Catalyst for preparing ε-caprolactone by co-oxidation of toluene, its preparation method and application

Abstract

The present invention belongs to the technical field of catalyst preparation, and particularly relates to a catalyst for preparing ε-caprolactone by toluene co-oxidation, a preparation method thereof, and an application. The preparation method of the catalyst for preparing ε-caprolactone by toluene co-oxidation provided by the present invention, based on the principle of surface tension, adopts an improved wet chemical method to load V-Co and Fe-Sn active metals on the inner and outer surfaces of carbon nanotubes respectively, and obtains a novel VCo-in-CNT-out-FeSn catalyst. This catalyst can be effectively applied to the preparation of ε-caprolactone by toluene co-oxidation of cyclohexanone, and has high catalytic reaction efficiency, good product selectivity, easy separation of the catalyst from the product, and good reusability. Compared with directly using benzaldehyde as a co-oxidant in the prior art, the catalyst of the present invention uses toluene as a co-oxidant when in use. Toluene is inexpensive, and the entire process has high economy and has good industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a catalyst for preparing ε-caprolactone by co-oxidation of toluene, a preparation method thereof, and an application thereof. Background Art

[0002] ε-Caprolactone, with the molecular formula C6H 10 O2, is an important organic synthesis monomer. Its polymer, poly(ε-caprolactone) (PCL), has good biocompatibility, thermoplasticity, and biodegradability, and has a wide range of applications in various fields such as household appliances, medicine, and environmental protection materials. In addition, ε-caprolactone is also an excellent organic solvent and an important organic synthesis intermediate, and can react with various compounds to prepare fine chemicals with unique properties. Therefore, ε-caprolactone products are of great significance for the production, application, and development of new synthetic materials.

[0003] In the prior art, the methods for preparing ε-caprolactone can be mainly divided into peroxyacid oxidation method, hydrogen peroxide oxidation method, and oxygen / air oxidation method. Patent applications CN111662266A, CN114438522A, and CN102367246A use peracetic acid as an oxidant to oxidize cyclohexanone to prepare ε-caprolactone. This method has the advantages of low cost and easy synthesis, but the by-products generated after the reaction of peracetic acid are miscible with ε-caprolactone, increasing the difficulty and cost of separation, and having the disadvantages of difficult separation of the later product, easy corrosion of equipment, and environmental pollution. Patent applications CN101161649A, CN112707883A, and CN102351836A use hydrogen peroxide as an oxidant to oxidize cyclohexanone to prepare ε-caprolactone. The selectivity of ε-caprolactone can reach 100%, and the main by-product of the reaction is H2O, which is green and environmentally friendly, reducing the difficulty of subsequent product separation and purification. However, the oxidation ability of hydrogen peroxide is weak, and the high-concentration hydrogen peroxide solution increases the risk of production operation. A large amount of water in the low-concentration hydrogen peroxide solution will cause the product ε-caprolactone to hydrolyze to form hydroxy acids or acyloxy acids, reducing the yield and selectivity of the product.

[0004] Patent application CN101205225A discloses a method for preparing lactones by bionic catalytic oxidation of ketone compounds. Using safe and inexpensive oxygen as the oxidant, toluene as the solvent, and preparing a metal porphyrin catalyst, the conversion rate of cyclohexanone and the yield of ε-caprolactone both reached 96%. However, a large amount of aldehyde substances were added as co-oxidants in this method, increasing the production cost. Porphyrin catalysts have the disadvantage of being easily decomposed and inactivated, and it is difficult to recycle and reuse them. To solve the problem of catalyst deactivation, patent application CN105440005A discloses a method for catalytically preparing ε-caprolactone using a composite oxide MgO / Fe2O3 catalyst. This catalyst is simple to prepare and has good stability. The conversion rate of cyclohexanone is 93%, and the selectivity of ε-caprolactone is 92%. However, a large amount of p-methylbenzaldehyde was used as a co-oxidant in this reaction, and the p-methylbenzoic acid generated in the reaction would react with MgO, causing catalyst loss. To further solve the problems of high cost of aldehyde co-oxidants and easy catalyst loss in the later stage, patent application CN106967039A discloses a new method for preparing ε-caprolactone. This method uses toluene as a co-oxidant and nitrate as a catalyst, significantly reducing the reaction cost. The conversion rate of cyclohexanone is 49.4%, and the selectivity of ε-caprolactone is 96.1%. However, this method adds azobisisobutyronitrile or N-hydroxyphthalimide as an initiator. Both of these initiators are unstable and difficult to separate in the later stage. The water generated in the reaction is likely to cause the dissolution of the nitrate catalyst, resulting in catalyst loss. The product ε-caprolactone is also likely to react with organic nitrogen compounds. Therefore, it is difficult to recycle the nitrate as a catalyst.

