Catalyst for preparing cyclohexanone through cyclohexanol dehydrogenation coupled phenol hydrogenation as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for preparing cyclohexanone by cyclohexanol dehydrogenation coupled phenol hydrogenation, the catalyst has a composite metal hydrotalcite structure, the metal components comprise ruthenium, magnesium and aluminum, the metal components are uniformly dispersed in hydrotalcite, and the ruthenium, the magnesium and the aluminum respectively account for 1-5wt%, 10-30wt% and 1-10wt% of the total mass of the catalyst. The acid-base property, the specific surface area and the pore structure of the catalyst are optimized by adjusting the ratio of magnesium to aluminum, so that the dispersion of ruthenium is improved, the interaction between ruthenium and a hydrotalcite carrier is increased, and the synergistic effect of all the element components enables active centers in cyclohexanol dehydrogenation, hydrogen transfer and phenol hydrogenation processes to be efficiently combined together, so that the catalytic activity of the catalyst is improved. Rich alkaline sites are generated in the catalyst, the dehydration side reaction of cyclohexanol can be effectively inhibited, meanwhile, the selectivity of cyclohexanone prepared through phenol hydrogenation is improved, it is ensured that the phenol hydrogenation reaction and the cyclohexanol dehydrogenation reaction can be effectively coupled, and cyclohexanone is efficiently prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of heterogeneous catalysis, and in particular to a catalyst for preparing cyclohexanone by dehydrogenating cyclohexanol and coupling phenol hydrogenation, as well as a preparation method and application thereof. Background Art

[0002] Cyclohexanone, a key chemical raw material, is a key intermediate in the synthesis of caprolactam and adipic acid, which are then used in the production of nylon 6 and nylon 66. Cyclohexanone is also a crucial solvent, widely used in coatings, paints, inks, rubber, and plastics. With the rapid development of high-end manufacturing industries such as apparel and textiles, new energy vehicles, electronics, and machinery, demand for nylon products is increasing. The vast downstream market is also driving the growing demand for cyclohexanone, making my country the world's largest producer of cyclohexanone.

[0003] Currently, the main industrial processes for producing cyclohexanone include cyclohexane oxidation, cyclohexene hydration, cyclohexanol dehydrogenation, and phenol hydrogenation. Cyclohexane oxidation, the predominant method for industrial cyclohexanone production, suffers from issues such as low reaction conversion, harsh conditions, high energy consumption, and significant pollution. Cyclohexene hydration, on the other hand, has a lengthy reaction process and low per-pass conversion during the hydration process, requiring further dehydrogenation of the resulting cyclohexanol. Cyclohexanol dehydrogenation and phenol hydrogenation, on the other hand, have attracted widespread attention due to their advantages of simple operation, low byproducts, and high yields.

[0004] Cyclohexanol dehydrogenation reaction mainly uses Cu and Zn catalysts. This reaction is an endothermic process (Δ H =65 kJ / mol), but suffers from thermodynamic equilibrium limitations and low single-pass cyclohexanol conversion. While increasing the temperature can improve the single-pass cyclohexanol conversion, excessively high temperatures can trigger catalyst sintering and side reactions. Cu-based catalysts are typically used at temperatures between 220 and 250°C. Furthermore, the acidity of the catalyst can lead to dehydration side reactions.

[0005] Chinese patent publication CN101757923A discloses a CuO-ZnO-Al2O3 catalyst with rare metals and alkali metals added as additives. The catalyst comprises a CuO content in the range of 25-75% by molar ratio, a ZnO content in the range of 30-65% by molar ratio, and an Al2O3 content in the range of 1-10% by molar ratio. At 230°C, the catalyst achieves a cyclohexanol conversion rate of approximately 48% and a cyclohexanone selectivity exceeding 99%. Chinese patent document CN116262234A discloses a cyclohexanol dehydrogenation catalyst with Cu as the main active component, with at least two of Mo, W, and Zn oxides added as a first auxiliary agent; one of the precious metals Au and Ag added as a second auxiliary agent; and one of the alkali metals Li, Na, and K added as a third auxiliary agent. The catalyst carrier is alumina, silica, or a molecular sieve; wherein the CuO content is 20 to 60 wt% of the catalyst mass. The catalyst has a conversion rate and selectivity of over 99%, and the introduction of the alkali metal not only reduces the acidity of the catalyst surface but also improves the stability of the catalyst.

