Process for the preparation of anhydrous peroxy acid product and process for the preparation of caprolactone

Abstract

The present application relates to the chemical technology field, disclose a kind of preparation method of anhydrous peroxy acid product and the preparation method of caprolactone.The preparation method of anhydrous peroxy acid product includes the following steps: (1) in the presence of homogeneous acidic catalyst, hydrogen peroxide is reacted with organic acid, then the reaction product is divided into water phase and peroxy acid phase;(2) the homogeneous acidic catalyst in the peroxy acid phase is removed.The preparation method of caprolactone includes: the anhydrous peroxy acid product is oxidized with cyclohexanone.The method can catalyze the synthesis of peroxy acid with homogeneous acidic catalyst, can keep high synthesis efficiency of peroxy acid, and by removing homogeneous acidic catalyst from peroxy acid product, the refined anhydrous oxygen acid product is used for oxidizing cyclohexanone to prepare caprolactone, which can improve the selectivity and yield of caprolactone.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a method for preparing anhydrous peroxyacid products and a method for preparing caprolactone. Background Technology

[0002] Organic peroxy acids are high-performance oxidants with stronger oxidizing power than hydrogen peroxide. In daily life, they are used as highly efficient disinfectants and sterilizers, and can also be used as bleaching agents for textiles, paper, paraffin, and oils. In industry, they are mainly used as highly selective oxidants to oxidize cyclohexanone to produce caprolactone.

[0003] 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.

[0004] To avoid the influence of the strong acid center of the homogeneous catalyst on the downstream synthesis of caprolactone, existing technologies mostly use weak acid catalysts for the preparation of anhydrous peroxy acids.

[0005] CN1034500C discloses a method for synthesizing peroxypropionic acid using boric acid as a catalyst. Boric acid is a weak acid and has a weak impact on the synthesis of caprolactone downstream, so it will not produce too many side reactions. However, the weak acidity of boric acid will limit the synthesis efficiency of peroxy acid and significantly increase the reaction residence time.

[0006] CN103570667A discloses a continuous method for preparing caprolactone. Boric acid is used as a catalyst and hydrogen peroxide as an oxidant. Organic carboxylic acids are continuously oxidized in multiple reactive distillation columns to obtain peroxyacid. The peroxyacid is then continuously introduced into multiple stirred tanks connected in series to react and obtain a caprolactone solution. Boric acid is a weak acid and has little effect on the polymerization of caprolactone, but its catalytic efficiency for peroxyacid synthesis is low. The series connection of multiple reactive distillation columns increases energy consumption and 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 the use of weakly acidic catalysts to prepare anhydrous peroxy acids limits the synthesis efficiency of peroxy acids; and where the use of strongly acidic catalysts to prepare anhydrous peroxy acids results in side reactions caused by residual strongly acidic catalysts in the peroxy acids when used for the oxidation of cyclohexanone to caprolactone, reducing the selectivity of the oxidation reaction and the product yield. This invention provides a method for preparing anhydrous peroxy acid products and a method for preparing caprolactone. The method of this invention uses a homogeneous acidic catalyst to catalyze the synthesis of peroxy acids, maintaining a high synthesis efficiency. Subsequently, by removing the homogeneous acidic catalyst from the peroxy acid product, a purified anhydrous peroxy acid product is obtained. When this product is used for the oxidation of cyclohexanone to caprolactone, the selectivity of the oxidation reaction and the caprolactone yield can be improved.

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

[0009] (1) In the presence of a homogeneous acidic catalyst, hydrogen peroxide is reacted with an organic acid, and then the reaction products are separated into an aqueous phase and a peroxyacid phase.

[0010] (2) Remove the homogeneous acid catalyst from the peroxy acid phase.

[0011] Preferably, in step (1), the water content in the peroxyacid phase is less than 0.2% by weight.

[0012] Preferably, the homogeneous acidic catalyst is capable of releasing H₂. + Protic acids.

[0013] Preferably, the acidity coefficient pKa of the homogeneous acid catalyst is -4 to 8, and more preferably -3 to 5;

[0014] More preferably, the homogeneous acidic catalyst is selected from at least one of sulfuric acid, nitric acid, heteropolyacids, and isopolyacids.

[0015] More preferably, the heteropolyacid is selected from one or more of phosphomolybdic acid, phosphotungstic acid, and silicotungstic acid.

[0016] More preferably, the isopolyacid is selected from one or more of decatungstic acid, heptatungstic acid, octamolybdic acid, and dodecamolybdic acid.

