A catalyst for the indirect preparation of cyclohexanol from cyclohexene and its synthetic method.

Abstract

This invention discloses a catalyst and its synthesis method for the indirect preparation of cyclohexanol from cyclohexene. Using ZSM-5 molecular sieve as the main component, Ga(NO3)3 and Zr(NO3)4 are introduced, along with a soft template agent. The catalyst is obtained through hydrothermal crystallization, ion exchange, and calcination. This catalyst exhibits excellent catalytic performance in the reaction of cyclohexene with ethanol via etherification followed by hydrolysis to prepare cyclohexanol, with an etherification conversion rate exceeding 98%, a hydrolysis conversion rate exceeding 90%, and a cyclohexanol selectivity exceeding 99%. This technology provides a new approach to heterogeneous catalytic reactions and holds promise for the industrial production of cyclohexanol from cyclohexene.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and specifically to a catalyst for the indirect preparation of cyclohexanol from cyclohexene and its synthesis method. Background Technology

[0002] Cyclohexanol is an important organic chemical raw material, widely used in the production of caprolactam, adipic acid, and other chemicals, and has significant applications in the coatings, pharmaceuticals, and fragrance industries. Traditional cyclohexanol preparation processes include cyclohexane oxidation, phenol hydrogenation, and cyclohexene hydration, but these methods suffer from poor selectivity, multiple products, difficulty in separating byproducts, and high energy consumption. In recent years, the etherification reaction of cyclohexene with alcohols has attracted attention as a single-step process; however, existing research lacks effective catalyst systems and process coupling, failing to establish a complete continuous reaction process. Developing a new integrated process for the etherification and hydrolysis of cyclohexene with ethanol to prepare cyclohexanol would overcome the limitations of traditional stepwise reaction processes.

[0003] Existing Ga or Zr monometallic doped ZSM-5 molecular sieves can only improve one of the acidity or hydrothermal stability, but cannot simultaneously optimize the efficient matching of the etherification and hydrolysis two-step reactions. How Ga-Zr bimetals can achieve a "1+1>2" effect through interaction and pore synergy has not yet been reported. Summary of the Invention

[0004] This invention provides a catalyst for the indirect preparation of cyclohexanol from cyclohexene and its synthesis method. The catalyst is a Ga-Zr-ZSM-5 catalyst, which has excellent reaction performance and good stability, and can be applied to the industrial production of cyclohexene etherification followed by hydrolysis to prepare cyclohexanol.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A catalyst for the indirect preparation of cyclohexanol from cyclohexene is based on ZSM-5 molecular sieve, with Ga(NO3)3 and Zr(NO3)4 introduced and synergistically doped, and natural polysaccharide organic soft template agent added. After hydrothermal crystallization, ion exchange and calcination, Ga-Zr-ZSM-5 catalyst is obtained.

[0007] The preparation method of the Ga-Zr-ZSM-5 catalyst of the present invention includes the following steps:

[0008] (1) Preparation of precursor gel: ZSM-5 molecular sieve is added to alkaline solution and the pH is adjusted to 11-12 to form a uniformly mixed gel; Ga-containing metal modifier and Zr-containing metal modifier are dissolved in deionized water to obtain a solution; the solution is slowly added dropwise to the above gel and stirred continuously for 2-3 h to form a uniform precursor gel.

[0009] (2) Introduction of seed crystals and soft template: ZSM-5 seed crystals and soft template agent were added to the above precursor gel, and the mixture was stirred evenly and then allowed to stand for aging for 4-6 hours.

