Dealumination method of Beta molecular sieve

Abstract

The invention relates to a dealumination method of a Beta molecular sieve, and belongs to the technical field of molecular sieve post-treatment. Comprising the following steps: S1, adding a dispersion protective agent and a raw material Beta molecular sieve into neutral water, quickly stirring uniformly, and emulsifying for a period of time to obtain emulsified slurry; s2, adding the emulsified slurry in the step S1 into an acid treatment agent, heating to 60-120 DEG C, adding a complexing agent, and stirring at constant temperature for dealumination for 1-10 hours; and S3, after dealumination is completed, carrying out suction filtration while hot, washing with hot water for multiple times, drying a filter cake at 80-120 DEG C for 2-5 hours, then heating to 450-550 DEG C, and roasting for 1-5 hours to obtain the Beta molecular sieve product with high crystallinity and high silica-alumina ratio. The method has the advantages of simple operation steps, strong dealumination capability, no damage to the molecular sieve skeleton structure, high crystallinity, and promotion of the wide application of the high silica-alumina ratio Beta molecular sieve.

Description

Technical Field

[0001] The present invention belongs to the technical field of post-treatment of molecular sieves, and particularly relates to a method for acid treatment and dealumination of Beta zeolite molecular sieve. Background Art

[0002] Beta zeolite has a three-dimensional dodecasil 12-ring large pore channel structure and a larger effective micropore volume. Its channels are an open system without cages, and the pore diameter is between 0.75 - 0.8 and 1.2 - 1.3 nm. This structure not only facilitates the diffusion of reactant molecules and product molecules, making it have high catalytic stability, but also maintains its good selectivity for reactant molecules and reaction intermediate molecules. It has characteristics such as acid resistance and good anti-coking property, and good selective catalytic performance. Therefore, Beta zeolite has many unique properties and has very important application prospects in the fields of flue gas reduction and petrochemical industry.

[0003] The silica-alumina ratio (SiO2 / Al2O3) is an important parameter of zeolite molecular sieves, which affects the hydrothermal stability, adsorption performance, acidity, catalytic activity, etc. of molecular sieves. High-silica Beta zeolite has more obvious hydrophobicity and better hydrothermal stability in catalysis, so its catalytic life is relatively longer than that of conventional Beta zeolite. The silica-alumina ratio of Beta zeolite prepared by the conventional hydrothermal synthesis method is generally less than or equal to 50, and it is difficult to synthesize Beta zeolite with a higher silica-alumina ratio.

[0004] In order to obtain high-silica Beta zeolite, industrial production tends to first synthesize low-silica Beta zeolite and then obtain high-silica Beta zeolite by post-treatment methods. The commonly used post-treatment methods mainly have two types: steam treatment method and acid treatment method. The treatment temperature of the steam treatment method is 500 - 600 °C, and the dealumination is limited to aluminum-rich molecular sieves, which easily leads to the generation and deposition of amorphous substances, causing the blockage of micropores and mesopores. Moreover, this method has a high cost, and the increase in the silica-alumina ratio is limited, making it difficult to obtain Beta zeolite with a higher silica-alumina ratio. The acid treatment method uses conventional acids to react with aluminum in the zeolite molecular sieve to remove aluminum in the zeolite. However, in the actual dealumination process, while increasing the silica-alumina ratio of the molecular sieve, the silicon hydroxyl defect sites after dealumination damage the crystal structure, resulting in a significant reduction in the relative crystallinity of the molecular sieve, and even framework collapse, thereby leading to a decrease in catalytic activity and catalyst stability, which is not conducive to its application in actual production.

[0005] The currently used treatment methods all obtain high-silica Beta zeolite at the expense of the relative crystallinity of the molecular sieve. Thus, there is an insoluble contradiction between increasing the silica-alumina ratio of the catalyst and maintaining the relative crystallinity of the catalyst, and it is very difficult to simultaneously consider these two problems in the process of conventional post-treatment modification of molecular sieves. Summary of the Invention

[0006] According to the background problem, the problem to be solved by the present invention is:

[0007] The current treatment methods usually sacrifice the relative crystallinity of the molecular sieve to obtain a high silicon-aluminum ratio Beta molecular sieve. It is difficult for the conventional molecular sieve post-treatment modification process to take both issues into consideration at the same time.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A Beta molecular sieve dealumination method comprises the following steps:

