A method for synthesizing ε-caprolactone

Abstract

The invention discloses a method for synthesizing ε-caprolactone from cyclohexanone in a green and safe manner, and belongs to the technical field of heterocyclic compounds and organic chemical raw material manufacturing, including: cyclohexanone is oxidized and converted into a mixture aqueous solution of ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers, the peroxide of the mixture aqueous solution is removed, ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers are polycondensed and converted into 6-hydroxycaproic acid linear oligomers, and 6-hydroxycaproic acid linear oligomers are depolymerized to be converted into ε-caprolactone or / and ε-caprolactone cyclic dimers. The present invention provides cyclohexanone and hydrogen peroxide as reaction raw materials, and the whole route does not centrally prepare organic peroxides and does not use organic solvents, thereby greatly reducing the combustion and explosion risks caused by the large-scale use of organic peroxides and organic solvents, and by the scheme of polycondensation-depolymerization, the ε-caprolactone yield is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of heterocyclic compounds and organic chemical raw material manufacturing, and more specifically, the invention relates to a method for green and safe synthesis of epsilon-caprolactone from cyclohexanone. Background Art

[0002] ε-caprolactone can be used to produce polycaprolactone and its copolymers, polycaprolactone polyols and polycaprolactone polyurethanes. The current annual output has exceeded 100,000 tons, but it is still in short supply. Although cyclohexanone, 1,6-hexanediol, 6-hydroxycaproate and other raw materials can be used to synthesize ε-caprolactone, in large-scale production, considering the economic cost, most domestic and foreign companies choose cyclohexanone as the raw material to produce ε-caprolactone through the Baeyer-Villiger (BV) oxidation method.

[0003] The oxidants used in the BV oxidation method include peroxyacid, hydrogen peroxide, and molecular oxygen. Among them, the oxidation of cyclohexanone with peroxyacid is the mainstream technical route for the current production of ε-caprolactone. However, due to the high chemical activity of peroxyacid, it decomposes violently after heating, and there is a risk of combustion and explosion when it comes into contact with open flames, high heat, friction, vibration, or impact. The oxygen source storage and production process of this route are potential safety hazards. In addition, organic solvents such as ethyl acetate and ethyl propionate are also required in the peroxyacid oxidation of cyclohexanone route, which not only has a negative impact on the green environmental protection of this route, but also further increases the risk of combustion and explosion. In 2017, a pipeline explosion occurred in the ε-caprolactone production workshop of Daicel Japan due to the enrichment of peracetic acid. The molecular oxygen route has attracted the attention of researchers because of its high green safety of oxygen source. It usually uses oxygen and aldehyde to generate peroxyacid in situ under the action of a catalyst, and then further oxidizes cyclohexanone to prepare ε-caprolactone and produce carboxylic acid as a by-product. The main problem of this route is that it needs to consume at least an equivalent amount of aldehyde and produce a large amount of carboxylic acid as a by-product, and the atom economy is low. In comparison, the oxygen source used in the hydrogen peroxide oxidation of cyclohexanone route is green and safe, and the production process also has high potential in terms of greenness and safety.

[0004] In 2001, Corma et al. used Sn-beta molecular sieve prepared by hydrothermal method to catalyze hydrogen peroxide oxidation of cyclohexanone. The cyclohexanone conversion rate in 1,4-dioxane solution reached 52%, and the selectivity of ε-caprolactone exceeded 98% (Nature, 2001, 412(6845), 423). Subsequently, a large number of inventions and reports on the technology of tin catalyzing hydrogen peroxide oxidation of cyclohexanone were reported. Among them, the technical effect is better, such as Catal. Commun, 2007, 8(3), 305-309 reported that the montmorillonite (MMT) supported tin catalyst Sn-MMT prepared by ion exchange technology, with 30% H2O2 as oxidant in n-butanol solution, the cyclohexanone conversion rate is as high as 100%, and the caprolactone selectivity is as high as 100%. The direct synthesis of ε-caprolactone by oxidation of cyclohexanone with hydrogen peroxide is simple, but in order to prevent the residual water in hydrogen peroxide from causing hydrolysis of the generated ε-caprolactone, it is inevitable to use a large amount of organic solvents (the mass ratio is about 4 to 35 times that of cyclohexanone). This is not green enough, and the use and post-treatment of a large amount of organic solvents also increase safety risks and economic costs.

[0005] At present, there is no complete technical route for preparing ε-caprolactone with high yield using cyclohexanone and hydrogen peroxide as raw materials without using organic solvents. The existing technology can prepare cyclohexanone peroxide by oxidizing cyclohexanone with hydrogen peroxide and then catalyze the conversion of cyclohexanone peroxide into poly-6-hydroxycaproic acid (Journal of Qingdao University of Science and Technology (Natural Science Edition), 2020, 41(5), 28-32). However, since this technology involves a large amount of cyclohexanone peroxide intermediates, its safety remains to be verified, and it is still unknown how to remove the residual peroxide in the prepared poly-6-hydroxycaproic acid and whether it can further achieve efficient cyclodepolymerization. In addition, the existing technology can catalyze the oxidation of cyclohexanone with hydrogen peroxide to prepare 6-hydroxycaproic acid (China Petroleum Refining and Petrochemicals (English Edition), 2018, 20(03), 1-6), but the amount of water solvent used is large and the solution concentration is low, which is not conducive to the removal of residual peroxide and the preparation and cyclodepolymerization of 6-hydroxycaproic acid linear oligomers, and there is no related technical report on the further conversion and utilization of its 6-hydroxycaproic acid aqueous solution. Summary of the invention

[0006] An object of the present invention is to solve the above-mentioned problems and / or disadvantages and to provide advantages which will be described hereinafter.

