Method for preparing caprolactone and method for preparing anhydrous peroxy acid product

Abstract

The present invention relates to the field of chemical engineering technology, and in particular, to a method for preparing caprolactone and a method for preparing an anhydrous peroxy acid product. The method for preparing caprolactone comprises: (1) in the presence of a homogeneous acidic catalyst, reacting hydrogen peroxide with an organic acid, and dehydrating the resultant reaction product to give a peroxy acid phase comprising the homogeneous acidic catalyst; (2) removing the homogeneous acidic catalyst in the peroxy acid phase to give the anhydrous peroxy acid product; and (3) subjecting the anhydrous peroxy acid product and cyclohexanone to an oxidation reaction. According to the method of the present invention, the peroxy acid is synthesized by using a homogeneous acidic catalyst, and the anhydrous peroxy acid product can be prepared by first dehydrating and then removing the catalyst. By oxidizing cyclohexanone with the anhydrous peroxy acid product to produce caprolactone, high caprolactone selectivity and yield can be achieved.

Description

Methods for preparing caprolactone and anhydrous peroxy acid products

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Chinese Patent Application No. 202411713430.8, filed on November 27, 2024, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of caprolactone synthesis technology, specifically to a method for preparing caprolactone and a method for preparing anhydrous peroxy acid products. Background Technology

[0004] ε-caprolactone is an important organic synthesis intermediate. Currently, the main method for the industrial production of ε-caprolactone is the cyclohexanone oxidation method, among which the peroxy acid oxidation of cyclohexanone is one of the most common and effective methods.

[0005] The synthesis reaction of peroxyacids is RCOOH + H₂O₂ → RCOOOH + H₂O. This reaction is a nucleophilic reaction. Due to the weak affinity of hydrogen peroxide, it is difficult for it to undergo nucleophilic reactions with the carbonyl positions of organic acids, resulting in limited reaction kinetics and a low reaction rate. In the production of peroxyacids, strong acidic heteropoly acids, nitric acid, sulfuric acid, and acidic resins are usually used as catalysts to improve reaction efficiency. Solid acidic resins are generally considered ideal catalysts due to their strong acidity and efficient separation from the catalyst. However, studies have found that acidic resins are prone to swelling and loss of active components in the strong oxidizing environment of peroxyacids. Long-term operation leads to irreversible deactivation of the catalyst, thus limiting the application of heterogeneous catalytic materials such as acidic resins. Homogeneous catalysts can avoid the destruction of active components. However, because the reaction is homogeneous, acidic catalyst residues remain in the product solution and cannot be separated. These residual catalysts affect the quality of the peroxyacid product. When used to oxidize cyclohexanone to produce caprolactone, the residual catalyst can cause side reactions such as ring-opening, isomerization, and polycondensation of caprolactone, reducing the caprolactone yield. This is especially exacerbated by the high-temperature environment of the distillation column during subsequent product separation and purification. Furthermore, the presence of water in the peroxyacid also reduces the caprolactone yield, necessitating the removal of water from the raw materials and reaction products.

[0006] To avoid the influence of the strong acid centers of homogeneous catalysts on downstream caprolactone synthesis, existing technologies mostly employ weak acid catalysts for the preparation of anhydrous peroxy acids. For example, patent application CN103570667A discloses a continuous method for preparing caprolactone, in which boric acid is used as a catalyst and hydrogen peroxide as an oxidant to continuously oxidize organic carboxylic acids in multiple reactive distillation columns to obtain peroxy acids; then, the peroxy acids and cyclohexanone are continuously introduced into multiple stirred tanks connected in series for reaction to obtain a caprolactone solution. Boric acid is a weak acid and has little effect on the polymerization of caprolactone, but its catalytic efficiency for peroxy acid synthesis is low, and the series connection of multiple reactive distillation columns increases energy consumption, which is also unfavorable for industrial production. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems in existing technologies where strong acid catalysts are used to prepare anhydrous peroxyacid. When this peroxyacid is used to oxidize cyclohexanone to produce caprolactone, residual strong acid catalyst and / or water in the peroxyacid can cause side reactions, reducing the selectivity of the oxidation reaction and the yield of caprolactone. This invention provides a method for preparing caprolactone and anhydrous peroxyacid products. The method described in this invention can achieve higher cyclohexanone conversion, caprolactone selectivity, and caprolactone yield.

[0008] To achieve the above objectives, the present invention provides a method for preparing caprolactone, the method comprising the following steps:

[0009] (1) In the presence of a homogeneous acid catalyst, hydrogen peroxide is reacted with an organic acid, and the resulting reaction product is dehydrated to obtain a peroxyacid phase containing a homogeneous acid catalyst.

[0010] (2) Remove the homogeneous acidic catalyst from the peroxy acid phase to obtain anhydrous peroxy acid product;

[0011] (3) The anhydrous peroxy acid product is subjected to an oxidation reaction with cyclohexanone.

[0012] A second aspect of this invention provides a method for preparing anhydrous peroxyacid products, the method comprising the following steps:

[0013] (1) In the presence of a homogeneous acid catalyst, hydrogen peroxide is reacted with an organic acid, and the resulting reaction product is dehydrated to obtain a peroxyacid phase containing a homogeneous acid catalyst.

[0014] (2) Remove the homogeneous acid catalyst from the peroxy acid phase.

[0015] According to the method for preparing caprolactone described in this invention, a homogeneous acidic catalyst is used to catalyze the synthesis of peroxy acid. By first dehydrating and then removing the acidic catalyst, an anhydrous peroxy acid product with extremely low water and acidic catalyst content can be obtained. Using this anhydrous peroxy acid product to oxidize cyclohexanone to produce caprolactone, high caprolactone selectivity and yield can be obtained. Furthermore, when the crude caprolactone product is subsequently purified and refined using a distillation column, the high-temperature environment in the column bottom is less likely to cause polycondensation side reactions, resulting in a high overall yield of caprolactone product.

[0016] In a preferred embodiment, introducing a specific nitrogen-containing basic compound during the oxidation of cyclohexanone to caprolactone can further eliminate the influence of residual acidic catalyst in the anhydrous peroxy acid product on the preparation of caprolactone, thereby further improving the selectivity and yield of caprolactone. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0018] The method for preparing caprolactone according to the present invention includes the following steps:

[0019] (1) In the presence of a homogeneous acid catalyst, hydrogen peroxide is reacted with an organic acid, and the resulting reaction product is dehydrated to obtain a peroxyacid phase containing a homogeneous acid catalyst.

[0020] (2) Remove the homogeneous acidic catalyst from the peroxy acid phase to obtain anhydrous peroxy acid product;

[0021] (3) The anhydrous peroxy acid product is subjected to an oxidation reaction with cyclohexanone.

[0022] In the method described in this invention, step (1) involves synthesizing a peroxyacid product from organic acid and hydrogen peroxide under the action of a homogeneous acidic catalyst, while simultaneously performing dehydration to obtain a substantially anhydrous peroxyacid phase. Preferably, the dehydration conditions are such that the water content in the peroxyacid phase is less than 0.2% by weight. The water removed during the dehydration process includes water introduced by the hydrogen peroxide, water generated during the reaction, etc.

[0023] In step (1), the reaction is preferably carried out in the presence of a solvent, wherein the solvent is an organic compound that can form an azeotrope with water and, upon cooling, form an oil-water two-phase mixture with water. Using such a solvent facilitates solvent separation and recovery, and facilitates the separation of the peroxyacid product into an aqueous phase and a peroxyacid phase. In some embodiments, the solvent is selected from at least one of propyl formate, butyl formate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, dioxane, acetonitrile, and cyclohexane.

[0024] In step (1), the homogeneous acidic catalyst can be a common catalyst in the art capable of releasing H2. + The homogeneous acid catalyst has an acidity coefficient pKa of -4 to 8. To improve the synthesis efficiency of peroxy acids, preferably, the homogeneous acid catalyst is a strong acid catalyst, i.e., the acid dissociation constant of the homogeneous acid catalyst is -3 to 5. In some preferred embodiments, the homogeneous acid catalyst is selected from at least one of sulfuric acid, nitric acid, heteropolyacids, and isopolyacids. The heteropolyacid can be selected from one or more of phosphomolybdic acid, phosphotungstic acid, and silicotungstic acid. The isopolyacid can be selected from one or more of decatungstic acid, heptatungstic acid, octamolybdic acid, and dodecamolybdic acid. The catalyst used in this invention can be initially in a liquid or solid state. When the homogeneous catalyst is initially in a liquid state, it becomes homogeneous after mixing with the reaction system, and the boiling point of the homogeneous acid catalyst is higher than that of the peroxy acid. When the homogeneous catalyst is initially in a solid state, it completely dissolves after mixing with the reaction system, forming a homogeneous phase. When the homogeneous acidic catalyst is a heteropolyacid or isopolyacid, because it is a solid with a high molecular weight and has the properties of a salt, its boiling point in the reaction system is between 380-1500℃, which is much higher than the boiling point of the organic compounds in the reaction system.

[0025] In step (1), the organic acid can be any conventional choice in the art, as long as it is a liquid-phase organic acid or an organic acid soluble in a solvent. Specifically, the organic acid can be an aliphatic carboxylic acid and / or an aromatic carboxylic acid. Preferably, the organic acid is a C1-C10 carboxylic acid. More preferably, the organic acid is at least one selected from formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and benzoic acid, and more preferably at least one selected from acetic acid, propionic acid, and butyric acid.

[0026] In step (1), the hydrogen peroxide can be any conventional choice in the art. The concentration of the hydrogen peroxide can be 10-90% by weight, preferably 25-50% by weight.

