A method and system for simultaneously producing ε-caprolactone and crotonic acid

Abstract

The invention discloses a method and system for simultaneously producing ε-caprolactone and crotonic acid. The system sequentially includes an oxidation tower, a first rectifying tower, a crystallization tower, and a second rectifying tower; an injection port and an exhaust port are provided on the outside of the oxidation tower, and a bubbler is provided inside. A mixed solution of cyclohexanone, crotonaldehyde, and a solvent is input into the oxidation tower by the injection port, and oxygen is bubbled into the reaction solution by the bubbler in the oxidation tower; the bottom of the oxidation tower is connected to the first rectifying tower, the bottom of the first rectifying tower is connected to the crystallization tower, and the bottom of the crystallization tower is connected to the bottom extraction of the second rectifying tower. The present invention achieves the purpose of simultaneously producing ε-caprolactone and crotonic acid in a low-temperature reaction, while obtaining a product through simple two rectifications and a cooling crystallization, with low reaction and separation energy consumption and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of production of ε-caprolactone and crotonic acid, and in particular to a method and system for simultaneously producing ε-caprolactone and crotonic acid by oxidizing cyclohexanone and crotonaldehyde. Background Art

[0002] ε-Caprolactone is a monomer that can be used to synthesize a variety of biodegradable polymers, and is often used as a monomer for the polymer polycaprolactone, which has widespread applications in 3D printing materials, coatings, and pharmaceuticals. Currently, the industrial method for preparing ε-caprolactone is the oxidation of cyclohexanone with peracetic acid. However, peracetic acid carries significant transportation and storage risks and is expensive. The acid byproduct produced during the reaction can easily lead to further reactions of the product, such as ester polymerization, reducing yield and causing pollution hazards. Therefore, it is necessary to explore the use of greener, more environmentally friendly, and safer oxidants to replace peracetic acid. Oxygen, a cheap, readily available, and environmentally friendly oxidant, can form a co-oxidation system with aldehydes to oxidize cyclic ketones to lactones, making it a key research focus for replacing peracetic acid.

[0003] Currently, the oxygen co-oxidation method of cyclohexanone mostly uses benzaldehyde for co-oxidation, but benzaldehyde is relatively expensive, and the production of benzoic acid after the reaction increases the processing cost. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the present invention aims to provide a method and system for simultaneously producing ε-caprolactone and crotonic acid.

[0005] In order to achieve this object, the present invention adopts the following technical solutions:

[0006] A system for simultaneously producing ε-caprolactone and crotonic acid comprises, in sequence, an oxidation tower, a first distillation tower, a crystallization tower, and a second distillation tower; the oxidation tower is provided with an inlet and an exhaust port on the outside and a bubbler on the inside; a mixed liquid of cyclohexanone, crotonaldehyde, and a solvent is fed into the oxidation tower through the inlet, and oxygen is bubbled into the reaction liquid through the bubbler in the oxidation tower; the bottom of the oxidation tower is connected to the first distillation tower, the bottom of the first distillation tower is connected to the crystallization tower, and the bottom of the crystallization tower is connected to the extraction outlet at the bottom of the second distillation tower.

[0007] The bubbler extends from the top of the oxidation tower to below the reaction liquid level, forming a coil at the bottom.

[0008] An output pipe is provided on the top of the first distillation tower for returning the light component to be mixed with the raw material liquid and then re-input into the oxidation tower.

[0009] A method for simultaneously producing ε-caprolactone and crotonic acid comprises the following steps: using the system, mixing three streams of solvent, crotonaldehyde and cyclohexanone, and adding them to an oxidation tower; bubbling oxygen from the bottom of the oxidation tower into the mixed liquid for oxidation, and discharging the remaining oxygen from the top of the oxidation tower; extracting the reaction liquid from the bottom of the oxidation tower and inputting it into a first distillation tower for separation; extracting the remaining unreacted crotonaldehyde, cyclohexanone and solvent from the top of the first distillation tower, returning them to be combined with the raw material liquid, and then re-entering the oxidation tower; extracting a mixed liquid of crotonic acid and ε-caprolactone products from the bottom of the first distillation tower, and entering a crystallization tower for cooling and crystallization; cooling the product mixture and precipitating most of the crotonic acid product, and extracting the remaining reaction liquid from a second distillation tower; separating the ε-caprolactone product at the top of the second distillation tower, and obtaining the crotonic acid product at the bottom of the second distillation tower.

