Molecular sieve modification method

Abstract

The invention discloses a molecular sieve modification method which comprises the following steps: (1) preparation of sodium fluoroaluminate seed crystal loaded silicon dioxide microspheres: mixing the silicon dioxide microspheres with a modifier solution for reaction, and filtering, washing and drying the reaction product to obtain the sodium fluoroaluminate seed crystal loaded silicon dioxide microspheres; and (2) preparation of the ammonium fluosilicate modified molecular sieve: mixing the silicon dioxide microspheres loaded with the sodium fluoroaluminate seed crystal obtained in the step (1), the molecular sieve and an ammonium fluosilicate solution for reaction, and separating, washing, drying and roasting a reaction product to obtain the ammonium fluosilicate modified molecular sieve. The method can achieve the purposes of efficiently removing fluoride and improving the yield of the molecular sieve product at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieves and relates to a molecular sieve modification method, in particular to an ammonium fluorosilicate modification method of a 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 CN113950460A discloses a method for improving Si / Al of molecular sieves, comprising: ion-exchanging a molecular sieve synthesized without using an organic structure directing agent to prepare a sodium type, a proton type or an ammonium type, and then contacting the zeolite after ion exchange with an ammonium fluorosilicate solution for dealumination. When Beta or mordenite is treated by this method, the Si / Al of the molecular sieve can be effectively improved while retaining a high crystallinity.

[0004] Patent CN114477217A discloses an ultra-stable Y-type molecular sieve and a preparation method thereof, which specifically includes: (1) adding a fluorine-containing aqueous solution to an ammonium fluorosilicate solution, and then mixing it with the Y-type molecular sieve raw powder, washing and drying to obtain a pretreated Y-type molecular sieve; (2) mixing the pretreated Y-type molecular sieve, ammonium salt and water, and then adding an acid solution, stirring, washing and drying to obtain a sample; (3) subjecting the sample obtained in step (2) to a hydrothermal ultra-stabilization treatment, drying and obtaining an ultra-stable Y-type molecular sieve. After the method uses ammonium fluorosilicate to pretreat the Y molecular sieve, it can ensure that the molecular sieve has less skeleton collapse during the subsequent hydrothermal coupling acid treatment process and the molecular sieve crystal structure is intact.

[0005] It is true that ammonium fluorosilicate modified molecular sieves are widely used due to their unique advantages, but there is a problem of fluoride residue in the process of ammonium fluorosilicate modified molecular sieves, which further destroys the crystal structure of the molecular sieves. However, none of the patents that have been published mentions the above problem. Summary of the invention

[0006] The inventor 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. However, this method has low removal efficiency, and the loss of molecular sieve products will inevitably occur during the modification process. Therefore, it is urgent to develop a new ammonium fluorosilicate modification method that can improve the yield of molecular sieve products while ensuring the efficient removal of fluoride in advance.

[0007] In view of the deficiencies of the prior art, the present invention provides a molecular sieve modification method. In the process of ammonium fluorosilicate modification of molecular sieve, porous silica microspheres loaded with sodium fluoroaluminate seeds are added to the reaction system, and the seed epitaxial growth method is used to achieve efficient removal of fluoride in the reaction system. The method can simultaneously achieve the purpose of efficiently removing fluoride and improving the yield of molecular sieve products.

[0008] The first aspect of the present invention provides a molecular sieve modification method, the method comprising the following contents: (1) Preparation of silica microspheres loaded with sodium fluoroaluminate crystal seeds: mixing silica microspheres with a modifier solution to react, filtering, washing, and drying the reaction product to obtain silica microspheres loaded with sodium fluoroaluminate crystal 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 are mixed and reacted, and the reaction product is separated, washed, dried and calcined to obtain the ammonium fluorosilicate modified molecular sieve.

[0009] 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-600m 2 / g, preferably 300m 2 / g-500m 2 / g; pore volume is 0.5cm 3 / g-1.2cm 3 / g, preferably 0.6cm 3 / g-1cm 3 / g, wherein the proportion of mesopores and macropores in the total pore volume is greater than 90%; the average pore diameter is 5nm-15nm, preferably 7nm-10nm.