[0010] (3) Crystallization: The aged precursor gel is transferred to a stainless steel reactor lined with polytetrafluoroethylene and crystallized at 160~180°C. o Crystallize at C for 12-48 h. After crystallization, cool, filter, and wash until neutral. The resulting solid is then cooled to 80-120 °C. o Dry at C for 6-12 h, then in air or an inert atmosphere at 400-800 °C. o Calcination with C for 2-6 h removes template agent and impurities to obtain Ga-Zr modified ZSM-5 molecular sieve;

[0011] (4) Ion exchange: Ga-Zr modified ZSM-5 molecular sieve was added to a 1 mol / L NH4NO3 solution, and the solution was heated at 75-85°C. o The reaction is carried out at C for 2-3 hours, followed by washing and drying. This process is repeated 3 times, and then the reaction is carried out at 500-550°C. o The Ga-Zr-ZSM-5 catalyst was obtained by calcining with C for 4-5 hours.

[0012] The silicon-aluminum molar ratio of the ZSM-5 molecular sieve in step (1) is 20-80:1.

[0013] The alkaline solution in step (1) is at least one of ammonia, potassium hydroxide and sodium hydroxide, and the concentration of the alkaline solution is 0.1-0.5 mol / L; the molar ratio of the gel system is: n(SiO2) / n(Al2O3)=20~80, n(H2O) / n(SiO2)=30~150.

[0014] The Ga-containing metal modifier in step (1) is at least one of gallium nitrate, gallium chloride, or gallium sulfate; the Zr-containing metal modifier is at least one of zirconium nitrate, zirconium oxychloride, or zirconium sulfate; the total loading of Ga and Zr is 0.1-10 wt% of ZSM-5 molecular sieve, and the molar ratio of Ga to Zr is 1-2:1.

[0015] The amount of ZSM-5 seed crystals added in step (2) is 1-10 wt% of the silicon source content in the ZSM-5 molecular sieve synthesis system, preferably 5 wt%; the soft template agent is at least one of sodium alginate, chitosan, guar gum or pentamethylolpropane, and the amount of soft template agent added is 1-5 wt% of the mass of ZSM-5 molecular sieve.

[0016] The preferred roasting temperature in step (3) is 500~700℃. o C, the roasting time is preferably 3~5 h.

[0017] This invention also relates to the application of the Ga-Zr-ZSM-5 catalyst as a catalyst in the preparation of cyclohexanol by etherification of cyclohexene and ethanol followed by hydrolysis, wherein the cyclohexene conversion rate is not less than 98% and the cyclohexanol selectivity is not less than 99%.

[0018] This invention employs the above technical solutions to provide a modified ZSM-5 molecular sieve catalyst. Through Ga-Zr synergistic doping and soft template-controlled structure, it achieves for the first time a highly efficient coupling of cyclohexene etherification and hydrolysis reactions. This catalyst possesses a uniform acidity distribution and good structural stability, effectively solving the problems of easy deactivation and uneven distribution of acid centers in traditional ZSM-5 molecular sieves under high temperature and humidity conditions. Through bifunctional catalysis, it significantly improves the conversion rate of cyclohexene and the yield of cyclohexanol, overcoming the limitations of traditional stepwise reaction processes and providing a highly efficient catalytic scheme for the integrated etherification-hydrolysis preparation of cyclohexanol from cyclohexene and ethanol.

[0019] The present invention has the following beneficial effects:

[0020] (1) This invention introduces Ga and Zr into the ZSM-5 molecular sieve framework simultaneously through a one-step in-situ crystallization method, achieving uniform dispersion and synergistic effect of bimetallic active centers within the molecular sieve channels, rather than the surface physical loading of the traditional impregnation method. The Ga-Zr-ZSM-5 catalyst provided by this invention has a cyclohexanol yield of about 90%, which is significantly higher than that of the catalyst obtained in the comparative example. This demonstrates that the acid regulation of Ga and the oxygen-rich vacancy activation ability of Zr produce a coupling effect of 1+1>2, solving the technical problem that single-metal modification cannot simultaneously optimize the synergistic matching of etherification and hydrolysis.

[0021] (2) The Ga-Zr-ZSM-5 catalyst not only has an excellent micro-mesoporous composite channel structure, which improves the mass transfer performance of the channel and enhances the adsorption and diffusion performance of cyclohexene in the catalyst channel, but also effectively prevents the occurrence of side reactions.