[0027] In step (1), based on a total of 100 parts by weight of the homogeneous acidic catalyst, the hydrogen peroxide, the organic acid, and the solvent, the amount of the homogeneous acidic catalyst can be 0.01-15 parts by weight, the amount of hydrogen peroxide is 5-70 parts by weight, the amount of the organic acid is 5-70 parts by weight, and the amount of the solvent is 5-70 parts by weight. Preferably, based on a total of 100 parts by weight of the homogeneous acidic catalyst, the hydrogen peroxide, the organic acid, and the solvent, the amount of the homogeneous acidic catalyst can be 0.05-10 parts by weight, the amount of hydrogen peroxide is 10-60 parts by weight, the amount of the organic acid is 10-50 parts by weight, and the amount of the solvent is 10-50 parts by weight.

[0028] In step (1), the reaction can be carried out directly in a reactive distillation column to synthesize anhydrous peroxyacid; alternatively, a pre-reaction can be performed first, followed by reactive distillation in a reactive distillation column to obtain an aqueous phase and a peroxyacid phase. The reaction of hydrogen peroxide with organic acids to synthesize peroxyacid is an equilibrium reaction. The presence of water inhibits the reaction process. The reaction in a reactive distillation column, through reactive distillation, can break the chemical equilibrium, remove water from the system, and separate the reaction products into an aqueous phase and a peroxyacid phase. In this invention, anhydrous peroxyacid can be synthesized using one or more reactive distillation columns according to specific synthesis requirements. Multiple reactive distillation columns can be set up in series, parallel, or series-parallel configurations. In this invention, the process in step (1) can be carried out using a continuous or intermittent reaction method.

[0029] In the first embodiment, the reaction in step (1) is carried out in a reactive distillation column. In this embodiment, the reaction conditions include: a bottom temperature of 40-65°C, a top temperature of 25-40°C, and a pressure of 1-15 kPa. In this invention, the pressure is absolute pressure.

[0030] In the second embodiment, the reaction in step (1) includes a pre-reaction and a main reaction carried out sequentially. The pre-reaction is conducted in at least one reactor selected from a microchannel reactor, a fixed-bed reactor, a batch reactor, a static mixing reactor, and a membrane reactor. The main reaction is conducted in a reactive distillation column. In this embodiment, the conditions for the pre-reaction include a temperature of 40-65°C, a pressure of 80 kPa-1 MPa, and a time of 1-5 hours. The conditions for the main reaction include a bottom temperature of 40-65°C, a top temperature of 27-40°C, and a pressure of 1-15 kPa.

[0031] By carrying out the reaction and dehydration process in step (1) according to the two implementation methods described above, not only can the water in the peroxyacid phase be fully removed, but the combustion and explosion during the dehydration process can also be avoided.

[0032] In step (1), there are no specific restrictions on the order in which the various materials are added. The solvent, organic acid, hydrogen peroxide, and homogeneous acidic catalyst can be introduced into the reactor as separate feeds, or they can be mixed in pairs and then mixed with other materials before being introduced into the reactor. In a preferred embodiment, hydrogen peroxide and solvent do not form a liquid-liquid two-phase feed.

[0033] In the method described in this invention, the purpose of step (2) is mainly to separate the homogeneous acidic catalyst from the peroxy acid phase obtained in step (1). The inventors have discovered through research that, in a preferred embodiment, by removing the homogeneous acidic catalyst through evaporation based on the boiling point difference between the homogeneous acidic catalyst and the peroxy acid in the system, the separation of the homogeneous acidic catalyst and the peroxy acid can be better achieved.

[0034] In this invention, to achieve the separation of homogeneous acidic catalyst and peroxy acid, the evaporation temperature is higher than the boiling point of peroxy acid but lower than the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system. When removing the homogeneous acidic catalyst from the peroxy acid phase, the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system is higher than that of peroxy acid. During the evaporation process, the peroxy acid with the lower boiling point in the system can be vaporized and collected, and after condensation, a refined peroxy acid product is obtained; the liquid homogeneous acidic catalyst with the higher boiling point in the system is collected as a residue. In some preferred embodiments, to improve the separation effect between the homogeneous acidic catalyst and peroxy acid and reduce the content of the homogeneous acidic catalyst in the peroxy acid product, when removing the homogeneous acidic catalyst from the peroxy acid phase, the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system is more than 40°C higher than that of peroxy acid.

[0035] This invention, by defining the relationship between the boiling point of the homogeneous acidic catalyst and the boiling point of the peroxyacid, can remove the catalyst from the peroxyacid phase to a content ≤50 ppm, further improving the selectivity and yield of caprolactone. In a preferred embodiment, the evaporation temperature during the removal of the homogeneous acidic catalyst from the peroxyacid phase is at least 10°C lower than the boiling point of the homogeneous acidic catalyst in the peroxyacid phase system.

[0036] In some embodiments, the evaporation temperature in step (2) can be 10-130°C; to prevent the peroxy acid from burning or exploding during the separation and purification process, the evaporation temperature is preferably 20-85°C. In some embodiments, the evaporation pressure can be 0.5-90 kPa; to ensure separation efficiency, the evaporation pressure is preferably 1-25 kPa. In some embodiments, the evaporation residence time can be 1-3600 s; to avoid the decomposition of the peroxy acid during the separation and purification process, the residence time should not be too long, and the evaporation residence time is preferably 5-1200 s.

[0037] In a preferred embodiment, step (2), the process of removing the homogeneous acidic catalyst by evaporation, is carried out in a falling film evaporator. According to this preferred embodiment, not only can the efficient removal of impurities such as homogeneous acidic catalyst, metal ions, and condensate be achieved, but also combustion and explosion during the evaporation process can be avoided.

[0038] In a preferred embodiment, step (2) includes: separating the peroxy acid from the crude peroxy acid product by evaporation, removing the homogeneous acidic catalyst from the crude peroxy acid product, and then liquefying and condensing the peroxy acid to obtain a refined anhydrous peroxy acid product. In this invention, the heat exchange equipment used for condensation can be a condensing heat exchanger. In some embodiments, in order to condense and liquefy the peroxy acid product separated by evaporation, the peroxy acid product needs to be condensed to -20℃ to 30℃. To ensure product collection efficiency and save energy, the preferred temperature is -10℃ to 15℃.

[0039] Anhydrous peroxy acid products are prepared according to steps (1) and (2). The conversion rate of hydrogen peroxide can reach over 99.5%, the yield of peroxy acid can reach over 95%, and an anhydrous peroxy acid product with an acid catalyst content ≤50 ppm, a water content ≤0.2 wt%, and a peroxy acid concentration of 5–50 wt% can be obtained. In addition to a small amount of acid catalyst and water, the anhydrous peroxy acid product also contains raw material hydrogen peroxide and organic acids. Using this anhydrous peroxy acid product as an oxidant to prepare caprolactone can further improve the conversion rate of cyclohexanone, the selectivity of caprolactone, and the yield.

[0040] In step (3), in order to improve the conversion rate of cyclohexanone and avoid the need to solve the problem of separating residual cyclohexanone in the subsequent caprolactone separation and purification process, the molar ratio of cyclohexanone to peroxy acid in the anhydrous peroxy acid product is preferably 1:1-1.5, more preferably 1:1.2-1.4.

[0041] In step (3), the conditions for the oxidation reaction may include: a temperature of 30-80°C and a time of 1-8 hours.

[0042] In a preferred embodiment, to further eliminate the influence of residual acidic catalyst in the anhydrous peroxy acid product on the preparation of caprolactone and to further improve the selectivity and yield of caprolactone, the oxidation reaction in step (3) is carried out in the presence of a nitrogen-containing basic compound, wherein the nitrogen-containing basic compound has a lone pair of electrons on its N atom. More preferably, the nitrogen-containing basic compound is selected from at least one of methylamine, ethylamine, triethylamine, trimethylamine, ethylenediamine, urea, ethanolamine, isopropylamine, tert-butylamine, aniline, benzylamine, cyclohexylamine, dicyclohexylamine, pyridine, dimethylpyridine, pyrrole, indole, acridine, carbazole, and quinoline. Even more preferably, the molar ratio of the homogeneous acidic catalyst in the anhydrous peroxy acid product to the nitrogen-containing basic compound is 1:1-30, more preferably 1:3-10.

[0043] In some embodiments, the process of oxidizing the anhydrous peroxy acid product with cyclohexanone includes: placing cyclohexanone in a reactor, heating to the reaction temperature, turning on magnetic or mechanical stirring, then adding the anhydrous peroxy acid product to the cyclohexanone, and continuing the reaction for a period of time after the addition is complete. The reactor can be a reactor conventionally used in the art, such as a batch reactor. In a preferred embodiment, the anhydrous peroxy acid product can be added to the cyclohexanone by slow dropwise addition.

[0044] In this invention, the method for preparing caprolactone may further include: refining the crude caprolactone product obtained from the oxidation reaction by distillation. The distillation can be performed according to conventional procedures in the art. In some embodiments, the distillation and refining process includes: a first stage, in which light components with boiling points lower than caprolactone are separated from the crude caprolactone product from the top of a column by vacuum or atmospheric distillation, and crude caprolactone product free of light components is obtained from the bottom of the column. The top temperature of the light component removal column can be 20-50°C, and the top pressure can be 0.5-100 kPaA. The light components include organic acids, solvents, and micro-reaction peroxy acids contained in the anhydrous peroxypropionic acid product. In a second stage, pure caprolactone is separated from the top of the column by vacuum distillation, and heavy components with boiling points higher than caprolactone are separated from the bottom of the column, and refined caprolactone product is obtained from the top of the column. The top temperature of the heavy component removal column can be 50-100°C, and the pressure can be 0.5-5 kPaA. The heavy components include oligomers formed after caprolactone condensation and catalysts after salt formation. The anhydrous peroxy acid product prepared by the method of this invention is used as an oxidant to prepare caprolactone. After distillation and purification, the yield of caprolactone is ≥95%.

