A method for modifying a molecular sieve

Abstract

The application discloses a molecular sieve modification method, which comprises the following steps: (1) preparing silica microspheres loaded with sodium fluoroaluminate seeds: mixing silica microspheres with a modifier solution to perform a reaction, and then performing filtration, washing and drying treatment on a reaction product to obtain the silica microspheres loaded with the sodium fluoroaluminate seeds; and (2) preparing ammonium fluosilicate modified molecular sieves: mixing the silica microspheres loaded with the sodium fluoroaluminate seeds obtained in the step (1), molecular sieves and an ammonium fluosilicate solution to perform a reaction, and then performing separation, washing, drying and calcination on a reaction product to obtain the ammonium fluosilicate modified molecular sieves. The method can simultaneously achieve the purposes of efficiently removing fluorides and improving the yield of molecular sieve products.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of molecular sieves, and relates to a molecular sieve modification method, in particular to an ammonium fluosilicate modification method of a molecular sieve. BACKGROUND

[0002] Molecular sieves are widely used in important fields such as petroleum and chemical industry, fine chemical industry and the like due to their strong acidity and unique three-dimensional pore structure, and 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 a heterogeneous catalytic process, the catalytic activity of the molecular sieve needs to be improved by adjusting the distribution of active sites and the accessibility of the active sites. The commonly used molecular sieve modification methods include ion exchange method, chemical treatment, steam treatment and heteroatom isomorphous substitution method. The ammonium fluosilicate isomorphous substitution modification of the molecular sieve has the characteristics of relatively mild reaction conditions, low non-framework aluminum content in the modified molecular sieve and few crystal structure defects, and has certain advantages in maintaining the high crystallinity of the molecular sieve, especially when the molecular sieve has a high degree of dealumination.

[0003] Patent CN113950460A discloses a method for improving the Si / Al of a molecular sieve, which comprises: ion exchanging a molecular sieve synthesized without using an organic structure directing agent to obtain a sodium type, a proton type or an ammonium type, and then contacting the ion-exchanged zeolite with an ammonium fluosilicate solution to perform dealumination. When Beta or mordenite is treated by using this method, the Si / Al of the molecular sieve can be effectively improved while the high crystallinity of the molecular sieve is maintained.

[0004] Patent CN114477217A discloses an ultrastable Y-type molecular sieve and a preparation method thereof, which specifically comprises: (1) adding a fluorine-containing aqueous solution into an ammonium fluosilicate solution, and then mixing the solution with Y-type molecular sieve raw powder, to obtain pretreated Y-type molecular sieve after washing and drying; (2) mixing the pretreated Y-type molecular sieve, an ammonium salt and water, and then adding an acid solution, to obtain a sample after stirring, washing and drying; and (3) performing hydrothermal ultrastabilization treatment on the sample obtained in step (2), and drying to obtain the ultrastable Y-type molecular sieve. After the Y-type molecular sieve is pretreated by using the ammonium fluosilicate, the framework collapse of the molecular sieve is small during the subsequent hydrothermal coupling acid treatment process, and the crystal structure of the molecular sieve is complete.

[0005] Although the ammonium fluosilicate modification of the molecular sieve is widely used due to its unique advantages, there is a problem of fluoride residue in the process of modifying the molecular sieve by using the ammonium fluosilicate, which further damages the crystal structure of the molecular sieve. However, the above problem is not mentioned in the disclosed patents. SUMMARY

[0006] The inventors found through investigation that there is only one method in the prior art that can solve the problem of fluoride residue, i.e. the washing precipitation method. The method is to remove fluoride in the system by washing with a large amount of water and taking advantage of the density difference between fluoride and molecular sieve materials, and the above process is repeated multiple times until the fluoride content meets the requirements. However, the removal efficiency of the method is low, and the molecular sieve product will inevitably be lost during the modification process. Therefore, it is urgent to develop a new ammonium fluosilicate modification method that can efficiently remove fluoride in advance while improving the yield of molecular sieve products.

