Method for electrochemically preparing epsilon-caprolactone

Abstract

The invention provides a method for electrochemically preparing epsilon-caprolactone. The method comprises the following steps: mixing cyclohexanone, an electrolyte, water and an organic solvent to form an electrolyte, adding the electrolyte into a double-chamber electrochemical reactor, introducing current to carry out an electrolytic reaction, and generating epsilon-caprolactone at an anode. By adopting the method disclosed by the invention, oxyhydroxide can be generated in situ, and efficient selective conversion of cyclohexanone is realized. The method can replace the use of a high-risk material peroxy acid in the existing method, the process is greener and safer, the conditions are milder, and the method has a better industrial prospect.

Description

Technical Field

[0001] The invention relates to a method for electrochemically preparing epsilon-caprolactone, and belongs to the field of organic electrochemical synthesis. Background Art

[0002] ε-caprolactone is an important aliphatic lactone, which can be used for toughening and modification of epoxy resin in downstream, and can be used as an excellent strong polar solvent to dissolve some insoluble resins. At the same time, ε-caprolactone is also an important chemical intermediate, with good biodegradability, biocompatibility and polymer compatibility, and can be used to synthesize a variety of polymers with different properties, such as polycaprolactone degradable plastics, etc., mainly used in TPU medical hoses, degradable surgical sutures, medical plates / radiotherapy positioning membranes, etc.

[0003] Hunan Juren, Daicel and Ingevity are the three major caprolactone monomer producers in the world. They basically adopt the Baeyer-Vlliger oxidation method, where propionic acid reacts with hydrogen peroxide under the action of a catalyst to generate peroxypropionic acid, and the strong oxidizing property of peroxypropionic acid is used to oxidize cyclohexanone to obtain crude caprolactone. The crude product is distilled to obtain the product ε-caprolactone. However, this process involves the production, storage, transportation and use of a large amount of organic peroxides, which has high requirements for safe production. In addition, the reaction process produces a large amount of organic waste acid by-products. The development of a safer and more environmentally friendly ε-caprolactone production process has received increasing attention.

[0004] The electrochemical method is an old method, a brand-new technology, a greener process, and a more environmentally friendly process. With the future reduction of electricity prices, it has obvious competitiveness. CN 114438522 A discloses a method for preparing ε-caprolactone from cyclohexanone. Cyclohexanone is used as a raw material, chlorate and acetate are used as catalysts, and an electrochemical method is used to prepare ε-caprolactone. However, the method still involves peracetic acid to catalyze the oxidation of cyclohexanone to prepare ε-caprolactone, and the safety problem of peracetic acid is not solved.

[0005] Therefore, it is of great significance to develop a novel electrochemical process route to prepare ε-caprolactone. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for preparing ε-caprolactone by electrochemical method. The method can replace the use of peroxyacid, a high-risk material, in the prior method, and the process is greener, safer, and the conditions are milder, which has a good industrialization prospect.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for electrochemically preparing ε-caprolactone, the method comprising the steps of:

[0009] Cyclohexanone, electrolyte, water and organic solvent are mixed into an electrolyte, added into a double-chamber electrochemical reactor, and current is passed through for electrolytic reaction to generate ε-caprolactone at the anode.

[0010] In one embodiment, the concentration of cyclohexanone in the electrolyte is 0.01-2M (M represents mol / L), which can be one of 0.01M, 0.1M, 0.5M, 1M, 1.5M or 2M, but is not limited to the listed values.

[0011] In one embodiment, the electrolyte is one or more combinations of lithium perchlorate, sodium perchlorate, sodium sulfate, and sodium hexafluorophosphate;

[0012] The concentration of the electrolyte in the electrolyte solution is 0.1-2 M, and can be one of 0.1 M, 0.4 M, 0.8 M, 1.6 M or 2 M, but is not limited to the listed values.