[0005] Based on the above research status, it can be seen that further developing catalysts with good stability, environmental friendliness, and high catalytic efficiency for the preparation of ε-caprolactone is of great significance for promoting the industrial production of ε-caprolactone. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a preparation method of a catalyst for preparing ε-caprolactone by toluene co-oxidation, which can prepare a catalyst with high selectivity, high activity, and suitable for the preparation of ε-caprolactone by toluene co-oxidation.

[0007] Another purpose of the present invention is to provide a catalyst for preparing ε-caprolactone by toluene co-oxidation, which can be effectively used for the preparation of ε-caprolactone by toluene co-oxidation of cyclohexanone, and has a short reaction time, high efficiency, good product selectivity, easy separation of the catalyst from the product, and good reusability.

[0008] The purpose of the present invention is also to provide an application of a catalyst for preparing ε-caprolactone by toluene co-oxidation.

[0009] To achieve the above purposes, the technical solution adopted in the preparation method of the catalyst for preparing ε-caprolactone by toluene co-oxidation of the present invention is:

[0010] A preparation method of a catalyst for preparing ε-caprolactone by co-oxidation of toluene, comprising the following steps:

[0011] (1) Mix vanadium chloride and cobalt chloride in a solvent to obtain a mixed solution A;

[0012] Separately, mix iron chloride and tin chloride in water to obtain a mixed solution B;

[0013] (2) Add carbon nanotubes to the mixed solution A for dispersion, then evaporate the solvent, and perform heat treatment at 160-200 °C to obtain a composite material with vanadium and cobalt loaded on the inner surface of the carbon nanotube channels, denoted as VCo-in-CNT;

[0014] Perform ultrasonic mixing treatment on VCo-in-CNT and xylene, and then perform washing treatment with acid and water in sequence to obtain a xylene dispersion containing VCo-in-CNT;

[0015] (3) Mix and stir the xylene dispersion containing VCo-in-CNT obtained in step (2), the mixed solution B, and ammonium bicarbonate at a temperature of 70-100 °C, and perform heat treatment at 160-200 °C after stirring. Through the heat treatment, iron and tin are loaded on the outer surface of the carbon nanotube channels, thus obtaining the catalyst for preparing ε-caprolactone by co-oxidation of toluene, denoted as VCo-in-CNT-out-FeSn.

[0016] The preparation method of the catalyst provided by the present invention, based on the principle of surface tension, adopts an improved wet chemical method, and loads V-Co and Fe-Sn active metals on the inner and outer surfaces of carbon nanotubes respectively to obtain a novel VCo-in-CNT-out-FeSn catalyst. This catalyst can be effectively applied to the catalytic reaction process of preparing ε-caprolactone by co-oxidation of cyclohexanone with toluene, and has high catalytic reaction efficiency and good product selectivity. Moreover, compared with directly using benzaldehyde as a co-oxidant, the catalyst prepared by the present invention is applicable to the toluene co-catalytic system, and toluene has a lower price, so the entire process has high economy and good industrialization prospects.

[0017] Preferably, in step (1), the vanadium chloride is vanadium trichloride; the cobalt chloride is cobalt chloride hexahydrate; the solvent is acetone; the iron chloride is iron trichloride; the tin chloride is tin tetrachloride.

[0018] By controlling the types and ratios of active metals in the raw materials, effective loading of active metals on the inner and outer surfaces of the catalyst can be achieved. Further, in step (1), the molar ratio of vanadium atoms in vanadium chloride to cobalt atoms in cobalt chloride is 1:1; the molar ratio of iron atoms in iron chloride to tin atoms in tin chloride is 3:7; the ratio of the sum of the molar amounts of vanadium atoms in vanadium chloride and cobalt atoms in cobalt chloride to the sum of the molar amounts of iron atoms in iron chloride and tin atoms in tin chloride is 1:(2 - 6), more preferably 1:4.

[0019] Further, in step (2), the diameter of the carbon nanotubes is 6 - 10 nm. The carbon nanotubes selected in the present invention have a pore diameter smaller than the molecular dynamic diameter of ε-caprolactone, avoiding competitive adsorption of the product ε-caprolactone on the VCo active sites on the inner surface of the carbon nanotubes. Therefore, the catalytic reaction efficiency and product selectivity can be improved.

