Mesoporous zsm-5 molecular sieve based fluidized bed catalyst, its preparation method and application

Abstract

The application provides a mesoporous ZSM-5 molecular sieve based fluidized bed catalyst and a preparation method and application thereof, and belongs to the technical field of catalytic materials. The mesoporous ZSM-5 molecular sieve, kaolin, a zinc compound, an aluminum-based binder and water are mixed to obtain a catalyst colloid; the catalyst colloid is sequentially subjected to spray forming and calcination to obtain the mesoporous ZSM-5 molecular sieve based fluidized bed catalyst. The mesoporous ZSM-5 molecular sieve based fluidized bed catalyst provided by the application is used for catalyzing aldehyde and ammonia gas phase cyclization condensation reaction to synthesize pyridine and alkyl pyridine, and the product yield is high.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, and in particular to a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, its preparation method, and its application. Background Technology

[0002] In recent years, the demand for pyridine and its derivatives has increased rapidly in fields such as pesticides, pharmaceuticals, feed additives, and fragrances. The synthesis of pyridine based on the gas-phase cyclization condensation reaction of aldehydes and ammonia was first proposed by chemist Alexei Yevgenyevich Tsitsibabin in 1924. This method uses aldehydes containing α-H and ammonia as raw materials, and generates pyridine and alkylpyridines through a gas-phase cyclization condensation reaction. Currently, the production process of synthesizing pyridine and alkylpyridines based on the gas-phase cyclization condensation reaction of aldehydes and ammonia is used in the production of various products due to its low raw material cost and adjustable process.

[0003] The improvement of catalysts used in the gas-phase cyclization condensation reaction of aldehydes and ammonia to pyridine and alkylpyridine has always been a research hotspot. The development of these catalysts can be summarized in three stages: the stage using amorphous aluminosilicates as catalysts, the stage using crystalline aluminosilicates as catalysts, and the recent stage using metal-modified zeolite molecular sieves as catalysts. ZSM-5 molecular sieves possess a unique pore structure, good acid resistance, and thermal stability, making them suitable as catalysts for pyridine synthesis. Currently, methods for improving their performance mainly focus on loading metal cations (such as Ti, Pb, Cr, Mn, Ni, Co, Ag, Cu, Cd, etc.) onto ZSM-5 molecular sieves using impregnation and ion exchange methods. However, low product yields remain a problem when used for the catalytic synthesis of pyridine and alkylpyridine. Summary of the Invention

[0004] The purpose of this invention is to provide a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, its preparation method, and its application. The mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst provided by this invention is used to catalyze the gas-phase cyclization condensation reaction of aldehydes and ammonia to synthesize pyridine and alkylpyridine, with a high product yield.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, comprising the following steps:

[0007] Mesoporous ZSM-5 molecular sieve, kaolin, zinc compound, aluminum-based binder and water were mixed to obtain catalyst colloid;

[0008] The catalyst colloid was sequentially spray-molded and calcined to obtain the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst.

[0009] Preferably, the mesoporous ZSM-5 molecular sieve is an unmodified mesoporous ZSM-5 molecular sieve or a phosphorus-modified mesoporous ZSM-5 molecular sieve;

[0010] The unmodified mesoporous ZSM-5 molecular sieve has a silica-to-alumina ratio of 50-250 mol / mol and a total specific surface area of ​​300-500 m² / mol. 2 / g, with an external specific surface area of ​​40~120m² 2 / g, total pore volume is 0.20~0.35cm³ 3 / g, mesoporous pore volume is 0.05~0.25cm³ 3 / g, Na2O content ≤0.02wt%;

[0011] The phosphorus-modified mesoporous ZSM-5 molecular sieve comprises a molecular sieve matrix and phosphorus loaded on the molecular sieve matrix, wherein the molecular sieve matrix is ​​the unmodified mesoporous ZSM-5 molecular sieve; the content of P2O5 in the phosphorus-modified mesoporous ZSM-5 molecular sieve is 0.2~2.0wt%, and the content of Na2O is ≤0.02wt%.

[0012] Preferably, the preparation method of the mesoporous ZSM-5 molecular sieve includes the following steps:

[0013] Silica sol, tetrapropylammonium hydroxide, and water are mixed to obtain a first mixture; the first mixture is subjected to a first crystallization treatment to obtain a first crystallized product; the first crystallized product is subjected to a first calcination to obtain amorphous seed crystals.

[0014] The amorphous seed crystals, silica sol, tetrapropylammonium hydroxide, water, NaOH and NaAlO2 are mixed to obtain a second mixture; the second mixture is subjected to a second crystallization treatment to obtain a second crystallized product; the second crystallized product is subjected to a second calcination to obtain the unmodified mesoporous ZSM-5 molecular sieve.

[0015] The unmodified mesoporous ZSM-5 molecular sieve, phosphorus compound, and water are mixed, and the resulting molecular sieve slurry is subjected to a hydrothermal reaction to obtain the phosphorus-modified mesoporous ZSM-5 molecular sieve.

[0016] Preferably, the temperature of the first crystallization treatment is 85~95℃ and the time is 20~24h; the mass of the amorphous seed crystal is 10~15% of the mass of SiO2 in the silica sol in the second mixture; the temperature of the second crystallization treatment is 135~165℃ and the time is 70~74h.

[0017] Preferably, the mass ratio of the unmodified mesoporous ZSM-5 molecular sieve to water is 1:5~20; the amount of phosphorus compound used is calculated as P2O5, and the concentration of phosphorus compound in the molecular sieve slurry is 0.1~10.0 mol / L; the hydrothermal reaction temperature is 50~180℃, the pH value is 0.5~6.5, and the time is 0.5~12h.

