Preparation Method and Application of Modified Molecular Sieve

Abstract

The present invention provides a preparation method and application of a modified molecular sieve. The preparation method includes: Step S1, mixing a silicate compound, a quaternary ammonium template agent and water, and then successively performing a hydrolysis reaction and distillation to obtain a sol mixture and a fraction with a boiling range of 60-100 °C; Step S2, successively performing a crystallization reaction and liquid separation on the sol mixture to obtain an aqueous solution and an organic solution; Step S3, adjusting the pH value of the aqueous solution to 7-10, and then successively performing a first solid-liquid separation, a first drying and a first calcination to obtain a molecular sieve precursor; Step S4, mixing the fraction with a boiling range of 60-100 °C, the organic solution and the molecular sieve precursor, and then successively performing etching, a second solid-liquid separation, a second drying and a second calcination to obtain a modified molecular sieve. When the modified molecular sieve prepared by the present invention is used as a catalyst for synthesizing caprolactam, it has high selectivity and conversion rate, long operating life, environmental friendliness and better catalytic performance.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical industry, and in particular, to a preparation method and application of a modified molecular sieve. Background Art

[0002] Caprolactam is an important intermediate in the industrial production of nylon, and it is of great significance for the widespread application of nylon. The Beckmann rearrangement of cyclohexanone oxime also plays a major role as a key step in the caprolactam production process. At present, caprolactam is mainly produced industrially by the traditional liquid-phase rearrangement process using concentrated sulfuric acid as a catalyst. Although the reaction conditions of this process are relatively mild and the conversion rate and selectivity are also relatively ideal, a large amount of ammonium sulfate is produced as a by-product during the process, which easily leads to equipment corrosion and environmental pollution. Therefore, in recent years, more and more technical personnel have begun to pay attention to solid acid catalysts such as molecular sieves and use them to replace conventional concentrated sulfuric acid catalysts for catalytic applications. For example, existing patents such as USP4061724, JP59164617, and CN1338427 have successively reported the synthesis methods of MFI-type silicon molecular sieves and revealed their applications in the synthesis of caprolactam. However, the reaction temperature required for the gas-phase Beckmann rearrangement process is relatively high, resulting in easy deactivation of the catalyst, poor stability, and relatively low selectivity of the catalyst, thus limiting its further popularization and application. To solve this problem, some researchers have used alkali modification to adjust the composition and quantity of acidic sites and optimize the morphological structure of MFI-type silicon molecular sieves to improve their performance in the gas-phase Beckmann rearrangement of cyclohexanone oxime.

[0003] For example, patents CN1164576 and CN104307556 both prepared modified MFI molecular sieves by means of aliphatic amines and quaternary ammonium bases, enabling the conversion rate of cyclohexanone oxime to be greater than 99% and the selectivity of caprolactam to be greater than 95%. However, this modified MFI molecular sieve is difficult to form, and even if it can be formed, its catalyst strength is relatively low, still unable to meet the requirements of industrialization. Moreover, using aliphatic amines and quaternary ammonium bases as raw materials, the cost is relatively high and the "three wastes" emissions are large, increasing the cost of the catalyst. Patent CN114349018A discloses a method for in-situ modifying silicon molecular sieves using organic amines generated by high-temperature pyrolysis, avoiding the use of other alkali modification reagents. However, the carbon components of the catalyst prepared by this method are severely lost during the regeneration process, resulting in a significant decline in performance and a low total life of the catalyst.

[0004] Therefore, the methods of modifying molecular sieves with alkali in the above-mentioned prior arts all have problems such as relatively low selectivity, poor stability, environmental unfriendliness, or low total life. There is an urgent need to provide a preparation method and application of a modified molecular sieve to improve the above problems. Summary of the Invention

[0005] The main object of the present invention is to provide a preparation method and application of a modified molecular sieve, so as to solve the problems in the prior art that when the molecular sieve is used in the gas-phase rearrangement reaction of cyclohexanone oxime, the catalyst has low selectivity, poor stability, environmental unfriendliness, or low total life.

[0006] To achieve the above object, according to one aspect of the present invention, a preparation method of a modified molecular sieve is provided. The preparation method of the modified molecular sieve includes: Step S1, mixing a silicate compound, a quaternary ammonium template agent and water, and then carrying out hydrolysis reaction and distillation in sequence to obtain a sol mixture and a fraction with a boiling range of 60-100 °C; Step S2, carrying out crystallization reaction and liquid separation on the sol mixture in sequence to obtain an aqueous solution and an organic solution; Step S3, adjusting the pH value of the aqueous solution to 7-10, and then carrying out first solid-liquid separation, first drying and first calcination on it in sequence to obtain a molecular sieve precursor; Step S4, mixing the fraction with a boiling range of 60-100 °C, the organic solution and the molecular sieve precursor, and then carrying out etching, second solid-liquid separation, second drying and second calcination in sequence to obtain a modified molecular sieve.

