Modified ZSM-5 molecular sieve and application thereof in preparation of cyclohexanol by cyclohexene hydration

Abstract

The invention relates to the technical field of cyclohexene hydration and catalysts, and discloses a modified ZSM-5 molecular sieve and application thereof in cyclohexanol preparation through cyclohexene hydration. The modified ZSM-5 molecular sieve comprises a ZSM-5 molecular sieve inner core, the inner core is subjected to sulfonation treatment after broaching, and then the surface of the inner core is coated with SiO2 to form a core-shell structure; and carrying out hydrophobic modification on the ZrO2-SiO2 coated SO3H-ZSM-5 molecular sieve, and depositing a zirconium oxide layer on the surface of the ZrO2-SiO2 coated SO3H-ZSM-5 molecular sieve to obtain the ZrO2-SiO2 coated The molecular sieve is used as a catalyst in a cyclohexene hydration reaction, the conversion rate reaches 25% or above, the selectivity reaches 99.5% or above, the activity is still stable after the molecular sieve is recycled 6 times, the catalyst is excellent in catalytic performance, a new thought is provided for a current two-phase catalytic reaction, and meanwhile the molecular sieve is expected to be applied to a cyclohexene hydration industrial device.

Description

Technical Field

[0001] The present invention relates to the technical field of cyclohexene hydration and catalysts, and in particular to a modified ZSM-5 molecular sieve and its application in catalysis of preparing cyclohexanol by cyclohexene hydration. Background Art

[0002] Cyclohexanol is a core intermediate in the nylon 6 and nylon 66 industries, and its demand is highly correlated with the global development of the engineering plastics and chemical fiber industries. Of the three major routes for industrial cyclohexanol production, cyclohexene hydration has gradually become the mainstream process due to its advantages such as low hydrogen consumption and few by-products. However, this technology still has some areas for improvement, such as insufficient catalyst activity. Traditional solid acid catalysts (such as HZSM-5 molecular sieve) are limited by their microporous structure, resulting in low mass transfer efficiency and single-pass conversion rates generally below 15%. Furthermore, the hydration reaction is a reversible exothermic process, and the equilibrium conversion rate is temperature-dependent. Conventional processes require multi-stage reaction-separation coupling to improve efficiency, resulting in high energy consumption. Furthermore, catalyst deactivation and regeneration are difficult, acidic sites are easily covered by reaction intermediates, and ion exchange resin catalysts suffer from swelling, poor mechanical strength, and a short lifespan.

[0003] In view of the above problems, in recent years, many studies have focused on catalyst structure regulation and reaction process optimization. In CN117160522A, ZSM-5 molecular sieve is desiliconized with alkaline solution to change pore structure, and then a metal salt solution is added for ion exchange to obtain modified ZSM-5 molecular sieve catalyst. The catalyst preparation is simple, but the conversion rate is limited, and it is less than 15% after the improvement. The preparation of multi-stage pore ZSM 5 molecular sieves is disclosed in CN111253217A, with aluminosilicate materials of microporous ZSM-5 skeleton topology and mesoporous channel, wherein the mesoporous channel makes it easier for the acidic center inside the molecular sieve to contact with reactant molecules, so as to improve reaction rate and conversion rate, but conversion rate improvement is still limited, less than 18%. Current catalyst modification research mainly focuses on ZSM-5 molecular sieve, and although catalytic performance has been improved to a certain extent, effect is still unsatisfactory and has yet to be further improved. Summary of the Invention

[0004] The present invention provides a modified ZSM-5 molecular sieve and its application in preparing cyclohexanol by cyclohexene hydration. The modified ZSM-5 molecular sieve has excellent catalytic performance and good stability and is expected to be applied to the industrial production of cyclohexene hydration.

[0005] The technical solution of the present invention is to provide a modified ZSM-5 molecular sieve, including a ZSM-5 molecular sieve core, which is pore-enlarged and then sulfonated, and then coated with SiO2 on its surface to form a core-shell structure; and then hydrophobically modified and a zirconium oxide layer is deposited on the surface to obtain a ZrO2-SiO2@SO3H-ZSM-5 molecular sieve.