[0017] Preferably, the organic acid is an aliphatic carboxylic acid and / or an aromatic carboxylic acid.

[0018] Preferably, the organic acid is a C1-C10 carboxylic acid.

[0019] 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.

[0020] Preferably, 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.

[0021] 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.

[0022] Preferably, 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.

[0023] Preferably, in step (1), the reaction is carried out in a reactive distillation column.

[0024] More preferably, the reaction conditions include: a bottom temperature of 35-85°C, a top temperature of 20-40°C, a pressure of 1 kPa-0.5 MPa, and a time of 1-5 hours.

[0025] Preferably, 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 reactor selected from 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.

[0026] Preferably, the pre-reaction conditions include: a temperature of 35-80°C, a pressure of 10 kPa-1 MPa, and a time of 0.5-5 hours.

[0027] Preferably, the conditions for the main reaction include: a bottom temperature of 35-85°C, a top temperature of 20-40°C, a pressure of 1 kPa-0.5 MPa, and a time of 1-5 hours.

[0028] Preferably, in step (2), the homogeneous acidic catalyst is removed by evaporation.

[0029] Preferably, when the homogeneous acidic catalyst in the peroxy acid phase is removed, the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system is higher than the boiling point of the peroxy acid.

[0030] Preferably, when the homogeneous acidic catalyst in the peroxy acid phase is removed, the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system is more than 40°C higher than the boiling point of the peroxy acid.

[0031] Preferably, when removing the homogeneous acidic catalyst from the peroxyacid phase, the evaporation temperature is at least 10°C lower than the boiling point of the homogeneous acidic catalyst in the peroxyacid phase system.

[0032] Preferably, in step (2), the evaporation temperature is 10-130℃, more preferably 20-85℃; the evaporation pressure is 0.5-90kPa, more preferably 1-25kPa; and the evaporation residence time is 1-3600s, more preferably 5-1200s.

[0033] A second aspect of the present invention provides a method for preparing caprolactone, the method comprising: preparing an anhydrous peroxy acid product according to the method described above, and then subjecting the anhydrous peroxy acid product to an oxidation reaction with cyclohexanone.

[0034] Preferably, in the anhydrous peroxy acid product, 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.

[0035] Preferably, the molar ratio of cyclohexanone to peroxy acid in the anhydrous peroxy acid product is 1:1-1.5.

[0036] Preferably, the conditions for the oxidation reaction include: a temperature of 30-80°C and a time of 1-8 hours.

[0037] Preferably, 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.

[0038] Preferably, the nitrogen-containing basic compound is selected from one or more of methylamine, ethylamine, triethylamine, trimethylamine, ethylenediamine, urea, ethanolamine, isopropylamine, tert-butylamine, aniline, benzylamine, cyclohexylamine, dicyclohexylamine, pyridine, dimethylpyridine, pyrrole, indole, acridine, carbazole and quinoline.

[0039] Preferably, the molar ratio of the homogeneous acidic catalyst to the nitrogen-containing basic compound in the anhydrous peroxy acid product is 1:1-30, more preferably 1:3-10.

[0040] Preferably, the method further includes: refining the crude caprolactone product obtained from the oxidation reaction by distillation.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] (1) In the preparation method of the anhydrous peroxy acid product of the present invention, on the one hand, the use of a homogeneous acidic catalyst to catalyze the synthesis of peroxy acid can avoid problems such as catalyst swelling, loss and deactivation of active components. The catalyst separated from the product can still maintain stable catalytic activity and peroxy acid yield when reused subsequently. On the other hand, the present invention efficiently separates the acidic catalyst in the synthesized crude anhydrous peroxy acid product (peroxy acid phase), and the refined anhydrous peroxy acid product obtained contains only trace amounts of acidic catalyst. Even if the residual catalyst is a strong acid, it can reduce the influence of the strong acid center of the catalyst on the synthesis of caprolactone and improve the synthesis process of caprolactone. Thirdly, in the existing technology for preparing peroxyacid products, the catalyst is removed first, followed by water removal. This sequential operation easily leads to reverse reactions, resulting in a large amount of hydrogen peroxide in the final peroxyacid product. Hydrogen peroxide causes a ring-opening reaction of caprolactone, yielding a large amount of hydroxyhexanoic acid. Simultaneously, hydrogen peroxide undergoes a condensation reaction with cyclohexanone, thus affecting the yield and purity of caprolactone. The method described in this invention, following a specific sequence, first obtains anhydrous peroxyacid products and then removes the catalyst, reducing the occurrence of reverse reactions and thereby improving the yield and purity of caprolactone. In summary, this method not only improves the synthesis efficiency of peroxyacid but also, when the refined anhydrous peroxyacid product is used to oxidize cyclohexanone to produce caprolactone, it exhibits excellent cyclohexanone conversion and caprolactone selectivity. Furthermore, the high-temperature environment in the distillation column during subsequent purification of caprolactone minimizes the risk of condensation side reactions, further improving the overall yield of the caprolactone product.