[0045] This invention also provides a method for preparing anhydrous peroxyacid products, the method comprising the following steps:

[0046] (1) In the presence of a homogeneous acid catalyst, hydrogen peroxide is reacted with an organic acid, and the resulting reaction product is dehydrated to obtain a peroxyacid phase containing a homogeneous acid catalyst.

[0047] (2) Remove the homogeneous acid catalyst from the peroxy acid phase.

[0048] In the method described in this invention, step (1) involves synthesizing a peroxyacid product from organic acid and hydrogen peroxide under the action of a homogeneous acidic catalyst, while simultaneously performing dehydration to obtain a substantially anhydrous peroxyacid phase. Preferably, the dehydration conditions are such that the water content in the peroxyacid phase is less than 0.2% by weight. The water removed during the dehydration process includes water introduced by the hydrogen peroxide, water generated during the reaction, etc.

[0049] In step (1), the reaction is preferably carried out in the presence of a solvent, wherein the solvent is an organic compound that can form an azeotrope with water and, upon cooling, form an oil-water two-phase mixture with water. Using such a solvent facilitates solvent separation and recovery, and facilitates the separation of the peroxyacid product into an aqueous phase and a peroxyacid phase. In some embodiments, the solvent is selected from at least one of propyl formate, butyl formate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, dioxane, acetonitrile, and cyclohexane.

[0050] In step (1), the homogeneous acidic catalyst can be a common catalyst in the art capable of releasing H2. + The homogeneous acid catalyst has an acidity coefficient pKa of -4 to 8. To improve the synthesis efficiency of peroxy acids, preferably, the homogeneous acid catalyst is a strong acid catalyst, i.e., the acid dissociation constant of the homogeneous acid catalyst is -3 to 5. In some preferred embodiments, the homogeneous acid catalyst is selected from at least one of sulfuric acid, nitric acid, heteropolyacids, and isopolyacids. The heteropolyacid can be selected from one or more of phosphomolybdic acid, phosphotungstic acid, and silicotungstic acid. The isopolyacid can be selected from one or more of decatungstic acid, heptatungstic acid, octamolybdic acid, and dodecamolybdic acid. The catalyst used in this invention can be initially in a liquid or solid state. When the homogeneous catalyst is initially in a liquid state, it becomes homogeneous after mixing with the reaction system, and the boiling point of the homogeneous acid catalyst is higher than that of the peroxy acid. When the homogeneous catalyst is initially in a solid state, it completely dissolves after mixing with the reaction system, forming a homogeneous phase. When the homogeneous acidic catalyst is a heteropolyacid or isopolyacid, because it is a solid with a high molecular weight and has the properties of a salt, its boiling point in the reaction system is between 380-1500℃, which is much higher than the boiling point of the organic compounds in the reaction system.

[0051] In step (1), the organic acid can be any conventional choice in the art, as long as it is a liquid-phase organic acid or an organic acid soluble in a solvent. Specifically, the organic acid can be an aliphatic carboxylic acid and / or an aromatic carboxylic acid. Preferably, the organic acid is a C1-C10 carboxylic acid. More preferably, the organic acid is at least one selected from formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and benzoic acid, and more preferably at least one selected from acetic acid, propionic acid, and butyric acid.

[0052] In step (1), the hydrogen peroxide can be any conventional choice in the art. The concentration of the hydrogen peroxide can be 10-90% by weight, preferably 25-50% by weight.

[0053] In step (1), based on a total of 100 parts by weight of the homogeneous acidic catalyst, the hydrogen peroxide, the organic acid, and the solvent, the amount of the homogeneous acidic catalyst can be 0.01-15 parts by weight, the amount of hydrogen peroxide is 5-70 parts by weight, the amount of the organic acid is 5-70 parts by weight, and the amount of the solvent is 5-70 parts by weight. Preferably, based on a total of 100 parts by weight of the homogeneous acidic catalyst, the hydrogen peroxide, the organic acid, and the solvent, the amount of the homogeneous acidic catalyst can be 0.05-10 parts by weight, the amount of hydrogen peroxide is 10-60 parts by weight, the amount of the organic acid is 10-50 parts by weight, and the amount of the solvent is 10-50 parts by weight.

[0054] In step (1), the reaction can be carried out directly in a reactive distillation column to synthesize anhydrous peroxyacid; alternatively, a pre-reaction can be performed first, followed by reactive distillation in a reactive distillation column to obtain an aqueous phase and a peroxyacid phase. The reaction of hydrogen peroxide with organic acids to synthesize peroxyacid is an equilibrium reaction. The presence of water inhibits the reaction process. The reaction in a reactive distillation column, through reactive distillation, can break the chemical equilibrium, remove water from the system, and separate the reaction products into an aqueous phase and a peroxyacid phase. In this invention, anhydrous peroxyacid can be synthesized using one or more reactive distillation columns according to specific synthesis requirements. Multiple reactive distillation columns can be set up in series, parallel, or series-parallel configurations. In this invention, the process in step (1) can be carried out using a continuous or intermittent reaction method.

[0055] In the first embodiment, the reaction in step (1) is carried out in a reactive distillation column. In this embodiment, the reaction conditions include: a bottom temperature of 40-65°C, a top temperature of 25-40°C, and a pressure of 1-15 kPa. In this invention, the pressure is absolute pressure.

[0056] In the second embodiment, the reaction in step (1) includes a pre-reaction and a main reaction carried out sequentially. The pre-reaction is conducted in at least one reactor selected from a microchannel reactor, a fixed-bed reactor, a batch reactor, a static mixing reactor, and a membrane reactor. The main reaction is conducted in a reactive distillation column. In this embodiment, the conditions for the pre-reaction include a temperature of 40-65°C, a pressure of 80 kPa-1 MPa, and a time of 1-5 hours. The conditions for the main reaction include a bottom temperature of 40-65°C, a top temperature of 27-40°C, and a pressure of 1-15 kPa.

[0057] By carrying out the reaction and dehydration process in step (1) according to the two implementation methods described above, not only can the water in the peroxyacid phase be fully removed, but the combustion and explosion during the evaporation process can also be avoided.

[0058] In step (1), there are no specific restrictions on the order in which the various materials are added. The solvent, organic acid, hydrogen peroxide, and homogeneous acidic catalyst can be introduced into the reactor as separate feeds, or they can be mixed in pairs and then mixed with other materials before being introduced into the reactor. In a preferred embodiment, hydrogen peroxide and solvent do not form a liquid-liquid two-phase feed.

[0059] In the method described in this invention, the purpose of step (2) is mainly to separate the homogeneous acidic catalyst from the peroxy acid phase obtained in step (1). The inventors have discovered through research that, in a preferred embodiment, by removing the homogeneous acidic catalyst through evaporation based on the boiling point difference between the homogeneous acidic catalyst and the peroxy acid in the system, the separation of the homogeneous acidic catalyst and the peroxy acid can be better achieved.

[0060] In this invention, to achieve the separation of homogeneous acidic catalyst and peroxy acid, the evaporation temperature is higher than the boiling point of peroxy acid but lower than the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system. When removing the homogeneous acidic catalyst from the peroxy acid phase, the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system is higher than that of peroxy acid. During the evaporation process, the peroxy acid with the lower boiling point in the system can be vaporized and collected, and after condensation, a refined peroxy acid product is obtained; the liquid homogeneous acidic catalyst with the higher boiling point in the system is collected as a residue. In some preferred embodiments, to improve the separation effect between the homogeneous acidic catalyst and peroxy acid and reduce the content of the homogeneous acidic catalyst in the peroxy acid product, when removing the homogeneous acidic catalyst from the peroxy acid phase, the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system is more than 40°C higher than that of peroxy acid.

[0061] This invention, by defining the relationship between the boiling point of the homogeneous acidic catalyst and the boiling point of the peroxyacid, can remove the catalyst from the peroxyacid phase to a content ≤50 ppm, further improving the selectivity and yield of caprolactone. In a preferred embodiment, the evaporation temperature during the removal of the homogeneous acidic catalyst from the peroxyacid phase is at least 10°C lower than the boiling point of the homogeneous acidic catalyst in the peroxyacid phase system.

[0062] In some embodiments, the evaporation temperature in step (2) can be 10-130°C; to prevent the peroxy acid from burning or exploding during the separation and purification process, the evaporation temperature is preferably 20-85°C. In some embodiments, the evaporation pressure can be 0.5-90 kPa; to ensure separation efficiency, the evaporation pressure is preferably 1-25 kPa. In some embodiments, the evaporation residence time can be 1-3600 s; to avoid the decomposition of the peroxy acid during the separation and purification process, the residence time should not be too long, and the evaporation residence time is preferably 5-1200 s.

[0063] In a preferred embodiment, step (2), the process of removing the homogeneous acidic catalyst by evaporation, is carried out in a falling film evaporator. According to this preferred embodiment, not only can the efficient removal of impurities such as homogeneous acidic catalyst, metal ions, and condensate be achieved, but also combustion and explosion during the evaporation process can be avoided.

[0064] In a preferred embodiment, step (2) includes: separating the peroxy acid from the crude peroxy acid product by evaporation, removing the homogeneous acidic catalyst from the crude peroxy acid product, and then liquefying and condensing the peroxy acid to obtain a refined anhydrous peroxy acid product. In this invention, the heat exchange equipment used for condensation can be a condensing heat exchanger. In some embodiments, in order to condense and liquefy the peroxy acid product separated by evaporation, the peroxy acid product needs to be condensed to -20℃ to 30℃. To ensure product collection efficiency and save energy, the preferred temperature is -10℃ to 15℃.

