Metal-modified zsm-5 molecular sieve catalyst, its preparation method and application

Abstract

The application provides a metal-modified ZSM-5 molecular sieve catalyst and a preparation method and application thereof, and comprises the following steps: mixing ZSM-5 molecular sieve, tetraethyl orthosilicate, trichloroacetic acid and water to react, and filtering to obtain an intermediate; mixing the intermediate, a melamine solution and a metal salt solution, and drying and calcining to obtain the metal-modified ZSM-5 molecular sieve catalyst. The prepared catalyst has good catalytic activity, selectivity, stability and the like, and the preparation process is simple and easy to operate.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a metal-modified ZSM-5 molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] ZSM-5 molecular sieves, with their unique pore structure and high specific surface area, are widely used in catalysis, such as in naphtha steam cracking (SC) and refinery fluidized catalytic cracking (FCC) for the production of low-carbon olefins (C2–C4 olefins). Metal modification of ZSM-5 molecular sieves can enhance their catalytic activity and selectivity for low-carbon olefins, thereby increasing the yield of low-carbon olefins.

[0003] The catalytic activity and selectivity of metal-modified ZSM-5 molecular sieves are related to the metal loading rate. The preparation process of metal-modified ZSM-5 molecular sieves directly affects the metal loading rate. During catalyst preparation, the loaded metal is easily lost, thus affecting the catalytic activity and selectivity of the catalyst. In addition, as the silica-alumina ratio of ZSM-5 molecular sieves increases, their hydrothermal stability also gradually improves. However, the synthesis of ZSM-5 molecular sieves with high silica-alumina ratios is more difficult, and the framework structure of the molecular sieve is easily destroyed during the synthesis process, affecting the structural stability of ZSM-5 molecular sieves. Therefore, how to further improve the catalytic activity, selectivity, and stability of the catalyst is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This invention provides a method for preparing a metal-modified ZSM-5 molecular sieve catalyst. The catalyst obtained has advantages such as good catalytic activity, selectivity, and stability, and the preparation process is simple and easy to operate.

[0005] In one aspect, the present invention provides a method for preparing a metal-modified ZSM-5 molecular sieve catalyst, comprising the following steps: mixing and reacting ZSM-5 molecular sieve, tetraethyl orthosilicate, trichloroacetic acid, and water, and obtaining an intermediate by filtration; mixing the intermediate, melamine solution, and metal salt solution, and obtaining the metal-modified ZSM-5 molecular sieve catalyst by drying and calcination.

[0006] According to one embodiment of the present invention, the process of mixing the intermediate, melamine solution and metal salt solution includes: first mixing and stirring the intermediate and melamine solution for 10 min to 30 min to obtain a mixture, and then mixing the mixture with the metal salt solution.

[0007] According to one embodiment of the present invention, the melamine solution includes melamine and an organic solvent, wherein the mass ratio of the organic solvent to the melamine is (0.4-1):1.

[0008] According to one embodiment of the present invention, the mass ratio of melamine to the ZSM-5 molecular sieve is (0.03 to 0.3):1.

[0009] According to one embodiment of the present invention, the organic solvent is selected from at least one of acetic acid and ethylene glycol.

[0010] According to one embodiment of the present invention, the mass ratio of trichloroacetic acid to the ZSM-5 molecular sieve is (0.8 to 3.5):1; and / or, the mass ratio of tetraethyl orthosilicate to the ZSM-5 molecular sieve is (0.2 to 0.6):1.

[0011] According to one embodiment of the present invention, the reaction conditions are: temperature 80°C, time 10 min-60 min.

[0012] According to one embodiment of the present invention, the drying conditions are: temperature 100℃~110℃, time 8h-14h; and / or, the calcination conditions are: temperature 480℃~580℃, time 1h~4h.

[0013] In a second aspect, the present invention provides a metal-modified ZSM-5 molecular sieve catalyst, which is prepared by the above-described preparation method.

[0014] A third aspect of the present invention provides a method for preparing low-carbon olefins, comprising: reacting an alkane feedstock under the catalytic action of the aforementioned metal-modified ZSM-5 molecular sieve catalyst to obtain low-carbon olefins.