[0007] Furthermore, the weight ratio of the fraction with a boiling range of 60-100 °C, the organic solution and the molecular sieve precursor is (1-4):(0.5-5):1, preferably (2-4):(2-5):1.

[0008] Furthermore, the molar ratio of the silicate compound, the quaternary ammonium template agent and water is 1:(0.05-2.0):(10-150), preferably 1:(0.1-0.8):(15-50); preferably, the raw materials for the hydrolysis reaction further include an aluminum source; more preferably, the aluminum source is selected from sodium metaaluminate and / or potassium metaaluminate; further preferably, the dosage of the aluminum source and the molar ratio of the silicate compound is (0.0001-0.005):1.

[0009] Furthermore, the raw materials for the hydrolysis reaction further include a titanium source; more preferably, the titanium source is selected from one or more of tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate or tetrabutyl titanate; further preferably, the dosage of the titanium source and the molar ratio of the silicate compound is (0.0001-0.01):1.

[0010] Furthermore, the silicate compound is selected from one or more of tetraethyl orthosilicate, tetrapropyl orthosilicate or tetrabutyl orthosilicate; the quaternary ammonium template agent is selected from one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium bromide, tetraethylammonium chloride or tetrapropylammonium chloride; more preferably, the quaternary ammonium template agent is tetrapropylammonium hydroxide.

[0011] Further, the reaction temperature of the hydrolysis reaction is 20 - 40°C, and the reaction time is 2 - 4 h; the treatment temperature of the distillation is 70 - 100°C, and the treatment time is 1 - 6 h; the temperature of the crystallization reaction is 150 - 200°C, and the time is 48 - 96 h.

[0012] Further, an organic acid is used to adjust the pH value of the aqueous solution. Preferably, the organic acid is selected from one or more of formic acid, acetic acid, propionic acid, oxalic acid, 1,3 - propanedicarboxylic acid, benzoic acid, terephthalic acid, phthalic acid, isophthalic acid, or trimellitic acid; preferably, the etching is carried out in an autoclave. More preferably, the etching treatment temperature is 80 - 200°C, the treatment pressure is 0.2 - 3.0 MPa, and the treatment time is 2 - 180 h.

[0013] Further, after the first solid - liquid separation and before the first drying, step S3 further includes a step of first washing the material after the first solid - liquid separation; preferably, the detergent used for the first washing is selected from one or more of water, methanol, ethanol, isopropanol, n - butanol, acetonitrile, formamide, or acetone; preferably, the treatment temperature of the first drying is 40 - 120°C, and the treatment time is 4 - 120 h; preferably, the treatment temperature of the first calcination is 400 - 600°C, and the treatment time is 1 - 72 h.

[0014] Further, after the second solid - liquid separation and before the second drying, step S4 further includes a step of second washing the material after the second solid - liquid separation; preferably, the detergent used for the second washing is selected from one or more of water, methanol, ethanol, isopropanol, n - butanol, acetonitrile, formamide, or acetone.

[0015] Further, the treatment temperature of the second drying is 50 - 160°C, and the treatment time is 1 - 180 h; preferably, the treatment temperature of the second calcination is 350 - 550°C, and the treatment time is 1 - 96 h.

[0016] In order to achieve the above object, according to one aspect of the present invention, a catalyst for catalytically preparing caprolactam from cyclohexanone oxime is provided. The catalyst comprises a modified molecular sieve prepared by the above - mentioned preparation method of the modified molecular sieve.

[0017] When the prepared modified molecular sieve is used as a catalyst for catalytically synthesizing caprolactam from cyclohexanone oxime by applying the technical solution of the present invention, the modified molecular sieve has excellent catalytic performance, manifested as high product selectivity and conversion rate, and the catalyst has a long service life, is environmentally friendly, and has better catalytic performance. Detailed Embodiments

[0018] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0019] As described in the background art section of the present invention, when molecular sieves in the prior art are used to catalyze the gas-phase rearrangement reaction of cyclohexanone oxime, the catalyst has problems such as low selectivity, poor stability, environmental unfriendliness, or low total lifespan. To solve the above problems, the present invention provides a preparation method of a modified molecular sieve, and the preparation method of the modified molecular sieve includes: Step S1, mixing a silicate compound, a quaternary ammonium template agent, and water, and then successively performing a hydrolysis reaction and distillation to obtain a sol mixture and a fraction with a boiling range of 60-100°C; Step S2, successively performing a crystallization reaction and liquid separation on the sol mixture to obtain an aqueous solution and an organic solution; Step S3, adjusting the pH value of the aqueous solution to 7-10, and then successively performing first solid-liquid separation, first drying, and first calcination to obtain a molecular sieve precursor; Step S4, mixing the fraction with a boiling range of 60-100°C, the organic solution, and the molecular sieve precursor, and then successively performing etching, second solid-liquid separation, second drying, and second calcination to obtain a modified molecular sieve.