[0022] (3) The Ga-Zr-ZSM-5 catalyst provided by the present invention, when used as a catalyst in the reaction of cyclohexene etherification and rehydrolysis to prepare cyclohexanol, shows high conversion rate and selectivity. The catalyst has high activity, stable structure and easy separation, high recovery rate and can be reused.

[0023] (4) This invention uses natural polysaccharide soft template agent to replace traditional organic amine template agent, which has no nitrogen oxide emission during the roasting process; at the same time, the reaction conditions are mild and do not require high-pressure hydrogen (such as phenol hydrogenation method) or strong acid catalyst (such as concentrated sulfuric acid required by direct hydration method), the amount of waste emissions is significantly reduced, which meets the green chemical evaluation system and provides a new path for the sustainable production of cyclohexanol. Detailed Implementation

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials used in the following examples are commercially available products.

[0025] Example 1

[0026] Preparation and application of Ga-Zr-ZSM-5 catalyst Al

[0027] Step 1: Take 5 g of ZSM-5 molecular sieve with a silicon-aluminum molar ratio of 20:1 and add it to 30 mL of 0.5 mol / L sodium hydroxide solution. Adjust the pH to 11 to obtain a homogeneous gel.

[0028] Ga(NO3)3·xH2O and Zr(NO3)4·5H2O were dissolved in deionized water at a molar ratio of Ga:Zr = 1:1, with a total loading of 5 wt% of ZSM-5 molecular sieve, to obtain a solution. This solution was then slowly added dropwise to the above gel and stirred for 2 h to form a uniform precursor gel.

[0029] Step 2: Add 5 wt% ZSM-5 seed crystals (based on the silicon source content of the ZSM-5 molecular sieve synthesis system) and 1 wt% sodium alginate (based on the mass of the ZSM-5 molecular sieve) to the above precursor gel as a soft template agent, continue stirring until homogeneous, and let stand for 5 h for aging.

[0030] Step 3: Transfer the aged precursor gel to a stainless steel reactor lined with polytetrafluoroethylene (PTFE), and heat at 160°C. o C crystallization for 48 h, followed by cooling, filtration, and washing until neutral. The resulting solid was then subjected to 100°C. o Dry at C for 12 h, then at 500 h in air. o C calcination for 4 h yielded Ga-Zr modified ZSM-5 molecular sieve;

[0031] Step 5: Add the Ga-Zr modified ZSM-5 molecular sieve to a 1 mol / L NH4NO3 solution, and heat at 80°C. o The reaction was carried out at C for 2 hours, followed by washing and drying. This process was repeated 3 times, and then the mixture was reacted at 500 °C. o The Ga-Zr-ZSM-5 catalyst was obtained by calcination at C for 4 h.

[0032] The catalyst was used in the etherification and subsequent hydrolysis of cyclohexene to prepare cyclohexanol. The specific steps are as follows: 10 g of cyclohexene, 30 g of ethanol, and 1.0 g of catalyst were weighed and added to a sealed reactor. The mixture was then heated to 80°C. o C. The reaction proceeds for 3 hours under 0.3 MPa nitrogen atmosphere to etherify cyclohexylethyl ether; the product, after heat exchange, is directly fed into a hydrolysis reactor, where cyclohexene and deionized water (volume ratio 1:5) are reacted at 130°C.o C. React at 0.3 MPa for 3 h. After the reaction, cool to room temperature, depressurize, remove the material from the reactor, centrifuge, and take out the supernatant for gas chromatography analysis. The results are shown in Table 1.

[0033] Example 2

[0034] Preparation and application of Ga-Zr-ZSM-5 catalyst A2

[0035] In step one, the silicon-to-aluminum ratio was 50:1, and the other steps were the same as in Example 1. The results are shown in Table 1.

[0036] Example 3

[0037] Preparation and application of Ga-Zr-ZSM-5 catalyst A3

[0038] In step one, the silicon-to-aluminum ratio was 80:1, and the other steps were the same as in Example 1. The results are shown in Table 1.