[0065] Anhydrous peroxy acid products are prepared according to steps (1) and (2). The conversion rate of hydrogen peroxide can reach over 99.5%, the yield of peroxy acid can reach over 95%, and an anhydrous peroxy acid product with an acid catalyst content ≤50 ppm, a water content ≤0.2 wt%, and a peroxy acid concentration of 5–50 wt% can be obtained. In addition to a small amount of acid catalyst and water, the anhydrous peroxy acid product also contains raw material hydrogen peroxide and organic acids. Using this anhydrous peroxy acid product as an oxidant to prepare caprolactone can further improve the conversion rate of cyclohexanone, the selectivity of caprolactone, and the yield.

[0066] The following examples further illustrate the preparation methods of the anhydrous peroxyacid product and caprolactone according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0067] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0068] In the following embodiments:

[0069] For the analysis methods of peroxides such as hydrogen peroxide and peroxyacid, refer to the national standard "Peracetic Acid Solution GB / T19104-2021";

[0070] For analytical methods of materials such as caprolactone and cyclohexanone, refer to the industry standard "Industrial ε-caprolactone HG / T 5618-2019";

[0071] The formula for calculating the conversion rate of cyclohexanone is: X = (A 环己酮的初始峰面积 -A 反应后结束后环己酮峰面积 ) / A 环己酮的初始峰面积 *100%;

[0072] Formula for calculating the selectivity of caprolactone: S CPL =A 己内酯峰面积 / (A 己内酯峰面积 *C 1校正因子 +A 剩余环己酮峰面积 *C 2校正因子 +A 重组分 峰面积 *C 3校正因子 )*100%.

[0073] The yield of peroxyacid is calculated using S. PAA =M 得到的过氧酸质量 / M 过氧化氢理论转化为过氧酸的质量 *100%;

[0074] The yield of caprolactone is calculated as Y = M. 得到的己内酯产品质量 / M 环己酮理论转化为己内酯的质量 *100%.

[0075] Example 1

[0076] Preparation process of anhydrous peroxy acid products:

[0077] (1) Weigh 1500g of ethyl propionate, 1500g of propionic acid and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor (i.e., a reaction vessel). Weigh 5g of heteropoly acid (phosphotungstic acid, with a boiling point higher than 380℃ in the following peroxypropionic acid phase) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1h to obtain hydrous peroxypropionic acid. After analysis, the concentration of peroxypropionic acid is 10% by weight and the selectivity of the reaction is 100%. The aqueous peroxypropionic acid was then transferred to a distillation column with an absolute pressure of 15 kPa, a bottom temperature of 60°C, and a top temperature of 30°C. Ethyl propionate and water formed an azeotrope, which entered the top condenser. The condensed material was an oil-water two-phase mixture. Ethyl propionate was completely refluxed as the oil phase, while the aqueous phase was completely collected. The residence time of the reaction was 1.5 h. The peroxypropionic acid phase was collected from the bottom of the column. The conversion rate of hydrogen peroxide was calculated to be 100%, and the water content in the peroxypropionic acid phase was 0.08% by weight. Based on the material balance, the yield of peroxypropionic acid was 95.5%.

[0078] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa absolute, and the residence time of the material during the evaporation process was 120 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the gaseous peroxypropionic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied to collect anhydrous peroxypropionic acid product A1. Analysis showed that the anhydrous peroxypropionic acid product A1 contained 7 ppm of catalyst, 0.1 wt% water, and 29.7 wt% peroxypropionic acid.

[0079] Preparation process of caprolactone:

[0080] The mixture was prepared according to the following formula: the molar ratio of peroxypropionic acid to cyclohexanone in anhydrous peroxypropionic acid product A1 was 1.05:1, and the molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) in anhydrous peroxypropionic acid product A1 was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and mechanical stirring was started. Anhydrous peroxypropionic acid product A1 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.8%, and the selectivity for caprolactone was 9%. 9.5%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by reducing pressure. The top temperature of the light component removal column is 30°C and the top pressure is 3 kPaA. The bottom of the column yields crude caprolactone product free of light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by reducing pressure distillation. The top temperature of the heavy component removal column is 95°C and the pressure is 1.5 kPaA. The yield of caprolactone is 95.2%.

[0081] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxypropionic acid were 95.5%, 94.5%, 95.3%, 94.6%, and 95.4%, respectively, indicating that the activity of the catalyst did not decrease.

[0082] Example 2

[0083] Preparation process of anhydrous peroxy acid products:

[0084] (1) Weigh 1000g of ethyl propionate, 1000g of propionic acid, and 1500g of hydrogen peroxide (50wt%) and place them in a batch reactor. Weigh 5g of a polyacid (heptatungstic acid, with a boiling point >1000℃ in the following peroxypropionic acid phase) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 50℃ and the absolute pressure to 80kPa, and react for 4h to obtain hydrous peroxypropionic acid. Analysis showed that the concentration of peroxypropionic acid was 12% by weight, and the selectivity of the reaction was 100%. Then Aqueous peroxypropionic acid was transferred to a distillation column. The absolute pressure was 5 kPa, the bottom temperature was 45°C, and the top temperature was 27°C. Ethyl propionate and water formed an azeotrope, which entered the top condenser. The condensed material was an oil-water two-phase mixture. Ethyl propionate was completely refluxed as the oil phase, and the water phase was completely collected. The residence time of the reaction was 5.5 h. The peroxypropionic acid phase was collected from the bottom of the column. The conversion rate of hydrogen peroxide was calculated to be 99.4%, the water content in the peroxypropionic acid phase was 0.15%, and the yield of peroxypropionic acid was 95.1%.

[0085] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 80°C, the evaporation pressure at 10 kPa absolute, and the residence time of the material during the evaporation process was 70 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the peroxypropionic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 5°C, and then liquefied to collect anhydrous peroxypropionic acid product A2. Analysis showed that the anhydrous peroxypropionic acid product A2 contained 5 ppm of catalyst, 0.15 wt% water, and 47.6 wt% peroxypropionic acid.

[0086] Preparation process of caprolactone:

[0087] The anhydrous perpropionic acid product A2 was prepared with a perpropionic acid to cyclohexanone molar ratio of 1:1 and a catalyst to nitrogen-containing basic compound (triethylamine) molar ratio of 1:3. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 55℃, and mechanical stirring was started. Anhydrous perpropionic acid product A2 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 3.5-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.3%, and the selectivity for caprolactone was 9%. 5.9%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by reducing pressure. The top temperature of the light component removal column is 30°C and the top pressure is 3 kPaA. The bottom of the column yields crude caprolactone product without light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by reducing pressure distillation. The top temperature of the heavy component removal column is 78°C and the pressure is 1.5 kPaA. The yield of caprolactone is 94.2%.

[0088] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxypropionic acid were 92.8%, 91.5%, 91.9%, 92.7%, and 92.2%, respectively, and the catalyst activity did not decrease.

[0089] Example 3

[0090] Preparation process of anhydrous peroxy acid products:

[0091] (1) 1500g of propyl formate, 1500g of propionic acid, and 900g of hydrogen peroxide (50wt%) were weighed and placed in a batch reactor. 12g of sulfuric acid (concentration 98 wt%, boiling point 338℃ in the peroxypropionic acid phase below) was weighed and added as a catalyst for pre-reaction. The reaction temperature was set at 60℃ and the absolute pressure at 500kPa, and the reaction was carried out for 2.5h to obtain hydrous peroxypropionic acid. Analysis showed that the concentration of peroxypropionic acid was 12.5 wt%, and the selectivity of the reaction was 99%. The aqueous peroxypropionic acid was then transferred to a distillation column at an absolute pressure of 10 kPa, a bottom temperature of 55°C, and a top temperature of 35°C. Propyl formate and water formed an azeotrope, which entered the top condenser. The condensed material was an oil-water two-phase mixture. Propyl formate was refluxed as the oil phase, while the aqueous phase was completely collected. The residence time of the reaction was 5 hours. The peroxypropionic acid phase was collected from the bottom of the column. The calculated conversion rate of hydrogen peroxide was 99.2%, the water content in the peroxypropionic acid phase was 0.08% by weight, and the yield of peroxypropionic acid was 94.5%.

[0092] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 40°C, the evaporation pressure at 2.5 kPa absolute, and the residence time of the material during the evaporation process was 30 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the gaseous peroxypropionic acid product was collected from the top and entered a condenser heat exchanger to cool the product to -5°C, and then liquefied to collect anhydrous peroxypropionic acid product A3. Analysis showed that the anhydrous peroxypropionic acid product A3 contained 25 ppm of catalyst, 0.08% water by weight, and 28.9% peroxypropionic acid by weight.

[0093] Preparation process of caprolactone:

[0094] The mixture was prepared according to the following formula: the molar ratio of peroxypropionic acid to cyclohexanone in anhydrous peroxypropionic acid product A3 was 1.25:1, and the molar ratio of catalyst to nitrogen-containing basic compound (n-hexylamine) in anhydrous peroxypropionic acid product A3 was 1:10. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 45℃, and mechanical stirring was started. Anhydrous peroxypropionic acid product A3 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 6-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.5%, and the selectivity for caprolactone was [not specified]. 97.2%; then the product obtained from the oxidation reaction was subjected to distillation. The distillation process included separating the light components with boiling points lower than caprolactone from the top of the column by reducing pressure. The top temperature of the light component removal column was 30°C, and the top pressure was 3 kPaA. The bottom of the column yielded crude caprolactone product free of light components. The heavy components with boiling points higher than caprolactone were separated from the bottom of the column by reducing pressure distillation. The top temperature of the heavy component removal column was 78°C, and the pressure was 1.5 kPaA. The yield of caprolactone was 95.7%.

