A method for preparing a monolithic zsm-5 fully crystalline molecular sieve catalyst

Abstract

The application discloses a preparation method of a whole ZSM-5 full-crystalline molecular sieve, which comprises the following steps: stirring and kneading ZSM-5 molecular sieve raw powder and a precursor to prepare a wet powder body, then performing extrusion molding or directly performing crystallization after the extrusion molding to obtain a wet molding body, and finally drying and calcining the wet molding body to obtain the ZSM-5 full-crystalline molecular sieve. By using the specific precursor, the application avoids the decline of catalytic activity caused by the addition of inert components such as silica sol and aluminum sol as a binder, and can simplify the preparation process of the full-crystalline ZSM-5 molecular sieve and reduce the use of organic amine in the secondary crystallization process, so that the application has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of molecular sieve, and particularly relates to a preparation method of a monolithic ZSM-5 full crystalline molecular sieve. BACKGROUND

[0002] ZSM-5 molecular sieve material has been widely used in industry due to its unique adjustable microporous structure, high stability and catalytic activity. Since the conventional synthesized molecular sieve is in powder form and is not easy to be shaped, it needs to be shaped in industrial application to achieve a certain mechanical strength before being applied, which requires adding a certain amount of additives, such as various binders (silica sol, alumina sol, etc.), natural mineral soil (kaolin, attapulgite), in the shaping process of the molecular sieve. After kneading and mixing, the specific shape is made through a granulating device (extruding machine, etc.). The use of various additives will improve the mechanical properties of the shaped sample to a certain extent, but will also cause a series of problems, such as changing the silicon-aluminum ratio of the shaped molecular sieve, and the added binder is usually inert, which means that the active component is reduced and the acidity is not easy to control. In addition, the specific surface area of the conventional additive is small, which will reduce the specific surface area of the overall sample and block the pores of the molecular sieve, affecting its mass transfer performance. Therefore, the full crystalline ZSM-5 molecular sieve has been developed to solve the problems of low crystallinity, low activity, poor shaping degree and poor industrial application of the ZSM-5 molecular sieve prepared by the prior art.

[0003] Patent CN 104226360A uses ZSM-5 molecular sieve with a silicon-aluminum molar ratio of SiO2 / Al2O3 of 20-1000, 0-5% of rare earth elements, and 0-5% of at least one element in groups VB and VIB to form a full crystalline ZSM-5 molecular sieve catalyst, which solves the problems of low crystallinity, low activity, poor strength, and difficulty in industrial application after ZSM-5 molecular sieve catalyst is formed. Patent CN 114713278A discloses a preparation method of a full crystalline ZSM-35 molecular sieve and its application in olefin isomerization reaction, which mainly solves the problems of low crystallinity, low activity, poor strength, severe pulverization, and difficulty in industrial application after the ZSM-35 molecular sieve catalyst prepared by the prior art is formed. However, the preparation method of the full crystalline catalyst reported in the above patents still has many problems, such as the use of specific organic amine templates in the secondary crystallization process, which increases the cost and pollutes the environment. More importantly, the morphology and grain size of some special molecular sieve powders differ greatly in their forming requirements, and the formed samples need to be subjected to gas-phase secondary crystallization, which easily leads to the un-molding of molecular sieves sensitive to water content during the secondary crystallization process. In addition, the gas-phase recrystallization also requires modification of the conventional molecular sieve crystallization reactor, and the samples after secondary crystallization need to be dried and calcined, which makes the process complex in actual production. In addition, the introduction of inert binder components in the preparation process of conventional formed molecular sieve catalysts will cause the reduction of active sites of the molecular sieve and the difficulty in accurate control. Therefore, it has great application potential to develop a rapid, economical, and convenient preparation method of a full crystalline monolithic molecular sieve. SUMMARY

[0004] The purpose of the present application is to overcome the problems existing in the preparation technology of ZSM-5 molecular sieve, such as the reduction of active sites and the difficulty in accurate control after conventional extrusion forming, the generation of a large amount of ammonia-containing wastewater during gas-phase secondary crystallization, and the complex process, and to provide a new preparation method of a full crystalline monolithic ZSM-5 molecular sieve. The molecular sieve prepared by the method has the advantages of easy accurate control of active sites, high mechanical strength, and simple and easy-to-implement preparation process.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A full crystalline monolithic ZSM-5 molecular sieve, and a preparation method thereof, comprises the following steps:

[0007] (1) knead the ZSM-5 molecular sieve powder and the precursor to obtain a wet powder;

[0008] (2) extrude the obtained wet powder to form a wet body, or directly crystallize the obtained wet powder after extrusion to form a wet body;

[0009] (3) drying and calcining the wet shaped body obtained in step (2) to obtain a shaped ZSM-5 full-crystalline molecular sieve.