[0007] In view of the deficiencies of the prior art, the present application provides a molecular sieve modification method. In the process of modifying the ammonium fluosilicate molecular sieve, porous silica microspheres loaded with sodium fluoroaluminate seeds are added to the reaction system to achieve efficient removal of fluoride in the reaction system by using the seed epitaxial growth method. The method can simultaneously achieve the purposes of efficient removal of fluoride and improvement of the yield of molecular sieve products.

[0008] The first aspect of the present application provides a molecular sieve modification method, which comprises the following contents:

[0009] (1) Preparation of silica microspheres loaded with sodium fluoroaluminate seeds: mixing silica microspheres with a modifier solution for reaction, and then obtaining silica microspheres loaded with sodium fluoroaluminate seeds after filtering, washing and drying the reaction product;

[0010] (2) Preparation of ammonium fluosilicate modified molecular sieve: mixing the silica microspheres loaded with sodium fluoroaluminate seeds obtained in step (1), molecular sieve and ammonium fluosilicate solution for reaction, and then obtaining ammonium fluosilicate modified molecular sieve after separating, washing, drying and calcining the reaction product.

[0011] In the above modification method, the particle size of the silica microspheres in step (1) is 200 μm-2 mm, preferably 300 μm-1 mm; the specific surface area is 200 m 2 / g-600 m 2 / g, preferably 300 m 2 / g-500 m 2 / g; the pore volume is 0.5 cm 3 / g-1.2 cm 3 / g, preferably 0.6 cm 3 / g-1 cm 3 / g, wherein the proportion of mesopore and macropore pore volume to total pore volume is greater than 90%; the average pore size is 5 nm-15 nm, preferably 7 nm-10 nm.

[0012] In the modification method, the modifier solution in step (1) comprises a modifier and a solvent; the modifier comprises sodium aluminate and ammonium fluoride, the molar ratio of sodium aluminate to ammonium fluoride is 1:6; the solvent is deionized water; the ratio of ammonium fluoride to solvent is 0.01-0.10 mol / L, preferably 0.03-0.06 mol / L.

[0013] In the modification method, the mixing sequence of sodium aluminate and ammonium fluoride with the solvent in step (1) is not required, for example, sodium aluminate is first mixed with the solvent, then ammonium fluoride is added for mixing, or ammonium fluoride is first mixed with the solvent, then sodium aluminate is added for mixing, or sodium aluminate and ammonium fluoride are mixed with the solvent respectively, then the two are mixed, preferably, sodium aluminate and ammonium fluoride are mixed with the solvent respectively, then the two are mixed.

[0014] In the modification method, the solid-liquid ratio of the silica microspheres to the modifier solution in step (1) is 1: (20-30) g / mL.

[0015] In the modification method, the reaction conditions for mixing the silica microspheres with the modifier solution in step (1) are as follows: the reaction temperature is 0℃-20℃, preferably 2℃-10℃; the reaction time is 1h-3h.

[0016] In the modification method, the specific operation steps of the filtering, washing and drying treatment in step (1) are as follows: the reaction product is filtered to obtain a solid phase material; the solid phase material is washed with water until it is neutral, and then dried at a temperature of 80℃-120℃ for 12h-24h.

[0017] In the modification method, the content of sodium fluoroaluminate crystal seeds in the silica microspheres loaded with sodium fluoroaluminate crystal seeds obtained in step (1) is 1wt.%-10wt.%.

[0018] In the modification method, the molecular sieve in step (2) is a microporous molecular sieve, which comprises any one of Y molecular sieve, ZSM-5 molecular sieve and Beta molecular sieve; the particle size of the molecular sieve is 500nm-10μm, preferably 1μm-2μm; the silicon-aluminum ratio (molar ratio of SiO2 / Al2O3) of the molecular sieve is 3-80, preferably 5-30; the specific surface area of the molecular sieve is 380m 2 / g-900m 2 / g, the pore volume is 0.15cm 3 / g-0.38cm 3 / g.

[0019] In the modification method, the concentration of the ammonium fluosilicate solution in step (2) is 0.02mol / L-0.15mol / L, preferably 0.05mol / L-0.1mol / L.

[0020] In the modification method, the solid-liquid ratio of the molecular sieve and the ammonium fluosilicate solution in step (2) is 1: (20-50) g / mL.

