidic solution in step (2) are: reaction temperature 5℃-30℃, preferably 10℃-20℃, and reaction time 30min-60min.

[0028] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the acidic gas generated during the reaction of waste activated carbon and acidic solution in step (2) is treated by washing with sodium hydroxide alkaline solution.

[0029] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, in step (3), the modified molecular sieve precursor is calcined in an air atmosphere at a temperature of 500℃-600℃ for 2h-5h.

[0030] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieves, the solid yield of the modified molecular sieve in step (3) is 85%-95%.

[0031] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, the washing process involves washing with water until neutral; the drying process operating conditions are as follows: drying temperature 80℃-120℃, drying time 12h-24h.

[0032] A second aspect of this invention provides a modified molecular sieve obtained by the above-described preparation method. The modified molecular sieve has a silica-to-alumina ratio of 5-150 and a specific surface area of ​​350 m². 2 / g-850m 2 / g, pore volume 0.16cm 3 / g-0.40cm 3 / g, the relative crystallinity of the modified molecular sieve is 90%-110%, and the residual fluorine content in the modified molecular sieve is less than 0.1%.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention utilizes the adsorption effect of modified activated carbon materials on fluorides to achieve efficient removal of fluorides during the process of modifying molecular sieves with ammonium fluorosilicate, thereby effectively improving the yield of modified molecular sieve products.

[0035] This invention modifies the surface of activated carbon with fluorocarbon surfactants to improve the affinity and binding force between the activated carbon material and fluorides in the reaction system, thereby enhancing the adsorption effect of the activated carbon material on fluorides.

[0036] In the method of this invention, the activated carbon material can be reused after regeneration treatment, saving costs and reducing pollution. Implementation

[0037] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0039] In this invention, the elemental composition of the molecular sieve was determined by XRF characterization; the crystal structure and relative crystallinity of the molecular sieve were determined by XRD characterization, and the standard sample was a molecular sieve that had not been modified with ammonium fluorosilicate; the average particle size of the molecular sieve was determined by laser particle size analyzer; and the pore structure information of the activated carbon material was determined by N2 adsorption-desorption characterization.

[0040] In this invention, the yield of modified molecular sieve solids is calculated as follows:

[0041]

[0042] Example 1

[0043] (1) Lithium 3-[2-(perfluoroalkyl)ethylthio]propionate was added to water to prepare a solution with a mass fraction of 0.05%, and then activated carbon (specific surface area 1577 m²) was added. 2 / g, pore volume 1.03cm 3 The activated carbon (with a mesoporous pore volume of 64% and an average pore size of 11.9 nm) was added to the above solution at a solid-liquid ratio of 1:50 g / mL with a fluorocarbon surfactant solution. The solution was stirred at 40°C for 2 h, filtered, and dried at 100°C for 24 h to obtain the modified activated carbon.

[0044] (2) Y molecular sieve (particle size 1.5 μm, silica-alumina ratio 5.1, specific surface area 875 m²) 2 / g, pore volume 0.36cm 3(g) was mixed with a 0.05 mol / L ammonium fluorosilicate solution at a solid-liquid ratio of 1:40 g / mL. Then, modified activated carbon was added to the mixture at a mass ratio of 1:20 to the molecular sieve. The mixture was treated at 90℃ for 4 hours. After the reaction was complete, the reaction products were separated to obtain waste activated carbon and modified molecular sieve precursors. The separation equipment included a 200-mesh stainless steel screen and slow-speed filter paper with a pore size of 1μm-3μm arranged in an overlapping manner. Both the waste activated carbon and the modified molecular sieve precursors were washed with water until neutral and then dried at 100℃ for 24 hours. The dried modified molecular sieve precursors were calcined in air at 550℃ for 2 hours to obtain modified Y molecular sieves. The obtained modified Y molecular sieves had a silicon-to-aluminum ratio of 8.9, a residual fluorine content of 0 wt%, and a specific surface area of ​​845 m². 2 / g, pore volume 0.38cm 3 / g, the solid yield of modified Y molecular sieve is 95%, and the relative crystallinity of modified Y molecular sieve is 103%.

