A method for improving the catalytic performance of a ZSM-5 molecular sieve for the hydration of cyclohexene to produce cyclohexanol

Abstract

This invention provides a method for improving the catalytic performance of ZSM-5 molecular sieves used in the hydration of cyclohexene to prepare cyclohexanol, belonging to the field of catalysis technology. This method employs a dissolution-recrystallization post-treatment technique to control the surface acidity and surface silica-alumina ratio of ZSM-5, allowing additional aluminum sources to enter the molecular sieve framework. This effectively controls the surface acidity and surface silica-alumina ratio of ZSM-5 molecular sieves, increases acidic sites, and enhances the catalyst activity in the hydration of cyclohexene to cyclohexanol. The molecular sieve prepared by this method exhibits advantages such as high cyclohexene conversion and good cyclohexanol selectivity in the catalytic reaction of cyclohexene hydration to cyclohexanol.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, specifically to a method for controlling the surface acidity of ZSM-5 molecular sieves using a dissolution-recrystallization method and its application in the catalytic hydration of cyclohexene to prepare cyclohexanol. Background Technology

[0002] Cyclohexanol is a core intermediate in the Nylon 6 and Nylon 66 industrial chain, and is mostly used to prepare adipic acid and caprolactam. Currently, there are three main routes for the industrial production of cyclohexanol: hydrogenation of phenol to cyclohexanol, oxidation of cyclohexane to cyclohexanol, and hydration of cyclohexene to cyclohexanol. Among these, hydration of cyclohexene to cyclohexanol has advantages such as high selectivity and mild reaction conditions, giving it a significant advantage over other methods and making it the current main production route for cyclohexanol. The cyclohexene hydration reaction is a protonic acid-catalyzed reaction, requiring a catalyst with a strong acidic site. ZSM-5 molecular sieves with silicon-aluminum components are the mainstream catalyst for the industrial hydration of cyclohexene to cyclohexanol. The reaction of cyclohexene hydration to cyclohexanol catalyzed by ZSM-5 molecular sieve is a typical "oil-water-solid" three-phase reaction. Cyclohexene and water need to diffuse to the acidic sites inside the catalyst to react. Cyclohexene has extremely low solubility in water, and the contact area with water during the reaction is limited. The mass transfer resistance between the water and oil phases during the reaction prevents cyclohexene from effectively approaching the active sites, which greatly limits the occurrence of the reaction. Therefore, controlling the acidity of the catalyst surface can provide more accessible active sites for the reaction.

[0003] CN121182511A employs inorganic alkali low-temperature modification of ZSM-5 molecular sieves, achieving regulation of the microalgae pyrolysis reaction pathway under relatively mild conditions through a mild desilication process. CN106000450A utilizes alkali treatment followed by loading with elements such as P, La, and Ce to regulate the acidity and stability of ZSM-5. CN117756134A increases the acidic sites of H-ZSM-5 through solid-phase synthesis and in-situ cerium doping. CN120515482A coats the surface of loaded ZSM-5 molecular sieves with SiO2, then performs hydrophobic modification on the SiO2 layer and deposits a zirconium oxide layer to improve the surface acidity and cyclohexene hydration performance of the ZSM-5 sieve.