[0018] Preferably, on a dry basis, the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst contains 30-60% mesoporous ZSM-5 molecular sieve by mass; on a dry basis, the kaolin content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 10-60% kaolin by mass; on a zinc oxide basis, the zinc compound content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 0.5-5% zinc compound by mass; and on an alumina basis, the aluminum-based binder content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 9-25% zinc oxide by mass.

[0019] Preferably, the average particle size of the particulate material obtained by spray molding is 50~90μm; the calcination temperature is 200~800℃, and the holding time is 0.5~6h.

[0020] This invention provides a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst prepared by the preparation method described above.

[0021] This invention provides the application of the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst described above in the catalytic gas-phase cyclization condensation reaction of aldehydes and ammonia to prepare pyridine and alkylpyridine.

[0022] Preferably, the conditions for the aldehyde-ammonia phase cyclization condensation reaction include: the reaction raw materials include formaldehyde, acetaldehyde and ammonia, and the molar ratio of formaldehyde, acetaldehyde and ammonia is 1~3:1~3:2~12; the reaction temperature is 430~530℃.

[0023] Beneficial Effects: This invention utilizes mesoporous ZSM-5 molecular sieves to prepare mesoporous ZSM-5 molecular sieve-based fluidized bed catalysts. These catalysts are then used to catalyze the gas-phase cyclization condensation reaction of aldehydes and ammonia to synthesize pyridine and alkylpyridines, achieving high product yields. Specifically, the use of mesoporous ZSM-5 molecular sieves avoids the temporary deactivation caused by rapid coking during the catalyst reaction. Furthermore, the zinc modification enhances the aromatization ability of the mesoporous ZSM-5 molecular sieves, which is beneficial for improving the yield and selectivity of pyridine and alkylpyridines.

[0024] Furthermore, the mesoporous ZSM-5 molecular sieve of the present invention is an unmodified mesoporous ZSM-5 molecular sieve or a phosphorus-modified mesoporous ZSM-5 molecular sieve. Phosphorus modification is beneficial to improving the stability of the ZSM-5 molecular sieve framework and the hydrothermal stability of the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, thereby improving the product yield.

[0025] The test results of this invention show that, using the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst provided by this invention, under the conditions of a reaction temperature of 475℃ and a molar ratio of formaldehyde, acetaldehyde and ammonia of 2:2:4, the sum of the yields of pyridine and trimethylpyridine is higher than 43.0 wt%, the catalyst has excellent stability, high yield of the target product and excellent selectivity.

[0026] Furthermore, the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst of the present invention has the characteristics of simple preparation process and environmental friendliness. Attached Figure Description

[0027] Figure 1 XRD patterns of amorphous and conventional seed crystals;

[0028] Figure 2 TEM image of unmodified mesoporous ZSM-5 molecular sieve;

[0029] Figure 3 Ar physical adsorption isotherm for unmodified mesoporous ZSM-5 molecular sieve;

[0030] Figure 4 TEM image of unmodified conventional ZSM-5 molecular sieve;

[0031] Figure 5 Ar physical adsorption isotherm for unmodified conventional ZSM-5 molecular sieve;

[0032] Figure 6 Ar physical adsorption isotherms for phosphorus-modified mesoporous ZSM-5 molecular sieve and phosphorus-modified conventional ZSM-5 molecular sieve. Detailed Implementation

[0033] This invention provides a method for preparing a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, comprising the following steps:

[0034] Mesoporous ZSM-5 molecular sieve, kaolin, zinc compound, aluminum-based binder and water were mixed to obtain catalyst colloid;

[0035] The catalyst colloid was sequentially spray-molded and calcined to obtain the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst.

[0036] In this invention, unless otherwise specified, all raw materials used are commercially available products well known to those skilled in the art or prepared using methods well known to those skilled in the art.

[0037] This invention involves mixing mesoporous ZSM-5 molecular sieves, kaolin, zinc compounds, aluminum-based binders, and water to obtain a catalyst colloid. In one embodiment, the mesoporous ZSM-5 molecular sieve can be either unmodified or phosphorus-modified. This invention uses phosphorus-modified mesoporous ZSM-5 molecular sieves to prepare a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst. This catalyst is then used to catalyze the gas-phase cyclization condensation reaction of aldehydes and ammonia to synthesize pyridine and alkylpyridine, achieving high product yields.

[0038] In one embodiment of the present invention, the silicon-to-aluminum ratio of the unmodified mesoporous ZSM-5 molecular sieve can be 50~250 mol / mol, more specifically 80~150 mol / mol, and even more specifically 110~120 mol / mol, and more specifically 113 mol / mol. The silicon-to-aluminum ratio mentioned in this invention specifically refers to the molar ratio of SiO2 to Al2O3; the total specific surface area can be 300~500 m² / m³. 2 / g, which can be further increased to 400~465m 2 / g, specifically 451m 2 / g; External specific surface area can be 40~120m² 2 / g, which can be further increased to 75~90m 2 / g, specifically 86m 2 / g; total pore volume can be 0.20~0.35cm³. 3 / g, and can be further reduced to 0.25~0.30cm 3 / g, specifically 0.28cm 3 / g; mesoporous pore volume can be 0.05~0.25cm³ 3 / g, and further can be 0.1~0.2cm 3 / g, specifically 0.15cm 3 / g; Na2O content ≤0.02wt%. As one embodiment of the present invention, when the Na2O content in the unmodified mesoporous ZSM-5 molecular sieve is higher than 0.02wt%, it is preferable to treat the unmodified mesoporous ZSM-5 molecular sieve with a conventional ion exchange method (i.e., a conventional method for preparing H-type molecular sieves) to make the Na2O content ≤0.02wt%.