[0006] Optionally, the mass ratio of the ZSM-5 molecular sieve core, SiO2 shell structure and ZrO2 layer is (80-90):(8-18):(2~6).

[0007] Optionally, the silicon-aluminum molar ratio in the ZSM-5 molecular sieve is 60-150:1.

[0008] The present invention also relates to a method for preparing the modified ZSM-5 molecular sieve, comprising the following steps: S1, ZSM-5 molecular sieve is treated with alkaline solution for pore expansion, washed, filtered, dried and then calcined to obtain a pore-expanded ZSM-5 molecular sieve; S2, the expanded ZSM-5 molecular sieve is mixed with a solution containing mercaptosilane, filtered and washed after the reaction, and then added to a hydrogen peroxide solution for reaction, filtered and washed to obtain SO3H-ZSM-5 molecular sieve; S3, SO3H-ZSM-5 molecular sieve and silica sol are mixed, filtered, washed, dried and calcined to obtain SiO2@SO3H-ZSM-5 molecular sieve; After surface hydrophobic modification of S4 and SiO2@SO3H-ZSM-5 molecular sieves, they were added into zirconium salt solution for impregnation, and finally filtered, washed, dried and calcined to obtain ZrO2-SiO2@SO3H-ZSM-5 molecular sieves.

[0009] Optionally, the alkali in S1 is sodium hydroxide and / or potassium hydroxide; the treatment process is performed by heating and reflux; after the treatment, water washing, acid washing and water washing are performed in sequence, and the calcination temperature is 500-600°C.

[0010] Optionally, the mercaptosilane solution in S2 comprises a solvent comprising a mixture of toluene and water in a mass ratio of 20-30:1; the mercaptosilane is at least one of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, trimethoxysilylmethylmercaptan, and 3-mercaptopropylmethyldimethoxysilane. The reaction temperature for mixing the expanded ZSM-5 molecular sieve in S2 with the mercaptosilane solution is 80-110°C for 3-5 hours. The concentration of hydrogen peroxide is 0.5-10 wt%, and the reaction temperature in hydrogen peroxide is 30-50°C for 1-3 hours.

[0011] Alternatively, the silica sol S3 is prepared by dissolving cetyltrimethylammonium bromide (CTAB) in water, adjusting the pH to 10-11 with aqueous ammonia, and then dropwise adding ethyl silicate (TEOS). The molar ratio of CTAB:TEOS:water is 0.01-0.1:1:200-500. The silica sol is mixed with SO3H-ZSM-5 molecular sieves at a reaction temperature of 60-80°C for 4-6 hours.

[0012] Optionally, S4 meets at least one of the following conditions: 1) When modifying the surface hydrophobicity, add SiO2@SO3H-ZSM-5 molecular sieve to ethanol solution, add ammonia water to adjust the pH to 10-11, add long-chain silane reagent dropwise, and react at 50-80°C. After the reaction is completed, filter, wash, dry and calcine to complete the modification; 2) When adding a zirconium salt solution for impregnation, the zirconium salt is one of zirconium nitrate, zirconium chloride, zirconium acetate, zirconium citrate or ammonium zirconium carbonate, and the concentration is 0.5~5wt%.

[0013] The present invention also relates to the use of the modified ZSM-5 molecular sieve as a catalyst in the preparation of cyclohexanol by hydration of cyclohexene.

[0014] The present invention has the following beneficial effects: During the preparation process of the modified ZSM-5 molecular sieve of the present invention, the pore volume and pore diameter are increased through pore expansion and sulfonic acid group modification, which is beneficial for mass transfer and has higher conversion rate and selectivity. The microporous-mesoporous porous structure of the molecular sieve catalyst also facilitates the rapid removal of the product cyclohexanol, preventing the occurrence of side reactions. Because the molecular sieve uses long-chain silane to perform hydrophobic modification on the mesoporous surface, the adsorption and diffusion properties of hydrophobic cyclohexene in the pores are enhanced, creating a high-concentration environment of cyclohexene inside the catalyst, thereby breaking the thermodynamic limitations of the reaction, promoting the reaction further toward cyclohexanol, and improving the conversion rate. The ZrO2 loaded on the mesoporous surface has abundant oxygen vacancies, which can enhance the activation ability of water molecules. The ZrO2 as Lweis acid and the sulfonic acid groups as B acid centers synergistically catalytically activate water and cyclohexene, rapidly reacting to produce cyclohexanol, which is then removed from the mesoporous channels inside the catalyst.