[0006] Cyclohexanone can also be prepared by selective hydrogenation of phenol, but the reaction requires the use of a large amount of precious metal Pd catalyst. The molar ratio of phenol to Pd reported in the literature is usually between 20 and 50 (Journal of the American Chemical Society, 2011, 133(8): 2362–2365.; Chinese Journal of Catalysis, 2016, 37(2): 234–239.; Catalysis Letters, 2023, 153(1): 208–218.). In addition, the phenol hydrogenation process mainly uses high-pressure, flammable, and highly reducing H2 as a hydrogen source, which has problems such as safety, environmental protection, and over-hydrogenation.

[0007] Chinese patent publication CN101709027A discloses a catalyst for the one-step hydrogenation of phenol to cyclohexanone. The catalyst comprises a Lewis acid (such as AlCl3, ZnCl2, or SnCl2) and a supported metal catalyst (such as Pd or Pt). The molar ratio of the Lewis acid to the supported metal catalyst is within a range of 10:1 to 1:10. The reaction temperature is 20 to 100°C, and the hydrogen pressure is 1 to 4 MPa. The catalyst achieves a phenol conversion rate of 99.9% and a cyclohexanone selectivity of 95%.

[0008] Chinese patent publication CN110563564A discloses a supported Pd-based catalyst, wherein the Pd content is 0.1-5 wt%, the carrier content is 95-99.9 wt%, and the carrier comprises at least two crystalline forms of alumina (γ-Al2O3, α-Al2O3, β-Al2O3, θ-Al2O3, δ-Al2O3, etc.). The reaction temperature is 160°C, the hydrogen pressure is 0.1 MPa, and the phenol mass space velocity is 0.6 h -1 When the reaction temperature is 200 °C, the conversion rate of phenol can reach 99.5%, and the selectivity of cyclohexanone can reach 97%.

[0009] As previously discussed, the dehydrogenation of cyclohexanol to cyclohexanone is subject to thermodynamic equilibrium and exhibits low single-pass conversion. Phenol hydrogenation to cyclohexanone requires flammable molecular hydrogen and an expensive Pd catalyst. Using cyclohexanol as the hydrogen source and coupling the phenol hydrogenation reaction with the cyclohexanol dehydrogenation reaction not only effectively utilizes the hydrogen removed from the cyclohexanol and reduces reaction energy consumption, but more importantly, both reactions produce the same product, cyclohexanone.

[0010] However, to date, no literature or patents have reported on this coupled system. Combining the aforementioned patents and related literature reveals that this may be because the two separate reactions have distinct requirements for catalyst composition and properties. For example, a catalyst's alkalinity favors the dehydrogenation of cyclohexanol to cyclohexanone, while its acidity can lead to a dehydration side reaction. Phenol hydrogenation to cyclohexanone requires the assistance of an acidic center. Furthermore, cyclohexanol dehydrogenation is primarily performed with Cu-based catalysts, while phenol hydrogenation typically utilizes large amounts of the precious metal Pd catalyst (Cu-based catalysts are essentially inactive for phenol hydrogenation under the same reaction conditions). Therefore, coupling cyclohexanol dehydrogenation with phenol hydrogenation to produce cyclohexanone places higher demands on the catalyst's composition, structure, and surface acidity. The design and preparation of a multifunctional catalyst with tunable acidity and alkalinity is key to achieving this coupled reaction and represents a significant innovation. Summary of the Invention

[0011] In order to solve the above technical problems, the present invention discloses a catalyst for preparing cyclohexanone by coupling cyclohexanol dehydrogenation with phenol hydrogenation. The catalyst can simultaneously catalyze phenol hydrogenation and cyclohexanol dehydrogenation to jointly prepare cyclohexanone.

[0012] A catalyst for preparing cyclohexanone by dehydrogenating cyclohexanol and hydrogenating phenol has a composite metal hydrotalcite structure. The metal components are ruthenium, magnesium, and aluminum, which are uniformly dispersed in the hydrotalcite. The ruthenium, magnesium, and aluminum account for 1-5 wt%, 10-30 wt%, and 1-10 wt% of the total mass of the catalyst, respectively.

[0013] In the present invention, a catalyst having a layered hydrotalcite-like structure is prepared using metal salts of ruthenium, magnesium, and aluminum. The metal components in the catalyst have a high degree of dispersion. Simultaneously, the acidity and alkalinity, specific surface area, and pore structure of the catalyst are optimized by adjusting the magnesium / aluminum ratio, thereby improving the dispersion of ruthenium and increasing the interaction between ruthenium and the hydrotalcite support. The synergistic effect between the aforementioned elemental components enables the active centers of the cyclohexanol dehydrogenation, hydrogen transfer, and phenol hydrogenation processes to be efficiently combined. Abundant basic sites are generated in the catalyst, which can effectively inhibit the dehydration side reaction of cyclohexanol, while improving the selectivity of phenol hydrogenation to prepare cyclohexanone, ensuring that the phenol hydrogenation reaction and the cyclohexanol dehydrogenation reaction can be effectively coupled, thereby efficiently preparing cyclohexanone.

