Fau structure molecular sieve and method for making same

Abstract

The application relates to the field of molecular sieve preparation, and discloses a FAU structure molecular sieve and a preparation method thereof. The preparation method comprises the following steps: (1) performing first ion exchange on Na-FAU molecular sieve and an ammonium salt; (2) performing filtration, washing and first calcination on the product obtained in the step (1), to obtain a calcined molecular sieve; (3) performing second ion exchange on the calcined molecular sieve obtained in the step (2) and an ammonium salt, fluorosilicic acid and an organic acid; (4) performing filtration, washing and second calcination on the product obtained in the step (3), to obtain a second calcined molecular sieve; and (5) performing third ion exchange on the second calcined molecular sieve obtained in the step (4) and fluorosilicic acid, an organic acid and an ammonium salt, and then performing filtration and washing, to obtain a FAU structure molecular sieve product. The preparation method can obtain the FAU structure molecular sieve with high silicon-aluminum ratio, crystallinity and specific surface area.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve preparation, specifically to a method for preparing FAU structured molecular sieves and the FAU structured molecular sieves obtained by this method. Background Technology

[0002] VOCs are one of the most critical factors in air pollution, and have become the second most significant contributor after SO2. x NO x VOCs, the third largest gaseous pollutant emitted annually, have complex compositions, diverse treatment technologies, and varying applicability, requiring high standards for technology selection and system matching. Various methods exist for VOCs removal, with adsorption being the most effective due to its high efficiency, low energy consumption, simple operation, and recyclability. Rotary adsorption concentration technology is a feasible technology developed for treating large volumes of low-concentration VOCs. The adsorption effect of adsorption depends primarily on the properties of the adsorbent, the types of gaseous pollutants, and the process conditions of the adsorption system (such as operating temperature and humidity). Therefore, the key issue in adsorption lies in the selection of the adsorbent. While most solids possess some adsorption capacity, only solids with high selectivity and large adsorption capacity can be used as industrial adsorbents. Adsorbents should have a dense microporous structure, large internal surface area, good adsorption performance, stable chemical properties, resistance to acids and alkalis, water, high temperature and pressure, and be resistant to breakage and low air resistance. Commonly used adsorbents include molecular sieves, activated carbon (granular) and activated carbon fibers, activated alumina, and silica gel. High silica-to-alumina ratio molecular sieves are characterized by high inertness and non-flammability, good hydrophobicity, and strong VOCs adsorption capacity at low concentrations. They exhibit excellent selectivity for VOCs in environments with high relative humidity, enabling efficient VOCs adsorption.

[0003] High silica-to-alumina ratio Y molecular sieves can be obtained through direct synthesis and post-treatment modification.

[0004] For the direct synthesis of high-silica Y molecular sieves, organic structure-directing agents are usually required. US4,714,601 discloses a polymorph of FAU called ECR 4 with a silica-to-alumina ratio greater than 6, which is obtained by hydrothermal crystallization at 70–120 °C in the presence of seed crystals using alkyl or hydroxyalkyl quaternary ammonium salts as template agents. US4,931,267 discloses a polymorph of FAU called ECR 32 with a silica-to-alumina ratio greater than 6, which is obtained by hydrothermal crystallization at 90–120 °C using tetrapropyl and / or tetrabutylammonium hydroxide as structure-directing agents, and has high thermal stability. Delprato et al. (Zeolites, 1990, 10(6):546552) first synthesized a cubic FAU molecular sieve with a framework silica-to-alumina ratio close to 9.0 using crown ethers as template agents, but the high cost and high toxicity of crown ethers limit their industrial application. Subsequently, US5,385,717 synthesized Y-type molecular sieves with a silica-to-alumina ratio greater than 6 using polyethylene oxide as a template agent. Although the silica-to-alumina ratio of Y-type molecular sieves prepared by the template agent method can reach above 6.0, the template agent used is expensive, increasing production costs. In addition, the removal of the template agent affects the relative crystallinity of the molecular sieve and causes environmental pollution.