[0015] The modified ZSM-5 molecular sieve provided by the present invention is prepared by expanding the pores of the ZSM-5 molecular sieve, then modifying the surface by sulfonation, and then coating the ZSM-5 molecular sieve with a SiO2 layer. After further hydrophobic modification, a zirconium oxide layer is deposited on the outer mesoporous layer by an impregnation method to obtain nanoparticles with a core-shell porous composite structure. The nanoparticles are used as catalysts in the reaction of preparing cyclohexanol by hydration of cyclohexene, showing high conversion rate and selectivity, high catalytic activity, stable structure, easy separation, high recovery rate, and can be reused. DETAILED DESCRIPTION

[0016] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials used in the following examples are commercially available products unless otherwise specified.

[0017] The modified ZSM-5 molecular sieve involved in the present invention uses ZSM-5 molecular sieve as raw material and is modified by sequentially performing alkali pore expansion, sulfonation, surface silanization, hydrophobic treatment and impregnation deposition of a zirconium oxide layer to obtain a ZrO2-SiO2@SO3H-ZSM-5 molecular sieve.

[0018] The specific steps involved are as follows: 1) Add ZSM-5 molecular sieve to alkaline solution, heat and reflux, then filter and wash, transfer to acid solution, acid wash, wash with water until neutral, dry, and calcine to obtain the pore-enlarged ZSM-5 molecular sieve.

[0019] The ZSM-5 molecular sieve has a silicon-aluminum molar ratio of 60-150:1, more preferably 80-120:1. In a preferred embodiment, the alkaline solution may be a sodium hydroxide or potassium hydroxide solution. Furthermore, the concentration of the alkaline solution is preferably 0.1-2 mol / L. The acid solution is preferably a hydrochloric acid solution, preferably with a concentration of 0.5-2 mol / L. The calcination temperature is preferably 500-600°C, more preferably 550°C.

[0020] 2) The expanded ZSM-5 molecular sieve is added to a solvent and dispersed by ultrasonic treatment. Then, an appropriate amount of mercaptosilane is added. After reacting for a period of time, the mixture is filtered and separated, washed with ethanol, and then transferred to 20 ml of hydrogen peroxide solution for reaction. After the reaction, the mixture is filtered and washed with water to obtain SO3H-ZSM-5 molecular sieve.

[0021] The solvent is preferably a mixture of toluene and water, with a mass ratio of 20 to 30:1. The mercaptosilane is preferably at least one of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, trimethoxysilylmethyl mercaptan, and 3-mercaptopropylmethyldimethoxysilane. The reaction temperature is preferably 80 to 110° C., and the reaction time is preferably 3 to 5 hours.

[0022] Preferably, the concentration of hydrogen peroxide is 0.5-10 wt %, and the oxidation reaction temperature in hydrogen peroxide is 30-50° C., and the reaction time is 1-3 h.

[0023] 3) Mixing the SO3H-ZSM-5 molecular sieve with silica sol, followed by filtration, washing, drying, and calcination to obtain the SiO2@SO3H-ZSM-5 molecular sieve. The silica sol is preferably prepared by dissolving cetyltrimethylammonium bromide (CTAB) in water, adjusting the pH to 10-11 with aqueous ammonia, and then dropwise adding ethyl silicate (TEOS). More preferably, the molar ratio of CTAB:TEOS:water is 0.01-0.1:1:200-500.

[0024] 4) The SiO2@SO3H-ZSM-5 is subjected to surface hydrophobic modification, preferably using a long-chain silane for modification. First, SiO2@SO3H-ZSM-5 particles are added to ethanol, and the pH is adjusted to 10-11 with ammonia water. Under stirring, an appropriate amount of a long-chain silane reagent is added dropwise. The reaction is preferably carried out at 50-80°C for 2 hours. After filtering and washing with water, the surface-hydrophobically modified SiO2@SO3H-ZSM-5 is obtained. The long-chain silane is preferably triethoxyoctylsilane, perfluorodecyltriethoxysilane or hydrogenated polydimethylsiloxane.