[0021] In the modification method, the mass ratio of the silica microspheres loaded with sodium fluoroaluminate seed crystals and the molecular sieve in step (2) is 1: (5-15).

[0022] In the modification method, the operation conditions of the reaction in step (2) are as follows: the reaction temperature is 60-100 ℃, preferably 80-90 ℃; and the reaction time is 3-5 h.

[0023] In the modification method, the separation equipment used 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 material flow, and preferably the first filter medium and the second filter medium are arranged in an overlapping manner from top to bottom; the size of the first filter medium is 80-300 mesh, preferably 100-200 mesh, and in the present application, the first filter medium is a 200-mesh stainless steel screen; and the size of the second filter medium is 100 nm-5 μm, preferably 500 nm-3 μm, and in the present application, the second filter medium is a slow filter paper with a pore size of 1-3 μm.

[0024] In the modification method, the separation process in step (2) is as follows: the reaction product enters the separation equipment, and the waste silica microspheres and the filtered material are obtained by separation through the first filter medium; and the filtered material is separated through the second filter medium to obtain the modified molecular sieve precursor.

[0025] In the modification method, the waste silica microspheres in step (2) are recycled and processed, and the specific operation process is as follows: the waste silica microspheres are mixed with an acidic solution for reaction, and after filtration, washing and drying, regenerated silica microspheres are obtained; and the regenerated silica microspheres are subjected to the process of step (1) again.

[0026] In the modification method, the acidic solution in step (2) is sulfuric acid, and the concentration of the sulfuric acid is 60wt.%-80wt.%.

[0027] In the modification method, the solid-liquid ratio of the waste silica microspheres and the acidic solution in step (2) is 1: (6-15) g / mL, preferably 1: (8-10) g / mL.

[0028] In the modification method, the operation conditions for the mixing reaction of the waste silica microspheres and the acidic solution in step (2) are as follows: the reaction temperature is 0-20 ℃, and the reaction time is 30-60 min.

[0029] In the modification method, the acidic gas generated in the mixing reaction of the waste silica microspheres and the acidic solution in step (2) is washed and treated with a sodium hydroxide lye.

[0030] In the above modification method, the washing process in step (2) is to wash with water until neutral; the drying process operation conditions are as follows: drying temperature 80℃-120℃, drying time 12h-24h; the modified molecular sieve precursor is calcined in air atmosphere, the calcination temperature is 500℃-600℃, and the calcination time is 2h-5h.

[0031] In the above modification method, the solid yield of the modified molecular sieve in step (2) is 80%-95%.

[0032] A second aspect of this invention provides an ammonium fluorosilicate-modified molecular sieve obtained by the above-described modification method. The modified molecular sieve has a relative crystallinity of 90%-110%, a residual fluorine content of 0wt%-0.2wt%, a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 5-150, and a specific surface area of ​​350 m² / g. 2 / g-850m 2 / g, pore volume is 0.16cm 3 / g-0.40cm 3 / g.

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

[0034] This invention first loads a layer of sodium fluoroaluminate seed crystals onto the surface of porous silica microspheres, and then utilizes the epitaxial growth of the crystals to achieve efficient separation and removal of fluorides during the ammonium fluorosilicate-modified molecular sieve process. While ensuring the molecular sieve modification effect, it significantly improves the yield of the modified molecular sieve product, and the silica microspheres can be reused after regeneration. Implementation

[0035] 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.

[0036] 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.

[0037] In this invention, the elemental composition of the molecular sieve material and the silica microspheres loaded with sodium fluoroaluminate seeds was determined by XRF characterization; the crystal structure and relative crystallinity of the molecular sieve were determined by XRD characterization; the average particle size of the molecular sieve was determined by laser particle size analyzer; and the pore structure information of the silica microspheres was determined by N2 adsorption-desorption characterization.

