A method for preparing epsilon-caprolactone by using a tin-kerolite composite catalyst to catalyze the oxidation of cyclohexanone by hydrogen peroxide

Abstract

The application discloses a method for preparing epsilon-caprolactone by catalyzing cyclohexanone with hydrogen peroxide by using a tin-zeolite composite catalyst. Zeolite is used as a catalyst carrier, and tin is applied to the acid-activated zeolite. The tin serves as an active component and forms a bimetallic active catalyst with Mg elements in the zeolite, promotes the reaction, and improves the conversion rate of cyclohexanone and the selectivity of epsilon-caprolactone. The catalyst is simple to prepare, cheap and easy to obtain, the reaction condition is mild, and the subsequent treatment is simple. The tin is applied to the zeolite to serve as a catalyst to participate in the reaction, the selectivity of the reaction is high, and the conversion rate is also high.

Description

Technical Field

[0001] This invention relates to the preparation of ε-caprolactone, and particularly to a method for preparing ε-caprolactone by catalyzing the oxidation of cyclohexanone with hydrogen peroxide using a tin-sepiolite composite catalyst. Background Technology

[0002] ε-caprolactone is an important polyester monomer, mainly used in the synthesis of polycaprolactone. Polycaprolactone obtained by ring-opening polymerization of caprolactone has good biodegradability, shape memory, thermoplasticity, and molding processability, and plays an important role in biodegradable plastics, tissue engineering, and biomedicine.

[0003] Industrially, ε-caprolactone is mainly prepared by the Baeyer-Villiger oxidation process of cyclohexanone and peroxyacid. However, using peroxyacid as both an oxidant and catalyst has many drawbacks: it generates large amounts of organic carboxylic acid waste, causing severe environmental pollution; the product is difficult to purify and separate, resulting in poor atom economy; and the production of organic peroxyacids requires the use of high-concentration hydrogen peroxide, which is unstable and poses a significant transportation hazard. Therefore, researchers have adopted hydrogen peroxide as an oxidant to replace peroxyacid. When hydrogen peroxide participates in the reaction, the only byproduct is water, and it exhibits high utilization of reactive oxygen species.

[0004] Zhu Qianqian et al. (Master's Thesis, Study on Catalytic Performance of Green Baeyer-Villiger Oxidation Catalyst for Synthesis of ε-Caprolactone from Cyclohexanone [D], Beijing Institute of Petrochemical Technology, 2020) prepared MgO as a catalyst using Mg(NO3)2·6H2O as a precursor and Na2CO3 as a precipitant. The highest yield of ε-caprolactone was 83.25% under the reaction with hydrogen peroxide as oxidant and acetonitrile as solvent, and the conversion rate of cyclohexanone was 95.33%.

[0005] Rafaael AS et al. (Journal of Molecular Catalysis A: Chemical, 287.1-2(2008):41-44) used alumina as a catalyst and 70 wt% aqueous or anhydrous hydrogen peroxide as an oxidant to catalyze the BV oxidation of cyclohexanone. The reaction was carried out in ethyl acetate under azeotropic dehydration conditions at 90 °C, with a molar ratio of cyclohexanone to oxidant of 1:4. Under these conditions, the conversion rate of cyclohexanone was 53% and the selectivity was 98%.

[0006] Nowak et al. (Applied Catalysis A: General, 2007, 321(1): 40-48.) loaded Nb and Sn onto mesoporous molecular sieves MCM-41 and MCM-48, respectively, and reacted them in acetonitrile solvent. The selectivity of ε-caprolactone reached more than 97% to 98%, but the conversion of cyclohexanone was only 36% to 43%.

[0007] Zheng Xiaoming et al. (Master's Thesis, Preparation of Sn-Beta Molecular Sieves and Study on the Oxidation Performance of Cyclohexanone [D], Dalian University of Technology, 2020) prepared Sn-beta molecular sieves as catalysts and used hydrogen peroxide as a green oxidant to oxidize cyclohexanone to prepare ε-caprolactone. The effects of different conditions on the reaction were studied, and the regulatory role of different metal salts as additives was explored. The optimal reaction conditions for the Sn-beta catalyst were: n(cyclohexanone / H2O2) = 2, 90℃, reaction time 2 h, 1,4-dioxane as solvent, solvent to cyclohexanone mass ratio of 40, and catalyst dosage of 0.5 g. The reaction results showed that the cyclohexanone conversion rate was 32.43%, the selectivity of ε-caprolactone was 88.15%, and the effective utilization rate of hydrogen peroxide was 72.15%.