[0043] (2) In the method for preparing caprolactone described in this invention, the anhydrous peroxy acid product prepared by the aforementioned method is used as an oxidant to prepare caprolactone, which can improve the yield of caprolactone while having a high cyclohexanone conversion rate and caprolactone selectivity.

[0044] In a preferred embodiment, the addition of a specific nitrogen-containing basic compound during the preparation of caprolactone can further eliminate the influence of residual acidic catalyst in anhydrous peroxy acid products on the preparation of caprolactone, thereby further improving the selectivity and yield of caprolactone. Detailed Implementation

[0045] 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.

[0046] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0047] The method for preparing anhydrous peroxyacid products provided by this invention includes the following steps:

[0048] (1) In the presence of a homogeneous acidic catalyst, hydrogen peroxide is reacted with an organic acid, and then the reaction products are separated into an aqueous phase and a peroxyacid phase.

[0049] (2) Remove the homogeneous acid catalyst from the peroxy acid phase.

[0050] In the anhydrous peroxy acid product preparation method of this invention, compared with heterogeneous catalysts such as solid acidic resins, the use of homogeneous acidic catalysts to synthesize peroxy acid can avoid catalyst swelling and loss of active components. However, after the reaction, the homogeneous acidic catalyst remains in the peroxy acid product. When the residual homogeneous acidic catalyst is used to oxidize cyclohexanone to prepare caprolactone, it can easily cause side reactions, reducing the selectivity and yield of caprolactone. The inventors accidentally discovered that a certain method can be used to remove the homogeneous acidic catalyst from the peroxy acid product, thereby reducing the amount of homogeneous acidic catalyst in the peroxy acid product. The inventors found that in a preferred embodiment, by limiting the decomposition temperature and evaporation temperature difference of the peroxy acid based on the boiling point difference between the liquid homogeneous acidic catalyst and the peroxy acid, the homogeneous acidic catalyst can be removed by evaporation, which can better separate the homogeneous acidic catalyst from the peroxy acid. The separated catalyst can be reused subsequently, and the catalyst activity and peroxy acid yield can still be stably maintained at a high level. Furthermore, removing the catalyst from the peroxy acid product first, followed by water removal, can easily lead to a reverse reaction, resulting in a large amount of hydrogen peroxide in the final peroxy acid product. Hydrogen peroxide can cause caprolactone to undergo a ring-opening reaction, yielding a large amount of hydroxyhexanoic acid. Simultaneously, hydrogen peroxide can undergo a condensation reaction with cyclohexanone, thus affecting the yield and purity of caprolactone. However, the method described in this invention, which follows a specific order to first obtain anhydrous peroxy acid product and then remove the catalyst from the peroxy acid product, can reduce the occurrence of reverse reactions, thereby improving the yield and purity of caprolactone.

[0051] In the method described in this invention, step (1) is the step of synthesizing a peroxyacid product from an organic acid and hydrogen peroxide under the action of a homogeneous acidic catalyst, and then separating it into an aqueous phase and a peroxyacid phase. In this invention, the reaction in step (1) is 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, can form an oil-water two-phase mixture with water; using this solvent facilitates solvent separation and recovery, and facilitates the separation of the peroxyacid product into an aqueous phase and a peroxyacid phase, thereby obtaining a peroxyacid phase with a lower water content. In some embodiments, the solvent may be 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.

[0052] In step (1), the homogeneous acidic catalyst can be a common catalyst in the art capable of releasing H2. + The homogeneous acid catalyst is a protic acid, wherein the acidity coefficient pKa of the homogeneous acid catalyst can be -4 to 8. To improve the synthesis efficiency of peroxyacid, 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. In some more preferred embodiments, the heteropolyacid is selected from one or more of phosphomolybdic acid, phosphotungstic acid, and silicotungstic acid. In other more preferred embodiments, the isopolyacid is 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 state or a 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 peroxyacid. 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.

[0053] In this invention, 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. In some embodiments, the organic acid is an aliphatic carboxylic acid and / or an aromatic carboxylic acid; preferably, the organic acid is a C1-C10 carboxylic acid. In a more preferred embodiment, the organic acid is at least one selected from formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and benzoic acid. In a further preferred embodiment, to further improve the separation effect between the homogeneous acidic catalyst and the peroxy acid, the organic acid is at least one selected from acetic acid, propionic acid, and butyric acid.