[0045] (3) The waste activated carbon obtained in step (2) is added to a sulfuric acid solution with a concentration of 80% by mass at a solid-liquid ratio of 1:10 g / mL. The mixture is stirred at 10°C for 1 hour. The gas generated during the reaction is washed with sodium hydroxide solution with a concentration of 1 mol / L. After filtration and separation, the mixture is washed with water until neutral and dried at 100°C for 24 hours to obtain regenerated activated carbon.

[0046] Example 2

[0047] (1) Lithium 3-[2-(perfluoroalkyl)ethylthio]propionate was added to water to prepare a 0.08% mass fraction solution, and then activated carbon (specific surface area 1577 m²) was added. 2 / g, pore volume 1.03cm 3 The activated carbon (with a mesoporous pore volume of 64% and an average pore size of 11.9 nm) was added to the fluorocarbon surfactant solution at a solid-liquid ratio of 1:30 g / mL. The mixture was stirred at 30°C for 1 h, filtered, and dried at 100°C for 24 h to obtain the modified activated carbon.

[0048] (2) Y molecular sieve (particle size 1.5 μm, silica-alumina ratio 5.1, specific surface area 875 m²) 2 / g, pore volume 0.36cm 3A mixture of activated carbon (g) and a 0.1 mol / L ammonium fluorosilicate solution was prepared at a solid-liquid ratio of 1:30 g / mL. Modified activated carbon was then added to the mixture at a mass ratio of 1:20 to the molecular sieve. The mixture was treated at 80°C for 3 hours. After the reaction was complete, the reaction products were separated to obtain spent activated carbon and modified molecular sieve precursors. The separation equipment included a 200-mesh stainless steel screen and slow-speed filter paper with a pore size of 1 μm-3 μm arranged in an overlapping manner. Both the spent activated carbon and the modified molecular sieve precursors were washed with water until neutral and then dried at 100°C for 24 hours. The dried modified molecular sieve precursors were calcined in air at 500°C for 4 hours to obtain modified Y molecular sieve. The obtained modified Y molecular sieve had a silicon-to-aluminum ratio of 11.9, a residual fluorine content of 0 wt%, and a specific surface area of ​​832 m². 2 / g, pore volume 0.38cm 3 / g, the solid yield of modified Y molecular sieve is 92%, and the relative crystallinity of modified Y molecular sieve is 98%.

[0049] (3) The waste activated carbon recovered in step (2) is added to a sulfuric acid solution with a concentration of 70% by mass at a solid-liquid ratio of 1:15 g / mL. The mixture is stirred at 5°C for 1 h. The gas generated during the reaction is washed with sodium hydroxide alkaline solution with a concentration of 1 mol / L. The activated carbon is separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated activated carbon.

[0050] Example 3

[0051] (1) Lithium 3-[2-(perfluoroalkyl)ethylthio]propionate was added to water to prepare a 0.02% mass fraction solution, and then activated carbon (specific surface area 1577 m²) was added. 2 / g, pore volume 1.03cm 3 The activated carbon (with a mesoporous pore volume of 64% and an average pore size of 14.9 nm) was added to the fluorocarbon surfactant solution at a solid-liquid ratio of 1:80 g / mL. The mixture was stirred at 50°C for 3 hours, filtered, and dried at 100°C for 24 hours to obtain the modified activated carbon.

