Method for preparing gallium-doped hollow ZSM-5 molecular sieve through microwaves and application of gallium-doped hollow ZSM-5 molecular sieve

Abstract

The invention discloses a method for preparing a gallium-doped hollow ZSM-5 molecular sieve through microwaves and application of the gallium-doped hollow ZSM-5 molecular sieve, and relates to the technical field of molecular sieve catalyst preparation. The preparation method comprises the following steps: mixing a silicon source, a template agent and deionized water, stirring to prepare a precursor, transferring the precursor into a digestion tank, carrying out microwave hydrothermal treatment, and roasting in a muffle furnace to remove the template agent to obtain a pure silicon molecular sieve; the method comprises the following steps: taking a pure silicon molecular sieve, adding an aluminum source, a template agent and deionized water, carrying out ultrasonic treatment, transferring into a digestion tank, carrying out microwave hydrothermal and dissolution-recrystallization, and roasting the obtained product in a muffle furnace to remove the template agent so as to obtain a hollow ZSM-5 molecular sieve; the method comprises the following steps: taking a hollow ZSM-5 molecular sieve, adding gallium nitrate and deionized water, carrying out ultrasonic treatment, transferring into a digestion tank, and carrying out gallium doping under microwave irradiation; and putting the dried product into a tubular furnace, and carrying out heat preservation in an argon atmosphere at 200-300 DEG C to obtain the gallium-doped hollow ZSM-5 molecular sieve. The microwave hydrothermal process and the dissolution-recrystallization process are combined, so that the preparation time of the hollow ZSM-5 molecular sieve is effectively shortened, and the energy consumption is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieve catalyst preparation, and in particular to a method for preparing gallium-doped hollow ZSM-5 molecular sieves by microwave and application thereof. Background Art

[0002] With the continuous development of catalytic technology, ZSM-5 molecular sieves have been widely used in the fields of petrochemicals and fine chemicals due to their unique acidity, excellent thermal stability and good shape selectivity, especially in the methanol aromatization to aromatics (MTA reaction), where they have shown excellent catalytic performance. Traditional ZSM-5 molecular sieves still have many limitations in the application of methanol aromatization to aromatics (MTA reaction). Due to pore blockage and carbon deposition, the reactants or intermediates are inefficient in the mass transfer process, and the catalyst is rapidly deactivated, which seriously affects the product selectivity and yield of the methanol to aromatics reaction.

[0003] In order to solve the above problems, in recent years, the structure of molecular sieves has been optimized by means of multi-stage pore modification and hollow structure design. Commonly used structural control methods include acid dissolution, alkali dissolution and dissolution-recrystallization technology. Among them, dissolution-recrystallization technology has attracted attention because it can construct a relatively complete hollow structure. However, traditional dissolution-recrystallization technology uses external heating methods, such as conventional hydrothermal, and heat needs to be transferred from the heating source to the reaction medium and gradually conducted to the inside of the reaction system. This heating mode is prone to cause local overheating or uneven temperature distribution, especially in complex reaction systems, resulting in uneven distribution of the pore structure of the prepared molecular sieve, resulting in unsatisfactory catalytic effect and poor selectivity. The above-mentioned traditional heating methods also have the disadvantages of long preparation time and high energy consumption. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing gallium-doped hollow ZSM-5 molecular sieve by microwave and its application, so as to solve the problem that the prior art process is complicated and the catalytic effect of the prepared molecular sieve is not ideal.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for preparing gallium-doped hollow ZSM-5 molecular sieve by microwave, characterized in that it comprises the following steps:

[0006] S1. Mix the silicon source, template and deionized water and stir for 1 to 6 hours to obtain a precursor a;

[0007] S2. The precursor a is transferred to a digestion tank and subjected to microwave hydrothermal treatment to obtain product a;

[0008] S3. The product a is placed in a muffle furnace and calcined to remove the template to obtain a pure silicon molecular sieve;

[0009] S4. Take pure silicon molecular sieve, add aluminum source, template and deionized water, and ultrasonicate for 1 to 3 hours to obtain precursor b;

