A method for dealuminating a beta molecular sieve

Abstract

The present application relates to a kind of Beta molecular sieve dealuminization method, belong to molecular sieve post-processing technical field.It includes the following steps:S1: dispersing protective agent, raw material Beta molecular sieve is added in neutral water, is stirred uniformly quickly, emulsified for a period of time, and emulsified slurry is obtained;S2: emulsified slurry in step S1 is added to acid treatment agent, is heated to 60~120 ℃, and complexing agent is added, and dealuminization is stirred for 1~10 hours;S3: after dealuminization is completed, hot suction filtration is carried out, and hot water is washed multiple times, and filter cake is dried at 80~120 ℃ for 2~5 hours, then is heated to 450~550 ℃ and calcined for 1~5 hours, and high crystallinity high silica-alumina ratio Beta molecular sieve product is obtained.The present application is simple in operation step, strong in dealuminization capacity, does not damage molecular sieve skeleton structure, high crystallinity, and promotes the wide application of high silica-alumina ratio Beta molecular sieve.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of molecular sieve post-treatment, and particularly relates to a method for acid treatment and dealumination of Beta molecular sieve. BACKGROUND

[0002] Beta zeolite has a three-dimensional 12-membered ring large pore channel structure and a larger effective micropore volume, the channel thereof is an open system without a cage structure, the channel diameter is between 0.75-0.8 and 1.2-1.3 nm, the structure is not only beneficial to the diffusion of reactant molecules and product molecules and makes the Beta zeolite have higher catalytic stability, but also does not lose the selectivity to the reactant molecules and reaction intermediate product molecules. The Beta zeolite has good acid resistance and coking resistance and better selective catalytic performance. Therefore, the Beta zeolite has many unique performances and has a very important application prospect in the fields of flue gas harm reduction and petroleum chemical industry.

[0003] The silicon-aluminum ratio (SiO2 / Al2O3) is an important parameter of zeolite molecular sieve, and affects the hydrothermal stability, adsorption performance, acidity and catalytic activity of the molecular sieve. The high-silicon Beta molecular sieve has more obvious hydrophobicity and better hydrothermal stability in catalysis, and thus has a longer catalytic life compared with the conventional Beta molecular sieve. The silicon-aluminum ratio of the Beta molecular sieve prepared by the conventional hydrothermal synthesis method is generally less than or equal to 50, and it is more difficult to synthesize a Beta molecular sieve with a higher silicon-aluminum ratio.

[0004] In order to obtain a high-silicon Beta molecular sieve, industrial production tends to first synthesize a low-silicon Beta molecular sieve, and then obtain a high-silicon Beta molecular sieve by a post-treatment method. There are two common post-treatment methods: a water vapor treatment method and an acid treatment method. The water vapor treatment method has a treatment temperature of 500-600 DEG C, and the dealumination is limited to aluminum-rich molecular sieves, which is easy to cause the generation and deposition of amorphous substances, causing the blockage of micropores and mesopores. Moreover, the method has a high cost, a limited silicon-aluminum ratio improvement range, and is difficult to achieve a Beta molecular sieve with a higher silicon-aluminum ratio. The acid treatment method is to react a conventional acid with aluminum in the zeolite molecular sieve to remove aluminum in the zeolite. However, in the actual dealumination process, while improving the silicon-aluminum ratio of the molecular sieve, the silicon hydroxyl defect site destroys the crystal structure of the molecular sieve, resulting in a significant reduction of the relative crystallinity of the molecular sieve, even the collapse of the framework, and thus leading to the reduction of catalytic activity and catalyst stability, which is not conducive to the application in actual production.

[0005] The current treatment method is to obtain a high-silicon Beta molecular sieve at the expense of the relative crystallinity of the molecular sieve. Thus, there is an unsolvable contradiction between improving the silicon-aluminum ratio of the catalyst and maintaining the relative crystallinity of the catalyst, and the conventional molecular sieve post-treatment modification process is difficult to simultaneously consider both problems. SUMMARY

[0006] According to the problems described in the background, the problem to be solved by the present application is:

[0007] The current treatment method generally obtains high-silicon aluminum ratio Beta molecular sieve at the expense of sacrificing the relative crystallinity of the molecular sieve. The conventional post-treatment modification process of the molecular sieve is difficult to simultaneously consider both problems.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

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

[0010] S1: adding a dispersing protective agent and a raw Beta molecular sieve into neutral water, uniformly stirring quickly, emulsifying for a period of time, and obtaining an emulsified slurry;

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

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

[0013] S2: adding the emulsified slurry in step S1 into an acid treatment agent, heating to 60-120℃, adding a complexing agent, and constant-temperature stirring dealumination for 1-10 hours;

[0014] S3: after the dealumination is completed, hot suction filtration is performed, and hot water is used for multiple times of washing, the filter cake is dried at 80-120℃ for 2-10 hours, and then heating to 450-550℃ for calcination for 1-5 hours, to obtain a Beta molecular sieve product with high relative crystallinity and high silicon aluminum ratio.

