Preparation method of ammonium fluosilicate modified molecular sieve

Abstract

The invention discloses an ammonium fluosilicate modified molecular sieve preparation method, which comprises: (1) contacting active carbon with a fluorocarbon surfactant aqueous solution to carry out modification treatment so as to obtain modified active carbon; (2) mixing the modified activated carbon obtained in the step (1), a molecular sieve and an ammonium fluosilicate solution for reaction, and separating a reaction product to obtain waste activated carbon and a modified molecular sieve precursor; and (3) washing, drying and roasting the modified molecular sieve precursor obtained in the step (2) to obtain the modified molecular sieve. The method has the advantages of simplicity and convenience in operation, low cost, high fluoride removal efficiency, high modified molecular sieve product yield and the like.

Description

Technical Field

[0001] The invention relates to the technical field of petrochemical industry, and in particular to a method for preparing an ammonium fluorosilicate modified molecular sieve. Background Art

[0002] Molecular sieves are widely used in important fields such as petrochemicals and fine chemicals due to their strong acidity and unique three-dimensional pore structure. For example, they can be used as catalysts, catalyst carriers, ion exchangers and adsorbents. When used in catalytic and adsorption separation processes, most molecular sieves need to be modified to adjust the properties of the molecular sieves. For example, in the multiphase catalytic process, it is necessary to improve the catalytic activity of the molecular sieve by adjusting the distribution of active sites and the accessibility of active sites. Currently, the commonly used molecular sieve modification methods include ion exchange, chemical treatment, steam treatment and heteroatom isomorphous replacement. Among them, ammonium fluorosilicate isomorphous replacement modified molecular sieves have the characteristics of relatively mild reaction conditions, low non-framework aluminum content in the modified molecular sieves, and few crystal structure defects. Especially when the degree of dealumination of the molecular sieve is high, this method has certain advantages in maintaining the high crystallinity of the molecular sieve.

[0003] Patent CN111686787A discloses a hydrocracking catalyst carrier and its preparation method and application. The hydrocracking catalyst carrier is made of a Y-type zeolite / alumina composite material modified by ammonium fluorosilicate, and the Y-type zeolite / alumina composite material modified by ammonium fluorosilicate is prepared by mixing, hydrothermal crystallization and ammonium fluorosilicate modification of activated alumina, a directing agent, a silicon source and water. The composite material has the heat stability, pore characteristics and surface properties of activated alumina, and has the characteristics of improved acidity, open pore structure, high mesopore content and more acid center exposure of Y molecular sieve. When it is used as a carrier of a hydrocracking catalyst, it shows more superior properties in improving the conversion rate of macromolecules when processing heavy oil raw materials.

[0004] Patent CN110372004A discloses a method for regulating the microscopic aluminum distribution of a ZSM-5 molecular sieve and its application. The method comprises: using an ion exchange method to load cobalt ions onto the Na-type ZSM-5 molecular sieve 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 a product B; washing, drying and calcining the product B to obtain a ZSM-5 molecular sieve after microscopic aluminum distribution regulation. The prepared molecular sieve is suitable for catalytic cracking reactions of C4 hydrocarbons.

[0005] Patent CN112237947A discloses a method for preparing a dewaxing catalyst carrier, which specifically comprises: (A) contacting a slurry containing HZSM-5 molecular sieve with ammonium fluorosilicate to carry out dealumination and siliconization reaction to obtain a modified molecular sieve; wherein the Si / Al2 of the HZSM-5 molecular sieve is greater than 120, and the average grain size is 5-50 μm; (B) mixing the modified molecular sieve with a binder, and then mixing with an acid solution for peptization, and sequentially molding and calcining the peptized mixture to obtain a carrier; the catalyst prepared with the carrier is subjected to a dewaxing reaction on waxy crude oil, and the obtained lubricating base oil has not only a low pour point but also a high viscosity index, and can also improve the liquid yield of the lubricating base oil. Summary of the invention

[0006] The inventors have found through research that there is a problem of "fluoride residue" in the process of ammonium fluorosilicate modified molecular sieves in the prior art, and the residual fluoride will destroy the crystal structure of the molecular sieve under high temperature conditions. However, none of the prior art mentions the problem of "fluoride residue". Further, the inventors have found through research that there is only one method in the prior art that can solve the problem of "fluoride residue", namely the washing precipitation method. This method is to wash with a large amount of water, and then use the density difference between fluoride and molecular sieve material to remove fluoride in the system, and repeat the above process many times until the fluoride content meets the requirements. This method has low removal efficiency, and will inevitably cause the loss of molecular sieve products during the modification process, resulting in a low yield of modified molecular sieve products.

