Three-layer multi-core structure catalyst for high-selectivity synthesis of monomethylamine and preparation method of three-layer multi-core structure catalyst

Abstract

The invention belongs to the field of methanol conversion and utilization, and particularly relates to a three-layer multi-core structure catalyst for high-selectivity synthesis of monomethylamine and a preparation method of the three-layer multi-core structure catalyst. The core layer of the catalyst is gamma-aluminum oxide, the middle layer of the catalyst is a mordenite (MOR) molecular sieve, and the outer layer of the catalyst is porous SiO2. The preparation of the multi-core MOR layer adopts a steam-assisted crystallization method, the preparation method is simple, no organic waste liquid is generated, the preparation method is environment-friendly, the multi-core MOR layer can be used in a reaction for preparing methylamine through continuous gas phase catalytic amination of methanol after being modified by ammonium ion exchange and chemical liquid phase deposition (CLD), the methanol conversion rate reaches 98.6% under the reaction conditions that the temperature is 340 DEG C, the methanol liquid hourly space velocity is 1.5 h <-1 >, the ammonia-alcohol ratio is 3 and the pressure is normal, and the method is suitable for industrial production. The mass ratio of monomethylamine is greater than 60%, and the method has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of methanol conversion and utilization, and particularly relates to a three-layer multi-core structure catalyst for synthesizing monomethylamine with high selectivity and a preparation method thereof. BACKGROUND

[0002] Monomethylamine is an important basic chemical product, which has a relatively wide application in the fields of batteries, medicines, dyes, explosives, etc. For example, its downstream product N-methyl pyrrolidone (NMP) can be used as an excellent solvent and plays a crucial role in the fields of lithium batteries, high-precision electronics, and synthesis of polymers.

[0003] Currently, the production of monomethylamine usually adopts a continuous gas phase catalytic amination method of methanol, which uses methanol and ammonia as raw materials, and obtains monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA) through gas phase catalytic reaction under the action of a catalyst at high temperature and high pressure. The proportion of the reaction products is controlled by thermodynamic equilibrium, and the molar composition ratio of monomethylamine, dimethylamine, and trimethylamine is 23:27:50. The selectivity of trimethylamine, which has a low demand, is the highest, while the selectivity of monomethylamine, which has a low demand, is the lowest. In order to improve the selectivity of low-carbon amines, researchers take catalysts with shape-selective catalytic ability, such as mordenite molecular sieves, as the basis, and through post-treatment modification, they inhibit the excessive generation of trimethylamine and promote the improvement of the selectivity of low-carbon amines.

[0004] Chinese patent CN 116273144 A discloses a preparation method of a modified mordenite for preparing a high-proportion monomethylamine catalyst and a product. By synthesizing mordenite with different silicon-aluminum ratios and performing washing, ion exchange, molding, drying, and calcination on the mordenite, the methanol conversion rate is greater than 97% at a reaction temperature of 400-440℃, and the mass ratio of monomethylamine is 40-60%. Patent CN 115970749 A discloses a modified CHA molecular sieve, a preparation method thereof, a monomethylamine catalyst, a preparation method and application thereof, and a method for increasing the production of monomethylamine. By modifying the CHA molecular sieve, a catalyst with smaller pore size is obtained, which can achieve a methanol conversion rate of 68% and a mass ratio of monomethylamine of 66% at 400℃. The reaction temperature of the currently disclosed high-activity catalytic system, which uses methanol and ammonia as raw materials and mainly produces monomethylamine, is about 400℃, and the reaction energy consumption is high. Therefore, it is of great significance to design a monomethylamine catalyst product with a required reaction temperature lower than 350℃ and high methanol conversion rate and monomethylamine selectivity. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a three-layer multi-core structure catalyst for synthesizing monomethylamine with high selectivity and low activity temperature, a preparation method and application thereof.