[0013] In one embodiment, the organic solvent can be any one of acetonitrile, methanol, butanol, and acetone.

[0014] In one embodiment, the volume ratio of water to organic solvent is between 3:7 and 7:3, and can be one or more combinations of 3:7, 4:6, 5:5, 6:4 or 7:3, but is not limited to the listed values.

[0015] In one embodiment, the anode is selected from an electrode material comprising one or more combinations of iron (Fe), cobalt (Co), and nickel (Ni);

[0016] In some specific examples, the anode is an electrode material comprising a metal substrate and a surface metal coating structure; wherein the metal substrate may be one or more combinations of foamed iron, foamed cobalt, foamed nickel, foamed nickel-iron, and a wire mesh containing iron, cobalt or nickel; the surface metal coating may be one or more combinations of iron, cobalt, and nickel;

[0017] Preferably, the thickness of the surface metal coating is between 1 and 10 μm, and may be 1 μm, 2 μm, 4 μm, 6 μm, 8 μm or 10 μm, but is not limited to the listed values;

[0018] It is an existing technology to load metal on the surface of a metal substrate to form a coating of a certain thickness. This type of electrode material can be a common commercially available product that can be purchased, or it can be prepared by technicians themselves referring to existing methods, for example, by one or more combinations of methods such as electroplating, spraying, and hydrothermal in-situ loading. These methods are all conventional operations in the field and the present invention has no special restrictions on this.

[0019] In one embodiment, the dual-chamber electrochemical reactor further comprises a cathode in addition to the anode;

[0020] Preferably, the cathode is a Pt / Ti electrode;

[0021] In the electrochemical method of the present invention, there is no restriction on the shapes of the anode and cathode, and their arrangement in the reactor. All electrode shapes and arrangements of cathodes and anodes that can achieve electrolysis function are covered by the method of the present invention.

[0022] In one embodiment, the dual-chamber electrochemical reactor is a diaphragm dual-chamber reactor, and the diaphragm is an ion membrane;

[0023] Preferably, the ion membrane is a cation exchange membrane material, more preferably any one of Nafion324, Nafion117, Nafion115, Nafion212, F-9010, F-6080 or DN350;

[0024] Preferably, the distance between the diaphragm and the anode and cathode is 0.1-0.5 cm, which can be one or a combination of 0.1 cm, 0.2 cm, 0.3 cm, 0.4 cm or 0.5 cm, but is not limited to the listed values.

[0025] In one embodiment, the electrolysis reaction, the electrolysis temperature is between 10 and 50°C, which can be one of 10°C, 20°C, 30°C, 40°C or 50°C, but is not limited to the listed values;

[0026] The electrolysis time is 1 to 4 hours, and can be one of 1 hour, 2 hours, 3 hours or 4 hours, but is not limited to the listed values.

[0027] In one embodiment, the electrolysis reaction has a current density of 1000 to 5000 A / m 2 , can be 1000A / m 2 、2000A / m 2 、3000A / m 2 、3500A / m 2 、4000A / m 2 or 5000A / m 2 One of, but not limited to, the listed values;

[0028] The voltage range is 2 to 6V, and can be one of 2V, 3V, 4V, 5V or 6V, but is not limited to the listed values.

[0029] The preparation method provided by the present invention uses cyclohexanone as a raw material in an electrochemical double-chamber reactor, prepares ε-caprolactone at the anode, and generates hydrogen at the cathode. After the electrolysis reaction is completed, the reaction system obtained contains a mixed solution of ε-caprolactone, and the pure ε-caprolactone can be obtained by subsequent post-treatment processes such as desolvation and distillation. These post-treatment processes are all known processes in the field, and the present invention does not make specific requirements here.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) In the present invention, cyclohexanone is used as a raw material, and in an electrode material containing one or more elements of Fe, Co, and Ni, an active hydroxyl oxide species is generated in situ by an electrochemical method, which can replace the peroxypropionic acid oxide species in the traditional process and efficiently catalyze and activate cyclohexanone to prepare ε-caprolactone.