[0008] In summary, the existing technology mainly has the following problems:

[0009] (1) Low selectivity, using acetonitrile as a sacrificial agent;

[0010] (2) The catalyst has low activity, resulting in low conversion rate of cyclohexanone. In addition, the use of high-concentration hydrogen peroxide increases the reaction cost.

[0011] (3) The catalyst is complex to prepare and has a high production cost. The use of transition metal elements reduces the catalytic activity.

[0012] (4) Cyclohexanone has a low conversion rate and the preparation cost of Sn-beta molecular sieve as a catalyst is high. Summary of the Invention

[0013] To address the aforementioned technical problems, this invention provides a method for preparing ε-caprolactone by catalyzing the oxidation of cyclohexanone with hydrogen peroxide using a tin-sepiolite composite catalyst. Sepiolite is used as the catalyst support, and metallic tin is applied to acid-activated sepiolite. Tin, as the active component, together with Mg in the sepiolite, forms a bimetallic active catalyst, promoting the reaction and improving the conversion rate of cyclohexanone and the selectivity of ε-caprolactone.

[0014] The technical solution of the present invention is as follows:

[0015] A method for preparing ε-caprolactone by catalytic oxidation of cyclohexanone with hydrogen peroxide using a tin-sepiolite composite catalyst includes the following steps:

[0016] (1) Dissolve 40%~60% of the Mg in sepiolite with acid;

[0017] (2) The SnCl2 solution and the sepiolite obtained in step (1) were interacted for 1 to 4 hours by impregnation, and then a bifunctional tin-sepiolite composite catalyst was formed by calcining Sn and Mg in sepiolite;

[0018] (3) Add tin sepiolite composite catalyst to the mixture of cyclohexanone and hydrogen peroxide to carry out catalytic reaction to obtain the product ε-caprolactone.

[0019] Furthermore, in step (1), the acid is dilute hydrochloric acid or dilute sulfuric acid.

[0020] Furthermore, in step (2), the ratio of SnCl2 solution to sepiolite satisfies the molar ratio of Sn to Mg being 0.5~8, preferably 1~4.

[0021] Furthermore, in step (2), the calcination temperature is 350℃~550℃ and the calcination time is 1~6 hours.

[0022] Furthermore, in step (2), the mass percentage of Sn in the tin sepiolite composite catalyst is 5%~20%.

[0023] Furthermore, in step (3), the mass of the tin sepiolite composite catalyst is 10% to 30% of cyclohexanone.

[0024] Furthermore, in step (3), the reaction temperature is 40~90℃, the reaction time is 1~8 hours, and the molar ratio of cyclohexanone to hydrogen peroxide is 1:1~8, preferably 1:2~6.

[0025] Furthermore, step (3) also includes adding an organic solvent, which is one or more of n-butanol, 1,2-dichloroethane, and 1,4-dioxane.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention obtains a bifunctional catalyst by acid dissolving magnesium-containing sepiolite, then using it as a support to load tin, and calcining it. The process is simple and the preparation cost is low. The resulting catalyst can demonstrate the synergistic effect of magnesium, tin and sepiolite, and is used to prepare ε-caprolactone from cyclohexanone, with both high activity and selectivity.

[0028] (2) The present invention avoids the use of acetonitrile as a sacrificial agent, thereby reducing the generation of harmful byproducts.

[0029] (3) The tin sepiolite composite catalyst obtained by the present invention has low cost and good effect, and has good prospects for industrial application. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope image of untreated sepiolite in Example 1 of the present invention.

[0031] Figure 2 This is a scanning electron microscope image of the tin-sepiolite composite catalyst prepared in Example 1 of the present invention.

[0032] Figure 3 The X-ray diffraction pattern is shown for the tin sepiolite composite catalyst prepared in Example 1 of this invention.

[0033] Figure 4 X-ray energy dispersive spectroscopy analysis of the tin sepiolite composite catalyst prepared in Example 1 of this invention.

[0034] Figure 5 This is the Fourier transform infrared spectrum of the untreated sepiolite in Example 1 of the present invention.

[0035] Figure 6 The Fourier transform infrared spectrum is shown for the tin-sepiolite composite catalyst prepared in Example 1 of this invention. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto. Example 1

[0037] 40% of the Mg in sepiolite was dissolved in dilute hydrochloric acid solution. Then, using stannous chloride hydrate as the tin source, 0.1675 g of stannous chloride dihydrate was dissolved in water and mixed with 2 g of acid-dissolved sepiolite, stirring for 2 hours. Next, 0.2 mol / L NaOH solution was added to adjust the pH to 10, and stirring continued for 24 hours. After rotary evaporation, the mixture was thoroughly rinsed, dried, and completely crushed. Finally, it was placed in a ceramic crucible and calcined in a box-type resistance furnace at 350℃ for 3 hours to obtain a 5% tin-containing sepiolite composite catalyst.