[0014] Preferably, the metal components in the catalyst for preparing cyclohexanone by dehydrogenation of cyclohexanol coupled with hydrogenation of phenol further include one or more of copper, cobalt and scandium.

[0015] In the present invention, as the types of metal elements in the catalyst increase, the conversion rate of the catalyst to phenol and cyclohexanol gradually increases.

[0016] Further preferably, the metal components in the catalyst for preparing cyclohexanone by dehydrogenation of cyclohexanol coupled with hydrogenation of phenol are ruthenium, magnesium, aluminum, copper, cobalt and scandium, and based on the total mass of the catalyst as 100 wt%, Ru is 1 to 5 wt%, Mg is 10 to 30 wt%, Al is 1 to 10 wt%, Cu is 5 to 15 wt%, Co is 5 to 15 wt%, and Sc is 1 to 10 wt%.

[0017] In the present invention, a catalyst having a layered hydrotalcite-like structure is prepared using ruthenium, magnesium, aluminum, copper, cobalt and scandium. Ruthenium, magnesium, aluminum, copper, cobalt and scandium are uniformly distributed in the hydrotalcite. The introduction of Sc, Cu and Co can not only effectively improve the conversion rate of cyclohexanol and phenol, but also improve the selectivity of cyclohexanone.

[0018] The present invention also provides a method for preparing the catalyst for preparing cyclohexanone by dehydrogenating cyclohexanol and coupling phenol hydrogenation, comprising the following steps: (1) Dissolving a soluble salt of a metal component in water to obtain solution A; (2) Dissolve sodium hydroxide and sodium carbonate in water to obtain solution B; (3) Solution A and solution B are added dropwise to the reactor simultaneously under stirring, and the pH value of the reaction solution is controlled at 9.5-10.5 to obtain a suspension after the reaction; (4) The suspension obtained in step (3) is subjected to hydrothermal crystallization, filtered, and the obtained solid is washed with water until the filtrate is neutral and then dried to obtain a catalyst for the dehydrogenation of cyclohexanol coupled with the hydrogenation of phenol to prepare cyclohexanone.

[0019] The invention discloses a catalyst for preparing cyclohexanone by coupling cyclohexanol dehydrogenation with phenol hydrogenation through a coprecipitation method. The preparation method is simple and easy to operate.

[0020] Preferably, in step (2), the molar ratio of sodium hydroxide to sodium carbonate is 0.2-0.6:0.1-0.3.

[0021] Preferably, in step (3), the hydrothermal crystallization temperature is 100-120°C and the time is 12-24 h.

[0022] Preferably, in step (4), the drying temperature is 60-80°C and the drying time is 12-24 hours.

[0023] The present invention also provides the use of the catalyst in catalyzing the reaction of cyclohexanol dehydrogenation coupled with phenol hydrogenation to prepare cyclohexanone.

[0024] Preferably, the method for using the catalyst in the catalytic dehydrogenation of cyclohexanol coupled with the hydrogenation of phenol to prepare cyclohexanone comprises the following steps: adding cyclohexanol, phenol and the above catalyst into a reactor, filling it with nitrogen, heating it to 170-250° C. and reacting it for 10-180 min to obtain cyclohexanone.

[0025] More preferably, the molar ratio of cyclohexanol to phenol is 100:1-10.

[0026] More preferably, the added amount of the catalyst is 0.05-0.4 g.

[0027] More preferably, the reaction pressure is 1.0-3.0 MPa.

[0028] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, a catalyst having a layered hydrotalcite-like structure is prepared using ruthenium, magnesium, and aluminum. The metal components in the catalyst have a high degree of dispersion, and the synergistic effect between the various elemental components enables the active centers of the cyclohexanol dehydrogenation, hydrogen transfer, and phenol hydrogenation processes to be efficiently combined. Abundant basic sites are generated in the catalyst, which can effectively inhibit the dehydration side reaction of cyclohexanol, while improving the selectivity of phenol hydrogenation to prepare cyclohexanone, ensuring that the phenol hydrogenation reaction and the cyclohexanol dehydrogenation reaction can be effectively coupled, thereby efficiently preparing cyclohexanone. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figures 1-3 They are the XRD pattern, SEM pattern and elemental composition mapping diagram of the catalyst in Example 1 respectively. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited to the following examples.

[0031] The raw materials used in the present invention are all commercially available.