[0005] In post-processing modification methods, high silica-to-alumina ratio (S / A) Y-type molecular sieves can be obtained through acid treatment, hydrothermal calcination, and gas-solid phase modification. While acid treatment or hydrothermal calcination can yield high S / A ratio Y-type molecular sieves, the sieve's framework structure is easily damaged, resulting in a significant decrease in relative crystallinity and a substantial impact on the stability and acidity of the Y-type molecular sieve. Shen Baojian et al. disclosed a method for preparing high S / A ratio Y-type zeolite with abundant secondary pores in CN103539151B. This method first synthesizes FeY molecular sieves, then performs two ammonium exchange processes and hydrothermal calcination, resulting in Y-type zeolite with a higher S / A ratio and more abundant secondary pores. A representative method for obtaining high S / A ratio Y-type molecular sieves through gas-solid phase modification is CN102553630B, which uses in-situ crystallization to prepare NaY / matrix, followed by gas-phase ultrastabilization treatment to prepare a high S / A ratio small-crystal Y-type zeolite catalytic cracking catalyst with high activity, hydrothermal stability, and good selectivity for the target product. In existing methods, when preparing molecular sieves with high silica-to-alumina ratios using post-processing modification, the dealumination process can damage the molecular sieve structure, resulting in significant losses in crystallinity and specific surface area. This is especially true when preparing molecular sieves with silica-to-alumina ratios greater than 30, where it is difficult to retain a high specific surface area. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem of reduced crystallinity and specific surface area when preparing FAU structured molecular sieves with high silicon-to-aluminum ratio in the prior art, and to provide a method for preparing FAU structured molecular sieves that can obtain FAU structured molecular sieves with high silicon-to-aluminum ratio, crystallinity and specific surface area at the same time.

[0007] After conducting in-depth research on the preparation method of FAU structured molecular sieves with high silicon-to-aluminum ratio, the inventors of this invention unexpectedly discovered that by using a combination of fluorosilicic acid and organic acid as a dealuminating agent, the silicon-to-aluminum ratio can be increased without affecting the framework structure of the molecular sieve, thereby obtaining FAU structured molecular sieves with high silicon-to-aluminum ratio, crystallinity, and specific surface area.

[0008] To achieve the above objectives, the present invention provides a method for preparing FAU-structured molecular sieves, the method comprising the following steps:

[0009] (1) Na-FAU molecular sieve is subjected to a first ion exchange with ammonium salt; in the first ion exchange, the weight ratio of Na-FAU molecular sieve to ammonium salt and water on a dry basis is 1:0.4 to 1:5 to 10, and the value of the first ion exchange solution is 3 to 4.5.

[0010] (2) The product obtained in step (1) is filtered, washed, and first calcined to obtain a calcined molecular sieve;

[0011] (3) The monazine molecular sieve obtained in step (2) is subjected to a second ion exchange with ammonium salt, fluorosilicic acid and organic acid; in the second ion exchange, the weight ratio of the monazine molecular sieve to ammonium salt, fluorosilicic acid, organic acid and water on a dry basis is 1:0.01~0.4:0.05~0.2:0.02~0.3:5~10, and the pH value of the second ion exchange solution is 2.5~3.5;

[0012] (4) The product obtained in step (3) is filtered, washed, and calcined a second time to obtain a double-calcined molecular sieve;

[0013] (5) The bis(4) molecular sieve obtained in step (4) is subjected to a third ion exchange with fluorosilicic acid, organic acid and ammonium salt, then filtered and washed to obtain FAU structure molecular sieve product; in the third ion exchange, the weight ratio of bis(4) molecular sieve to ammonium salt, fluorosilicic acid, organic acid and water on a dry basis is 1:0.01~0.4:0.01~0.1:0.01~0.1:5~10, and the pH value of the third ion exchange solution is 1.6~2.6.

[0014] Preferably, the FAU structured molecular sieve is a Y-type molecular sieve.

[0015] Preferably, the ammonium salt is selected from one or more of ammonium sulfate, ammonium chloride, ammonium oxalate, ammonium fluoride, ammonium fluorosilicate, and ammonium fluoroborate.

[0016] Preferably, in step (3) and / or step (5), the organic acid is selected from one or more of ethylenediaminetetraacetic acid, oxalic acid, citric acid, and sulfosalicylic acid.