[0010] S5. The precursor b is transferred to a digestion tank, subjected to microwave hydrothermal treatment and dissolution-recrystallization to obtain product b;

[0011] S6. The product b is placed in a muffle furnace and calcined to remove the template to obtain a hollow ZSM-5 molecular sieve;

[0012] S7. Take a hollow ZSM-5 molecular sieve, add gallium nitrate and deionized water, and ultrasonicate for 1 to 3 hours to obtain a mixture c;

[0013] S8. The mixture c is transferred to a digestion tank, gallium-doped under microwave irradiation, and the product is filtered, washed, and dried;

[0014] S9. The dried product was placed in a tubular furnace and kept warm at 200-300° C. in an argon atmosphere for 2-4 hours to obtain a gallium-doped hollow ZSM-5 molecular sieve, named Ga@Hol-ZSM-5.

[0015] A further technical solution is that in step S1, the silicon source is tetraethyl orthosilicate (TEOS), the template agent is tetrapropylammonium hydroxide (TPAOH), the amount of tetrapropylammonium hydroxide is 0.36-0.375 g / ml, and the amount of tetraethyl orthosilicate is 0.36-0.37 g / ml.

[0016] A further technical solution is that the microwave hydrothermal treatment in step S2 is carried out under microwave irradiation at 150-180° C. for 1-4 hours, and the microwave power is 1000-2000W.

[0017] A further technical solution is that in step S3, the temperature is raised to 500-700° C. at a heating rate of 5-20° C. / min and kept at this temperature for 3-6 hours.

[0018] A further technical solution is that in step S3, the average pore size of the pure silicon molecular sieve is 1 to 40 nanometers, and the specific surface area is 500 to 800 m 2 / g, and the particle size is 0.5 to 2 microns.

[0019] A further technical solution is that in step S4, the aluminum source is aluminum isopropoxide, the template agent is tetrapropylammonium hydroxide (TPAOH), the amount of pure silicon molecular sieve is 0.05-0.06 g / ml, the amount of tetrapropylammonium hydroxide is 0.19-0.20 g / ml, and the amount of aluminum isopropoxide is 0.001-0.003 g / ml.

[0020] A further technical solution is that the microwave hydrothermal and dissolution-recrystallization in step S5 is carried out under microwave irradiation at 150-180° C. for 1-4 hours, and the microwave power is 1000-2000W.

[0021] A further technical solution is that in step S6, the temperature is raised to 500-700° C. at a heating rate of 5-20° C. / min and kept at this temperature for 3-6 hours.

[0022] A further technical solution is that in step S7, the amount of hollow ZSM-5 molecular sieve is 0.1-0.2 / ml, and the amount of gallium nitrate is 0.004-0.006 g / ml; in step S8, the microwave immersion power is 1200-1500 W, the insulation temperature is 60-100° C., and the insulation time is 2-4 hours.

[0023] A further technical solution is to use the gallium-doped hollow ZSM-5 molecular sieve as a catalyst for methanol aromatization to produce aromatics, specifically, the gallium-doped hollow ZSM-5 molecular sieve is pressed into thin sheets and placed vertically in a reactor for methanol gas to pass through.

[0024] Reaction mechanism:

[0025] The construction process of the hollow structure of ZSM-5 molecular sieve: Under alkaline conditions, the surface and internal Si-OH groups of ZSM-5 molecular sieve easily lose protons to form Si-O - and with TPA in the template + The ions combine through electrostatic interaction to form Si-O-TPA intermediates, which effectively protect the surface structure of the molecular sieve. + It is difficult for ions to directly enter the interior of the molecular sieve, and OH - The ions can diffuse into the interior of the molecular sieve and dissolve its internal structure. The dissolved Si groups migrate to the outer surface of the molecular sieve through diffusion and interact with the TPA on the outer surface. + The new Si-O-TPA intermediate is generated by combining, and the template agent is finally removed during the subsequent calcination process to form a ZSM-5 molecular sieve with a hollow structure. Microwaves play an important role in this process. Their uniform heating characteristics not only accelerate the dissociation of Si-OH groups and the dissolution of internal structures, but also significantly promote the formation and uniformity of the Si-O-TPA intermediate. At the same time, under the action of the microwave field, TPA + The high-speed vibration, rotation and dipole flipping of ions enhance their diffusion efficiency on the surface of the molecular sieve and accelerate the migration and recrystallization of internal dissolved products. This fine process control not only shortens the reaction time, but also improves the regularity of the hollow structure and the stability of the molecular sieve, making the prepared hollow ZSM-5 molecular sieve have excellent structural characteristics and application potential.