[0020] In step (2), preferably, the dispersion is ultrasonic dispersion, and the ultrasonic dispersion time is 6 - 10 h. Through the ultrasonic dispersion process, to ensure that the air inside the carbon nanotubes is completely discharged, and at the same time, with the help of surface tension and capillary action, the solution of vanadium and cobalt chlorides is promoted to enter the pores of the carbon nanotubes.

[0021] The evaporation of the solvent in step (2) is preferably carried out under stirring conditions. During the stirring process, the solvent is slowly evaporated, and a concentration difference is generated during the solvent evaporation process. Driven by the concentration difference, it is easier for vanadium and cobalt chlorides to enter the carbon nanotube channels.

[0022] In step (2), a material structure with vanadium and cobalt loaded inside the carbon nanotube channels is obtained through heat treatment. Preferably, the heat treatment is carried out in an air atmosphere, the air flow rate is 20 - 30 mL / min, and the heat treatment time is 15 - 20 h.

[0023] Further, after heat treatment, the total mass of vanadium and cobalt elements loaded inside the carbon nanotube channels accounts for 4 - 8% of the mass of the carbon nanotubes.

[0024] In step (2), the mass ratio of VCo-in-CNT to the volume of xylene is (8 - 12) g:(20 - 30) mL.

[0025] In step (2), the time of the ultrasonic mixing treatment is 6 - 10 h. Xylene is added and ultrasonic treatment is carried out. Under the action of capillary force and surface tension, the xylene solution can fill into the carbon nanotube channels.

[0026] Preferably, the acid is a hydrochloric acid solution with a concentration of 0.0005 to 0.002 mol / L. In this pickling process, on the one hand, vanadium and cobalt metal ions on the outer surface of the carbon nanotubes are removed, and on the other hand, the hydroxyl groups on the surface of the carbon nanotubes react with the acid to form carboxyl groups, making the carbon nanotubes have stronger hydrophilicity. Moreover, the acid solution and the xylene mixture solution do not show mutual solubility, and the VCo-in-CNT channels are still filled with xylene. After pickling, water washing is carried out to remove the excess acid.

[0027] Preferably, in step (3), the mass of ammonium bicarbonate accounts for 4 to 8 wt% of the mass of VCo-in-CNT, more preferably 6 wt%.

[0028] Furthermore, in step (3), the heat treatment is carried out in an air atmosphere with an air flow rate of 20 to 30 mL / min and a heat treatment time of 15 to 20 h. Since carboxyl groups are introduced on the surface of the carbon nanotubes during the acid treatment process, the carbon nanotubes have stronger hydrophilicity, which helps to extract VCo-in-CNT from the xylene solution into the aqueous solution of iron and tin chlorides. At the same time, due to the relatively high boiling point of xylene, water will evaporate first while the carbon nanotube channels are still occupied by the xylene solution. Therefore, after heat treatment, iron and tin are uniformly loaded on the outer surface of VCo-in-CNT.

[0029] The catalyst for preparing ε-caprolactone by the co-oxidation of toluene in the present invention is prepared by the preparation method described above.

[0030] The catalyst (VCo-in-CNT-out-FeSn) for preparing ε-caprolactone by the co-oxidation of toluene provided by the present invention can realize the co-oxidation of toluene and cyclohexanone to prepare ε-caprolactone, with a short reaction time, high efficiency, good product selectivity, easy separation of the catalyst from the product, and good reusability. In addition, compared with directly using benzaldehyde as the co-oxidant, toluene has a low price, high reaction process economy, and good industrialization prospects. After the reaction, toluene can be directly removed from the reaction solution by vacuum distillation, and then the product ε-caprolactone is taken out from the side line of rectification, with simple operation and low energy consumption.

[0031] The application of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene in the present invention is specifically the application as a catalyst in the co-oxidation of toluene and cyclohexanone to prepare ε-caprolactone.

[0032] As a further preferred solution, the process conditions for preparing ε-caprolactone by the co-oxidation of toluene are as follows: using VCo-in-CNT-out-FeSn as the catalyst, oxygen as the oxidant, and cyclohexanone and toluene as the reactants for the reaction; wherein, the mass ratio of cyclohexanone to toluene is 2:1, and the mass ratio of the catalyst to cyclohexanone is 0.01 - 0.04:1; the reaction pressure is 0.5 - 2 MPa, the reaction temperature is 160 - 170 °C, and the reaction time is 4 - 10 h.

