Preparation method of mesoporous Zn-ZSM-5 molecular sieve for preparing aromatic hydrocarbon from methanol

Abstract

The invention discloses a preparation method of a mesoporous Zn-ZSM-5 molecular sieve for preparing aromatic hydrocarbon from methanol, and belongs to the technical field of synthesis of inorganic materials. Aiming at the problems that a conventional mesoporous Zn / ZSM-5 molecular sieve catalyst Zn blocks orifices, the mesoporous structure is disordered, the molecular sieve solid yield is low, a molecular sieve framework is seriously damaged and the like, the preparation method comprises the following steps: uniformly mixing zinc gluconate with an aluminum source, a silicon source and a template agent, putting the mixture into a closed reaction container, carrying out hydrothermal crystallization, and sequentially washing, drying and roasting to obtain the mesoporous Zn / ZSM-5 molecular sieve catalyst. The sodium type molecular sieve is obtained; the preparation method comprises the following steps: carrying out multiple ion exchange on a sodium type molecular sieve by using an ammonium chloride solution, and sequentially carrying out suction filtration, washing, drying and roasting to obtain the mesoporous Zn-ZSM-5 molecular sieve. According to the preparation method of the methanol-to-aromatic hydrocarbon Zn / ZSM-5 molecular sieve provided by the invention, the obtained molecular sieve is used in the methanol-to-aromatic hydrocarbon process, and has the characteristics of high carbon deposition resistance, high aromatic hydrocarbon selectivity, low Zn wastage rate and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic material synthesis, and particularly relates to a method for preparing a mesoporous Zn-ZSM-5 molecular sieve for preparing aromatics from methanol. Background Art

[0002] Aromatic hydrocarbons, particularly light aromatics such as benzene, toluene, and xylene (BTX), are important basic chemical raw materials. Currently, their sources primarily come from catalytic reforming of petroleum fractions and pyrolysis gasoline, with smaller amounts coming from crude benzene and coal tar, by-products of the coking industry. With my country's rapid economic development, demand for aromatics has steadily increased, necessitating the development of novel aromatics production routes.

[0003] Because methanol can be obtained from a variety of carbon-containing resources, such as coal, natural gas, and biomass, the methanol-to-aromatics (MTA) route has recently attracted widespread attention from researchers and industry, and is considered a key approach in the "coal-to-oil" strategy. Among MTA catalysts, Zn / ZSM-5 zeolites, due to their suitable pore structure, excellent stability, and moderate acidity, exhibit advantages such as high aromatics selectivity and excellent catalytic stability in the MTA reaction. Zn exhibits high dehydrogenation and aromatization capabilities in the MTA reaction and is inexpensive. Existing methods for preparing Zn / ZSM-5 include ion exchange, mechanical grinding, and impregnation. While these methods are simple, Zn species often accumulate on the zeolite surface or at the pore openings in the form of clusters or large particles, resulting in pore blockage and hindering the diffusion of reactants and products (Microporous and Mesoporous Materials, 2014, 197:252–261). In addition, because the kinetic size of the aromatic product is close to or greater than the ZSM-5 pore diameter, diffusion transmission in the molecular sieve pores is restricted, and it is easy to overreact and generate carbon deposition on the acid position of the molecular sieve, resulting in catalyst deactivation. In the prior art, an impregnation method is often adopted to introduce zinc element (CN108435235A-a kind of mesoporous Zn_ZSM_5 molecular sieve and low-cost preparation method), or zinc salt and complexing agent are mixed and added into the molecular sieve synthesis mother liquor (CN111056559A-a kind of preparation method of thin-flaked Zn_ZSM_5 molecular sieve for methanol aromatization), or zinc-containing mesoporous silicon-aluminum balls (CN115301282A-a kind of hollow litchi-shaped Zn_ZSM_5 molecular sieve catalyst and preparation method thereof) are prepared. These methods not only increase the step of introducing zinc, making the preparation process more complicated, but also introduce materials such as complexing agents, resulting in an increase in cost.