[0039] Example 4

[0040] Preparation and application of Ga-Zr-ZSM-5 catalyst A4

[0041] In step one, the pH was adjusted to 11.5 using 50 mL of 0.5 mol / L potassium hydroxide solution, and the rest was the same as in Example 1. The results are shown in Table 1.

[0042] Example 5

[0043] Preparation and application of Ga-Zr-ZSM-5 catalyst A5

[0044] In step one, the pH was adjusted to 12 using 80 mL of 0.5 mol / L ammonia water, and the rest was the same as in Example 1. The results are shown in Table 1.

[0045] Example 6

[0046] Preparation and application of Ga-Zr-ZSM-5 catalyst A6

[0047] In step one, Ga(NO3)3·xH2O and Zr(NO3)4·5H2O were used in a molar ratio of Ga:Zr=1.5:1. The total loading of Ga and Zr was 5 wt% of ZSM-5 molecular sieve dissolved in deionized water. Other steps were the same as in Example 1. The results are shown in Table 1.

[0048] Example 7

[0049] Preparation and application of Ga-Zr-ZSM-5 catalyst A7

[0050] In step one, Ga(NO3)3·xH2O and Zr(NO3)4·5H2O were used in a molar ratio of Ga:Zr=2:1. The total loading of Ga and Zr was 5 wt% of ZSM-5 molecular sieve dissolved in deionized water. Other steps were the same as in Example 1. The results are shown in Table 1.

[0051] Example 8

[0052] Preparation and application of Ga-Zr-ZSM-5 catalyst A8

[0053] Except for the addition of 5 wt% ZSM-5 seed crystals in step two, the rest is the same as in Example 1, and the results are shown in Table 1.

[0054] Example 9

[0055] Preparation and application of Ga-Zr-ZSM-5 catalyst A9

[0056] In step two, 10 wt% ZSM-5 seed crystals of silicon source content were added to the ZSM-5 molecular sieve synthesis system. Other steps were the same as in Example 1. The results are shown in Table 1.

[0057] Example 10

[0058] Preparation and application of Ga-Zr-ZSM-5 catalyst A10

[0059] In step two, the soft template agent is chitosan, and everything else is the same as in Example 1. The results are shown in Table 1.

[0060] Example 11

[0061] Preparation and application of Ga-Zr-ZSM-5 catalyst Al1

[0062] In step two, the soft template agent is guar gum, and the other steps are the same as in Example 1. The results are shown in Table 1.

[0063] Example 12

[0064] Preparation and application of Ga-Zr-ZSM-5 catalyst Al2

[0065] In step three, at 170 o C crystallization for 24 h, other steps were the same as in Example 1, and the results are shown in Table 1.

[0066] Example 13

[0067] Preparation and application of Ga-Zr-ZSM-5 catalyst Al3

[0068] In step three, at 180 o Except for C crystallization for 12 h, the process was the same as in Example 1, and the results are shown in Table 1.

[0069] Comparative Example 1

[0070] Preparation and application of HZSM-5 catalyst B1

[0071] Without introducing gallium and zirconium sources, the remaining preparation steps were the same as in Example 1. The obtained catalyst was used for the etherification-rehydrolysis reaction of cyclohexene under the same reaction conditions as in Example 1, and the results are shown in Table 1.

[0072] Comparative Example 2

[0073] Preparation and application of Ga-ZSM-5 catalyst B2

[0074] Only Ga(NO3)3·xH2O was added, without adding Zr(NO3)4·5H2O. The remaining steps were the same as in Example 1. The resulting catalyst was used in the reaction under the same conditions as in Example 1. The results are shown in Table 1.

[0075] Comparative Example 3

[0076] Preparation and application of Zr-ZSM-5 catalyst B3

[0077] Only Zr(NO3)4·5H2O was added, without adding Ga(NO3)3·xH2O. The remaining steps were the same as in Example 1. The resulting catalyst was used in the reaction under the same conditions as in Example 1. The results are shown in Table 1.

