Modified molecular sieve, preparation method thereof and application of modified molecular sieve in ammoximation reaction

Abstract

The invention provides a modified molecular sieve as well as a preparation method and application thereof in ammoximation reaction, and belongs to the technical field of organic chemistry. The preparation method comprises the following steps: preparing a titanium silicalite molecular sieve through a sol-gel reaction, preparing a wrinkled graphene oxide coated titanium silicalite molecular sieve through spray drying, carrying out surface polydopamine modification, and dipping in ammonium chloride to prepare the modified molecular sieve. The organic base (polydopamine) and ammonium chloride are compounded to modify the titanium silicalite molecular sieve, so that the activity of the catalyst is improved, the catalytic performance is enhanced, and the selectivity of the catalyst is improved. The modified molecular sieve can be recycled, the catalyst can be regenerated after being roasted after being recycled, the catalytic activity is not reduced, and the service life of the catalyst is remarkably prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of organic chemistry, and particularly relates to a modified molecular sieve, a preparation method thereof, and an application thereof in ammoximation reaction. Background Art

[0002] Titanium silicalite molecular sieve is a heteroatom molecular sieve containing isolated tetracoordinated Ti species formed by partially substituting Si or Al atoms in the molecular sieve framework with Ti atoms. The framework tetracoordinated Ti exhibits unique Lewis acidity, endowing the titanium silicalite molecular sieve with excellent selective catalytic oxidation ability. The catalytic system composed of it and H2O2 has good catalytic activity for selective oxidation processes such as olefin epoxidation, aldehyde and ketone ammoximation, and phenol hydroxylation.

[0003] In the prior art, technical problems such as matching the hydrolysis rate and crystallization rate of silicon-titanium precursors to synthesize a titanium silicalite molecular sieve catalyst with a high framework Ti content have been solved. However, in the prior art, there is less research on the stability of titanium silicalite molecular sieve catalysts, and the existing titanium silicalite molecular sieves have low catalytic activity and poor selectivity.

[0004] CN111468182A reports the modification and pore expansion of TS-1 catalyst using carbonate, and CN104028300A reports the pore expansion of the catalyst using organic amine. However, both are the pore expansion of partial regions after the shaping of the TS-1 catalyst, and the increase in the overall pore volume of the catalyst is limited, resulting in poor activity. CN115724766B reports a method for ammoximation, in which a carbonyl compound, hydrogen peroxide, ammonia, a solvent, and a halogen-containing titanium silicalite molecular sieve are contacted to obtain a liquid product containing oxime. This method has a simple operation process, mild reaction conditions, high conversion rate of carbonyl compounds, good selectivity of oxime, and long catalyst life, and is suitable for industrial applications. However, the catalytic activity of this halogen-containing titanium silicalite molecular sieve is still limited, and the conversion rate and selectivity of the product cannot be increased to close to 100%, so as to avoid the separation and purification steps, which is further beneficial to its industrial application. Summary of the Invention

[0005] The purpose of the present invention is to provide a modified molecular sieve, a preparation method thereof, and an application thereof in ammoximation reaction. By compound-modifying titanium silicalite molecular sieve with an organic base (polydopamine) and ammonium chloride, the activity of the catalyst is improved, the catalytic performance is enhanced, the selectivity of the catalyst is improved, and it can be recycled. After recycling, the catalyst can be regenerated by calcination, and the catalytic activity is not reduced, and the catalyst life is significantly increased.

[0006] The technical solution of the present invention is realized as follows:

[0007] The present invention provides a method for preparing a modified molecular sieve. A titanium-silicon molecular sieve is prepared through a sol-gel reaction, and a wrinkled graphene oxide-coated titanium-silicon molecular sieve is prepared by spray drying, followed by surface modification with polydopamine and impregnation with ammonium chloride to obtain the modified molecular sieve.