[0025] 5) The hydrophobically modified SiO2@SO3H-ZSM-5 particles are added to a pre-prepared zirconium salt solution for impregnation, followed by filtration, washing, drying, oven drying, and calcination to obtain porous ZrO2-SiO2@SO3H-ZSM-5 molecular sieve particles.

[0026] Preferably, the zirconium salt is one of zirconium nitrate, zirconium chloride, zirconium acetate, zirconium citrate, or ammonium zirconium carbonate, and the concentration of the zirconium salt solution is 0.5-5 wt %. The impregnation is preferably performed at room temperature for 24 hours, and the calcination temperature is preferably 500° C.

[0027] When the modified ZSM-5 molecular sieve prepared by the present invention is used as a catalyst in the hydration of cyclohexene to produce cyclohexanol, the added amount is preferably 5% of the mass of the cyclohexene. In the cyclohexene hydration reaction, the mass ratio of cyclohexene to water is preferably 1:3. The reaction is carried out in a sealed reactor, first purged with nitrogen three times, and then heated. The reaction conditions are preferably 120°C, 0.6 MPa, and 500 rpm for 60 minutes.

[0028] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0029] Example 1: The preparation steps of the modified ZSM-5 molecular sieve catalyst A1 are as follows: Step 1: Add 5g of ZSM-5 molecular sieve with a silicon-aluminum ratio of 80:1 to 30ml of 0.5mol / L sodium hydroxide solution, heat and reflux for 6h, then filter and wash, transfer to 20mL of 1mol / L HCl solution, acid wash, and then wash with water until neutral. After drying, calcinate at 550℃ to obtain the pore-enlarged ZSM-5 molecular sieve; Step 2: Take 2 g of the expanded ZSM-5 molecular sieve, add 50 ml of a mixed solution of toluene and water in a mass ratio of 20:1, and ultrasonicate for 10 minutes. Then, add 0.6 ml of 3-mercaptopropyltrimethoxysilane to the solution, react at 90 ° C for 3 hours, filter and separate, wash with ethanol, and then transfer to 20 ml of 0.5% hydrogen peroxide solution, react at 30 ° C for 1 hour, filter, and wash with water to obtain SO3H-ZSM-5 molecular sieve; Step 3: Take 0.1g of hexadecyltrimethylammonium bromide (CTAB) and dissolve it in 50ml of deionized water. Add ammonia water to adjust the pH to 11, slowly add 1.5g of tetraethyl orthosilicate (TEOS), and stir magnetically for 30 minutes to form a silica sol. Then add the above-mentioned SO3H-ZSM-5 molecular sieve, ultrasonicate for 30 minutes, stir at 500rpm at 60-80℃ for 5h, cool, filter and separate, wash with ethanol and deionized water in turn until neutral, dry in vacuum at 60℃ for 12h, and then calcined at 550℃ for 4h to obtain surface silanized SiO2@SO3H-ZSM-5 particles; Step 4: Add the above SiO2@SO3H-ZSM-5 particles to 50ml of ethanol solution, adjust the pH to 11 with 28% ammonia water, add 0.1ml of perfluorooctyltriethoxysilane dropwise with stirring, react at 60°C for 2h, filter, and wash with water to obtain SiO2@SO3H-ZSM-5 with hydrophobic surface modification; Step 5: Add the hydrophobically modified SiO2@SO3H-ZSM-5 particles to a pre-prepared 1%wt zirconium nitrate solution, immerse at room temperature for 24 hours, then filter, wash, dry, oven dry, and calcine at 500°C for 4 hours to obtain a porous ZrO2-SiO2@SO3H-ZSM-5 molecular sieve catalyst A1.

[0030] The catalyst was used in the hydration reaction of cyclohexene to prepare cyclohexanol, with the following steps: 10 g of cyclohexene, 30 g of water, and 0.5 g of the catalyst were weighed and added to a sealed reactor. The atmosphere was replaced with nitrogen three times, and then the temperature was raised and the reaction was carried out at 120° C., 0.6 MPa, and 500 rpm for 60 min. After the reaction, the temperature was cooled to room temperature, the pressure was released, the contents of the reactor were removed, and the reaction was centrifuged. The catalyst was recycled six times, and the supernatant was removed and analyzed by gas chromatography. The results are shown in Table 1.