[0007] In order to achieve these purposes and other advantages according to the present invention, a method for green and safe synthesis of ε-caprolactone from cyclohexanone is provided, comprising: oxidizing cyclohexanone to convert it into an aqueous solution of a mixture of ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers; after removing peroxide from the aqueous solution of the mixture, polycondensing the mixture of ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers into 6-hydroxycaproic acid linear oligomers; and depolymerizing 6-hydroxycaproic acid linear oligomers into ε-caprolactone and / or ε-caprolactone cyclic dimers.

[0008] Preferably, the method specifically comprises the following steps:

[0009] Step 1: using a modified molecular sieve as a catalyst and hydrogen peroxide as an oxidant to oxidize a cyclohexanone aqueous solution into a mixture aqueous solution of ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers;

[0010] Step 2: solid-liquid separation, separating the modified molecular sieve and the mixture aqueous solution;

[0011] Step 3, removing residual peroxide in the aqueous solution of the mixture by heating, ultrasound or catalytic decomposition;

[0012] Step 4: distilling the aqueous mixture after the peroxide is removed to remove water, and continuously increasing the temperature and / or reducing the pressure to further remove the incompletely converted cyclohexanone and converting the mixture of ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers / oligomers into 6-hydroxycaproic acid linear oligomers / oligomers; wherein the water and cyclohexanone removed by distillation are recycled to step 1;

[0013] Step 5: converting the 6-hydroxycaproic acid linear oligomer / oligomer into ε-caprolactone and / or ε-caprolactone cyclic dimer by cyclodepolymerization under catalytic, heating and reduced pressure conditions, wherein the ε-caprolactone cyclic dimer is converted into 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomer / oligomer by hydrolysis and then recycled to step 4, or directly recycled to the step 5 reactor to be converted into oligomers by ring-opening polymerization.

[0014] Preferably, in the step 1, the modified molecular sieve is a hydrogen-type β molecular sieve that has been subjected to dealumination treatment or a tin mesoporous molecular sieve that has been subjected to stannous ion loading treatment;

[0015] The silicon-aluminum ratio in the hydrogen-type β molecular sieve after dealuminization is 30~600:1.

[0016] Preferably, the tin mesoporous molecular sieve treated with stannous ion loading is one of a tin β molecular sieve catalyst, a Sn-USY molecular sieve catalyst and a Sn-MCM-41 molecular sieve catalyst.

[0017] Preferably, in the step 1, the concentration of hydrogen peroxide is ≥10wt%; in the cyclohexanone aqueous solution, the mass ratio of water to cyclohexanone is 2-10:1, the molar ratio of cyclohexanone to hydrogen peroxide is 0.8-1.2:1, and the mass ratio of cyclohexanone to the catalyst is 20-200:1.

[0018] Preferably, in the step 1, the oxidation conversion temperature is 60-100° C., the reaction time is 1-60 h, the cyclohexanone conversion rate is ≥85%, and the hydrogen peroxide utilization rate is ≥95%.

[0019] Preferably, in step 2, the solid-liquid separation method is decantation, filtration and / or centrifugation.

[0020] Preferably, in step 3, the method of removing the peroxide in the aqueous mixture by heating comprises: heating to boiling, the boiling time being ≥ 10 min;

[0021] The method of ultrasonically removing peroxides from the aqueous solution of the mixture includes ultrasonic treatment time ≥ 10 minutes;

[0022] The catalytic decomposition to remove peroxides in the aqueous mixture solution includes adding 0.1-1.0 wt% of metal oxides or metal ions to the aqueous mixture solution, and the catalytic decomposition time is ≥20 minutes. The metal oxides include manganese dioxide and iron oxide, and the metal ions include iron ions and copper ions.

[0023] Preferably, in the step 4, the conditions for removing moisture are normal pressure and a distillation temperature of 100-150° C.;

[0024] The temperature is continuously increased and / or the pressure is / are decreased to finally maintain ≤3 kPa and 160-220° C. The average polymerization degree of the prepared 6-hydroxyhexanoic acid linear oligomer is 5-100.

[0025] Preferably, in the step five, the heating reaction temperature is 180-240° C., and the reduced pressure condition is ≤1 kPa.

[0026] The present invention has the following beneficial effects: since the ε-caprolactone synthesis route provided by the present invention uses cyclohexanone and hydrogen peroxide as reaction raw materials and the entire route does not centrally prepare organic peroxides and does not use organic solvents, the combustion and explosion risks caused by the large-scale use of organic peroxides and organic solvents are greatly reduced, thereby having higher safety and being more conducive to large-scale industrial production.

[0027] Since the catalyst, water, incompletely converted cyclohexanone and the by-product ε-caprolactone cyclic dimer in the ε-caprolactone synthesis route provided by the present invention can be recycled, the whole route has a high total yield, low material loss, and less "three wastes" emission, thereby having better economic cost and greenness, and is conducive to improving product competitiveness.