[0095] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxypropionic acid were 93.5%, 94.2%, 93.8%, 94.4%, and 94.6%, respectively, indicating that the activity of the catalyst did not decrease.

[0096] Example 4

[0097] Anhydrous peroxy acid and caprolactone were prepared according to the method in Example 1, except that propionic acid was replaced with butyric acid. The specific process is as follows:

[0098] Preparation process of anhydrous peroxy acid products:

[0099] (1) Weigh 1500g of ethyl propionate, 1500g of butyric acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor. Weigh 5g of heteropoly acid (phosphotungstic acid) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1h to obtain hydrous peroxybutyric acid. The concentration of peroxybutyric acid was 13.2 wt%, and the selectivity of the reaction was 100%. Then, the hydrous peroxybutyric acid was transferred to… In the distillation column, the absolute pressure is 15 kPa, the bottom temperature is 60°C, and the top temperature is 30°C. Ethyl propionate and water form an azeotrope and enter the top condenser. The condensed material is an oil-water two-phase mixture. Ethyl propionate is completely refluxed as the oil phase, and the water phase is completely collected. The residence time of the reaction is 2 hours. The peroxybutyric acid phase is collected from the bottom. The conversion rate of hydrogen peroxide is calculated to be 99.2%, and the water content in the peroxybutyric acid phase is 0.1% by weight. According to the material balance, the yield of peroxybutyric acid is 95.2%.

[0100] (2) The crude anhydrous peroxybutyric acid collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa absolute, and the evaporation time at 120 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the peroxybutyric acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied and collected as anhydrous peroxybutyric acid product A4. Analysis showed that the anhydrous peroxybutyric acid product A4 contained 26 ppm of catalyst, 0.1 wt% water, and 36.5 wt% peroxybutyric acid.

[0101] Preparation process of caprolactone:

[0102] The ingredients were prepared according to the following formula: the molar ratio of peroxybutyric acid to cyclohexanone in anhydrous peroxybutyric acid product A4 was 1.05:1, and the molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) in anhydrous peroxybutyric acid product A4 was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and mechanical stirring was started. Anhydrous peroxybutyric acid product A4 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.6%, and the selectivity for caprolactone was 9%. 6.2%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by reducing pressure. The top temperature of the light component removal column is 35°C and the top pressure is 2 kPaA. The bottom of the column yields crude caprolactone product without light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by reducing pressure distillation. The top temperature of the heavy component removal column is 78°C and the pressure is 1.5 kPaA. The yield of caprolactone is 94.8%.

[0103] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxybutyric acid were 94.2%, 95.2%, 94.8%, 94.3%, and 95.1%, respectively, indicating that the activity of the catalyst did not decrease.

[0104] Example 5

[0105] Anhydrous peroxy acid and caprolactone were prepared according to the method in Example 1, except that propionic acid was replaced with acetic acid. The specific process is as follows:

[0106] Preparation process of anhydrous peroxy acid products:

[0107] (1) Weigh 1500g of ethyl propionate, 1500g of acetic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor. Weigh 5g of heteropoly acid (phosphotungstic acid) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1h to obtain hydrous peracetic acid. Analysis showed that the concentration of peracetic acid was 11% by weight and the selectivity of the reaction was 95.3%. Then, transfer the hydrous peracetic acid to... In the distillation column, the absolute pressure is 15 kPa, the bottom temperature is 60℃, and the top temperature is 30℃. Ethyl propionate and water form an azeotrope and enter the top condenser. The condensed material is an oil-water two-phase mixture. Ethyl propionate is completely refluxed as the oil phase, and the water phase is completely collected. The residence time of the reaction is 1.5 h. The peracetic acid phase is collected from the bottom. The conversion rate of hydrogen peroxide is calculated to be 99.1%, and the water content in the peracetic acid phase is 0.1% by weight. According to the material balance, the yield of peracetic acid is 92.6%.

[0108] (2) The crude anhydrous peracetic acid collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa absolute, and the residence time of the material during the evaporation process was 120 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the gaseous peracetic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied and collected as anhydrous peracetic acid product A5. Analysis showed that the anhydrous peracetic acid product A5 contained 7 ppm of catalyst, 0.1 wt% water, and 25.8 wt% peracetic acid.

[0109] Preparation process of caprolactone:

[0110] The mixture was prepared according to the following formula: peracetic acid to cyclohexanone molar ratio in anhydrous peracetic acid product A5 was 1.05:1, and the catalyst to nitrogen-containing basic compound (pyrrole) molar ratio in anhydrous peracetic acid product A5 was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and mechanical stirring was started. Anhydrous peracetic acid product A5 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.2%, and the selectivity for caprolactone was 93%. 0.3%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by means of reduced pressure. The top temperature of the light component removal column is 25°C and the top pressure is 4 kPaA. The bottom of the column yields crude caprolactone product without light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by means of reduced pressure distillation. The top temperature of the heavy component removal column is 78°C and the pressure is 1.5 kPaA. The yield of caprolactone is 91.6% by weight.

[0111] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peracetic acid five times according to the same process. The yields of peracetic acid were 91.6%, 92.2%, 92.5%, 91.1%, and 92.5%, respectively, indicating that the activity of the catalyst did not decrease.

[0112] Example 6

[0113] Anhydrous peroxy acid and caprolactone were prepared according to the method in Example 1, except that propionic acid was replaced with benzoic acid. The specific process is as follows:

[0114] Preparation process of anhydrous peroxy acid products:

[0115] (1) Weigh 1500g of ethyl propionate, 1500g of benzoic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor. Weigh 5g of heteropoly acid (phosphotungstic acid) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1h to obtain hydrous peroxybenzoic acid. Analysis showed that the concentration of peroxybenzoic acid was 19.5% by weight, and the selectivity of the reaction was 100%. Then, transfer the hydrous peroxybenzoic acid to... In the distillation column, the absolute pressure is 15 kPa, the bottom temperature is 60℃, and the top temperature is 30℃. Ethyl propionate and water form an azeotrope and enter the top condenser. The condensed material is an oil-water two-phase mixture. Ethyl propionate is completely refluxed as the oil phase, and the water phase is completely collected. The residence time of the reaction is 1.5 h. The peroxybenzoic acid phase is collected from the bottom. The conversion rate of hydrogen peroxide is calculated to be 99.3%, and the water content in the peroxybenzoic acid phase is 0.12% by weight. Based on the material balance, the yield of peroxybenzoic acid is 80.3%.

[0116] (2) The crude anhydrous peroxybenzoic acid collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa absolute, and the residence time of the material during the evaporation process was 120 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the gaseous peroxybenzoic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied and collected as anhydrous peroxybenzoic acid product A6. Analysis showed that the anhydrous peroxybenzoic acid product A6 contained 35 ppm of catalyst, 0.15 wt% water, and 40.6 wt% peroxybenzoic acid.

[0117] Preparation process of caprolactone:

[0118] The ingredients were prepared according to the following formula: the molar ratio of peroxybenzoic acid to cyclohexanone in anhydrous peroxybenzoic acid product A6 was 1.05:1, and the molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) in anhydrous peroxybenzoic acid product A6 was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and mechanical stirring was started. Anhydrous peroxybenzoic acid product A6 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.4%, and the selectivity for caprolactone was 8%. 9.9%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by means of reduced pressure. The top temperature of the light component removal column is 70°C and the top pressure is 0.3 kPaA. The bottom of the column yields crude caprolactone product without light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by means of reduced pressure distillation. The top temperature of the heavy component removal column is 78°C and the pressure is 1.5 kPaA. The yield of caprolactone is 88.4% by weight.

[0119] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxybenzoic acid five times according to the same process. The yields of peroxybenzoic acid were 78.3%, 79.4%, 80.2%, 79.2%, and 80.1%, respectively, indicating that the activity of the catalyst did not decrease.

[0120] Example 7

[0121] Anhydrous peroxyacid and caprolactone were prepared according to the method in Example 1, except that no nitrogen-containing basic compound was added during the preparation of caprolactone. The specific process is as follows:

[0122] Preparation process of anhydrous peroxy acid products:

[0123] (1) Weigh 1500g of ethyl propionate, 1500g of propionic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor (i.e., a reaction vessel). Weigh 5g of heteropoly acid (phosphotungstic acid, boiling point above 380℃) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1 hour to obtain hydrous peroxypropionic acid. Analysis showed that the concentration of peroxypropionic acid was 10% by weight, and the selectivity of the reaction was 100%. Then, the hydrous peroxypropionic acid... Perpropionic acid was transferred to a distillation column with an absolute pressure of 15 kPa, a bottom temperature of 60°C, and a top temperature of 30°C. Ethyl propionate and water formed an azeotrope, which entered the top condenser. The condensed material was an oil-water two-phase mixture. Ethyl propionate was refluxed as the oil phase, and the water phase was completely collected. The residence time of the reaction was 1.5 h. The perpropionic acid phase was collected from the bottom of the column. The conversion rate of hydrogen peroxide was calculated to be 100%, and the water content in the perpropionic acid phase was 0.07% by weight. Based on the material balance, the yield of perpropionic acid was 95.5%.