[0032] (2) In the present invention, the selectivity of ε-caprolactone can be as high as 99% or more, and the current efficiency can be as high as 95% or more. The process does not involve the production of highly dangerous peroxides, and the process is safer and greener. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below by specific implementation methods. The embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0034] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art and can be obtained commercially.

[0035] The sources of the main raw materials used in this implementation case and comparative example are as follows:

[0036] Cyclohexanone: purchased from Beijing Inokai Technology Co., Ltd., purity >98.0%;

[0037] Cation exchange membrane: purchased from DuPont, USA;

[0038] Pt / Ti electrode: purchased from Suzhou Borui Electrode Industry Co., Ltd.;

[0039] Anode 1 (a metal composition of Fe, Co, and Ni is coated on the surface of a foamed nickel substrate, with a coating thickness of 5 μm), anode 2 (a metal composition of Fe, Co, and Ni is coated on the surface of a foamed nickel-iron substrate, with a coating thickness of 3 μm), and anode 3 (a metal composition of Fe, Co, and Ni is coated on the surface of a nickel mesh, with a coating thickness of 4 μm) are prepared according to the following in-situ loading method:

[0040] Using a hydrothermal method, nitrate, urea and ammonium fluoride containing equal masses of Fe, Co and Ni were dissolved in 100 mL of water, and the substrate material was added. The hydrothermal reaction was carried out at 160°C for about 6 hours, wherein the total mass ratio of nitrate: urea: ammonium fluoride = 3:2:5. The hydrothermal material was calcined at 300°C for 2 hours in a nitrogen atmosphere and naturally cooled to room temperature; by adjusting the hydrothermal reaction time, coatings with thicknesses of 3um, 4um and 5um were obtained respectively.

[0041] Example 1

[0042] This embodiment provides a method for electrochemically preparing ε-caprolactone.

[0043] A double-chamber electrochemical reactor was used, in which the cation exchange membrane N115 was used as a diaphragm, the anode electrode was anode 1, the cathode was a Pt / Ti electrode, and the distances between the cation exchange membrane and the anode and cathode were all 0.2 cm.

[0044] Cyclohexanone, lithium perchlorate, water and acetonitrile are mixed to form an electrolyte, wherein the concentration of cyclohexanone is 2 M, the concentration of lithium perchlorate is 0.5 M, and the volume ratio of water to acetonitrile is 3:7.

[0045] The electrolyte was added into the double-chamber electrochemical reactor and current was passed through it with a current density of 4000 A / m 2 The electrolysis voltage was 3 V, and the electrolysis reaction was carried out at 40 ° C for 2 h. ε-caprolactone was generated at the anode 1 and hydrogen was produced at the cathode.

[0046] Gas chromatography was used to analyze the raw material conversion rate, product yield and current effect. The results are shown in Table 1 below.

[0047] Example 2

[0048] This embodiment provides a method for electrochemically preparing ε-caprolactone.

[0049] A double-chamber electrochemical reactor was used, in which the cation exchange membrane N212 was used as a diaphragm, the anode electrode was anode 2, the cathode was a Pt / Ti electrode, and the distances between the cation exchange membrane and the anode and cathode were all 0.3 cm.

[0050] Cyclohexanone, sodium perchlorate, water and methanol are mixed to form an electrolyte, wherein the concentration of cyclohexanone is 2 M, the concentration of sodium perchlorate is 0.3 M, and the volume ratio of water to methanol is 4:6.

[0051] The electrolyte was added into the double-chamber electrochemical reactor and current was passed through with a current density of 3500 A / m 2 The electrolysis voltage was 2.8 V, and the electrolysis reaction was carried out at 50 ° C for 2 hours. ε-caprolactone was generated at the anode 1 and hydrogen was produced at the cathode.