[0015] The implementation of this invention has at least the following beneficial effects:

[0016] The present invention provides a method for preparing metal-modified ZSM-5 molecular sieves. This method utilizes tetraethyl orthosilicate and trichloroacetic acid to perform a dealumination and silicon replenishment reaction on the ZSM-5 molecular sieve, increasing the silicon-aluminum ratio of the intermediate and thus improving catalyst stability. Melamine and a metal salt are then loaded onto the intermediate in the form of a complex. Because the metal-melamine complex has high stability and is not easily lost, the metal loading rate is increased. After drying and calcination, the resulting metal-modified ZSM-5 molecular sieve catalyst exhibits good catalytic activity, low-carbon olefin selectivity, and stability. Furthermore, the preparation process is simple, easy to operate, and operates under mild conditions, making it environmentally friendly and conducive to practical industrial production and application.

[0017] The metal-modified ZSM-5 molecular sieve catalyst provided by this invention, prepared by the above method, has advantages such as good catalytic activity, selectivity for low-carbon olefins and stability, and can be applied to the production of low-carbon olefins to improve the yield of low-carbon olefins. Attached Figure Description

[0018] Figure 1This is a nitrogen adsorption-desorption curve of the modified ZSM-5 molecular sieve catalyst in Example 1. Detailed Implementation

[0019] The specific embodiments listed below are merely descriptions of the principles and features of the present invention. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The preparation method of the metal-modified ZSM-5 molecular sieve catalyst provided by the present invention includes the following steps: mixing ZSM-5 molecular sieve, tetraethyl orthosilicate, trichloroacetic acid and water, reacting them, and filtering to obtain an intermediate; mixing the intermediate, melamine solution and metal salt solution, and drying and calcining to obtain the metal-modified ZSM-5 molecular sieve catalyst.

[0021] The inventors, through research and analysis, believe that in the preparation process of metal-modified ZSM-5 molecular sieve catalysts, first using tetraethyl orthosilicate and trichloroacetic acid to perform a dealumination and silicon replenishment reaction on the ZSM-5 molecular sieve is beneficial for increasing the silicon-aluminum ratio of the intermediate, further improving its thermal stability while maintaining high crystallinity, and extending the catalyst's lifespan. Furthermore, in metal-modified ZSM-5 molecular sieve catalysts, different metal loading rates result in varying reaction performance and selectivity for olefin products. This invention utilizes melamine and metal salts loaded onto the intermediate in the form of a complex. The metal-melamine complex has high stability and is not easily lost, thereby increasing the metal loading rate. This improves the catalyst's activity, stability, and selectivity for low-carbon olefins. The method of this invention also has advantages such as simple preparation process, easy operation, mild conditions, and environmental friendliness, which are beneficial for practical industrial production and application.

[0022] In this invention, the selected ZSM-5 molecular sieve includes, but is not limited to, ZSM-5 molecular sieves with a silica-to-alumina ratio of 20-300. The selected ZSM-5 molecular sieve can be obtained by conventional methods, such as commercial purchase.

[0023] It should be noted that, in this invention, the mass of ZSM-5 molecular sieve refers to the dry basis mass of ZSM-5 molecular sieve.

[0024] In this invention, ZSM-5 molecular sieve, tetraethyl orthosilicate, trichloroacetic acid and water are mixed to obtain a mixture. The mixture is subjected to a dealumination and silicon replenishment reaction under certain conditions to obtain an intermediate. The solid-liquid mass ratio in the mixture is 1:(10-15).

[0025] Among them, the dealumination and silicon replenishment reaction refers to the isomorphic replacement of aluminum atoms on the ZSM-5 molecular sieve framework with silicon atoms on tetraethyl orthosilicate to increase the silicon-aluminum ratio of the intermediate, thereby improving the thermal stability of the intermediate.

[0026] This invention does not limit the reaction process of ZSM-5 molecular sieve, tetraethyl orthosilicate, trichloroacetic acid, and water. For example, trichloroacetic acid and water can be mixed first to form a trichloroacetic acid solution, then the ZSM-5 molecular sieve and trichloroacetic acid solution can be mixed to undergo a dealumination reaction, followed by the addition of tetraethyl orthosilicate to undergo a silicon replenishment reaction, to obtain an intermediate.

[0027] The process of mixing trichloroacetic acid and water to form a trichloroacetic acid solution is carried out by stirring at room temperature, specifically at a temperature of 20℃~30℃ for 10min~30min.