[0010] S1: Add the dispersing protective agent and the raw material Beta molecular sieve into neutral water, stir quickly and evenly, and emulsify for a period of time to obtain an emulsified slurry;

[0011] The dispersing protective agent is polyacrylic acid; wherein the mass percentage of the dispersing protective agent to the Beta molecular sieve is 1%-10%;

[0012] The emulsification time is 0.5-10min;

[0013] S2: adding the emulsified slurry in step S1 to the acid treatment agent, heating to 60-120° C., adding a complexing agent, and stirring at a constant temperature to dealuminate for 1-10 hours;

[0014] S3: After the dealumination is completed, the filter is filtered while hot and washed with hot water for multiple times. The filter cake is dried at 80-120°C for 2-10 hours, and then heated to 450-550°C and calcined for 1-5 hours to obtain a Beta molecular sieve product with high relative crystallinity and high silicon-aluminum ratio.

[0015] Preferably, the Beta molecular sieve raw material SiO2 / Al2O3 is 15~60.

[0016] Preferably, the molecular sieve accounts for 20% to 40% by mass in the emulsified slurry.

[0017] In step S1, the dispersing protective agent is polyacrylic acid; it can not only protect the molecular sieve framework from being destroyed, but also improve the dealumination efficiency by dispersing the molecular sieve agglomerates, and can be completely burned out at high temperature without remaining in the molecular sieve to form impurities or residues to block the pores.

[0018] Emulsification can quickly disperse the protective agent and molecular sieve evenly, open the molecular sieve agglomeration state to the greatest extent, increase the contact active sites between the molecular sieve grains and the acid treatment agent, and greatly improve the dealumination efficiency. If the time is too short, the dispersion effect will not be achieved, and if the time is too long, the molecular sieve structure will be destroyed.

[0019] Preferably, the acid treatment agent is one of hydrochloric acid or sulfuric acid, and the concentration is 1-3.0 mol / L.

[0020] Preferably, the complexing agent is one or more of citric acid, oxalic acid, malonic acid, tartaric acid, ethylenediaminetetraacetic acid, and salicylic acid, and the mass ratio of the complexing agent to the molecular sieve is 1:5 to 50.

[0021] Preferably, the mass ratio of Beta zeolite to the acid treatment agent is 1:1.5 to 6.0.

[0022] In step S2, the complexing agent can quickly react with the removed aluminum to form a stable cyclic aluminum-organic acid complex, promoting the dealumination reaction; at the same time, it provides some hydrogen ions to cooperate with the acid treatment agent for dealumination.

[0023] Preferably, the hot water washing temperature is 50 to 80 °C. This washing temperature can prevent the molecular sieve from re-adsorbing non-framework aluminum during the washing process after dealumination, affecting the dealumination rate of the product.

[0024] In step S3, the calcination process can remove the residues during dealumination, the complexing agent that has not been thoroughly washed, and organic substances such as the added dispersion protectant. The remaining Al-O and Si-O in the framework simultaneously undergo structural rearrangement, and the structure of the remaining framework aluminum is rearranged, and the relative crystallinity is restored.

[0025] Preferably, the silicon-aluminum ratio (SiO2 / Al2O3) of the Beta zeolite after dealumination is ≥100, and the relative crystallinity is ≥80%. The present invention can adjust the relevant process according to the target requirement of SiO2 / Al2O3, or can also achieve a Beta zeolite with a high silicon-aluminum ratio close to pure silicon through secondary or multiple repetitions.

[0026] The beneficial effects of the present invention are as follows:

[0027] (1) Through the protection and emulsification dispersion of the dispersion protectant, the present invention performs dealumination treatment on Beta zeolite under the synergistic action of the acid treatment agent and the complexing agent, and after calcination and framework repair, a Beta zeolite with SiO2 / Al2O3 ≥ 100 and relative crystallinity ≥ 80% is synthesized, solving the contradiction that high silicon-aluminum ratio and high relative crystallinity cannot be achieved simultaneously in the post-treatment method of Beta zeolite, and avoiding the problems of molecular sieve framework collapse and non-framework aluminum deposition.