[0052] (2) Y molecular sieve (particle size 1.5 μm, silica-alumina ratio 5.1, specific surface area 875 m²) 2 / g, pore volume 0.36cm 3A mixture of activated carbon (g) and a 0.15 mol / L ammonium fluorosilicate solution was prepared at a solid-liquid ratio of 1:50 g / ml. Modified activated carbon was then added to the mixture at a mass ratio of 1:10 to the molecular sieve. The mixture was treated at 95°C for 5 hours. After the reaction was complete, the reaction products were separated to obtain spent activated carbon and modified molecular sieve precursors. The separation equipment included a 200-mesh stainless steel screen and slow-speed filter paper with a pore size of 1μm-3μm arranged in an overlapping manner. Both the spent activated carbon and the modified molecular sieve precursors were washed with water until neutral and then dried at 100°C for 24 hours. The dried modified molecular sieve precursors were calcined in air at 600°C for 2 hours to obtain modified Y molecular sieves. The obtained modified Y molecular sieves had a silicon-to-aluminum ratio of 16.8, a residual fluorine content of 0.06 wt%, and a specific surface area of ​​825 m². 2 / g, pore volume 0.39cm 3 / g, the solid yield of modified Y molecular sieve is 88%, and the relative crystallinity of modified Y molecular sieve is 94%.

[0053] (3) The waste activated carbon recovered in step (2) is added to a 60% mass fraction sulfuric acid solution at a solid-liquid ratio of 1:15 g / mL. The mixture is stirred at 20°C for 30 min. The gas generated during the reaction is washed with a 1 mol / L sodium hydroxide alkaline solution. The activated carbon is separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated activated carbon.

[0054] Example 4

[0055] The molecular sieve modification steps are the same as in Example 1, except that in step (1), sodium perfluorononenoxybenzenesulfonate is selected as the fluorocarbon surfactant. The resulting modified Y molecular sieve has a silica-to-alumina ratio of 8.5, a residual fluorine content of 0.02 wt%, and a specific surface area of ​​840 m². 2 / g, pore volume 0.38cm 3 / g, the solid yield of modified Y molecular sieve is 93%, and the relative crystallinity of modified Y molecular sieve is 101%.

[0056] Example 5

[0057] (1) Dissolve perfluorobutyl sulfonyl fluoride in water to prepare a 0.05% mass fraction solution, and then add activated carbon (specific surface area 695m²) 2 / g, pore volume 0.61cm 3 The activated carbon (with a mesoporous pore volume of 56% and an average pore size of 8.4 nm) was added to the fluorocarbon surfactant solution at a solid-liquid ratio of 1:50 g / mL. The mixture was stirred at 40°C for 2 hours, filtered, and dried at 100°C for 24 hours to obtain the modified activated carbon.

[0058] (2) ZSM-5 molecular sieve (particle size 2.3 μm, silica-alumina ratio 26.2, specific surface area 435 m²) 2 / g, pore volume 0.17cm 3 (g) was mixed with a 0.02 mol / L ammonium fluorosilicate solution at a solid-liquid ratio of 1:30 g / ml. Then, modified activated carbon was added to the mixture at a mass ratio of 1:50 (modified activated carbon to molecular sieve). The mixture was treated at 90℃ for 4 hours. After the reaction was complete, the reaction products were separated to obtain waste activated carbon and modified molecular sieve precursors. The separation equipment included a 200-mesh stainless steel screen and slow-speed filter paper with a pore size of 1μm-3μm arranged in an overlapping manner. Both the waste activated carbon and the modified molecular sieve precursors were washed with water until neutral and then dried at 100℃ for 24 hours. The dried modified molecular sieve precursors were calcined in air at 550℃ for 3 hours to obtain modified ZSM-5 molecular sieve. The obtained modified ZSM-5 molecular sieve had a silicon-to-aluminum ratio of 38.4, a residual fluorine content of 0 wt%, and a specific surface area of ​​405 m². 2 / g, pore volume 0.18cm 3 / g, the solid yield of modified ZSM-5 molecular sieve is 97%, and the relative crystallinity of modified ZSM-5 molecular sieve is 107%.

[0059] (3) The waste activated carbon recovered in step (2) is added to a 70% mass fraction sulfuric acid solution at a solid-liquid ratio of 1:10 g / ml. The mixture is stirred at 10°C for 1 hour. The gas generated during the reaction is washed with a 1 mol / L sodium hydroxide alkaline solution. The activated carbon is separated by filtration, washed with water until neutral, and dried at 100°C for 24 hours to obtain regenerated activated carbon.