[0008] As a further improvement of the present invention, the method includes the following steps:

[0009] S1. Preparation of titanium-silicon molecular sieve: Add tetrabutyl titanate and alkyl orthosilicate into ethanol, dropwise add ammonia water and water, stir and react, centrifuge, wash, dry, and calcine to obtain the titanium-silicon molecular sieve;

[0010] S2. Coating with wrinkled graphene oxide: Add graphene oxide into water, add the titanium-silicon molecular sieve, ultrasonically disperse evenly, and spray dry to obtain the wrinkled graphene oxide-coated titanium-silicon molecular sieve;

[0011] S3. Modification with polydopamine: Add the wrinkled graphene oxide-coated titanium-silicon molecular sieve into water, add dopamine hydrochloride and a catalyst, heat and stir to react, centrifuge, wash, and dry to obtain the modified graphene oxide-coated titanium-silicon molecular sieve;

[0012] S4. Impregnation with ammonium chloride: Add ammonium chloride into water, add the modified graphene oxide-coated titanium-silicon molecular sieve, impregnate, centrifuge, wash, and dry to obtain the modified molecular sieve.

[0013] As a further improvement of the present invention, in step S1, the mass ratio of tetrabutyl titanate, alkyl orthosilicate, ethanol, ammonia water and water is 10-12:8-10:120-150:7-15:10-15, the temperature of the stirring reaction is 35-45 °C, the time is 4-7 h, the temperature of the calcination is 400-500 °C, the time is 3-5 h, and the alkyl orthosilicate is methyl orthosilicate or ethyl orthosilicate.

[0014] As a further improvement of the present invention, in step S2, the mass ratio of graphene oxide to the titanium-silicon molecular sieve is 3-5:10.

[0015] As a further improvement of the present invention, in step S3, the mass ratio of the wrinkled graphene oxide-coated titanium-silicon molecular sieve, dopamine hydrochloride and the catalyst is 10:2-3:0.1-0.3, the catalyst is a Tris-HCl solution with a pH of 8.5-9.5, and the temperature of the heating and stirring reaction is 40-50 °C, the time is 3-5 h.

[0016] As a further improvement of the present invention, in step S4, the mass ratio of ammonium chloride to the modified graphene oxide-coated titanium-silicon molecular sieve is 1-2:10, and the impregnation time is 7-10 h.

[0017] The present invention further protects a modified molecular sieve prepared by the above preparation method.

[0018] The present invention further protects an ammoximation reaction, which uses the above modified molecular sieve as a catalyst for the reaction.

[0019] The present invention further protects a preparation method of a ketoxime, comprising the following steps:

[0020] Using ammonia, aldehyde / ketone, and hydrogen peroxide as raw materials, adding them to tert-butanol, and using the above modified molecular sieve as a catalyst for catalytic synthesis to obtain ketoxime.

[0021] As a further improvement of the present invention, the ketone is selected from at least one of methyl ethyl ketone, acetone, and acetaldehyde, the ammonia is ammonia water or ammonia gas, and the molar ratio of ammonia, aldehyde / ketone, and hydrogen peroxide is 1.5-3:1:1-1.2; the synthesis temperature is 60-70 °C, and the time is 5-6 h.

[0022] The present invention has the following beneficial effects:

[0023] In the present invention, titanium silicalite molecular sieve is coated with graphene oxide, and after spray drying, wrinkled titanium silicalite molecular sieve is obtained, which greatly increases the specific surface area of the carrier, helps to load organic base and ammonium chloride subsequently, increases the loading amount, and thus greatly improves the catalytic activity of the product. By compound modification of titanium silicalite molecular sieve with organic base (polydopamine) and ammonium chloride, the activity of the catalyst is improved, the catalytic performance is enhanced, and the selectivity of the catalyst is improved.

[0024] The modified molecular sieve of the present invention can be recycled. After recycling, it can be calcined to regenerate the catalyst, and the catalytic activity is not reduced, and the catalyst life is significantly increased.

[0025] In the present invention, when using the modified catalyst for the ammoximation reaction of the H2O2 system, the method of dropping H2O2 can be adopted to reduce the ineffective decomposition of H2O2, inhibit the occurrence of side reactions, and improve the effective utilization rate of H2O2. Specific Embodiments

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] Graphene oxide, with a purity > 99%, a thickness ≤ 5 nm, an average oxygen content of 35%, and an average sheet diameter of 20 μm, was purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.