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

[0016] Preferably, the mass percentage of the molecular sieve in the emulsified slurry is 20%-40%.

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

[0018] Emulsification can uniformly disperse the protective agent and the molecular sieve, maximally open the agglomeration state of the molecular sieve, improve the active sites of the molecular sieve crystal grains and the acid treatment agent, and greatly improve the dealumination efficiency. If the time is too short, the dispersion effect cannot be achieved, and if the time is too long, the structure of the molecular sieve will be damaged.

[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 1:5-50.

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

[0022] In step S2, the complexing agent can quickly form a stable cyclic aluminum-organic acid complex with the removed aluminum, promote the progress of the dealuminization reaction, and at the same time provide part of the hydrogen ions to cooperate with the acid treatment agent to dealuminize.

[0023] Preferably, the hot water washing temperature is 50-80℃. This water washing temperature can avoid the re-adsorption of non-framework aluminum during the water washing process after the dealuminization of the molecular sieve, and affect the dealuminization rate of the product.

[0024] In step S3, the calcination process can remove the residual fragments, un-washed complexing agent and added dispersing protective agent and other organic matters in the dealuminization process, and the remaining Al-O and Si-O in the framework simultaneously undergo structural rearrangement, and the remaining framework aluminum structure is rearranged, and the relative crystallinity is repaired.

[0025] Preferably, the SiO2 / Al2O3 of the Beta molecular sieve after dealuminization is ≥100, and the relative crystallinity is ≥80%. The present application can adjust the related process according to the target SiO2 / Al2O3, and also can reach the high SiO2 / Al2O3 of the Beta molecular sieve close to pure silicon through secondary or multiple iterations.

[0026] The beneficial effects of the present application are:

[0027] (1) The present application can synthesize the Beta molecular sieve with SiO2 / Al2O3≥100 and relative crystallinity≥80% by protecting and emulsifying and dispersing the dispersing protective agent, dealuminizing the Beta molecular sieve through the synergistic effect of the acid treatment agent and the complexing agent, and repairing the framework through calcination, solving the contradiction between high SiO2 / Al2O3 and high relative crystallinity in the post-processing method of the Beta molecular sieve, and avoiding the problems of framework collapse and non-framework aluminum deposition.

[0028] (2) The present application can dealuminize the Beta molecular sieve twice to iterate the Beta molecular sieve to the level close to pure silicon.

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

[0030] (4) The operation steps adopted by the present application are simple, the dealumination capacity is strong, the molecular sieve skeleton structure is not damaged, the relative crystallinity is high, the cost is low, and it has important significance in the field of actual chemical production, and promotes the wide application of high-silicon-aluminum ratio Beta molecular sieve. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The XRD comparison chart before and after dealumination of Example 1 of the present application.

[0032] Figure 2 The BET comparison chart before and after dealumination of Example 1 of the present application. DETAILED DESCRIPTION

[0033] In each of the following examples, the synthesized Beta molecular sieve is subjected to phase analysis by X-ray powder diffraction method, and the relative crystallinity of the product is calculated. The relative crystallinity is calculated by selecting two characteristic diffraction peaks between 21° and 23°, and the ratio of the sum of the areas of the two peaks of the sample to be tested to the sum of the areas of the two peaks of the Beta molecular sieve standard sample is the relative crystallinity of the sample. The SiO2 / Al2O3 of the sample is determined by using a Japanese Rigaku ZS X-ray fluorescence spectrometer.

[0034] Example 1

[0035] 10g dispersing protective agent and 300g Beta molecular sieve with a silicon-aluminum ratio of 50 and a relative crystallinity of 78% were added to 600g water, and quickly stirred to be uniform, and the obtained slurry was emulsified for 2min; the obtained slurry was added to 800g 2mol / L sulfuric acid, heated to 100℃, 50g oxalic acid was added, and dealumination was carried out at 100℃ for 3h, then hot filtration was carried out, washed with 60℃ hot water for three times, the filter cake was dried at 100℃ for 3h, and calcined at 500℃ for 3h; the product molecular sieve was obtained, the relative crystallinity was 85%, and SiO2 / Al2O3=635.

[0036] Example 2

[0037] 5g dispersing protective agent and 300g Beta molecular sieve with SiO2 / Al2O3=15 and a relative crystallinity of 79% were added to 1195g water, and quickly stirred to be uniform, and the obtained slurry was emulsified for 10min; the obtained slurry was added to 600g 2mol / L hydrochloric acid, heated to 60℃, 30g citric acid and 30g ethylenediaminetetraacetic acid were added, and dealumination was carried out at 60℃ for 10h, then hot filtration was carried out, washed with 50℃ hot water for three times, the filter cake was dried at 80℃ for 10h, and calcined at 520℃ for 2h; the product molecular sieve was obtained, the relative crystallinity was 82%, and SiO2 / Al2O3=479.