[0033] During the above reaction process of preparing ε-caprolactone by the co-oxidation of toluene, as the co-oxidant, toluene is first oxidized to benzaldehyde by air at the VCo active sites on the inner surface of the carbon nanotubes, and then the generated benzaldehyde detaches from the inner surface active sites and oxidizes cyclohexanone to obtain the ε-caprolactone product at the FeSn active sites on the outer surface of the carbon nanotubes.

[0034] Compared with the prior art, the present invention has the following technical advantages:

[0035] (1) The catalyst for preparing ε-caprolactone by the co-oxidation of toluene prepared in the present invention is used for the co-oxidation of cyclohexanone with toluene to prepare ε-caprolactone. Different metal active centers are loaded inside and outside the carbon nanotubes, realizing efficient catalysis of the reaction, with short reaction time, high efficiency, good product selectivity, easy separation of the catalyst from the product, and good reusability.

[0036] (2) Compared with directly using benzaldehyde as the co-oxidant in the prior art, the catalyst of the present invention can use the co-oxidation of toluene, and toluene is inexpensive, so the whole process has high economy and good industrialization prospects.

[0037] (3) After the reaction, toluene can be directly removed from the reaction solution by simple vacuum distillation, and then the product ε-caprolactone can be taken out from the side line of the rectification. The process operation is simple and energy-consuming is small, which is suitable for industrial application. Description of the Drawings

[0038] Figure 1 It is the TEM image of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene prepared in Example 1 of the present invention;

[0039] Figure 2 It is the infrared spectrum of the ε-caprolactone product obtained by the catalytic reaction using the catalyst for preparing ε-caprolactone by the co-oxidation of toluene in Example 1 of the present invention. Detailed Embodiments

[0040] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0041] Example 1

[0042] The catalyst for preparing ε-caprolactone by the co-oxidation of toluene in this example is prepared by a method including the following steps:

[0043] (1) Take 0.858 g of vanadium chloride and 1.298 g of cobalt chloride hexahydrate according to the molar ratio of vanadium atoms to cobalt atoms of n 钒 :n 钴 =1:1, dissolve them in the solvent acetone, and prepare a solution with the sum of the molar concentrations of the two substances being 1 mol / L, denoted as mixture A; among them, the total mass of vanadium and cobalt elements accounts for 6 wt% of the mass of carbon nanotubes;

[0044] Another, take 2.141 g of ferric chloride and 8.032 g of tin tetrachloride according to the molar ratio of iron atoms to tin atoms of n 铁 :n 锡 =3:7, and (n 铁 +n 锡 ):(n 钒 +n 钴 ) = 4:1 ratio, and prepare an aqueous solution with the sum of the molar concentrations of the two substances being 1 mol / L, denoted as mixture B.

[0045] (2) Disperse 10 g of carbon nanotubes with a diameter of 8 nm in mixture A, ultrasonically treat for 8 h, then stir at room temperature for 12 h to slowly volatilize the solvent acetone, and then dry at 180 °C in a tubular furnace for 18 h with an air flow rate of 25 mL / min to obtain a composite material with vanadium and cobalt loaded on the inner surface of the carbon nanotube channels, denoted as VCo-in-CNT;

[0046] Add 25 mL of xylene solution to the prepared VCo-in-CNT, ultrasonically treat for 8 h, then wash with 0.001 mol / L hydrochloric acid 3 times, and then wash with deionized water 3 times to obtain a xylene dispersion containing VCo-in-CNT.

[0047] (3) The xylene dispersion containing VCo-in-CNT was mixed with mixture B and ammonium bicarbonate at 80 °C and stirred for 12 h. The dosage of ammonium bicarbonate was 5 wt% of the mass fraction of VCo-in-CNT. After stirring, it was placed in a tubular furnace and treated at 180 °C for 18 h with an air flow rate of 25 mL / min, thus obtaining the catalyst for preparing ε-caprolactone by the co-oxidation of toluene, denoted as VCo-in-CNT-out-FeSn.

[0048] The application of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene in this example is specifically the application of VCo-in-CNT-out-FeSn as a catalyst in the co-oxidation of toluene with cyclohexanone to prepare ε-caprolactone. The process of the co-oxidation of toluene to prepare ε-caprolactone is specifically as follows: 19.629 g of cyclohexanone and 9.214 g of toluene with a molar ratio of 2:1 were successively added to a reaction kettle, and then the VCo-in-CNT-out-FeSn catalyst accounting for 2 wt% of the mass fraction of cyclohexanone was added. Oxygen was introduced to adjust the pressure to 1 MPa, and the reaction was carried out at 165 °C for 6 h. After the reaction, the catalyst was filtered while it was hot. The catalyst was washed three times with distilled water and then dried for recovery. After the reaction solution was distilled under reduced pressure to remove toluene, the product ε-caprolactone (4.623 g) was taken out from the side line of the rectification, and benzoic acid (11.012 g) was recovered.