[0028] (2) The method of the present invention can perform secondary repeated treatment on Beta zeolite and iterate Beta zeolite to nearly all-silicon level.

[0029] (3) The present invention effectively dredges the micropore channels and simultaneously introduces a mesoporous structure with good connectivity, to a certain extent improving the diffusion and mass transfer performance of reactant and product molecules.

[0030] (4) The operation steps adopted by the present invention are simple, with strong dealumination ability, without damaging the molecular sieve framework structure, high relative crystallinity, and low cost, which are of great significance in the actual chemical production field and promote the wide application of high-silica-alumina ratio Beta zeolites. Description of the Drawings

[0031] Figure 1 It is a comparative XRD diagram before and after dealumination of Example 1 of the present invention.

[0032] Figure 2 It is a comparative BET diagram before and after dealumination of Example 1 of the present invention. Detailed Embodiments

[0033] In the following examples, the Beta zeolites synthesized by X-ray powder diffraction method are used for phase analysis, and the relative crystallinity of the products is calculated. For the calculation of relative crystallinity, two characteristic diffraction peaks between 21° and 23° are selected. The ratio of the sum of the areas of these two peaks of the sample to be measured to the sum of the areas of these two peaks of the Beta zeolite standard sample is the relative crystallinity of the sample. The SiO2 / Al2O3 of the sample is measured using a Rigaku ZSX X-ray fluorescence spectrometer made in Japan.

[0034] Example 1

[0035] 10 g of a dispersion protecting agent and 300 g of Beta zeolite with a silica-alumina ratio of 50 and a relative crystallinity of 78% are added to 600 g of water, and stirred rapidly and evenly. The obtained slurry is emulsified for 2 min; the obtained slurry is added to 800 g of 2 mol / L sulfuric acid, heated to 100 °C, 50 g of oxalic acid is added, and dealumination is carried out by stirring at a constant temperature of 100 °C for 3 hours. Then, it is filtered while it is hot, washed three times with hot water at 60 °C, the filter cake is dried at 100 °C for 3 hours, and calcined at 500 °C for 3 hours; the obtained product zeolite has a relative crystallinity of 85% and SiO2 / Al2O3 = 635.

[0036] Example 2

[0037] 5 g of a dispersion protecting agent and 300 g of Beta zeolite with SiO2 / Al2O3 = 15 and a relative crystallinity of 79% are added to 1195 g of water, and stirred rapidly and evenly. The obtained slurry is emulsified for 10 min; the obtained slurry is added to 600 g of 2 mol / L hydrochloric acid, heated to 60 °C, 30 g of citric acid and 30 g of ethylenediaminetetraacetic acid are added, and dealumination is carried out by stirring at a constant temperature of 60 °C for 10 hours. Then, it is filtered while it is hot, washed three times with hot water at 50 °C, the filter cake is dried at 80 °C for 10 hours, and calcined at 520 °C for 2 hours; the obtained product zeolite has a relative crystallinity of 82% and SiO2 / Al2O3 = 479.

[0038] Example 3

[0039] 10 g of a dispersion protecting agent and 300 g of Beta zeolite with SiO2 / Al2O3 = 30 and a relative crystallinity of 79% were added to 600 g of water, and the mixture was rapidly stirred evenly. The resulting slurry was emulsified for 3 min. The obtained slurry was added to 1800 g of 3.0 mol / L sulfuric acid, heated to 120 °C, 6 g of oxalic acid was added, and the mixture was stirred at a constant temperature of 120 °C for 1 hour for dealumination. Then, it was filtered while it was hot, washed three times with 80 °C hot water, the filter cake was dried at 100 °C for 3 hours, and calcined at 550 °C for 1 hour; the obtained product zeolite had a relative crystallinity of 83% and SiO2 / Al2O3 = 686.

[0040] Example 4

[0041] 3 g of a dispersion protecting agent and 300 g of Beta zeolite with SiO2 / Al2O3 = 60 and a relative crystallinity of 78% were added to 447 g of water, and the mixture was rapidly stirred evenly. The resulting slurry was emulsified for 0.5 min. The obtained slurry was added to 450 g of 1.0 mol / L sulfuric acid, heated to 80 °C, 40 g of tartaric acid and 10 g of salicylic acid were added, and the mixture was stirred at a constant temperature of 80 °C for 3 hours for dealumination. Then, it was filtered while it was hot, washed three times with 65 °C hot water, the filter cake was dried at 120 °C for 2 hours, and calcined at 500 °C for 3 hours; the obtained product zeolite had a relative crystallinity of 85% and SiO2 / Al2O3 = 512.