[0006] The three-layer multi-core structure catalyst for synthesizing monomethylamine with high selectivity comprises a core layer of γ-alumina, an intermediate layer of mordenite (MOR) molecular sieve, and a porous SiO2 outer layer.

[0007] The preparation steps of the three-layer multi-core structure catalyst for synthesizing monomethylamine with high selectivity are as follows:

[0008] (1) Mixing a base source, an aluminum source, deionized water, a template agent, and a silicon source, stirring at 70-90 DEG C for 1.5-10 h to form a mixed sol, drying the mixed sol, and then grinding with γ-alumina, the molar amount of the base source being 0.15-0.3 times that of the silicon source, the molar amount of the aluminum source being 0.04-0.2 times that of the silicon source, and the molar amount of the γ-alumina being 0.01-0.2 times that of the silicon source, moving the mixed powder into a hydrothermal kettle for crystallization, washing, drying, and calcining the obtained product to obtain a multi-core MOR catalyst;

[0009] (2) Ammonium ion exchange of the multi-core MOR catalyst is performed at 70-80 DEG C for 1-3 h, and then the product is washed, dried, and stirred with a silicon source in a solvent, heated to reflux at 60-80 DEG C for 1-5 h, washed, dried, and calcined at 500-550 DEG C for 5-10 h to obtain the three-layer multi-core structure catalyst.

[0010] In step (1), the base source is at least one of sodium hydroxide and potassium hydroxide, the aluminum source is at least one of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum isopropoxide, and aluminum chloride, the template agent is at least one of tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylphosphonium hydroxide, and cetyltrimethylammonium bromide, and the silicon source is at least one of silica sol, tetraethyl orthosilicate, white carbon black, and sodium silicate.

[0011] The molar amount of the deionized water is 15-30 times that of the silicon source, and the molar amount of the template agent is 0.1-0.3 times that of the silicon source.

[0012] In step (1), the hydrothermal kettle crystallization is a steam-assisted crystallization method, the crystallization temperature is 140-210 DEG C, and the crystallization time is 12-96 h; the calcination temperature is 500-550 DEG C, and the calcination time is 5-10 h.

[0013] In step (2), the ammonium ion-exchanged ammonium salt is at least one of an aqueous solution of ammonium nitrate and ammonium chloride, with a concentration of 0.5-1.5 mol / L, and the amount used per gram of catalyst is 10-50 mL, and the ammonium ion exchange is performed 3-5 times.

[0014] In step (2), the silicon source is at least one of silica sol and tetraethyl orthosilicate, and the solvent is at least one of ethanol and n-hexane; the mass of the silicon source is 0.035-0.35 times the amount added to the multi-core MOR catalyst, and the amount of solvent used per gram of catalyst is 30-50 mL. The chemical liquid deposition (CLD) modification process is performed 1-3 times.

[0015] The application of the three-layer multi-core structure catalyst for synthesizing monomethylamine with high selectivity is used for continuous gas phase catalytic amination of methanol to prepare monomethylamine.

[0016] The reaction is carried out in a fixed bed, a fixed fluidized bed, a circulating fluidized bed or a moving bed reactor, the reaction raw materials are methanol and ammonia, the reaction temperature is 280-350℃, the reaction pressure is 0.1-3.0 MPa, the liquid hourly space velocity of methanol is 1-4 h -1 , and the ammonia / methanol molar ratio is 2.0-6.0.

[0017] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0018] (1) The multi-core MOR molecular sieve has multiple γ-alumina cores, which provides a large number of active sites for the dehydration reaction of methanol and ammonia;

[0019] (2) The three-layer multi-core structure catalyst coats a layer of porous SiO2 on the outer surface of the multi-core MOR molecular sieve by chemical liquid deposition, which not only inhibits the acidity of the outer surface of the multi-core MOR molecular sieve, but also shrinks the pores on the surface of the multi-core MOR molecular sieve, thereby enhancing the selective catalytic ability;

[0020] (3) The three-layer multi-core structure catalyst prepared by the present application has good methanol amination catalytic performance, the methanol conversion rate is 98.6% at normal pressure and 340℃, and the mass fraction of monomethylamine is greater than 60%, which can greatly improve the production capacity of monomethylamine. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic diagram of the three-layer multi-core structure catalyst.