[0028] Since the target product of step one in the ε-caprolactone synthesis route provided by the present invention is a mixture of ε-caprolactone, 6-hydroxycaproic acid and linear oligomers thereof, compared with using only 6-hydroxycaproic acid as the target product (which requires a large amount of water as a solvent to promote the hydrolysis of ε-caprolactone and 6-hydroxycaproic acid linear oligomers to improve the selectivity of 6-hydroxycaproic acid), efficient conversion can be achieved at a higher concentration. Therefore, under the same equipment scale and time, the production / processing volume of the oxidation conversion in step one, the solid-liquid separation in step two, the removal of residual peroxides in step three and the removal of water in step four can be increased, thereby improving the efficiency of the entire route and reducing the energy consumption of the entire route.

[0029] Since the step three of the ε-caprolactone synthesis route provided by the present invention centrally removes the residual peroxide, the oxygen generated by the decomposition of the peroxide can be centrally collected and processed, and the residual peroxide can be prevented from further oxidizing the 6-hydroxyhexanoic acid linear oligomers in the subsequent step four to convert their terminal hydroxyl groups into terminal carboxyl groups, thereby improving the cyclization depolymerization reaction rate and yield in step five (the cyclization depolymerization is mainly a "biting back" and "zipper connection" reaction mechanism of the terminal hydroxyl groups, and if the terminal hydroxyl groups are converted into terminal carboxyl groups, the reaction will be blocked).

[0030] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The hydrogen nuclear magnetic resonance spectrum (CDCl3, 400M) of the aqueous solution of the mixture prepared in step 1 of Example 1;

[0032] Figure 2 The hydrogen nuclear magnetic resonance spectrum (CDCl3, 400M) of the polymer obtained in step 4 of Example 1;

[0033] Figure 3 This is a gas chromatogram of the depolymerization product (prepared into a 10% CH2Cl2 solution) obtained in step 5 of Example 1. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0035] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0036] The residual peroxide content was detected by indirect iodine titration and peroxide test paper, the cyclohexanone conversion was calculated by nuclear magnetic resonance hydrogen spectroscopy, the target product selectivity was calculated by gas chromatography, the hydrogen peroxide utilization rate was calculated by comprehensively considering the hydrogen peroxide feed ratio, residual peroxide content and cyclohexanone conversion rate, and the depolymerization product yield was calculated by calculating the mass change in the collecting bottle before and after the reaction.

[0037] Example 1

[0038] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0039] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.0245 g dealumized hydrogen-type β molecular sieve catalyst (0.5 wt%), 5.1 g 30% hydrogen peroxide solution (45 mmol), and 4.9 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 60°C with stirring for 10 h, and condense under reflux using a spherical condenser.

[0040] Step 2: After the reaction is completed, filter and separate to obtain a mixture aqueous solution of the β molecular sieve catalyst and the mixture aqueous solution containing ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers.

[0041] Step 3, impurity removal of peroxide: the peroxide residue was 5.45wt%, 0.1wt% manganese dioxide was added to the aqueous mixture, and the reaction was carried out at 100°C for 10min to complete the impurity removal of the peroxide. The cyclohexanone conversion rate was 85.6% (theoretical value 90.0%), the hydrogen peroxide utilization rate was 95.1%, and the target product selectivity was 94.6%.

[0042] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 100°C for 4 h, react at 160°C under reduced pressure (400 Pa) for 10 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 21.

[0043] Step 5, depolymerization reaction: Under the catalysis of 0.5 mol % MgCl2, the reaction was carried out at 180°C under reduced pressure (50 Pa) for 6 h to carry out the depolymerization reaction of 6-hydroxyhexanoic acid linear oligomers.

[0044] like Figure 1 As shown, the aqueous mixture obtained in step 1 consists of ε-caprolactone, 6-hydroxycaproic acid, 6-hydroxycaproic acid linear oligomers and incompletely converted cyclohexanone, and the proportions of the four are 4.3%, 49.3%, 26.6% and 14.4% respectively according to the integrated area ratio.

[0045] like Figure 2 As shown, it is shown that step 4 obtains a 6-hydroxyhexanoic acid oligomer with a clear structure and no obvious impurities;

[0046] like Figure 3 As shown, according to the area normalization method, the yield of ε-caprolactone was 93.2%, and the yield of ε-caprolactone cyclic dimer was 4.9%.

[0047] Example 2

[0048] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0049] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.049 g dealumized hydrogen-type β molecular sieve catalyst (1.0 wt%), 6.8 g 30% hydrogen peroxide solution (60 mmol), and 4.9 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 60°C with stirring for 20 h, and condense under reflux using a spherical condenser.

[0050] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 4.42wt%.

[0051] Step 3: Removal of impurities from peroxide: 0.5 wt% copper oxide was added to the aqueous solution of the mixture, and the mixture was reacted at 80°C for 20 min to complete the removal of impurities from the peroxide. The cyclohexanone conversion rate was 99.2%, the hydrogen peroxide utilization rate was 99.5%, and the target product selectivity was 97.2%.

[0052] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 100°C for 6 h, react at 160°C under reduced pressure (200 Pa) for 10 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 25.