[0049] By gas chromatography test, the conversion rate of cyclohexanone was 21.83%, the selectivity of ε-caprolactone was 92.76%, the yield of ε-caprolactone was 20.24%, the conversion rate of toluene was 95.74%, the selectivity of benzaldehyde was 5.82%, and the selectivity of benzoic acid was 94.18%.

[0050] The transmission electron microscope was used to analyze the microstructure of the VCo-in-CNT-out-FeSn catalyst prepared in Example 1, and the obtained TEM image was as Figure 1 shown.

[0051] It can be Figure 1 seen that the metal active components were uniformly loaded on the inner and outer surfaces of the carbon nanotubes, indicating that the novel catalyst with different metal active centers loaded on the inner and outer surfaces of the carbon nanotubes was successfully prepared in this invention.

[0052] The infrared spectrometer was used to analyze the infrared spectrum of the ε-caprolactone prepared in Example 1, and the obtained infrared spectrum was as Figure 2 shown.

[0053] It can be Figure 2 seen that the stretching vibration peaks of —CH2— and C—H were at 2936 and 2863 cm -1 , and the C—О stretching vibration peak of ε-caprolactone was at 1732 cm -1 . The stretching vibration peaks at 1168 and 1055 cm -1The peak at this position is the stretching vibration peak of C—O, which is consistent with the structure of ε-caprolactone, indicating that this substance is an ε-caprolactone product.

[0054] Example 2

[0055] The catalyst for preparing ε-caprolactone by toluene co-oxidation in this example is different from that in Example 1 in the preparation steps: in step (1), according to the ratio of n 铁 +n 锡 ∶n 钒 +n 钴 =2∶1, 0.858 g of vanadium chloride, 1.298 g of cobalt chloride hexahydrate, 1.071 g of ferric chloride, and 4.012 g of tin tetrachloride were weighed.

[0056] The technological process of preparing ε-caprolactone by toluene co-oxidation uses the catalyst of Example 2, and other parameters are the same as those in Example 1. In this example, finally 3.785 g of ε-caprolactone product was obtained, 9.815 g of benzoic acid was recovered, the conversion rate of cyclohexanone was 18.74%, the selectivity of ε-caprolactone was 88.45%, the yield of ε-caprolactone was 16.58%, the conversion rate of toluene was 87.48%, the selectivity of benzaldehyde was 8.13%, and the selectivity of benzoic acid was 91.87%.

[0057] Example 3

[0058] The catalyst for preparing ε-caprolactone by toluene co-oxidation in this example is different from that in Example 1 in the preparation steps: in step (1), according to the ratio of n 铁 +n 锡 ∶n 钒 +n 钴 =6∶1, 0.858 g of vanadium chloride, 1.298 g of cobalt chloride hexahydrate, 3.211 g of ferric chloride, and 12.035 g of tin tetrachloride were weighed.

[0059] The technological process of preparing ε-caprolactone by toluene co-oxidation uses the catalyst of Example 3, and other parameters are the same as those in Example 1. In this example, finally 3.917 g of ε-caprolactone product was obtained, 9.908 g of benzoic acid was recovered, the conversion rate of cyclohexanone was 18.77%, the selectivity of ε-caprolactone was 91.43%, the yield of ε-caprolactone was 17.16%, the conversion rate of toluene was 89.3%, the selectivity of benzaldehyde was 9.14%, and the selectivity of benzoic acid was 90.86%.

[0060] Example 4

[0061] The catalyst for preparing ε-caprolactone by toluene co-oxidation in this example is different from that in Example 1 in the preparation steps: in step (2), carbon nanotubes with a diameter of 6 nm are used.

[0062] The process for preparing ε-caprolactone by the co-oxidation of toluene uses the catalyst of Example 4, and other parameters are the same as those of Example 1. In this example, the final product obtained is 3.528 g of ε-caprolactone, 9.409 g of recovered benzoic acid, the conversion rate of cyclohexanone is 17.46%, the selectivity of ε-caprolactone is 88.52%, the yield of ε-caprolactone is 15.46%, the conversion rate of toluene is 83.72%, the selectivity of benzaldehyde is 7.97%, and the selectivity of benzoic acid is 92.03%.