[0007] In view of the shortcomings of the prior art, the present invention provides a method for preparing an ammonium fluorosilicate modified molecular sieve. The method introduces surface-modified activated carbon in the molecular sieve modification process, and utilizes the adsorption and enrichment effect of the modified activated carbon on fluoride to achieve the purpose of efficiently removing fluoride. The method has the advantages of simple operation, low cost, high fluoride removal efficiency, and high yield of modified molecular sieve products.

[0008] The first aspect of the present invention provides a method for preparing an ammonium fluorosilicate modified molecular sieve, the method comprising the following contents: (1) contacting the activated carbon with an aqueous solution of a fluorocarbon surfactant to perform a modification treatment to obtain modified activated carbon; (2) mixing the modified activated carbon and molecular sieve obtained in step (1) with an ammonium fluorosilicate solution to react, and separating the reaction products to obtain waste activated carbon and a modified molecular sieve precursor; (3) The modified molecular sieve precursor obtained in step (2) is washed, dried, and calcined to obtain a modified molecular sieve.

[0009] Furthermore, in the preparation method of the ammonium fluorosilicate modified molecular sieve, the particle size of the activated carbon in step (1) is 10-50 mesh, preferably 20-30 mesh; the specific surface area is 500m 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 mesopore volume accounts for 40%-80% of the total pore volume, preferably 50%-70%; the average pore diameter is 5nm-25nm, preferably 10nm-15nm.

[0010] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, the fluorocarbon surfactant in step (1) is one or more of lithium 3-[2-(perfluoroalkyl)ethylthio]propionate, perfluorobutylsulfonyl fluoride and sodium perfluorononenyloxybenzenesulfonate, preferably lithium 3-[2-(perfluoroalkyl)ethylthio]propionate.

[0011] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieve, the concentration of the fluorocarbon surfactant aqueous solution in step (1) is 0.01wt.%-0.10wt.%, preferably 0.03wt%-0.05wt%.

[0012] Furthermore, in the preparation method of the ammonium fluorosilicate modified molecular sieve, in step (1), the ratio of the activated carbon to the fluorocarbon surfactant aqueous solution is 1:(20-100), preferably 1:(40-60), measured in g / mL.

[0013] Furthermore, in the preparation method of the above-mentioned ammonium fluorosilicate modified molecular sieve, the modification process in step (1) is: reacting the activated carbon with the fluorocarbon surfactant aqueous solution at 30-60° C. for 1-3 hours, and then filtering and drying to obtain the modified activated carbon.

[0014] Furthermore, in the preparation method of the ammonium fluorosilicate modified molecular sieve, 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 0.5 μm-10 μm, preferably 1 μm-2 μm; the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) of the molecular sieve is 3-80, preferably 5-30; the specific surface area is 380 m 2 / g-900m 2 / g, pore volume is 0.15cm 3 / g-0.38cm 3 / g.

[0015] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieve, the concentration of the ammonium fluorosilicate solution in step (2) is 0.02 mol / L-0.15 mol / L, preferably 0.05 mol / L-0.1 mol / L.

[0016] Furthermore, in the preparation method of the ammonium fluorosilicate modified molecular sieve, in step (2), the ratio of the molecular sieve to the ammonium fluorosilicate solution is 1:(20-50) in terms of g / mL.

[0017] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieve, the mass ratio of the modified activated carbon to the molecular sieve in step (2) is 1:(10-50), preferably 1:(10-30).

[0018] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, the reaction conditions in step (2) are as follows: the reaction temperature is 60-100°C, preferably 80-90°C; the reaction time is 3h-6h, preferably 4h-5h.