[0026] Gallium-doped ZSM-5 molecular sieve can regulate the acidity distribution of the molecular sieve, enhance the selectivity of the acidic active sites, promote the aromatization process of the reactants, and effectively inhibit the formation of carbon deposits. Microwave impregnation directly acts on the material, greatly improving the efficiency and uniformity of gallium loading on the molecular sieve, and also making the metal and the molecular sieve firmly combined, improving the thermal stability and service life of the catalyst, thereby significantly enhancing the catalytic activity and product selectivity of the catalytic reaction.

[0027] In the application process, the methanol to aromatics (MTA) reaction can be divided into three main stages. First, in the methanol dehydration stage (such as the Figure 6 As shown in the figure, methanol is dehydrated to dimethyl ether (DME) under the action of the acid sites of the catalyst, and dimethyl ether is further cracked to generate active intermediates such as methyl cations and carbon cations, providing a reaction basis for subsequent reactions. Gallium doping can optimize the acid distribution of ZSM-5 molecular sieves, enhance the activity of weakly acidic sites, promote the efficient dehydration of methanol, and provide active species for subsequent reactions. Secondly, in the stage of light olefin generation and polymerization (such as attached Figure 7 The methyl cation reacts with the intermediates to form low-carbon olefins, which are further polymerized to form high-carbon olefins or chain alkanes. Gallium, through its excellent dehydrogenation ability, effectively regulates the reaction path of the intermediates, inhibits the formation of by-products, and accumulates precursors for the cyclization reaction. Finally, in the cyclization and dehydrogenation aromatization stage (as shown in the attached Figure 8 As shown in Figure 2, high-carbon olefins and chain alkanes undergo cyclization to form cycloalkanes under the action of acidic catalysts, and then are converted into aromatics (such as benzene, toluene and xylene) through dehydrogenation reactions. Gallium plays a key dehydrogenation function in this stage, accelerating the conversion of cycloalkanes to aromatics while inhibiting the formation of carbon deposits, thereby improving the stability of the catalyst and the yield of aromatic products.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention combines microwave hydrothermal technology with a dissolution-recrystallization process to provide an efficient heating and crystallization method, which effectively shortens the preparation time of the hollow ZSM-5 molecular sieve and reduces energy consumption.

[0030] 2. The present invention directly acts on TPA in the template through microwaves + ions, causing them to vibrate, rotate and flip at high speed in the reaction medium, thus improving their interaction with the Si-O - The contact efficiency is improved, thereby achieving the uniform and efficient preparation of hollow ZSM-5 molecular sieves.

[0031] 3. The present invention adopts microwave impregnation technology to evenly distribute gallium atoms in the ZSM-5 molecular sieve framework with high crystallinity, thus maintaining excellent catalytic performance in high-temperature reactions and extending the service life of the catalyst.

[0032] 4. The hollow ZSM-5 molecular sieve prepared by the present invention has a large specific surface area and a unique pore structure, which effectively reduces the carbon deposition phenomenon during the catalytic process, improves the mass transfer efficiency, and enhances the anti-carbon deposition performance of the catalyst.

[0033] 5. The preparation method of the present invention is simple and fast, suitable for large-scale production, and can be widely used in industrial catalytic reactions such as methanol to aromatics, achieving efficient catalysis and improving the practicability and economy of the overall process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a process flow chart of the present invention.

[0035] Figure 2 This is an X-ray powder diffraction spectrum diagram of Si-1, hollow ZSM-5 molecular sieve and gallium-doped hollow ZSM-5 molecular sieve in Example 1 of the present invention.