[0060] Example 6

[0061] (1) Add lithium 3-[2-(perfluoroalkyl)ethylthio]propionate to water to prepare a 0.05% mass fraction solution, and then add activated carbon (specific surface area 1220 m²) 2 / g, pore volume 0.89cm 3 The activated carbon (with a mesoporous pore volume of 59% and an average pore size of 9.6 nm) was added to the fluorocarbon surfactant solution at a solid-liquid ratio of 1:50 g / mL. The mixture was stirred at 40°C for 2 hours, filtered, and dried at 100°C for 24 hours to obtain the modified activated carbon.

[0062] (2) Beta molecular sieve (particle size 1.0 μm, silica-alumina ratio 30.5, specific surface area 581 m²) 2 / g, pore volume 0.31cm 3(g) was mixed with a 0.03 mol / L ammonium fluorosilicate solution at a solid-liquid ratio of 1:50 g / mL. Then, modified activated carbon was added to the mixture at a mass ratio of 1:40 (modified activated carbon to molecular sieve). The mixture was treated at 90℃ for 4 hours. After the reaction was complete, the reaction products were separated to obtain waste activated carbon and modified molecular sieve precursors. The separation equipment included a 200-mesh stainless steel screen and slow-speed filter paper with a pore size of 1μm-3μm arranged in an overlapping manner. Both the waste activated carbon and the modified molecular sieve precursors were washed with water until neutral and then dried at 100℃ for 24 hours. The dried modified molecular sieve precursors were calcined in air at 550℃ for 3 hours to obtain modified beta molecular sieves. The obtained modified beta molecular sieves had a silicon-to-aluminum ratio of 74.1, a residual fluorine content of 0 wt%, and a specific surface area of ​​565 m². 2 / g, pore volume 0.33cm 3 / g, the solid yield of modified beta molecular sieve is 93%, and the relative crystallinity of modified beta molecular sieve is 99%.

[0063] (3) The waste activated carbon recovered in step (2) is added to an 80% mass fraction sulfuric acid solution at a solid-liquid ratio of 1:15 g / mL. The mixture is stirred at 30°C for 1 h. The gas generated during the reaction is washed with a 1 mol / L sodium hydroxide alkaline solution. The activated carbon is separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated activated carbon.

[0064] Example 7

[0065] The modification process of the molecular sieve ammonium fluorosilicate is the same as in Example 1, except that the activated carbon in step (1) is the regenerated activated carbon obtained in Example 1. The resulting modified Y molecular sieve has a silicon-to-aluminum ratio of 8.8, a residual fluorine content of 0 wt%, and a specific surface area of ​​830 m². 2 / g, pore volume 0.38cm 3 / g, the solid yield of modified Y molecular sieve is 96%, and the relative crystallinity of modified Y molecular sieve is 101%.

[0066] Comparative Example 1

[0067] The modification process of the molecular sieve with ammonium fluorosilicate is the same as in Example 1, except that no activated carbon is added during the modification process. After modification, the fluoride is removed from the reaction system through three washing-natural sedimentation processes. The modified molecular sieve is then obtained through filtration, washing, drying, and calcination. The resulting modified Y molecular sieve has a silica-to-alumina ratio of 9.0, a residual fluorine content of 0 wt%, and a specific surface area of ​​827 m². 2 / g, pore volume 0.38cm 3 / g, the solid yield of modified Y molecular sieve was 73%, and the relative crystallinity of modified Y molecular sieve was 100%. The results show that although the traditional natural sedimentation method can effectively remove fluorides from the molecular sieve modification system, the solid yield of the modified molecular sieve product is low.