[0038] In the present application, the modified molecular sieve solid yield is calculated as follows:

[0039]

[0040] Example 1

[0041] (1) Ammonium fluoride and sodium aluminate were added to water to prepare a modifier solution, the molar ratio of sodium aluminate to ammonium fluoride was 1:6, and the concentration of ammonium fluoride solution was 0.06 mol / L; the silica microspheres (specific surface area 456 m 2 / g, pore volume 0.89 cm 3 / g, mesopore and macropore volume accounted for 97% of the total pore volume, and the average pore size was 8.4 nm) were added to the above-mentioned modifier solution at a solid-liquid ratio of 1:30 g / mL, and the silica microspheres were stirred at 5°C for 2h, then separated by filtration, washed to neutral, and dried at 100°C for 24h to obtain silica microspheres loaded with sodium fluoroaluminate seeds, wherein the content of sodium fluoroaluminate seeds was 4.41wt%.

[0042] (2) Y molecular sieve (particle size 1.5 μm, SiO2 / Al2O3 molar ratio 5.1, specific surface area 875 m 2 / g, pore volume 0.36 cm 3 / g) was mixed with an ammonium fluosilicate solution with a concentration of 0.03 mol / L at a solid-liquid ratio of 1:30 g / mL, and then mixed with the silica microspheres loaded with sodium fluoroaluminate seeds at a mass ratio of 1:10, and then treated at 90°C for 3h; after the reaction was completed, the reaction product was separated to obtain waste silica and modified molecular sieve precursor; the separation equipment used for separation included a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1 μm-3 μm arranged in an overlapping manner. The waste silica and the modified molecular sieve precursor were both washed with water until neutral, and then dried at 100°C for 24h. The modified molecular sieve precursor after drying was calcined at 550°C in an air atmosphere for 2h to obtain modified Y molecular sieve. The silicon-aluminum ratio of the obtained modified Y molecular sieve was 7.2, the residual fluorine content was 0wt%, the specific surface area of the modified Y molecular sieve was 833 m 2 / g, the pore volume was 0.37 cm 3 / g, the solid yield of the modified Y molecular sieve was 97%, and the relative crystallinity of the modified Y molecular sieve was 100%.

[0043] (3) The waste silica microspheres recovered in step (2) were added to an 80wt% mass fraction of sulfuric acid solution at a solid-liquid ratio of 1:10 (g:ml), and stirred at 10°C for 1h; the gas generated during the reaction was washed with 1 mol / L concentration of sodium hydroxide lye, the silica microspheres were separated by filtration, washed with water until neutral, and dried at 100°C for 24h to obtain regenerated silica microspheres.

[0044] Example 2

[0045] (1) The same as step (1) in Example 1.

[0046] (2) Y molecular sieve (particle size 1.5 μm, SiO2 / Al2O3molar ratio 5.1, specific surface area 875 m 2 / g, pore volume 0.36 cm 3 / g) was mixed with an ammonium fluosilicate solution with a concentration of 0.1 mol / L at a solid-liquid ratio of 1:20 g / mL, then silica microspheres loaded with sodium fluoroaluminate seed crystals were added to the above mixture at a mass ratio of 1:5, and the mixture was treated at 80°C for 4 h. After the reaction was completed, the reaction product was separated to obtain waste silica and modified molecular sieve precursor. The separation equipment used for separation included a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1 μm-3 μm, which were arranged in an overlapping manner. The waste silica and the modified molecular sieve precursor were both washed with water until neutral, and then dried at 100°C for 24 h. The modified molecular sieve precursor after drying was calcined at 600°C in an air atmosphere for 2 h to obtain modified Y molecular sieve. The silicon-aluminum ratio of the obtained modified Y molecular sieve was 9.2, the residual fluorine content was 0 wt%, the specific surface area of the modified Y molecular sieve was 841 m 2 / g, the pore volume was 0.38 cm 3 / g, the solid yield of the modified Y molecular sieve was 95%, and the relative crystallinity of the modified Y molecular sieve was 96%.

[0047] (3) The waste silica microspheres recovered in step (2) were added to a 70% mass fraction sulfuric acid solution at a solid-liquid ratio of 1:15 g / mL, and stirred at 5°C for 1 h. The gas generated during the reaction process was washed with a 1 mol / L sodium hydroxide solution. The silica microspheres were separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated silica microspheres.

[0048] Example 3

[0049] (1) The same as step (1) in Example 1.