[0063] Example 5

[0064] The catalyst for preparing ε-caprolactone by the co-oxidation of toluene in this example is different from that of Example 1 in the preparation steps in that: in step (2), carbon nanotubes with a diameter of 10 nm are used.

[0065] The process for preparing ε-caprolactone by the co-oxidation of toluene uses the catalyst of Example 5, and other parameters are the same as those of Example 1. In this example, the final product obtained is 3.511 g of ε-caprolactone, 9.854 g of recovered benzoic acid, the conversion rate of cyclohexanone is 17.59%, the selectivity of ε-caprolactone is 87.44%, the yield of ε-caprolactone is 15.38%, the conversion rate of toluene is 89.42%, the selectivity of benzaldehyde is 9.76%, and the selectivity of benzoic acid is 90.24%.

[0066] Example 6

[0067] The catalyst for preparing ε-caprolactone by the co-oxidation of toluene in this example has the same catalyst preparation steps as those of Example 1. The difference between the process for preparing ε-caprolactone by the co-oxidation of toluene and that of Example 1 is that: during the reaction, a VCo-in-CNT-out-FeSn catalyst accounting for 1 wt% of the mass of cyclohexanone is added.

[0068] In this example, the final product obtained is 4.212 g of ε-caprolactone, 9.976 g of recovered benzoic acid, the conversion rate of cyclohexanone is 20.37%, the selectivity of ε-caprolactone is 90.58%, the yield of ε-caprolactone is 18.45%, the conversion rate of toluene is 87.59%, the selectivity of benzaldehyde is 6.74%, and the selectivity of benzoic acid is 93.26%.

[0069] Example 7

[0070] The catalyst for preparing ε-caprolactone by the co-oxidation of toluene in this example has the same catalyst preparation steps as those of Example 1. The difference between the process for preparing ε-caprolactone by the co-oxidation of toluene and that of Example 1 is that: during the reaction, a VCo-in-CNT-out-FeSn catalyst accounting for 3 wt% of the mass of cyclohexanone is added.

[0071] In this example, the final product obtained was 4.227 g of ε-caprolactone, 10.514 g of recovered benzoic acid, the conversion rate of cyclohexanone was 20.18%, the selectivity of ε-caprolactone was 91.75%, the yield of ε-caprolactone was 18.52%, the conversion rate of toluene was 91.56%, the selectivity of benzaldehyde was 5.97%, and the selectivity of benzoic acid was 94.03%.

[0072] Comparative Example 1

[0073] The catalyst of this comparative example was prepared in basically the same process as in Example 1. The difference between the two was that in step (1), 0.472 g of vanadium chloride and 1.665 g of cobalt chloride hexahydrate were weighed according to the ratio of n 钒 ∶n 钴 = 3∶7; among them, the total mass of vanadium and cobalt elements accounted for 6 wt% of the mass of carbon nanotubes. The process for preparing ε-caprolactone by the co-oxidation of toluene was the same as in Example 1.

[0074] Finally, 3.871 g of ε-caprolactone, 10.119 g of recovered benzoic acid were obtained, the conversion rate of cyclohexanone was 18.69%, the selectivity of ε-caprolactone was 90.73%, the yield of ε-caprolactone was 16.96%, the conversion rate of toluene was 90.8%, the selectivity of benzaldehyde was 7.74%, and the selectivity of benzoic acid was 91.26%.

[0075] Comparative Example 2

[0076] The catalyst of this comparative example was prepared in basically the same process as in Example 1. The difference between the two was that in step (1), 1.102 g of vanadium chloride and 0.714 g of cobalt chloride hexahydrate were weighed according to the ratio of n 钒 ∶n 钴 = 7∶3; among them, the total mass of vanadium and cobalt elements accounted for 6 wt% of the mass of carbon nanotubes. The process for preparing ε-caprolactone by the co-oxidation of toluene was the same as in Example 1.

[0077] Finally, 4.075 g of ε-caprolactone, 9.822 g of recovered benzoic acid were obtained, the conversion rate of cyclohexanone was 19.32%, the selectivity of ε-caprolactone was 92.39%, the yield of ε-caprolactone was 17.85%, the conversion rate of toluene was 86.22%, the selectivity of benzaldehyde was 6.72%, and the selectivity of benzoic acid was 93.28%.