[0028] ZSM-5 molecular sieve is first reacted with trichloroacetic acid solution, which removes some aluminum from the ZSM-5 molecular sieve framework. During the removal of aluminum, vacancies are left in the original positions of aluminum atoms. These vacancies increase the diameter of the molecular sieve's pore structure and also affect its stability. At this point, tetraethyl orthosilicate is added, and silicon atoms are used to fill the vacancies. Since the bond length of Si-O is shorter than that of Al-O, the diameter of the pore structure on the surface of the molecular sieve can be reduced. Through this removal of aluminum and addition of silicon process, the silicon-aluminum ratio of the product is increased while ensuring the crystallinity retention, thereby improving the thermal stability of the product.

[0029] Furthermore, by controlling the conditions of the dealumination and silica replenishment reaction, the degree of shrinkage of the pore structure on the surface of the molecular sieve can be controlled, thereby obtaining ZSM-5 molecular sieves with different degrees of surface pore size shrinkage. In this invention, by adjusting the conditions of the dealumination and silica replenishment reaction, the molecular sieve framework can be made into mesoporous structures through the dealumination and silica replenishment reaction. This facilitates the mass transfer of reactants during subsequent catalysis, slows down the formation of coke and carbon deposits, thereby avoiding a decrease in catalyst activity and improving catalyst stability.

[0030] In the aforementioned dealumination and silicon replenishment reaction, the reaction temperature affects the degree of shrinkage of the pore structure on the molecular sieve surface. This is because the reaction temperature directly affects the reaction rate. If the temperature is too high, the dealumination and silicon replenishment reaction rate will be too fast, making it difficult to control the pore structure of the molecular sieve and hindering the retention of the molecular sieve's framework structure. If the temperature is too low, the dealumination and silicon replenishment reaction rate will be too slow, which is detrimental to the subsequent reactions. In one embodiment of the present invention, the temperature of the dealumination and silicon replenishment reaction is 80°C.

[0031] The dealumination and silicon replenishment reaction can be carried out under stirring, with the dealumination reaction taking 10-30 minutes and the silicon replenishment reaction taking 20-60 minutes.

[0032] The dealumination and silicon replenishment reaction conditions in this invention are mild. During the dealumination and silicon replenishment reaction, silicon atoms are used to selectively replace aluminum atoms on the molecular sieve framework. This maintains the framework structure of ZSM-5 zeolite molecular sieve and also produces a mesoporous intermediate. This improves the preparation efficiency while ensuring the quality of the product. When applied to catalysis, it is beneficial for the mass transfer of reaction raw materials and slows down the formation of coke and carbon deposits.

[0033] After reacting ZSM-5 molecular sieve, tetraethyl orthosilicate, trichloroacetic acid, and water, an intermediate is obtained through solid-liquid separation. This solid-liquid separation can be performed using conventional methods in the field, such as vacuum filtration. Specifically, the reaction product is placed in a vacuum filtration flask, and a vacuum pump is used to reduce the pressure in the flask, achieving solid-liquid separation. The intermediate is obtained by washing the solid phase obtained through vacuum filtration.

[0034] The ratio of ZSM-5 molecular sieve, tetraethyl orthosilicate, and trichloroacetic acid also affects the silicon-to-aluminum ratio of the resulting intermediate and the degree of shrinkage of the pore structure on the molecular sieve surface. If too much trichloroacetic acid is added, the proportion of aluminum atoms extracted from the ZSM-5 molecular sieve will be high, resulting in an excessively large pore diameter, which is detrimental to the sieve's framework structure. If too little trichloroacetic acid and tetraethyl orthosilicate are added, it will hinder the formation of mesoporous structures and the improvement of the silicon-to-aluminum ratio. If too much tetraethyl orthosilicate is added, it will lead to a waste of raw materials. In one embodiment of the present invention, the mass ratio of trichloroacetic acid to ZSM-5 molecular sieve is (0.8–3.5):1, for example, 0.8:1, 0.9:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, or any combination thereof. The mass ratio of tetraethyl orthosilicate to ZSM-5 molecular sieve is (0.2 to 0.6):1, for example, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1 or any combination thereof.

[0035] By mixing an intermediate, a melamine solution, and a metal salt solution, the metal ions in the metal salt solution react with the melamine in the melamine solution to form a metal-melamine complex, which is then loaded onto the intermediate. Due to the high stability of the metal-melamine complex, it is not easily lost during subsequent solid-liquid separation, thereby increasing the metal loading rate.