[0050] (2) Y molecular sieve (particle size 1.5 μm, SiO2 / Al2O3molar ratio 5.1, specific surface area 875 m 2 / g, pore volume 0.36 cm 3 / g) and the ammonium fluorosilicate solution with a concentration of 0.15 mol / L was mixed at a solid-liquid ratio of 1:50 g / mL, then the silica microspheres were added into the above mixture at a mass ratio of the silica microspheres loaded with sodium fluoroaluminate seeds to the molecular sieve of 1:15, and the mixture was treated at 90°C for 5 h. After the reaction was completed, the reaction product was separated to obtain waste silica and modified molecular sieve precursor. The separation equipment used for the separation included a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1-3 μm, which were arranged in an overlapping manner. The waste silica and the modified molecular sieve precursor were both washed with water until neutral, and then dried at 100°C for 24 h. The modified molecular sieve precursor after drying was calcined in an air atmosphere at 500°C for 4 h to obtain the modified Y molecular sieve. The silicon-aluminum ratio of the obtained modified Y molecular sieve was 15.8, the residual fluorine content was 0.03 wt%, the specific surface area of the modified Y molecular sieve was 818 m 2 / g, the pore volume was 0.40 cm 3 / g, the solid yield of the modified Y molecular sieve was 92%, and the relative crystallinity of the modified Y molecular sieve was 92%.

[0051] (3) The waste silica microspheres recovered in step (2) were added into 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 in the reaction process was washed with a 1 mol / L concentration sodium hydroxide lye. The silica microspheres were separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated silica microspheres.

[0052] Example 4

[0053] (1) Ammonium fluoride and sodium aluminate were added into water to prepare a modifier solution. The molar ratio of sodium aluminate to ammonium fluoride was 1:6, and the concentration of the ammonium fluoride solution was 0.03 mol / L. The silica microspheres (specific surface area 333 m 2 / g, pore volume 0.56 cm 3 / g, mesopore and macropore volume ratio 94%, average pore diameter 7.2 nm) were added into the modifier solution at a solid-liquid ratio of 1:20 g / mL, and stirred at 2°C for 1 h. The silica microspheres loaded with sodium fluoroaluminate seeds were separated by filtration, washed until neutral, and dried at 100°C for 24 h. The content of the sodium fluoroaluminate seeds in the obtained silica microspheres loaded with sodium fluoroaluminate seeds was 1.47 wt%.

[0054] (2) ZSM-5 molecular sieve (particle size 2.3 μm, SiO2 / Al2O3 molar ratio 26.2, specific surface area 435 m 2 / g, pore volume 0.17 cm 3 / g) and the ammonium fluorosilicate solution with a concentration of 0.02 mol / L were mixed at a solid-liquid ratio of 1:30 g / mL, then the silica microspheres were added into the mixture at a mass ratio of the silica microspheres loaded with sodium fluoroaluminate seeds to the molecular sieve of 1:10, and the mixture was treated at 90°C for 4 h. After the reaction was completed, the reaction product was separated to obtain waste silica and modified molecular sieve precursor. The separation equipment used for the separation included a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1-3 μm, which were arranged in an overlapping manner. The waste silica and the modified molecular sieve precursor were both washed with water until neutral, and then dried at 100°C for 24 h. The modified molecular sieve precursor after drying was calcined at 550°C in an air atmosphere for 2 h to obtain modified ZSM-5 molecular sieve. The silicon-aluminum ratio of the obtained modified ZSM-5 molecular sieve was 37.7, the residual fluorine content was 0 wt%, the specific surface area of the modified ZSM-5 molecular sieve was 411 m 2 / g, the pore volume was 0.19 cm 3 / g, the solid yield of the modified ZSM-5 molecular sieve was 98%, and the relative crystallinity of the modified ZSM-5 molecular sieve was 105%.

[0055] (3) The waste silica microspheres recovered in step (2) were added into a 70% mass fraction sulfuric acid solution at a solid-liquid ratio of 1:10 g / mL, and stirred at 5°C for 1 h. The gas generated in the reaction process was washed with a 1 mol / L concentration sodium hydroxide lye. The silica microspheres were separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated silica microspheres.