[0017] Preferably, the pH values ​​of the first ion exchange solution, the second ion exchange solution, and the third ion exchange solution are adjusted using an inorganic acid; more preferably, the inorganic acid is selected from one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0018] Preferably, in step (1), the temperature of the first ion exchange is 70-95°C and the time is 0.5h or more.

[0019] Preferably, in step (2), the conditions for the first calcination include: a temperature of 350 to 650°C, a steam atmosphere of 1 to 100%, and a time of 0.5 hours or more.

[0020] Preferably, in step (3), the temperature of the second ion exchange is 50-90°C and the time is 0.5h or more.

[0021] Preferably, in step (4), the conditions for the second calcination include: a temperature of 350-650°C, a steam atmosphere of 1-100%, and a time of 0.5 hours or more.

[0022] Preferably, in step (5), the temperature of the third ion exchange is 50-90°C and the time is 0.5h or more.

[0023] A second aspect of the present invention provides an FAU-structured molecular sieve prepared using the preparation method of the present invention described above.

[0024] Through the above technical solution, this invention employs a combination of fluorosilicic acid and organic acids to perform two-stage dealumination modification on the molecular sieve, while simultaneously adjusting the pH value of the system with inorganic acids. This allows for better preservation of the framework integrity during dealumination and the construction of an intracrystalline mesoporous structure. Compared with molecular sieves provided by existing technologies, at the same high silica-to-alumina ratio, higher crystallinity, higher specific surface area, and larger mesopore volume are achieved.

[0025] The preparation method of the present invention is simple to operate and can obtain FAU structured molecular sieves with a high silicon-to-aluminum ratio, crystallinity and specific surface area of ​​more than 30. Detailed Implementation

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] The first aspect of this invention provides a method for preparing FAU-structured molecular sieves, the method comprising the following steps:

[0028] (1) Na-FAU molecular sieve is subjected to a first ion exchange with ammonium salt; in the first ion exchange, the weight ratio of Na-FAU molecular sieve to ammonium salt and water on a dry basis is 1:0.4 to 1:5 to 10, and the value of the first ion exchange solution is 3 to 4.5.

[0029] (2) The product obtained in step (1) is filtered, washed, and first calcined to obtain a calcined molecular sieve;

[0030] (3) The monazine molecular sieve obtained in step (2) is subjected to a second ion exchange with fluorosilicic acid, organic acid and ammonium salt; in the second ion exchange, the weight ratio of the monazine molecular sieve to ammonium salt, fluorosilicic acid, organic acid and water on a dry basis is 1:0.01~0.4:0.05~0.2:0.02~0.3:5~10, and the pH value of the second ion exchange solution is 2.5~3.5;

[0031] (4) The product obtained in step (3) is filtered, washed, and calcined a second time to obtain a double-calcined molecular sieve;

[0032] (5) The bis(4) molecular sieve obtained in step (4) is subjected to a third ion exchange with fluorosilicic acid, organic acid and ammonium salt, then filtered and washed to obtain FAU structure molecular sieve product; in the third ion exchange, the weight ratio of bis(4) molecular sieve to ammonium salt, fluorosilicic acid, organic acid and water on a dry basis is 1:0.01~0.4:0.01~0.1:0.01~0.1:5~10, and the pH value of the third ion exchange solution is 1.6~2.6.

[0033] In this invention, the FAU-structured molecular sieve is a Y-type molecular sieve. Na-FAU molecular sieves are not particularly limited and can be prepared using conventional methods or commercially available.

[0034] In this invention, the silicon-to-aluminum ratio of the obtained FAU structure molecular sieve product can reach 30 or more, preferably 33 or more.

[0035] According to the present invention, in step (1), the ammonium salt may be one or more selected from ammonium chloride, ammonium sulfate, ammonium oxalate, ammonium fluoride, ammonium fluorosilicate, and ammonium fluoroborate.