[0010] Further, the b-axis thickness of the ZSM-5 molecular sieve raw powder is less than 100 nm (preferably, the b-axis thickness is 5-40 nm), and the (c+a) / b of the molecular sieve crystal size is greater than or equal to 16.

[0011] Further, the precursor is a seed crystal precursor or a gel precursor.

[0012] Still further, the seed crystal precursor is prepared by mixing a silicon source and a template agent, adding an aluminum source after hydrolysis at 30-60°C for 1-12 h, and then aging at 50-200°C for 0.5-168 h, and has a water content of 30-60%.

[0013] Still further, the gel precursor is prepared by mixing a silicon source and a template agent, adding an aluminum source after hydrolysis at 30-60°C for 1-12 h, and then aging at 50-200°C for 0.5-168 h, and then adding a mineralizer, and stirring at 30-160°C for 30 min, and has a water content of 70-90%.

[0014] The molar ratio of the silicon source and the template agent is 0.01-100; the amount of the aluminum source is converted according to the Si / Al atomic ratio of 10-3000 with the silicon source; and the amount of the mineralizer is 0.01%-10% of the mass of the silicon source.

[0015] The silicon source is tetraethyl orthosilicate, silica sol or white carbon black; the template agent is tetrapropylammonium hydroxide or tetrapropylammonium bromide; the aluminum source is aluminum isopropoxide, aluminum chloride hexahydrate or aluminum sulfate; and the mineralizer is ammonium fluoride or hydrofluoric acid.

[0016] Further, the ratio of the weight of water in the precursor used in step (1) to the dry weight of the ZSM-5 molecular sieve raw powder is 0.5-2 (preferably, 0.7-1.5).

[0017] Further, the temperature of the crystallization in step (2) is 80-200°C (preferably, 100-140°C), and the time is 3-10 h (preferably, 6-9 h).

[0018] Further, the temperature of the calcination in step (3) is 400-600°C, the time is 2-6 h, and the temperature rising rate is 5-10°C / min.

[0019] Further, the average radial crushing strength of the obtained molecular sieve is 70-120 N.

[0020] The significant advantages of the present application are:

[0021] (1) The present application uses specific seed precursor or gel precursor instead of conventional silica sol or alumina sol used for molding as a binder, avoids the decline of catalytic activity caused by the addition of inert components, and makes it easy to control the water content of ZSM-5 molecular sieve during the extrusion process, facilitating kneading and extrusion molding.

[0022] (2) The molded sample contains molecular sieve seeds, so it does not need harsh sealed hydrothermal conditions, and only needs to complete the secondary crystallization during the drying process. This not only simplifies the preparation process of the molded ZSM-5 full crystalline molecular sieve, but also reduces the use of organic amines (such as n-butylamine, ethylamine, etc.) in the secondary crystallization process, which is more environmentally friendly.

[0023] (3) The activity of the molded catalyst can be precisely controlled by adjusting the formulation of the precursor. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The XRD patterns of the samples before and after crystallization of Example 2.

[0025] Figure 2 The SEM images of the samples before (left) and after (right) crystallization of Example 2.

[0026] Figure 3 The XRD patterns of the samples before and after crystallization of Example 7.

[0027] Figure 4 The SEM images of the samples before (left) and after (right) crystallization of Example 7.

[0028] Figure 5 The NH3-TPD patterns of the samples after crystallization of Example 2 and Comparative Example 2. DETAILED DESCRIPTION

[0029] A monolithic ZSM-5 full crystalline molecular sieve, the preparation method thereof comprising the following steps:

[0030] (1) Mix the silicon source and the template agent, hydrolyze at 30-60°C for 1-12h, then add the aluminum source, and then age at 50-200°C for 0.5-168h to obtain a seed precursor with a water content of 30-60%; or mix the silicon source and the template agent, hydrolyze at 30-60°C for 1-12h, then add the aluminum source, and then age at 50-200°C for 0.5-168h, then add the mineralizer, and then stir at 30-160°C for 30min to obtain a gel precursor with a water content of 70-90%;

[0031] (2) Stir and knead the ZSM-5 molecular sieve raw powder with the seed precursor or the gel precursor prepared in step (1) to obtain a wet powder;

[0032] (3) extruding the obtained wet powder to obtain a wet molding body; or extruding the obtained wet powder and then putting it into a reaction kettle to crystallize at 80-200℃ for 3-10h to obtain a wet molding body;

[0033] (4) drying the wet molding body obtained in step (3) and calcining it at 400-600℃ for 2-6h (the temperature rising rate is 5-10℃ / min) to obtain a molded ZSM-5 full crystalline molecular sieve.