[0056] Example 5

[0057] (1) Ammonium fluoride and sodium aluminate were added into water to prepare a modifier solution. The molar ratio of sodium aluminate to ammonium fluoride was 1:6, and the concentration of the ammonium fluoride solution was 0.09 mol / L. The silica microspheres (specific surface area 511 m 2 / g, pore volume 0.93 cm 3 / g, mesopore and macropore volume ratio 97%, average pore diameter 7.9 nm) were added into the modifier at a solid-liquid ratio of 1:30 g / mL, and stirred at 10°C for 1 h. The silica microspheres loaded with sodium fluoroaluminate seeds were separated by filtration, washed until neutral, and dried at 100°C for 24 h. The content of sodium fluoroaluminate seeds in the obtained silica microspheres loaded with sodium fluoroaluminate seeds was 6.62 wt%.

[0058] (2) The beta molecular sieve (particle size 1.0 μm, SiO2 / Al2O3 molar ratio 30.5, specific surface area 581 m 2 / g, pore volume 0.31 cm 3 / g) and the ammonium fluosilicate solution with a concentration of 0.15 mol / L was mixed at a solid-liquid ratio of 1:50 g / mL, then the silica microspheres were added into the above mixture at a mass ratio of the silica microspheres loaded with sodium fluoroaluminate seeds to the molecular sieve of 1:10, and the mixture was treated at 90°C for 5 h. After the reaction was completed, the reaction product was separated to obtain waste silica and modified molecular sieve precursor. The separation equipment used for the separation included a 200-mesh stainless steel screen and a slow filter paper with a pore size of 1-3 μm, which were arranged in an overlapping manner. The waste silica and the modified molecular sieve precursor were washed with water until neutral, and then dried at 100°C for 24 h. The modified molecular sieve precursor after drying was calcined at 500°C in an air atmosphere for 3 h to obtain modified beta molecular sieve. The silicon-aluminum ratio of the obtained modified beta molecular sieve was 121.5, the residual fluorine content was 0.07 wt%, the specific surface area of the modified beta molecular sieve was 530 m 2 / g, the pore volume was 0.35 cm 3 / g, the solid yield of the modified beta molecular sieve was 95%, and the relative crystallinity of the modified beta molecular sieve was 91%.

[0059] (3) The waste silica microspheres recovered in step (2) were added into a 80% mass fraction sulfuric acid solution at a solid-liquid ratio of 1:15 g / mL, and stirred at 0°C for 2 h. The gas generated in the reaction process was washed with a 1 mol / L concentration sodium hydroxide lye. The silica microspheres were separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated silica microspheres.

[0060] Example 6

[0061] The ammonium fluosilicate modification process of the molecular sieve was the same as in Example 1, except that the silica microspheres in step (1) were the regenerated silica microspheres obtained in Example 1. The silicon-aluminum ratio of the obtained modified Y molecular sieve was 7.0, the residual fluorine content was 0.02 wt%, the specific surface area of the modified Y molecular sieve was 823 m 2 / g, the pore volume was 0.38 cm 3 / g, the solid yield of the modified Y molecular sieve was 96%, and the relative crystallinity of the modified Y molecular sieve was 101%.

[0062] Comparative Example 1

[0063] The ammonium fluosilicate modification process of the molecular sieve was the same as in Example 1, except that no silica microspheres were added in the ammonium fluosilicate modification process of the molecular sieve, and after the modification was completed, the fluoride was removed from the reaction system by three times of natural sedimentation, and the modified molecular sieve was recovered by filtration, washing and drying. The silicon-aluminum ratio of the obtained modified Y molecular sieve was 7.5, the residual fluorine content was 0 wt%, the specific surface area of the modified Y molecular sieve was 830 m 2 / g, the pore volume was 0.38 cm 3 / g, the relative crystallinity of the modified Y molecular sieve was 96%. The results show that although the fluorides in the modified molecular sieve system can be effectively removed by using the traditional natural sedimentation method, the yield of the modified molecular sieve product is low.