[0004] To solve this problem, an effective solution strategy is to introduce mesoporous structures into ZSM-5 zeolite grains to promote the timely diffusion of aromatic product molecules out of the pores, thereby inhibiting carbon deposition in the pores of the zeolite (Fuel, 2023, 340: 127440). Common methods for constructing mesoporous structures include soft / hard template methods, alkali treatment, and steam treatment. However, these methods have many disadvantages, such as complex template synthesis steps, poor pore connectivity, disordered pore structure, low zeolite solid yield, severe damage to the zeolite framework, and high cost. Therefore, the development of new mesoporous Zn / ZSM-5 synthesis and preparation methods has become an important challenge. Summary of the Invention

[0005] In response to the problems of Zn clogging the pores, disordered mesoporous structure, low molecular sieve solid yield, and severe damage to the molecular sieve framework in conventional mesoporous Zn / ZSM-5 molecular sieve catalysts, the present invention provides a method for preparing Zn / ZSM-5 molecular sieves for methanol-to-aromatics. The obtained molecular sieve is used in the methanol-to-aromatics process and has the characteristics of strong resistance to carbon deposition, high aromatics selectivity, and low Zn loss rate.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing a mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics comprises the following steps:

[0008] Step 1: uniformly mix zinc gluconate with an aluminum source, a silicon source, and a template, place the mixture in a sealed reaction vessel for hydrothermal crystallization, and then sequentially wash, dry, and calcine to obtain a sodium molecular sieve;

[0009] Step 2: subjecting the sodium molecular sieve to multiple ion exchanges with ammonium chloride solution, followed by filtering, washing, drying, and calcining to obtain the mesoporous Zn-ZSM-5 molecular sieve.

[0010] On the one hand, the glucose structure in zinc gluconate acts as a pore-forming agent during molecular sieve synthesis, inducing the formation of mesopores within the molecular sieve grains. Using other zinc sources (such as conventional zinc nitrate or zinc chloride) does not create pores. On the other hand, the zinc element in zinc gluconate is evenly distributed within the molecular sieve grains during molecular sieve synthesis, acting as an active center for aromatization.

[0011] Furthermore, in step 1, the ratio of the molar number of Al atoms in the aluminum source to the molar number of the silicon source calculated as SiO2 is 1:100 to 1:10.

[0012] Furthermore, in step 1, the ratio of the molar number of Zn atoms in zinc gluconate to the molar number of the silicon source calculated as SiO2 is 1:1000 to 1:10.

[0013] Furthermore, the aluminum source in step 1 is one or more of sodium metaaluminate, aluminum nitrate, aluminum sulfate, aluminum isopropoxide, and pseudo-boehmite.

[0014] Furthermore, the silicon source in step 1 is one or more of silica sol, ethyl orthosilicate, white carbon black, and sodium silicate.

[0015] Furthermore, the template agent in step 1 is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, n-propylamine, n-butylamine, and ethylenediamine.

[0016] Furthermore, in step 1, the hydrothermal crystallization reaction temperature is 150-200° C., and the time is 4-120 hours.

[0017] Furthermore, in step 2, the calcination temperature is 550-650° C., and the calcination time is 5-24 hours.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The present invention adopts zinc gluconate as a zinc source and a pore-forming agent, and introduces Zn and a mesoporous structure into a ZSM-5 molecular sieve at one time without adding an external zinc source. This provides a simple method for preparing a mesoporous Zn / ZSM-5 molecular sieve catalyst for methanol to aromatics. At the same time, the catalyst has the characteristics of strong resistance to carbon deposition, high aromatics selectivity and low Zn loss rate in the MTA reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 is the XRD pattern of the molecular sieve obtained in Example 1;

[0022] Figure 2 is the NH3-TPD diagram of the molecular sieve obtained in Example 1;

[0023] Figure 3 Schematic diagram of the nitrogen adsorption-desorption isotherm of the molecular sieve obtained in Example 9. DETAILED DESCRIPTION

[0024] To gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description thereof. However, the present invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a comprehensive understanding of the present disclosure.

[0025] Example 1

[0026] 0.41g sodium aluminate and 0.21g zinc gluconate were dissolved in 24g deionized water. After complete dissolution, 16.27g tetrapropylammonium hydroxide aqueous solution (concentration of 25wt%) was added and stirred for 10min. Then, 15g silica sol (JN-40) was slowly added dropwise to the mixed solution. The obtained mixed solution was fully stirred for 1h at room temperature, transferred to a closed reactor, and reacted at 170℃ for 24h. After the reaction, the obtained product was centrifuged three times, dried in an 80℃ oven for 12h, taken out and calcined at 550℃ for 16h to obtain a sodium molecular sieve sample.

[0027] 5 g of sodium molecular sieve powder was exchanged with 200 mL of 1 M ammonium chloride solution at 80°C twice, each time for 4 hours. After the exchange, it was filtered, washed with deionized water, dried at 100°C overnight, and then calcined at 560°C in an air atmosphere for 5 hours to obtain a hydrogen-type molecular sieve catalyst.