[0036] This invention does not limit the mixing method of the intermediate, melamine solution, and metal salt solution. In order to ensure that the metal-melamine complex can be uniformly loaded on the intermediate, the process of mixing the intermediate, melamine solution, and metal salt solution includes: first, mixing and stirring the intermediate and melamine solution for 10 min to 30 min to make the melamine solution and intermediate uniformly mixed to obtain a mixture; then, mixing the mixture with the metal salt solution so that the metal ions in the metal salt solution are uniformly loaded on the intermediate in the form of a metal-melamine complex under the action of the melamine solution.

[0037] In this invention, the melamine solution includes melamine and an organic solvent. Melamine is dissolved in the organic solvent, and then the intermediate and the melamine solution are mixed. By introducing the organic solvent, the dispersion of melamine and the intermediate can be improved. Under the action of the organic solvent, melamine can be uniformly dispersed on the surface of the intermediate, which also facilitates sufficient contact with the metal salt solution in the subsequent process.

[0038] In the melamine solution, the mass ratio of organic solvent to melamine is (0.4 to 1):1, for example, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1 or any combination thereof.

[0039] The organic solvent is selected from at least one of acetic acid and ethylene glycol.

[0040] The melamine solution also contains water, which can further improve the dispersion of melamine.

[0041] The mass ratio of melamine to ZSM-5 molecular sieve is (0.03 to 0.3):1, for example, 0.03:1, 0.05:1, 0.08:1, 0.1:1, 0.12:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, or any combination thereof.

[0042] After mixing and reacting the intermediate, melamine solution, and metal salt solution, the reaction product is obtained. The reaction product is then subjected to solid-liquid separation, drying, and calcination to obtain the metal-modified ZSM-5 molecular sieve catalyst.

[0043] Solid-liquid separation is performed to collect the solid phase from the reaction products. The solid-liquid separation process can be carried out using conventional separation methods in the art, such as filtration or vacuum filtration.

[0044] Drying a solid phase is done to remove excess moisture from its surface. The drying conditions are as follows: temperature 100℃~110℃, for example, 100℃, 105℃, 110℃ or any combination thereof; time 8h~14h, for example, 8h, 9h, 10h, 11h, 12h, 13h, 14h or any combination thereof.

[0045] Calcination is performed to form a metal oxide from the metal-melamine complex supported on the surface of the intermediate. The calcination conditions are: temperature 480℃~580℃, for example, 480℃, 500℃, 550℃, 580℃ or any combination thereof; time 1h~4h, for example, 1h, 2h, 3h, 4h or any combination thereof.

[0046] In this invention, the metal salt solution comprises a metal salt and water, wherein the metal element in the metal salt is selected from at least one of Fe, Cu, Ti, Zr, Mn, and Zn. Based on 100% of the total weight of the metal-modified ZSM-5 molecular sieve catalyst, the mass percentage of the metal element is 0.02-10%, wherein the mass of the metal element is based on the corresponding metal oxide. The mass percentage of the ZSM-5 molecular sieve is 92-99.98%.

[0047] The present invention also includes post-processing of the calcined product, which includes pressing the calcined product into tablets at 20 MPa and sieving it to 20-40 mesh particles to obtain the metal-modified ZSM-5 molecular sieve catalyst.

[0048] This invention also provides a metal-modified ZSM-5 molecular sieve catalyst, prepared using the above-described method. It possesses advantages such as good catalytic activity, selectivity for low-carbon olefins, and stability, and can be applied to the production of low-carbon olefins to improve their yield.

[0049] This invention also provides a method for preparing low-carbon olefins, comprising: reacting an alkane feedstock under the catalysis of the aforementioned metal-modified ZSM-5 molecular sieve catalyst to obtain low-carbon olefins. The alkane feedstock includes C6-C10 alkanes.

[0050] The preparation process of the aforementioned low-carbon olefins can be carried out in a fixed bed, for example, in a continuous flow fixed-bed reactor. Specifically, the catalyst can be packed into the reactor, the reactor can be purged with an inert gas, and then the alkane feedstock can be passed through the catalyst to react. The reaction conditions are: temperature 630℃, feed mass hourly space velocity (MHSV) of 6 h⁻¹. -1 Alkane feedstock can be pumped into the reactor.