[0019] Furthermore, in the preparation method of the above-mentioned ammonium fluorosilicate modified molecular sieve, the separation equipment used for separation in step (2) includes two layers of filter media, which include a first filter medium and a second filter medium in the order of contact with the logistics, and preferably the first filter medium and the second filter medium are arranged in an overlapping manner; the first filter medium has a size of 80 mesh-300 mesh, preferably 100 mesh-200 mesh, and specifically in the present invention, the first filter medium adopts a 200 mesh stainless steel screen; the second filter medium has a size of 100nm-5μm, preferably 500nm-3μm, and specifically in the present invention, the second filter medium adopts a slow filter paper with a pore size of 1μm-3μm.

[0020] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, 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 a modified molecular sieve precursor.

[0021] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, the waste activated carbon in step (2) is regenerated, and the specific operation process is as follows: the waste activated carbon is mixed with an acidic solution for reaction, and the regenerated activated carbon is obtained after filtering, washing and drying; the acidic solution is sulfuric acid, and the concentration of the sulfuric acid is 60wt.%-80wt.%.

[0022] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieve, the regenerated activated carbon in step (2) repeats the process of step (1).

[0023] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, in step (2), the solid-liquid ratio of the waste activated carbon to the acidic solution is 1:(6-15), preferably 1:(8-10), measured in g / mL.

[0024] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, the operating conditions for the mixed reaction of the waste activated carbon and the acidic solution in step (2) are: reaction temperature 5°C-30°C, preferably 10°C-20°C, and reaction time 30min-60min.

[0025] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, the acidic gas generated during the mixed reaction of the waste activated carbon and the acidic solution in step (2) is washed with sodium hydroxide alkaline solution.

[0026] Furthermore, in the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, in step (3), the modified molecular sieve precursor is calcined in an air atmosphere, the calcination temperature is 500° C.-600° C., and the calcination time is 2 h-5 h.

[0027] Furthermore, in the above-mentioned method for preparing ammonium fluorosilicate modified molecular sieve, the solid yield of the modified molecular sieve in step (3) is 85%-95%.

[0028] Furthermore, in the preparation method of the above-mentioned ammonium fluorosilicate modified molecular sieve, the washing process is washing with water until neutral; the operating conditions of the drying process are as follows: drying temperature 80°C-120°C, drying time 12h-24h.

[0029] The second aspect of the present invention provides a modified molecular sieve obtained by the above preparation method. The silicon-aluminum ratio of the modified molecular sieve is 5-150, and the specific surface area of ​​the modified molecular sieve is 350m 2 / g-850m 2 / g, pore volume is 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%.

[0030] Compared with the prior art, the present invention has the following beneficial effects: The present invention utilizes the adsorption effect of modified activated carbon materials on fluorides, realizes the efficient removal of fluorides in the process of ammonium fluorosilicate modified molecular sieves, and effectively improves the yield of modified molecular sieve products.

[0031] The present invention uses a fluorocarbon surfactant to perform surface modification treatment on activated carbon, thereby improving the affinity and binding force between the activated carbon material and the fluoride in the reaction system, thereby enhancing the adsorption effect of the activated carbon material on the fluoride.

[0032] The activated carbon material in the method of the present invention can be reused after being regenerated, thereby saving costs and reducing pollution. Implementation

[0033] The present invention is further described in detail below in conjunction with specific examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0034] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, were purchased from conventional biochemical reagent stores.

[0035] In the present invention, the elemental components of the molecular sieve are determined by XRF characterization; the crystal structure and relative crystallinity of the molecular sieve are determined by XRD characterization, and the standard sample is a molecular sieve that has not been modified by ammonium fluorosilicate; the average particle size of the molecular sieve is determined by a laser particle size analyzer; and the pore structure information of the activated carbon material is determined by N2 adsorption-desorption characterization.

[0036] In the present invention, the calculation method of the modified molecular sieve solid yield is as follows:

[0037] Example 1 (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 1577m 2 / g, pore volume 1.03cm 3 / g, mesopore volume accounts for 64%, and the average pore size is 11.9nm) and fluorocarbon surfactant solution at a solid-liquid ratio of 1:50g / mL. Activated carbon is added to the above solution, stirred at 40°C for 2h, separated by filtration and dried at 100°C for 24h to obtain modified activated carbon.