[0032] Example 1 (1) Weigh 1.208 g Cu(NO3)2·3H2O, 1.455 g Co(NO3)2·6H2O, 5.128 g Mg(NO3)2·6H2O, 1.688 g Al(NO3)3·9H2O, 1.167 g ScCl3·6H2O, and 2.02 mL RuCl3 (0.05 g / mL) aqueous solution and dissolve them in 200 mL distilled water, which is referred to as solution A. (2) Weigh 16 g of NaOH and 13.25 g of Na2CO3 and dissolve them in 400 mL of distilled water, which is called solution B. (3) Use a peristaltic pump to add the mixture of solutions A and B dropwise, stirring continuously to ensure uniform mixing. At the same time, adjust the peristaltic pump flow rate to maintain the pH of the mixed solution at around 9.5. After the addition is completed, continue stirring for 0.5 h. Then, transfer the suspension into a 500 mL polytetrafluoroethylene-lined hydrothermal autoclave and crystallize at 100 °C for 14 h. The obtained solid is filtered and washed with distilled water until neutral. Then, it is dried at 80 °C to obtain the hexametallic catalyst, which is recorded as catalyst A.

[0033] Figures 1-3 They are the XRD pattern, SEM pattern and elemental composition mapping pattern of the catalyst of Example 1. Figure 1 As shown, the catalyst prepared in the present invention has all typical characteristic diffraction peaks of the hydrotalcite structure, which are basically consistent with the structure of the hydrotalcite with the standard card number 00-035-0965, indicating that the catalyst prepared in the present invention has a complete hydrotalcite structure. Figure 2 The SEM results show that the solid layer flakes in this catalyst are about 12.7~12.9 nanometers thick and about 111.9~114.1 nanometers long. These solid flakes are stacked into a flower ball structure. Figure 3 The elemental analysis results further confirmed that the various elements in the catalyst were distributed very evenly.

[0034] Examples 2 to 5 The preparation method is similar to that of Example 1, with the differences shown in the table below.

[0035] Table 1: Raw material dosage for the preparation of catalysts in Examples 1 to 5

[0036] Application Example 1 The coupled reaction of cyclohexanol dehydrogenation and phenol hydrogenation was carried out in a stainless steel autoclave equipped with a thermocouple and a polytetrafluoroethylene (PTFE) liner. The specific experimental procedures were as follows: 100 mmol of cyclohexanol, 5 mmol of phenol, and 0.4 g of catalyst A were added to the reactor and stirred to mix thoroughly. The reactor was then filled with nitrogen and replaced five times to remove air from the interior. The reactor was then filled with 2 MPa of nitrogen and sealed. The sealed reactor was transferred to an electric heating mantle. After heating to the set temperature (230°C), magnetic stirring was initiated (800 rpm) and a timer was set (15 min).

[0037] Application Examples 2 to 21 The method is similar to that of Application Example 1, with the differences shown in the table below.

[0038] Table 2: Differences between Application Examples 1 to 21

[0039] After the reaction was completed, the reactor was quickly moved to an ice-water bath for cooling. After the reactor temperature dropped to room temperature, an appropriate amount of the mixed solution after the reaction was centrifuged. Finally, the product was analyzed by gas chromatography. The reaction results are shown in Table 3.

[0040] Table 3: Activity of the coupled reaction of cyclohexanol dehydrogenation and phenol hydrogenation in Application Examples 1 to 21

[0041] As shown in Table 3, in Application Examples 1 to 5, as the number of metal species in the catalyst gradually increased, the phenol conversion rate and the cyclohexanol conversion rate both increased. In addition, the introduction of elements such as Sc and Cu (catalysts D, C, and A) was also beneficial to improving the selectivity of cyclohexanone.

[0042] In Application Examples 1, 6-9, when Catalyst A was used for the phenol hydrogenation reaction coupled with the cyclohexanol dehydrogenation reaction, the cyclohexanol conversion and cyclohexanone selectivity increased continuously with the increase in the amount of phenol added, while the phenol conversion showed a trend of first increasing and then decreasing due to the influence of the cyclohexanol dehydrogenation reaction; In Application Examples 1 and 10-13, Catalyst A exhibited high activity for the coupled reaction of cyclohexanol dehydrogenation and phenol hydrogenation over a wide temperature range (170-250°C). With increasing reaction temperature, the cyclohexanol conversion increased continuously, while the phenol conversion first increased and then decreased, while the cyclohexanone selectivity gradually decreased. Within the temperature range of 210-230°C, the reaction activity and selectivity for the target product, cyclohexanone, were high. In Application Examples 1, 14-17, Catalyst A achieved high phenol conversion (93.1%), cyclohexanol conversion (14.3%), and cyclohexanone selectivity (98.1%) at a relatively short reaction time (15 min). However, when the reaction time was too long, the phenol conversion and cyclohexanone selectivity decreased due to the formation of by-products. In Application Examples 1 and 18-21, Catalyst A can achieve high phenol conversion (85.5%), cyclohexanol conversion (12.8%), and cyclohexanone selectivity (99.0%) at a relatively low catalyst dosage (0.2 g); further increasing the catalyst dosage can further improve the phenol conversion and cyclohexanol conversion.