[0020] First, the present invention mixes a silicate compound, a quaternary ammonium template agent, and water and then performs a hydrolysis reaction. During this hydrolysis reaction: in the first step of hydrolysis of the silicate compound, monosilicic acid (containing Si-OH bonds) and the corresponding alcohol are generated, and then further condensation polymerization reactions occur between monosilicic acids or between monosilicic acids and some partially unhydrolyzed silicate compounds that may exist to generate polymers such as disilicic acid, trisilicic acid, or cyclic polysilicic acid. These polymers form tiny and dispersed colloidal particles in the reaction system, and these colloidal particles are interconnected by van der Waals forces, hydrogen bonds, or chemical bond forces to form a spatially open framework structure, which is called a sol (this sol is in a disordered state). After the above hydrolysis reaction, the system includes the above sol, the corresponding alcohol, and an aqueous solution of the quaternary ammonium template agent. Continuing to distill this mixed system, a fraction with a boiling range of 60-100°C (the corresponding alcohol and the remaining water carried by azeotropy) and a sol mixture (containing silicate polymers, quaternary ammonium salts or quaternary ammonium base solutions, water, and the remaining corresponding alcohol) are obtained.

[0021] Secondly, the present invention performs a crystallization reaction on the above sol mixture to strengthen the interaction between molecules (the silicate anions in the silicate polymer and the quaternary ammonium cations in the quaternary ammonium salt or quaternary ammonium base), making the structure of the modified molecular sieve more compact and regular. During the crystallization reaction, a part of the quaternary ammonium template agent participates in the construction of the molecular sieve structure and plays a role in filling the internal pores of the molecular sieve; another part of the quaternary ammonium template agent will decompose into the corresponding tertiary amine during the crystallization process. Then, liquid separation is continued on the material after the crystallization reaction to obtain an aqueous solution containing the suspended particles after crystallization and an organic solution containing the above decomposition product, tertiary amine.

[0022] Next, the present invention continues to adjust the pH value of the above aqueous phase to 7-10. By adjusting the surface charge of the suspended particles in the aqueous phase, the degree of aggregation of the suspended particles is enhanced, and the agglomeration between the suspended particles is promoted, so that they are easily filtered out. After the first solid-liquid separation, a filter cake containing the molecular sieve precursor and a filtrate are obtained. The filter cake is successively subjected to the first drying and the first calcination to dry and remove the water and pH regulator contained therein, and the template agent filled in the internal pores of the molecular sieve is removed by calcination, thereby obtaining the molecular sieve precursor.

[0023] Finally, the present invention etches the above molecular sieve precursor, a fraction with a boiling range of 60-100 °C (corresponding alcohol and the remaining water co-boiled) and an organic phase solution (tertiary amine). Among them, in a system using the fraction with a boiling range of 60-100 °C (corresponding alcohol and the remaining water co-boiled) as a solvent, the organic phase solution (tertiary amine) can react with the terminal silicon hydroxyl groups (Si-OH) on the surface of the molecular sieve precursor to form silicate (which can be removed by subsequent washing), etching away the terminal silicon hydroxyl groups on the surface of the molecular sieve precursor to form a pore structure, so that the number of terminal silicon hydroxyl groups on the surface of the molecular sieve precursor is significantly reduced, and further, the active centers of the terminal silicon hydroxyl groups on the surface of the molecular sieve can be effectively inhibited. Such a modified molecular sieve has excellent hydrophobicity when used as a catalyst in subsequent applications. And when it is applied to a catalytic reaction, the reaction products can quickly diffuse out of the pores of the modified molecular sieve, further reducing the occurrence of side reactions in the catalytic reaction, improving the reaction selectivity and the yield of the target product. At the same time, as the number of terminal silicon hydroxyl groups on the surface of the molecular sieve precursor decreases, the content of nested silicon hydroxyl groups per unit area in the corresponding molecular sieve precursor increases. Such a modified molecular sieve can also improve the activity and stability of the catalyst when used as a catalyst in subsequent applications, thereby improving the selectivity of the catalytic reaction and extending the total life of the catalyst.