[0036] To further improve the performance of the obtained FAU-structured molecular sieve, preferably, in the first ion exchange, the weight ratio of Na-FAU molecular sieve to ammonium salt and water (on a dry basis) is 1:0.6-0.8:7-9. Preferably, the pH value of the first ion exchange solution is 3.2-3.7. The pH value of the first ion exchange solution is adjusted by an inorganic acid, which can be one or more selected from hydrochloric acid, sulfuric acid, and nitric acid, preferably sulfuric acid.

[0037] Other conditions for the first ion exchange include a temperature of 70–95°C, preferably 80–85°C, and a time of 0.5 h or more, preferably 0.5–2 h.

[0038] According to the present invention, in step (2), the conditions for the first calcination include: a temperature of 350-650°C, a water vapor atmosphere of 1-100%, and a time of 0.5h or more; preferably, a temperature of 500-600°C, a water vapor atmosphere of 90-100%, and a time of 1-5h.

[0039] According to the present invention, in step (3), the organic acid may be one or more selected from ethylenediaminetetraacetic acid, oxalic acid, citric acid, and sulfosalicylic acid; the ammonium salt may be one or more selected from ammonium chloride, ammonium sulfate, ammonium oxalate, ammonium fluoride, ammonium fluorosilicate, and ammonium fluoroborate.

[0040] To further improve the performance of the obtained FAU-structured molecular sieve, preferably, the weight ratio of the bis(2-methyl)-methyl molecular sieve to ammonium salt, fluorosilicic acid, organic acid, and water, on a dry basis, is 1:0.2–0.4:0.05–0.1:0.06–0.15:7–9. Preferably, the pH value of the second ion exchange solution is 2.7–3. The pH value of the second ion exchange solution is adjusted by an inorganic acid, which can be one or more selected from hydrochloric acid, sulfuric acid, and nitric acid, preferably hydrochloric acid or sulfuric acid.

[0041] Other conditions for the second ion exchange include a temperature of 50–90°C, preferably 70–80°C, and a time of 0.5 h or more, preferably 0.5–2 h.

[0042] According to the present invention, in step (4), the conditions for the second calcination include: a temperature of 350-650°C, a steam atmosphere of 1-100% and a time of 0.5h or more; preferably, a temperature of 500-600°C, a steam atmosphere of 90-100% and a time of 1-5h.

[0043] According to the present invention, in step (5), the organic acid may be one or more selected from ethylenediaminetetraacetic acid, oxalic acid, citric acid, and sulfosalicylic acid; the ammonium salt may be one or more selected from ammonium chloride, ammonium sulfate, ammonium oxalate, ammonium fluoride, ammonium fluorosilicate, and ammonium fluoroborate.

[0044] To further improve the performance of the obtained FAU-structured molecular sieve, preferably, the weight ratio of the dibaked molecular sieve to ammonium salt, fluorosilicic acid, organic acid, and water (on a dry basis) is 1:0.2–0.3:0.02–0.05:0.03–0.06:7–9. Preferably, the pH of the third ion exchange solution is 2–2.2. The pH of the third ion exchange solution is adjusted by an inorganic acid, which can be one or more selected from hydrochloric acid, sulfuric acid, and nitric acid, preferably sulfuric acid.

[0045] Other conditions for the third ion exchange include a temperature of 50–90°C, preferably 75–85°C, and a time of 0.5 h or more, preferably 0.5–2 h.

[0046] In this invention, the ammonium salts used in steps (1), (3), and (5) may be the same or different; the organic acids used in steps (3) and (5) may be the same or different.

[0047] Furthermore, in steps (3) and (5), if ammonium fluorosilicate is used as an ammonium salt, the amount of fluorosilicic acid used is calculated as the total of fluorosilicic acid and fluorosilicic acid.

[0048] In this invention, the method of filtering and washing the molecular sieve is not particularly limited, and any conditions commonly used for the treatment of FAU structure molecular sieves can be adopted. The washing temperature is preferably above 50°C, for example, 50 to 70°C.

[0049] In addition, to improve the effectiveness of the first, second, and third ion exchanges, the molecular sieves and the corresponding ion exchange solutions are brought into contact under stirring conditions during the above treatment process.

[0050] A second aspect of the present invention provides an FAU-structured molecular sieve prepared using the preparation method of the present invention described above.