[0010] In the above modification method, the modifier solution in step (1) comprises a modifier and a solvent; the modifier comprises sodium aluminate and ammonium fluoride, and the molar ratio of sodium aluminate to ammonium fluoride is 1:6; the solvent is deionized water; and the ratio of ammonium fluoride to solvent is 0.01-0.10, preferably 0.03-0.06, in mol / L.

[0011] In the above modification method, there is no requirement for the order of mixing sodium aluminate and ammonium fluoride with the solvent in step (1), such as sodium aluminate is first mixed with the solvent and then ammonium fluoride is added for mixing, ammonium fluoride is first mixed with the solvent and then sodium aluminate is added for mixing, sodium aluminate and ammonium fluoride are separately mixed with the solvent and then the two are mixed, preferably sodium aluminate and ammonium fluoride are separately mixed with the solvent and then the two are mixed.

[0012] In the above modification method, the solid-to-liquid ratio of the silica microspheres to the modifier solution in step (1) is 1:(20-30) in g / mL.

[0013] In the above modification method, the reaction conditions for the reaction of the silica microspheres and the modifier solution in step (1) are as follows: the reaction temperature is 0°C-20°C, preferably 2°C-10°C; and the reaction time is 1h-3h.

[0014] In the above modification method, the specific operation steps of filtering, washing and drying 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, the drying temperature is 80°C-120°C, and the drying time is 12h-24h.

[0015] In the above modification method, the content of sodium fluoroaluminate seeds in the silica microspheres loaded with sodium fluoroaluminate seeds obtained in step (1) is 1 wt.%-10 wt.%.

[0016] In the above modification method, 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 500nm-10μm, preferably 1μm-2μm; the silicon-aluminum ratio (SiO 2 / Al 2 O 3 The molar ratio is 3-80, preferably 5-30; the specific surface area of ​​the molecular sieve is 380m 2 / g-900m 2 / g, pore volume is 0.15cm 3 / g-0.38cm 3 / g.

[0017] In the above modification method, 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.

[0018] In the above modification method, the solid-liquid ratio of the molecular sieve to the ammonium fluorosilicate solution in step (2) is 1:(20-50) in g / mL.

[0019] In the above modification method, the mass ratio of the silica microspheres loaded with sodium fluoroaluminate seeds to the molecular sieve in step (2) is 1:(5-15).

[0020] In the above modification method, the operating conditions of the reaction in step (2) are as follows: reaction temperature 60-100°C, preferably 80-90°C; reaction time 3h-5h.

[0021] In the above-mentioned modification method, 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 to 300 mesh, preferably 100 mesh to 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 to 5μm, preferably 500nm to 3μm, and specifically in the present invention, the second filter medium adopts a slow filter paper with a pore size of 1μm to 3μm.

[0022] In the above modification method, 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 silica microspheres and filtered material; the filtered material is separated by a second filter medium to obtain a modified molecular sieve precursor.

[0023] In the above modification method, the waste silica microspheres in step (2) are recycled, and the specific operation process is as follows: the waste silica microspheres are mixed with an acidic solution for reaction, and regenerated silica microspheres are obtained after filtering, washing and drying; the regenerated silica microspheres repeat the process of step (1).

[0024] In the above modification method, the acidic solution in step (2) is sulfuric acid, and the concentration of the sulfuric acid is 60wt.%-80wt.%.

[0025] In the above modification method, the solid-liquid ratio of the waste silica microspheres to the acidic solution in step (2) is 1:(6-15) in g / mL, preferably 1:(8-10).

[0026] In the above modification method, the operating conditions for the mixed reaction of the waste silica microspheres and the acidic solution in step (2) are: reaction temperature 0-20°C, reaction time 30min-60min.

[0027] In the above modification method, the acidic gas generated during the mixing reaction of the waste silica microspheres and the acidic solution in step (2) is washed with sodium hydroxide solution.