[0028] The structure and acidity of hydrogen molecular sieve samples were analyzed, such as Figure 1 and Figure 2 shown.

[0029] Example 2

[0030] 0.33g of sodium aluminate and 0.43g of zinc gluconate were dissolved in 33g of deionized water. After complete dissolution, 16.27g of tetrapropylammonium hydroxide aqueous solution (concentration of 25wt%) was added and stirred for 10min. Then, 20.83 of ethyl orthosilicate was slowly added dropwise to the mixed solution. The resulting mixed solution was stirred at room temperature for 1h, transferred to a closed reactor, and reacted at 180℃ for 48h. After the reaction, the product was centrifuged three times, dried in an 80℃ oven for 12h, and then taken out and calcined at 580℃ for 20h to obtain a sodium molecular sieve sample.

[0031] 5 g of sodium molecular sieve powder was exchanged with 200 mL of 1 M ammonium chloride solution at 80°C twice, each time for 4 hours. After the exchange, it was filtered, washed with deionized water, dried at 100°C overnight, and then calcined at 560°C in an air atmosphere for 5 hours to obtain a hydrogen-type molecular sieve catalyst.

[0032] Example 3

[0033] 0.08g of sodium aluminate and 4.5g of zinc gluconate were dissolved in 33g of deionized water. After complete dissolution, 16.27g of tetrapropylammonium hydroxide aqueous solution (concentration of 25wt%) was added and stirred for 10min. Then, 20.83 of ethyl orthosilicate was slowly added dropwise to the mixed solution. The resulting mixed solution was stirred at room temperature for 1h, transferred to a closed reactor, and reacted at 150℃ for 96h. After the reaction, the product was centrifuged three times, dried in an 80℃ oven for 12h, and then taken out and calcined at 650℃ for 20h to obtain a sodium molecular sieve sample.

[0034] 5 g of sodium molecular sieve powder was exchanged with 200 mL of 1 M ammonium chloride solution at 80°C twice, each time for 4 hours. After the exchange, it was filtered, washed with deionized water, dried at 100°C overnight, and then calcined at 560°C in an air atmosphere for 5 hours to obtain a hydrogen-type molecular sieve catalyst.

[0035] Example 4

[0036] Dissolve 0.27g of sodium metaaluminate and 0.84g of zinc gluconate in 45g of deionized water. Once completely dissolved, add 1.18g of n-propylamine and stir for 10 minutes. Then, slowly add 20.83g of ethyl orthosilicate dropwise to the mixed solution. After stirring thoroughly at room temperature for 1 hour, transfer the resulting mixed solution to a sealed reactor and react at 180°C for 120 hours. After the reaction, the resulting product is centrifuged three times, dried in an 80°C oven for 12 hours, and then calcined at 600°C for 20 hours to obtain a sodium molecular sieve sample.

[0037] 5 g of sodium molecular sieve powder was exchanged with 200 mL of 1 M ammonium chloride solution at 80°C twice, each time for 4 hours. After the exchange, it was filtered, washed with deionized water, dried at 100°C overnight, and then calcined at 560°C in an air atmosphere for 5 hours to obtain a hydrogen-type molecular sieve catalyst.

[0038] Example 5

[0039] The implementation steps are similar to those of Example 4, except that the aluminum source is 1.25 g of aluminum nitrate nonahydrate.

[0040] Example 6

[0041] The implementation steps are similar to those of Example 4, except that the template agent is 1.46 g of n-butylamine.

[0042] Example 7

[0043] The catalytic performance of the catalyst obtained in Example 2 was evaluated. The fixed bed reaction temperature was 450°C, the reaction pressure was 100 kPa, and the methanol space velocity was 4 h -1 Nitrogen was used as the diluent gas with a partial pressure of 66.7 kPa. The product distribution and life of the catalyst are shown in Table 1.

[0044] Table 1 Catalytic performance of methanol to aromatics in Example 2

[0045]

[0046] Example 8

[0047] 0.33g of sodium aluminate and 1.26g of zinc gluconate were dissolved in 33g of deionized water. After complete dissolution, 16.27g of tetrapropylammonium hydroxide aqueous solution (concentration of 25wt%) was added and stirred for 10min. Then, 20.83 of ethyl orthosilicate was slowly added dropwise to the mixed solution. The resulting mixed solution was stirred at room temperature for 1h, transferred to a closed reactor, and reacted at 160℃ for 48h. After the reaction was completed, the product was centrifuged three times, dried in an 80℃ oven for 12h, and then taken out and calcined at 600℃ for 10h to obtain a sodium molecular sieve sample.