[0053] Step 5, depolymerization reaction: Under the catalysis of 2 mol% MgBr2, the reaction was carried out at 180°C under reduced pressure (150 Pa) for 4 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 88.6%, and the yield of ε-caprolactone cyclic dimer was 7.3%.

[0054] Example 3

[0055] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0056] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.147 g Sn-β molecular sieve catalyst (1.0 wt%) treated with stannous ion loading, 7.7 g 30% hydrogen peroxide solution (68 mmol), and 14.7 g deionized water into a 100 mL round-bottom flask, heat and stir in an oil bath at 65 °C for 30 h, and condense and reflux using a spherical condenser.

[0057] Step 2: After the reaction is completed, the catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 4.75wt%.

[0058] Step 3: Removal of impurities from peroxide: The mixture aqueous solution was ultrasonically treated for 30 min to remove impurities from peroxide. The cyclohexanone conversion rate was 98.7%, the hydrogen peroxide utilization rate was 99.5%, and the target product selectivity was 98.1%.

[0059] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 120°C for 6 h, react at 180°C under reduced pressure (200 Pa) for 8 h, and dehydrate and polycondense the oxidation product to prepare a 6-hydroxyhexanoic acid linear oligomer with a degree of polymerization of 34.

[0060] Step 5, depolymerization reaction: Under the catalysis of 1 mol% ZnCl2, the reaction was carried out at 220℃ under reduced pressure (300Pa) for 2h to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 82.1%, and the yield of ε-caprolactone cyclic dimer was 13.6%. The prepared ε-caprolactone cyclic dimer was added to the polycaprolactone condensation polymer and kept at 180℃ nitrogen atmospheric pressure for 2h (ε-caprolactone cyclic dimer was obtained by ring-opening polymerization to obtain PCL oligomers), and then the depolymerization reaction was carried out. The yield of ε-caprolactone was 91.0%, and the yield of ε-caprolactone cyclic dimer was 8.3%.

[0061] Example 4

[0062] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0063] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.245 g Sn-β molecular sieve catalyst (5.0 wt%) treated with stannous ion loading, 8.5 g 30% hydrogen peroxide solution (75 mmol), and 14.7 g deionized water into a 100 mL round-bottom flask, heat and stir in an oil bath at 65 °C for 40 h, and condense and reflux using a spherical condenser.

[0064] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 4.21wt%.

[0065] Step 3: Removal of impurities from peroxide: The mixture aqueous solution was heated to 80° C. for 10 min to complete the removal of impurities from peroxide. The cyclohexanone conversion rate was 99.2%, the hydrogen peroxide utilization rate was 99.4%, and the target product selectivity was 98.6%.

[0066] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 140°C for 8 h, react at 180°C under reduced pressure (400 Pa) for 8 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 45.

[0067] Step 5, depolymerization reaction: Under the catalysis of 2 mol% Zn(OAc)2, the reaction was carried out at 230°C under reduced pressure (400 Pa) for 8 hours to carry out the depolymerization reaction of 6-hydroxyhexanoic acid linear oligomers. The yield of ε-caprolactone was 71.5%, and the yield of ε-caprolactone cyclic dimer was 25.6%.

[0068] Example 5

[0069] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0070] Step 1, oxidation reaction: 4.9 g cyclohexanone (50 mmol), 0.049 g Sn-MCM-41 molecular sieve catalyst (1.0 wt%) treated with stannous ion loading, 5.7 g 30% hydrogen peroxide solution (50 mmol), and 24.5 g deionized water were added into a 100 mL round-bottom flask, heated in an oil bath at 70 ° C with stirring for 50 h, and condensed and refluxed using a spherical condenser.

[0071] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 3.76wt%.

[0072] Step 3: Removal of impurities from peroxide: 0.2 wt % of manganese dioxide was added to the aqueous mixture and reacted for 10 min to complete the removal of impurities from the peroxide. The cyclohexanone conversion rate was 98.9%, the hydrogen peroxide utilization rate was 99.0%, and the target product selectivity was 97.8%.

[0073] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 150°C for 8 h, react at 200°C under reduced pressure (400 Pa) for 6 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 48.

[0074] Step 5, depolymerization reaction: Under the catalysis of 1 mol% SnCl2, the reaction was carried out at 230°C under reduced pressure (300 Pa) for 10 h to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 62.3%, and the yield of ε-caprolactone cyclic dimer was 33.1%.

[0075] Example 6

[0076] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0077] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.098 g dealumized hydrogen-type β molecular sieve catalyst (2.0 wt%), 6.0 g 30% hydrogen peroxide solution (53 mmol), and 24.5 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 70°C with stirring for 60 h, and condense under reflux using a spherical condenser.

[0078] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 3.52wt%.

[0079] Step 3: Removal of impurities from peroxide: 1.0 wt% of silver powder was added to the aqueous mixture and reacted for 30 min to complete the removal of impurities from the peroxide. The cyclohexanone conversion rate was 99.3%, the hydrogen peroxide utilization rate was 98.7%, and the target product selectivity was 98.9%.

[0080] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 100°C for 12 h, react at 200°C under reduced pressure (200 Pa) for 6 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 18.