[0031] Example 2: The preparation and application of the modified ZSM-5 molecular sieve catalyst A2 were the same as in Example 1 except that the silicon-aluminum ratio in step 1 was 60:1. The results are shown in Table 1.

[0032] Example 3: The preparation and application of the modified ZSM-5 molecular sieve catalyst A3 were the same as in Example 1 except that the silicon-aluminum ratio in step 1 was 120:1. The results are shown in Table 1.

[0033] Comparative Example 1: The preparation and application of the modified ZSM-5 molecular sieve catalyst B1 were the same as in Example 1 except that the silicon-aluminum ratio in step 1 was 30:1. The results are shown in Table 1.

[0034] Example 4: The preparation and application of the modified ZSM-5 molecular sieve catalyst A4 were the same as in Example 1 except that trimethoxysilylmethyl mercaptan was used in step 2. The results are shown in Table 1.

[0035] Example 5: The preparation and application of the modified ZSM-5 molecular sieve catalyst A5 were the same as in Example 1 except that 3-mercaptopropyltriethoxysilane was used in step 2. The results are shown in Table 1.

[0036] Example 6: The preparation and application of the modified ZSM-5 molecular sieve catalyst A6 were the same as in Example 1 except that the mercaptosilanization reaction temperature in step 2 was 105° C. The results are shown in Table 1.

[0037] Comparative Example 2: In the preparation and application of the modified ZSM-5 molecular sieve catalyst B1, the disulfonation treatment was not performed in the catalyst preparation step. Instead, 2 g of the ZSM-5 molecular sieve after pore expansion in step 1 was used for step 3 treatment. Other treatments were the same as in Example 1. The results are shown in Table 1.

[0038] Example 7: The preparation and application of the modified ZSM-5 molecular sieve catalyst A7 were the same as in Example 1 except that 2% hydrogen peroxide was used in step 2. The results are shown in Table 1.

[0039] Example 8: The preparation and application of the modified ZSM-5 molecular sieve catalyst A8 were the same as in Example 1 except that 9% hydrogen peroxide was used in step 2. The results are shown in Table 1.

[0040] Comparative Example 3: The preparation and application of the modified ZSM-5 molecular sieve catalyst B3 were the same as in Example 1 except that 20% hydrogen peroxide was used in step 2. The results are shown in Table 1.

[0041] Example 9: In the preparation and application of the modified ZSM-5 molecular sieve catalyst A9, except that the amount of CTAB added in step 3 was 0.25 g, the rest was the same as in Example 1. The results are shown in Table 1.

[0042] Example 10: In the preparation and application of the modified ZSM-5 molecular sieve catalyst A10, except that the amount of TEOS added in step 3 was 2.5 g, the rest was the same as in Example 1. The results are shown in Table 1.

[0043] Comparative Example 4: In the preparation and application of the modified ZSM-5 molecular sieve catalyst B4, the step three silanization coating treatment was not performed in the catalyst preparation step. Instead, the SO3H-ZSM-5 molecular sieve prepared in step two was subjected to step four treatment. Other treatments were the same as in Example 1. The results are shown in Table 1.

[0044] Example 11: The preparation and application of the modified ZSM-5 molecular sieve catalyst A11 were the same as in Example 1 except that triethoxyoctylsilane was used in step 4. The results are shown in Table 1.

[0045] Comparative Example 5: In the preparation and application of the modified ZSM-5 molecular sieve catalyst B5, the hydrophobic modification treatment in step 4 was not performed in the catalyst preparation step. Instead, the surface silanized SiO2@SO3H-ZSM-5 particles prepared in step 3 were treated in step 5. Other treatments were the same as in Example 1. The results are shown in Table 1.

[0046] Example 12: The preparation and application of the modified ZSM-5 molecular sieve catalyst A12 were the same as in Example 1 except that zirconium acetate was used in step 5. The results are shown in Table 1.

[0047] Example 13: The preparation and application of the modified ZSM-5 molecular sieve catalyst A13 were the same as in Example 1, except that the zirconium nitrate concentration in step 5 was 0.5% wt. The results are shown in Table 1.