[0054] In the method described in this invention, the hydrogen peroxide is a conventional raw material with a concentration of 10-90% by weight, preferably 25-50% by weight.

[0055] In some embodiments, 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. To improve the yield of the prepared peroxyacid, in a preferred embodiment, 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.

[0056] In this invention, the reaction can be directly synthesized into anhydrous peroxy acid through reactive distillation; alternatively, a pre-reaction can be performed first, followed by reactive distillation in a reactive distillation column to obtain an aqueous phase and a peroxy acid phase. The reaction of hydrogen peroxide with organic acids to synthesize peroxy acid is an equilibrium reaction. The presence of water inhibits the reaction process. The reaction in the 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 peroxy acid phase. The peroxy acid phase has a low water content; in some embodiments, the water content is less than 0.2% by weight. In this invention, anhydrous peroxy acid 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.

[0057] In one embodiment, the reaction in step (1) is carried out in a reactive distillation column, meaning that only the main reaction occurs, without any pre-reaction. In this embodiment, the reaction conditions include: a bottom temperature of 35-85°C, a top temperature of 20-40°C, a pressure of 1 kPa-0.5 MPa, and a time of 1-5 hours.

[0058] In another embodiment, the reaction in step (1) includes a pre-reaction and a main reaction carried out sequentially, with the pre-reaction occurring first and the main reaction occurring later. 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; the main reaction is carried out in a reactive distillation column.

[0059] In this invention, to increase the reaction rate and prevent the decomposition of peroxyacid and hydrogen peroxide, the pre-reaction temperature is preferably 35-80°C. In some embodiments, the pre-reaction pressure is 10 kPa-1 MPa, preferably 50 kPa-0.5 MPa. In this invention, the pressure is absolute pressure. In other embodiments, the pre-reaction time is 0.5-5 hours.

[0060] In this invention, during the main reaction, the temperature of the bottom of the distillation column is 35-85°C, and the temperature of the top of the column is 20-40°C. In some embodiments, the pressure of the main reaction is 1 kPa-0.5 MPa, preferably 2 kPa-0.2 MPa. In other embodiments, the duration of the main reaction is 1-5 hours.

[0061] In the method described in this invention, there is no specific restriction on the order of feeding. Solvent, organic acid, hydrogen peroxide, and homogeneous acid 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. Preferably, hydrogen peroxide and solvent do not form a liquid-liquid two-phase feed.

[0062] The purpose of step (2) is mainly to separate the homogeneous acidic catalyst from the peroxy acid phase obtained in step (1). Through research, the inventors have found that, in the preferred embodiment, the homogeneous acidic catalyst can be removed by evaporation based on the boiling point difference between the homogeneous acidic catalyst and the peroxy acid in the system, which can better achieve the separation of the homogeneous acidic catalyst and the peroxy acid.

[0063] In this invention, to achieve the separation of homogeneous acidic catalyst and peroxy acid, 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 the peroxy acid. During the evaporation process, the peroxy acid with a 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 a higher boiling point in the system is collected as a residue. In some preferred embodiments, to improve the separation effect of the homogeneous acidic catalyst and peroxy acid and reduce the content of 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 the peroxy acid.

[0064] 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.

[0065] 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.

[0066] In this invention, the equipment used in step (2), which removes the homogeneous acidic catalyst by evaporation, can be any evaporation equipment commonly used in the art. In some embodiments, the evaporation equipment can be a circulating evaporator or a membrane evaporator. The circulating evaporator is selected from central circulating tube evaporators, rotary frame evaporators, externally heated evaporators, or forced circulation evaporators, etc., while the membrane evaporator is selected from rising film evaporators, falling film evaporators, rising-falling film evaporators, or scraped agitated evaporators, etc. In a more preferred embodiment, the evaporation equipment is preferably a membrane evaporator.

[0067] 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℃.

[0068] The anhydrous peroxy acid product prepared according to the aforementioned method can achieve a hydrogen peroxide conversion rate of over 99.5% and a peroxy acid yield of over 95%. Furthermore, the acid catalyst content can be ≤50 ppm, and the water content ≤0.2 wt%, resulting in an anhydrous peroxy acid product with a concentration of 5–50 wt%. The water removed from the anhydrous peroxy acid product includes water introduced by hydrogen peroxide and water generated during the reaction. Besides a small amount of acid catalyst and water, the anhydrous peroxy acid product also contains the raw material hydrogen peroxide and organic acids.