[0036] Figure 3 This is a scanning electron microscope image of Si-1, hollow ZSM-5 molecular sieve and gallium-doped hollow ZSM-5 molecular sieve in Example 1 of the present invention.

[0037] Figure 4 Transmission electron microscope images and EDS element distribution diagrams of Si-1, hollow ZSM-5 molecular sieve and gallium-doped hollow ZSM-5 molecular sieve in Example 1 of the present invention.

[0038] Figure 5 It is the product distribution diagram of the MTA reaction of each ZSM-5 molecular sieve in Example 1 of the present invention and the comparative example.

[0039] Attached Figure 6 This is a reaction principle diagram of one stage of the MTA reaction of the present invention.

[0040] Attached Figure 7 It is a reaction principle diagram of the two-stage process of MTA reaction of the present invention.

[0041] Attached Figure 8 It is a reaction principle diagram of the three-stage process of MTA reaction of the present invention.

[0042] Attached Fig. 9 This is a diagram showing the formation mechanism of the hollow structure of the ZSM-5 molecular sieve in the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] Example 1

[0045] A gallium-doped hollow ZSM-5 molecular sieve preparation method comprises the following steps:

[0046] 1. Weigh 7.4 g of tetrapropylammonium hydroxide and 7.3 g of tetraethyl orthosilicate, add 20 mL of deionized water, and stir at room temperature for 4 hours to obtain a mixture a;

[0047] 2. Transfer the mixture a to a polytetrafluoroethylene digestion tank, keep it at 170°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product a. The hydrothermal product a is filtered, washed, and dried overnight;

[0048] 3. Place the hydrothermal product a in a muffle furnace, heat the temperature to 550°C at a heating rate of 10°C / min, and keep it warm for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-1.

[0049] 4. Weigh 1.2 g Si-1, 0.04 g aluminum isopropoxide and 3.9 g tetrapropylammonium hydroxide, add 20 mL deionized water, and ultrasonicate for 1 hour to obtain a mixture b.

[0050] 5. Transfer the mixture b to a polytetrafluoroethylene digestion tank, keep it at 170°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product b. The hydrothermal product b is filtered, washed, and dried overnight;

[0051] 6. Place the hydrothermal product b in a muffle furnace, heat the temperature to 550°C at a heating rate of 10°C / min, and keep it warm for 5 hours to remove the template agent. The product is a hollow ZSM-5 molecular sieve, named Hollow-ZSM-5.

[0052] 7. Weigh 0.1g of gallium nitrate, add 20ml of deionized water, and stir to form a homogeneous solution

[0053] 8. Weigh 2 g of Hollow-ZSM-5, add it to the solution, and sonicate for 1 hour to obtain a mixture a.

[0054] 9. Transfer the mixture a to a polytetrafluoroethylene digestion tank and keep it warm at 80°C for 2 hours under microwave irradiation at a power of 1200 W to obtain product a. After suction filtration and washing, the product a is dried at 60°C overnight.

[0055] 10. The dried product a was transferred to a tubular furnace, and heated to 200°C at a heating rate of 2°C / min under an argon atmosphere, and kept warm for 2 h to obtain a gallium-doped hollow ZSM-5 molecular sieve catalyst, named Ga@Hol-ZSM-5.

[0056] Figure 2 The X-ray diffraction patterns of the ZSM-5 series samples are shown, and the diffraction peaks are consistent with the standard PDF#44-0003 data, indicating that the prepared ZSM-5 series samples have formed a typical MFI structure, which is the characteristic structure of the ZSM-5 molecular sieve. Figure 3 The microstructure of the ZSM-5 series samples is shown. The results show that the morphology of the samples is uniform and no obvious change in the grain morphology is observed. Figure 4 The structural characteristics of the ZSM-5 series samples are shown, among which the Hollow-ZSM-5 and Ga@Hol-ZSM-5 samples clearly show a hollow structure, proving the stability and feasibility of the process described in the present invention. Figure 4 The element distribution of Ga@Hol-ZSM-5 sample is also shown, and the results show that Ga element is uniformly distributed in the molecular sieve, further verifying the effectiveness of the doping process.