[0038] (2) Y molecular sieve (particle size 1.5 μm, silicon-aluminum ratio 5.1, specific surface area 875 m 2 / g, pore volume 0.36cm 3 / g) is mixed with an ammonium fluorosilicate solution with a concentration of 0.05mol / L at a solid-liquid ratio of 1:40g / mL, and then the modified activated carbon is added to the above mixture at a mass ratio of modified activated carbon to molecular sieve of 1:20, and treated at 90°C for 4h. After the reaction is completed, the reaction product is separated to obtain waste activated carbon and modified molecular sieve precursor; the separation equipment used for separation includes a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1μm-3μm arranged in an overlapping manner. The waste activated carbon and the modified molecular sieve precursor are washed with water to neutrality and dried at 100°C for 24h. The dried modified molecular sieve precursor is calcined at 550°C in an air atmosphere for 2h to obtain a modified Y molecular sieve. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 8.9, the residual fluorine content is 0wt%, and the specific surface area of ​​the modified Y molecular sieve is 845m 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%.

[0039] (3) The waste activated carbon obtained in step (2) was added to a sulfuric acid solution with a concentration of 80% by mass at a solid-liquid ratio of 1:10 g / mL, and stirred at 10°C for 1 h. The gas generated during the reaction was washed with a 1 mol / L sodium hydroxide solution, separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated activated carbon.

[0040] Example 2 (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 1577m 2 / g, pore volume 1.03cm 3 / g, mesopore volume accounts for 64%, and the average pore size is 11.9nm) and the solid-liquid ratio of the fluorocarbon surfactant solution is 1:30g / mL. Activated carbon is added into the above solution, stirred at 30℃ for 1h, separated by filtration and dried at 100℃ for 24h to obtain modified activated carbon.

[0041] (2) Y molecular sieve (particle size 1.5 μm, silicon-aluminum ratio 5.1, specific surface area 875 m 2 / g, pore volume 0.36cm 3 / g) is mixed with a 0.1mol / L ammonium fluorosilicate solution at a solid-liquid ratio of 1:30g / mL, and then the modified activated carbon is added to the above mixture at a mass ratio of modified activated carbon to molecular sieve of 1:20, and treated at 80°C for 3h. After the reaction is completed, the reaction product is separated to obtain waste activated carbon and modified molecular sieve precursor; the separation equipment used for separation includes a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1μm-3μm, which are arranged in an overlapping manner. The waste activated carbon and the modified molecular sieve precursor are washed with water to neutrality and dried at 100°C for 24h. The dried modified molecular sieve precursor is calcined at 500°C in an air atmosphere for 4h to obtain a modified Y molecular sieve. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 11.9, the residual fluorine content is 0wt%, and the specific surface area of ​​the modified Y molecular sieve is 832m 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%.

[0042] (3) The waste activated carbon recovered in step (2) was added to a sulfuric acid solution with a concentration of 70% by mass at a solid-liquid ratio of 1:15 g / mL, and stirred at 5°C for 1 h. The gas generated during the reaction was washed with 1 mol / L sodium hydroxide solution. The activated carbon was separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated activated carbon.

[0043] Example 3 (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 1577m 2 / g, pore volume 1.03cm 3 / g, mesopore volume accounts for 64%, and the average pore size is 14.9nm) and the solid-liquid ratio of the fluorocarbon surfactant solution is 1:80g / mL. Activated carbon is added into the above solution, stirred at 50℃ for 3h, separated by filtration and dried at 100℃ for 24h to obtain modified activated carbon.

[0044] (2) Y molecular sieve (particle size 1.5 μm, silicon-aluminum ratio 5.1, specific surface area 875 m 2 / g, pore volume 0.36cm 3 / g) is mixed with an ammonium fluorosilicate solution with a concentration of 0.15mol / L at a solid-liquid ratio of 1:50g / ml, and then the modified activated carbon is added to the above mixture at a mass ratio of modified activated carbon to molecular sieve of 1:10, and treated at 95°C for 5h. After the reaction is completed, the reaction product is separated to obtain waste activated carbon and modified molecular sieve precursor; the separation equipment used for separation includes a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1μm-3μm, which are arranged in an overlapping manner. The waste activated carbon and the modified molecular sieve precursor are washed with water to neutrality and dried at 100°C for 24h. The dried modified molecular sieve precursor is calcined at 600°C in an air atmosphere for 2h to obtain a modified Y molecular sieve. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 16.8, the residual fluorine content is 0.06wt%, and the specific surface area of ​​the modified Y molecular sieve is 825m 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%.