[0038] Two mmol of cyclohexanone and four mmol of 30% hydrogen peroxide were placed in a 50 mL three-necked flask. Then, 0.04 g of the 5% tin-loaded tin-sepiolite composite catalyst obtained in Example 1 and 10 mL of 1,2-dichloroethane were added as solvent. A stir bar was added, and the mixture was reacted at 70 °C for 4 h. After separation and filtration, the reaction solution was mixed with a certain amount of the internal standard chlorobenzene for gas chromatography detection. Analysis and calculations showed that the conversion rate of cyclohexanone was 90.46%, and the selectivity for ε-caprolactone was 85.93%.

[0039] The morphology of the prepared tin-sepiolite composite catalyst and untreated sepiolite was observed using a SU3500 scanning electron microscope. The results are as follows: Figure 1 and Figure 2 As shown. From Figure 1 It can be seen that sepiolite is flaky and has rod-shaped fibers on its surface. Figure 2 After loading tin, crystals were observed on the surface, indicating that a porous flocculent catalyst was successfully prepared.

[0040] Figure 3 The X-ray diffraction pattern shows a characteristic diffraction peak of tin oxide at 2θ=26°, indicating the successful preparation of the tin-sepiolite composite catalyst. Furthermore, elemental analysis was used to determine the tin loading on the sepiolite. Figure 4 The presence of tin was detected by EDS energy dispersive spectroscopy, indicating the successful preparation of a tin-sepiolite composite catalyst.

[0041] from Figure 5 and Figure 6 The Fourier transform infrared spectrum shows that the 1300-900 cm⁻¹ -1 and 600-400 cm -1 The peak is the vibrational absorption peak of the silicon-oxygen bond, which is still retained in tin-loaded sepiolite, indicating that the internal structure of sepiolite is preserved after modification and loading. Some peaks are missing after tin loading, possibly because they were washed away during modification. The vibrational absorption peak of the tin-oxygen bond is at 469.13 cm⁻¹. -1 Therefore, it can be concluded that tin has successfully been loaded. Example 2

[0042] 60% of the Mg in sepiolite was dissolved in dilute hydrochloric acid solution. Then, using stannous chloride hydrate as the tin source, 0.1675 g of stannous chloride dihydrate was dissolved in water and mixed with 2 g of acid-dissolved sepiolite, stirring for 2 hours. Next, 0.2 mol / L NaOH solution was added to adjust the pH to 10, and stirring continued for 24 hours. After rotary evaporation, the mixture was thoroughly rinsed, dried, and completely crushed. Finally, it was placed in a ceramic crucible and calcined in a box-type resistance furnace at 350℃ for 3 hours to obtain a 5% tin-containing sepiolite composite catalyst.

[0043] Two mmol of cyclohexanone and eight mmol of 30% hydrogen peroxide were placed in a 50 ml three-necked flask. Then, 0.04 g of the tin-loaded (5%) tin-sepiolite composite catalyst obtained in Example 2 and 10 ml of 1,4-dioxane were added as solvent. A stir bar was added, and the mixture was reacted at 70 °C for 4 h. After separation and filtration, the reaction solution was mixed with a certain amount of the internal standard chlorobenzene for gas chromatography detection.

[0044] Analysis and calculations showed that the conversion rate of cyclohexanone was 95.77% and the selectivity of ε-caprolactone was 89.56%. Example 3

[0045] 50% of the Mg in sepiolite was dissolved in dilute hydrochloric acid solution. Then, using stannous chloride hydrate as the tin source, 0.1675 g of stannous chloride dihydrate was dissolved in water and mixed with 2 g of acid-dissolved sepiolite, stirring for 2 hours. Next, 0.2 mol / L NaOH solution was added to adjust the pH to 10, and stirring continued for 24 hours. After rotary evaporation, the mixture was thoroughly rinsed, dried, and completely crushed. Finally, it was placed in a ceramic crucible and calcined in a box-type resistance furnace at 350℃ for 3 hours to obtain a 5% tin-containing sepiolite composite catalyst.