[0048] Comparative Example 6: The preparation and application of the modified ZSM-5 molecular sieve catalyst B6 were the same as in Example 1 except that step 5 was not performed in the catalyst preparation process. The results are shown in Table 1.

[0049] Comparative Example 7: The preparation and application of the modified ZSM-5 molecular sieve catalyst B7 were the same as in Example 1, except that the zirconium nitrate concentration in the catalyst preparation step was 10% by weight. The results are shown in Table 1.

[0050] Comparative Example 8: In the preparation and application of the modified ZSM-5 molecular sieve catalyst B8, except that ammonium titanate was used in step 5, the rest was the same as in Example 1 to obtain TiO2-SiO2@SO3H-ZSM-5. The results are shown in Table 1.

[0051] Comparative Example 9: In the preparation and application of the modified ZSM-5 molecular sieve catalyst B9, except for using aluminum nitrate in step 5, the rest is the same as in Example 1 to obtain Al2O3-SiO2@SO3H-ZSM-5. The results are shown in Table 1.

[0052] Table 1

[0053] From the results in the table, it can be found that in comparative example 1, when the silicon-aluminum ratio is too low, the reaction conversion rate is low and the stability is also poor. When the silicon-aluminum ratio is low, the aluminum content is high, the molecular sieve structure stability is poor, and the thermal stability is also poor. The skeleton structure may collapse during the subsequent modification process, affecting the activity of the catalyst, and also affecting the stability during recycling.

[0054] In Comparative Example 2, the conversion rate of the catalyst that was not sulfonated decreased significantly, indicating that sulfonation provided the catalyst with Br acid active sites, significantly increasing the catalytic activity of the catalyst.

[0055] In Comparative Example 3, when 20% hydrogen peroxide was used, the catalyst activity decreased significantly. Hydrogen peroxide has strong oxidizing properties and will decompose to produce hydroxyl radicals. These free radicals may damage the active sites or structures on the surface of the ZSM-5 molecular sieve, destroying the acid centers and affecting the catalytic performance. However, low-concentration hydrogen peroxide plays a certain catalytic role in the sulfonation process of mercaptosiloxane, accelerates the reaction, and helps cross-link the siloxane chains and fix the sulfonic acid groups.

[0056] In comparative example 4, the catalytic activity decreased significantly due to the absence of a silicon oxide layer. In contrast, in example 1, the surface was coated with a silicon oxide shell, which not only improved the stability of the ZSM-5 core but also provided a mesoporous surface for subsequent impregnation and hydrophobic modification, thereby enhancing the catalyst activity.

[0057] In Comparative Example 5, the catalyst surface was not hydrophobically modified, and a large amount of water molecules would diffuse into the interior of the catalyst, which was not conducive to forming a high-concentration cyclohexene environment and could not break the thermodynamic equilibrium. However, after hydrophobic modification, the adsorption and diffusion properties of hydrophobic cyclohexene in the pores could be enhanced, creating a high-concentration cyclohexene environment inside the catalyst, thereby breaking the thermodynamic limitations of the reaction, pushing the reaction further towards cyclohexanol, and improving the conversion rate.

[0058] In Comparative Examples 6 and 7, no zirconium salt was added or a high concentration of zirconium salt was added, which was not conducive to improving the conversion rate of the reaction. The ZrO2 layer has abundant oxygen vacancies, which can enhance the activation ability of water molecules. At the same time, it can also form L acid and B acid synergistic catalyst effects with the internal sulfonic acid groups. However, high concentrations of zirconium salt may block the surface pores or disperse unevenly during impregnation deposition, affecting the catalyst activity.

[0059] In Comparative Examples 8 and 9, titanium salts and aluminum salts are used for surface modification, but the effect is poor. Titanium atoms and aluminum atoms may be more likely to aggregate or their structures may be destroyed during high-temperature calcination. Zirconium has better high-temperature resistance. Zirconium ions form strong Si-O-Zr bonds with the hydroxyl groups on the surface of silicon oxide, which promotes metal dispersion and the resulting catalyst has higher activity.

[0060] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the appended claims.