[0069] The present invention provides a method for preparing caprolactone, comprising: preparing an anhydrous peroxy acid product according to the method described above, and then subjecting the anhydrous peroxy acid product to an oxidation reaction with cyclohexanone. Using the anhydrous peroxy acid product prepared by the aforementioned method as an oxidant to prepare caprolactone can improve the yield of caprolactone while maintaining a high cyclohexanone conversion rate and caprolactone selectivity.

[0070] In some preferred embodiments, the anhydrous peroxy acid product prepared according to the method described above has a low water content and a low content of homogeneous acidic catalyst. In the anhydrous peroxy acid product, the content of homogeneous acidic catalyst is ≤50 ppm, the water content is ≤0.2 wt%, and the concentration of peroxy acid is 5-50 wt%. 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.

[0071] In some preferred embodiments, 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 can be 1:1-1.5.

[0072] In some preferred embodiments, to increase the reaction rate and avoid side reactions such as thermal decomposition of the raw material peroxyacid and polycondensation of caprolactone under high-temperature conditions, the oxidation reaction temperature is 30-80°C. In other embodiments, to increase the conversion rate and ensure that cyclohexanone is fully converted, the oxidation reaction time is 1-8 hours.

[0073] In the method described in this invention, the inventors discovered through research that, in order to further eliminate the influence of residual acidic catalyst in anhydrous peroxyacid products on the preparation of caprolactone and further improve the selectivity and yield of caprolactone, a specific nitrogen-containing basic compound can be added. In a preferred embodiment, the oxidation reaction is carried out in the presence of a nitrogen-containing basic compound, wherein the nitrogen atom of the nitrogen-containing basic compound has a lone pair of electrons.

[0074] In some embodiments, the nitrogen-containing basic compound may be selected from one or more of methylamine, ethylamine, triethylamine, trimethylamine, ethylenediamine, urea, ethanolamine, isopropylamine, tert-butylamine, aniline, benzylamine, cyclohexylamine, dicyclohexylamine, pyridine, dimethylpyridine, pyrrole, indole, acridine, carbazole, and quinoline. In some embodiments, 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.

[0075] In the method for preparing caprolactone according to the present invention, 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 cyclohexanone is completely added. The reactor can be a reactor commonly used in the art, such as a batch reactor. In a preferred embodiment, the anhydrous peroxy acid product can be added to the cyclohexanone in a slow dripping manner, with a dripping time of approximately 0.5 hours.

[0076] In this invention, the method for preparing caprolactone further includes: 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 one embodiment, the distillation 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 the 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, obtaining purified caprolactone product 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 the catalyst after salt formation. Using the anhydrous peroxy acid product prepared by the method of this invention as an oxidant to prepare caprolactone, the yield of caprolactone after distillation and purification is ≥95%.

[0077] 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.

[0078] 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.

[0079] In the following embodiments:

[0080] For the analysis methods of peroxides such as hydrogen peroxide and peroxyacid, refer to the national standard "Peracetic Acid Solution GB / T19104-2021";

[0081] For analytical methods of materials such as caprolactone and cyclohexanone, refer to the industry standard "Industrial ε-caprolactone HG / T5618-2019";

[0082] 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%;

[0083] 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%.

[0084] 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%;

[0085] 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%.

[0086] Example 1

[0087] Preparation process of anhydrous peroxy acid products:

[0088] (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., 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 80℃ 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. The absolute pressure was 15 kPa, the bottom temperature was 80°C, and the top temperature was 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, and the water 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%.

[0089] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0090] Preparation process of caprolactone:

[0091] 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 magnetic or mechanical stirring was started. Anhydrous peroxypropionic acid product A1 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 99.8%, and the selectivity of caprolactone was [not specified]. The yield was 99.5%. 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 by reducing 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 separated from the bottom of the column by reduced pressure distillation, and purified caprolactone product was obtained 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 95.2%.

[0092] 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.

[0093] Example 2

[0094] Preparation process of anhydrous peroxy acid products:

[0095] (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 70℃ and the pressure to 30kPa, 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 40°C, and the top temperature was 20°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%.

[0096] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0097] Preparation process of caprolactone:

[0098] The anhydrous peroxypropionic acid product A2 was prepared with a 1:1 molar ratio of peroxypropionic acid to cyclohexanone and a 1:3 molar ratio of catalyst to nitrogen-containing basic compound (triethylamine). 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 55°C, and magnetic or mechanical stirring was started. Anhydrous peroxypropionic 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 [not specified]. 95.9%; 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%.