[0078] Comparative Example 3

[0079] The catalyst of this comparative example was prepared in basically the same process as in Example 1. The difference between the two was that in step (1), according to n 钒 ∶n 钴Weigh 0.286 g of vanadium chloride and 0.433 g of cobalt chloride hexahydrate in a ratio of 1:1; among them, the total mass of vanadium and cobalt elements accounts for 2 wt% of the mass of carbon nanotubes. The process of preparing ε-caprolactone by co-oxidation of toluene is the same as that in Example 1.

[0080] Finally, 4.241 g of the product ε-caprolactone was obtained, 10.536 g of benzoic acid was recovered, the conversion rate of cyclohexanone was 20.17%, the selectivity of ε-caprolactone was 89.73%, the yield of ε-caprolactone was 18.58%, the conversion rate of toluene was 92.71%, the selectivity of benzaldehyde was 6.94%, and the selectivity of benzoic acid was 93.06%.

[0081] Comparative Example 4

[0082] The catalyst of this comparative example has basically the same preparation process as that in Example 1, and the difference between the two is that in step (1), according to n 钒 ∶n 钴 Weigh 1.43 g of vanadium chloride and 2.163 g of cobalt chloride hexahydrate in a ratio of 1:1; among them, the total mass of vanadium and cobalt elements accounts for 10 wt% of the mass of carbon nanotubes. The process of preparing ε-caprolactone by co-oxidation of toluene is the same as that in Example 1.

[0083] Finally, 3.972 g of the product ε-caprolactone was obtained, 10.386 g of benzoic acid was recovered, the conversion rate of cyclohexanone was 19.46%, the selectivity of ε-caprolactone was 89.41%, the yield of ε-caprolactone was 17.40%, the conversion rate of toluene was 91.83%, the selectivity of benzaldehyde was 7.39%, and the selectivity of benzoic acid was 92.61%.

[0084] Comparative Example 5

[0085] The catalyst of this comparative example has basically the same preparation process as that in Example 1, and the difference between the two is that in step (1), n 铁 :n 锡 Weigh 3.568 g of ferric chloride and 5.731 g of tin tetrachloride in a ratio of 1:1. The process of preparing ε-caprolactone by co-oxidation of toluene is the same as that in Example 1.

[0086] Finally, 4.097 g of the product ε-caprolactone was obtained, 10.113 g of benzoic acid was recovered, the conversion rate of cyclohexanone was 19.63%, the selectivity of ε-caprolactone was 91.43%, the yield of ε-caprolactone was 17.94%, the conversion rate of toluene was 89.47%, the selectivity of benzaldehyde was 7.72%, and the selectivity of benzoic acid was 92.28%.

[0087] Comparative Example 6

[0088] The catalyst of this comparative example has basically the same preparation process as that in Example 1, and the difference between the two is that in step (1), n 铁 :n 锡Weigh 4.996 g of ferric chloride and 3.438 g of stannic chloride at a ratio of 7:3. The process of preparing ε-caprolactone by the co-oxidation of toluene is the same as that in Example 1.

[0089] Finally, 4.073 g of ε-caprolactone was obtained, 10.351 g of benzoic acid was recovered, the conversion rate of cyclohexanone was 20.06%, the selectivity of ε-caprolactone was 88.94%, the yield of ε-caprolactone was 17.84%, the conversion rate of toluene was 90.54%, the selectivity of benzaldehyde was 6.38%, and the selectivity of benzoic acid was 93.62%.

[0090] By analyzing Example 1 and Comparative Examples 1-2, it can be seen that when n 钒 : n 钴 = 1:1 is selected during the preparation of the catalyst, it can effectively improve the conversion rate of toluene, and then improve the conversion rate of cyclohexanone and the yield of ε-caprolactone. By analyzing Example 1 and Comparative Examples 3-4, it can be seen that when the mass fraction of vanadium and cobalt elements in the carbon nanotubes is 6% during the preparation of the catalyst, it can effectively improve the conversion rate of toluene, and then improve the conversion rate of cyclohexanone and the yield of ε-caprolactone. By analyzing Example 1 and Comparative Examples 5-6, it can be seen that when n 铁 : n 锡 = 3:7 is selected, it can effectively improve the conversion rate of cyclohexanone and the yield of ε-caprolactone.

[0091] In summary, the catalyst for the co-oxidation of toluene to prepare ε-caprolactone prepared in the present invention has different metal active centers loaded inside and outside the carbon nanotubes. After being used for the co-oxidation of toluene and cyclohexanone to prepare ε-caprolactone, it realizes efficient catalysis of the reaction, with a short reaction time, high efficiency, and good product selectivity. Moreover, the catalyst is easy to separate from the product and has good reusability. In addition, compared with directly using benzaldehyde as the co-oxidant in the prior art, toluene is inexpensive, the entire process has high economy, and has good industrialization prospects. After the reaction, toluene can be directly removed from the reaction solution by simple vacuum distillation, and then the product ε-caprolactone can be obtained by side-line rectification. The process operation is simple and energy-consuming is small, which is suitable for industrial applications.