[0028] In the above modification method, the washing process in step (2) 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; the modified molecular sieve precursor is calcined in an air atmosphere, the calcination temperature is 500°C-600°C, and the calcination time is 2h-5h.

[0029] In the above modification method, the solid yield of the modified molecular sieve in step (2) is 80%-95%.

[0030] The second aspect of the present invention provides an ammonium fluorosilicate modified molecular sieve obtained by the above modification method. The relative crystallinity of the modified molecular sieve is 90%-110%, the residual fluorine content in the modified molecular sieve is 0wt%-0.2wt%, and the silicon-aluminum ratio (SiO 2 / Al 2 O 3 The molar ratio is 5-150; the specific surface area of ​​the molecular sieve is 350m 2 / g-850m 2 / g, pore volume is 0.16cm 3 / g-0.40cm 3 / g.

[0031] Compared with the prior art, the present invention has the following beneficial effects: The present invention first loads a layer of sodium fluoroaluminate seed crystals on the surface of porous silica microspheres, and then utilizes the epitaxial growth of the crystals to achieve efficient separation and removal of fluoride in the process of ammonium fluorosilicate modified molecular sieves. While ensuring the molecular sieve modification effect, the yield of the modified molecular sieve product is greatly improved, and the silica microspheres can be reused after regeneration treatment. Implementation

[0032] 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.

[0033] 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.

[0034] In the present invention, the elemental composition of the molecular sieve material and the silica microspheres loaded with sodium fluoroaluminate seeds is determined by XRF characterization; the crystal structure and relative crystallinity of the molecular sieve are determined by XRD characterization; the average particle size of the molecular sieve is determined by a laser particle size analyzer; the pore structure information of the silica microspheres is determined by N 2 Adsorption-desorption characterization was determined.

[0035] In the present invention, the calculation method of the modified molecular sieve solid yield is as follows:

[0036] Example 1 (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 ammonium fluoride solution was 0.06 mol / L; silica microspheres (specific surface area 456 m 2 / g, pore volume 0.89cm 3 / g, the proportion of mesopores and macropores in the total pore volume is 97%, and the average pore size is 8.4nm) and the solid-to-liquid ratio of the modifier solution is 1:30g / mL. Silica microspheres are added to the above-mentioned modifier solution, stirred at 5°C for 2h, separated by filtration, washed to neutrality, and dried at 100°C for 24h to obtain silica microspheres loaded with sodium fluoroaluminate seeds, wherein the sodium fluoroaluminate seed content is 4.41wt%.

[0037] (2) Y molecular sieve (particle size 1.5 μm, SiO 2 / Al 2 O 3 Molar ratio 5.1, specific surface area 875m 2 / g, pore volume 0.36cm 3 / g) was mixed with an ammonium fluorosilicate solution with a concentration of 0.03mol / L at a solid-liquid ratio of 1:30g / mL, and then mixed with silica microspheres loaded with sodium fluoroaluminate seeds and molecular sieves at a mass ratio of 1:10, and 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 1μm-3μm arranged in an overlapping manner. The waste silica and the modified molecular sieve precursor were washed with water to neutrality and dried at 100°C for 24h. The dried modified molecular sieve precursor was 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 was 7.2, the residual fluorine content was 0wt%, and the specific surface area of ​​the modified Y molecular sieve was 833m 2 / g, pore volume 0.37cm 3 / g, the solid yield of modified Y molecular sieve is 97%, and the relative crystallinity of modified Y molecular sieve is 100%.

[0038] (3) The waste silica microspheres recovered in step (2) were added to a sulfuric acid solution of 80 wt% 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 silica microspheres were separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated silica microspheres.

[0039] Example 2 (1) Same as step (1) in Example 1.