[0081] Step 5: Depolymerization reaction: Under the catalysis of 1 mol% Bu2Sn(OMe)2, the reaction was carried out at 240°C under reduced pressure (500 Pa) for 12 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 66.7%, and the yield of ε-caprolactone cyclic dimer was 31.5%.

[0082] Example 7

[0083] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0084] Step 1, oxidation reaction: 4.9 g cyclohexanone (50 mmol), 0.147 g Sn-β molecular sieve catalyst (3.0 wt%) treated with stannous ion loading, 7.7 g 30% hydrogen peroxide solution (68 mmol), and 24.5 g deionized water were added into a 100 mL round-bottom flask, heated in an oil bath at 75 °C with stirring for 10 h, and condensed and refluxed using a spherical condenser.

[0085] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 2.81 wt%.

[0086] Step 3: Removal of impurities from peroxide: 0.2 wt % of ferric oxide was added to the aqueous mixture and reacted for 10 min to complete the removal of impurities from peroxide. The cyclohexanone conversion rate was 98.6%, the hydrogen peroxide utilization rate was 99.5%, and the target product selectivity was 97.9%.

[0087] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 120°C for 12 h, react at 220°C under reduced pressure (200 Pa) for 4 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 26.

[0088] Step 5, depolymerization reaction: Under the catalysis of 0.5 mol% Ti(OiPr)4, the reaction was carried out at 180°C under reduced pressure (150 Pa) for 4 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 88.6%, and the yield of ε-caprolactone cyclic dimer was 7.3%.

[0089] Example 8

[0090] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0091] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.245 g dealuminated hydrogen-type β molecular sieve catalyst (5.0 wt%), 8.5 g 30% hydrogen peroxide solution (75 mmol), and 24.5 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 75 °C with stirring for 20 h, and condense under reflux using a spherical condenser.

[0092] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 2.60wt%.

[0093] Step 3: Removal of impurities from peroxide: The mixture aqueous solution was ultrasonically treated for 60 min to remove impurities from peroxide, with a cyclohexanone conversion rate of 99.5%, a hydrogen peroxide utilization rate of 99.4%, and a target product selectivity of 98.8%.

[0094] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 120°C for 18 h, react at 220°C under reduced pressure (400 Pa) for 4 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 42.

[0095] Step 5, depolymerization reaction: Under the catalysis of 1 mol% MgCl2, the reaction was carried out at 220°C under reduced pressure (50 Pa) for 8 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 89.8%, and the yield of ε-caprolactone cyclic dimer was 5.6%.

[0096] Example 9

[0097] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0098] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.098 g Sn-USY molecular sieve catalyst (2.0 wt%) treated with stannous ion loading, 5.7 g 30% hydrogen peroxide solution (50 mmol), and 39.2 g deionized water into a 100 mL round-bottom flask, heat and stir in an 80 ° C oil bath for 30 h, and condense and reflux using a spherical condenser.

[0099] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 2.42wt%.

[0100] Step 3: Removal of impurities from peroxide: The mixture aqueous solution was heated at 100° C. for 30 min to complete the removal of impurities from peroxide, with a cyclohexanone conversion rate of 98.9%, a hydrogen peroxide utilization rate of 99.3%, and a target product selectivity of 97.8%.

[0101] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 140°C for 10 h, react at 160°C under reduced pressure (400 Pa) for 8 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 68.

[0102] Step 5, depolymerization reaction: Under the catalysis of 1 mol% MgBr2, the reaction was carried out at 200°C under reduced pressure (100Pa) for 6 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 90.1%, and the yield of dimer was 6.9%. The prepared ε-caprolactone cyclic dimer was added to the depolymerization reaction bottle in the depolymerization step, and kept warm at 200°C nitrogen atmosphere and normal pressure for 40 minutes (ring-opening polymerization to obtain PCL oligomers), followed by a depolymerization reaction. The yield of ε-caprolactone was 91.8%, and the yield of ε-caprolactone cyclic dimer was 8.6%.

[0103] Example 10

[0104] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0105] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.098 g dealumized hydrogen-type β molecular sieve catalyst (2.0 wt%), 6.2 g 30% hydrogen peroxide solution (55 mmol), and 39.2 g deionized water into a 100 mL round-bottom flask, heat in an 80°C oil bath with stirring for 40 h, and condense under reflux using a spherical condenser.

[0106] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 2.12 wt%.

[0107] Step 3: Removal of impurities from peroxide: 0.5 wt % of manganese dioxide was added to the aqueous mixture and reacted for 10 min to complete the removal of impurities from the peroxide. The cyclohexanone conversion rate was 98.1%, the hydrogen peroxide utilization rate was 99.2%, and the target product selectivity was 97.5%.

[0108] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 140°C for 18 h, react at 160°C under reduced pressure (400 Pa) for 10 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 79.

[0109] Step 5, depolymerization reaction: Under the catalysis of 2 mol% ZnCl2, the reaction was carried out at 190°C under reduced pressure (100 Pa) for 6 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 83.2%, and the yield of ε-caprolactone cyclic dimer was 13.9%.

[0110] Embodiment 11

[0111] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0112] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.147 g Sn-MCM-41 molecular sieve catalyst (3.0 wt%) treated with stannous ion loading, 7.7 g 30% hydrogen peroxide solution (68 mmol), and 39.2 g deionized water into a 100 mL round-bottom flask, heat and stir in an oil bath at 85 °C for 50 h, and condense and reflux using a spherical condenser.