[0124] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa absolute, and the residence time of the material during the evaporation process was 120 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the gaseous peroxypropionic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied to collect anhydrous peroxypropionic acid product A1. Analysis showed that the anhydrous peroxypropionic acid product A1 contained 7 ppm of catalyst, 0.1 wt% water, and 29.7 wt% peroxypropionic acid.

[0125] Preparation process of caprolactone:

[0126] The anhydrous peroxypropionic acid product A1 was prepared according to a molar ratio of peroxypropionic acid to cyclohexanone of 1.05:1. 50g of cyclohexanone was weighed and placed in a batch reactor, heated to 50℃, and mechanical stirring was started. Anhydrous peroxypropionic acid product A1 was slowly added dropwise to the cyclohexanone, completing the addition in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.8%, and the selectivity for caprolactone was 95.0%. The product obtained from the oxidation reaction was then subjected to distillation. The process includes separating the light components with boiling points lower than caprolactone from the top of the column by reducing pressure. The top temperature of the light component removal column is 30°C, and the top pressure is 3 kPaA. The bottom of the column yields crude caprolactone product free of light components. Then, the heavy components with boiling points higher than caprolactone are separated from the bottom of the column by reducing pressure distillation. The top temperature of the heavy component removal column is 95°C, and the pressure is 1.5 kPaA. The yield of caprolactone is 75.2% by weight.

[0127] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxypropionic acid were 94.5%, 95.6%, 95.1%, 94.9%, and 95.4%, respectively, indicating that the activity of the catalyst did not decrease.

[0128] Example 8

[0129] Anhydrous peroxy acid and caprolactone were prepared according to the method in Example 1, except that the ratios of ethyl propionate, propionic acid, hydrogen peroxide, and catalyst were different. The specific process is as follows:

[0130] Preparation process of anhydrous peroxy acid products:

[0131] (1) Weigh 1500g of ethyl propionate, 2800g of propionic acid, and 200g of hydrogen peroxide (50wt%) and place them in a batch reactor. Weigh 5g of heteropoly acid (phosphotungstic acid) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1h to obtain hydrous peroxypropionic acid. Analysis showed that the concentration of peroxypropionic acid was 2.5 wt%, and the selectivity of the reaction was 100%. Then, transfer the hydrous peroxypropionic acid to... In the distillation column, the absolute pressure is 15 kPa, the bottom temperature is 60℃, and the top temperature is 30℃. Ethyl propionate and water form an azeotrope and enter the top condenser. The condensed material is an oil-water two-phase mixture. Ethyl propionate is completely refluxed as the oil phase, and the water phase is completely collected. The residence time of the reaction is 1.5 h. The peroxypropionic acid phase is collected from the bottom. The conversion rate of hydrogen peroxide is calculated to be 99.5%, and the water content in the peroxypropionic acid phase is 0.08%. Based on material balance, the yield of peroxypropionic acid is 76.5%.

[0132] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa absolute, and the residence time of the material during the evaporation process was 120 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the peroxypropionic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied and collected as anhydrous peroxypropionic acid product A8. Analysis showed that the anhydrous peroxypropionic acid product A8 contained 10 ppm of catalyst, 0.1 wt% water, and 4.2 wt% peroxypropionic acid.

[0133] Preparation process of caprolactone:

[0134] The mixture was prepared according to the following formula: the molar ratio of peroxypropionic acid to cyclohexanone in anhydrous peroxypropionic acid product A8 was 1.05:1, and the molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) in anhydrous peroxypropionic acid product A8 was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and mechanical stirring was started. Anhydrous peroxypropionic acid product A8 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was greater than 98.2%, and the selectivity of caprolactone was higher than 9%. 0.8%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by means of reduced pressure. The top temperature of the light component removal column is 30°C and the top pressure is 3 kPaA. The bottom of the column yields crude caprolactone product without light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by means of reduced pressure distillation. The top temperature of the heavy component removal column is 78°C and the pressure is 1.5 kPaA. The yield of caprolactone is 87.5% by weight.

[0135] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxypropionic acid were 74.5%, 75.6%, 75.4%, 76.1%, and 76.4%, respectively, indicating that the activity of the catalyst did not decrease.

[0136] Example 9

[0137] Anhydrous peroxy acid and caprolactone were prepared according to the method of Example 1, except that the residence time of the evaporation process in step (2) was 2000 s. The specific process is as follows:

[0138] Preparation process of anhydrous peroxy acid products:

[0139] (1) Weigh 1500g of ethyl propionate, 1500g of propionic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor (i.e., a reaction vessel). Weigh 5g of heteropoly acid (phosphotungstic acid, boiling point above 380℃) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1 hour to obtain hydrous peroxypropionic acid. Analysis showed that the concentration of peroxypropionic acid was 10% by weight, and the selectivity of the reaction was 100%. Then, the hydrous peroxypropionic acid... Perpropionic acid was transferred to a distillation column with an absolute pressure of 15 kPa, a bottom temperature of 60°C, and a top temperature of 30°C. Ethyl propionate and water formed an azeotrope, which entered the top condenser. The condensed material was an oil-water two-phase mixture. Ethyl propionate was completely refluxed as the oil phase, while the water phase was completely collected. The residence time of the reaction was 1.5 h. The perpropionic acid phase was collected from the bottom of the column. The conversion rate of hydrogen peroxide was calculated to be 100%, and the water content in the perpropionic acid phase was 0.08% by weight. Based on the material balance, the yield of perpropionic acid was 95.5%.

[0140] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa absolute, and the residence time of the material during the evaporation process was 2000 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the gaseous peroxypropionic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied and collected as anhydrous peroxypropionic acid product A9. Analysis showed that the anhydrous peroxypropionic acid product A9 contained 5 ppm of catalyst, 0.1 wt% water, and 21.5 wt% peroxypropionic acid.

[0141] Preparation process of caprolactone:

[0142] The mixture was prepared according to the following formula: the molar ratio of peroxypropionic acid to cyclohexanone in anhydrous peroxypropionic acid product A9 was 1.05:1, and the molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) in anhydrous peroxypropionic acid product A9 was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and mechanical stirring was started. Anhydrous peroxypropionic acid product A9 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.1%, and the selectivity for caprolactone was 99%. 0.2%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by means of reduced pressure. The top temperature of the light component removal column is 30°C and the top pressure is 3 kPaA. The bottom of the column yields crude caprolactone product without light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by means of reduced pressure distillation. The top temperature of the heavy component removal column is 78°C and the pressure is 1.5 kPaA. The yield of caprolactone is 90.3% by weight.

[0143] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxypropionic acid were 95.5%, 94.5%, 95.2%, 94.8%, and 95.2%, respectively, indicating that the activity of the catalyst did not decrease.

[0144] Example 10

[0145] Anhydrous peroxy acid and caprolactone were prepared according to the method in Example 1, except that the evaporation temperature was controlled at 85°C and the evaporation pressure at 3 kPa. The specific process is as follows:

[0146] Preparation process of anhydrous peroxy acid products:

[0147] (1) Weigh 1500g of ethyl propionate, 1500g of propionic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor (i.e., a reaction vessel). Weigh 5g of heteropoly acid (phosphotungstic acid, boiling point above 380℃) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1 hour to obtain hydrous peroxypropionic acid. Analysis showed that the concentration of peroxypropionic acid was 10% by weight, and the selectivity of the reaction was 100%. Then, the hydrous peroxypropionic acid... Perpropionic acid was transferred to a distillation column with an absolute pressure of 15 kPa, a bottom temperature of 60°C, and a top temperature of 30°C. Ethyl propionate and water formed an azeotrope, which entered the top condenser. The condensed material was an oil-water two-phase mixture. Ethyl propionate was refluxed as the oil phase, and the water phase was completely collected. The residence time of the reaction was 1.5 h. The perpropionic acid phase was collected from the bottom of the column. The conversion rate of hydrogen peroxide was calculated to be 100%, and the water content in the perpropionic acid phase was 0.07% by weight. Based on the material balance, the yield of perpropionic acid was 95.5%.

[0148] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 90°C, the evaporation pressure at 30 kPa absolute, and the evaporation time at 1200 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the gaseous peroxypropionic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied to collect anhydrous peroxypropionic acid product A1. Analysis showed that the anhydrous peroxypropionic acid product A1 contained 6 ppm of catalyst, 0.1 wt% water, and 22.5 wt% peroxypropionic acid.

[0149] Preparation process of caprolactone:

[0150] The mixture was prepared according to the following formula: the molar ratio of peroxypropionic acid to cyclohexanone in anhydrous peroxypropionic acid product A1 was 1.05:1, and the molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) in anhydrous peroxypropionic acid product A1 was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and mechanical stirring was started. Anhydrous peroxypropionic acid product A1 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone to carry out the oxidation reaction. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.3%, and the selectivity for caprolactone was 95%. 0.0%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by means of reduced pressure. The top temperature of the light component removal column is 30°C and the top pressure is 3 kPaA. The bottom of the column yields crude caprolactone product without light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by means of reduced pressure distillation. The top temperature of the heavy component removal column is 78°C and the pressure is 1.5 kPaA. The yield of caprolactone is 92.3% by weight.

[0151] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxypropionic acid were 95.5%, 94.5%, 95.4%, 94.8%, and 95.6%, respectively, indicating that the activity of the catalyst did not decrease.

[0152] Example 11

[0153] In this embodiment, the synthesis of peroxypropionic acid did not involve a pre-reaction.