[0022] Figure 2 is an internal schematic diagram of the steam-assisted crystallization method.

[0023] Figure 3 is a chromatogram for data analysis of Example 3. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, specific and understandable, the present application will be further described in detail below in combination with the drawings and examples.

[0025] Example 1

[0026] 0.90 g of sodium hydroxide, 0.25 g of sodium metaaluminate, 27.95 g of deionized water, 3.16 g of tetraethylammonium hydroxide (35 wt% aqueous solution), and 15.0 g of silica sol (30 wt% aqueous solution) were sequentially added into a 100 mL beaker, and after stirring at 90°C for 1.5 h, drying was performed; 1.53 g of γ-alumina was ground with the dried solid in a planetary ball mill, and then the powder was placed in a Teflon container in an autoclave, 2.0 g of deionized water was added to the bottom of the 200 mL autoclave, and the autoclave was placed in an oven at 210°C for crystallization for 12 h, and after natural cooling, the solid was washed with deionized water and dried; then the solid was placed in a muffle furnace and calcined at 550°C for 5 h in an air atmosphere to obtain a catalyst precursor; 3.0 g of the catalyst precursor was stirred in 150 mL of an ammonium nitrate aqueous solution (0.5 mol / L) at 80°C for 1 h, washed with deionized water, and dried, and this ammonium ion exchange process was repeated 5 times; the dried solid was mixed with 0.11 g of tetraethyl orthosilicate in 90 mL of ethanol solvent, heated and stirred at 80°C for 1 h, the product was washed with deionized water and dried, and then the solid was calcined at 550°C for 5 h in an air atmosphere, and the CLD process was repeated 3 times to obtain a three-layer multi-core structure catalyst C-M-A-1.

[0027] 2 mL of the above catalyst with a particle size of 20-40 was taken and evaluated in a fixed bed reactor, the catalyst was heated to 340°C under normal pressure in an ammonia atmosphere, and then methanol was introduced, the methanol liquid hourly space velocity was 1.5 h -1 , and the ammonia / methanol molar ratio was 3.0. The reaction products were analyzed online by gas chromatography, and the catalytic performance of the catalyst at 30 h was as shown in Table 1.

[0028] Example 2

[0029] A mixture of 0.60 g of sodium hydroxide, 0.62 g of sodium metaaluminate, 15.10 g of deionized water, 6.31 g of tetraethylammonium hydroxide (35 wt% aqueous solution), and 15.0 g of silica sol (30 wt% aqueous solution) was sequentially added to a 100 mL beaker, stirred at 80°C for 3 h, and then dried; 0.77 g of γ-alumina was added to the dried solid in a planetary ball mill, and then the powder was placed in a Teflon container in an autoclave, 2.0 g of deionized water was added to the bottom of the 200 mL autoclave, and the autoclave was placed in an oven at 170°C for crystallization for 48 h; after natural cooling, the solid was washed with deionized water and dried; then the solid was placed in a muffle furnace and calcined at 550°C for 6 h in an air atmosphere to obtain a catalyst precursor; 3.0 g of the catalyst precursor was stirred in 100 mL of an ammonium nitrate aqueous solution (1.0 mol / L) at 80°C for 2 h, washed with deionized water, and dried; the ammonium ion exchange process was repeated 4 times; the dried solid was added to 0.52 g of tetraethyl orthosilicate in 120 mL of n-hexane solvent, heated and stirred at 60°C for 2 h, the product was washed with deionized water and dried, and then the solid was calcined at 500°C for 10 h in an air atmosphere to obtain a three-layer multi-core structure catalyst, which was denoted as C-M-A-2.