[0034] In step (1), the molar ratio of the silicon source to the template agent is 0.01-100, the amount of the aluminum source is converted according to the Si / Al atomic ratio of 10-3000 with the silicon source; and the amount of the mineralizer is 0.01%-10% of the mass of the silicon source. The silicon source is tetraethyl orthosilicate, silica sol or white carbon black; the template agent is tetrapropylammonium hydroxide or tetrapropylammonium bromide; the aluminum source is aluminum isopropoxide, aluminum chloride hexahydrate or aluminum sulfate; and the mineralizer is ammonium fluoride or hydrofluoric acid.

[0035] In step (2), the b-axis thickness of the ZSM-5 molecular sieve raw powder is less than 100 nm, and the crystal size of the molecular sieve is (c+a) / b≥16. The ratio of the weight of water in the used precursor to the dry weight of the used ZSM-5 molecular sieve raw powder is 0.5-2.

[0036] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0037] The used powdered ZSM-5 molecular sieve is prepared according to the literature (Dai, W.; Kouvatas, C.; Tai, W.; Wu, G.; Guan, N.; Li, L.; Valtchev, V. Platelike MFI Crystals with Controlled Crystal Faces Aspect Ratio. Journal of the American Chemical Society 2021, 143, 1993-2004.), and its b-axis thickness is about 20 nm, and the crystal size is (c+a) / b=20.

[0038] Preparation of the seed crystal of Example 1

[0039] Take 20g of TEOS and 28.12g of TPAOH, mix and stir for 2h, then hydrolyze at 40℃ for 4h, then remove alcohol at 45℃, when alcoholysis is complete, add 0.1g aluminum chloride hexahydrate, crystallize at 70℃ for 72h to obtain seeds. The mass fraction of each component in the obtained seeds is: SiO2 18.95%, TPAOH 23.08%, H2O 57.9%, AlCl3 0.07%.

[0040] Example 2

[0041] Take 15g of powdered ZSM-5 molecular sieve and 15g of the seeds prepared in Example 1, mix and stir, then extrude the obtained wet powder in a mold with a diameter of 4mm and a length of 4-6mm; take a part and put it into a reaction kettle, crystallize at 90℃ for 6h, then dry the crystallized sample, calcine at 550℃ for 6h to obtain crystallized ZSM-5 nanosheet molecular sieve; another part is directly dried and calcined at 550℃ for 6h to obtain uncrystallized ZSM-5 nanosheet molecular sieve.

[0042] Example 3

[0043] Take 15g of powdered ZSM-5 molecular sieve and 15g of the seeds prepared in Example 1, mix and stir, then extrude the obtained wet powder in a mold with a diameter of 4mm and a length of 4-6mm, then put it into a reaction kettle, crystallize at 120℃ for 3h, then dry the crystallized sample, calcine at 550℃ for 6h to obtain crystallized ZSM-5 nanosheet molecular sieve.

[0044] Example 4

[0045] Take 15g of powdered ZSM-5 molecular sieve and 15g of the seeds prepared in Example 1, mix and stir, then extrude the obtained wet powder in a mold with a diameter of 4mm and a length of 4-6mm, then put it into a reaction kettle, crystallize at 150℃ for 5h, then dry the crystallized sample, calcine at 550℃ for 6h to obtain crystallized ZSM-5 nanosheet molecular sieve.

[0046] Preparation of gel precursor

[0047] First, 1.79g of tetrapropylammonium bromide is dissolved in 50g of deionized water, then 5.408g of tetrapropylammonium hydroxide, 20g of tetraethyl orthosilicate are added, and stirred at 35-40℃ water bath or oil bath for 2h until clear and not turbid, then add the aluminum chloride solution prepared by 0.093g of aluminum chloride hexahydrate and 34.6g of deionized water, and then add the ammonium fluoride solution prepared by 2.845g of ammonium fluoride and 51.8g of deionized water, after aging at 90℃ for 72h, stir at 90℃ for 30min to obtain the gel precursor. The mass fraction of water in the obtained gel precursor is controlled at 10-20%.

[0048] Example 6

[0049] Take 15 g of powdered ZSM-5 molecular sieve and 15 g of the prepared gel precursor of Example 6 and mix them by stirring. Then, the obtained wet powder is extruded into a wet molded body in a mold with a diameter of 4 mm and a length of 4-6 mm. After that, the wet molded body is placed in a reactor and crystallized at 100°C for 8 h. Then, the crystallized sample is dried and calcined at 550°C for 6 h to obtain a crystallized and molded ZSM-5 nanosheet molecular sieve.

[0050] Comparative Example 1

[0051] Take 15 g of powdered ZSM-5 molecular sieve and 15 g of commercially available JN-40 silica sol (SiO2about 40 wt.%) and mix them by stirring. Then, the obtained wet powder is extruded into a wet molded body in a mold with a diameter of 4 mm and a length of 4-6 mm. A small amount of the wet molded body is dried and calcined at 550°C for 6 h to obtain an uncrystallized sample. The remaining wet molded body is placed in a closed crystallization kettle with a screen, and a n-butylamine solution (10 wt.%) is added to the kettle. Then, the kettle is crystallized at 180°C for 24 h. After that, the crystallized sample is dried and calcined at 550°C for 4 h to obtain a crystallized sample.