[0052] Gas chromatography was used to analyze the raw material conversion rate, product yield and current effect. The results are shown in Table 1 below.

[0053] Example 3

[0054] This embodiment provides a method for electrochemically preparing ε-caprolactone.

[0055] A double-chamber electrochemical reactor was used, in which the cation exchange membrane N117 was used as a diaphragm, the anode electrode was anode 3, the cathode was a Pt / Ti electrode, and the distances between the cation exchange membrane and the anode and cathode were all 0.4 cm.

[0056] Cyclohexanone, sodium sulfate, water and acetonitrile are mixed to form an electrolyte, wherein the concentration of cyclohexanone is 1.6 M, the concentration of sodium sulfate is 0.4 M, and the volume ratio of water to acetonitrile is 1:1.

[0057] The electrolyte was added into the double-chamber electrochemical reactor and current was passed through with a current density of 2800 A / m 2 The electrolysis voltage was 2.2 V, and the electrolysis reaction was carried out at 30°C for 2 h. ε-caprolactone was generated at the anode 1 and hydrogen was produced at the cathode.

[0058] The raw material conversion rate, product yield and current effect were analyzed by gas chromatography. The results are shown in Table 1 below.

[0059] Comparative Example 1

[0060] This embodiment provides a method for electrochemically preparing ε-caprolactone. Except that copper is used as the anode, other conditions are the same as those in Embodiment 1.

[0061] The performance of the products obtained in the above examples and comparative examples was analyzed, and the results are shown in Table 1.

[0062] Table 1 ε-caprolactone yield and current efficiency under different conditions

[0063]

[0064]

Claims

1. A method for electrochemically preparing ε-caprolactone, characterized in that: The method steps include: Cyclohexanone, electrolyte, water and organic solvent are mixed into an electrolyte, added into a double-chamber electrochemical reactor, and current is passed through for electrolytic reaction to generate ε-caprolactone at the anode.

2. The method according to claim 1, characterized in that: The concentration of the cyclohexanone in the electrolyte is 0.01-2M.

3. The method according to claim 1, characterized in that The electrolyte is one or a combination of lithium perchlorate, sodium perchlorate, sodium sulfate, and sodium hexafluorophosphate; and / or The concentration of the electrolyte in the electrolyte is 0.1-2M.

4. The method according to claim 1, characterized in that: The organic solvent is selected from any one of acetonitrile, methanol, butanol and acetone; and / or The volume ratio of water to organic solvent is 3:7 to 7:

3.

5. The method according to claim 1, characterized in that: The anode is selected from electrode materials containing one or a combination of multiple elements of iron, cobalt and nickel.

6. The method according to claim 5, characterized in that The anode is an electrode material comprising a metal substrate and a surface metal coating structure; wherein the metal substrate is one or more combinations of foamed iron, foamed cobalt, foamed nickel, foamed nickel-iron, and wire mesh containing iron, cobalt or nickel; the surface metal coating is one or more combinations of iron, cobalt and nickel; Preferably, the thickness of the surface metal coating is between 1 and 10 μm.

7. The method according to claim 1, characterized in that In the dual-chamber electrochemical reactor, the cathode is a Pt / Ti electrode.

8. The method according to claim 1, characterized in that: The dual-chamber electrochemical reactor is a diaphragm dual-chamber reactor, and the diaphragm is an ion membrane; Preferably, the ion membrane is a cation exchange membrane material, more preferably any one of Nafion324, Nafion117, Nafion115, Nafion212, F-9010, F-6080 or DN350; Preferably, the distance between the diaphragm and the anode and cathode is 0.1-0.5 cm.

9. The method according to claim 1, characterized in that: The electrolysis reaction has an electrolysis temperature of 10 to 50° C. and an electrolysis time of 1 to 4 hours.

10. The method according to claim 1, characterized in that The electrolysis reaction has a current density of 1000 to 5000 A / m 2 , the voltage range is 2~6V.

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