[0039] In one embodiment of the present invention, the phosphorus-modified mesoporous ZSM-5 molecular sieve comprises a molecular sieve matrix and phosphorus loaded on the molecular sieve matrix, wherein the molecular sieve matrix is ​​the unmodified mesoporous ZSM-5 molecular sieve. In another embodiment of the present invention, the P2O5 content in the phosphorus-modified mesoporous ZSM-5 molecular sieve can be 0.2~2.0 wt%, specifically 0.2 wt%, 0.5 wt%, 0.78 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, or 2.0 wt%; the Na2O content is ≤0.02 wt%. In another embodiment of the present invention, when the Na2O content in the phosphorus-modified mesoporous ZSM-5 molecular sieve is higher than 0.02 wt%, it is preferable to treat the phosphorus-modified mesoporous ZSM-5 molecular sieve using a conventional ion exchange method (i.e., a conventional method for preparing H-type molecular sieves) to reduce the Na2O content to ≤0.02 wt%. In one embodiment of the present invention, the selectable ranges of the silica-to-alumina ratio, total specific surface area, external specific surface area, total pore volume, and mesopore volume of the phosphorus-modified mesoporous ZSM-5 molecular sieve are consistent with those of the unmodified mesoporous ZSM-5 molecular sieve; specifically, the silica-to-alumina ratio of the phosphorus-modified mesoporous ZSM-5 molecular sieve is 115 mol / mol, and the total specific surface area is 465 m² / mol. 2 / g, with an external specific surface area of ​​79m² 2 / g, total pore volume is 0.30cm³ 3 / g, mesoporous pore volume is 0.16cm³ 3 / g.

[0040] In one embodiment of the present invention, the unmodified mesoporous ZSM-5 molecular sieve is specifically prepared using raw materials including amorphous seed crystals (denoted as "Protozeolite" seed crystals), and the phosphorus-modified mesoporous ZSM-5 molecular sieve is specifically prepared by phosphorus modification of the unmodified mesoporous ZSM-5 molecular sieve. A detailed description follows.

[0041] As one embodiment of the present invention, the preparation method of the mesoporous ZSM-5 molecular sieve may include the following steps:

[0042] Silica sol, tetrapropylammonium hydroxide, and water are mixed to obtain a first mixture; the first mixture is subjected to a first crystallization treatment to obtain a first crystallized product; the first crystallized product is subjected to a first calcination to obtain amorphous seed crystals.

[0043] The amorphous seed crystals, silica sol, tetrapropylammonium hydroxide, water, NaOH and NaAlO2 are mixed to obtain a second mixture; the second mixture is subjected to a second crystallization treatment to obtain a second crystallized product; the second crystallized product is subjected to a second calcination to obtain the unmodified mesoporous ZSM-5 molecular sieve.

[0044] The unmodified mesoporous ZSM-5 molecular sieve, phosphorus compound, and water are mixed, and the resulting molecular sieve slurry is subjected to a hydrothermal reaction to obtain the phosphorus-modified mesoporous ZSM-5 molecular sieve.

[0045] This invention involves mixing silica sol, tetrapropylammonium hydroxide, and water to obtain a first mixture. In one embodiment, the silica sol contains 30 wt% SiO2, specifically Ludox HS-30; the tetrapropylammonium hydroxide is used in the form of an aqueous solution, meaning the silica sol, the tetrapropylammonium hydroxide aqueous solution, and water are mixed to obtain the first mixture; the water can be deionized water; the tetrapropylammonium hydroxide aqueous solution contains 25 wt% tetrapropylammonium hydroxide; the amount of silica sol used is based on SiO2, and the molar ratio of SiO2, TPAOH, and H2O in the first mixture can be 1:0.45:23.

[0046] After obtaining the first mixture, the present invention performs a first crystallization treatment on the first mixture to obtain a first crystallized product. In one embodiment of the present invention, the temperature of the first crystallization treatment can be 85~95℃, specifically 90℃; the time can be 20~24h, specifically 22h; the first crystallization treatment can be carried out in a stainless steel hydrothermal reactor with a polytetrafluoroethylene liner. In another embodiment of the present invention, the first crystallization treatment preferably further includes: centrifuging the obtained liquid, collecting the solid product and washing it with water by centrifugation, and then drying it in an oven at 75~80℃ for 10~12h to obtain the first crystallized product.

[0047] After obtaining the first crystallized product, the present invention subjectes the first crystallized product to a first calcination to obtain amorphous seed crystals. In one embodiment of the present invention, the temperature of the first calcination can be 545~555℃, specifically 550℃; the holding time can be 5.5~6.5h, specifically 6h; the first calcination can be carried out in an air atmosphere.

[0048] After obtaining the amorphous seed crystals, the present invention mixes the amorphous seed crystals, silica sol, tetrapropylammonium hydroxide, water, NaOH, and NaAlO2 to obtain a second mixture. As one embodiment of the present invention, the mixing can specifically be as follows: a first mixing of silica sol, an aqueous solution of tetrapropylammonium hydroxide, and water; a second mixing of the amorphous seed crystals; and a third mixing of an aqueous solution of NaOH and NaAlO2. As one embodiment of the present invention, the amounts of silica sol, NaAlO2, and NaOH are calculated as oxides, and the molar ratio of SiO2, Al2O3, Na2O, tetrapropylammonium hydroxide, and H2O in the second mixture can be 1:0.00667:0.16:0.05:15; the mass of the amorphous seed crystals is 10-15% of the mass of SiO2 in the silica sol of the second mixture, specifically 13%.