[0004] Currently, ZSM-5 molecular sieve catalysts used in industry still suffer from low single-pass conversion of cyclohexene. Further development of simple acid regulation methods suitable for industrial molecular sieves is needed to improve the single-pass conversion of cyclohexene during the reaction process. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for improving the catalytic performance of ZSM-5 molecular sieves used in the hydration of cyclohexene to prepare cyclohexanol. This method regulates the surface acidity and surface silica-alumina ratio of the ZSM-5 molecular sieve through a dissolution-recrystallization method, providing more active sites for the reaction of cyclohexene hydration to prepare cyclohexanol. This improves the activity of the ZSM-5 molecular sieve catalyst in the hydration of cyclohexene to prepare cyclohexanol, solving the problems of poor mass transfer efficiency and low conversion rate of ZSM-5 molecular sieve catalysts in the current industrial process of cyclohexene hydration to prepare cyclohexanol.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for improving the catalytic performance of ZSM-5 molecular sieves for the hydration of cyclohexene to cyclohexanol, the method employing an additional aluminum source and basic TPA. + The ZSM-5 raw powder was dissolved and recrystallized using a cationic solution. By adjusting the raw material ratio and post-treatment conditions, the surface acidity and surface silicon-aluminum ratio of ZSM-5 were controlled, thereby improving its catalytic performance in the hydration of cyclohexene to cyclohexanol.

[0007] As a specific embodiment of the present invention, the method includes the following steps: S1. Mix NaOH and H2O evenly, then add aluminum source and heat to obtain aluminum-containing precursor solution; S2, add alkaline TPA + The cationic solution is mixed with the aluminum-containing precursor solution; S3. Mix the ground ZSM-5 raw powder with the solution obtained in S2 and stir evenly to obtain a molecular sieve mixture; S4. Transfer the obtained molecular sieve mixture to a polytetrafluoroethylene reactor for crystallization; S5. After crystallization, the molecular sieve is washed with water and centrifuged to obtain a precipitate. After drying, it is calcined to remove the template agent and obtain a hydrated catalyst.

[0008] Furthermore, in S1, the aluminum source is one, two, or more of aluminum hydroxide, sodium aluminate, and boehmite.

[0009] Furthermore, in S1, the molar ratio of aluminum source (based on aluminum atoms), NaOH and H2O in the aluminum-containing precursor solution is 1:1:15-70.

[0010] Furthermore, the mass concentration of aluminum atoms in the S1 aluminum-containing precursor solution is 2-6%.

[0011] Furthermore, in S2, alkaline TPA + The cation solution is a TPAOH solution, or a solution composed of TPABr and NaOH.

[0012] Furthermore, in the method, alkaline TPA + The amount of cation solution used is: ZSM-5 raw powder (calculated as SiO2) and TPA. + The molar ratio of cations is 1:0.05-0.25.

[0013] Furthermore, in the method, the molar ratio of ZSM-5 raw powder (calculated as SiO2) to aluminum-containing precursor solution (calculated as aluminum atoms) is 1:0.04-0.15.

[0014] Furthermore, in step S4, the crystallization temperature is 160~180 ℃ and the crystallization time is 24~48 h.

[0015] Preferably, in step S4, the crystallization temperature is 180 °C and the crystallization time is 48 h.

[0016] Furthermore, in step S5, the calcination temperature is 450~600 ℃, and the calcination time is 2~8 h.

[0017] Preferably, in step S5, the calcination temperature is 550 °C and the calcination time is 6 h.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention regulates the surface silica-alumina ratio and surface acidity of ZSM-5 molecular sieves by dissolving and recrystallizing ZSM-5 raw powder, thereby increasing the active sites for the reaction of cyclohexene with water and improving the conversion rate of cyclohexene. Detailed Implementation

[0019] The technical solution of the present invention will be further described below through embodiments.

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention relates to the post-processing of ZSM-5 molecular sieves and their catalytic reaction of cyclohexene hydration to cyclohexanol. Using ZSM-5 raw powder as raw material, a ZSM-5 molecular sieve with controllable surface acidity is obtained through a dissolution and recrystallization process, which can effectively improve the conversion rate of cyclohexene and the yield of cyclohexanol.

[0022] Evaluation of cyclohexene hydration reaction: The ZSM-5 catalyst obtained in this invention is used in the reaction of cyclohexene hydration to prepare cyclohexanol. The steps are as follows: 30 mL of cyclohexene, 30 mL of water, and 7.20 g of catalyst are added to a 100 mL reaction vessel, purged with nitrogen three times, and then heated to 124 °C, 0.5 MPa, and 900 r / min for 60 min. After the reaction is completed, the mixture is cooled, the pressure is released, and the supernatant is taken out for gas chromatography analysis.