[0030] The catalyst performance evaluation was performed as in Example 1.

[0031] Example 3

[0032] The catalyst precursor was prepared as in Example 2; 3.0 g of the catalyst precursor was stirred in 100 mL of an ammonium chloride aqueous solution (1.0 mol / L) at 80°C for 2 h, washed with deionized water, and dried; the ammonium ion exchange process was repeated 4 times; the dried solid was added to 0.52 g of tetraethyl orthosilicate in 120 mL of n-hexane solvent, heated and stirred at 60°C for 2 h, the product was washed with deionized water and dried, and then the solid was calcined at 500°C for 10 h in an air atmosphere; the CLD process was repeated twice to obtain a three-layer multi-core structure catalyst, which was denoted as C-M-A-3.

[0033] The catalyst performance evaluation was performed as in Example 1. After 30 h of reaction, the methanol conversion rate reached 98.6%, which was a significant improvement compared with the molecular sieve without a γ-alumina core; the monomethylamine mass ratio was 60.4%, which was a certain improvement compared with Example 2 with only one CLD process, indicating that the CLD process significantly promoted the generation of monomethylamine.

[0034] Example 4

[0035] A 0.45 g of sodium hydroxide, 1.23 g of sodium metaaluminate, 3.60 g of deionized water, 9.47 g of tetraethylammonium hydroxide (35 wt% aqueous solution), 15.0 g of silica sol (30 wt% aqueous solution) were sequentially added into a 100 mL beaker, and after stirring at 70°C for 10 h, drying was performed; 0.08 g of γ-alumina was ground with the dried solid in a planetary ball mill, and then the powder was placed in a Teflon container in an autoclave, 2.0 g of deionized water was added to the bottom of the 200 mL autoclave, and the autoclave was placed in an oven at 140°C for crystallization for 96 h, and after natural cooling, the solid was washed with deionized water and dried; then the solid was placed in a muffle furnace and calcined at 500°C for 10 h in an air atmosphere to obtain a catalyst precursor; 3.0 g of the catalyst precursor was stirred with 30 mL of an ammonium nitrate aqueous solution (1.5 mol / L) in a 70°C water bath for 3 h, washed with deionized water and dried, and this ammonium ion exchange process was repeated 3 times; the dried solid was heated and stirred with 1.05 g of tetraethyl orthosilicate in 150 mL of n-hexane solvent at 60°C for 5 h, the product was washed with deionized water and dried, and then the solid was calcined at 500°C for 10 h in an air atmosphere to obtain a three-layer multi-core structure catalyst C-M-A-4.

[0036] The catalyst performance evaluation was performed as in Example 1.

[0037] Example 5

[0038] The catalyst precursor was prepared as in Example 4; 3.0 g of the catalyst precursor was stirred with 100 mL of an ammonium nitrate aqueous solution (1.0 mol / L) in a 70°C water bath for 3 h, washed with deionized water and dried, and this ammonium ion exchange process was repeated 3 times; the dried solid was heated and stirred with 0.78 g of tetraethyl orthosilicate in 150 mL of n-hexane solvent at 70°C for 1.5 h, the product was washed with deionized water and dried, and then the solid was calcined at 550°C for 6 h in an air atmosphere to obtain a three-layer multi-core structure catalyst, which was denoted as C-M-A-5.

[0039] The catalyst performance evaluation was performed as in Example 1.