[0024] In a preferred embodiment, in step S4, the weight ratio of the fraction with a boiling range of 60-100 °C, the organic phase solution and the molecular sieve precursor is (1-4):(0.5-5):1. Optimizing the weight ratio of the fraction with a boiling range of 60-100 °C, the organic phase solution and the molecular sieve precursor within this range can enable the components to better cooperate, more effectively inhibit the active centers of the terminal silicon hydroxyl groups on the surface of the molecular sieve precursor, further reduce the occurrence of side reactions, thereby improving the activity and stability of the catalyst, improving the selectivity of the reaction and extending the total life of the catalyst. Further preferably, it is (2-4):(2-5):1.

[0025] In order to further promote the complete progress of the hydrolysis reaction, and to promote the hydrolysis of silicate compounds to first generate monosilicic acid and the corresponding alcohol, and further polycondense to form polysilicic acid, thereby facilitating the formation of a sol in a disordered state, it is preferred that the molar ratio of the silicate compound, the quaternary ammonium template agent, and water is 1:(0.05 - 2.0):(10 - 150), and more preferably 1:(0.1 - 0.8):(15 - 50).

[0026] In a preferred embodiment, using the above-mentioned silicate compound, quaternary ammonium template agent, and water raw materials of the present application, a fully siliceous molecular sieve can be prepared. When this molecular sieve is subsequently used as a catalyst, it can improve the activity and stability of the catalyst, thereby improving the selectivity of the catalytic reaction and extending the total life of the catalyst.

[0027] In some preferred embodiments, in order to further obtain a modified molecular sieve containing silicon and aluminum, improve the activity and stability of the catalyst, and improve the selectivity of the reaction, it is preferred that the raw materials for the hydrolysis reaction further include an aluminum source. More preferably, the aluminum source is selected from sodium aluminate and / or potassium aluminate; even more preferably, the molar ratio of the amount of the aluminum source to the silicate compound is (0.0001 - 0.005):1, so that a modified ZSM-5 molecular sieve with a silicon-aluminum ratio greater than 200 can be prepared.

[0028] In some other preferred embodiments, in order to further obtain a modified molecular sieve containing silicon and titanium, improve the catalytic performance and total life of the catalyst, it is preferred that the raw materials for the hydrolysis reaction further include a titanium source. More preferably, the titanium source is selected from one or more of tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, or tetrabutyl titanate. Even more preferably, the molar ratio of the amount of the titanium source to the silicate compound is (0.0001 - 0.01):1, so that a modified TS-1 molecular sieve with a silicon-titanium ratio greater than 100 can be prepared.

[0029] In a preferred embodiment, the silicate compound is selected from one or more of tetraethyl orthosilicate, tetrapropyl orthosilicate, or tetrabutyl orthosilicate, so that a fraction with a boiling range of 60 - 100 °C (i.e., the corresponding alcohol) can be generated during the hydrolysis reaction, thereby preparing for subsequent etching. In order to further promote the full hydrolysis of the silicate compound, it is preferred that the quaternary ammonium template agent is selected from one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium bromide, tetraethylammonium chloride, or tetrapropylammonium chloride.

[0030] To further promote the complete hydrolysis of the hydrolysis reaction, thereby facilitating the formation of a sol mixture with a spatially open framework structure through the connection of micelles by van der Waals forces, hydrogen bonds or chemical bond forces, the reaction temperature of the hydrolysis reaction is preferably 20-40°C, and the reaction time is 2-4h. To further obtain a fraction with a boiling range of 60-100°C with a higher yield, the treatment temperature of the distillation is preferably 70-100°C, and the treatment time is 1-6h. To further promote the crystallization reaction of the sol mixture to be more complete, thereby strengthening the intermolecular interaction, making the structure of the modified molecular sieve more compact and regular, and at the same time promoting the participation of quaternary ammonium template agents in the construction of the molecular sieve structure and their effective decomposition during the crystallization process, the reaction temperature of the crystallization reaction is preferably 150-200°C, and the reaction time is 48-96h.

[0031] In a preferred embodiment, an organic acid is used to adjust the pH value of the aqueous solution. Preferably, the organic acid is selected from one or more of formic acid, acetic acid, propionic acid, oxalic acid, 1,3-propanedioic acid, benzoic acid, terephthalic acid, phthalic acid, isophthalic acid or trimellitic acid, so as to better adjust the surface charge of the suspended particles in the aqueous phase, thereby enhancing the degree of aggregation between the suspended particles and promoting the agglomeration between the suspended particles to make it easy to filter out. To further promote the complete etching, better etch the terminal silanol groups on the surface of the molecular sieve precursor to form a pore structure, effectively inhibit the active centers of the terminal silanol groups on the surface of the molecular sieve precursor, and further improve the catalytic performance of the modified molecular sieve and extend its total life, the etching is preferably carried out in an autoclave. Further preferably, the etching treatment temperature is 80-200°C, the treatment pressure is 0.2-3.0MPa, and the treatment time is 2-180h.