[0010] Beneficial effects of the present invention:

[0011] The present invention uses oxygen as an oxidant and crotonaldehyde and cyclohexanone as raw materials to propose a new process for the simultaneous production of crotonic acid and caprolactone. Cyclohexanone can be oxidized to caprolactone via BV oxidation. When oxygen is used as an oxidant, an aldehyde is often added as a sacrificial oxidizing agent. The present invention uses crotonaldehyde as a sacrificial agent, allowing the reaction to simultaneously produce crotonic acid and caprolactone. Furthermore, the process is relatively simple to separate, with a single distillation step separating the two products from the remaining raw materials. The remaining raw materials are then mixed with new raw materials and re-reacted, improving atomic utilization. Furthermore, the present invention conducts the reaction at low temperatures (normal pressure) and without the need for a catalyst, reducing separation difficulty, reaction costs, and process energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of the system structure for the simultaneous production of ε-caprolactone and crotonic acid;

[0013] In the figure: sample inlet 1, bubbler 2, oxidation tower 3, exhaust port 4, first distillation tower 5, crystallization tower 6, second distillation tower 7.

[0014] Figure 2 It is the chromatogram of the mixture of the reaction solution and the internal standard substance n-heptane after the reaction;

[0015] The peaks from left to right are: n-heptane, ethyl acetate, crotonaldehyde, cyclohexanone, caprolactone, and crotonic acid.

[0016] Figure 3 This is the mass spectrum of cyclohexanone;

[0017] Among them, m / z=98.06 is the cyclohexanone peak.

[0018] Figure 4 This is the mass spectrum of crotonaldehyde;

[0019] Among them, m / z=70.04 is the crotonaldehyde peak.

[0020] Figure 5 is the mass spectrum of caprolactone;

[0021] Among them, m / z=114.0496 is the caprolactone peak.

[0022] Figure 6 This is the mass spectrum of crotonic acid and n-heptane;

[0023] Among them, m / z=100.12 is the n-heptane peak, and m / z=85.0979 is the crotonic acid peak. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Crotonic acid, also known as butenoic acid, is an unsaturated fatty acid with active chemical properties. It has a wide range of applications, including the preparation of various resins, coatings, fungicides, and plasticizers. It is also an important pharmaceutical intermediate. Currently, it is primarily produced industrially through the oxidation of crotonaldehyde with oxygen.

[0026] Crotonaldehyde and cyclohexanone can both be oxidized using oxygen, but their combination to form a co-oxidation system has not yet been demonstrated. Crotonaldehyde can act as a sacrificial oxidant in cyclohexanone oxygen oxidation systems, promoting the oxidation of cyclohexanone and simultaneously producing the corresponding product, crotonic acid.

[0027] like Figure 1 As shown, a system for simultaneously producing ε-caprolactone and crotonic acid includes an inlet 1, a bubbler 2, an oxidation tower 3, a first distillation tower 5, a crystallization tower 6, and a second distillation tower 7.

[0028] The reaction liquid after the reaction is collected from the oxidation tower and subjected to joint analysis by gas chromatography and mass spectrometry. Figure 2 This is the gas chromatography result of the mixture, where the peaks from left to right are: n-heptane, ethyl acetate, crotonaldehyde, cyclohexanone, caprolactone, and crotonic acid. Figure 3 、 4 , 5, and 6 are the mass spectrometry analysis diagrams of each component, and the results are: Figure 3 is the mass spectrum of cyclohexanone, where m / z=98.06 is the cyclohexanone peak; Figure 4 is the mass spectrum of crotonaldehyde, where m / z=70.04 is the crotonaldehyde peak; Figure 5 This is the mass spectrum of caprolactone, where m / z=114.0496 is the caprolactone peak. Figure 6 This is the mass spectrum of crotonic acid and n-heptane; m / z=100.12 is the n-heptane peak, and m / z=85.0979 is the crotonic acid peak.