[0051] By employing the method of the present invention described above, FAU-structured molecular sieves possessing high silica-to-alumina ratio, high crystallinity, and high specific surface area can be obtained. Specifically, the FAU-structured molecular sieve of the present invention can achieve a silica-to-alumina ratio of 30 or higher, a crystallinity of 75% or higher, and a specific surface area of ​​760 m². 2 / g or more.

[0052] The present invention will be described in detail below through examples. In the present invention, crystallinity is determined using the standard method of RIPP145-90; n(SiO2) / n(Al2O3), i.e., the silicon-aluminum ratio, is calculated from the content of silicon oxide and aluminum oxide, and the content of silicon oxide and aluminum oxide is determined using the standard method of GB / T 30905-2014; specific surface area is determined using the standard method of GB5816; pore volume is determined using the standard method of GB5816.

[0053] Example 1

[0054] 100g of NaY molecular sieve (produced by Qilu Branch of Catalyst Company, on a dry basis) was mixed with ammonium sulfate and water at a weight ratio of NaY molecular sieve:ammonium sulfate:water = 1:0.7:8. The mixture was stirred until homogeneous, and the pH of the slurry was adjusted to 3.7 with a 20% sulfuric acid solution. The mixture was heated to 80℃ and stirred at a constant temperature for 0.5h, then filtered and washed with water. The resulting product was calcined at 560℃ under a 100% steam atmosphere for 2h to obtain a bis-calcined molecular sieve. The bis-calcined molecular sieve was then mixed with ammonium sulfate, fluorosilicic acid, and oxalic acid at a weight ratio of bis-calcined molecular sieve:ammonium sulfate:fluorosilicic acid:oxalic acid:water = 1:0.4:0.08:0.08:8. The pH was adjusted to 2.9 with sulfuric acid, and the mixture was heated to 80℃ and stirred at a constant temperature for 0.5h. The mixture was filtered and washed with 50℃ washing water. The resulting product was calcined at 560℃ under a 100% steam atmosphere for 1h to obtain a di-calcined molecular sieve. The obtained dibaked molecular sieve was mixed with ammonium sulfate, fluorosilicic acid, and oxalic acid in a weight ratio of dibaked molecular sieve:ammonium sulfate:fluorosilicic acid:oxalic acid:water = 1:0.2:0.05:0.03:8. The pH was adjusted to 2.0 with an inorganic acid, and the mixture was heated to 80℃ and stirred at a constant temperature for 0.5 h. After filtration and washing in 50℃ water, the modified molecular sieve HAY-1 was obtained. The physicochemical properties of the molecular sieve are listed in Table 1.

[0055] Example 2

[0056] 100g of NaY molecular sieve (produced by Qilu Branch of Catalyst Company, on a dry basis) was mixed with ammonium sulfate and water at a weight ratio of NaY molecular sieve:ammonium sulfate:water = 1:0.6:9. The mixture was stirred until homogeneous, and the pH of the slurry was adjusted to 3.5 with a 20% sulfuric acid solution. The mixture was heated to 85℃ and stirred at a constant temperature for 0.5h, then filtered and washed with water. The resulting product was calcined at 500℃ under a 100% steam atmosphere for 2h to obtain a bis-calcined molecular sieve. The bis-calcined molecular sieve was then mixed with ammonium sulfate, fluorosilicic acid, and citric acid at a weight ratio of bis-calcined molecular sieve:ammonium sulfate:fluorosilicic acid:citric acid:water = 1:0.2:0.05:0.12:8. The pH was adjusted to 2.7 with sulfuric acid, and the mixture was heated to 70℃ and stirred at a constant temperature for 0.5h. The mixture was filtered and washed with 50℃ washing water. The resulting product was calcined at 500℃ under a 100% steam atmosphere for 2h to obtain a di-calcined molecular sieve. The obtained dibaked molecular sieve was mixed with ammonium sulfate, fluorosilicic acid, and citric acid in a weight ratio of dibaked molecular sieve:ammonium sulfate:fluorosilicic acid:citric acid:water = 1:0.3:0.02:0.06:8. The pH was adjusted to 2.2 with an inorganic acid, and the mixture was heated to 80℃ and stirred at a constant temperature for 0.5 h. After filtration and washing in 50℃ water, the modified molecular sieve HAY-2 was obtained. The physicochemical properties of the molecular sieve are listed in Table 1.