[0113] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 1.82 wt%.

[0114] Step 3: Removal of impurities from peroxide: 1.0 wt% of copper oxide was added to the aqueous mixture and reacted for 30 min to complete the removal of impurities from the peroxide. The cyclohexanone conversion rate was 98.6%, the hydrogen peroxide utilization rate was 99.5%, and the target product selectivity was 98.2%.

[0115] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 150°C for 12 h, react at 180°C under reduced pressure (500 Pa) for 10 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 86.

[0116] Step 5, depolymerization reaction: Under the catalysis of 1 mol% Zn(OAc)2, the reaction was carried out at 180°C under reduced pressure (100 Pa) for 10 h to carry out the depolymerization reaction of 6-hydroxyhexanoic acid linear oligomers. The yield of ε-caprolactone was 73.6%, and the yield of ε-caprolactone cyclic dimer was 22.4%.

[0117] Example 12

[0118] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0119] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.245 g dealumized hydrogen-type β molecular sieve catalyst (5.0 wt%), 8.5 g 30% hydrogen peroxide solution (75 mmol), and 39.2 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 85°C with stirring for 60 h, and condense under reflux using a spherical condenser.

[0120] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 1.72 wt%.

[0121] Step 3: Removal of impurities from peroxide: 0.1 wt% of silver powder was added to the aqueous mixture and reacted for 10 min to complete the removal of impurities from the peroxide. The cyclohexanone conversion rate was 98.9%, the hydrogen peroxide utilization rate was 98.8%, and the target product selectivity was 97.8%.

[0122] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 150°C for 14 h, react at 180°C under reduced pressure (200 Pa) for 10 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 89.

[0123] Step 5, depolymerization reaction: Under the catalysis of 2 mol% SnCl2, the reaction was carried out at 200°C and reduced pressure (150 Pa) for 10 h to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 65.4%, and the yield of ε-caprolactone cyclic dimer was 31.5%.

[0124] Embodiment 13

[0125] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0126] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.0245 g Sn-USY molecular sieve catalyst (0.5 wt%) treated with stannous ion loading, 6.0 g 30% hydrogen peroxide solution (53 mmol), and 49.0 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 90 °C with stirring for 1 h, and condense and reflux using a spherical condenser.

[0127] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 1.64 wt%.

[0128] Step 3: Removal of impurities from peroxide: The mixture aqueous solution was ultrasonically treated for 30 min to remove impurities from the peroxide. The cyclohexanone conversion rate was 98.3%, the hydrogen peroxide utilization rate was 98.5%, and the target product selectivity was 98.4%.

[0129] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 100°C for 18 h, react at 200°C under reduced pressure (300 Pa) for 6 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 95.

[0130] Step 5, depolymerization reaction: Under the catalysis of 1 mol% Bu2Sn(OMe)2, the reaction was carried out at 220°C under reduced pressure (150Pa) for 12 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 64.9%, and the yield of ε-caprolactone cyclic dimer was 29.6%.

[0131] Embodiment 14

[0132] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0133] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.049 g Sn-β molecular sieve catalyst (1.0 wt%) treated with stannous ion loading, 6.8 g 30% hydrogen peroxide solution (60 mmol), and 49.0 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 90 ° C with stirring for 5 h, and condense and reflux using a spherical condenser.

[0134] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 1.52 wt%.

[0135] Step 3: Removal of impurities from peroxide: The mixture aqueous solution was reacted at 80° C. for 10 min to complete the removal of impurities from peroxide, with a cyclohexanone conversion rate of 98.9%, a hydrogen peroxide utilization rate of 99.6%, and a target product selectivity of 98.3%.

[0136] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 100°C for 18 h, react at 200°C under reduced pressure (400 Pa) for 6 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 97.

[0137] Step 5, depolymerization reaction: Under the catalysis of 1 mol% Ti(OiPr)4, the reaction was carried out at 230°C under reduced pressure (200 Pa) for 12 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 74.3%, and the yield of ε-caprolactone cyclic dimer was 21.4%.

[0138] Embodiment 15

[0139] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0140] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.147 g Sn-MCM-41 molecular sieve catalyst (3.0 wt%) treated with stannous ion loading, 8.5 g 30% hydrogen peroxide solution (75 mmol), and 49.0 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 95 °C with stirring for 10 h, and condense and reflux using a spherical condenser.

[0141] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 1.36wt%.

[0142] Step 3: Removal of impurities from peroxide: 0.5 wt % of ferric oxide was added to the aqueous mixture and reacted for 10 min to complete the removal of impurities from peroxide. The cyclohexanone conversion rate was 99.6%, the hydrogen peroxide utilization rate was 99.4%, and the target product selectivity was 98.9%.

[0143] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 120°C for 4 h, react at 160°C under reduced pressure (400 Pa) for 4 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 8.

[0144] Step 5, depolymerization reaction: Under the catalysis of 1 mol% MgCl2, the reaction was carried out at 240°C under reduced pressure (200Pa) for 4 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 90.4%, and the yield of dimer was 5.1%. The prepared ε-caprolactone cyclic dimer and water were mixed at a ratio of 1:5 and hydrolyzed at 140°C for 2 hours to obtain 6-hydroxycaproic acid and its linear oligomers, which were added to the aqueous solution of the mixture to carry out the polycondensation-depolymerization reaction of steps 4 and 5. The yield of ε-caprolactone was 90.6%, and the yield of ε-caprolactone cyclic dimer was 7.8%.