[0029] A mixture of cyclohexanone, crotonaldehyde, and a solvent is fed into an oxidation tower 3 through an inlet 1. Oxygen is bubbled into the reaction liquid through a bubbler 2 within the oxidation tower 3, and excess reaction gas is discharged from an exhaust port 4. A first distillation tower 5 is connected to the bottom of the oxidation tower 3, which is in turn connected to the top of a crystallization tower 6. The top of the first distillation tower 5 extracts gas that is refluxed to the oxidation tower 3, while the bottom of the crystallization tower 6 is connected to the bottom of the second distillation tower 7.

[0030] Example

[0031] Cyclohexanone and crotonaldehyde are used as raw materials in a molar ratio of 1:2. The mixture is mixed with the solvent cyclohexanone and solvent in a mass ratio of 1:10. The mixture is then sprayed through inlet 1 into oxidation tower 3, where it undergoes an oxidation reaction with oxygen introduced through bubbler 2 at the bottom of the tower. The reaction temperature is 40°C. Excess reaction gases are discharged through exhaust port 4. The reaction liquid is withdrawn from the bottom of the oxidation tower and fed into a first distillation tower 5. The light component solvent and remaining unreacted reactants are obtained at the top of the first distillation tower. The refluxed liquid is combined with the raw material mixture and then re-entered into oxidation tower 3 to participate in the reaction. The oxidation product, ε-caprolactone and crotonic acid, is obtained at the bottom of the tower. The product mixture is fed into crystallization tower 5 for cooling and crystallization to produce the crotonic acid product. The remaining liquid is then fed into a second distillation tower 7 for a second distillation to produce caprolactone and crotonic acid products.

[0032] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for simultaneously producing ε-caprolactone and crotonic acid, characterized in that: A system for simultaneously producing ε-caprolactone and crotonic acid is adopted, which comprises an oxidation tower, a first distillation tower, a crystallization tower, and a second distillation tower in sequence; the oxidation tower is provided with an inlet and an exhaust port on the outside and a bubbler on the inside; a mixed liquid of cyclohexanone, crotonaldehyde and a solvent is fed into the oxidation tower through the inlet, and oxygen is bubbled into the reaction liquid through the bubbler in the oxidation tower; the bottom of the oxidation tower is connected to the first distillation tower, the bottom of the first distillation tower is connected to the crystallization tower, and the bottom of the crystallization tower is connected to the extraction outlet at the bottom of the second distillation tower; the three streams of solvent, crotonaldehyde and cyclohexanone are mixed and fed into the oxidation tower, and oxygen is bubbled from the bottom of the oxidation tower into the mixed liquid to Oxidation is carried out, and the remaining oxygen is discharged from the top of the oxidation tower; the reaction liquid is taken out from the bottom of the oxidation tower and input into the first distillation tower for separation, the remaining unreacted crotonaldehyde, cyclohexanone and solvent are taken out from the top of the first distillation tower, returned to merge with the raw material liquid and then re-enter the oxidation tower, the bottom of the first distillation tower is taken out crotonic acid and ε-caprolactone product mixed liquid, enters the crystallization tower for cooling crystallization, after the product mixture is cooled, most of the crotonic acid product is precipitated and taken out, the remaining reaction liquid enters the second distillation tower, the top of the second distillation tower is separated to obtain ε-caprolactone product, and the bottom of the second distillation tower obtains crotonic acid product.

2. The method according to claim 1, characterized in that The bubbler extends from the top of the oxidation tower to below the reaction liquid level, forming a coil at the bottom.

3. The method according to claim 1, characterized in that An output pipe is provided on the top of the first distillation tower for returning the light component to be mixed with the raw material liquid and then re-input into the oxidation tower.

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