[0040] Example 6

[0041] A mixture of 0.57 g of sodium hydroxide, 0.77 g of sodium metaaluminate, 6.67 g of deionized water, 4.73 g of tetraethylammonium hydroxide (35 wt% aqueous solution), and 15.0 g of silica sol (30 wt% aqueous solution) was added to a 100 mL beaker in sequence, and dried after stirring at 85°C for 2 h; 0.77 g of γ-alumina was ground with the dried solid in a planetary ball mill, and then the powder was placed in a Teflon container in an autoclave, while 2.0 g of deionized water was added to the bottom of the 200 mL autoclave, and the autoclave was placed in an oven at 170°C for crystallization for 72 h, and then naturally cooled, and the solid was washed with deionized water and dried; then the solid was placed in a muffle furnace and calcined at 500°C for 10 h in an air atmosphere to obtain a catalyst precursor; 3.0 g of the catalyst precursor was stirred in 75 mL of an ammonium nitrate aqueous solution (1.0 mol / L) at 80°C for 2 h, and then washed with deionized water and dried, and this ammonium ion exchange process was repeated 4 times; the dried solid was mixed with 0.11 g of tetraethyl orthosilicate in 150 mL of n-hexane solvent, and heated and stirred at 60°C for 2 h under reflux, and then the product was washed with deionized water and dried, and then the solid was calcined at 550°C for 5 h in an air atmosphere, and this CLD process was repeated 2 times to obtain a three-layer multi-core structure catalyst, which was recorded as C-M-A-6.

[0042] The catalyst performance evaluation was performed as in Example 1.

[0043] Comparative Example 1

[0044] A mixture of 0.45 g of sodium hydroxide, 1.23 g of sodium metaaluminate, 3.60 g of deionized water, 9.47 g of tetraethylammonium hydroxide (35 wt% aqueous solution), and 15.0 g of silica sol (30 wt% aqueous solution) was added to a 100 mL beaker in sequence, and dried after stirring at 70°C for 5 h, and then the powder was ground in a planetary ball mill and placed in a Teflon container in an autoclave, while 2.0 g of deionized water was added to the bottom of the 200 mL autoclave, and the autoclave was placed in an oven at 210°C for crystallization for 12 h, and then naturally cooled, and the solid was washed with deionized water and dried; then the solid was placed in a muffle furnace and calcined at 550°C for 5 h in an air atmosphere, and then stirred in 100 mL of an ammonium nitrate aqueous solution (1.0 mol / L) at 80°C for 2 h, and then washed with deionized water and dried, and this ammonium ion exchange process was repeated 3 times, and the dried powder was calcined at 500°C for 5 h in an air atmosphere to obtain the M-1 catalyst.

[0045] The catalyst performance evaluation was performed as in Example 1.

[0046] Comparative Example 2

[0047] The catalyst precursor was prepared as in Example 4; 3.0 g thereof was stirred in 100 mL of an aqueous ammonium nitrate solution (1.5 mol / L) at 70°C for 3 h in a water bath, washed with deionized water and dried, and the ammonium ion exchange process was repeated three times, followed by calcination at 500°C for 5 h in an air atmosphere to obtain M-A-1.

[0048] The catalyst performance evaluation was performed as in Example 1.

[0049] Table 1 Methanol amination performance of the catalysts of Examples 1-6 and Comparative Examples 1-2

[0050] Catalyst Methanol conversion (%) Monomethylamine (%) Dimethylamine (%) Trimethylamine (%) Example 1 99.1 52.8 25.7 21.5 Example 2 98.9 56.6 30.6 12.8 Example 3 98.6 60.4 33.8 5.8 Example 4 91.1 49.3 26.0 24.7 Example 5 91.3 46.8 33.1 20.1 Example 6 98.7 41.2 30.7 28.1 Comparative Example 1 85.4 27.3 32.0 40.7 Comparative Example 2 90.2 25.9 36.6 37.5

[0051] Figure 1 A schematic diagram of a three-layer multi-core structure catalyst. The core layer is γ-alumina, the middle layer is MOR molecular sieve, and the outer layer is porous SiO2.

[0052] Figure 2 A schematic diagram of the internal part of the steam-assisted crystallization method. The internal part of the hydrothermal kettle is provided with a support and a polytetrafluoroethylene container. During crystallization, the powder is placed in the polytetrafluoroethylene container, a small amount of deionized water is added at the bottom of the hydrothermal kettle, and the kettle is left to crystallize.