[0064] Comparative Example 2

[0065] The process of modifying the molecular sieve with ammonium fluosilicate was the same as that in Example 1, except that the silica microspheres without the loaded sodium fluoroaluminate seed crystals were added in the process of modifying the molecular sieve with ammonium fluosilicate. The silicon-aluminum ratio of the obtained modified Y molecular sieve was 5.8, the residual fluorine content was 9.23wt%, the specific surface area of the modified Y molecular sieve was 653m 2 / g, the pore volume was 0.32cm 3 / g, the solid yield of the modified Y molecular sieve was 102%, and the relative crystallinity of the modified Y molecular sieve was 72%. The results show that when the silica microspheres are not loaded with sodium fluoroaluminate seed crystals, the sodium fluoroaluminate fluorides generated in the process of modifying the molecular sieve with ammonium fluosilicate cannot be effectively removed from the silica microspheres by the way of crystal epitaxial growth, and the adsorption and binding force of the silica microspheres to the fluorides is poor, resulting in a large amount of fluorine remaining in the modified molecular sieve product. On the one hand, the solid yield of the modified molecular sieve is high (the impurity content is extremely high), and on the other hand, the crystallinity of the modified molecular sieve is seriously reduced.

[0066] Comparative Example 3

[0067] The process of modifying the molecular sieve with ammonium fluosilicate was the same as that in Example 1, except that step (1) was omitted, and then 2wt% (relative to the mass of the molecular sieve) of sodium fluoroaluminate crystals were directly added as seed crystals in the process of modifying the molecular sieve with ammonium fluosilicate. After the modification was completed, the modified molecular sieve was recovered by filtration, washing and drying. The silicon-aluminum ratio of the obtained modified Y molecular sieve was 5.3, the residual fluorine content was 12.1wt%, the specific surface area of the modified Y molecular sieve was 588m 2 / g, the pore volume was 0.26cm 3 / g, the solid yield of the modified Y molecular sieve was 105%, and the relative crystallinity of the modified Y molecular sieve was 65%. It is shown that when the sodium fluoroaluminate crystals are directly added as seed crystals, because the particle size of the sodium fluoroaluminate crystals is similar to that of the molecular sieve, the molecular sieve and the sodium fluoroaluminate cannot be effectively separated by using the filtering separation method of the present application. On the one hand, this leads to a high solid yield of the modified molecular sieve (extremely high impurity content), and on the other hand, the crystallinity of the modified molecular sieve is seriously reduced.

[0068] By comparing the experimental results in the examples and the comparative examples, it can be found that, in the ammonium fluosilicate modified molecular sieve system, adding a certain amount of silica microspheres loaded with sodium fluoroaluminate seed crystals can realize efficient separation of fluorides in the modified molecular sieve product by using the crystal epitaxial growth effect, greatly improves the yield of the modified molecular sieve product while ensuring the modification effect of the molecular sieve, and the recovered silica microspheres can be reused after treatment.

Claims

1. A method for modifying molecular sieves, characterized in that: The method includes the following: (1) Preparation of silica microspheres loaded with sodium fluoroaluminate seeds: silica microspheres were mixed with a modifier solution and reacted. The reaction product was filtered, washed and dried to obtain silica microspheres loaded with sodium fluoroaluminate seeds. (2) Preparation of ammonium fluorosilicate modified molecular sieve: The silica microspheres loaded with sodium fluoroaluminate seeds obtained in step (1), the molecular sieve, and the ammonium fluorosilicate solution were mixed and reacted. The reaction product was separated, washed, dried, and calcined to obtain the ammonium fluorosilicate modified molecular sieve. The silica microspheres mentioned in step (1) have a particle size of 200 μm-2 mm and a specific surface area of ​​200 m². 2 / g-600m 2 / g; pore volume is 0.5cm 3 / g-1.2cm 3 / g, of which mesopores and macropores account for more than 90% of the total pore volume; the average pore size is 5nm-15nm; 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; the particle size of the molecular sieve is 500 nm-10 μm; the silicon-to-aluminum ratio of the molecular sieve is 3-80, and the silicon-to-aluminum ratio is the SiO2 / Al2O3 molar ratio; the specific surface area of ​​the molecular sieve is 380 m² / m³. 2 / g-900m 2 / g, pore volume 0.15cm 3 / g-0.38cm 3 / g; 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.