[0099] 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.

[0100] Example 3

[0101] Preparation process of anhydrous peroxy acid products:

[0102] (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 perpropionic acid phase below) was weighed and added as a catalyst for pre-reaction. The reaction temperature was set at 60℃ and the pressure at 500kPa, and the reaction was carried out for 2.5h to obtain hydrous perpropionic acid. Analysis showed that the concentration of perpropionic 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 15 kPa, a bottom temperature of 65°C, and a top temperature of 40°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 completely 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%.

[0103] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0104] Preparation process of caprolactone:

[0105] 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 magnetic or mechanical stirring was started. Anhydrous peroxypropionic acid product A3 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 6-hour settling period. Analysis showed that the conversion rate of cyclohexanone was 99.5%, and the selectivity of caprolactone was [not specified]. The yield was 97.2%. 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 by reducing 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 separated from the bottom of the column by reduced pressure distillation, and purified caprolactone product was obtained from the top of the column. 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%.

[0106] 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.

[0107] Example 4

[0108] The method of Example 1 was implemented, except that propionic acid was replaced with butyric acid.

[0109] Preparation process of anhydrous peroxy acid products:

[0110] (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 80℃ 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, under absolute pressure of 15 kPa, bottom temperature of 80°C, and top temperature of 30°C, ethyl propionate and water form an azeotrope that enters the top condenser. 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 2 hours. The peroxybutyric acid phase is collected from the bottom of the column. 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. Based on material balance, the yield of peroxybutyric acid is 95.2%.

[0111] (2) The crude anhydrous peroxybutyric acid collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-film evaporator with a stirrer. 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, 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.

[0112] Preparation process of caprolactone:

[0113] The ingredients were prepared according to the following formula: Peroxybutyric acid to cyclohexanone molar ratio in anhydrous peroxybutyric acid product A4 was 1.05:1, and the catalyst to nitrogen-containing basic compound (pyrrole) molar ratio 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 magnetic or 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 [not specified]. 96.2%; 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 35°C, and the top pressure was 2 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 94.8%.

[0114] 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.

[0115] Example 5

[0116] The method of Example 1 was implemented, except that propionic acid was replaced with acetic acid.

[0117] Preparation process of anhydrous peroxy acid products:

[0118] (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 80℃ 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 80℃, 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%.

[0119] (2) The crude anhydrous peracetic acid collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0120] Preparation process of caprolactone:

[0121] The ingredients were 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 magnetic or 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 9%. 3.3%; 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.

[0122] 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.

[0123] Example 6

[0124] The method of Example 1 was implemented, except that propionic acid was replaced with benzoic acid.

[0125] Preparation process of anhydrous peroxy acid products:

[0126] (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 80℃ 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 80℃, 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%.

[0127] (2) The crude anhydrous peroxybenzoic acid collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0128] Preparation process of caprolactone:

[0129] The ingredients were prepared according to the following formula: 1.05:1 molar ratio of peroxybenzoic acid to cyclohexanone in anhydrous peroxybenzoic acid product A6, and 1:5 molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) in anhydrous peroxybenzoic acid product A6. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and magnetic or 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 [not specified]. 89.9%; 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 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 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 88.4% by weight.

[0130] 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.

[0131] Example 7

[0132] The method of Example 1 was followed, except that no nitrogen-containing basic compound was added during the preparation of caprolactone.

[0133] Preparation process of anhydrous peroxy acid products:

[0134] (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 80℃ 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 80°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 0.07% by weight. Based on the material balance, the yield of perpropionic acid was 95.5%.

[0135] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0136] Preparation process of caprolactone:

[0137] The mixture was prepared according to a molar ratio of peroxypropionic acid to cyclohexanone of 1.05:1 in anhydrous peroxypropionic acid product A1. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50°C, and magnetic or mechanical stirring was started. Anhydrous peroxypropionic acid product A1 was slowly added dropwise to the cyclohexanone over 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 without 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 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 75.2% by weight.

[0138] 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.

[0139] Example 8

[0140] The method was implemented according to Example 1, except that the ratio of ethyl propionate, propionic acid, hydrogen peroxide and catalyst was different.

[0141] Preparation process of anhydrous peroxy acid products:

[0142] (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 80℃ 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 80℃, 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 the material balance, the yield of peroxypropionic acid is 76.5%.

[0143] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0144] Preparation process of caprolactone:

[0145] The ingredients were 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 magnetic or mechanical stirring was started. Anhydrous peroxypropionic acid product A8 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 greater than 98.2%, and the selectivity of caprolactone was higher than [missing value]. 90.8%; 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 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 87.5% by weight.