[0032] To further remove the water and organic acid contained in the molecular sieve precursor filter cake obtained by the first solid-liquid separation and avoid affecting the etching of the molecular sieve precursor, preferably after the first solid-liquid separation and before the first drying, the preparation method further includes a step of first washing the material after the first solid-liquid separation. Further preferably, the detergent used for the first washing is selected from one or more of water, methanol, ethanol, isopropanol, n-butanol, acetonitrile, formamide or acetone. To further remove impurities such as detergents and residual organic acids, the treatment temperature of the first drying is preferably 40-120°C, and the treatment time is 4-120h; to further calcine and remove the template agent filled in the pores of the molecular sieve precursor, thereby improving the catalytic performance of the modified molecular sieve, the treatment temperature of the first calcination is preferably 400-600°C, and the treatment time is 1-72h.

[0033] In a preferred embodiment, after the second solid-liquid separation and before the second drying, the preparation method further includes a step of washing the material after the second solid-liquid separation; thereby, the remaining organic phase solution on the surface of the modified molecular sieve, the fraction with a boiling range of 60-100 °C, and the silicate generated during the etching process can be better removed, thereby improving the catalytic performance of the modified molecular sieve and extending its total lifespan. Preferably, the detergent used for washing is selected from one or more of water, methanol, ethanol, isopropanol, n-butanol, acetonitrile, formamide, or acetone.

[0034] In order to further improve the catalytic performance of the modified molecular sieve and more effectively remove the detergent, the remaining organic phase solution, and the fraction with a boiling range of 60-100 °C, preferably, the treatment temperature for the second drying is 50-160 °C, and the treatment time is 1-180 h, more preferably 4-36 h; thereby further avoiding the influence of the presence of impurities on the activity of the modified molecular sieve, and further improving the catalytic performance of the modified molecular sieve and extending the total lifespan of the catalyst. Preferably, the treatment temperature for the second calcination is 350-550 °C, and the treatment time is 1-96 h, more preferably 2-12 h.

[0035] On the other hand, the present invention also provides a catalyst for catalytically preparing caprolactam from cyclohexanone oxime, and this catalyst includes the modified molecular sieve prepared by the above-mentioned preparation method of the modified molecular sieve. As described above, when the modified molecular sieve is used as a catalyst for preparing caprolactam from cyclohexanone oxime, this catalyst has high activity, shows high product selectivity and product yield during the catalytic process, and this catalyst has excellent stability, a long total lifespan, and is environmentally friendly.

[0036] The following further describes the present application in detail with specific examples, and these examples should not be construed as limiting the scope claimed by the present application.

[0037] Example 1

[0038] 416 g of tetraethyl orthosilicate, 200 g of 40% aqueous solution of tetrapropylammonium hydroxide, and 160 g of ultrapure water (the molar ratio of the three is 1:0.2:20 in sequence) were mixed and subjected to a hydrolysis reaction at 25 °C for 3 h, then the alcohol was removed by distillation at 80 °C for 3 h, and 440 g of the fraction with a boiling range of 75 - 90 °C and a sol mixture were collected; the sol mixture was placed in an autoclave and subjected to a crystallization reaction at 170 °C for 72 h, and then liquid separation was carried out to obtain 31.5 g of an organic phase solution and an aqueous phase solution; 39.2 g of acetic acid was added dropwise to the aqueous phase solution under mechanical stirring to adjust the pH value to 8.43, then filtration was carried out, the filter cake after filtration was washed three times with ultrapure water, first dried at 120 °C for 24 h, and first calcined at 500 °C for 8 h to obtain 110.2 g of a molecular sieve precursor; this molecular sieve precursor was a pure silica Silicalite-1 molecular sieve. 110.2 g of the molecular sieve precursor, 31.5 g of the organic phase solution, and 440 g of the fraction with a boiling range of 75 - 90 °C were placed in an autoclave for etching, the weight ratio of the fraction with a boiling range of 75 - 90 °C, the organic phase solution, and the molecular sieve precursor was 4:0.29:1, the pressure was 0.8 MPa, and the reaction was carried out at 140 °C for 60 h to obtain an etching product, then the etching product was subjected to second solid-liquid separation, second washed with 95% ethanol, and second dried in an oven at 80 °C for 36 h, and then calcined in a muffle furnace at 500 °C for 4 h to obtain a modified molecular sieve.