[0028] Example 1

[0029] This embodiment provides a method for preparing a modified molecular sieve, comprising the following steps:

[0030] S1. Preparation of titanium silicalite molecular sieve: Add 10 g of tetrabutyl titanate and 8 g of methyl orthosilicate to 120 g of ethanol, dropwise add 7 g of ammonia water and 10 g of water, stir and react at 35 °C for 4 h, centrifuge, wash, dry, and calcine at 400 °C for 3 h to obtain titanium silicalite molecular sieve;

[0031] S2. Coating with wrinkled graphene oxide: Add 3 g of graphene oxide to 200 mL of water, add 10 g of titanium silicalite molecular sieve, disperse by ultrasonic wave at 1000 W for 15 min, and spray dry to obtain titanium silicalite molecular sieve coated with wrinkled graphene oxide;

[0032] S3. Modification with polydopamine: Add 10 g of titanium silicalite molecular sieve coated with wrinkled graphene oxide to 200 mL of water, add 2 g of dopamine hydrochloride and 0.1 g of catalyst, heat to 40 °C, stir and react for 3 h, centrifuge, wash, dry to obtain modified graphene oxide coated titanium silicalite molecular sieve;

[0033] The catalyst is a Tris-HCl solution with a pH of 8.5;

[0034] S4. Impregnation with ammonium chloride: Add 1 g of ammonium chloride to 100 mL of water, add 10 g of modified graphene oxide coated titanium silicalite molecular sieve, impregnate for 7 h, centrifuge, wash, dry to obtain the modified molecular sieve.

[0035] Example 2

[0036] This embodiment provides a method for preparing a modified molecular sieve, comprising the following steps:

[0037] S1. Preparation of titanium silicalite molecular sieve: Add 12 g of tetrabutyl titanate and 10 g of tetraethyl orthosilicate to 150 g of ethanol, dropwise add 15 g of ammonia water and 15 g of water, stir and react at 45 °C for 7 h, centrifuge, wash, dry, and calcine at 500 °C for 5 h to obtain titanium silicalite molecular sieve;

[0038] S2. Coating with wrinkled graphene oxide: Add 5 g of graphene oxide to 200 mL of water, add 10 g of titanium silicalite molecular sieve, disperse by ultrasonic wave at 1000 W for 15 min, and spray dry to obtain titanium silicalite molecular sieve coated with wrinkled graphene oxide;

[0039] S3. Modification with polydopamine: Add 10 g of titanium silicalite molecular sieve coated with wrinkled graphene oxide to 200 mL of water, add 3 g of dopamine hydrochloride and 0.3 g of catalyst, heat to 50 °C, stir and react for 5 h, centrifuge, wash, dry to obtain modified graphene oxide coated titanium silicalite molecular sieve;

[0040] The catalyst is a Tris-HCl solution with a pH of 9.5;

[0041] S4. Ammonium chloride impregnation: Add 2 g of ammonium chloride to 100 mL of water, add 10 g of modified graphene oxide-coated titanium silicalite molecular sieve, impregnate for 10 h, centrifuge, wash, and dry to obtain the modified molecular sieve.

[0042] Example 3

[0043] This example provides a method for preparing a modified molecular sieve, including the following steps:

[0044] S1. Preparation of titanium silicalite molecular sieve: Add 11 g of tetrabutyl titanate and 9 g of tetraethyl orthosilicate to 135 g of ethanol, dropwise add 11 g of ammonia water and 12 g of water, stir and react at 40 °C for 5.5 h, centrifuge, wash, dry, and calcine at 450 °C for 4 h to obtain the titanium silicalite molecular sieve;

[0045] S2. Wrinkle graphene oxide coating: Add 4 g of graphene oxide to 200 mL of water, add 10 g of titanium silicalite molecular sieve, ultrasonically disperse at 1000 W for 15 min, and spray dry to obtain the wrinkled graphene oxide-coated titanium silicalite molecular sieve;