[0052] Comparative Example 2

[0053] Take 20 g of TEOS and 28.12 g of TPAOH, mix and stir them for 2 h, and then hydrolyze them at 40°C for 4 h. Then, the alcohol is removed at 45°C. When the alcohol removal is complete, the seed crystals are obtained by crystallizing at 70°C for 72 h. The mass fraction of each component in the obtained seed crystals is: SiO2 19.0%, TPAOH 23.1%, and H2O 57.9%.

[0054] Take 15 g of powdered ZSM-5 molecular sieve and 15 g of the prepared seed crystals and mix them by stirring. Then, the obtained wet powder is extruded into a wet molded body in a mold with a diameter of 4 mm and a length of 4-6 mm. After that, the wet molded body is placed in a reactor and crystallized at 90°C for 6 h. Then, the crystallized sample is dried and calcined at 550°C for 6 h to obtain a molded ZSM-5 nanosheet molecular sieve.

[0055] Table 1. Strength comparison of samples obtained in examples and comparative examples

[0056]

[0057] As can be seen from the embodiment content, the crystallinity of the sample added with the precursor for molding is obviously improved after crystallization, which is due to the fact that part of the silica sol is recrystallized in the secondary crystallization process of the agglomerated seeds before crystallization, thereby enhancing the overall crystallinity of the sample. At the same time, the acid amount of the molecular sieve can be controlled by adjusting the three dimensions of the amount of seed added, the crystallization conditions and the content of the aluminum source in the seed. In the process of molding by using the seed precursor, if the seed does not contain the aluminum source, the overall acid amount will be reduced, thereby causing the reduction of the strength and the catalytic activity.

[0058] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be covered by the present application.

Claims

1. A method for preparing a monolithic ZSM-5 fully crystalline molecular sieve, characterized in that, The method comprises the following steps: (1) knead the ZSM-5 zeolite powder with a precursor to obtain a wet powder; (2) extrude the wet powder to obtain a wet molding body; or directly crystallize the wet powder after extruding to obtain a wet molding body; (3) dry and calcine the wet molding body obtained in step (2) to obtain a molded ZSM-5 full-crystalline zeolite; The precursor in step (1) is a seed precursor or a gel precursor; The seed precursor is prepared by mixing a silicon source and a template agent, hydrolyzing at 30-60℃ for 1-12h, then adding an aluminum source, and aging at 50-200℃ for 0.5-168h; The gel precursor is prepared by mixing a silicon source and a template agent, hydrolyzing at 30-60℃ for 1-12h, then adding an aluminum source, and aging at 50-200℃ for 0.5-168h, then adding a mineralizer, and stirring at 30-160℃ for 30min; The molar ratio of the silicon source to the template agent is 0.01-100; the amount of the aluminum source is converted according to the Si / Al atomic ratio of 10-3000 with the silicon source; and the amount of the mineralizer is 0.01%-10% of the mass of the silicon source; The silicon source is tetraethyl orthosilicate, silica sol or white carbon black; the template agent is tetrapropylammonium hydroxide or tetrapropylammonium bromide; the aluminum source is aluminum isopropoxide, aluminum chloride hexahydrate or aluminum sulfate; and the mineralizer is ammonium fluoride or hydrofluoric acid.

2. The method of making a monolithic ZSM-5 fully crystalline molecular sieve of claim 1, wherein, The b-axis thickness of the ZSM-5 zeolite powder in step (1) is less than 100 nm, and the (c+a) / b of the crystal size of the zeolite is greater than or equal to 16.

3. The method of making a monolithic ZSM-5 fully crystalline molecular sieve of claim 1, wherein, The water content of the seed precursor is 30-60%, and the water content of the gel precursor is 70-90%.

4. The method of making a monolithic ZSM-5 fully crystalline molecular sieve of claim 1, wherein, The ratio of the weight of water in the precursor to the dry weight of the ZSM-5 zeolite powder used in step (1) is 0.5-2.

5. The method of making a monolithic ZSM-5 fully crystalline molecular sieve of claim 1, wherein, The temperature of the crystallization in step (2) is 80-200℃, and the time is 3-10h.

6. The method of making a monolithic ZSM-5 fully crystalline molecular sieve of claim 1, wherein, The temperature of the calcination in step (3) is 400-600℃, and the time is 2-6h.

7. A monolithic ZSM-5 fully crystalline molecular sieve prepared according to the method of claim 1, wherein, The average radial crushing strength of the zeolite is 70-120N.

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