[0057] Example 2

[0058] The reaction process of methanol to aromatics catalyzed by gallium-doped hollow ZSM-5 molecular sieve Ga@Hol-ZSM-5 includes the following steps:

[0059] 0.4 g of the Ga@Hol-ZSM-5 catalyst prepared in Example 1 was weighed, pressed into catalyst flakes with a diameter of 0.8 cm (matching the inner diameter of the fixed bed reactor), and placed vertically in the fixed bed reactor.

[0060] The methanol space velocity was set to 0.8 h-1, the carrier gas was argon, and the reaction temperature was 450° C. The fixed bed reactor was connected to a gas chromatograph to qualitatively and quantitatively analyze the product distribution.

[0061] Comparative Example 1

[0062] This comparative example is compared with Example 2. The difference from Example 2 is that the catalyst used in this reaction is Si-1 which has formed a ZSM-5 molecular sieve MFI structure in Example 1. The specific steps are as follows:

[0063] 0.4 g of Si-1 catalyst was weighed and pressed into catalyst flakes with a diameter of 0.8 cm, which were placed vertically in a fixed bed reactor.

[0064] The methanol space velocity was set to 0.8 h-1, the carrier gas was argon, and the reaction temperature was 450° C. The fixed bed reactor was connected to a gas chromatograph to qualitatively and quantitatively analyze the product distribution.

[0065] Comparative Example 2

[0066] This comparative example is compared with Example 2. The difference from Example 2 is that the catalyst used in this reaction is the Hollow-ZSM-5 with a hollow structure prepared in Example 1. The specific steps are as follows:

[0067] 0.4 g of Hollow-ZSM-5 catalyst was weighed and pressed into catalyst flakes with a diameter of 0.8 cm, which were placed vertically in a fixed bed reactor.

[0068] The methanol space velocity was set to 0.8 h-1, the carrier gas was argon, and the reaction temperature was 450° C. The fixed bed reactor was connected to a gas chromatograph to qualitatively and quantitatively analyze the product distribution.

[0069] Comparative Example 3

[0070] This comparative example is compared with Example 2. The difference from Example 2 is that the catalyst used in this reaction is ZSM-5 prepared by conventional hydrothermal method (purchased from Tianjin Nanhua Catalyst Co., Ltd.). The specific steps are as follows:

[0071] 0.4 g of ZSM-5 catalyst was weighed and pressed into catalyst flakes with a diameter of 0.8 cm, which were placed vertically in a fixed bed reactor.

[0072] The methanol space velocity was set to 0.8 h-1, the carrier gas was argon, and the reaction temperature was 450° C. The fixed bed reactor was connected to a gas chromatograph to qualitatively and quantitatively analyze the product distribution.

[0073] The product distribution of Example 2 and Comparative Examples 1, 2, and 3 is shown in the attached Figure 5 As shown in the figure, the performance of different types of ZSM-5 zeolites (including Si-1, Hollow-ZSM-5, Ga@Hol-ZSM-5 and ZSM-5) in product distribution is shown. The ratio of aromatic products to other products is mainly compared. The gallium-doped Ga@Hol-ZSM-5 sample performed well in the selectivity of aromatic products, reaching 37%, which is significantly higher than other samples. In contrast, the undoped samples (such as Hollow-ZSM-5 and ZSM-5) have a low aromatic yield, and Si-1 has no catalytic activity due to the lack of reactive active sites. This shows that the catalytic advantage of ZSM-5 zeolite in aromatic selectivity is significantly improved through gallium doping and hollow structure modification.

[0074] Example 3

[0075] A gallium-doped hollow ZSM-5 molecular sieve preparation method comprises the following steps:

[0076] 1. Weigh 7.4 g of tetrapropylammonium hydroxide and 7.3 g of tetraethyl orthosilicate, add 20 mL of deionized water, and stir at room temperature for 4 hours to obtain a mixture a;

[0077] 2. Transfer the mixture a to a polytetrafluoroethylene digestion tank, keep it at 180°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product a. Filter and wash the hydrothermal product a, and then dry it overnight;

[0078] 3. Place the hydrothermal product a in a muffle furnace, heat the temperature to 560°C at a heating rate of 10°C / min, and keep it warm for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-2.