2. The modification method according to claim 1, characterized in that: The silica microspheres mentioned in step (1) have a particle size of 300 μm-1 mm and a specific surface area of ​​300 m². 2 / g-500m 2 / g; pore volume is 0.6cm 3 / g-1cm 3 / g; average pore size is 7nm-10nm.

3. The modification method according to claim 1, characterized in that: The modifier solution in step (1) includes a modifier and a solvent; the modifier includes sodium aluminate and ammonium fluoride, and the molar ratio of sodium aluminate to ammonium fluoride is 1:6; the solvent is deionized water; the ratio of ammonium fluoride to solvent is 0.01-0.10 in mol / L.

4. The modification method according to claim 3, characterized in that: The ratio of ammonium fluoride to solvent is 0.03-0.06 in mol / L.

5. The modification method according to claim 1, characterized in that: The solid-liquid ratio of the silica microspheres to the modifier solution in step (1) is 1:(20-30) in g / mL.

6. The modification method according to claim 1, characterized in that: The reaction conditions for the reaction of silica microspheres and modifier solution in step (1) are as follows: reaction temperature is 0℃-20℃; reaction time is 1h-3h.

7. The modification method according to claim 6, characterized in that: The reaction temperature is 2℃-10℃.

8. The modification method according to claim 1, characterized in that: The specific operation steps of the filtration, washing and drying process in step (1) are as follows: the reaction product is filtered to obtain solid material; the solid material is washed with water until neutral and then dried at a temperature of 80℃-120℃ for 12h-24h.

9. The modification method according to claim 1, characterized in that: The sodium fluoroaluminate seed content in the silica microspheres loaded with sodium fluoroaluminate seed obtained in step (1) is 1 wt.%-10 wt.%.

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

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

12. The modification method according to claim 11, characterized in that: In step (2), the concentration of ammonium fluorosilicate solution is 0.05 mol / L-0.1 mol / L.

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

14. The modification method according to claim 1, characterized in that: In step (2), the mass ratio of silica microspheres loaded with sodium fluoroaluminate seeds to molecular sieve is 1:(5-15).

15. The modification method according to claim 1, characterized in that: The operating conditions for the reaction described in step (2) are as follows: reaction temperature 60-100℃; reaction time 3h-5h.

16. The modification method according to claim 15, characterized in that: The operating conditions for the reaction described in step (2) are as follows: reaction temperature 80℃-90℃.

17. The modification method according to claim 1, characterized in that: In step (2), the first and second filter media are arranged in an overlapping manner.

18. The modification method according to claim 1, characterized in that: In step (2), the size of the first filter medium is 100-200 mesh; the size of the second filter medium is 500nm-3μm.

19. The modification method according to claim 1, characterized in that: The reaction products enter the separation equipment and are separated by the first filter medium to obtain waste silica microspheres and filtered material; the filtered material is then separated by the second filter medium to obtain modified molecular sieve precursor.

20. The modification method according to claim 19, characterized in that: In step (2), the waste silica microspheres are recycled. The specific operation process is as follows: the waste silica microspheres are mixed with an acidic solution and reacted. After filtration, washing and drying, regenerated silica microspheres are obtained. The regenerated silica microspheres repeat the process of step (1).

21. The modification method according to claim 20, characterized in that: In step (2), the acidic solution is sulfuric acid, and the concentration of the sulfuric acid is 60 wt.%-80 wt.%.

22. The modification method according to claim 20, characterized in that: In step (2), the solid-liquid ratio of the waste silica microspheres to the acidic solution is 1:(6-15) in g / mL.

23. The modification method according to claim 22, characterized in that: In step (2), the solid-liquid ratio of the waste silica microspheres to the acidic solution is 1:(8-10) in g / mL.

24. The modification method according to claim 20, characterized in that: In step (2), the reaction conditions for mixing waste silica microspheres with acidic solution are: reaction temperature 0-20℃, reaction time 30min-60min.

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

26. The modification method according to claim 1, characterized in that: In step (2), the solid yield of the modified molecular sieve is 80%-95%.