[0078] Comparative Example 4

[0079] The Ga-Zr / ZSM-5 catalyst B4 was prepared by an equal-volume impregnation method. Specifically, HZSM-5 molecular sieves were impregnated in a mixed solution containing Ga(NO3)3·xH2O and Zr(NO3)4·5H2O (molar ratio Ga:Zr = 1:1), followed by drying, calcination, and ion exchange treatment. The remaining conditions were the same as in Example 1. The catalyst was used in the reaction under the same conditions as in Example 1, and the results are shown in Table 1.

[0080] Comparative Example 5

[0081] In the preparation of Ga-Zr-microporous ZSM-5 catalyst B5, no alkali treatment for desilication was performed in step one. Ga and Zr were directly introduced using conventional microporous ZSM-5 as a support. The remaining steps were the same as in Example 1. The obtained catalyst was used for the reaction under the same conditions as in Example 1. The results are shown in Table 1.

[0082] Table 1. Reaction evaluation results of the catalysts obtained in Examples 1-13 and Comparative Examples 1-5

[0083] catalyst Etherification conversion rate / % Hydrolysis conversion rate / % Selectivity / % Example 1 A1 98.5 92.4 99.1 Example 2 A2 99.2 93.1 99.3 Example 3 A3 99.4 93.5 99.8 Example 4 A4 99.2 93.2 99.7 Example 5 A5 98.9 93.0 99.5 Example 6 A6 98.7 93.1 99.6 Example 7 A7 99.4 93.5 99.8 Example 8 A8 99.3 90.3 99.4 Example 9 A9 98.7 93.1 99.6 Example 10 A10 98.9 93.0 99.5 Example 11 A11 98.1 90.2 99.3 Example 12 A12 99.2 93.2 99.7 Example 13 A13 99.4 93.5 99.8 Comparative Example 1 B1 85.6 78.9 88.4 Comparative Example 2 B2 82.3 76.4 84.7 Comparative Example 3 B3 81.5 75.8 83.9 Comparative Example 4 B4 86.8 81.2 89.6 Comparative Example 5 B5 83.4 78.1 86.2

[0084] The reaction results shown in Table 1 reveal that Comparative Example 1, without the introduction of gallium and zirconium modification, relied solely on the acidic sites of the molecular sieve itself for the reaction. Due to the lack of acid regulation and synergistic effects brought about by metal modification, its acidity distribution was singular and there were many side reactions, resulting in a significant reduction in the conversion rates of etherification and hydrolysis reactions as well as the selectivity of the target product. This indicates that HZSM-5 alone is insufficient to meet the requirements for efficient reactions.

[0085] Comparative Example 2 only introduced gallium for single-metal modification. Although it improved the acidity characteristics of the molecular sieve to some extent, due to the lack of synergistic regulation by zirconium, the distribution of gallium species was uneven. The type and intensity of acidic sites were difficult to balance the two reaction steps of etherification and hydrolysis, resulting in the overall reaction efficiency and selectivity being significantly lower than those of the catalyst in the example.

[0086] Comparative Example 3 only introduced zirconium for modification. Zirconium species mainly play the role of regulating acid strength and stabilizing structure, but its ability to promote etherification reaction is limited, and it lacks the synergistic effect of gallium species in promoting intermediate conversion, thus exhibiting low conversion rate and selectivity.

[0087] Comparative Example 4 introduced gallium and zirconium elements using a post-loaded equal-volume impregnation method. The metal species were mainly distributed on the outer surface of the molecular sieve or at the pore inlet, with poor dispersion. It was difficult to form uniform and stable synergistic active centers, thus limiting the effective diffusion of reactants and the full utilization of active sites. Its catalytic performance was significantly weaker than the catalyst prepared by the in-situ introduction method in the examples.