[0039] Example 2

[0040] 416 g of tetraethyl orthosilicate, 200 g of 40% aqueous solution of tetrapropylammonium hydroxide, 160 g of ultrapure water and 0.81 g of sodium metaaluminate (the molar ratio of the four is 1:0.2:20:0.0001 in sequence) were mixed and subjected to a hydrolysis reaction at 40 °C for 2 h, then the alcohol was distilled off at 70 °C for 6 h, and 410 g of the fraction with a distillation range of 75-90 °C and a sol mixture were collected; the sol mixture was placed in an autoclave and subjected to a crystallization reaction at 200 °C for 48 h, and then liquid separation was carried out to obtain 19.3 g of an organic phase solution and an aqueous phase solution; 42.7 g of acetic acid was added dropwise to the aqueous phase solution under mechanical stirring to adjust the pH value to 7.02, then filtration was carried out, the filter cake after filtration was washed three times with ultrapure water, first dried at 120 °C for 4 h, and first calcined at 400 °C for 72 h to obtain 102.5 g of a molecular sieve precursor; the molecular sieve precursor was a silicon-aluminum ZSM-5 molecular sieve. 102.5 g of the molecular sieve precursor, 5.1 g of the organic phase solution and 103 g of the fraction with a distillation range of 75-90 °C were etched in an autoclave, and the weight ratio of the fraction with a distillation range of 75-90 °C, the organic phase solution and the molecular sieve precursor was 1:0.05:1, the pressure was 0.8 MPa, and the reaction was carried out at 200 °C for 2 h to obtain an etched product, then the etched product was subjected to second solid-liquid separation, second washed with 95% ethanol, and second dried in an oven at 160 °C for 1 h, and then calcined in a muffle furnace at 550 °C for 1 h to obtain a modified molecular sieve.

[0041] Example 3

[0042] 416 g of tetraethyl orthosilicate, 200 g of 40% aqueous solution of tetrapropylammonium hydroxide, 160 g of ultrapure water, and 6.80 g of tetrabutyl titanate (the molar ratios of the four are 1:0.2:20:0.0002 in sequence) were mixed and subjected to a hydrolysis reaction at 20 °C for 4 h, then the alcohol was distilled off at 100 °C for 1 h, and 440 g of the fraction with a distillation range of 75 - 90 °C and a sol mixture were collected; the sol mixture was placed in an autoclave and subjected to a crystallization reaction at 150 °C for 96 h, and then liquid separation was carried out to obtain 58.6 g of an organic phase solution and an aqueous phase solution; 37.1 g of acetic acid was added dropwise to the aqueous phase solution under mechanical stirring to adjust the pH value to 10, then filtration was carried out, the filter cake after filtration was washed three times with ultrapure water, first dried at 40 °C for 120 h, and first calcined at 600 °C for 1 h to obtain 116.5 g of a molecular sieve precursor; this molecular sieve precursor was a silicon-titanium TS-1 molecular sieve. 116.5 g of the molecular sieve precursor, 58.6 g of the organic phase solution, and 240 g of the fraction with a distillation range of 75 - 90 °C were subjected to etching in an autoclave, and the weight ratio of the fraction with a distillation range of 75 - 90 °C, the organic phase solution, and the molecular sieve precursor was 2:0.05:1, the pressure was 0.8 MPa, and the reaction was carried out at 80 °C for 180 h to obtain an etched product, then the etched product was subjected to second solid-liquid separation, second washed with 95% ethanol, and second dried in an oven at 140 °C for 4 h, and then calcined in a muffle furnace at 350 °C for 96 h to obtain a modified molecular sieve.

[0043] Example 4

[0044] The difference from Example 1 is only that the organic acid is formic acid and the second detergent is water.

[0045] Example 5

[0046] The difference from Example 1 is only that the organic acids are formic acid and acetic acid and the second detergent is methanol.

[0047] Example 6

[0048] The difference from Example 1 is only that the organic acid is propionic acid and the second detergent is ethanol.

[0049] Example 7

[0050] The difference from Example 1 is only that the organic acid is oxalic acid and the second detergent is isopropyl alcohol.

[0051] Example 8

[0052] The difference from Example 1 is only that the organic acid is 1,3-propanedioic acid and the second detergent is n-butanol.

[0053] Example 9

[0054] The difference from Example 1 is only that the organic acid is benzoic acid and the second detergent is acetonitrile.

[0055] Example 10

[0056] The difference from Example 1 is only that the organic acid is terephthalic acid and the second detergent is formamide and water.

[0057] Example 11

[0058] The difference from Example 1 is only that the organic acid is phthalic acid and the second detergent is acetone.

[0059] Example 12

[0060] The difference from Example 1 is only that the organic acid is isophthalic acid and the second detergent is ethanol and water.

[0061] Example 13

[0062] The difference from Example 1 is only that the organic acid is mellitic acid and the second detergent is ethanol and water.

[0063] Example 14

[0064] The difference from Example 1 is only that the weight ratio of the fraction with a boiling range of 75 - 90 °C, the organic phase solution and the molecular sieve precursor is 4:5:1.