[0057] Example 3

[0058] 100g of NaY molecular sieve (produced by Qilu Branch of Catalyst Company, on a dry basis) was mixed with ammonium sulfate and water at a weight ratio of NaY molecular sieve:ammonium sulfate:water = 1:0.8:8. The mixture was stirred until homogeneous, and the pH of the slurry was adjusted to 3.2 with a 20% sulfuric acid solution. The mixture was heated to 80℃ and stirred at a constant temperature for 0.5h, then filtered and washed with water. The resulting product was calcined at 560℃ under a 100% steam atmosphere for 1h to obtain a mono-calcined molecular sieve. The mono-calcined molecular sieve was then mixed with ammonium sulfate, fluorosilicic acid, and ethylenediaminetetraacetic acid at a weight ratio of mono-calcined molecular sieve:ammonium sulfate:fluorosilicic acid:ethylenediaminetetraacetic acid:water = 1:0.2:0.09:0.06:8. The pH was adjusted to 2.9 with hydrochloric acid, and the mixture was heated to 80℃ and stirred at a constant temperature for 0.5h. The mixture was filtered and washed with 50℃ washing water. The resulting product was calcined at 600℃ under a 100% steam atmosphere for 1h to obtain a di-calcined molecular sieve. The obtained dibaked molecular sieve was mixed with ammonium sulfate, fluorosilicic acid, and ethylenediaminetetraacetic acid (EDTA) at a weight ratio of dibaked molecular sieve:ammonium sulfate:fluorosilicic acid:EDTA:water = 1:0.2:0.03:0.05:8. The pH was adjusted to 2.1 with an inorganic acid, and the mixture was heated to 80℃ and stirred at a constant temperature for 0.5 h. After filtration and washing with 50℃ water, the modified molecular sieve HAY-3 was obtained. The physicochemical properties of the molecular sieve are listed in Table 1.

[0059] Example 4

[0060] The modified molecular sieve was prepared according to the method of Example 1, except that a calcined molecular sieve was mixed with ammonium sulfate, fluorosilicic acid, and oxalic acid in a weight ratio of calcined molecular sieve:ammonium sulfate:fluorosilicic acid:oxalic acid:water = 1:0.4:0.12:0.05:8 to obtain the modified molecular sieve HAY-4. The physicochemical properties of the molecular sieve are listed in Table 1.

[0061] Example 5

[0062] The modified molecular sieve was prepared according to the method of Example 1, except that a calcined molecular sieve was mixed with ammonium sulfate, fluorosilicic acid, and oxalic acid in a weight ratio of calcined molecular sieve:ammonium sulfate:fluorosilicic acid:oxalic acid:water = 1:0.4:0.18:0.02:8 to obtain the modified molecular sieve HAY-5. The physicochemical properties of the molecular sieve are listed in Table 1.

[0063] Example 6

[0064] The modified molecular sieve was prepared according to the method of Example 1, except that the obtained dibaked molecular sieve was mixed with ammonium sulfate, fluorosilicic acid, and citric acid in a weight ratio of dibaked molecular sieve:ammonium sulfate:fluorosilicic acid:citric acid:water = 1:0.3:0.05:0.03:8; thus obtaining the modified molecular sieve HAY-6. The physicochemical properties of the molecular sieve are listed in Table 1.

[0065] Example 7

[0066] The modified molecular sieve was prepared according to the method of Example 1, except that the obtained dibaked molecular sieve was mixed with ammonium sulfate, fluorosilicic acid, and citric acid in a weight ratio of dibaked molecular sieve:ammonium sulfate:fluorosilicic acid:citric acid:water = 1:0.3:0.08:0.01:8; thus obtaining the modified molecular sieve HAY-7. The physicochemical properties of the molecular sieve are listed in Table 1.