[0088] In Comparative Example 5, ZSM-5 was not treated with alkali to remove silicon during the preparation process. The resulting molecular sieve was mainly composed of a single microporous structure, and the diffusion of the pores was restricted, which was not conducive to the mass transfer and transformation of larger molecular intermediates in the pores. In particular, it showed a significant diffusion restriction effect in the hydrolysis step, resulting in a significant decrease in reaction conversion rate and selectivity.

[0089] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims

1. A method for synthesizing a catalyst for the indirect preparation of cyclohexanol from cyclohexene, characterized in that, Includes the following steps: (1) Add ZSM-5 molecular sieve to an alkaline solution and adjust the pH to 11-12 to form a uniformly mixed gel; dissolve the Ga-containing metal modifier and the Zr-containing metal modifier in water to obtain a solution; add the solution dropwise to the above gel and stir continuously for 2-3 hours to form a uniform precursor gel. (2) Add ZSM-5 seed crystals and soft template agent to the above precursor gel, stir evenly and let stand for aging for 4-6 h; (3) The aged precursor gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene and heated at 160-180 °C. o Crystallize at C for 12-48 h. After crystallization, cool, filter, and wash until neutral. The resulting solid is dried and then incubated at 400-800 °C in air or an inert atmosphere. o Ga-Zr modified ZSM-5 molecular sieve was obtained by calcining at C for 2-6 h. (4) Add Ga-Zr modified ZSM-5 molecular sieve to NH4NO3 solution and heat at 75-85°C. o The reaction is carried out at C for 2-3 hours, followed by washing and drying. This process is repeated 3 times, and then the reaction is carried out at 500-550°C. o The Ga-Zr-ZSM-5 catalyst was obtained by calcining with C for 4-5 hours.

2. The method for synthesizing a catalyst for the indirect preparation of cyclohexanol from cyclohexene according to claim 1, characterized in that, The silicon-aluminum molar ratio of the ZSM-5 molecular sieve in step (1) is 20-80:

1.

3. The method for synthesizing a catalyst for the indirect preparation of cyclohexanol from cyclohexene according to claim 1, characterized in that, The alkaline solution in step (1) is at least one of ammonia, potassium hydroxide and sodium hydroxide, and the concentration of the alkaline solution is 0.1-0.5 mol / L.

4. The method for synthesizing a catalyst for the indirect preparation of cyclohexanol from cyclohexene according to claim 1, characterized in that, The molar ratio of the gel system in step (1) is: n(SiO2) / n(Al2O3) = 20~80, n(H2O) / n(SiO2) = 30~150.

5. The method for synthesizing a catalyst for the indirect preparation of cyclohexanol from cyclohexene according to claim 1, characterized in that, The Ga-containing metal modifier in step (1) is at least one of gallium nitrate, gallium chloride, or gallium sulfate; the Zr-containing metal modifier is at least one of zirconium nitrate, zirconium oxychloride, or zirconium sulfate.

6. The method for synthesizing a catalyst for the indirect preparation of cyclohexanol from cyclohexene according to claim 1, characterized in that, The total loading of Ga and Zr in step (1) is 0.1-10 wt% of ZSM-5 molecular sieve, and the molar ratio of Ga to Zr is 1-2:

1.

7. The method for synthesizing a catalyst for the indirect preparation of cyclohexanol from cyclohexene according to claim 1, characterized in that, The amount of ZSM-5 seed crystals added in step (2) is 1-10 wt% of the silicon source content in the ZSM-5 molecular sieve synthesis system.

8. The method for synthesizing a catalyst for the indirect preparation of cyclohexanol from cyclohexene according to claim 1, characterized in that, The soft template agent in step (2) is at least one of sodium alginate, chitosan, guar gum or pentamethylolpropane, and the amount of soft template agent added is 1-5 wt% of the mass of ZSM-5 molecular sieve.

9. The Ga-Zr-ZSM-5 catalyst obtained by the synthesis method according to any one of claims 1 to 8.

10. The application of the Ga-Zr-ZSM-5 catalyst as described in claim 9 in the preparation of cyclohexanol by etherification of cyclohexene with ethanol followed by hydrolysis.