[0146] 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.

[0147] Example 9

[0148] The method is implemented according to Example 1, except that in step (2), the residence time of the evaporation process is 2000s.

[0149] Preparation process of anhydrous peroxy acid products:

[0150] (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 80℃ 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 80°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 material balance, the yield of perpropionic acid was 95.5%.

[0151] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0152] Preparation process of caprolactone:

[0153] The ingredients were 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 magnetic or 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 9%. 9.2%; 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 90.3% by weight.

[0154] 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.

[0155] Example 10

[0156] The method was implemented according to Example 1, except that the evaporation temperature was controlled at 85°C and the evaporation pressure was 3 kPa.

[0157] Preparation process of anhydrous peroxy acid products:

[0158] (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 80℃ 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 80°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 0.07% by weight. Based on the material balance, the yield of perpropionic acid was 95.5%.

[0159] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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.

[0160] Preparation process of caprolactone:

[0161] 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 magnetic or mechanical stirring was started. Anhydrous peroxypropionic acid product A1 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 99.3%, and the selectivity for caprolactone was 9%. 5.0%; 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.

[0162] 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.

[0163] Example 11

[0164] In this embodiment, the synthesis of peroxypropionic acid did not involve a pre-reaction.

[0165] Preparation process of anhydrous peroxy acid products:

[0166] (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 80℃, 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%. 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%.

[0167] (2) The peroxypropionic acid phase collected from the bottom of the reactive distillation column was vaporized and separated using a scraped-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 at 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 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.

[0168] Preparation process of caprolactone:

[0169] 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 magnetic or 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 of caprolactone was [not specified]. The yield was 96.5%. 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 by vacuum distillation. 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 separated from the bottom of the column by vacuum distillation, and purified caprolactone product was obtained from the top of the column. The top temperature of the heavy component removal column was 78°C, and the pressure was 1.5 kPaA. The yield of caprolactone was 94.8% by weight.

[0170] 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.

[0171] Comparative Example 1

[0172] The method of Example 1 is the same as in Example 1, except that step (2) is not performed.

[0173] Preparation process of anhydrous peroxy acid products:

[0174] (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 80℃ 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 80℃, and the column temperature to 80℃. 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%.

[0175] Preparation process of caprolactone:

[0176] The perpropionic acid to cyclohexanone molar ratio in the perpropionic acid phase was 1.05:1, and the catalyst to nitrogen-containing basic compound (pyrrole) molar ratio in the perpropionic acid phase was 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and magnetic or mechanical stirring was started. Anhydrous perpropionic acid product A1 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 99.0%, and the selectivity for 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. Crude caprolactone product without light components is obtained from the bottom of the column. The heavy components with boiling points higher than caprolactone are separated from the bottom of the column by reducing pressure distillation. Refined caprolactone product is obtained from the top of the column. 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%.

[0177] 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.

[0178] Comparative Example 2

[0179] The method was implemented according to Example 1, except that a heterogeneous acidic catalyst (bissulfonic acid-based polystyrene resin) was used instead of the heteropoly acid (phosphotungstic acid).

[0180] Preparation process of anhydrous peroxy acid products:

[0181] (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 80℃ and the pressure to atmospheric pressure (100kPa). React for 1h 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 80℃, 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%.

[0182] (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:

[0183] The anhydrous peroxypropionic acid product 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. The temperature was raised to 50℃, and magnetic or mechanical stirring was started. Anhydrous peroxypropionic acid was slowly added dropwise to the cyclohexanone, completing the addition in 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 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 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 78.0%.

[0184] 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%.

[0185] Comparative Example 3

[0186] The method of Example 1 was implemented, except that after the pre-reaction, the catalyst was separated in step (2) and then dehydrated in a reactive distillation column.

[0187] Preparation process of anhydrous peroxy acid products:

[0188] (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 80℃ 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%.

[0189] (2) The prepared peroxypropionic acid aqueous solution was vaporized and separated using a scraped-plate stirred thin-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 then 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.

[0190] (3) The aqueous peroxypropionic acid product was transferred to a distillation column with an absolute pressure of 15 kPa, a bottom temperature of 80°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%.