[0065] Example 15

[0066] The difference from Example 1 is only that the weight ratio of the fraction with a boiling range of 75 - 90 °C, the organic phase solution and the molecular sieve precursor is 2:2:1.

[0067] Example 16

[0068] The difference from Example 1 is only that tetrapropylammonium chloride is used.

[0069] Example 17

[0070] The difference from Example 1 is only that tetraethylammonium bromide is used.

[0071] Comparative Example 1

[0072] The difference from Example 1 is only that step S4 is absent.

[0073] Catalytic performance test:

[0074] Take the modified molecular sieves prepared in the above examples and comparative examples as catalysts, add them to an ethanol solution containing 20% cyclohexanone oxime, use nitrogen as the carrier gas, and the space velocity is 0.8 h -1The cyclohexanone oxime / ethanol solution is mixed with ammonia and undergoes a rearrangement reaction in a 360°C bed to synthesize caprolactam. The conversion rate of cyclohexanone oxime, the selectivity of caprolactam, and the stable operation time of the catalyst are calculated. The specific catalyst evaluation test results are shown in Table 1.

[0075] Table 1

[0076] Conversion rate (%) Selectivity (%) Service life (h) Example 1 99.7 97.0 1400 Example 2 99.9 96.5 1250 Example 3 99.9 96.1 1960 Example 4 99.5 97.2 1400 Example 5 99.5 96.4 1240 Example 6 99.6 97.0 1440 Example 7 99.3 96.0 1300 Example 8 99.5 97.2 1520 Example 9 99.9 96.2 1600 Example 10 99.5 96.8 1180 Example 11 99.5 96.5 1500 Example 12 99.5 97.6 1480 Example 13 99.7 97.3 1480 Example 14 99.6 96.9 1320 Example 15 99.7 96.8 1250 Example 16 99.7 96.1 1065 Example 17 99.8 96.0 1130 Comparative Example 1 99.8 95.3 476

[0077] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0078] From the test results of Examples 1, 2, 3 and Comparative Example 1, it can be found that when the preparation method of the modified molecular sieve of the present invention is adopted, especially in step S4, the fraction with a boiling range of 75-90°C, the organic phase solution and the molecular sieve precursor are mixed and then etched, second solid-liquid separation, second drying and second calcination are carried out in sequence to obtain the modified molecular sieve as a catalyst for catalyzing the synthesis of caprolactam from cyclohexanone oxime, the modified molecular sieve has excellent catalytic performance, manifested as higher product selectivity and higher reactant conversion rate, and the catalyst has a longer operation life.

[0079] From the test results of Examples 1, 2, 3, 14, and 15, it can be found that when the preparation method of the modified molecular sieve of the present invention is adopted, when the weight ratio of the fraction with a boiling range of 75-90°C, the organic phase solution and the molecular sieve precursor is within the range of (1-4):(0.05-5):1, the modified molecular sieve has excellent catalytic performance, manifested as higher product selectivity and higher reactant conversion rate, and the catalyst has a longer operation life. Especially when the weight ratio of the fraction with a boiling range of 75-90°C, the organic phase solution and the molecular sieve precursor is within the range of (2-4):(2-5):1, the product selectivity of the catalytic reaction of the modified molecular sieve is higher and the catalytic performance is better.

[0080] From the test results of Examples 1, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13, it can be found that when the preparation method of the modified molecular sieve of the present invention is adopted, the pH value of the aqueous solution is adjusted with an organic acid, where the organic acid is selected from one or more of formic acid, acetic acid, propionic acid, oxalic acid, 1,3-propanedioic acid, benzoic acid, terephthalic acid, phthalic acid, isophthalic acid or trimellitic acid, and the detergent used for the second washing is selected from one or more of water, methanol, ethanol, isopropanol, n-butanol, acetonitrile, formamide or acetone, the prepared modified molecular sieve has excellent catalytic performance, manifested as higher product selectivity and higher reactant conversion rate, and the catalyst has a longer operation life.

[0081] From the test results of Examples 1, 16, and 17, it can be found that when the preparation method of the modified molecular sieve of the present invention is adopted, wherein the quaternary ammonium template agent is selected from one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium bromide, tetraethylammonium chloride, or tetrapropylammonium chloride, when the obtained modified molecular sieve is used as a catalyst for the synthesis of caprolactam from cyclohexanone oxime, the modified molecular sieve has excellent catalytic performance, manifested as high product selectivity and high reactant conversion rate, and the catalyst has a long service life. Especially when the quaternary ammonium template agent used is tetrapropylammonium hydroxide, the catalytic performance is better.