[0049] After obtaining the second mixture, the present invention performs a second crystallization treatment on the second mixture to obtain a second crystallized product. In one embodiment of the present invention, the temperature of the second crystallization treatment can be 135~165℃, specifically 140℃, 145℃, 150℃, 155℃, or 160℃; the time can be 70~74h, specifically 72h; the second crystallization treatment can be carried out in a stainless steel hydrothermal reactor with a polytetrafluoroethylene liner. In another embodiment of the present invention, the second crystallization treatment preferably further includes: centrifuging the obtained liquid, collecting the solid product and washing it with water by centrifugation, and then drying it in an oven at 75~80℃ for 10~12h to obtain the second crystallized product.

[0050] After obtaining the second crystallized product, the present invention subjectes the second crystallized product to a second calcination to obtain the unmodified mesoporous ZSM-5 molecular sieve. In one embodiment of the present invention, the temperature of the second calcination can be 545~555℃, specifically 550℃; the holding time can be 5.5~6.5h, specifically 6h; the second calcination can be carried out in an air atmosphere.

[0051] After obtaining the unmodified mesoporous ZSM-5 molecular sieve, the present invention mixes the unmodified mesoporous ZSM-5 molecular sieve, a phosphorus compound, and water, and subjectes the resulting molecular sieve slurry to a hydrothermal reaction to obtain the phosphorus-modified mesoporous ZSM-5 molecular sieve. As one embodiment of the present invention, the phosphorus compound may include one or more of phosphoric acid, ammonium phosphate, phosphate ester, metaphosphoric acid, ammonium metaphosphoric acid, metaphosphoric acid ester, hypophosphoric acid, ammonium hypophosphoric acid ester, and hypophosphoric acid ester; the above-mentioned phosphorus compound can be fully soluble in water, facilitating the uniform dispersion of phosphorus elements inside and outside the pores of the unmodified mesoporous ZSM-5 molecular sieve.

[0052] In one embodiment of the present invention, the mass ratio of the unmodified mesoporous ZSM-5 molecular sieve to water can be 1:5 to 20, specifically 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:15 or 1:20; the amount of phosphorus compound is calculated as P2O5, and the concentration of phosphorus compound in the molecular sieve slurry can be 0.1 to 10.0 mol / L, specifically 0.1 mol / L, 0.5 mol / L, 1.0 mol / L, 3.0 mol / L, 5.0 mol / L, 8.0 mol / L or 10.0 mol / L. In one embodiment of the present invention, the temperature of the hydrothermal reaction can be 50~180℃, more specifically 80~120℃, and more specifically 80℃, 90℃, 100℃, 110℃, or 120℃; the pH value is 0.5~6.5, and more specifically 1, 1.3, 2, 3, 4, or 5; the time is 0.5~12h, more specifically 1~5h, and more specifically 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h. In another embodiment of the present invention, when the system does not meet the above pH requirements, a pH adjuster is preferably used to adjust the pH value of the system to the above range; the pH adjuster may include one or more of hydrochloric acid, nitric acid, and sulfuric acid. Compared with the impregnation method, the present invention uses a hydrothermal method to prepare phosphorus-modified mesoporous ZSM-5 molecular sieves, which can more uniformly disperse phosphorus elements inside and outside the pores of the molecular sieve matrix.

[0053] As one embodiment of the present invention, the hydrothermal reaction preferably further includes: separating the obtained liquid material into solid and liquid components, collecting the solid material and washing and drying it sequentially to obtain the phosphorus-modified mesoporous ZSM-5 molecular sieve; the solid-liquid separation method can be filtration; the washing method can be water washing; the drying temperature can be 75~80℃ and the time can be 10~12h.

[0054] After obtaining the mesoporous ZSM-5 molecular sieve, this invention mixes the mesoporous ZSM-5 molecular sieve, kaolin, zinc compound, aluminum-based binder, and water to obtain a catalyst colloid. In one embodiment of this invention, the kaolin may include hydrated kaolin or thermally or chemically treated kaolin; the water content of the hydrated kaolin may be 10-15 wt%, specifically 14.5 wt%. In another embodiment of this invention, the zinc compound may be a soluble zinc salt, which may include one or more of zinc nitrate, zinc chloride, and zinc acetate; this invention, through zinc modification, is beneficial for improving the aromatization performance of the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst. In one embodiment of the present invention, the aluminum-based binder may include aluminum sol and / or sol-gelled boehmite; the sol-gelled boehmite is obtained by sol treatment of boehmite, the reagent used in the sol treatment may include formic acid, the mass ratio of formic acid to boehmite may be 0.10~0.50:1, the temperature of the sol treatment may be 25~80℃, the time may be 1~6h, and the sol treatment is preferably carried out under stirring conditions.

[0055] In one embodiment of the present invention, on a dry basis, the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst contains 30-60% mesoporous ZSM-5 molecular sieve by mass, specifically 30%, 35%, 40%, 45%, 50%, 55%, or 60%; and on a dry basis, the kaolin content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 10-60% kaolin by mass, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, or 45%. The zinc compound content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 0.5% to 50% (calculated as zinc oxide), specifically 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. The aluminum-based binder content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 9% to 25% (calculated as alumina), specifically 10%, 12%, 15%, 18%, 20%, 22%, or 25%. In this invention, the amounts of the mesoporous ZSM-5 molecular sieve, kaolin, zinc compound, and aluminum-based binder used in the preparation of the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst only need to meet the above requirements.