[0145] Example 16

[0146] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0147] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.0245 g dealumized hydrogen-type β molecular sieve catalyst (0.5 wt%), 5.7 g 30% hydrogen peroxide solution (50 mmol), and 73.5 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 95°C with stirring for 20 h, and condense under reflux using a spherical condenser.

[0148] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 1.12 wt%.

[0149] Step 3: Removal of impurities from peroxide: 0.2 wt % of manganese dioxide was added to the aqueous mixture and reacted for 30 min to complete the removal of impurities from peroxide. The cyclohexanone conversion rate was 99.7%, the hydrogen peroxide utilization rate was 99.6%, and the target product selectivity was 98.6%.

[0150] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 120°C for 6 h, react at 200°C under reduced pressure (400 Pa) for 4 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 17.

[0151] Step 5, depolymerization reaction: Under the catalysis of 1 mol% MgBr2, the reaction was carried out at 180°C under reduced pressure (150 Pa) for 4 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 89.4%, and the yield of ε-caprolactone cyclic dimer was 6.8%.

[0152] Embodiment 17

[0153] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0154] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.049 g Sn-MCM-41 molecular sieve catalyst (1.0 wt%) treated with stannous ion loading, 6.0 g 30% hydrogen peroxide solution (53 mmol), and 73.5 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 100 °C with stirring for 1 h, and condense and reflux using a spherical condenser.

[0155] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 1.08 wt%.

[0156] Step 3: Removal of impurities from peroxide: 0.5 wt % of copper oxide was added to the aqueous mixture and reacted for 10 min to complete the removal of impurities from the peroxide. The cyclohexanone conversion rate was 98.2%, the hydrogen peroxide utilization rate was 99.3%, and the target product selectivity was 97.9%.

[0157] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 140°C for 8 h, react at 200°C under reduced pressure (400 Pa) for 8 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 28.

[0158] Step 5, depolymerization reaction: Under the catalysis of 1 mol% ZnCl2, the reaction was carried out at 200°C and reduced pressure (300 Pa) for 6 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 84.1%, and the yield of ε-caprolactone cyclic dimer was 11.8%.

[0159] Embodiment 18

[0160] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0161] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.098 g dealumized hydrogen-type β molecular sieve catalyst (2.0 wt%), 6.2 g 30% hydrogen peroxide solution (55 mmol), and 73.5 g deionized water into a 100 mL round-bottom flask, heat in an oil bath at 100 °C with stirring for 5 h, and condense and reflux using a spherical condenser.

[0162] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 0.86wt%.

[0163] Step 3: Removal of impurities from peroxide: 1.0 wt% of silver powder was added to the aqueous mixture and reacted for 30 min to complete the removal of impurities from the peroxide. The cyclohexanone conversion rate was 98.6%, the hydrogen peroxide utilization rate was 99.2%, and the target product selectivity was 98.1%.

[0164] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 140°C for 10 h, react at 220°C under reduced pressure (400 Pa) for 8 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 34.

[0165] Step 5: Depolymerization reaction: Under the catalysis of 1 mol% Zn(OAc)2, the reaction was carried out at 220°C under reduced pressure (400 Pa) for 6 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 72.8%, and the yield of ε-caprolactone cyclic dimer was 21.9%.

[0166] Embodiment 19

[0167] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0168] Step 1, oxidation reaction: 4.9 g cyclohexanone (50 mmol), 0.147 g Sn-β molecular sieve catalyst (3.0 wt%) treated with stannous ion loading, 7.7 g 30% hydrogen peroxide solution (68 mmol), and 98.0 g deionized water were added into a 100 mL round-bottom flask, heated in an oil bath at 100 °C with stirring for 10 h, and condensed and refluxed using a spherical condenser.

[0169] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the peroxide residue is 0.76wt%.

[0170] Step 3: Removal of impurities from peroxide: The mixture aqueous solution was ultrasonically treated for 60 min to remove impurities from the peroxide. The cyclohexanone conversion rate was 99.2%, the hydrogen peroxide utilization rate was 99.5%, and the target product selectivity was 98.7%.

[0171] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 150°C for 12 h, react at 220°C under reduced pressure (200 Pa) for 10 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 42.

[0172] Step 5, depolymerization reaction: Under the catalysis of 0.5 mol% SnCl2, the reaction was carried out at 230°C under reduced pressure (300 Pa) for 8 hours to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 63.2%, and the yield of ε-caprolactone cyclic dimer was 33.6%.

[0173] Embodiment 20

[0174] A method for green and safe synthesis of ε-caprolactone from cyclohexanone comprises the following steps:

[0175] Step 1, oxidation reaction: add 4.9 g cyclohexanone (50 mmol), 0.245 g Sn-USY molecular sieve catalyst (5.0 wt%) treated with stannous ion loading, 8.5 g 30% hydrogen peroxide solution (75 mmol), and 98.0 g deionized water into a 100 mL round-bottom flask, heat and stir in an oil bath at 100 °C for 20 h, and condense and reflux using a spherical condenser.