[0045] (3) The waste activated carbon recovered in step (2) was added to a 60% mass fraction sulfuric acid solution at a solid-liquid ratio of 1:15 g / mL, and stirred at 20°C for 30 min. The gas generated during the reaction was washed with 1 mol / L sodium hydroxide solution. The activated carbon was separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated activated carbon.

[0046] Example 4 The molecular sieve modification steps are the same as those in Example 1, except that the fluorocarbon surfactant in step (1) is sodium perfluorononenyloxybenzenesulfonate. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 8.5, the residual fluorine content is 0.02 wt%, and the specific surface area of ​​the modified Y molecular sieve is 840 m 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%.

[0047] Example 5 (1) Perfluorobutylsulfonyl fluoride was added to water to prepare a 0.05% mass fraction solution, and then activated carbon (specific surface area 695m 2 / g, pore volume 0.61cm 3 / g, mesopore volume accounts for 56%, and the average pore size is 8.4nm) and the solid-liquid ratio of the fluorocarbon surfactant solution is 1:50g / mL. Activated carbon is added into the above solution, stirred at 40℃ for 2h, separated by filtration and dried at 100℃ for 24h to obtain modified activated carbon.

[0048] (2) ZSM-5 molecular sieve (particle size 2.3 μm, silicon-aluminum ratio 26.2, specific surface area 435 m2 / g, pore volume 0.17cm 3 / g) and ammonium fluorosilicate solution with a concentration of 0.02mol / L are mixed at a solid-liquid ratio of 1:30g / ml, and then the modified activated carbon is added to the above mixture at a mass ratio of modified activated carbon to molecular sieve of 1:50, and treated at 90°C for 4h. After the reaction is completed, the reaction product is separated to obtain waste activated carbon and modified molecular sieve precursor; the separation equipment used for separation includes a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1μm-3μm arranged in an overlapping manner. The waste activated carbon and the modified molecular sieve precursor are washed with water to neutrality and dried at 100°C for 24h. The dried modified molecular sieve precursor is calcined at 550°C in an air atmosphere for 3h to obtain a modified ZSM-5 molecular sieve. The silicon-aluminum ratio of the obtained modified ZSM-5 molecular sieve is 38.4, the residual fluorine content is 0wt%, and the specific surface area of ​​the modified ZSM-5 molecular sieve is 405m 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%.

[0049] (3) The waste activated carbon recovered in step (2) was added to a 70% by mass sulfuric acid solution at a solid-liquid ratio of 1:10 g / ml, and stirred at 10°C for 1 h. The gas generated during the reaction was washed with 1 mol / L sodium hydroxide solution. The activated carbon was separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated activated carbon.

[0050] Example 6 (1) Lithium 3-[2-(perfluoroalkyl)ethylthio]propionate was added to water to prepare a 0.05% mass fraction solution, and then activated carbon (specific surface area 1220m 2 / g, pore volume 0.89cm 3 / g, mesopore volume accounts for 59%, and the average pore size is 9.6nm) and the solid-liquid ratio of the fluorocarbon surfactant solution is 1:50g / mL. Activated carbon is added into the above solution, stirred at 40℃ for 2h, separated by filtration and dried at 100℃ for 24h to obtain modified activated carbon.