[0056] After obtaining the catalyst colloid, the present invention sequentially performs spray molding and calcination on the catalyst colloid to obtain the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst. In one embodiment of the present invention, the average particle size of the particulate material obtained by spray molding can be 50~90μm; the calcination temperature can be 200~800℃, further 500~750℃, specifically 500℃, 550℃, 600℃, 650℃, 680℃, 700℃, or 750℃; the holding time can be 0.5~6h, specifically 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 5h, or 6h; the calcination can be carried out in an air atmosphere.

[0057] This invention provides a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst prepared by the preparation method described above.

[0058] This invention provides the application of the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst described above in the catalytic gas-phase cyclization condensation reaction of aldehydes and ammonia to prepare pyridine and alkylpyridine.

[0059] In one embodiment of the present invention, the conditions for the aldehyde-ammonia phase cyclization condensation reaction include: the reactants include formaldehyde, acetaldehyde, and ammonia; the molar ratio of formaldehyde, acetaldehyde, and ammonia can be 1~3:1~3:2~12, more preferably 2:2:3~5, specifically 2:2:4; the reaction temperature can be 430~530℃, more preferably 470~480℃, specifically 475℃. In another embodiment of the present invention, the alkylpyridine can be trimethylpyridine.

[0060] Current methods for improving catalysts in the gas-phase cyclization condensation reaction of aldehydes and ammonia to synthesize pyridine and alkylpyridine mainly focus on loading metal cations onto ZSM-5 molecular sieves using impregnation and ion exchange methods. These methods generally suffer from poor catalyst stability, low pyridine selectivity, and low yield. The poor catalyst stability is primarily caused by the following reasons: 1) During the gas-phase cyclization condensation of aldehydes and ammonia to prepare pyridine and alkylpyridine, a large amount of carbon is deposited on the catalyst. This carbon deposit covers the active sites of the catalyst, causing a rapid decline in catalyst activity. Furthermore, carbon deposits can clog the micropores of the molecular sieve, leading to a rapid deterioration in the molecular sieve's reactivity; 2) During the high-temperature hydrothermal regeneration of carbon-deposited ZSM-5 molecular sieves, the highly reactive Al atoms in the zeolite molecular sieve framework easily detach from the framework, resulting in permanent deactivation of the molecular sieve. To address these problems, this invention uses mesoporous ZSM-5 molecular sieves as raw material and modifies them with phosphorus. This not only reduces carbon deposition on the molecular sieve but also improves the hydrothermal stability of the aluminum atoms in the molecular sieve framework, thereby increasing the yield and selectivity of pyridine and alkylpyridine. Meanwhile, compared to impregnation, hydrothermal modification promotes the migration of phosphorus oxides into the depths of the molecular sieve channels and strengthens coordination bonding with skeletal aluminum. High-temperature hydrothermal treatment also helps to clear the pores of the phosphorus-modified ZSM-5 molecular sieve. The mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst described in this invention can be used as a fluidized bed catalyst for the gas-phase cyclization condensation reaction of aldehydes and ammonia to synthesize pyridine and alkylpyridine, exhibiting excellent stability, high yield of target products, and excellent selectivity.

[0061] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0062] All raw materials used in the following experiments are commercially available industrial products, with no other special requirements.

[0063] Preparation Example 1

[0064] The preparation of unmodified mesoporous ZSM-5 molecular sieves includes the following steps:

[0065] (1) Silica sol (Ludox HS-30, SiO2 content 30wt%), tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH content 25wt%; purchased from Kent Catalytic Materials Co., Ltd.) and deionized water were stirred and mixed evenly to obtain a mixture; the amount of silica sol was based on SiO2, and the molar ratio of SiO2, TPAOH and H2O in the mixture was 1:0.45:23; the mixture was transferred to a stainless steel hydrothermal reactor with a polytetrafluoroethylene liner, and the stainless steel hydrothermal reactor was placed in a 90℃ oven for crystallization treatment under static conditions for 22h; after the crystallization treatment was completed, the obtained liquid was centrifuged, the solid product was collected and washed with deionized water by centrifugation, and then dried in an 80℃ oven for 12h, and then placed in a muffle furnace and calcined at 550℃ in an air atmosphere for 6h to obtain “Protozeolite” seed crystals;

[0066] (2) Silica sol (Ludox HS-30, SiO2 content 30wt%), tetrapropylammonium hydroxide aqueous solution (TPAOH content 25wt%; purchased from Kent Catalytic Materials Co., Ltd.) and deionized water were stirred and mixed evenly. The “Protozeolite” seed crystals were added and stirred and mixed evenly. Then, a mixed aqueous solution of NaOH and NaAlO2 was added and stirred and mixed evenly to obtain a mixture. The amounts of silica sol, NaAlO2, and NaOH were calculated as oxides. The molar ratio of SiO2, Al2O3, Na2O, TPAOH, and H2O in the mixture was 1:0.00667:0.16:0.05:15. The “Pro… The mass of the "tozeolite" seed crystals is 13 wt% of the mass of the SiO2. The mixture is transferred to a stainless steel hydrothermal reactor with a polytetrafluoroethylene liner. The stainless steel hydrothermal reactor is placed in an oven at 160°C and crystallized under static conditions for 72 h. After crystallization, the resulting liquid is centrifuged, the solid product is collected and washed with deionized water, and then dried in an oven at 80°C for 12 h. Subsequently, it is placed in a muffle furnace and calcined at 550°C in air for 6 h. The calcined material is then subjected to ion exchange treatment to make the Na2O content ≤0.02 wt%, resulting in unmodified mesoporous ZSM-5 molecular sieve.