[0176] Step 2: After the reaction is completed, the β molecular sieve catalyst and the mixture aqueous solution are separated by filtration, and the residual peroxide is 1.21 wt%.

[0177] Step 3: Removal of impurities from peroxide: The mixture aqueous solution was heated at 100° C. for 30 min to complete the removal of impurities from peroxide. The cyclohexanone conversion rate was 99.7%, the hydrogen peroxide utilization rate was 98.9%, and the target product selectivity was 98.6%.

[0178] Step 4, polycondensation reaction: under N2 protection, heat in an oil bath at 150°C for 18 h, react at 220°C under reduced pressure (300 Pa) for 10 h, and dehydrate and polycondense the oxidation product to prepare 6-hydroxyhexanoic acid linear oligomers with a degree of polymerization of 36.

[0179] Step 5, depolymerization reaction: Under the catalysis of 0.5 mol% Ti(OiPr)4, the reaction was carried out at 250°C under reduced pressure (100 Pa) for 10 h to carry out the depolymerization reaction of 6-hydroxycaproic acid linear oligomers. The yield of ε-caprolactone was 73.2%, and the yield of ε-caprolactone cyclic dimer was 22.5%.

[0180] The number of devices and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be obvious to those skilled in the art.

[0181] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for synthesizing ε-caprolactone, characterized in that The following steps are involved: Step 1: using a modified molecular sieve as a catalyst and hydrogen peroxide as an oxidant to oxidize a cyclohexanone aqueous solution into a mixture aqueous solution of ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers; Step 2: solid-liquid separation, separating the modified molecular sieve and the mixture aqueous solution; Step 3, removing residual peroxide in the aqueous solution of the mixture by heating, ultrasound or catalytic decomposition; Step 4: distilling the aqueous mixture after the peroxide is removed to remove water, and continuously increasing the temperature and / or reducing the pressure to further remove the incompletely converted cyclohexanone and converting the mixture of ε-caprolactone, 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomers / oligomers into 6-hydroxycaproic acid linear oligomers / oligomers; wherein the water and cyclohexanone removed by distillation are recycled to step 1; Step 5, converting the 6-hydroxycaproic acid linear oligomer / oligomer into ε-caprolactone or / and ε-caprolactone cyclic dimer through cyclization depolymerization under catalytic, heating and reduced pressure conditions, wherein the ε-caprolactone cyclic dimer is converted into 6-hydroxycaproic acid and 6-hydroxycaproic acid linear oligomer / oligomer through hydrolysis and then recycled to step 4, or directly recycled to the step 5 reactor to be converted into oligomers through ring-opening polymerization; In the step 1, the modified molecular sieve is a hydrogen-type β molecular sieve that has been subjected to dealumination treatment or a tin mesoporous molecular sieve that has been subjected to stannous ion loading treatment; The silicon-aluminum ratio in the hydrogen-type β molecular sieve after dealuminization is 30~600:

1.

2. The method for synthesizing ε-caprolactone according to claim 1, characterized in that The tin mesoporous molecular sieve treated with stannous ion loading is one of the tin beta molecular sieve catalyst, Sn-USY molecular sieve catalyst and Sn-MCM-41 molecular sieve catalyst.

3. The method for synthesizing ε-caprolactone according to claim 1, characterized in that In the step 1, the concentration of hydrogen peroxide is ≥10wt%; in the cyclohexanone aqueous solution, the mass ratio of water to cyclohexanone is 2-10:1, the molar ratio of cyclohexanone to hydrogen peroxide is 0.8-1.2:1, and the mass ratio of cyclohexanone to the catalyst is 20-200:

1.

4. The method for synthesizing ε-caprolactone according to claim 1, characterized in that In the step 1, the oxidation conversion temperature is 60-100° C., the reaction time is 1-60 hours, the cyclohexanone conversion rate is ≥85%, and the hydrogen peroxide utilization rate is ≥95%.

5. The method for synthesizing ε-caprolactone according to claim 1, characterized in that In the step 2, the solid-liquid separation method is decantation, filtration and / or centrifugation.

6. The method for synthesizing ε-caprolactone according to claim 1, characterized in that In the step 3, the method of removing the peroxide in the aqueous solution of the mixture by heating comprises: heating to boiling, the boiling time being ≥ 10 min; The method of ultrasonically removing peroxides from the aqueous solution of the mixture includes ultrasonic treatment time ≥ 10 minutes; The catalytic decomposition to remove peroxides in the aqueous mixture solution includes adding 0.1-1.0 wt% of metal oxides or metal ions to the aqueous mixture solution, and the catalytic decomposition time is ≥20 minutes. The metal oxides include manganese dioxide and iron oxide, and the metal ions include iron ions and copper ions.

7. The method for synthesizing ε-caprolactone according to claim 1, characterized in that In the step 4, the conditions for removing moisture are normal pressure and distillation temperature of 100-150°C; The temperature is continuously increased and / or the pressure is / are decreased to finally maintain ≤3 kPa and 160-220° C. The average polymerization degree of the prepared 6-hydroxyhexanoic acid linear oligomer is 5-100.

8. The method for synthesizing ε-caprolactone according to claim 1, characterized in that In the step 5, the heating reaction temperature is 180-240° C., and the reduced pressure condition is ≤1 kPa.

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