[0051] (2) Beta molecular sieve (particle size 1.0 μm, silicon-aluminum ratio 30.5, specific surface area 581 m 2 / g, pore volume 0.31cm 3 / g) is mixed with an ammonium fluorosilicate solution with a concentration of 0.03mol / L at a solid-liquid ratio of 1:50g / mL, and then the modified activated carbon is added to the above mixture at a mass ratio of modified activated carbon to molecular sieve of 1:40, and treated at 90°C for 4h. After the reaction is completed, the reaction product is separated to obtain waste activated carbon and modified molecular sieve precursor; the separation equipment used for separation includes a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1μm-3μm arranged in an overlapping manner. The waste activated carbon and the modified molecular sieve precursor are washed with water to neutrality and dried at 100°C for 24h. The dried modified molecular sieve precursor is calcined at 550°C in an air atmosphere for 3h to obtain a modified beta molecular sieve. The silicon-aluminum ratio of the obtained modified beta molecular sieve is 74.1, the residual fluorine content is 0wt%, and the specific surface area of ​​the modified beta molecular sieve is 565m 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%.

[0052] (3) The waste activated carbon recovered in step (2) was added to an 80% by mass sulfuric acid solution at a solid-liquid ratio of 1:15 g / mL, and stirred at 30°C for 1 h. The gas generated during the reaction was washed with 1 mol / L sodium hydroxide solution. The activated carbon was separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated activated carbon.

[0053] Example 7 The modification process of the molecular sieve ammonium fluorosilicate is the same as that in Example 1, except that the activated carbon in step (1) is the regenerated activated carbon obtained in Example 1. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 8.8, the residual fluorine content is 0wt%, and the specific surface area of ​​the modified Y molecular sieve is 830m 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%.

[0054] Comparative Example 1 The modification process of the molecular sieve ammonium fluorosilicate is the same as that of Example 1, except that no activated carbon is added during the modification of the molecular sieve with ammonium fluorosilicate. After the modification is completed, the fluoride is removed from the reaction system by three washing-natural sedimentation methods, and the modified molecular sieve is obtained by filtration, washing, drying and calcination. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 9.0, the residual fluorine content is 0wt%, and the specific surface area of ​​the modified Y molecular sieve is 827m 2 / g, pore volume 0.38cm 3 / g, the solid yield of modified Y molecular sieve is 73%, and the relative crystallinity of modified Y molecular sieve is 100%. The results show that although the traditional natural sedimentation method can also effectively remove fluoride in the molecular sieve modification system, the solid yield of the modified molecular sieve product is low.

[0055] Comparative Example 2 The modification process of the molecular sieve ammonium fluorosilicate is the same as that of Example 1, except that activated carbon is added during the modification process of the molecular sieve, but the activated carbon does not undergo the fluorine modification process in step (1). The silicon-aluminum ratio of the obtained modified Y molecular sieve is 8.4, the residual fluorine content is 1.1 wt%, and the specific surface area of ​​the modified Y molecular sieve is 850 m 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 98%. The results show that when the activated carbon is not fluorine-modified, the affinity and binding force of the activated carbon material for the fluoride in the molecular sieve modification reaction system are weak, resulting in a certain amount of fluorine residue in the modified molecular sieve product.

[0056] By comparing the experimental results in the embodiments and comparative examples, it can be found that by adding a certain amount of fluorine-modified activated carbon to the ammonium fluorosilicate modified molecular sieve system and utilizing the adsorption and enrichment effect of activated carbon, the problem of fluorine residue in the modified molecular sieve product can be effectively solved. While ensuring the molecular sieve modification effect, the yield of the modified molecular sieve product is greatly improved. At the same time, the activated carbon material can be reused after treatment.

Claims

1. A method for preparing an ammonium fluorosilicate modified molecular sieve, characterized in that: The method includes the following contents: (1) contacting the activated carbon with an aqueous solution of a fluorocarbon surfactant to perform a modification treatment to obtain modified activated carbon; (2) mixing the modified activated carbon and molecular sieve obtained in step (1) with an ammonium fluorosilicate solution to react, and separating the reaction products to obtain waste activated carbon and a modified molecular sieve precursor; (3) The modified molecular sieve precursor obtained in step (2) is washed, dried, and calcined to obtain a modified molecular sieve.

2. The method according to claim 1, characterized in that: The particle size of the activated carbon in step (1) is 10-50 mesh, preferably 20-30 mesh; the specific surface area is 500m 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 mesopore volume accounts for 40%-80% of the total pore volume, preferably 50%-70%; the average pore diameter is 5nm-25nm, preferably 10nm-15nm.