[0040] (2) Y molecular sieve (particle size 1.5 μm, SiO 2 / Al 2 O 3 Molar ratio 5.1, specific surface area 875m 2 / g, pore volume 0.36cm 3 / g) is mixed with an ammonium fluorosilicate solution with a concentration of 0.1mol / L at a solid-liquid ratio of 1:20g / mL, and then the silica microspheres loaded with sodium fluoroaluminate seeds and the molecular sieve are added to the above mixture at a mass ratio of 1:5, and treated at 80°C for 4h. After the reaction is completed, the reaction product is separated to obtain waste silica and a 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 silica 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 9.2, the residual fluorine content is 0wt%, and the specific surface area of ​​the modified Y molecular sieve is 841m 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 96%.

[0041] (3) The waste silica microspheres recovered in step (2) were added to a 70% by mass 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 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.

[0042] Example 3 (1) Same as step (1) in Example 1.

[0043] (2) Y molecular sieve (particle size 1.5 μm, SiO 2 / Al2 O 3 Molar ratio 5.1, specific surface area 875m 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 silica microspheres loaded with sodium fluoroaluminate seeds and the molecular sieve are added to the above mixture at a mass ratio of 1:15, and treated at 90°C for 5h. After the reaction is completed, the reaction product is separated to obtain waste silica and a 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 silica 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 15.8, the residual fluorine content is 0.03wt%, and the specific surface area of ​​the modified Y molecular sieve is 818m 2 / g, pore volume 0.40cm 3 / g, the solid yield of modified Y molecular sieve is 92%, and the relative crystallinity of modified Y molecular sieve is 92%.

[0044] (3) The waste silica microspheres recovered in step (2) were 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 silica microspheres were separated by filtration, washed with water until neutral, and dried at 100°C for 24 h to obtain regenerated silica microspheres.

[0045] Example 4 (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 ammonium fluoride solution was 0.03 mol / L; silica microspheres (specific surface area 333 m 2 / g, pore volume 0.56cm 3 / g, mesopore and macropore volume accounted for 94%, and the average pore size was 7.2nm) and the solid-to-liquid ratio of the modifier solution was 1:20g / mL. Silica microspheres were added to the modifier solution and stirred at 2°C for 1h. The silica microspheres loaded with sodium fluoroaluminate seeds were separated by filtration, washed to neutrality, and dried at 100°C for 24h. The content of sodium fluoroaluminate seeds in the obtained silica microspheres loaded with sodium fluoroaluminate seeds was 1.47wt%.

[0046] (2) ZSM-5 molecular sieve (particle size 2.3 μm, SiO 2 / Al 2 O 3Molar ratio 26.2, specific surface area 435m 2 / 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 silica microspheres are added to the above mixture at a mass ratio of 1:10 of silica microspheres loaded with sodium fluoroaluminate seeds and molecular sieves, and treated at 90°C for 4h. After the reaction is completed, the reaction product is separated to obtain waste silica 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 silica 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 ZSM-5 molecular sieve. The silicon-aluminum ratio of the obtained modified ZSM-5 molecular sieve is 37.7, the residual fluorine content is 0wt%, and the specific surface area of ​​the modified ZSM-5 molecular sieve is 411m 2 / g, pore volume 0.19cm 3 / g, the solid yield of modified ZSM-5 molecular sieve is 98%, and the relative crystallinity of modified ZSM-5 molecular sieve is 105%.

[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 1:10 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 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 5 (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 ammonium fluoride solution was 0.09 mol / L; silica microspheres (specific surface area 511 m 2 / g, pore volume 0.93cm 3 / g, mesopore and macropore volume accounts for 97%, average pore size 7.9nm) and the solid-to-liquid ratio of the modifier solution is 1:30g / mL. Silica microspheres are added to the modifier and stirred at 10°C for 1h. The silica microspheres loaded with sodium fluoroaluminate seeds are separated by filtration, washed to neutrality, and dried at 100°C for 24h. The content of sodium fluoroaluminate seeds in the obtained silica microspheres loaded with sodium fluoroaluminate seeds is 6.62wt%.