[0048] 5 g of sodium molecular sieve powder was exchanged with 200 mL of 1 M ammonium chloride solution at 80°C twice, each time for 4 hours. After the exchange, it was filtered, washed with deionized water, dried at 100°C overnight, and then calcined at 560°C in an air atmosphere for 5 hours to obtain a hydrogen-type molecular sieve catalyst.

[0049] The pore structure of hydrogen molecular sieve samples was analyzed, such as Figure 3 As shown, it can be seen that the sample has a large hysteresis loop when P / P0>0.7, indicating that there is a mesoporous structure in the sample.

[0050] The catalytic performance of the obtained catalyst was evaluated. The fixed bed reaction temperature was 450 °C, the reaction pressure was 100 kPa, and the methanol space velocity was 4 h -1 Nitrogen was used as the diluent gas with a partial pressure of 66.7 kPa. The product distribution and life of the catalyst are shown in Table 2.

[0051] Table 2 Catalytic performance of methanol to aromatics in Example 8

[0052]

[0053] The problems of conventional mesoporous Zn / ZSM-5 molecular sieves mainly come from their preparation methods. Usually, mesopores are constructed in the molecular sieve grains by alkali treatment, steam treatment, soft and hard template methods, etc. These treatment methods can lead to problems such as disordered molecular sieve mesoporous structure, low molecular sieve solid yield, and destruction of the molecular sieve framework. Zn is introduced by impregnation method, ion exchange method, etc. These methods can cause zinc species to deposit on the surface of the molecular sieve grains, resulting in problems such as Zn blocking the pores and uneven Zn distribution. In the present invention, zinc gluconate is used as a pore-forming agent to induce the molecular sieve to produce multi-level pores. The mechanism is that since the sugar molecule structure is rich in hydroxyl groups, it can be adsorbed on the hydroxyl surface of the silica-alumina gel through hydrogen bonds or electrostatic attraction, inducing the formation of mesopores by inhibiting the growth of the crystal face, opening up an innovative and simple preparation method.

[0054] Any matters not described in detail in this specification are prior art known to those skilled in the art. Although the above description of the present invention is based on specific embodiments to facilitate understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the specific embodiments. As long as various modifications are within the spirit and scope of the present invention as defined and determined by the appended claims, such modifications will be obvious to those skilled in the art, and all inventions and creations utilizing the concepts of the present invention are protected.

Claims

1. A method for preparing mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics, characterized by: The following steps are involved: Step 1: uniformly mix zinc gluconate with an aluminum source, a silicon source, and a template, place the mixture in a sealed reaction vessel for hydrothermal crystallization, and then sequentially wash, dry, and calcine to obtain a sodium molecular sieve; Step 2: subjecting the sodium molecular sieve to multiple ion exchanges with ammonium chloride solution, followed by filtering, washing, drying, and calcining to obtain the mesoporous Zn-ZSM-5 molecular sieve.

2. The method for preparing a mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics according to claim 1, characterized in that: In step 1, the ratio of the molar number of Al atoms in the aluminum source to the molar number of the silicon source calculated as SiO2 is 1:100 to 1:

10.

3. The method for preparing a mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics according to claim 1, characterized in that: In the step 1, the ratio of the molar number of Zn atoms in the zinc gluconate to the molar number of the silicon source calculated as SiO2 is 1:1000 to 1:

10.

4. The method for preparing a mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics according to claim 1, characterized in that: In step 1, the aluminum source is one or more of sodium metaaluminate, aluminum nitrate, aluminum sulfate, aluminum isopropoxide, and pseudo-boehmite.

5. The method for preparing a mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics according to claim 1, characterized in that: In step 1, the silicon source is one or more of silica sol, ethyl orthosilicate, white carbon black, and sodium silicate.

6. The method for preparing a mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics according to claim 1, characterized in that: In the step 1, the template agent is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, n-propylamine, n-butylamine, and ethylenediamine.

7. The method for preparing a mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics according to claim 1, characterized in that: The hydrothermal crystallization reaction temperature in step 1 is 150-200° C., and the reaction time is 4-120 hours.

8. The method for preparing a mesoporous Zn-ZSM-5 molecular sieve for methanol to aromatics according to claim 1, characterized in that: In step 2, the calcination temperature is 550-650° C., and the calcination time is 5-24 hours.

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