[0023] Formulas for calculating cyclohexene conversion and cyclohexanol selectivity: Cyclohexene conversion rate: (n0 is the molar amount of cyclohexene before the reaction, n) i (This refers to the molar amount of cyclohexene after the reaction). Cyclohexanol selectivity: (n) x (This refers to the molar amount of cyclohexanol produced). Example 1

[0024] Mix 0.95 g NaOH and 7.8 g H2O evenly, then add 1.85 g Al(OH)3 and heat at 100 ℃ to obtain an aluminum precursor solution with an aluminum atomic mass concentration of 6%.

[0025] 10 g of ZSM-5 raw powder (calculated as SiO2) was ground evenly, and 10 g of 6% aluminum-containing precursor solution was added. The mixture was stirred evenly, and then 20.336 g of TPAOH (25 wt%) was added. The mixture was stirred evenly again, and then water (19.66 g) was added to bring the solid-liquid mass ratio to 1:5. The mixture was then placed in a polytetrafluoroethylene reactor and crystallized at 180 °C for 48 h. The crystallized molecular sieve was centrifuged and filtered, washed with water, dried, ground evenly, and then calcined in a muffle furnace at 550 °C for 6 h to remove the template agent, thus obtaining the modified catalyst A1. The activity of the catalyst was evaluated according to the cyclohexene hydration reaction evaluation procedure, and the results are shown in Table 1. Example 2

[0026] In the preparation and application of the post-treatment ZSM-5 molecular sieve catalyst A2, except that the amount of TPAOH (25 wt%) added was 27.11 g and water (12.89 g) was added to make the solid-liquid mass ratio 1:5, everything else was the same as in Example 1, and the results are shown in Table 1. Example 3

[0027] In the preparation and application of the post-treatment ZSM-5 molecular sieve catalyst A3, except that the amount of TPAOH (25 wt%) added was 6.78 g and water (33.22 g) was added to make the solid-liquid mass ratio 1:5, everything else was the same as in Example 1, and the results are shown in Table 1. Example 4

[0028] In the preparation and application of the post-treatment ZSM-5 molecular sieve catalyst A3, except that the amount of TPAOH (25 wt%) added was 13.56 g and water (26.44 g) was added to make the solid-liquid mass ratio 1:5, everything else was the same as in Example 1, and the results are shown in Table 1. Example 5

[0029] Mix 0.31 g NaOH and 9.6 g H2O evenly, then add 0.61 g Al(OH)3 and heat at 100 °C to obtain an aluminum precursor solution with an aluminum atomic mass concentration of 2%.

[0030] In the preparation and application of the post-processed ZSM-5 molecular sieve catalyst A4, except for the addition of 10 g of 2% aluminum-containing precursor solution, everything else was the same as in Example 1, and the results are shown in Table 1. Example 6

[0031] Mix 0.62 g NaOH and 8.6 g H2O evenly, then add 1.21 g Al(OH)3 and heat at 100 °C to obtain an aluminum precursor solution with an aluminum atomic mass concentration of 4%.

[0032] In the preparation and application of the post-treatment ZSM-5 molecular sieve catalyst A5, except for the addition of 10 g of 4% aluminum-containing precursor solution and 29.66 g of water, everything else was the same as in Example 1, and the results are shown in Table 1.

[0033] Comparative Example 1: Untreated ZSM-5 raw powder B1 was ground and its cyclohexene hydration reaction activity was evaluated directly. The results are shown in Table 1.

[0034] Comparative Example 2: The preparation and application of the post-processed ZSM-5 molecular sieve catalyst B2 were the same as in Example 1, except that no aluminum-containing precursor solution was added. The results are shown in Table 1.