[0042] Example 5

[0043] Secondary dealumination was carried out on the basis of Example 1.

[0044] 10 g of a dispersion protecting agent and 300 g of Beta zeolite with SiO2 / Al2O3 = 635 and a relative crystallinity of 85% were added to 600 g of water, and the mixture was rapidly stirred evenly. The resulting slurry was emulsified for 2 min. The obtained slurry was added to 800 g of 2 mol / L sulfuric acid, heated to 100 °C, 20 g of oxalic acid and 20 g of malonic acid were added, and the mixture was stirred at a constant temperature of 100 °C for 3 hours for dealumination. Then, it was filtered while it was hot, washed three times with 70 °C hot water, the filter cake was dried at 100 °C for 3 hours, and calcined at 450 °C for 5 hours; the obtained product zeolite had a relative crystallinity of 87% and SiO2 / Al2O3 = 1728.

[0045] Comparative Example 1

[0046] The dispersion protecting agent was not added in Comparative Example 1.

[0047] 300 g of Beta zeolite with SiO2 / Al2O3 = 50 and a relative crystallinity of 78% was added to 600 g of water and stirred rapidly until homogeneous. The resulting slurry was emulsified for 2 min. The obtained slurry was added to 800 g of 2 mol / L sulfuric acid, heated to 95 °C, 50 g of oxalic acid was added, and the mixture was stirred at 95 °C for 3 h for dealumination under constant temperature. Then, it was filtered while it was hot, washed three times with 70 °C hot water, the filter cake was dried at 100 °C for 3 h, and calcined at 500 °C for 3 h; the obtained product zeolite had a relative crystallinity of 68% and SiO2 / Al2O3 = 418. The zeolite framework collapsed.

[0048] Comparative Example 2

[0049] In Comparative Example 2, emulsification and dispersion were not used, and dealumination was directly carried out by acid leaching.

[0050] 10 g of a dispersion protecting agent and 300 g of Beta zeolite with SiO2 / Al2O3 = 50 and a relative crystallinity of 78% were added to 600 g of water and stirred until homogeneous. The obtained slurry was added to 600 g of 2 mol / L sulfuric acid, heated to 100 °C, 50 g of oxalic acid was added, and the mixture was stirred at 100 °C for 3 h for dealumination under constant temperature. Then, it was filtered while it was hot, washed three times with 60 °C hot water, the filter cake was dried at 100 °C for 3 h, and calcined at 500 °C for 3 h; the obtained product zeolite had a relative crystallinity of 73% and SiO2 / Al2O3 = 535.

[0051] Comparative Example 3

[0052] In Comparative Example 3, a complexing agent was not used, and dealumination was directly carried out by acid leaching.

[0053] 10 g of a dispersion protecting agent and 300 g of Beta zeolite with SiO2 / Al2O3 = 50 and a relative crystallinity of 78% were added to 600 g of water and stirred rapidly until homogeneous. The resulting slurry was emulsified for 2 min. The obtained slurry was added to 800 g of 2 mol / L sulfuric acid, heated to 95 °C, and directly stirred at a constant temperature for 3 h for dealumination. Then, it was filtered while it was hot, washed three times with 65 °C hot water, the filter cake was dried at 100 °C for 3 h, and calcined at 500 °C for 3 h; the obtained product zeolite had a relative crystallinity of 70% and SiO2 / Al2O3 = 325.

[0054] The embodiments described in the present invention are only descriptions of the preferred embodiments of the present invention and should not be regarded as limitations of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope of the present invention. The protection scope of the present invention should be subject to the scope defined by the claims.