[0079] 4. Weigh 1.2 g Si-2, 0.04 g aluminum isopropoxide and 3.9 g tetrapropylammonium hydroxide, add 20 mL deionized water, and ultrasonicate for 1 hour to obtain a mixture b.

[0080] 5. Transfer the mixture b to a polytetrafluoroethylene digestion tank, keep it at 150°C for 4 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product b. The hydrothermal product b is filtered, washed, and dried overnight;

[0081] 6. The hydrothermal product b was placed in a muffle furnace, heated to 600°C at a heating rate of 10°C / min, and kept warm for 4 hours to remove the template agent. The product was a hollow ZSM-5 molecular sieve, named Hollow-ZSM-5.

[0082] 7. Weigh 0.1g of gallium nitrate, add 20ml of deionized water, and stir to form a homogeneous solution

[0083] 8. Weigh 2 g of Hollow-ZSM-5, add it to the solution, and sonicate for 1 hour to obtain a mixture a.

[0084] 9. Transfer the mixture a to a polytetrafluoroethylene digestion tank and keep it warm at 80°C for 2 hours under microwave irradiation at a power of 1200 W to obtain product a. After suction filtration and washing, the product a is dried at 60°C overnight.

[0085] 10. The dried product a was transferred to a tubular furnace, and heated to 250°C at a heating rate of 2°C / min under an argon atmosphere, and kept warm for 2 h to obtain a gallium-doped hollow ZSM-5 molecular sieve catalyst, named Ga@Hol-ZSM-5.

[0086] Example 4

[0087] A gallium-doped hollow ZSM-5 molecular sieve preparation method comprises the following steps:

[0088] 1. Weigh 7.4 g of tetrapropylammonium hydroxide and 7.3 g of tetraethyl orthosilicate, add 20 mL of deionized water, and stir at room temperature for 4 hours to obtain a mixture a;

[0089] 2. Transfer the mixture a to a polytetrafluoroethylene digestion tank, keep it at 170°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product a. The hydrothermal product a is filtered, washed, and dried overnight;

[0090] 3. Place the hydrothermal product a in a muffle furnace, heat the temperature to 550°C at a heating rate of 10°C / min, and keep it warm for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-1.

[0091] 4. Weigh 1.2 g Si-1, 0.04 g aluminum isopropoxide and 3.9 g tetrapropylammonium hydroxide, add 20 mL deionized water, and ultrasonicate for 1 hour to obtain a mixture b.

[0092] 5. Transfer the mixture b to a polytetrafluoroethylene digestion tank, keep it at 160°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product b. The hydrothermal product b is filtered, washed, and dried overnight;

[0093] 6. The hydrothermal product b was placed in a muffle furnace, heated to 600°C at a heating rate of 10°C / min, and kept warm for 4 hours to remove the template agent. The product was a hollow ZSM-5 molecular sieve, named Hollow-ZSM-5.

[0094] 7. Weigh 0.1g of gallium nitrate, add 20ml of deionized water, and stir to form a homogeneous solution

[0095] 8. Weigh 2 g of Hollow-ZSM-5, add it to the solution, and sonicate for 1 hour to obtain a mixture a.

[0096] 9. Transfer the mixture a to a polytetrafluoroethylene digestion tank and keep it warm at 80°C for 2 hours under microwave irradiation at a power of 1200 W to obtain product a. After suction filtration and washing, the product a is dried at 60°C overnight.

[0097] 10. The dried product a was transferred to a tubular furnace, and heated to 300°C at a heating rate of 2°C / min under an argon atmosphere, and kept warm for 2 h to obtain a gallium-doped hollow ZSM-5 molecular sieve catalyst, named Ga@Hol-ZSM-5.