[0038] Example 3

[0039] Beta zeolite with SiO2 / Al2O3=30 and relative crystallinity of 79% was added into 600 g water, and stirred rapidly to be uniform, and the obtained slurry was emulsified for 3 min; the obtained slurry was added into 1800 g 3.0 mol / L sulfuric acid, heated to 120°C, 6 g oxalic acid was added, and aluminum was removed at 120°C for 1 h, then filtered while hot, washed with 80°C hot water for 3 times, the filter cake was dried at 100°C for 3 h, and calcined at 550°C for 1 h; the product zeolite was obtained, with relative crystallinity of 83% and SiO2 / Al2O3=686.

[0040] Example 4

[0041] Beta zeolite with SiO2 / Al2O3=60 and relative crystallinity of 78% was added into 447 g water, and stirred rapidly to be uniform, and the obtained slurry was emulsified for 0.5 min; the obtained slurry was added into 450 g 1.0 mol / L sulfuric acid, heated to 80°C, 40 g tartaric acid and 10 g salicylic acid were added, and aluminum was removed at 80°C for 3 h, then filtered while hot, washed with 65°C hot water for 3 times, the filter cake was dried at 120°C for 2 h, and calcined at 500°C for 3 h; the product zeolite was obtained, with relative crystallinity of 85% and SiO2 / Al2O3=512.

[0042] Example 5

[0043] Secondary aluminum removal was carried out based on Example 1.

[0044] Beta zeolite with SiO2 / Al2O3=635 and relative crystallinity of 85% was added into 600 g water, and stirred rapidly to be uniform, and the obtained slurry was emulsified for 2 min; the obtained slurry was added into 800 g 2 mol / L sulfuric acid, heated to 100°C, 20 g oxalic acid and 20 g malonic acid were added, and aluminum was removed at 100°C for 3 h, then filtered while hot, washed with 70°C hot water for 3 times, the filter cake was dried at 100°C for 3 h, and calcined at 450°C for 5 h; the product zeolite was obtained, with relative crystallinity of 87% and SiO2 / Al2O3=1728.

[0045] Comparative Example 1

[0046] Comparative Example 1 did not add dispersing protective agent.

[0047] Beta zeolite with SiO2 / Al2O3=50 and relative crystallinity of 78% was added into 600 g water, and stirred quickly to be uniform, and the obtained slurry was emulsified for 2 min; the obtained slurry was added into 800 g 2 mol / L sulfuric acid, heated to 95 ℃, 50 g oxalic acid was added, and aluminum was removed by stirring at 95 ℃ for 3 h, then filtered while hot, washed with 70 ℃ hot water for 3 times, the filter cake was dried at 100 ℃ for 3 h, and calcined at 500 ℃ for 3 h; the product zeolite was obtained, with relative crystallinity of 68% and SiO2 / Al2O3=418. The framework of the zeolite collapsed.

[0048] Comparative Example 2

[0049] Comparative Example 2 does not use emulsification and dispersion, and directly removes aluminum by acid leaching.

[0050] Beta zeolite with SiO2 / Al2O3=50 and relative crystallinity of 78% was added into 600 g water, and stirred quickly to be uniform, and the obtained slurry was emulsified for 2 min; the obtained slurry was added into 800 g 2 mol / L sulfuric acid, heated to 95 ℃, 50 g oxalic acid was added, and aluminum was removed by stirring at 95 ℃ for 3 h, then filtered while hot, washed with 70 ℃ hot water for 3 times, the filter cake was dried at 100 ℃ for 3 h, and calcined at 500 ℃ for 3 h; the product zeolite was obtained, with relative crystallinity of 68% and SiO2 / Al2O3=418. The framework of the zeolite collapsed.

[0051] Comparative Example 3

[0052] Comparative Example 3 does not use complexing agent, and directly removes aluminum by acid leaching.

[0053] Beta zeolite with SiO2 / Al2O3=50 and relative crystallinity of 78% was added into 600 g water, and stirred quickly to be uniform, and the obtained slurry was emulsified for 2 min; the obtained slurry was added into 800 g 2 mol / L sulfuric acid, heated to 95 ℃, 50 g oxalic acid was added, and aluminum was removed by stirring at 95 ℃ for 3 h, then filtered while hot, washed with 70 ℃ hot water for 3 times, the filter cake was dried at 100 ℃ for 3 h, and calcined at 500 ℃ for 3 h; the product zeolite was obtained, with relative crystallinity of 68% and SiO2 / Al2O3=418. The framework of the zeolite collapsed.