[0046] Two mmol of cyclohexanone and four mmol of 30% hydrogen peroxide were placed in a 50 mL three-necked flask. Then, 0.04 g of the 5% tin-loaded tin-sepiolite composite catalyst obtained in Example 3 and 10 mL of 1-butanol were added as solvent. A stir bar was added, and the mixture was reacted at 70 °C for 4 h. After separation and filtration, the reaction solution was mixed with a certain amount of the internal standard chlorobenzene for gas chromatography detection. Analysis and calculations showed that the conversion rate of cyclohexanone was 93.49%, and the selectivity for ε-caprolactone was 84.13%. Example 4

[0047] 50% of the Mg in sepiolite was dissolved in dilute hydrochloric acid solution. Then, using stannous chloride hydrate as the tin source, 0.3349 g of stannous chloride dihydrate was dissolved in water and mixed with 2 g of acid-dissolved sepiolite, stirring for 2 hours. Next, 0.2 mol / L NaOH solution was added to adjust the pH to 10, and stirring continued for 24 hours. After rotary evaporation, the mixture was thoroughly rinsed, dried, and completely crushed. Finally, it was placed in a ceramic crucible and calcined in a box-type resistance furnace at 350℃ for 3 hours to obtain a 10% tin-sepiolite composite catalyst.

[0048] Two mmol of cyclohexanone and four mmol of 40% hydrogen peroxide were placed in a 50 mL three-necked flask. Then, 0.04 g of the 5% tin-loaded tin-sepiolite composite catalyst obtained in Example 3 and 10 mL of 1-butanol were added as solvent. A stir bar was added, and the mixture was reacted at 70 °C for 4 h. After separation and filtration, the reaction solution was mixed with a certain amount of the internal standard chlorobenzene for gas chromatography detection. Analysis and calculations showed that the conversion rate of cyclohexanone was 97.24%, and the selectivity for ε-caprolactone was 91.64%.

Claims

1. A method for preparing ε-caprolactone by catalyzing the oxidation of cyclohexanone with hydrogen peroxide using a tin-zeolite composite catalyst, characterized by, The method comprises the following steps: (1) dissolving 40-60% of Mg in sepiolite by acid; (2) interacting SnCl2 solution and sepiolite obtained in step (1) by dipping method for 1-4 hours, the dosage ratio of SnCl2 solution and sepiolite satisfies the molar ratio of Sn and Mg is 0.5-8, then forming a bifunctional Sn-sepiolite composite catalyst by calcining Sn and Mg in sepiolite, the mass percentage of Sn in the Sn-sepiolite composite catalyst is 5-10%; (3) adding the Sn-sepiolite composite catalyst into the mixture of cyclohexanone and hydrogen peroxide to perform catalytic reaction, and obtaining product ε-caprolactone.

2. The process for the preparation of ε-caprolactone by the oxidation of cyclohexanone with hydrogen peroxide catalyzed by tin-zeolite composite catalyst according to claim 1, characterized in that, In step (1), the acid is dilute hydrochloric acid or dilute sulfuric acid.

3. The process for the preparation of ε-caprolactone by the oxidation of cyclohexanone with hydrogen peroxide catalyzed by tin-zeolite composite catalyst as claimed in claim 1, wherein the process is carried out at a temperature in the range of 60- 80°C. In step (2), the dosage ratio of SnCl2 solution and sepiolite satisfies the molar ratio of Sn and Mg is 1-4.

4. The process for the preparation of ε-caprolactone by the oxidation of cyclohexanone with hydrogen peroxide catalyzed by tin-zeolite composite catalyst as claimed in claim 1, wherein the process is carried out at a temperature in the range of 60- 80°C. In step (2), the calcination temperature is 350-550°C, and the calcination time is 1-6 hours.

5. The process for the preparation of ε-caprolactone by the oxidation of cyclohexanone with hydrogen peroxide catalyzed by tin-zeolite composite catalyst as claimed in claim 1, wherein the process is carried out at a temperature in the range of 60- 80°C. In step (3), the mass of the Sn-sepiolite composite catalyst is 10-30% of cyclohexanone.

6. The process for the preparation of ε-caprolactone by the oxidation of cyclohexanone with hydrogen peroxide catalyzed by tin-zeolite composite catalyst as claimed in claim 1, wherein the process is carried out at a temperature in the range of 60- 80°C. In step (3), the reaction temperature is 40-90°C, the reaction time is 1-8 hours, and the molar ratio of cyclohexanone and hydrogen peroxide is 1:1-8.

7. The process for the preparation of ε-caprolactone by the oxidation of cyclohexanone with hydrogen peroxide catalyzed by tin-zeolite composite catalyst as claimed in claim 1, wherein the process is carried out at a temperature in the range of 60- 80°C. In step (3), an organic solvent is further added, the organic solvent is one or more than two of n-butanol, 1,2-dichloroethane and 1,4-dioxane.

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