[0154] Preparation process of anhydrous peroxy acid products:

[0155] (1) Weigh 1500g of ethyl propionate, 1500g of propionic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor. Weigh 5g of heteropoly acid (phosphotungstic acid) as a catalyst and add it to the distillation column. The absolute pressure is 15kPa, the bottom temperature is 60℃, and the top temperature is 30℃. Ethyl propionate and water form an azeotrope and enter the top condenser. The condensed material is in the form of an oil-water two-phase mixture. Ethyl propionate is completely refluxed as the oil phase, and the water phase is completely collected. The residence time of the reaction is 4h. The peroxypropionic acid phase is collected from the bottom of the column. The conversion rate of hydrogen peroxide is calculated to be 99.5%, and the water content in the peroxypropionic acid phase is 0.12% by weight. According to the material balance, the yield of peroxypropionic acid is 88.7%.

[0156] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa, and the residence time of the material during the evaporation process was 120 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the peroxypropionic acid product was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and then liquefied to collect the anhydrous peroxypropionic acid product A11. Analysis showed that the anhydrous peroxypropionic acid product A11 contained 6 ppm of catalyst, 0.1 wt% water, and 29.2 wt% peroxypropionic acid.

[0157] Preparation process of caprolactone:

[0158] The mixture was prepared according to the following formula: the molar ratio of peroxypropionic acid to cyclohexanone in anhydrous peroxypropionic acid product A11 was 1.05:1, and the molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) in anhydrous peroxypropionic acid product A11 was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and mechanical stirring was started. Anhydrous peroxypropionic acid product A11 and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone for oxidation. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.3%, and the selectivity for caprolactone was 9%. 6.5%; then the product obtained from the oxidation reaction is subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by means of reduced pressure. The top temperature of the light component removal column is 30°C and the top pressure is 3 kPaA. The bottom of the column yields crude caprolactone product without light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by means of reduced pressure distillation. The top temperature of the heavy component removal column is 78°C and the pressure is 1.5 kPaA. The yield of caprolactone is 94.8% by weight.

[0159] In this embodiment, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid product five times according to the same process. The yields of peroxypropionic acid were 86.7%, 88.6%, 87.2%, 87.6%, and 88.5%, respectively, indicating that the activity of the catalyst did not decrease.

[0160] Comparative Example 1

[0161] Anhydrous peroxy acid and caprolactone were prepared according to the method of Example 1, except that step (2) was omitted, while all other operations were the same as in Example 1. The specific process is as follows:

[0162] Preparation process of anhydrous peroxy acid products:

[0163] (1) Weigh 1500g of ethyl propionate, 1500g of propionic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor. Weigh 5g of heteropoly acid (phosphotungstic acid) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1h to obtain hydrous peroxypropionic acid. Analysis showed that the concentration of peroxypropionic acid was 10% by weight, and the selectivity of the reaction was 100%. Then, transfer the hydrous peroxypropionic acid to a distillation column. Set the absolute pressure to 15kPa, the bottom temperature to 60℃, and the column temperature to 60℃. At a top temperature of 30℃, ethyl propionate and water form an azeotrope that enters the top condenser of the column. The condensed material is an oil-water two-phase mixture. Ethyl propionate is completely refluxed as the oil phase, while the water phase is completely collected. The residence time of the reaction is 1.5 hours. The peroxypropionic acid phase is collected from the bottom of the column, and anhydrous peroxypropionic acid product D1 is collected. It is calculated that the conversion rate of hydrogen peroxide is 100%, the water content in the peroxypropionic acid phase is 0.08 wt%, the catalyst content is 4500 ppm, and the concentration of peroxypropionic acid is 31 wt%. Based on material balance, the yield of peroxypropionic acid is 95.5%.

[0164] Preparation process of caprolactone:

[0165] The peroxypropionic acid to cyclohexanone molar ratio in the peroxypropionic acid phase was 1.05:1, and the catalyst to nitrogen-containing basic compound (pyrrole) molar ratio in the peroxypropionic acid phase was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃ and mechanical stirring was started. Anhydrous peroxypropionic acid product A1 and nitrogen-containing basic compound were slowly added dropwise to cyclohexanone to carry out the oxidation reaction. The addition was completed in 0.5h, and then the mixture was allowed to stand for another 2h. Analysis showed that the conversion rate of cyclohexanone was 99.0%, and the selectivity of caprolactone was 65.2%. The product obtained from the oxidation reaction is then subjected to distillation. The distillation process includes separating the light components with boiling points lower than caprolactone from the top of the column by reducing pressure. The top temperature of the light component removal column is 30°C, and the top pressure is 3 kPaA. The bottom of the column yields crude caprolactone product free of light components. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by reducing pressure distillation. The top of the column yields purified caprolactone product. The top temperature of the heavy component removal column is 95°C, and the pressure is 1.5 kPaA. The yield of caprolactone is 32.0%.

[0166] In this comparative example, the catalyst taken from the bottom of the evaporator was used to prepare anhydrous peroxy acid five times according to the same process. The yields of peroxypropionic acid were 95.0%, 94.8%, 95.8%, 94.9%, and 95.0%, respectively, indicating that the activity of the catalyst did not decrease.

[0167] Comparative Example 2

[0168] Anhydrous peroxy acid and caprolactone were prepared according to the method in Example 1, except that a heterogeneous acid catalyst (bissulfonic acid-based polystyrene resin) was used instead of the heteropoly acid (phosphotungstic acid). The specific process is as follows:

[0169] Preparation process of anhydrous peroxy acid products:

[0170] (1) Weigh 1500g of ethyl propionate, 1500g of propionic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor. Weigh 5g of disulfonic acid-based polystyrene resin as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1 hour to obtain hydrous peroxypropionic acid. Analysis showed that the concentration of peroxypropionic acid was 12% by weight and the selectivity of the reaction was 100%. Then, transfer the hydrous peroxypropionic acid to... In the distillation column, the absolute pressure is 15 kPa, the bottom temperature is 60℃, and the top temperature is 30℃. Ethyl propionate and water form an azeotrope and enter the top condenser. The condensed material is an oil-water two-phase mixture. Ethyl propionate is completely refluxed as the oil phase, and the water phase is completely collected. The residence time of the reaction is 1.5 h. The peroxypropionic acid phase is collected from the bottom. It is calculated that the conversion rate of hydrogen peroxide is 100%, and the water content in the peroxypropionic acid phase is 0.08% by weight. According to the material balance, the yield of peroxypropionic acid is 94.5%.

[0171] (2) Since the above catalyst is a heterogeneous catalyst, it can be directly used for the preparation of caprolactone after filtration and separation. The preparation process of caprolactone is as follows:

[0172] The anhydrous peroxypropionic acid product was prepared with a molar ratio of peroxypropionic acid to cyclohexanone of 1.05:1. 50g of cyclohexanone was weighed and placed in a batch reactor, heated to 50℃, and mechanical stirring was started. Anhydrous peroxypropionic acid was slowly added dropwise to the cyclohexanone over 0.5 hours, followed by a 2-hour settling period. Analysis showed a cyclohexanone conversion rate of 95.2% and a caprolactone selectivity of 83.4%. The product obtained from the oxidation reaction was then subjected to distillation. The distillation process included separating the lighter components (boiling points lower than caprolactone) from the top of the distillation column under reduced pressure. The top temperature of the light component removal column was 30℃, and the top pressure was 3 kPaA. Crude caprolactone product without light components was obtained from the bottom of the column. The heavier components (boiling points higher than caprolactone) were separated from the bottom of the distillation column under reduced pressure. Refined caprolactone product was obtained from the top of the column. The top temperature of the heavy component removal column was 95℃, and the pressure was 1.5 kPaA. The caprolactone yield was 78.0%.

[0173] After filtering and separating the catalyst in this comparative example, it was found that the catalyst morphology showed obvious swelling. Following the same process, the anhydrous peroxy acid product was prepared a second time, and the yield of peroxypropionic acid decreased to 71.2%. After separation again, the anhydrous peroxy acid product was prepared a third time, and the peroxy acid yield decreased to 45.5%.

[0174] Comparative Example 3

[0175] Anhydrous peroxy acid and caprolactone were prepared according to the method in Example 1, except that after the pre-reaction, the catalyst was separated in step (2) and then dehydrated in a reactive distillation column. The specific process is as follows:

[0176] Preparation process of anhydrous peroxy acid products:

[0177] (1) Weigh 1500g of ethyl propionate, 1500g of propionic acid, and 1000g of hydrogen peroxide (50wt%) and place them in a batch reactor (i.e., a reaction vessel). Weigh 5g of heteropoly acid (phosphotungstic acid, with a boiling point higher than 380℃ in the following peroxypropionic acid phase) as a catalyst and add it to the reactor for pre-reaction. Set the heating temperature to 65℃ and the pressure to atmospheric pressure (100kPa). React for 1h to obtain an aqueous solution of peroxypropionic acid. After analysis, the concentration of peroxypropionic acid is 10% by weight and the selectivity of the reaction is 100%.

[0178] (2) The prepared peroxypropionic acid aqueous solution was vaporized and separated using a falling film evaporator. The evaporation temperature was controlled at 70°C, the evaporation pressure at 6 kPa absolute, and the residence time of the material during the evaporation process was 120 s. The enriched high-concentration catalyst solution was collected from the bottom of the evaporator; the vapor-phase aqueous peroxypropionic acid was collected from the top and entered a condenser heat exchanger to cool the product to 0°C, and the aqueous peroxypropionic acid product was liquefied and collected. Analysis showed that the aqueous peroxypropionic acid product contained 6 ppm of catalyst, 11.2 wt% water, and 10.5 wt% peroxypropionic acid.