Claims

1. A modified ZSM-5 molecular sieve, characterized in that: The method comprises a ZSM-5 molecular sieve core, which is pore-enlarged and then subjected to a sulfonation treatment. The core is then coated with SiO2 on its surface to form a core-shell structure. The core is then hydrophobically modified and a zirconium oxide layer is deposited on the surface to obtain a ZrO2-SiO2@SO3H-ZSM-5 molecular sieve.

2. The modified ZSM-5 molecular sieve according to claim 1, characterized in that: The mass ratio of the ZSM-5 molecular sieve core, SiO2 shell structure and ZrO2 layer is (80-90): (8-18): (2~6).

3. The modified ZSM-5 molecular sieve according to claim 1, characterized in that: The molar ratio of silicon to aluminum in ZSM-5 molecular sieve is (60~150):

1.

4. The method for preparing the modified ZSM-5 molecular sieve according to any one of claims 1 to 3, wherein The following steps are involved: S1, ZSM-5 molecular sieve is treated with alkaline solution for pore expansion, washed, filtered, dried and then calcined to obtain a pore-expanded ZSM-5 molecular sieve; S2, the expanded ZSM-5 molecular sieve is mixed with a solution containing mercaptosilane, filtered and washed after the reaction, and then added to a hydrogen peroxide solution for reaction, filtered and washed to obtain SO3H-ZSM-5 molecular sieve; S3, SO3H-ZSM-5 molecular sieve and silica sol are mixed, filtered, washed, dried and calcined to obtain SiO2@SO3H-ZSM-5 molecular sieve; After surface hydrophobic modification of S4 and SiO2@SO3H-ZSM-5 molecular sieves, they were added into zirconium salt solution for impregnation, and finally filtered, washed, dried and calcined to obtain ZrO2-SiO2@SO3H-ZSM-5 molecular sieves.

5. The preparation method according to claim 4, characterized in that: The alkali in S1 is sodium hydroxide and / or potassium hydroxide; the treatment process is heated and refluxed; after the treatment, water washing, acid washing and water washing are carried out in sequence, and the calcination temperature is 500~600℃.

6. The preparation method according to claim 4, characterized in that: In the solution S2 containing mercaptosilane, the solvent is a mixture of toluene and water in a mass ratio of (20~30):1; the mercaptosilane is at least one of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, trimethoxysilylmethyl mercaptan, and 3-mercaptopropylmethyldimethoxysilane.

7. The preparation method according to claim 4, characterized in that: When the expanded ZSM-5 molecular sieve in S2 is mixed with a solution containing mercaptosilane, the reaction temperature is 80-110°C and the reaction time is 3-5 h; the hydrogen peroxide concentration is 0.5-10wt%, the reaction temperature in the hydrogen peroxide solution is 30-50°C and the reaction time is 1-3 h.

8. The preparation method according to claim 7, characterized in that: The S3 silica sol is prepared by dissolving hexadecyltrimethylammonium bromide (CTAB) in water, adding ammonia water to adjust the pH to 10-11, and adding ethyl silicate (TEOS) dropwise to mix. The molar ratio of CTAB:TEOS:water is (0.01-0.1):1:(200-500). When the silica sol is mixed with SO3H-ZSM-5 molecular sieve, the reaction temperature is 60-80°C and the reaction time is 4-6 hours.

9. The preparation method according to claim 4, characterized in that: At least one of the following conditions must be met in S4: 1) When modifying the surface hydrophobicity, add SiO2@SO3H-ZSM-5 molecular sieve to ethanol solution, add ammonia water to adjust the pH to 10-11, add long-chain silane reagent dropwise, and react at 50-80°C. After the reaction is completed, filter, wash, dry and calcine to complete the modification; 2) When adding a zirconium salt solution for impregnation, the zirconium salt is one of zirconium nitrate, zirconium chloride, zirconium acetate, zirconium citrate or ammonium zirconium carbonate, and the concentration is 0.5~5wt%.

10. Use of the modified ZSM-5 molecular sieve according to any one of claims 1 to 3 or the modified ZSM-5 molecular sieve obtained according to the preparation method according to any one of claims 4 to 9 as a catalyst in the preparation of cyclohexanol by hydration of cyclohexene.

Images