[0049] (2) Beta molecular sieve (particle size 1.0 μm, SiO 2 / Al 2 O 3Molar ratio 30.5, specific surface area 581m 2 / g, pore volume 0.31cm 3 / g) and ammonium fluorosilicate solution with a concentration of 0.15mol / L are mixed at a solid-liquid ratio of 1:50g / mL, and then silica microspheres are added to the above mixture at a mass ratio of 1:10 of silica microspheres loaded with sodium fluoroaluminate seeds and molecular sieves, and treated at 90°C for 5h. After the reaction is completed, the reaction product is separated to obtain waste silica 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 silica 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 3h to obtain a modified beta molecular sieve. The silicon-aluminum ratio of the obtained modified beta molecular sieve is 121.5, the residual fluorine content is 0.07wt%, and the specific surface area of ​​the modified beta molecular sieve is 530m 2 / g, pore volume 0.35cm 3 / g, the solid yield of modified beta molecular sieve is 95%, and the relative crystallinity of modified beta molecular sieve is 91%.

[0050] (3) The waste silica microspheres recovered in step (2) were added to an 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 during the reaction was washed with 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.

[0051] Example 6 The modification process of the molecular sieve ammonium fluorosilicate is the same as that of Example 1, except that the silica microspheres in step (1) are the regenerated silica microspheres obtained in Example 1. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 7.0, the residual fluorine content is 0.02 wt%, and the specific surface area of ​​the modified Y molecular sieve is 823 m 2 / g, pore volume 0.38cm 3 / g modified Y molecular sieve solid yield is 96%, and the relative crystallinity of the modified Y molecular sieve is 101%.

[0052] Comparative Example 1 The modification process of molecular sieve ammonium fluorosilicate is the same as that of Example 1, except that no silica microspheres are added during the modification of molecular sieve with ammonium fluorosilicate. After the modification is completed, the fluoride is removed from the reaction system by three natural sedimentation steps, and the modified molecular sieve is filtered, washed, and dried for recovery. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 7.5, 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 was 78%, and the relative crystallinity of modified Y molecular sieve was 96%. The results show that although the traditional natural sedimentation method can also effectively remove fluoride in the molecular sieve modification system, the yield of the modified molecular sieve product is low.

[0053] Comparative Example 2 The process of ammonium fluorosilicate modification of molecular sieve is the same as that of Example 1, except that silica microspheres without sodium fluoroaluminate seed are added during the process of ammonium fluorosilicate modification of molecular sieve. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 5.8, the residual fluorine content is 9.23wt%, and the specific surface area of ​​the modified Y molecular sieve is 653m 2 / g, pore volume 0.32cm 3 / g, the solid yield of modified Y molecular sieve is 102%, and the relative crystallinity of modified Y molecular sieve is 72%. The results show that when the silica microspheres are not loaded with sodium fluoroaluminate seeds, the sodium fluoroaluminate fluoride generated during the reaction of ammonium fluorosilicate modified molecular sieve cannot be efficiently removed with the silica microspheres by crystal epitaxial growth, and the silica microspheres themselves have poor adsorption and binding forces for fluoride, resulting in a large amount of fluorine residue 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.

[0054] Comparative Example 3 The process of modifying the molecular sieve with ammonium fluorosilicate is the same as that in Example 1, except that step (1) is omitted, and 2 wt% (relative to the mass of the molecular sieve) of sodium fluoroaluminate crystals are directly added as seeds during the process of modifying the molecular sieve with ammonium fluorosilicate. After the modification is completed, the modified molecular sieve is filtered, washed, dried and recovered. The silicon-aluminum ratio of the obtained modified Y molecular sieve is 5.3, the residual fluorine content is 12.1 wt%, and the specific surface area of ​​the modified Y molecular sieve is 588 m 2 / g, pore volume 0.26cm 3 / g, the solid yield of the modified Y molecular sieve is 105%, and the relative crystallinity of the modified Y molecular sieve is 65%. This indicates that when sodium fluoroaluminate crystals are directly added as seeds, the molecular sieve cannot be effectively separated from sodium fluoroaluminate by the filtration separation method of the present invention because the particle size of the sodium fluoroaluminate crystals is similar to that of the molecular sieve. On the one hand, this results in 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.