[0067] Comparative Example 1

[0068] 100g of NaY molecular sieve (produced by Qilu Branch of Catalyst Company, on a dry basis) was mixed with ammonium sulfate and water at a weight ratio of NaY molecular sieve:ammonium sulfate:water = 1:0.7:8. The mixture was stirred until homogeneous, heated to 80℃ and stirred at a constant temperature for 0.5h, then filtered and washed with water. The resulting product was calcined at 560℃ under a 100% steam atmosphere for 1h to obtain a bis-calcined molecular sieve. This bis-calcined molecular sieve was then mixed with ammonium sulfate at a weight ratio of bis-calcined molecular sieve:ammonium sulfate:water = 1:0.3:8. The pH was adjusted to 3.0 with sulfuric acid, heated to 80℃ and stirred at a constant temperature for 0.5h, then filtered and washed with 50℃ washing water. The resulting product was calcined at 560℃ under a 100% steam atmosphere for 1h to obtain a di-calcined molecular sieve. The obtained bis(2-calcium) molecular sieve was mixed with fluorosilicic acid at a weight ratio of bis(2-calcium) molecular sieve: fluorosilicic acid: water = 1:0.25:8. The pH was adjusted to 2.0 with sulfuric acid, and the mixture was heated to 80℃ and stirred at a constant temperature for 0.5 h. The mixture was then filtered and washed with washing water at 50℃. The modified molecular sieve DY-1 was obtained. The physicochemical properties of the molecular sieve are listed in Table 1.

[0069] Comparative Example 2

[0070] 100g of NaY molecular sieve (produced by Qilu Branch of Catalyst Company, on a dry basis) was mixed with ammonium sulfate and water at a weight ratio of NaY molecular sieve:ammonium sulfate:water = 1:0.6:9. The mixture was stirred until homogeneous, heated to 85℃ and stirred at a constant temperature for 0.5h, then filtered and washed with water. The resulting product was calcined at 500℃ under a 100% steam atmosphere for 2h to obtain a bis-calcined molecular sieve. This bis-calcined molecular sieve was then mixed with ammonium sulfate at a weight ratio of bis-calcined molecular sieve:ammonium sulfate:water = 1:0.4:8. The pH was adjusted to 3.0 with sulfuric acid, and the mixture was heated to 80℃ and stirred at a constant temperature for 0.5h. The mixture was then filtered and washed with washing water at a temperature ≥50℃. The resulting product was calcined at 550℃ under a 100% steam atmosphere for 2h to obtain a di-calcined molecular sieve. The obtained molecular sieve was mixed with ammonium sulfate, fluorosilicic acid, and oxalic acid in a weight ratio of 1:0.3:0.09:0.12:8 for the di-calcined molecular sieve, ammonium sulfate, fluorosilicic acid, and oxalic acid. The pH was adjusted to 2.8 with sulfuric acid, and the mixture was heated to 80°C and stirred for 0.5 h. The mixture was then filtered and washed with 50°C washing water. The modified molecular sieve DY-2 was obtained. The physicochemical properties of the molecular sieve are listed in Table 1.

[0071] Comparative Example 3

[0072] The modified molecular sieve was prepared according to the method of Example 1, except that only fluorosilicic acid was used in the second ion exchange. Specifically, a calcined molecular sieve was mixed with ammonium sulfate and fluorosilicic acid in a weight ratio of calcined molecular sieve:ammonium sulfate:fluorosilicic acid:water = 1:0.4:0.14:8 to obtain the modified molecular sieve DY-3. The physicochemical properties of the molecular sieve are listed in Table 1.

[0073] Comparative Example 4

[0074] The modified molecular sieve was prepared according to the method of Example 1, except that only oxalic acid was used in the second ion exchange. Specifically, a calcined molecular sieve was mixed with ammonium sulfate and oxalic acid in a weight ratio of calcined molecular sieve:ammonium sulfate:oxalic acid:water = 1:0.4:0.08:8 to obtain the modified molecular sieve DY-4. The physicochemical properties of the molecular sieve are listed in Table 1.

[0075] Table 1

[0076]

[0077] Table 1 (continued)

[0078]

[0079] As can be seen from the results in Table 1, the molecular sieves obtained by using the embodiments of the present invention all have a silicon-to-aluminum ratio of over 30, high crystallinity, abundant mesopores, and a large total specific surface area, which are significantly better than the molecular sieves obtained by various different preparation methods used in the comparative examples.