[0067] Preparation Example 2

[0068] The preparation of phosphorus-modified mesoporous ZSM-5 molecular sieves includes the following steps:

[0069] At room temperature (25°C), 25 mL of deionized water, 2.53 g of unmodified mesoporous ZSM-5 molecular sieve (1.0 wt% moisture content, from Preparation Example 1), and 1.6 g of phosphoric acid (85 wt% H3PO4 content) were added sequentially to a beaker equipped with a stirring device. The mixture was stirred until homogeneous to obtain a molecular sieve slurry (pH 1.3). The molecular sieve slurry was transferred to a stainless steel hydrothermal reactor with a polytetrafluoroethylene liner. The reactor was placed in an oven at 110°C for hydrothermal reaction for 2 h. After the reaction, the resulting liquid was filtered, the solid product was collected and washed with deionized water, and then dried in an oven at 80°C for 12 h. The dried material was subjected to ion exchange treatment to make the Na2O content ≤0.02 wt% to obtain phosphorus-modified mesoporous ZSM-5 molecular sieve.

[0070] Preparation Example 3

[0071] The preparation of unmodified conventional ZSM-5 molecular sieves includes the following steps:

[0072] (1) Silica sol (Ludox HS-30, SiO2 content 30wt%), tetrapropylammonium hydroxide aqueous solution (TPAOH content 25wt%; purchased from Kent Catalytic Materials Co., Ltd.) and deionized water were stirred and mixed evenly to obtain a mixture; the amount of silica sol was based on SiO2, and the molar ratio of SiO2, TPAOH and H2O in the mixture was 1:0.45:23; the mixture was transferred to a stainless steel hydrothermal reactor with a polytetrafluoroethylene liner, and the stainless steel hydrothermal reactor was placed in a 90℃ oven for crystallization treatment for 48h under static conditions, and then crystallized at 170℃ for 24h; after the crystallization treatment was completed, the obtained liquid was centrifuged, the solid product was collected and washed by centrifugation with deionized water, and then dried in an 80℃ oven for 12h, and then placed in a muffle furnace and calcined at 550℃ in an air atmosphere for 6h to obtain conventional seed crystals;

[0073] (2) Follow the steps of preparation 1 (2) except that “Protozeolite” seed crystals are replaced with conventional seed crystals, and finally unmodified conventional ZSM-5 molecular sieve is prepared.

[0074] Preparation Example 4

[0075] The preparation of phosphorus-modified conventional ZSM-5 molecular sieves includes the following steps:

[0076] At room temperature (25°C), 25 mL of deionized water, 2.53 g of unmodified conventional ZSM-5 molecular sieve (moisture content 1.3 wt%, from Preparation Example 3), and 1.6 g of phosphoric acid (H3PO4 content 85 wt%) were added sequentially to a beaker equipped with a stirring device. The mixture was stirred until homogeneous to obtain a molecular sieve slurry (pH 1.3). The molecular sieve slurry was transferred to a stainless steel hydrothermal reactor with a polytetrafluoroethylene liner. The reactor was placed in an oven at 110°C for hydrothermal reaction for 2 h. After the reaction, the resulting liquid was filtered, the solid product was collected and washed with deionized water, and then dried in an oven at 80°C for 12 h. The dried material was subjected to ion exchange treatment to make the Na2O content ≤0.02 wt% to obtain phosphorus-modified conventional ZSM-5 molecular sieve.

[0077] Figure 1 XRD patterns of "Protozeolite" seed crystals and conventional seed crystals, from Figure 1 As can be seen, compared to conventional seed crystals, "Protozeolite" seed crystals are an amorphous substance.

[0078] Figure 2 This is a TEM image of unmodified mesoporous ZSM-5 molecular sieve. Figure 3 The isotherm for Ar physical adsorption of unmodified mesoporous ZSM-5 molecular sieve. Figure 2 and Figure 3 It can be seen that ZSM-5 molecular sieves rich in mesopores can be prepared using Protozeolite seed crystals.

[0079] Figure 4 This is a TEM image of unmodified conventional ZSM-5 molecular sieve. Figure 5 The isotherm for Ar physical adsorption of unmodified conventional ZSM-5 molecular sieve. Figure 4 and Figure 5 It can be seen that the unmodified conventional ZSM-5 molecular sieve is a microporous molecular sieve.

[0080] Figure 6 These are the Ar gas physical adsorption isotherms of phosphorus-modified mesoporous ZSM-5 molecular sieve and phosphorus-modified conventional ZSM-5 molecular sieve. From Figure 6 It can be seen that even after phosphorus modification, the ZSM-5 molecular sieve, which is rich in mesopores, still contains a large number of mesopores.

[0081] Table 1 shows the physicochemical properties of different molecular sieves. As can be seen from Table 1, compared with conventional ZSM-5 molecular sieves, mesoporous ZSM-5 molecular sieves have higher specific surface area and pore volume. After phosphorus modification, the specific surface area and pore volume of ZSM-5 molecular sieves remain essentially unchanged.

[0082] Table 1 Physicochemical properties of molecular sieves

[0083]

[0084] Example 1

[0085] In a reactor equipped with a stirring device, 4303 g of deionized water, 1374 g of kaolin (moisture content 14.5 wt%), 2778 g of unmodified mesoporous ZSM-5 molecular sieve (moisture content 1.0 wt%; from Preparation Example 1), 4535 g of alumina sol (Al2O3 content 21.5 wt%) and 167 g of zinc chloride were added sequentially and stirred until homogeneous to obtain a catalyst colloid. The catalyst colloid was spray-granulated in a spray drying tower, and the resulting particulate material (average particle size 50~90 μm) was calcined in air at 650 °C for 120 min to obtain a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, denoted as Catalyst 1.