[0191] Preparation process of caprolactone:

[0192] The anhydrous peroxypropionic acid product was prepared with a molar ratio of peroxypropionic acid to cyclohexanone of 1.05:1, and a molar ratio of catalyst to nitrogen-containing basic compound (pyrrole) of 1:5. 50g of cyclohexanone was weighed and placed in a batch reactor. The temperature was raised to 50℃, and magnetic or mechanical stirring was started. The anhydrous peroxypropionic acid product and 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 98.6%, the selectivity for caprolactone was 68.1%, and the selectivity for hydroxyhexanoic acid was 18%. The yield was 6%, and 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 by vacuum distillation. 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 separated from the bottom of the column by vacuum distillation, and purified caprolactone product was obtained 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%.

[0193] 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 a high conversion rate of hydrogen peroxide and a high yield of peroxypropionic acid, but also has a low catalyst content and a low water content in the anhydrous peroxyacid products. Moreover, 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 rate of cyclohexanone and the yield of caprolactone are relatively high.

[0194] 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 anhydrous peroxyacid product, characterized in that, The method includes the following steps: (1) In the presence of a homogeneous acidic catalyst, hydrogen peroxide is reacted with an organic acid, and then the reaction products are separated into an aqueous phase and a peroxyacid phase. (2) Remove the homogeneous acid catalyst from the peroxy acid phase.

2. The method according to claim 1, characterized in that, In step (1), the water content in the peroxy acid 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 capable of releasing H2. + Protonic acids; Preferably, the acidity coefficient pKa of the homogeneous acid catalyst is -4 to 8, and more preferably -3 to 5; More preferably, the homogeneous acidic catalyst is selected from at least one of sulfuric acid, nitric acid, heteropolyacids, and isopolyacids; More preferably, the heteropolyacid is selected from one or more of phosphomolybdic acid, phosphotungstic acid, and silicotungstic acid; More preferably, the isopolyacid is selected from one or more of decatungstic acid, heptatungstic acid, octamolybdic acid, and dodecamolybdic acid.

4. The method according to any one of claims 1-3, characterized in that, The organic acid is 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.

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, 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.

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 35-85°C, a top temperature of 20-40°C, a pressure of 1 kPa-0.5 MPa, and a time of 1-5 hours.

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 35-80°C, a pressure of 10 kPa-1 MPa, and a time of 0.5-5 hours; Preferably, the conditions for the main reaction include: a bottom temperature of 35-85°C, a top temperature of 20-40°C, a pressure of 1 kPa-0.5 MPa, and a time of 1-5 hours.

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.

10. The method according to claim 9, characterized in that, When the homogeneous acidic catalyst in the peroxy acid phase is removed, the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system is higher than the boiling point of the peroxy acid. Preferably, when the homogeneous acidic catalyst in the peroxy acid phase is removed, the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system is more than 40°C higher than the boiling point of the peroxy acid.

11. The method according to claim 10, characterized in that, When removing the homogeneous acidic catalyst from the peroxy acid phase, the evaporation temperature is more than 10°C lower than the boiling point of the homogeneous acidic catalyst in the peroxy acid phase system.

12. The method according to any one of claims 9-11, characterized in that, In step (2), the evaporation temperature is 10-130℃, preferably 20-85℃; the evaporation pressure is 0.5-90kPa, preferably 1-25kPa; and the evaporation residence time is 1-3600s, preferably 5-1200s.

13. A method for preparing caprolactone, characterized in that, The method comprises: preparing an anhydrous peroxy acid product according to any one of claims 1-12, and then subjecting the anhydrous peroxy acid product to an oxidation reaction with cyclohexanone.

14. The method according to claim 13, characterized in that, The anhydrous peroxy acid product contains ≤50 ppm of homogeneous acidic catalyst, ≤0.2 wt% water, and 5-50 wt% peroxy acid.

15. The method according to claim 13 or 14, characterized in that, The molar ratio of cyclohexanone to peroxy acid in the anhydrous peroxy acid product is 1:1-1.

5.

16. The method according to any one of claims 13-15, characterized in that, The conditions for the oxidation reaction include: a temperature of 30-80℃ and a time of 1-8 hours.

17. The method according to any one of claims 13-16, characterized in that, 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.

18. The method according to claim 17, characterized in that, The nitrogen-containing basic compound is selected from one or more of methylamine, ethylamine, triethylamine, trimethylamine, ethylenediamine, urea, ethanolamine, isopropylamine, tert-butylamine, aniline, benzylamine, cyclohexylamine, dicyclohexylamine, pyridine, dimethylpyridine, pyrrole, indole, acridine, carbazole and quinoline.

19. The method according to claim 17 or 18, 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.

20. The method according to any one of claims 13-19, characterized in that, The method further includes: refining the crude caprolactone product obtained from the oxidation reaction by distillation.