[0051] The present invention will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0052] In the following examples and comparative examples, the raw materials used include: industrial ZSM-5 molecular sieve (loss on ignition 8.9 wt%), sourced from Lanzhou Petrochemical Catalyst Plant;

[0053] Melamine, acetic acid, ethylene glycol, trichloroacetic acid, tetraethyl orthosilicate, ferric chloride hexahydrate, copper chloride dihydrate, titanium sulfate, zirconium chloride, manganese chloride tetrahydrate, and zinc chloride—all materials were of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd.

[0054] The following examples and comparative examples were evaluated using the following methods:

[0055] The pore structure of the catalyst was determined using a low-temperature nitrogen adsorption-desorption method, and the metal content on the catalyst was determined using a fluorescence method. (For analytical methods, please refer to "Analytical Methods in Petrochemical Industry (RIPP Experimental Methods)", edited by Yang Cuiding et al., Science Press, 1990).

[0056] Catalyst performance evaluation: The reaction was carried out in a continuous flow fixed-bed reactor with a catalyst loading of 5 g and silica wool at both ends. The reactor was purged with N2 for 30 min before the reaction, using N2 as the carrier gas. The reactant was n-hexane, pumped into the reactor using a micro-pump. The reaction temperature was 630℃, and the feed mass hourly space velocity (WHSV) was 6 h⁻¹. -1 The reaction products were analyzed online using an SP-3420 gas chromatograph; catalyst lifetime data were taken from the start of feeding to the conversion rate dropping to 90% as a reference.

[0057] Using n-hexane as a raw material, the conversion rate of n-hexane and the selectivity of product distribution are calculated using the following formulas: In the formula w in and w out These represent the mass fractions of n-hexane in the reactants, w and w, respectively. out This represents the mass fraction of n-hexane in the reaction products. The mass fraction of a certain substance in the product; Modified metal retention rate = amount of metal loaded on the catalyst / total amount of metal added.

[0058] The evaluation results are shown in Table 1.

[0059] Example 1

[0060] (1) Mix 1.8g melamine, 0.72g ethylene glycol and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0061] (2) Mix 20g of ZSM-5 molecular sieve (dry basis mass) with a silicon-to-aluminum ratio of 35, 16g of trichloroacetic acid and 200g of deionized water, stir at 80℃ for 20min, then add 4g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, obtain intermediate (sample b).

[0062] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0063] (4) Weigh 2.89g of ferric chloride hexahydrate and add it to slurry c. Stir for 30min to obtain slurry d. Filter slurry d to obtain solid phase. Dry at 100℃ for 12h and calcine at 550℃ for 4h to obtain metal Fe modified ZSM-5 molecular sieve catalyst powder.

[0064] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C1 for evaluating the catalyst's reaction performance.

[0065] Example 2

[0066] (1) Mix 0.6g melamine, 0.24g acetic acid and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0067] (2) Mix 20g of ZSM-5 molecular sieve (dry basis mass) with a silicon-to-aluminum ratio of 20, 43g of trichloroacetic acid and 250g of deionized water, stir at 80℃ for 20min, then add 8g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, obtain intermediate (sample b).

[0068] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0069] (4) Weigh 0.02g of ferric chloride hexahydrate and add it to slurry c. Stir for 30min to obtain slurry d. Filter slurry d to obtain solid phase. Dry at 100℃ for 12h and calcine at 550℃ for 4h to obtain metal Fe modified ZSM-5 molecular sieve catalyst powder.

[0070] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C1 for evaluating the catalyst's reaction performance.

[0071] Example 3

[0072] (1) Mix 3g of melamine, 1.8g of acetic acid and 40g of deionized water at 25°C for 10 minutes to obtain a melamine solution (slurry a);

[0073] (2) Mix 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 100, 30g of trichloroacetic acid and 200g of deionized water, stir at 80℃ for 20min, then add 6g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, the intermediate (sample b) is obtained.

[0074] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0075] (4) Weigh 2.11g of copper chloride dihydrate and add it to slurry c. Stir for 30min to obtain slurry d. Filter slurry d to obtain solid phase. Dry at 100℃ for 12h and calcine at 550℃ for 4h to obtain metal Cu modified ZSM-5 molecular sieve catalyst powder.

[0076] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C3 for evaluating the catalyst's reaction performance.