[0046] S3. Polydopamine modification: Add 10 g of wrinkled graphene oxide-coated titanium silicalite molecular sieve to 200 mL of water, add 2.5 g of dopamine hydrochloride and 0.2 g of catalyst, heat to 45 °C, stir and react for 4 h, centrifuge, wash, and dry to obtain the modified graphene oxide-coated titanium silicalite molecular sieve;

[0047] The catalyst is a Tris-HCl solution with a pH of 9;

[0048] S4. Ammonium chloride impregnation: Add 1.5 g of ammonium chloride to 100 mL of water, add 10 g of modified graphene oxide-coated titanium silicalite molecular sieve, impregnate for 8 h, centrifuge, wash, and dry to obtain the modified molecular sieve.

[0049] Comparative Example 1

[0050] Compared with Example 3, the difference is that step S2 is not carried out.

[0051] Comparative Example 2

[0052] Compared with Example 3, the difference is that step S3 is not carried out.

[0053] Comparative Example 3

[0054] Compared with Example 3, the difference is that step S4 is not carried out.

[0055] Test Example 1

[0056] Use a high-throughput gas adsorption instrument to measure the specific surface area of the modified molecular sieves prepared in Examples 1-3 and Comparative Examples 1-3, and the results are shown in Table 1.

[0057] Table 1

[0058] Group <![CDATA[Specific surface area (m 2 / g)]]> Example 1 778.3 Example 2 782.1 Example 3 785.5 Comparative Example 1 556.2 Comparative Example 2 710.4 Comparative Example 3 756.7

[0059] As can be seen from the above table, the modified molecular sieves prepared in Examples 1-3 of the present invention have a relatively large specific surface area.

[0060] Example 4

[0061] A method for preparing a ketoxime, comprising the following steps:

[0062] 0.2 mol of ammonia water (molar amount of NH3, concentration of ammonia water is 20 wt%), 0.1 mol of butanone, and 0.11 mol of hydrogen peroxide (molar amount of H2O2, concentration of hydrogen peroxide is 25 wt%) are added to 50 mL of tert-butanol, mixed evenly, and the modified molecular sieve prepared in Example 1 is used as a catalyst for catalytic synthesis. The synthesis temperature is 60 °C and the time is 5 h to obtain butanone oxime, and chromatographic analysis is carried out.

[0063] Example 5

[0064] A method for preparing a ketoxime, comprising the following steps:

[0065] Taking 0.2 mol of ammonia water (molar amount of NH3, concentration of ammonia water is 20 wt%), 0.1 mol of butanone, and 0.11 mol of hydrogen peroxide (molar amount of H2O2, concentration of hydrogen peroxide is 25 wt%) as raw materials, adding them to 50 mL of tert-butanol, mixing evenly, and using the modified molecular sieve prepared in Example 2 as a catalyst for catalytic synthesis. The synthesis temperature is 70 °C and the time is 6 h to obtain butanone oxime, and chromatographic analysis is carried out.

[0066] Example 6

[0067] A method for preparing a ketoxime, comprising the following steps:

[0068] 0.2 mol of ammonia water (molar amount of NH3, concentration of ammonia water is 20 wt%), 0.1 mol of butanone, and 0.11 mol of hydrogen peroxide (molar amount of H2O2, concentration of hydrogen peroxide is 25 wt%) are added to 50 mL of tert-butanol, mixed evenly, and the modified molecular sieve prepared in Example 3 is used as a catalyst for catalytic synthesis. The synthesis temperature is 65 °C and the time is 5 h to obtain butanone oxime, and chromatographic analysis is carried out.

[0069] Comparative Example 4

[0070] Compared with Example 6, the difference is that the modified molecular sieve is prepared from Comparative Example 1.

[0071] Comparative Example 5

[0072] Compared with Example 6, the difference lies in that the modified molecular sieve is prepared from Comparative Example 2.