[0179] (3) The aqueous peroxypropionic acid product was transferred to a distillation column with an absolute pressure of 15 kPa, a bottom temperature of 60°C, and a top temperature of 30°C. Ethyl propionate and water formed an azeotrope and entered the top condenser. The condensed material was in the form of an oil-water two-phase mixture. Ethyl propionate was refluxed as the oil phase, and the aqueous phase was completely collected. The residence time of the reaction was 20 h. The anhydrous peroxypropionic acid product was collected from the bottom of the column. The hydrogen peroxide conversion rate was calculated to be 81.6%. The hydrogen peroxide content in the anhydrous peroxypropionic acid product was 2.3 wt%, the peroxypropionic acid concentration was 24.6 wt%, and the water content was 0.08 wt%. According to the material balance, the yield of peroxypropionic acid was 73.2%.

[0180] Preparation process of caprolactone:

[0181] The anhydrous peroxypropionic acid product was prepared with a peroxypropionic acid to cyclohexanone molar ratio of 1.05:1 and a catalyst to nitrogen-containing basic compound (pyrrole) molar ratio of 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50°C, and mechanical stirring was started. The anhydrous peroxypropionic acid product and the nitrogen-containing basic compound were slowly added dropwise to the cyclohexanone to initiate the oxidation reaction. The addition was completed in 0.5 hours, followed by a 2-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 98.6%, the selectivity for caprolactone was 68.1%, and the selectivity for hydroxyhexanoic acid was 18.6%. The selectivity for caprolactone oligomers was 12.1%. The product obtained from the oxidation reaction was then subjected to distillation. The distillation process included separating the light components with boiling points lower than caprolactone from the top of the column under reduced pressure. The top temperature of the light component removal column was 30°C, and the top pressure was 3 kPaA. Crude caprolactone product without light components was obtained from the bottom of the column. The heavy components with boiling points higher than caprolactone were then separated from the bottom of the column under reduced pressure, yielding purified caprolactone product from the top of the column. The top temperature of the heavy component removal column was 95°C, and the pressure was 1.5 kPaA. The yield of caprolactone was 58.4%.

[0182] As can be seen from the embodiments and comparative examples of the present invention, the method described in the present invention for preparing anhydrous peroxyacid products and caprolactone not only has high conversion rates of hydrogen peroxide and high yields of peroxypropionic acid, but also low catalyst and water content in the anhydrous peroxyacid products. Furthermore, even after subsequent reuse of the catalyst, the peroxyacid yield can still be maintained at a high level. When the anhydrous peroxyacid products prepared by the method described in the present invention are used to prepare caprolactone, the conversion rates of cyclohexanone and the yields of caprolactone are high.

[0183] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing caprolactone, characterized in that, The method includes the following steps: (1) In the presence of a homogeneous acid catalyst, hydrogen peroxide is reacted with an organic acid, and the resulting reaction product is dehydrated to obtain a peroxyacid phase containing a homogeneous acid catalyst. (2) Remove the homogeneous acidic catalyst from the peroxy acid phase to obtain anhydrous peroxy acid product; (3) The anhydrous peroxy acid product is subjected to an oxidation reaction with cyclohexanone.

2. The method according to claim 1, characterized in that, In step (1), the dehydration conditions are such that the water content in the peroxyacid phase is less than 0.2% by weight.

3. The method according to claim 1 or 2, characterized in that, The homogeneous acidic catalyst is selected from at least one of sulfuric acid, nitric acid, heteropolyacids, and isopolyacids.

4. The method according to any one of claims 1-3, characterized in that, The organic acid is at least one selected from formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and benzoic acid, preferably at least one selected from acetic acid, propionic acid, and butyric acid.

5. The method according to any one of claims 1-4, characterized in that, In step (1), the reaction is carried out in the presence of a solvent, which is an organic compound that can form an azeotrope with water and can form an oil-water two-phase mixture with water after cooling; Preferably, the solvent is selected from at least one of propyl formate, butyl formate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, dioxane, acetonitrile, and cyclohexane.

6. The method according to claim 5, characterized in that, In step (1), based on a total amount of 100 parts by weight of the homogeneous acidic catalyst, the hydrogen peroxide, the organic acid, and the solvent, the amount of the homogeneous acidic catalyst is 0.01-15 parts by weight, the amount of the hydrogen peroxide is 5-70 parts by weight, the amount of the organic acid is 5-70 parts by weight, and the amount of the solvent is 5-70 parts by weight.

7. The method according to any one of claims 1-6, characterized in that, In step (1), the reaction is carried out in a reactive distillation column; Preferably, the reaction conditions include: a bottom temperature of 40-65°C, a top temperature of 25-40°C, and a pressure of 1-15 kPa.

8. The method according to any one of claims 1-6, characterized in that, In step (1), the reaction process includes a pre-reaction and a main reaction carried out sequentially, wherein the pre-reaction is carried out in at least one of a microchannel reactor, a fixed-bed reactor, a batch reactor, a static mixing reactor, and a membrane reactor, and the main reaction is carried out in a reactive distillation column; Preferably, the pre-reaction conditions include: a temperature of 40-65°C, a pressure of 80 kPa-1 MPa, and a time of 1-5 hours; Preferably, the conditions for the main reaction include: a bottom temperature of 40-65°C, a top temperature of 27-40°C, and a pressure of 1-15 kPa.

9. The method according to any one of claims 1-8, characterized in that, In step (2), the homogeneous acidic catalyst is removed by evaporation; Preferably, the evaporation process is carried out in a falling film evaporator; Preferably, the evaporation temperature is higher than the boiling point of the peroxy acid and lower than the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system.

10. The method according to claim 1, characterized in that, In the anhydrous peroxy acid product obtained in step (2), the content of homogeneous acidic catalyst is ≤50ppm, the water content is ≤0.2% by weight, and the concentration of peroxy acid is 5-50% by weight.

11. The method according to claim 1 or 10, characterized in that, In step (3), the molar ratio of cyclohexanone to peroxy acid in the anhydrous peroxy acid product is 1:1-1.

5.

12. The method according to claim 1, 10, or 11, characterized in that, In step (3), the conditions for the oxidation reaction include: a temperature of 30-80°C and a time of 1-8 hours.

13. The method according to any one of claims 1 and 10-12, characterized in that, In step (3), the oxidation reaction is carried out in the presence of a nitrogen-containing basic compound, wherein the N atom of the nitrogen-containing basic compound has a lone pair of electrons; Preferably, the nitrogen-containing basic compound is selected from at least one of methylamine, ethylamine, triethylamine, trimethylamine, ethylenediamine, urea, ethanolamine, isopropylamine, tert-butylamine, aniline, benzylamine, cyclohexylamine, dicyclohexylamine, pyridine, dimethylpyridine, pyrrole, indole, acridine, carbazole, and quinoline.

14. The method according to claim 13, characterized in that, The molar ratio of the homogeneous acidic catalyst to the nitrogen-containing basic compound in the anhydrous peroxy acid product is 1:1-30, preferably 1:3-10.

15. The method according to any one of claims 1-14, characterized in that, The method further includes: refining the crude caprolactone product obtained from the oxidation reaction by distillation.

16. A method for preparing anhydrous peroxyacid product, characterized in that, The method includes the following steps: (1) In the presence of a homogeneous acid catalyst, hydrogen peroxide is reacted with an organic acid, and the resulting reaction product is dehydrated to obtain a peroxyacid phase containing a homogeneous acid catalyst. (2) Remove the homogeneous acid catalyst from the peroxy acid phase.

17. The method according to claim 16, characterized in that, In step (1), the dehydration conditions are such that the water content in the peroxyacid phase is less than 0.2% by weight.

18. The method according to claim 16 or 17, characterized in that, The homogeneous acidic catalyst is selected from at least one of sulfuric acid, nitric acid, heteropolyacids, and isopolyacids.

19. The method according to any one of claims 16-18, characterized in that, The organic acid is at least one selected from formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and benzoic acid, preferably at least one selected from acetic acid, propionic acid, and butyric acid.

20. The method according to any one of claims 16-19, characterized in that, In step (1), the reaction is carried out in the presence of a solvent, which is an organic compound that can form an azeotrope with water and can form an oil-water two-phase mixture with water after cooling; Preferably, the solvent is selected from at least one of propyl formate, butyl formate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, dioxane, acetonitrile, and cyclohexane.

21. The method according to claim 20, characterized in that, Based on a total weight of 100 parts by weight of the homogeneous acidic catalyst, the hydrogen peroxide, the organic acid, and the solvent, the amount of the homogeneous acidic catalyst is 0.01-15 parts by weight, the amount of the hydrogen peroxide is 5-70 parts by weight, the amount of the organic acid is 5-70 parts by weight, and the amount of the solvent is 5-70 parts by weight.

22. The method according to any one of claims 16-21, characterized in that, In step (1), the reaction is carried out in a reactive distillation column; Preferably, the reaction conditions include: a bottom temperature of 40-65°C, a top temperature of 25-40°C, and a pressure of 1-15 kPa.

23. The method according to any one of claims 16-21, characterized in that, In step (1), the reaction process includes a pre-reaction and a main reaction carried out sequentially, wherein the pre-reaction is carried out in at least one of a microchannel reactor, a fixed-bed reactor, a batch reactor, a static mixing reactor, and a membrane reactor, and the main reaction is carried out in a reactive distillation column; Preferably, the pre-reaction conditions include: a temperature of 40-65°C, a pressure of 80 kPa-1 MPa, and a time of 1-5 hours; Preferably, the reaction conditions include: a bottom temperature of 40-65°C, a top temperature of 27-40°C, and a pressure of 1-15 kPa.

24. The method according to any one of claims 16-23, characterized in that, In step (2), the homogeneous acidic catalyst is removed by evaporation; Preferably, the evaporation process is carried out in a falling film evaporator; Preferably, the evaporation temperature is higher than the boiling point of the peroxy acid and lower than the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system.