[0077] Example 4

[0078] (1) Mix 4.8g melamine, 3.4g ethylene glycol and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0079] (2) Mix 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 200, 36g of trichloroacetic acid and 300g of deionized water, stir at 80℃ for 20min, then add 8g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, the intermediate (sample b) is obtained.

[0080] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0081] (4) Weigh 3.38g of copper chloride dihydrate and add it to slurry c. Stir for 30min to obtain slurry d. Filter slurry d to obtain solid phase. Dry at 100℃ for 12h and calcine at 550℃ for 4h to obtain metal Cu modified ZSM-5 molecular sieve catalyst powder.

[0082] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C4 for evaluating the catalyst's reaction performance.

[0083] Example 5

[0084] (1) Mix 0.6g melamine, 0.5g ethylene glycol and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0085] (2) Mix 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 250, 40g of trichloroacetic acid and 200g of deionized water, stir at 80℃ for 20min, then add 10g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, obtain intermediate (sample b).

[0086] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0087] (4) Weigh 1.00g of titanium sulfate and add it to slurry c and stir for 30min to obtain slurry d; filter slurry d to obtain solid phase, dry at 100℃ for 12h, and calcine at 550℃ for 4h to obtain metal Ti modified ZSM-5 molecular sieve catalyst powder.

[0088] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C5 for evaluating the catalyst's reaction performance.

[0089] Example 6

[0090] (1) Mix 2.4g melamine, 2.4g acetic acid and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0091] (2) Mix 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 300, 42g of trichloroacetic acid and 200g of deionized water, stir at 80℃ for 20min, then add 12g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, the intermediate (sample b) is obtained.

[0092] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0093] (4) Weigh 4.00g of titanium sulfate and add it to slurry c and stir for 30min to obtain slurry d; filter slurry d to obtain solid phase, dry at 100℃ for 12h, and calcine at 550℃ for 4h to obtain metal Ti modified ZSM-5 molecular sieve catalyst powder.

[0094] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C6 for evaluating the catalyst's reaction performance.

[0095] Example 7

[0096] (1) Mix 0.3g melamine, 0.24g acetic acid and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0097] (2) Add 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 35 and 70g of trichloroacetic acid to 200g of deionized water, stir at 80℃ for 20min, then add 8g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, the intermediate (sample b) is obtained.

[0098] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0099] (4) Weigh 0.26g of zirconium chloride and add it to slurry c and stir for 30min to obtain slurry d; filter slurry d to obtain solid phase, dry at 100℃ for 12h, and calcine at 550℃ for 4h to obtain metal Zr modified ZSM-5 molecular sieve catalyst powder.

[0100] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C7 for evaluating the catalyst's reaction performance.

[0101] Example 8

[0102] (1) Mix 1.2g melamine, 0.96g ethylene glycol and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0103] (2) Add 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 100 and 60g of trichloroacetic acid to 200g of deionized water, stir at 80℃ for 20min, then add 6g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, the intermediate (sample b) is obtained.

[0104] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0105] (4) Weigh 1.02g of zirconium chloride and add it to slurry c and stir for 30min to obtain slurry d; filter slurry d to obtain solid phase, dry at 100℃ for 12h, and calcine at 550℃ for 4h to obtain metal Zr modified ZSM-5 molecular sieve catalyst powder.

[0106] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C8 for evaluating the catalyst's reaction performance.

[0107] Example 9

[0108] (1) Mix 4.2g of melamine, 3.78g of ethylene glycol and 40g of deionized water at 25°C for 10 minutes to obtain a melamine solution (slurry a);

[0109] (2) Add 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 300 and 50g of trichloroacetic acid to 200g of deionized water, stir at 80℃ for 20min, then add 10g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, the intermediate (sample b) is obtained.

[0110] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0111] (4) Weigh 5.04g of manganese chloride tetrahydrate and add it to slurry c. Stir for 30min to obtain slurry d solution. Filter slurry d to obtain solid phase. Dry at 100℃ for 12h and calcine at 550℃ for 4h to obtain metal Mn modified ZSM-5 molecular sieve catalyst powder.

[0112] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C9 for evaluating the catalyst's reaction performance.

[0113] Example 10

[0114] (1) Mix 6g of melamine, 6g of ethylene glycol and 40g of deionized water at 25°C for 10 minutes to obtain a melamine solution (slurry a);

[0115] (2) Add 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 35 and 56g of trichloroacetic acid to 200g of deionized water, stir at 80℃ for 20min, then add 12g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, the intermediate (sample b) is obtained.