[0068] Comparative Example 2

[0069] The modification process of the molecular sieve with ammonium fluorosilicate is the same as in Example 1, except that activated carbon is added during the molecular sieve modification process, but the activated carbon does not undergo the fluorine modification process in step (1). The resulting modified Y molecular sieve has a silicon-to-aluminum ratio of 8.4, a residual fluorine content of 1.1 wt%, and a specific surface area of ​​850 m². 2 / g, pore volume 0.38cm 3 / g, the solid yield of modified Y molecular sieve was 96%, and the relative crystallinity of modified Y molecular sieve was 98%. The results show that when activated carbon is not modified with fluorine, the affinity and binding force of activated carbon material to fluorides in the molecular sieve modification reaction system are weak, resulting in a certain amount of fluorine residue in the modified molecular sieve product.

[0070] By comparing the experimental results in the examples and comparative examples, it can be found that adding a certain amount of fluorine-modified activated carbon to the ammonium fluorosilicate modified molecular sieve system can effectively solve the problem of fluorine residue in the modified molecular sieve product by utilizing the adsorption and enrichment effect of activated carbon. While ensuring the modification effect of molecular sieve, the yield of modified molecular sieve product is greatly improved. At the same time, the activated carbon material can be reused after further treatment.

Claims

1. A method for preparing ammonium fluorosilicate modified molecular sieves, characterized in that: The method includes the following: (1) Modified activated carbon is obtained by contacting it with an aqueous solution of fluorocarbon surfactant. (2) The modified activated carbon and molecular sieve obtained in step (1) are mixed with ammonium fluorosilicate solution and reacted. The reaction products are separated to obtain waste activated carbon and modified molecular sieve precursors. (3) The modified molecular sieve precursor obtained in step (2) is washed, dried and calcined to obtain the modified molecular sieve; The fluorocarbon surfactant mentioned in step (1) is one or more of lithium 3-[2-(perfluoroalkyl)ethylthio]propionate, perfluorobutylsulfonyl fluoride, and sodium perfluorononenoxybenzenesulfonate; The modification process in step (1) is as follows: the activated carbon is reacted with an aqueous solution of fluorocarbon surfactant at 30-60℃ for 1-3 hours, and then filtered and dried to obtain modified activated carbon.

2. The method according to claim 1, characterized in that: The activated carbon in step (1) has a particle size of 10-50 mesh and a specific surface area of ​​500 m². 2 / g-1800m 2 / g; pore volume is 0.5cm 3 / g-1.5cm 3 / g, of which mesoporous pore volume accounts for 40%-80% of the total pore volume; the average pore size is 5nm-25nm.

3. The method according to claim 2, characterized in that: The activated carbon in step (1) has a particle size of 20-30 mesh and a specific surface area of ​​800 m². 2 / g-1500m 2 / g; pore volume is 0.8cm 3 / g-1.0cm 3 / g, of which mesoporous pore volume accounts for 50%-70% of the total pore volume; the average pore size is 10nm-15nm.

4. The method according to claim 1, characterized in that: The fluorocarbon surfactant mentioned in step (1) is lithium 3-[2-(perfluoroalkyl)ethylthio]propionate.

5. The method according to claim 1, characterized in that: The concentration of the aqueous solution of the fluorocarbon surfactant in step (1) is 0.01 wt.%-0.10 wt.%.

6. The method according to claim 5, characterized in that: The concentration of the fluorocarbon surfactant aqueous solution in step (1) is 0.03wt%-0.05wt%.

7. The method according to claim 1, characterized in that: In step (1), the ratio of activated carbon to the aqueous solution of fluorocarbon surfactant is 1:(20-100) in g / mL.

8. The method according to claim 7, characterized in that: In step (1), the ratio of activated carbon to the aqueous solution of fluorocarbon surfactant is 1:(40-60), expressed in g / mL.

9. The method according to claim 1, characterized in that: The molecular sieve mentioned in step (2) is a microporous molecular sieve, including any one of Y molecular sieve, ZSM-5 molecular sieve and Beta molecular sieve.