[0080] Furthermore, a comparison of Examples 1 and 6 with Examples 4-5 and 7 shows that by making the weight ratio of "mono-baked molecular sieve to ammonium salt, fluorosilicic acid, organic acid, and water on a dry basis 1:0.2-0.4:0.05-0.1:0.06-0.15:7-9" and "the weight ratio of di-baked molecular sieve to ammonium salt, fluorosilicic acid, organic acid, and water on a dry basis 1:0.2-0.3:0.02-0.05:0.03-0.06:7-9", the molecular sieve can have a higher specific surface area and crystallinity while ensuring a silicon-to-aluminum ratio of over 30.

[0081] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A process for the preparation of a FAU structure molecular sieve, characterized by, The preparation method comprises the following steps: (1) performing first ion exchange on the Na-FAU molecular sieve and an ammonium salt; in the first ion exchange, the weight ratio of the Na-FAU molecular sieve to the ammonium salt and water is 1:0.4-1:5-10 on a dry basis, and the pH value of the first ion exchange solution is 3-4.5; (2) filtering, washing and first calcining the product obtained in step (1) to obtain a calcined molecular sieve; (3) performing second ion exchange on the calcined molecular sieve obtained in step (2) and an ammonium salt, fluosilicic acid and an organic acid; in the second ion exchange, the weight ratio of the calcined molecular sieve to the ammonium salt, fluosilicic acid, organic acid and water is 1:0.01-0.4:0.05-0.2:0.02-0.3:5-10 on a dry basis, and the pH value of the second ion exchange solution is 2.5-3.5; (4) filtering, washing and second calcining the product obtained in step (3) to obtain a second calcined molecular sieve; (5) performing third ion exchange on the second calcined molecular sieve obtained in step (4) with fluosilicic acid, an organic acid and an ammonium salt, and then filtering and washing to obtain a FAU structure molecular sieve product; in the third ion exchange, the weight ratio of the second calcined molecular sieve to the ammonium salt, fluosilicic acid, organic acid and water is 1:0.01-0.4:0.01-0.1:0.01-0.1:5-10 on a dry basis, and the pH value of the third ion exchange solution is 1.6-2.

6.

2. The production method according to claim 1, wherein, The FAU structure molecular sieve is a Y-type molecular sieve.

3. The production method according to claim 1, wherein The ammonium salt is selected from one or more of ammonium chloride, ammonium sulfate, ammonium oxalate, ammonium fluoride, ammonium fluosilicate and ammonium fluoroborate.

4. The production method according to any one of claims 1 to 3, wherein The organic acid is selected from one or more of ethylenediaminetetraacetic acid, oxalic acid, citric acid and sulfosalicylic acid.

5. The production method according to any one of claims 1 to 3, wherein An inorganic acid is used to adjust the pH value of the first ion exchange solution, the second ion exchange solution and the third ion exchange solution.

6. The production method according to claim 5, wherein The inorganic acid is selected from one or more of hydrochloric acid, sulfuric acid and nitric acid.

7. The production method according to any one of claims 1 to 3, wherein In step (2), the first calcining conditions include a temperature of 350-650 DEG C, 1-100% water vapor atmosphere and a time of 0.5 h or more.

8. The production method according to claim 7, wherein In step (4), the second calcining conditions include a temperature of 350-650 DEG C, 1-100% water vapor atmosphere and a time of 0.5 h or more.

9. The method of making according to any one of claims 1-3, wherein, In step (1), the first ion exchange temperature is 70-95 DEG C, and the time is 0.5 h or more.

10. The method of making according to any one of claims 1-3, wherein, In step (3), the second ion exchange temperature is 50-90 DEG C, and the time is 0.5 h or more.

11. The method of making according to any one of claims 1-3, wherein, In step (5), the third ion exchange temperature is 50-90 DEG C, and the time is 0.5 h or more.

12. A FAU structure molecular sieve prepared by the preparation method in any one of claims 1-11.

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