[0116] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0117] (4) Weigh 4.18g of zinc chloride and add it to slurry c and stir for 30min to obtain slurry d; filter slurry d to obtain solid phase, dry at 100℃ for 12h, and calcine at 550℃ for 4h to obtain metal Zn modified ZSM-5 molecular sieve catalyst powder.

[0118] The catalyst powder was pressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C10 for evaluating the catalyst's reaction performance.

[0119] Example 11

[0120] (1) Mix 1.8g melamine, 0.72g ethylene glycol and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0121] (2) Mix 20g of ZSM-5 molecular sieve (dry basis mass) with a silicon-to-aluminum ratio of 35, 100g of trichloroacetic acid and 100g of deionized water, stir at 80℃ for 20min, then add 20g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, the intermediate (sample b) is obtained.

[0122] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0123] (4) Weigh 2.89g of ferric chloride hexahydrate and add it to slurry c. Stir for 30min to obtain slurry d. Filter slurry d to obtain solid phase. Dry at 100℃ for 12h and calcine at 550℃ for 4h to obtain metal Fe modified ZSM-5 molecular sieve catalyst powder.

[0124] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C11 for evaluating the catalyst's reaction performance.

[0125] Example 12

[0126] (1) Mix 1.8g melamine, 0.72g ethylene glycol and 40g deionized water at 25℃ for 10min to obtain a melamine solution (slurry a);

[0127] (2) Mix 20g of ZSM-5 molecular sieve (dry basis mass) with a silicon-to-aluminum ratio of 35, 16g of trichloroacetic acid and 200g of deionized water, stir at 25°C for 20min, then add 4g of tetraethyl orthosilicate and stir for 40min. After filtration and washing until neutral, obtain intermediate (sample b).

[0128] (3) Add sample b to slurry a and mix, stirring for 20 minutes to obtain slurry c;

[0129] (4) Weigh 2.89g of ferric chloride hexahydrate and add it to slurry c. Stir for 30min to obtain slurry d. Filter slurry d to obtain solid phase. Dry at 100℃ for 12h and calcine at 550℃ for 4h to obtain metal Fe modified ZSM-5 molecular sieve catalyst powder.

[0130] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst C12 for evaluating the catalyst's reaction performance.

[0131] Comparative Example 1

[0132] (1) Mix 20g of ZSM-5 molecular sieve (dry basis) with 300 silica-alumina ratio and 40g of deionized water at 25℃ for 10min to obtain slurry a;

[0133] (2) Add 2.89g of ferric chloride hexahydrate to slurry a and stir for 30min to obtain slurry b; filter slurry b to obtain solid phase, dry at 100℃ for 12h, and calcine at 550℃ for 4h to obtain metal Fe modified ZSM-5 molecular sieve catalyst powder.

[0134] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst D1 for evaluating the catalyst's reaction performance.

[0135] Comparative Example 2

[0136] 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 10 and 1.02g of titanium sulfate were mixed with 12g of deionized water at 25℃ and then impregnated with metallic Ti for modification. After drying at 100℃ for 12h, the catalyst powder modified with metallic Ti was obtained by calcination at 550℃ for 4h.

[0137] The catalyst powder was pressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst D2 for evaluating the catalyst's reaction performance.

[0138] Comparative Example 3

[0139] 10g of ZSM-5 (dry basis) with a silicon-to-aluminum ratio of 30 and 0.01g of ZrO2 particles were thoroughly mixed. 20g of deionized water was slowly added and stirred thoroughly. The solid-liquid mixture was transferred to a high-temperature reactor, where the reaction pressure was atmospheric pressure. The reactor was reacted at 240℃ for 6 hours. The reactor was then removed and cooled to room temperature in air. The reactor was then opened and dried at 140℃ for 10 hours to obtain Zr-modified ZSM-5 molecular sieve catalyst powder prepared by hydrothermal method.

[0140] The catalyst powder was pressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst D3 for evaluating the catalyst's reaction performance.