[0055]

[0056] As can be seen from the results in Table 1, in Example 5, the SiO2 / Al2O3 of the product in Example 1 was increased from 635 to 1728 by means of secondary dealumination, and the relative crystallinity remained ≥85%, indicating that the process of the present invention has repeatability. Further, it shows that the process method of the present invention can achieve a high-silica zeolite with a silica-alumina ratio close to pure silicon through iteration, broadening the application of high-silica Beta zeolite in the fields of hydrophobicity, catalysis, etc.

[0057] The dispersion protectant polyacrylic acid prevents the structural collapse caused by acid etching. Comparative Example 1 shows that when there is no protectant, the relative crystallinity drops from 78% to 68%, and the product shows framework collapse. Emulsification makes the zeolite evenly dispersed, exposing more active sites. In Comparative Example 2, when there is no emulsification, the dealumination efficiency decreases (SiO2 / Al2O3 is only 535), and the relative crystallinity loses 5%, indicating that the acid contact is insufficient in the agglomerated state. The complexing agent forms a stable complex with Al³⁺, promoting the forward progress of the dealumination reaction. In Comparative Example 3, when there is no complexing agent, SiO2 / Al2O3 is only 325, proving that the dealumination ability of single acid treatment is limited.

[0058] It can be Figure 1 seen that before and after dealumination, the XRD patterns have obvious diffraction peaks of Beta zeolite crystals at 2θ of 7.8° and 22.4°, indicating that the product has a good crystalline state and the zeolite framework is not damaged. After dealumination, the angle at 22.4° is sharper and the relative crystallinity is higher. As can be seen from the BET comparison diagram in Figure 2, after dealumination, the BET adsorption-desorption isotherm shows a more obvious hysteresis loop relative to that before dealumination at P / P0 greater than 0.4, indicating that a well-connected mesoporous structure appears in the sample, improving the diffusion and mass transfer performance of reactant and product molecules.

[0059] The present invention can be implemented in many different forms, and the present invention should not be construed as limited to the specific embodiments set forth herein. On the contrary, these embodiments are provided to explain the principles of the present invention and its practical applications, so that other technical personnel in the art can understand various embodiments of the present invention and various modifications suitable for specific intended applications.

Claims

1. A method for dealuminating Beta zeolite, characterized in that, The following steps are involved: S1: Add the dispersing protective agent and the raw material Beta molecular sieve into neutral water, stir quickly and evenly, and emulsify for a period of time to obtain an emulsified slurry; The dispersing protective agent is polyacrylic acid; wherein the mass percentage of the dispersing protective agent to the Beta molecular sieve is 1%-10%; The emulsification time is 0.5-10min; S2: adding the emulsified slurry in step S1 to the acid treatment agent, heating to 60-120° C., adding a complexing agent, and stirring at a constant temperature to dealuminate for 1-10 hours; S3: After the dealumination is completed, the filter is filtered while hot and washed with hot water for multiple times. The filter cake is dried at 80-120°C for 2-10 hours, and then heated to 450-550°C and calcined for 1-5 hours to obtain a Beta molecular sieve product with high crystallinity and high silicon-aluminum ratio.

2. The dealumination method of Beta zeolite according to claim 1, wherein, The Beta molecular sieve raw material SiO2 / Al2O3 is 15~60.

3. A method for dealuminating Beta zeolite according to claim 1, characterized in that, The molecular sieve mass accounts for 20% to 40% in the emulsified slurry.

4. A method for dealuminating Beta zeolite according to claim 1, characterized in that, The acid treatment agent is one of hydrochloric acid or sulfuric acid, and the concentration is 1-3.0 mol / L.

5. A method for dealuminating Beta zeolite according to claim 1, characterized in that, The complexing agent is one or more of citric acid, oxalic acid, malonic acid, tartaric acid, ethylenediaminetetraacetic acid and salicylic acid, and the mass ratio of the complexing agent to the molecular sieve is 1:5-50.

6. A method for dealuminating Beta zeolite according to claim 1, characterized in that, The mass ratio of Beta molecular sieve to acid treatment agent is 1:1.5~6.

0.

7. A method for dealuminating Beta zeolite according to claim 1, characterized in that, The hot water washing temperature is 50-80°C.

8. A method for dealuminating Beta zeolite according to claim 1, characterized in that, The Beta molecular sieve has a silicon-to-aluminum ratio (SiO2 / Al2O3) of ≥100 and a crystallinity of ≥80% after dealumination.

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