[0035] Table 1. Surface silica-to-alumina ratio and cyclohexene hydration reaction performance of ZSM-5 molecular sieves

[0036] As shown in Table 1, the surface Si / Al ratio of the untreated ZSM-5 raw powder (Comparative Example B1) was 16.09. For the sample (Comparative Example B2) which underwent desilication treatment with only alkaline TPAOH solution without adding an additional aluminum source, the surface Si / Al ratio increased to 18.05. This indicates that alkaline treatment preferentially removed silicon species from the framework, while also causing some aluminum removal. Furthermore, after catalyzing the hydration reaction of cyclohexene, the cyclohexene conversion rate decreased to 9.81%. In contrast, the catalysts prepared by introducing an additional aluminum source using the "dissolve-recrystallize" strategy described in this invention (Examples A1-A6) exhibited a regular change in their surface Si / Al molar ratio. In particular, the A1 and A2 samples, which showed the best activity, further reduced their surface Si / Al molar ratios to 13.43 and 13.20, respectively. This demonstrates that the post-treatment method of the present invention successfully introduces exogenous aluminum species into the surface or framework of molecular sieves, repairs lattice defects and increases surface acidic sites during recrystallization, effectively overcoming the limitations of traditional alkali treatment, and significantly improving the cyclohexene conversion rate while maintaining a high selectivity of 99.9%.

[0037] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the catalytic performance of ZSM-5 molecular sieves used in the hydration of cyclohexene to prepare cyclohexanol, characterized in that, This method uses an additional aluminum source and alkaline TPA. + The ZSM-5 raw powder was dissolved and recrystallized using a cationic solution. By adjusting the raw material ratio and post-treatment conditions, the surface acidity and surface silicon-aluminum ratio of ZSM-5 were controlled, thereby improving its catalytic performance in the hydration of cyclohexene to cyclohexanol.

2. The method according to claim 1, characterized in that, The method includes the following steps: S1. Mix NaOH and H2O evenly, then add aluminum source and heat to obtain aluminum-containing precursor solution; S2, add alkaline TPA + The cationic solution is mixed with the aluminum-containing precursor solution; S3. Mix the ground ZSM-5 raw powder with the solution obtained in S2 and stir evenly to obtain a molecular sieve mixture; S4. Transfer the obtained molecular sieve mixture to a polytetrafluoroethylene reactor for crystallization; S5. After crystallization, the molecular sieve is washed with water and centrifuged to obtain a precipitate. After drying, it is calcined to remove the template agent and obtain a hydrated catalyst.

3. The method according to claim 2, characterized in that, In S1, the aluminum source is one, two, or more of aluminum hydroxide, sodium aluminate, and boehmite.

4. The method according to claim 2, characterized in that, In S1, the molar ratio of aluminum source (based on aluminum atoms), NaOH and H2O in the aluminum-containing precursor solution is 1:1:15-70.

5. The method according to claim 2, characterized in that, In S1, the mass concentration of aluminum atoms in the aluminum precursor solution is 2-6%.

6. The method according to claim 2, characterized in that, In S2, alkaline TPA + The cation solution is a TPAOH solution, or a solution composed of TPABr and NaOH.

7. The method according to claim 2, characterized in that, In the method described, alkaline TPA + The amount of cation solution used is: ZSM-5 raw powder (calculated as SiO2) and TPA. + The molar ratio of cations is 1:0.05-0.

25.

8. The method according to claim 2, characterized in that, In the method, the molar ratio of ZSM-5 raw powder (calculated as SiO2) to aluminum-containing precursor solution (calculated as aluminum atoms) is 1:0.04-0.

15.

9. The method according to claim 2, characterized in that, In S4, the crystallization temperature is 160~180 ℃ and the crystallization time is 24~48 h.

10. The method according to claim 2, characterized in that, In step S5, the calcination temperature is 450~600 ℃ and the calcination time is 2~8 h.

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