[0098] Although the present invention is described herein with reference to a number of illustrative embodiments of the present invention, it will be appreciated that those skilled in the art may devise numerous other modifications and implementations that fall within the scope of the present disclosure. More specifically, within the scope of the present disclosure, drawings, and claims, a variety of variations and modifications may be made to the components or layout. In addition to variations and modifications to the components or layout, other uses will be apparent to those skilled in the art.

Claims

1. A method for preparing gallium-doped hollow ZSM-5 molecular sieve by microwave, characterized in that The steps include: S1. Mix the silicon source, template and deionized water and stir for 1 to 6 hours to obtain a precursor a; S2. Transfer the precursor a to a digestion tank and perform microwave hydrothermal treatment to obtain product a; S3. The product a is placed in a muffle furnace and calcined to remove the template to obtain a pure silicon molecular sieve; S4. Take pure silicon molecular sieve, add aluminum source, template and deionized water, and ultrasonicate for 1 to 3 hours to obtain precursor b; S5. The precursor b is transferred to a digestion tank, subjected to microwave hydrothermal treatment and dissolution-recrystallization to obtain product b; S6. The product b is placed in a muffle furnace and calcined to remove the template to obtain a hollow ZSM-5 molecular sieve; S7. Take a hollow ZSM-5 molecular sieve, add gallium nitrate and deionized water, and ultrasonicate for 1 to 3 hours to obtain a mixture c; S8. The mixture c is transferred to a digestion tank, gallium-doped under microwave irradiation, and the product is filtered, washed, and dried; S9. Place the dried product in a tube furnace and keep it warm at 200-300° C. in an argon atmosphere for 2-4 hours to obtain a gallium-doped hollow ZSM-5 molecular sieve.

2. The method according to claim 1, characterized in that: In step S1, the silicon source is tetraethyl orthosilicate, the template agent is tetrapropylammonium hydroxide, the amount of tetrapropylammonium hydroxide is 0.36-0.375 g / ml, and the amount of tetraethyl orthosilicate is 0.36-0.37 g / ml.

3. The method according to claim 1, characterized in that: The microwave hydrothermal treatment in step S2 is carried out by keeping the temperature at 150-180° C. for 1-4 hours under microwave irradiation, and the microwave power is 1000-2000W.

4. The method according to claim 1, characterized in that: In the step S3, the temperature is raised to 500-700° C. at a heating rate of 5-20° C. / min and kept at that temperature for 3-6 hours.

5. The method according to claim 1, characterized in that: The average pore size of the pure silicon molecular sieve in step S3 is 1 to 40 nanometers, and the specific surface area is 500 to 800 m 2 / g, and the particle size is 0.5 to 2 microns.

6. The method according to claim 1, characterized in that: In step S4, the aluminum source is aluminum isopropoxide, the template agent is tetrapropylammonium hydroxide, the amount of pure silicon molecular sieve is 0.05-0.06 g / ml, the amount of tetrapropylammonium hydroxide is 0.19-0.20 g / ml, and the amount of aluminum isopropoxide is 0.001-0.003 g / ml.

7. The method according to claim 1, characterized in that: The microwave hydrothermal treatment and dissolution-recrystallization in step S5 is carried out by keeping the temperature at 150-180° C. for 1-4 hours under microwave irradiation, and the microwave power is 1000-2000W.

8. The method according to claim 1, characterized in that: In the step S6, the temperature is raised to 500-700° C. at a heating rate of 5-20° C. / min and kept at this temperature for 3-6 hours.

9. The method according to claim 1, characterized in that: In step S7, the dosage of hollow ZSM-5 molecular sieve is 0.1-0.2 / ml, and the dosage of gallium nitrate is 0.004-0.006 g / ml; in step S8, the microwave immersion power is 1200-1500 W, the insulation temperature is 60-100° C., and the insulation time is 2-4 hours.

10. The method according to claim 1, characterized in that: The gallium-doped hollow ZSM-5 molecular sieve is used as a catalyst for aromatization of methanol to produce aromatics, specifically, the gallium-doped hollow ZSM-5 molecular sieve is pressed into thin sheets and vertically placed in a reactor for methanol gas to pass through.

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