Claims

1. A preparation method of a catalyst for preparing ε-caprolactone by the co-oxidation of toluene, characterized in that, It includes the following steps: (1) Mix vanadium chloride and cobalt chloride in a solvent to obtain a mixed solution A; Separately, mix iron chloride and tin chloride in water to obtain a mixed solution B; (2) Add carbon nanotubes to the mixed solution A for dispersion, then evaporate the solvent, and then conduct dry heat treatment at 160 - 200 °C to obtain a composite material with vanadium and cobalt loaded on the inner and outer surfaces of the carbon nanotubes; Ultrasonically mix the above composite material with xylene, and then sequentially wash it with acid and water to remove the outer surface active vanadium and cobalt metals, obtaining a xylene dispersion of VCo-in-CNT containing vanadium and cobalt loaded inside; (3) Mix and stir the xylene dispersion containing VCo-in-CNT obtained in step (2), the mixed solution B, and ammonium bicarbonate at a temperature of 70 - 100 °C, and then conduct heat treatment at 160 - 200 °C. The water evaporates prior to the xylene, and the carbon nanotube channels are occupied by xylene, enabling iron and tin to be loaded on the outer surface of the carbon nanotube channels, thus obtaining the catalyst for preparing ε-caprolactone by the co-oxidation of toluene, denoted as VCo-in-CNT-out-FeSn.

2. The preparation method of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene according to claim 1, characterized in that, In step (1), the vanadium chloride is vanadium trichloride; the cobalt chloride is cobalt chloride hexahydrate; the solvent is acetone; the iron chloride is iron trichloride; the tin chloride is tin tetrachloride.

3. The preparation method of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene according to claim 1 or 2, characterized in that, In step (1), the molar ratio of vanadium atoms in vanadium chloride to cobalt atoms in cobalt chloride is 1:1; the molar ratio of iron atoms in iron chloride to tin atoms in tin chloride is 3:7; the ratio of the sum of the molar amounts of vanadium atoms in vanadium chloride and cobalt atoms in cobalt chloride to the sum of the molar amounts of iron atoms in iron chloride and tin atoms in tin chloride is 1:(2 - 6).

4. The preparation method of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene according to claim 1, characterized in that, In step (2), the diameter of the carbon nanotubes is 6 - 10 nm.

5. The preparation method of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene according to claim 1, characterized in that, In step (2), the dispersion is ultrasonic dispersion, and the ultrasonic dispersion time is 6 - 10 h; the evaporation of the solvent is carried out with stirring to evaporate the solvent; the heat treatment is carried out in an air atmosphere, the air flow rate is 20 - 30 mL / min, and the heat treatment time is 15 - 20 h; the total mass of vanadium and cobalt elements loaded on the inner surface of the carbon nanotube channels accounts for 4 - 8 wt% of the mass of the carbon nanotubes.

6. The preparation method of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene according to claim 1, characterized in that, In step (2), the ultrasonic mixing treatment time is 6 - 10 h; the acid is a hydrochloric acid solution with a concentration of 0.0005 - 0.002 mol / L.

7. The preparation method of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene according to claim 1, characterized in that, In step (3), the heat treatment is carried out in an air atmosphere, the air flow rate is 20 - 30 mL / min, and the heat treatment time is 15 - 20 h.

8. A catalyst for preparing ε-caprolactone by the co-oxidation of toluene prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene according to claim 8, characterized in that, Application as a catalyst in the co-oxidation of toluene and cyclohexanone to prepare ε-caprolactone.

10. The application of the catalyst for preparing ε-caprolactone by the co-oxidation of toluene according to claim 9, characterized in that, The process conditions for the co-oxidation of toluene to prepare ε-caprolactone are: using VCo-in-CNT-out-FeSn as the catalyst, oxygen as the oxidant, and cyclohexanone and toluene as the reactants for the reaction; among them, the mass ratio of cyclohexanone to toluene is 2:1, the mass ratio of the catalyst to cyclohexanone is 0.01 - 0.04:1; the reaction pressure is 0.5 - 2 MPa, the reaction temperature is 160 - 170 °C, and the reaction time is 4 - 10 h.

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