[0086] Example 2

[0087] In a reactor equipped with a stirrer, 4612 g of deionized water, 1784 g of kaolin (moisture content 14.5 wt%), 2525 g of unmodified mesoporous ZSM-5 molecular sieve (moisture content 1.0 wt%; from Preparation Example 1), 4070 g of alumina sol (Al2O3 content 21.5 wt%) and 167 g of zinc chloride were added sequentially and stirred until homogeneous to obtain a catalyst colloid. The catalyst colloid was spray-granulated in a spray drying tower, and the resulting particulate material (average particle size 50~90 μm) was calcined in air at 600 °C for 180 min to obtain a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, denoted as catalyst 2.

[0088] Example 3

[0089] In a reactor equipped with a stirrer, 4920 g of deionized water, 2193 g of kaolin (moisture content 14.5 wt%), 2273 g of unmodified mesoporous ZSM-5 molecular sieve (moisture content 1.0 wt%; from Preparation Example 1), 3605 g of alumina sol (Al2O3 content 21.5 wt%) and 167 g of zinc chloride were added sequentially and stirred until homogeneous to obtain a catalyst colloid. The catalyst colloid was spray-granulated in a spray drying tower, and the resulting particulate material (average particle size 50~90 μm) was calcined in air at 650 °C for 120 min to obtain a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, denoted as catalyst 3.

[0090] Example 4

[0091] In a reactor equipped with a stirrer, 4909 g of deionized water, 2193 g of kaolin (with a moisture content of 14.5 wt%), 2284 g of phosphorus-modified mesoporous ZSM-5 molecular sieve (with a moisture content of 1.5 wt%; from Preparation Example 2), 3605 g of alumina sol (with an Al2O3 content of 21.5 wt%), and 167 g of zinc chloride were added sequentially and stirred until homogeneous to obtain a catalyst colloid. The catalyst colloid was spray-granulated in a spray drying tower (average particle size of 50-90 μm), and the resulting particulate material (average particle size of 50-90 μm) was calcined in air at 650 °C for 120 min to obtain a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, denoted as Catalyst 4.

[0092] Comparative Example 1

[0093] In a reactor equipped with a stirrer, 2978 g of deionized water, 1386 g of kaolin (moisture content 14.5 wt%), 1368 g of unmodified conventional ZSM-5 molecular sieve (moisture content 1.3 wt%; from Preparation Example 3) and 2163 g of alumina sol (Al2O3 content 21.5 wt%) were added sequentially and stirred until homogeneous to obtain a catalyst colloid. The catalyst colloid was spray-granulated in a spray drying tower, and the resulting particulate material (average particle size 50~90 μm) was calcined in air at 650 °C for 120 min. The resulting catalyst was designated as Catalyst 5.

[0094] Comparative Example 2

[0095] In a reactor equipped with a stirrer, 2948 g of deionized water, 1316 g of kaolin (moisture content 14.5 wt%), 1368 g of unmodified conventional ZSM-5 molecular sieve (moisture content 1.3 wt%; from Preparation Example 3), 2163 g of alumina sol (Al2O3 content 21.5 wt%) and 167 g of zinc chloride were added sequentially and stirred until homogeneous to obtain a catalyst colloid. The catalyst colloid was spray-granulated in a spray drying tower, and the resulting particulate material (average particle size 50~90 μm) was calcined in air at 650 °C for 120 min. The resulting catalyst was designated as Catalyst 6.

[0096] Comparative Example 3

[0097] In a reactor equipped with a stirrer, 2974 g of deionized water, 1386 g of kaolin (moisture content 14.5 wt%), 1372 g of phosphorus-modified conventional ZSM-5 molecular sieve (moisture content 1.6 wt%; from Preparation Example 4) and 2163 g of aluminum sol (Al2O3 content 21.5 wt%) were added sequentially and stirred until homogeneous to obtain a catalyst colloid. The catalyst colloid was spray-granulated in a spray drying tower, and the resulting particulate material (average particle size 50~90 μm) was calcined in air at 650 °C for 120 min. The resulting catalyst was designated as Catalyst 7.

[0098] Comparative Example 4

[0099] In a reactor equipped with a stirring device, 2982 g of deionized water, 1386 g of kaolin (moisture content 14.5 wt%), 1364 g of unmodified mesoporous ZSM-5 molecular sieve (moisture content 1.0 wt%; from Preparation Example 1) and 2163 g of alumina sol (Al2O3 content 21.5 wt%) were added sequentially and stirred until homogeneous to obtain a catalyst colloid. The catalyst colloid was spray-granulated in a spray drying tower, and the resulting particulate material (average particle size 50~90 μm) was calcined in air at 650 °C for 120 min. The resulting catalyst was designated as Catalyst 8.

[0100] Test Example 1

[0101] Catalyst 3 and catalyst 4 were subjected to hydrothermal treatment to evaluate their hydrothermal stability. The hydrothermal treatment conditions included: 100% water vapor, treatment temperature of 760°C, and treatment time of 12 hours.

[0102] Table 2 shows the specific surface area analysis results of catalysts 3 and 4 before and after hydrothermal treatment. As can be seen from Table 2, catalyst 4, namely the phosphorus-modified mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, exhibits a higher specific surface area retention rate and superior hydrothermal stability after hydrothermal treatment.

[0103] Table 2. Specific surface area analysis results of catalysts 3 and 4 before and after hydrothermal treatment.