[0043] Catalyst stability analysis Following the testing method of Application Example 1, after the reaction, the reaction solution was collected and the solid catalyst was separated by centrifugation. An appropriate amount of ethanol was added to the catalyst and centrifuged five times to remove the reaction solution adsorbed on the catalyst surface and internally. Finally, the resulting solid was dried in an 80°C vacuum oven. The same activity evaluation procedure was followed for the next experiment. The recyclable performance of Catalyst A in the coupled reaction of cyclohexanol dehydrogenation and phenol hydrogenation is shown in Table 4.

[0044] Table 4: Stability analysis of catalyst A

[0045] The catalyst A prepared by the present invention can still maintain a high reaction activity after being reused 5 times and has good stability.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A catalyst for preparing cyclohexanone by dehydrogenation of cyclohexanol coupled with hydrogenation of phenol, characterized in that: The catalyst has a composite metal hydrotalcite structure, wherein the metal components include ruthenium, magnesium and aluminum, and each metal component is uniformly dispersed in the hydrotalcite. The ruthenium, magnesium and aluminum account for 1-5 wt%, 10-30 wt% and 1-10 wt% of the total mass of the catalyst, respectively.

2. The catalyst for preparing cyclohexanone by dehydrogenation of cyclohexanol and coupling hydrogenation of phenol according to claim 1, characterized in that: The metal components in the catalyst also include one or more of copper, cobalt and scandium.

3. The catalyst for preparing cyclohexanone by dehydrogenation of cyclohexanol and coupling hydrogenation of phenol according to claim 2, characterized in that: The metal components in the catalyst are ruthenium, magnesium, aluminum, copper, cobalt and scandium. Based on the total mass of the catalyst as 100 wt%, Ru is 1-5 wt%, Mg is 10-30 wt%, Al is 1-10 wt%, Cu is 5-15 wt%, Co is 5-15 wt%, and Sc is 1-10 wt%.

4. The method for preparing a catalyst for preparing cyclohexanone by dehydrogenating cyclohexanol and coupling phenol hydrogenation according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Dissolving a soluble salt of a metal component in water to obtain solution A; (2) Dissolve sodium hydroxide and sodium carbonate in water to obtain solution B; (3) Solution A and solution B are added dropwise to the reactor simultaneously under stirring, and the pH value of the reaction solution is controlled at 9.5-10.5 to obtain a suspension after the reaction; (4) The suspension obtained in step (3) is subjected to hydrothermal crystallization, filtered, and the obtained solid is washed with water until the filtrate is neutral and then dried to obtain a catalyst for the dehydrogenation of cyclohexanol coupled with the hydrogenation of phenol to prepare cyclohexanone.

5. The method for preparing a catalyst for preparing cyclohexanone by dehydrogenation of cyclohexanol coupled with hydrogenation of phenol according to claim 4, characterized in that: In step (2), the molar ratio of sodium hydroxide to sodium carbonate is 0.2-0.6:0.1-0.

3.

6. The method for preparing a catalyst for preparing cyclohexanone by dehydrogenation of cyclohexanol coupled with hydrogenation of phenol according to claim 4, characterized in that: In step (3), the hydrothermal crystallization temperature is 100-120°C and the time is 12-24 hours.

7. Use of the catalyst according to any one of claims 1 to 3 in the catalytic dehydrogenation of cyclohexanol coupled with the hydrogenation of phenol to prepare cyclohexanone.

8. The use according to claim 7, characterized in that The method for using the catalyst in the reaction of catalyzing the dehydrogenation of cyclohexanol coupled with the hydrogenation of phenol to prepare cyclohexanone comprises the following steps: adding cyclohexanol, phenol and the catalyst according to any one of claims 1 to 3 into a reactor, filling it with nitrogen, heating it to 170-250° C. and reacting it for 10-180 minutes to obtain cyclohexanone.

9. The use according to claim 8, characterized in that The molar ratio of cyclohexanol to phenol is 100:1-10.

10. The use according to claim 8, characterized in that The added amount of the catalyst is 0.05~0.4 g.

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