[0053] Figure 3 A chromatogram for data analysis of Example 3. The chromatogram was analyzed by a CP-Volamine gas chromatography column and a FID detector. The peak with a retention time of 3.3 min is an impurity gas in ammonia, and the content is less than 10 ppm.

Claims

1. A three-layered multi-nucleus structured catalyst for the synthesis of monomethylamine with high selectivity, characterized in that: The core layer of the catalyst is gamma-alumina, the intermediate layer is mordenite molecular sieve, and the outer layer is porous SiO2.

2. The method of claim 1, wherein the three-layered multi-core structure catalyst is prepared by the steps of The method comprises the following steps: (1) mixing an alkali source, an aluminum source, deionized water, a template agent, and a silicon source, stirring the mixture at 70-90 DEG C for 1.5-10 h to form a mixed sol, drying the mixed sol, and then grinding the mixed sol with gamma-alumina, wherein the molar amount of the alkali source is 0.15-0.3 times the molar amount of the silicon source, the molar amount of the aluminum source is 0.04-0.2 times the molar amount of the silicon source, and the molar amount of the gamma-alumina is 0.01-0.2 times the molar amount of the silicon source, moving the mixed powder into a hydrothermal kettle for crystallization, washing, drying, and calcining the obtained product to obtain a multi-core MOR catalyst; (2) ammonium ion exchange of the multi-core MOR catalyst is performed at 70-80 DEG C for 1-3 h, the product is washed and dried, and then stirred with a silicon source in a solvent, heated to reflux at 60-80 DEG C for 1-5 h, and then washed, dried, and calcined at 500-550 DEG C for 5-10 h to obtain a three-layer multi-core structure catalyst.

3. The method of claim 2, wherein: In step (1), the alkali source is at least one of sodium hydroxide and potassium hydroxide, the aluminum source is at least one of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum isopropoxide, and aluminum chloride, the template agent is at least one of tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylphosphonium hydroxide, and cetyltrimethylammonium bromide, and the silicon source is at least one of silica sol, tetraethyl orthosilicate, white carbon black, and sodium silicate.

4. The method of claim 2, wherein: In step (1), the molar amount of the deionized water is 15-30 times the molar amount of the silicon source, and the molar amount of the template agent is 0.1-0.3 times the molar amount of the silicon source.

5. The method of claim 2, wherein: In step (1), the hydrothermal kettle crystallization is a steam-assisted crystallization method, the crystallization temperature is 140-210 DEG C, the crystallization time is 12-96 h, the calcination temperature is 500-550 DEG C, and the calcination time is 5-10 h.

6. The method of claim 2, wherein: In step (2), the ammonium salt for ammonium ion exchange is at least one of an aqueous solution of ammonium nitrate and ammonium chloride, the concentration is 0.5-1.5 mol / L, the amount used per gram of catalyst is 10-50 mL, and the ammonium ion exchange is performed 3-5 times.

7. The preparation method according to claim 2, characterized in that: In step (2), the silicon source is at least one of silica sol and tetraethyl orthosilicate, the solvent is at least one of ethanol and n-hexane, the mass of the silicon source is 0.035-0.35 times the amount of the multi-core MOR catalyst, and the amount of the solvent used per gram of catalyst is 30-50 mL.

8. Use of the high selectivity synthetic monomethylamine three-layer multi-nucleus structure catalyst according to claim 1, characterized in that: The method is used for continuous gas-phase catalytic amination of methanol to prepare methylamine.

9. Use according to claim 8, wherein: The reaction is carried out in a fixed bed, fixed fluidized bed, circulating fluidized bed or moving bed reactor, the reaction raw material is methanol and ammonia, the reaction temperature is 280-350℃, the reaction pressure is 0.1-3.0MPa, the liquid hourly space velocity of methanol is 1-4h -1 , and the ammonia / methanol molar ratio is 2.0-6.0.

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