[0104]

[0105] Test Example 2

[0106] Various catalysts were used to catalyze the gas-phase cyclization condensation reaction of aldehydes and ammonia to prepare pyridine, and their catalytic performance was evaluated. Specific conditions included: reaction temperature of 475℃, feed molar ratio of formaldehyde, acetaldehyde and ammonia of 2:2:4, and catalyst loading of 125g. The concentrations of pyridine and its derivatives were detected by gas chromatography (Pannuo A91Pro gas chromatograph) using an Agilent INNOWax column and a TCD detector.

[0107] Table 3 shows the catalytic performance evaluation results of each catalyst used in the gas-phase cyclization condensation reaction of aldehydes and ammonia to prepare pyridine. "Catalyst 3 hydrothermal treatment" and "Catalyst 4 hydrothermal treatment" indicate that catalysts 3 and 4, after hydrothermal treatment in Test Example 1, were used in the gas-phase cyclization condensation reaction of aldehydes and ammonia to prepare pyridine. All others used fresh catalysts. Table 3 shows that, based on the test results of catalysts 1-3, the higher the content of mesoporous molecular sieve, the higher the concentration of pyridine and trimethylpyridine in the product, and the higher the yield. Based on the test results of fresh catalysts 3-4 and hydrothermally treated catalysts 3-4, although the concentration and yield of pyridine and trimethylpyridine were slightly reduced when evaluating the fresh catalysts, the concentration and yield of pyridine and trimethylpyridine were higher when evaluating the hydrothermally treated catalysts, showing excellent activity stability. Based on the test results of catalysts 5-8, mesoporization of ZSM-5 molecular sieve and zinc modification can improve the selectivity of the catalysts for pyridine and trimethylpyridine.

[0108] Table 3. Evaluation results of catalytic performance of each catalyst

[0109]

[0110] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst, comprising the following steps: Mesoporous ZSM-5 molecular sieve, kaolin, zinc compound, aluminum-based binder and water were mixed to obtain catalyst colloid; The catalyst colloid was sequentially spray-molded and calcined to obtain the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst. The mesoporous ZSM-5 molecular sieve is an unmodified mesoporous ZSM-5 molecular sieve or a phosphorus-modified mesoporous ZSM-5 molecular sieve; the preparation method of the mesoporous ZSM-5 molecular sieve includes the following steps: Silica sol, tetrapropylammonium hydroxide, and water are mixed to obtain a first mixture; the first mixture is subjected to a first crystallization treatment to obtain a first crystallized product; the first crystallized product is subjected to a first calcination to obtain amorphous seed crystals; the temperature of the first crystallization treatment is 85~95℃, and the time is 20~22h; the temperature of the first calcination is 545~555℃, and the holding time is 5.5~6.5h. The amorphous seed crystals, silica sol, tetrapropylammonium hydroxide, water, NaOH, and NaAlO2 are mixed to obtain a second mixture; the second mixture is subjected to a second crystallization treatment to obtain a second crystallized product; the second crystallized product is subjected to a second calcination to obtain the unmodified mesoporous ZSM-5 molecular sieve; the mass of the amorphous seed crystals is 10-15% of the mass of SiO2 in the silica sol of the second mixture; the temperature of the second crystallization treatment is 135-165℃, and the time is 70-74h; The unmodified mesoporous ZSM-5 molecular sieve, phosphorus compound, and water are mixed, and the resulting molecular sieve slurry is subjected to a hydrothermal reaction to obtain the phosphorus-modified mesoporous ZSM-5 molecular sieve. The mass ratio of unmodified mesoporous ZSM-5 molecular sieve to water in the molecular sieve slurry is 1:5~20. The amount of phosphorus compound used is calculated as P2O5, and the concentration of phosphorus compound in the molecular sieve slurry is 0.1~10.0 mol / L. The hydrothermal reaction temperature is 110~180℃, the pH value is 0.5~6.5, and the time is 2~12h.

2. The preparation method according to claim 1, characterized in that, The unmodified mesoporous ZSM-5 molecular sieve has a silica-to-alumina ratio of 50-250 mol / mol and a total specific surface area of ​​300-500 m² / mol. 2 / g, with an external specific surface area of ​​40~120m² 2 / g, total pore volume is 0.20~0.35cm³ 3 / g, mesoporous pore volume is 0.05~0.25cm³ 3 / g, Na2O content ≤0.02wt%; The phosphorus-modified mesoporous ZSM-5 molecular sieve comprises a molecular sieve matrix and phosphorus loaded on the molecular sieve matrix, wherein the molecular sieve matrix is ​​the unmodified mesoporous ZSM-5 molecular sieve; the content of P2O5 in the phosphorus-modified mesoporous ZSM-5 molecular sieve is 0.2~2.0wt%, and the content of Na2O is ≤0.02wt%.

3. The preparation method according to claim 1, characterized in that, On a dry basis, the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst contains 30-60% mesoporous ZSM-5 molecular sieve by mass; the kaolin content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 10-60% by mass; the zinc compound content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 0.5-5% by mass (based on zinc oxide); and the aluminum-based binder content in the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst is 9-25% by mass (based on alumina).

4. The preparation method according to claim 3, characterized in that, The average particle size of the particulate material obtained by spray molding is 50~90μm; the calcination temperature is 200~800℃, and the holding time is 0.5~6h.

5. The mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the mesoporous ZSM-5 molecular sieve-based fluidized bed catalyst of claim 5 in the catalytic gas-phase cyclization condensation reaction of aldehydes and ammonia to prepare pyridine and alkylpyridine.

7. The application according to claim 6, characterized in that, The conditions for the aldehyde-ammonia phase cyclization condensation reaction include: the reaction raw materials include formaldehyde, acetaldehyde and ammonia, and the molar ratio of formaldehyde, acetaldehyde and ammonia is 1~3:1~3:2~12; the reaction temperature is 430~530℃.

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