[0055] By comparing the experimental results in the embodiments and comparative examples, it can be found that by adding a certain amount of silica microspheres loaded with sodium fluoroaluminate seeds to the ammonium fluorosilicate modified molecular sieve system, the efficient separation of fluoride in the modified molecular sieve product can be achieved by utilizing the crystal epitaxial growth effect, which greatly improves the yield of the modified molecular sieve product while ensuring the molecular sieve modification effect, and the recovered silica microspheres can be reused after treatment.

Claims

1. A molecular sieve modification method, characterized in that: The method includes the following contents: (1) Preparation of silica microspheres loaded with sodium fluoroaluminate crystal seeds: mixing silica microspheres with a modifier solution to react, filtering, washing, and drying the reaction product to obtain silica microspheres loaded with sodium fluoroaluminate crystal 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 are mixed and reacted, and the reaction product is separated, washed, dried and calcined to obtain the ammonium fluorosilicate modified molecular sieve.

2. The modification method according to claim 1, characterized in that: 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-600m 2 / g, preferably 300m 2 / g-500m 2 / g; pore volume is 0.5cm 3 / g-1.2cm 3 / g, preferably 0.6cm 3 / g-1cm 3 / g, wherein the proportion of mesopores and macropores in the total pore volume is greater than 90%; the average pore diameter is 5nm-15nm, preferably 7nm-10nm.

3. The modification method according to claim 1, characterized in that: The modifier solution in step (1) comprises a modifier and a solvent; the modifier comprises 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, preferably 0.03-0.06, in mol / L.

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

5. The modification method according to claim 1, characterized in that: The reaction conditions for the reaction of the silica microspheres and the modifier solution in step (1) are as follows: the reaction temperature is 0°C-20°C, preferably 2°C-10°C; and the reaction time is 1h-3h.

6. The modification method according to claim 1, characterized in that: 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, the drying temperature is 80°C-120°C, and the drying time is 12h-24h.

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

8. The modification method according to claim 1, characterized in that: 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 500nm-10μm, preferably 1μm-2μm; the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) 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, pore volume is 0.15cm 3 / g-0.38cm 3 / g.

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

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

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

13. The modification 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 modification method according to claim 13, characterized in that: The reaction product enters the separation device and is separated by a first filter medium to obtain waste silicon dioxide microspheres and filtered material; the filtered material is separated by a second filter medium to obtain a modified molecular sieve precursor.

15. The modification method according to claim 14, characterized in that: In step (2), the waste silica microspheres are recycled, and the specific operation process is as follows: the waste silica microspheres are mixed with an acidic solution for reaction, and regenerated silica microspheres are obtained after filtering, washing and drying; the regenerated silica microspheres repeat the process of step (1).

16. The modification method according to claim 15, characterized in that: In step (2), the acidic solution is sulfuric acid, and the concentration of the sulfuric acid is 60wt.%-80wt.%.

17. The modification method according to claim 15, characterized in that: In step (2), the solid-to-liquid ratio of the waste silica microspheres to the acidic solution is 1:(6-15) in g / mL, preferably 1:(8-10).

18. The modification method according to claim 15, characterized in that: The operating conditions for the mixed reaction of the waste silica microspheres and the acidic solution in step (2) are: reaction temperature 0-20° C., reaction time 30 min-60 min.

19. The modification method according to claim 1, characterized in that: The washing process in step (2) 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; the modified molecular sieve precursor is calcined in an air atmosphere, the calcination temperature is 500°C-600°C, and the calcination time is 2h-5h.

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

21. An ammonium fluorosilicate modified molecular sieve obtained by the modification method according to any one of claims 1 to 20.

22. The modified molecular sieve according to claim 21, characterized in that: The relative crystallinity of the modified molecular sieve is 90%-110%, the residual fluorine content is 0wt%-0.2wt%, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) is 5-150; the specific surface area of ​​the molecular sieve is 350m 2 / g-850m 2 / g, pore volume is 0.16cm 3 / g-0.40cm 3 / g.

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