3. The method according to claim 1, characterized in that: The fluorocarbon surfactant in step (1) is one or more of lithium 3-[2-(perfluoroalkyl)ethylthio]propionate, perfluorobutylsulfonyl fluoride and sodium perfluorononenyloxybenzenesulfonate, preferably lithium 3-[2-(perfluoroalkyl)ethylthio]propionate.

4. The method according to claim 1, characterized in that: The concentration of the fluorocarbon surfactant aqueous solution in step (1) is 0.01wt.%-0.10wt.%, preferably 0.03wt%-0.05wt%.

5. The method according to claim 1, characterized in that: In step (1), the ratio of the activated carbon to the aqueous solution of the fluorocarbon surfactant is 1:(20-100), preferably 1:(40-60), measured in g / mL.

6. The method according to claim 1, characterized in that: The modification process in step (1) is as follows: reacting the activated carbon with an aqueous solution of a fluorocarbon surfactant at 30-60° C. for 1-3 hours, and then filtering and drying to obtain modified activated carbon.

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

8. The method according to claim 1, characterized in that: The particle size of the molecular sieve is 0.5 μm-10 μm, preferably 1 μm-2 μm; the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) of the molecular sieve is 3-80, preferably 5-30; the specific surface area is 380 m 2 / g-900m 2 / g, pore volume is 0.15cm 3 / g-0.38cm 3 / g.

9. 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, preferably 0.05 mol / L-0.1 mol / L.

10. 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) in terms of g / mL.

11. 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), preferably 1:(10-30).

12. The method according to claim 1, characterized in that: The reaction conditions in step (2) are as follows: the reaction temperature is 60-100°C, preferably 80-90°C; the reaction time is 3h-6h, preferably 4h-5h.

13. The method according to claim 1, characterized in that: The separation device used in step (2) comprises two layers of filter media, which include a first filter medium and a second filter medium in the order of contact with the logistics. Preferably, the first filter medium and the second filter medium are arranged in an overlapping manner; the size of the first filter medium is 80 mesh-300 mesh, preferably 100 mesh-200 mesh; the size of the second filter medium is 100nm-5μm, preferably 500nm-3μm.

14. The method according to claim 13, characterized in that: The separation process in step (2) is as follows: the reaction product enters the separation device, and is separated by a first filter medium to obtain waste activated carbon and filtered material; the filtered material is separated by a second filter medium to obtain a modified molecular sieve precursor.

15. The method according to claim 14, characterized in that: In step (2), the waste activated carbon is regenerated, and the specific operation process is as follows: the waste activated carbon is mixed with an acidic solution for reaction, and the regenerated activated carbon is obtained after filtering, washing and drying; the acidic solution is sulfuric acid, and the concentration of the sulfuric acid is 60wt.%-80wt.%.

16. The method according to claim 15, characterized in that: The regenerated activated carbon in step (2) repeats the process of step (1).

17. The method according to claim 15, characterized in that: In the above-mentioned preparation method of ammonium fluorosilicate modified molecular sieve, in step (2), the solid-liquid ratio of the waste activated carbon to the acidic solution is 1:(6-15), preferably 1:(8-10), measured in g / mL.

18. The method according to claim 15, characterized in that: The operating conditions for the mixed reaction of the waste activated carbon and the acidic solution in step (2) are: reaction temperature 5°C-30°C, preferably 10°C-20°C, and reaction time 30min-60min.

19. 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 calcination temperature of 500° C. to 600° C. for a calcination time of 2 h to 5 h.

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

21. The method according to claim 1, characterized in that: The washing process is to wash with water until neutral; the operating conditions of the drying process are as follows: drying temperature 80°C-120°C, drying time 12h-24h.

22. A modified molecular sieve obtained by the method of any one of claims 1 to 21.

23. The modified molecular sieve according to claim 22, characterized in that: The relative crystallinity of the modified molecular sieve is 90%-110%, the residual fluorine content in the modified molecular sieve is less than 0.1%, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) of the modified molecular sieve is 5-150, and the specific surface area of ​​the modified molecular sieve is 350m 2 / g-850m 2 / g, pore volume is 0.16cm 3 / g-0.40cm 3 / g.

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