[0082] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a modified molecular sieve, characterized in that, The preparation method of the modified molecular sieve comprises the following steps: Step S1: Mix a silicate compound, a quaternary ammonium template agent and water, and then carry out hydrolysis reaction and distillation in sequence to obtain a sol mixture and a fraction with a boiling range of 60-100°C; Step S2: Carry out crystallization reaction and liquid separation on the sol mixture in sequence to obtain an aqueous solution and an organic solution; Step S3: Adjust the pH value of the aqueous solution to 7-10, and then carry out first solid-liquid separation, first drying and first calcination on it in sequence to obtain a molecular sieve precursor; Step S4: Mix the fraction with a boiling range of 60-100°C, the organic solution and the molecular sieve precursor, and then carry out etching, second solid-liquid separation, second drying and second calcination in sequence to obtain the modified molecular sieve.

2. The preparation method of the modified molecular sieve according to claim 1, wherein, The weight ratio of the fraction with a boiling range of 60-100°C, the organic solution and the molecular sieve precursor is (1-4):(0.5-5):

1.

3. The preparation method of the modified molecular sieve according to claim 2, wherein The weight ratio of the fraction with a boiling range of 60-100°C, the organic solution and the molecular sieve precursor is (2-4):(2-5):

1.

4. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The molar ratio of the silicate compound, the quaternary ammonium template agent and water is 1:(0.05-2.0):(10-150); The raw materials for the hydrolysis reaction further include an aluminum source; The raw materials for the hydrolysis reaction further include a titanium source.

5. The preparation method of the modified molecular sieve according to claim 4, characterized in that, The molar ratio of the silicate compound, the quaternary ammonium template agent and water is 1:(0.1-0.8):(15-50).

6. The preparation method of the modified molecular sieve according to claim 4, characterized in that, The aluminum source is selected from sodium aluminate and / or potassium aluminate; the titanium source is selected from one or more of tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate or tetrabutyl titanate.

7. The preparation method of the modified molecular sieve according to claim 4, characterized in that, The molar ratio of the dosage of the aluminum source to the silicate compound is (0.0001-0.005):1; the molar ratio of the dosage of the titanium source to the silicate compound is (0.0001-0.01):

1.

8. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The silicate compound is selected from one or more of tetraethyl orthosilicate, tetrapropyl orthosilicate or tetrabutyl orthosilicate.

9. The preparation method of the modified molecular sieve according to claim 8, wherein, The quaternary ammonium template agent is selected from one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium bromide, tetraethylammonium chloride or tetrapropylammonium chloride.

10. The preparation method of the modified molecular sieve according to claim 9, characterized in that, The quaternary ammonium template agent is tetrapropylammonium hydroxide.

11. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The reaction temperature of the hydrolysis reaction is 20-40°C, and the reaction time is 2-4 h.

12. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The treatment temperature of the distillation is 70-100°C, and the treatment time is 1-6 h.

13. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The temperature of the crystallization reaction is 150-200°C, and the time is 48-96 h.

14. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The pH value of the aqueous solution is adjusted by an organic acid.

15. The preparation method of the modified molecular sieve according to claim 14, wherein, The organic acid is selected from one or more of formic acid, acetic acid, propionic acid, oxalic acid, 1,3-propanedioic acid, benzoic acid, terephthalic acid, phthalic acid, isophthalic acid or trimesic acid.

16. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The etching is carried out in an autoclave, the treatment temperature of the etching is 80-200°C, the treatment pressure is 0.2-3.0 MPa, and the treatment time is 2-180 h.

17. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, After the first solid-liquid separation and before the first drying, step S3 further includes a step of first washing the material after the first solid-liquid separation; The detergent used in the first washing is selected from one or more of water, methanol, ethanol, isopropanol, n-butanol, acetonitrile, formamide or acetone.

18. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The treatment temperature of the first drying is 40 - 120 °C, and the treatment time is 4 - 120 h.

19. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The treatment temperature of the first calcination is 400 - 600 °C, and the treatment time is 1 - 72 h.

20. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, After the second solid-liquid separation and before the second drying, step S4 further includes a step of performing a second washing on the material after the second solid-liquid separation; The detergent used in the second washing is selected from one or more of water, methanol, ethanol, isopropanol, n-butanol, acetonitrile, formamide or acetone.

21. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The treatment temperature of the second drying is 50 - 160 °C, and the treatment time is 1 - 180 h.

22. The preparation method of the modified molecular sieve according to any one of claims 1 to 3, characterized in that, The treatment temperature of the second calcination is 350 - 550 °C, and the treatment time is 1 - 96 h.

23. A catalyst for preparing caprolactam by catalytically reacting cyclohexanone oxime, characterized in that, The catalyst comprises a modified molecular sieve prepared by the preparation method of the modified molecular sieve according to any one of claims 1 to 22.