[0141] Comparative Example 4

[0142] 6g of melamine, 6g of ethylene glycol, and 40g of deionized water were stirred at 25℃ for 10 minutes to obtain a melamine solution (slurry a). Then, 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 35 was added to slurry a and stirred for 20 minutes to obtain slurry b. Next, 2.89g of ferric chloride hexahydrate was weighed and added to slurry b and stirred for 30 minutes to obtain slurry c. Finally, slurry c was filtered to obtain a solid phase, which was dried at 100℃ for 12 hours and calcined at 550℃ for 4 hours to obtain Zn-modified ZSM-5 molecular sieve catalyst powder.

[0143] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst D4 for evaluating the catalyst's reaction performance.

[0144] Comparative Example 5

[0145] 20g of ZSM-5 molecular sieve (dry basis) with a silicon-to-aluminum ratio of 35 and 56g of trichloroacetic acid were added to 200g of deionized water and stirred at 80℃ for 20min. Then, 12g of tetraethyl orthosilicate was added and stirred for 40min. After filtration and washing until neutral, an intermediate (sample a) was obtained. Then, 2.89g of ferric chloride hexahydrate, 12g of deionized water and sample a were mixed evenly and modified by impregnation with Fe metal. Finally, the mixture was dried at 100℃ for 12h and then calcined at 550℃ for 4h to obtain Fe metal modified ZSM-5 molecular sieve catalyst powder.

[0146] The catalyst powder was compressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain metal-modified ZSM-5 molecular sieve catalyst D5 for evaluating the catalyst's reaction performance.

[0147] Table 1

[0148]

[0149] Table: Blank reagent * The sample is an unmodified ZSM-5 molecular sieve; " / " indicates no metal loading.

[0150] Figure 1 This is a nitrogen adsorption-desorption curve of the modified ZSM-5 molecular sieve catalyst in Example 1. According to... Figure 1It can be seen that the modified ZSM-5 molecular sieve catalyst in Example 1 contains a mesoporous structure.

[0151] As shown in Table 1, when the metal-modified ZSM-5 molecular sieve catalyst is prepared using the method provided by this invention, almost no metal is lost, resulting in a high metal retention rate, which improves the metal loading rate in the catalyst. Furthermore, the carbon deposition rate is below 0.02 wt% h, and the catalyst lifespan is above 80 h, exhibiting a lower carbon deposition rate and a longer catalyst lifespan. When this catalyst is applied to the preparation of low-carbon olefins, it can significantly improve the selectivity of low-carbon olefins, thereby increasing the yield of low-carbon olefins.

[0152] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a metal-modified ZSM-5 molecular sieve catalyst, characterized in that, Includes the following steps: ZSM-5 molecular sieve, tetraethyl orthosilicate, trichloroacetic acid, and water were mixed and reacted, and the intermediate was obtained by filtration. The intermediate, melamine solution, and metal salt solution were mixed, dried, and calcined to obtain the metal-modified ZSM-5 molecular sieve catalyst. The metal element in the metal salt is selected from at least one of Fe, Cu, Ti, Zr, Mn, and Zn; The mass ratio of trichloroacetic acid to the ZSM-5 molecular sieve is (0.8~3.5):1; The mass ratio of the tetraethyl orthosilicate to the ZSM-5 molecular sieve is (0.2~0.6):

1.

2. The preparation method according to claim 1, characterized in that, The process of mixing the intermediate, melamine solution, and metal salt solution includes: first, mixing and stirring the intermediate and melamine solution for 10-30 minutes to obtain a mixture, and then mixing the mixture with the metal salt solution.

3. The preparation method according to claim 1 or 2, characterized in that, The melamine solution includes melamine and an organic solvent, wherein the mass ratio of the organic solvent to the melamine is (0.4~1):

1.

4. The preparation method according to claim 3, characterized in that, The mass ratio of melamine to ZSM-5 molecular sieve is (0.03~0.3):

1.

5. The preparation method according to claim 3, characterized in that, The organic solvent is selected from at least one of acetic acid and ethylene glycol.

6. The preparation method according to claim 1, characterized in that, The reaction conditions are: temperature 80℃, time 10min-60min.

7. The preparation method according to claim 1, characterized in that, The drying conditions are: temperature 100℃~110℃, time 8h-14h; and / or, The calcination conditions are: temperature 480℃~580℃, time 1h~4h.

8. A metal-modified ZSM-5 molecular sieve catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. A method for preparing a low-carbon olefin, comprising: The alkane feedstock is reacted under the catalysis of the metal-modified ZSM-5 molecular sieve catalyst as described in claim 8 to produce low-carbon olefins.

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