10. The method according to claim 1, characterized in that: The molecular sieve has a particle size of 0.5 μm-10 μm; the silicon-aluminum (SiO2 / Al2O3) molar ratio of the molecular sieve is 3-80; and the specific surface area is 380 m². 2 / g-900m 2 / g, pore volume 0.15cm 3 / g-0.38cm 3 / g.

11. The method according to claim 10, characterized in that: The molecular sieve has a particle size of 1μm-2μm and a silicon-aluminum (SiO2 / Al2O3) molar ratio of 5-30.

12. The method according to claim 1, characterized in that: The concentration of the ammonium fluorosilicate solution in step (2) is 0.02 mol / L-0.15 mol / L.

13. The method according to claim 12, characterized in that: The concentration of the ammonium fluorosilicate solution in step (2) is 0.05 mol / L-0.1 mol / L.

14. The method according to claim 1, characterized in that: In step (2), the ratio of the molecular sieve to the ammonium fluorosilicate solution is 1:(20-50), expressed in g / mL.

15. The method according to claim 1, characterized in that: The mass ratio of the modified activated carbon to the molecular sieve in step (2) is 1:(10-50).

16. The method according to claim 15, characterized in that: The mass ratio of the modified activated carbon to the molecular sieve in step (2) is 1:(10-30).

17. The method according to claim 1, characterized in that: The reaction conditions in step (2) are as follows: the reaction temperature is 60-100℃; the reaction time is 3h-6h.

18. The method according to claim 17, characterized in that: The reaction conditions in step (2) are as follows: the reaction temperature is 80℃-90℃; the reaction time is 4h-5h.

19. The method according to claim 1, characterized in that: The separation equipment used in step (2) includes two layers of filter media, which are arranged in the order of contact with the material flow, including a first filter media and a second filter media; the size of the first filter media is 80-300 mesh; and the size of the second filter media is 100nm-5μm.

20. The method according to claim 19, characterized in that: In step (2), the first filter medium and the second filter medium are arranged in an overlapping manner; the size of the first filter medium is 100-200 mesh; the size of the second filter medium is 500nm-3μm.

21. The method according to claim 19, characterized in that: The separation process in step (2) is as follows: the reaction product enters the separation equipment and is separated by the first filter medium to obtain waste activated carbon and filtered material; the filtered material is separated by the second filter medium to obtain modified molecular sieve precursor.

22. The method according to claim 21, characterized in that: In step (2), the waste activated carbon is regenerated. The specific operation process is as follows: the waste activated carbon is mixed with an acidic solution and reacted. After filtration, washing and drying, regenerated activated carbon is obtained. The acidic solution is sulfuric acid, and the concentration of the sulfuric acid is 60wt.%-80wt.%.

23. The method according to claim 22, characterized in that: The process of regenerating activated carbon in step (2) is the same as that in step (1).

24. The method according to claim 22, characterized in that: In the above method for preparing ammonium fluorosilicate modified molecular sieve, in step (2), the solid-liquid ratio of waste activated carbon to acidic solution is 1:(6-15) in g / mL.

25. The method according to claim 24, characterized in that: In step (2), the solid-liquid ratio of waste activated carbon to acidic solution is 1:(8-10), expressed in g / mL.

26. The method according to claim 22, characterized in that: In step (2), the operating conditions for the reaction of waste activated carbon with acidic solution are: reaction temperature 5℃-30℃, reaction time 30min-60min.

27. The method according to claim 26, characterized in that: In step (2), the reaction conditions for mixing waste activated carbon with acidic solution are: reaction temperature 10℃-20℃.

28. The method according to claim 1, characterized in that: In step (3), the modified molecular sieve precursor is calcined in an air atmosphere at a temperature of 500℃-600℃ for 2h-5h.

29. The method according to claim 1, characterized in that: The solid yield of the modified molecular sieve in step (3) is 85%-95%.

30. The method according to claim 1, characterized in that: The washing process involves washing with water until neutral; the drying process is operated under the following conditions: drying temperature 80℃-120℃, drying time 12h-24h.