[0073] Comparative Example 6

[0074] Compared with Example 6, the difference lies in that the modified molecular sieve is prepared from Comparative Example 3.

[0075] Test Example 2

[0076] The reaction evaluations of Examples 4-6 and Comparative Examples 4-6 of the present invention were carried out, and the results are shown in Table 2.

[0077] Table 2

[0078]

[0079]

[0080] As can be seen from the above table, in the reactions of Examples 4-6 of the present invention, the conversion rate of methyl ethyl ketone is high and the selectivity of methyl ethyl ketone oxime is high.

[0081] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a modified molecular sieve, characterized in that, Prepare titanium silicalite molecular sieve through sol-gel reaction, prepare wrinkled graphene oxide-coated titanium silicalite molecular sieve by spray drying, modify the surface with polydopamine, impregnate with ammonium chloride, and obtain the modified molecular sieve.

2. The preparation method according to claim 1, wherein, It includes the following steps: S1. Preparation of titanium silicalite molecular sieve: Add tetrabutyl titanate and alkyl orthosilicate into ethanol, dropwise add ammonia water and water, stir and react, centrifuge, wash, dry, and calcine to obtain titanium silicalite molecular sieve; S2. Coating with wrinkled graphene oxide: Add graphene oxide into water, add titanium silicalite molecular sieve, ultrasonically disperse evenly, and spray dry to obtain wrinkled graphene oxide-coated titanium silicalite molecular sieve; S3. Modification with polydopamine: Add wrinkled graphene oxide-coated titanium silicalite molecular sieve into water, add dopamine hydrochloride and catalyst, heat and stir to react, centrifuge, wash, and dry to obtain modified graphene oxide-coated titanium silicalite molecular sieve; S4. Impregnation with ammonium chloride: Add ammonium chloride into water, add modified graphene oxide-coated titanium silicalite molecular sieve, impregnate, centrifuge, wash, and dry to obtain the modified molecular sieve.

3. The preparation method according to claim 2, characterized in that, In step S1, the mass ratio of tetrabutyl titanate, alkyl orthosilicate, ethanol, ammonia water and water is 10-12:8-10:120-150:7-15:10-15, the temperature of the stirring reaction is 35-45 °C, the time is 4-7 h, the temperature of the calcination is 400-500 °C, the time is 3-5 h, and the alkyl orthosilicate is methyl orthosilicate or ethyl orthosilicate.

4. The preparation method according to claim 2, wherein In step S2, the mass ratio of graphene oxide to titanium silicalite molecular sieve is 3-5:

10.

5. The preparation method according to claim 2, wherein In step S3, the mass ratio of wrinkled graphene oxide-coated titanium silicalite molecular sieve, dopamine hydrochloride and catalyst is 10:2-3:0.1-0.3, the catalyst is a Tris-HCl solution with pH = 8.5-9.5, and the temperature of the heating and stirring reaction is 40-50 °C, the time is 3-5 h.

6. The preparation method according to claim 2, characterized in that, In step S4, the mass ratio of ammonium chloride to modified graphene oxide-coated titanium silicalite molecular sieve is 1-2:10, and the impregnation time is 7-10 h.

7. A modified molecular sieve prepared by the preparation method according to any one of claims 1-6.

8. An ammoximation reaction, characterized in that, Use the modified molecular sieve described in claim 7 as a catalyst for reaction.

9. A method for preparing a ketoxime, characterized in that, It includes the following steps: Use ammonia, aldehyde / ketone, and hydrogen peroxide as raw materials, add them into tert-butanol, and use the above-mentioned modified molecular sieve as a catalyst for catalytic synthesis to obtain ketoxime.

10. The preparation method according to claim 9, characterized in that, The ketone is selected from at least one of methyl ethyl ketone, acetone, and acetaldehyde, the ammonia is ammonia water or ammonia gas, and the molar ratio of ammonia, aldehyde / ketone, and hydrogen peroxide is 1.5-3:1:1-1.2; the synthesis temperature is 60-70 °C, and the time is 5-6 h.

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