[0054] The embodiments described in the present application are only used to describe the preferred embodiments of the present application, and should not be regarded as a limitation on the present application. Without departing from the design idea of the present application, various modifications and improvements of the technical solutions of the present application made by the engineering technicians in the field should fall within the protection scope of the present application, and the protection scope of the present application should be limited by the scope defined in the claims.

[0055]

[0056] From the results of Table 1, it can be seen that the product SiO2 / Al2O3 of Example 1 is increased from 635 to 1728 by the way of secondary dealumination in Example 5, and the relative crystallinity is kept ≥ 85%, which shows that the process of the present application is reproducible. Further, it shows that the process of the present application can realize high-silicon aluminum ratio molecular sieve close to pure silicon through iteration, which widens the application of high-silicon aluminum ratio Beta molecular sieve in the fields of hydrophobicity and catalysis, etc.

[0057] The dispersing protective agent polyacrylic acid prevents the structure from collapsing caused by acid etching. Comparative Example 1 shows that the relative crystallinity is reduced from 78% to 68% without protective agent, and the product appears skeleton collapse. Emulsification makes the molecular sieve disperse uniformly, and exposes more active sites. In Comparative Example 2 without emulsification, the dealumination efficiency is reduced (SiO2 / Al2O3 is only 535), and the relative crystallinity is lost by 5%, which shows that the acid contact is insufficient in the agglomerated state. The complexing agent forms a stable complex with Al3+, which promotes the forward progress of the dealumination reaction. In Comparative Example 3 without complexing agent, SiO2 / Al2O3 is only 325, which proves that the dealumination ability of single acid treatment is limited.

[0058] From the results of Table 1, it can be seen that the product SiO2 / Al2O3 of Example 1 is increased from 635 to 1728 by the way of secondary dealumination in Example 5, and the relative crystallinity is kept ≥ 85%, which shows that the process of the present application is reproducible. Further, it shows that the process of the present application can realize high-silicon aluminum ratio molecular sieve close to pure silicon through iteration, which widens the application of high-silicon aluminum ratio Beta molecular sieve in the fields of hydrophobicity and catalysis, etc. Figure 1 It can be seen from the XRD spectra before and after dealumination that the Beta zeolite crystal diffraction peaks at 7.8° and 22.4° are obvious, which shows that the product has good crystalline state, and the molecular sieve skeleton is not damaged. After dealumination, the angle at 22.4° is more sharp, and the relative crystallinity is higher. From the BET comparison chart in FIG. 2, it can be seen that after dealumination, the BET adsorption-desorption isotherm appears a more obvious hysteresis loop at P / P0 greater than 0.4, which shows that the mesoporous structure with good connectivity appears in the sample, which improves the diffusion and mass transfer performance of the reactant and product molecules.

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

Claims

1. A method for dealuminating a Beta molecular sieve, characterized by, The method comprises the following steps: S1: adding a dispersing protective agent and a raw Beta molecular sieve into neutral water, uniformly stirring rapidly, emulsifying for a period of time, and obtaining an emulsified slurry; The dispersing protective agent is polyacrylic acid; the mass percentage of the dispersing protective agent to the Beta molecular sieve is 1%-10%; The emulsifying time is 0.5-10 min; S2: adding the emulsified slurry in step S1 into an acid treatment agent, heating to 60-120 DEG C, adding a complexing agent, and stirring at constant temperature for 1-10 hours to remove aluminum; S3: after the aluminum removal is completed, hot filtration is performed, hot water is used for multiple times of washing, the filter cake is dried at 80-120 DEG C for 2-10 hours, then heating to 450-550 DEG C for calcination for 1-5 hours, and a Beta molecular sieve product with high crystallinity and high silica-alumina ratio is obtained; The silica-alumina ratio SiO2 / Al2O3 of the Beta molecular sieve after aluminum removal is greater than or equal to 100, and the crystallinity is greater than or equal to 80%.

2. The method for dealumination of a Beta molecular sieve according to claim 1, wherein, The SiO2 / Al2O3 of the raw Beta molecular sieve is 15-60.

3. The method for dealumination of a Beta molecular sieve according to claim 1, wherein, The mass percentage of the molecular sieve in the emulsified slurry is 20%-40%.

4. The method for dealumination of a Beta molecular sieve according to claim 1, wherein, The acid treatment agent is one of hydrochloric acid or sulfuric acid, and the concentration is 1-3.0 mol / L.

5. The method of dealumination of a Beta molecular sieve according to claim 1, wherein, 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. The method of dealumination of a Beta molecular sieve according to claim 1, wherein, The mass ratio of the Beta molecular sieve to the acid treatment agent is 1:1.5-6.

0.

7. The method of dealumination of a Beta molecular sieve according to claim 1, wherein, The hot water washing temperature is 50-80 DEG C.

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